# 8. Configuration Reference

The operational functionality of BIND 9 is defined using the file named.conf, which is typically located in /etc or /usr/local/etc/namedb, depending on the operating system or distribution. A further file rndc.conf will be present if rndc is being run from a remote host, but is not required if rndc is being run from localhost (the same system as BIND 9 is running on).

## 8.1. Configuration File (named.conf)

The file `named.conf` may contain three types of entities:

Comment

  Multiple comment formats are supported.

Block

  Blocks are containers for statements which either have common functionality - for example, the definition of a cryptographic key in a `key` block - or which define the scope of the statement - for example, a statement which appears in a `zone` block has scope only for that zone.

  Blocks are organized hierarchically within `named.conf` and may have a number of different properties:

  - Certain blocks cannot be nested inside other blocks and thus may be regarded as the topmost-level blocks: for example, the `options` block and the `logging` block.

  - Certain blocks can appear multiple times, in which case they have an associated name to disambiguate them: for example, the `zone` block (`zone example.com { ... };`) or the `key` block (`key mykey { ... };`).

  - Certain blocks may be “nested” within other blocks. For example, the `zone` block may appear within a `view` block.

  The description of each block in this manual lists its permissible locations.

Statement

  - Statements define and control specific BIND behaviors.

  - Statements may have a single parameter (a Value) or multiple parameters (Argument/Value pairs). For example, the `recursion` statement takes a single value parameter - in this case, the string `yes` or `no` (`recursion yes;`) - while the `port` statement takes a numeric value defining the DNS port number (`port 53;`). More complex statements take one or more argument/value pairs. The `also-notify` statement may take a number of such argument/value pairs, such as `also-notify port 5353;`, where `port` is the argument and `5353` is the corresponding value.

  - Statements can appear in a single block - for example, an `algorithm` statement can appear only in a `key` block - or in multiple blocks - for example, an `also-notify` statement can appear in an `options` block where it has global (server-wide) scope, in a `zone` block where it has scope only for the specific zone (and overrides any global statement), or even in a `view` block where it has scope for only that view (and overrides any global statement).

The file `named.conf` may further contain one or more instances of the include Directive. This directive is provided for administrative convenience in assembling a complete `named.conf` file and plays no subsequent role in BIND 9 operational characteristics or functionality.

Note

Over a period of many years the BIND ARM acquired a bewildering array of terminology. Many of the terms used described similar concepts and served only to add a layer of complexity, possibly confusion, and perhaps mystique to BIND 9 configuration. The ARM now uses only the terms Block, Statement, Argument, Value, and Directive to describe all entities used in BIND 9 configuration.

### 8.1.1. Comment Syntax

The BIND 9 comment syntax allows comments to appear anywhere that whitespace may appear in a BIND configuration file. To appeal to programmers of all kinds, they can be written in the C, C++, or shell/Perl style.

#### 8.1.1.1. Syntax

    /* This is a BIND comment as in C */

    // This is a BIND comment as in C++

    # This is a BIND comment as in common Unix shells
    # and Perl

#### 8.1.1.2. Definition and Usage

Comments can be inserted anywhere that whitespace may appear in a BIND configuration file.

C-style comments start with the two characters /* (slash, star) and end with */ (star, slash). Because they are completely delimited with these characters, they can be used to comment only a portion of a line or to span multiple lines.

C-style comments cannot be nested. For example, the following is not valid because the entire comment ends with the first */:

    /* This is the start of a comment.
       This is still part of the comment.
    /* This is an incorrect attempt at nesting a comment. */
       This is no longer in any comment. */

C++-style comments start with the two characters // (slash, slash) and continue to the end of the physical line. They cannot be continued across multiple physical lines; to have one logical comment span multiple lines, each line must use the // pair. For example:

    // This is the start of a comment.  The next line
    // is a new comment, even though it is logically
    // part of the previous comment.

Shell-style (or Perl-style) comments start with the character `#` (number/pound sign) and continue to the end of the physical line, as in C++ comments. For example:

    # This is the start of a comment.  The next line
    # is a new comment, even though it is logically
    # part of the previous comment.

Warning

The semicolon (`;`) character cannot start a comment, unlike in a zone file. The semicolon indicates the end of a configuration statement.

### 8.1.2. Configuration Layout Styles

BIND is very picky about opening and closing brackets/braces, semicolons, and all the other separators defined in the formal syntaxes in later sections. There are many layout styles that can assist in minimizing errors, as shown in the following examples:

    // dense single-line style
    zone "example.com" in{type secondary; file "secondary.example.com"; primaries {10.0.0.1;};};
    //  single-statement-per-line style
    zone "example.com" in{
            type secondary;
            file "secondary.example.com";
            primaries {10.0.0.1;};
    };
    // spot the difference
    zone "example.com" in{
            type secondary;
    file "sec.secondary.com";
    primaries {10.0.0.1;}; };

### 8.1.3. `include` Directive

    include filename;

#### 8.1.3.1. `include` Directive Definition and Usage

The include directive inserts the specified file (or files if a valid glob expression is detected) at the point where the include directive is encountered. The include directive facilitates the administration of configuration files by permitting the reading or writing of some things but not others. For example, the statement could include private keys that are readable only by the name server.

### 8.1.4. Address Match Lists

#### 8.1.4.1. Syntax

An address match list is a list of semicolon-separated address_match_element s.

    { <address_match_element>; ... };

Each element is then defined as:

`address_match_element`

      [ ! ] ( <ip_address> | <netprefix> | key <server_key> | <acl_name> | { address_match_list } )

#### 8.1.4.2. Definition and Usage

Address match lists are primarily used to determine access control for various server operations. They are also used in the `listen-on` and `sortlist` statements. The elements which constitute an address match list can be any of the following:

- ip_address: an IP address (IPv4 or IPv6)

- netprefix: an IP prefix (in `/` notation)

- server_key: a key ID, as defined by the `key` statement

- acl_name: the name of an address match list defined with the `acl` statement

- a nested address match list enclosed in braces

Elements can be negated with a leading exclamation mark (`!`), and the match list names “any”, “none”, “localhost”, and “localnets” are predefined. More information on those names can be found in the description of the `acl` statement.

The addition of the key clause made the name of this syntactic element something of a misnomer, since security keys can be used to validate access without regard to a host or network address. Nonetheless, the term “address match list” is still used throughout the documentation.

When a given IP address or prefix is compared to an address match list, the comparison takes place in approximately O(1) time. However, key comparisons require that the list of keys be traversed until a matching key is found, and therefore may be somewhat slower.

The interpretation of a match depends on whether the list is being used for access control, defining `listen-on` ports, or in a `sortlist`, and whether the element was negated.

When used as an access control list, a non-negated match allows access and a negated match denies access. If there is no match, access is denied. The clauses `allow-notify`, `allow-recursion`, `allow-recursion-on`, `allow-query`, `allow-query-on`, `allow-query-cache`, `allow-query-cache-on`, `allow-transfer`, `allow-update`, `allow-update-forwarding`, and `blackhole` all use address match lists. Similarly, the `listen-on` option causes the server to refuse queries on any of the machine’s addresses which do not match the list.

Order of insertion is significant. If more than one element in an ACL is found to match a given IP address or prefix, preference is given to the one that came first in the ACL definition. Because of this first-match behavior, an element that defines a subset of another element in the list should come before the broader element, regardless of whether either is negated. For example, in `1.2.3/24; ! 1.2.3.13;` the 1.2.3.13 element is completely useless because the algorithm matches any lookup for 1.2.3.13 to the 1.2.3/24 element. Using `! 1.2.3.13; 1.2.3/24` fixes that problem by blocking 1.2.3.13 via the negation, but all other 1.2.3.* hosts pass through.

### 8.1.5. Glossary of Terms Used

Following is a list of terms used throughout the BIND configuration file documentation:

`acl_name`

  The name of an address_match_list as defined by the `acl` statement.

`address_match_list`

  See Address Match Lists.

`boolean`

  Either `yes` or `no`. The words `true` and `false` are also accepted, as are the numbers `1` and `0`.

`domain_name`

  A quoted string which is used as a DNS name; for example: `my.test.domain`.

`duration`

  A duration in BIND 9 can be written in three ways: as a single number representing seconds, as a string of numbers with TTL-style time-unit suffixes, or in ISO 6801 duration format.

  Allowed TTL time-unit suffixes are: “W” (week), “D” (day), “H” (hour), “M” (minute), and “S” (second). Examples: “1W” (1 week), “3d12h” (3 days, 12 hours).

  ISO 8601 duration format consists of the letter “P”, followed by an optional series of numbers with unit suffixes “Y” (year), “M” (month), “W” (week), and “D” (day); this may optionally be followed by the letter “T”, and another series of numbers with unit suffixes “H” (hour), “M” (minute), and “S” (second). Examples: “P3M10D” (3 months, 10 days), “P2WT12H” (2 weeks, 12 hours), “pt15m” (15 minutes). For more information on ISO 8601 duration format, see RFC 3339, appendix A.

  Both TTL-style and ISO 8601 duration formats are case-insensitive.

`fixedpoint`

  A non-negative real number that can be specified to the nearest one-hundredth. Up to five digits can be specified before a decimal point, and up to two digits after, so the maximum value is 99999.99. Acceptable values might be further limited by the contexts in which they are used.

`integer`

  A non-negative 32-bit integer (i.e., a number between 0 and 4294967295, inclusive). Its acceptable value might be further limited by the context in which it is used.

`ip_address`

  An ipv4_address or ipv6_address.

`ipv4_address`

  An IPv4 address with exactly four integer elements valued 0 through 255 and separated by dots (`.`), such as `192.168.1.1` (a “dotted-decimal” notation with all four elements present).

`ipv6_address`

  An IPv6 address, such as `2001:db8::1234`. IPv6-scoped addresses that have ambiguity on their scope zones must be disambiguated by an appropriate zone ID with the percent character (`%`) as a delimiter. It is strongly recommended to use string zone names rather than numeric identifiers, to be robust against system configuration changes. However, since there is no standard mapping for such names and identifier values, only interface names as link identifiers are supported, assuming one-to-one mapping between interfaces and links. For example, a link-local address `fe80::1` on the link attached to the interface `ne0` can be specified as `fe80::1%ne0`. Note that on most systems link-local addresses always have ambiguity and need to be disambiguated.

`netprefix`

  An IP network specified as an ip_address, followed by a slash (`/`) and then the number of bits in the netmask. Trailing zeros in an ip_address may be omitted. For example, `127/8` is the network `127.0.0.0` with netmask `255.0.0.0` and `1.2.3.0/28` is network `1.2.3.0` with netmask `255.255.255.240`. When specifying a prefix involving an IPv6-scoped address, the scope may be omitted. In that case, the prefix matches packets from any scope.

`percentage`

  An integer value followed by `%` to represent percent.

`port`

  An IP port integer. It is limited to 0 through 65535, with values below 1024 typically restricted to use by processes running as root. In some cases, an asterisk (`*`) character can be used as a placeholder to select a random high-numbered port.

`portrange`

  A list of a port or a port range. A port range is specified in the form of `range` followed by two port s, `port_low` and `port_high`, which represents port numbers from `port_low` through `port_high`, inclusive. `port_low` must not be larger than `port_high`. For example, `range 1024 65535` represents ports from 1024 through 65535. The asterisk (`*`) character is not allowed as a valid port or as a port range boundary.

`server-list`

  A named list of one or more ip_address es with optional tls_id, server_key, and/or port. A `server-list` list may include other `server-list` lists.

`server_key`

  A domain_name representing the name of a shared key, to be used for transaction security. Keys are defined using `key` blocks.

`size`
`sizeval`

  A 64-bit unsigned integer. Integers may take values 0 <= value <= 18446744073709551615, though certain parameters (such as `max-journal-size`) may use a more limited range within these extremes. In most cases, setting a value to 0 does not literally mean zero; it means “undefined” or “as big as possible,” depending on the context. See the explanations of particular parameters that use `size` for details on how they interpret its use. Numeric values can optionally be followed by a scaling factor: `K` or `k` for kilobytes, `M` or `m` for megabytes, and `G` or `g` for gigabytes, which scale by 1024, 1024*1024, and 1024*1024*1024 respectively.

  Some statements also accept the keywords `unlimited` or `default`: `unlimited` generally means “as big as possible,” and is usually the best way to safely set a very large number. `default` uses the limit that was in force when the server was started.

`tls_id`

  A named TLS configuration object which defines a TLS key and certificate. See `tls` block.

## 8.2. Blocks

A BIND 9 configuration consists of blocks, statements, and comments.

The following blocks are supported:

> `acl`

>   Defines a named IP address matching list, for access control and other uses.

> `controls`

>   Declares control channels to be used by the `rndc` utility.

> `dnssec-policy`

>   Describes a DNSSEC key and signing policy for zones. See `dnssec-policy` for details.

> `key`

>   Specifies key information for use in authentication and authorization using TSIG.

> `key-store`

>   Describes a DNSSEC key store. See key-store Grammar for details.

> `logging`

>   Specifies what information the server logs and where the log messages are sent.

> `options`

>   Controls global server configuration options and sets defaults for other statements.

> `remote-servers`

>   Defines a named list of servers for inclusion in various zone statements such as `parental-agents`, `primaries` or `also-notify` lists.

> `server`

>   Sets certain configuration options on a per-server basis.

> `statistics-channels`

>   Declares communication channels to get access to `named` statistics.

> `tls`

>   Specifies configuration information for a TLS connection, including a `key-file`, `cert-file`, `ca-file`, `dhparam-file`, `remote-hostname`, `ciphers`, `protocols`, `prefer-server-ciphers`, and `session-tickets`.

> `http`

>   Specifies configuration information for an HTTP connection, including `endpoints`, `listener-clients`, and `streams-per-connection`.

> `trust-anchors`

>   Defines DNSSEC trust anchors: if used with the `initial-key` or `initial-ds` keyword, trust anchors are kept up-to-date using RFC 5011 trust anchor maintenance; if used with `static-key` or `static-ds`, keys are permanent.

> `managed-keys`

>   Is identical to `trust-anchors`; this option is deprecated in favor of `trust-anchors` with the `initial-key` keyword, and may be removed in a future release.

> `trusted-keys`

>   Defines permanent trusted DNSSEC keys; this option is deprecated in favor of `trust-anchors` with the `static-key` keyword, and may be removed in a future release.

> `view`

>   Defines a view.

> `zone`

>   Defines a zone.

The `logging` and `options` statements may only occur once per configuration.

### 8.2.1. `acl` Block Grammar

acl

  Grammar: `acl <string> { <address_match_element>; ... }; // may occur multiple times`

  Blocks: topmost

  Tags: server

  Assigns a symbolic name to an address match list.

### 8.2.2. `acl` Block Definition and Usage

The `acl` statement assigns a symbolic name to an address match list. It gets its name from one of the primary uses of address match lists: Access Control Lists (ACLs).

The following ACLs are built-in:

> `any`

>   Matches all hosts.

> `none`

>   Matches no hosts.

> `localhost`

>   Matches the IPv4 and IPv6 addresses of all network interfaces on the system. When addresses are added or removed, the `localhost` ACL element is updated to reflect the changes.

> `localnets`

>   Matches any host on an IPv4 or IPv6 network for which the system has an interface. When addresses are added or removed, the `localnets` ACL element is updated to reflect the changes. Some systems do not provide a way to determine the prefix lengths of local IPv6 addresses; in such cases, `localnets` only matches the local IPv6 addresses, just like `localhost`.

### 8.2.3. `controls` Block Grammar

controls

  Grammar:

      controls {
      	inet ( <ipv4_address> | <ipv6_address> | * ) [ port ( <integer> | * ) ] allow { <address_match_element>; ... } [ keys { <string>; ... } ] [ read-only <boolean> ]; // may occur multiple times
      	unix <quoted_string> perm <integer> owner <integer> group <integer> [ keys { <string>; ... } ] [ read-only <boolean> ]; // may occur multiple times
      }; // may occur multiple times

  Blocks: topmost

  Tags: server

  Specifies control channels to be used to manage the name server.

### 8.2.4. `controls` Block Definition and Usage

The `controls` statement declares control channels to be used by system administrators to manage the operation of the name server. These control channels are used by the `rndc` utility to send commands to and retrieve non-DNS results from a name server.

unix

  Grammar: `unix <quoted_string> perm <integer> owner <integer> group <integer> [ keys { <string>; ... } ] [ read-only <boolean> ]; // may occur multiple times`

  Blocks: controls

  Tags: obsolete

  Specifies a Unix domain socket as a control channel.

  This option has been removed and using it will cause a fatal error.

inet

  Grammar controls: `inet ( <ipv4_address> | <ipv6_address> | * ) [ port ( <integer> | * ) ] allow { <address_match_element>; ... } [ keys { <string>; ... } ] [ read-only <boolean> ]; // may occur multiple times`

  Grammar statistics-channels: `inet ( <ipv4_address> | <ipv6_address> | * ) [ port ( <integer> | * ) ] [ allow { <address_match_element>; ... } ]; // may occur multiple times`

  Blocks: controls, statistics-channels

  Tags: server

  Specifies a TCP socket as a control channel.

  An `inet` control channel is a TCP socket listening at the specified port on the specified ip_address, which can be an IPv4 or IPv6 address. An ip_address of `*` (asterisk) is interpreted as the IPv4 wildcard address; connections are accepted on any of the system’s IPv4 addresses. To listen on the IPv6 wildcard address, use an ip_address of `::`. If `rndc` is only used on the local host, using the loopback address (`127.0.0.1` or `::1`) is recommended for maximum security.

  If no port is specified, port 953 is used. The asterisk `*` cannot be used for port.

  The ability to issue commands over the control channel is restricted by the `allow` and `keys` clauses.

  `allow`

    Connections to the control channel are permitted based on the address_match_list. This is for simple IP address-based filtering only; any server_key elements of the address_match_list are ignored.

  `keys`

    The primary authorization mechanism of the command channel is the list of server_key s. Each listed `key` is authorized to execute commands over the control channel. See Administrative Tools for information about configuring keys in `rndc`.

`read-only`

  If the `read-only` argument is `on`, the control channel is limited to the following set of read-only commands: `nta -dump`, `null`, `status`, `showzone`, `testgen`, and `zonestatus`. By default, `read-only` is not enabled and the control channel allows read-write access.

If no `controls` statement is present, `named` sets up a default control channel listening on the loopback address 127.0.0.1 and its IPv6 counterpart, ::1. In this case, and also when the `controls` statement is present but does not have a `keys` clause, `named` attempts to load the command channel key from the file `/etc/bind/rndc.key`. To create an `rndc.key` file, run `rndc-confgen -a`.

To disable the command channel, use an empty `controls` statement: `controls { };`.

### 8.2.5. `key` Block Grammar

key

  Grammar:

      key <string> {
      	algorithm <string>;
      	secret <string>;
      }; // may occur multiple times

  Blocks: topmost, view

  Tags: security

  Defines a shared secret key for use with TSIG or the command channel.

### 8.2.6. `key` Block Definition and Usage

The `key` statement defines a shared secret key for use with TSIG (see TSIG) or the command channel (see `controls`).

The `key` statement can occur at the top level of the configuration file or inside a `view` statement. Keys defined in top-level `key` statements can be used in all views. Keys intended for use in a `controls` statement must be defined at the top level.

The server_key, also known as the key name, is a domain name that uniquely identifies the key. It can be used in a `server` statement to cause requests sent to that server to be signed with this key, or in address match lists to verify that incoming requests have been signed with a key matching this name, algorithm, and secret.

algorithm

  Grammar: `algorithm <string>;`

  Blocks: key, view.key

  Tags: security

  Defines the algorithm to be used in a key clause.

  The `algorithm_id` is a string that specifies a security/authentication algorithm. The `named` server supports `hmac-md5`, `hmac-sha1`, `hmac-sha224`, `hmac-sha256`, `hmac-sha384`, and `hmac-sha512` TSIG authentication. Truncated hashes are supported by appending the minimum number of required bits preceded by a dash, e.g., `hmac-sha1-80`.

secret

  Grammar: `secret <string>;`

  Blocks: key, view.key

  Tags: security

  Defines a Base64-encoded string to be used as the secret by the algorithm.

  The `secret_string` is the secret to be used by the algorithm, and is treated as a Base64-encoded string.

### 8.2.7. `key-store` Block Grammar

key-store

  Grammar:

      key-store <string> {
      	directory <string>;
      	pkcs11-uri <quoted_string>;
      }; // may occur multiple times

  Blocks: topmost

  Tags: dnssec

  Configures a DNSSEC key store.

### 8.2.8. `key-store` Block Definition and Usage

The `key-store` statement defines how DNSSEC keys should be stored.

There is one built-in key store named `key-directory`. Configuring keys to use `key-store "key-directory"` is identical to using `key-directory`.

The following options can be specified in a `key-store` statement:

pkcs11-uri

  Grammar: `pkcs11-uri <quoted_string>;`

  Blocks: key-store

  Tags: dnssec, pkcs11

  The `uri` is a string that specifies a PKCS#11 URI Scheme (defined in RFC 7512). When set, `named` tries to create keys inside the corresponding PKCS#11 token. This requires BIND to be built with OpenSSL 3, and to have a PKCS#11 provider configured.

### 8.2.9. `logging` Block Grammar

logging

  Grammar:

      logging {
      	category <string> { <string>; ... }; // may occur multiple times
      	channel <string> {
      		buffered <boolean>;
      		file <quoted_string> [ versions ( unlimited | <integer> ) ] [ size <size> ] [ suffix ( increment | timestamp ) ];
      		null;
      		print-category <boolean>;
      		print-severity <boolean>;
      		print-time ( iso8601 | iso8601-utc | local | <boolean> );
      		severity <log_severity>;
      		stderr;
      		syslog [ <syslog_facility> ];
      	}; // may occur multiple times
      };

  Blocks: topmost

  Tags: logging

  Configures logging options for the name server.

### 8.2.10. `logging` Block Definition and Usage

The `logging` statement configures a wide variety of logging options for the name server. Its `channel` phrase associates output methods, format options, and severity levels with a name that can then be used with the `category` phrase to select how various classes of messages are logged.

Only one `logging` statement is used to define as many channels and categories as desired. If there is no `logging` statement, the logging configuration is:

    logging {
         category default { default_syslog; default_debug; };
         category unmatched { null; };
    };

If `named` is started with the `-L` option, it logs to the specified file at startup, instead of using syslog. In this case the logging configuration is:

    logging {
         category default { default_logfile; default_debug; };
         category unmatched { null; };
    };

The logging configuration is only established when the entire configuration file has been parsed. When the server starts up, all logging messages regarding syntax errors in the configuration file go to the default channels, or to standard error if the `-g` option was specified.

#### 8.2.10.1. The `channel` Phrase

channel

  Grammar:

      channel <string> {
      	buffered <boolean>;
      	file <quoted_string> [ versions ( unlimited | <integer> ) ] [ size <size> ] [ suffix ( increment | timestamp ) ];
      	null;
      	print-category <boolean>;
      	print-severity <boolean>;
      	print-time ( iso8601 | iso8601-utc | local | <boolean> );
      	severity <log_severity>;
      	stderr;
      	syslog [ <syslog_facility> ];
      }; // may occur multiple times

  Blocks: logging

  Tags: logging

  Defines a stream of data that can be independently logged.

All log output goes to one or more `channels`; there is no limit to the number of channels that can be created.

Every channel definition must include a destination clause that says whether messages selected for the channel go to a file, go to a particular syslog facility, go to the standard error stream, or are discarded. The definition can optionally also limit the message severity level that is accepted by the channel (the default is `info`), and whether to include a `named`-generated time stamp, the category name, and/or the severity level (the default is not to include any).

null

  Grammar: `null;`

  Blocks: logging.channel

  Tags: logging

  Causes all messages sent to the logging channel to be discarded.

  The `null` destination clause causes all messages sent to the channel to be discarded; in that case, other options for the channel are meaningless.

`file`

  The `file` destination clause directs the channel to a disk file. It can include additional arguments to specify how large the file is allowed to become before it is rolled to a backup file (`size`), how many backup versions of the file are saved each time this happens (`versions`), and the format to use for naming backup versions (`suffix`).

  The `size` option is used to limit log file growth. If the file ever exceeds the specified size, then `named` stops writing to the file unless it has a `versions` option associated with it. If backup versions are kept, the files are rolled as described below. If there is no `versions` option, no more data is written to the log until some out-of-band mechanism removes or truncates the log to less than the maximum size. The default behavior is not to limit the size of the file.

  File rolling only occurs when the file exceeds the size specified with the `size` option. No backup versions are kept by default; any existing log file is simply appended. The `versions` option specifies how many backup versions of the file should be kept. If set to `unlimited`, there is no limit.

  The `suffix` option can be set to either `increment` or `timestamp`. If set to `timestamp`, then when a log file is rolled, it is saved with the current timestamp as a file suffix. If set to `increment`, then backup files are saved with incrementing numbers as suffixes; older files are renamed when rolling. For example, if `versions` is set to 3 and `suffix` to `increment`, then when `filename.log` reaches the size specified by `size`, `filename.log.1` is renamed to `filename.log.2`, `filename.log.0` is renamed to `filename.log.1`, and `filename.log` is renamed to `filename.log.0`, whereupon a new `filename.log` is opened.

  Here is an example using the `size`, `versions`, and `suffix` options:

      channel an_example_channel {
          file "example.log" versions 3 size 20m suffix increment;
          print-time yes;
          print-category yes;
      };

syslog

  Grammar: `syslog [ <syslog_facility> ];`

  Blocks: logging.channel

  Tags: logging

  Directs the logging channel to the system log.

  The `syslog` destination clause directs the channel to the system log. Its argument is a syslog facility as described in the `syslog` man page. Known facilities are `kern`, `user`, `mail`, `daemon`, `auth`, `syslog`, `lpr`, `news`, `uucp`, `cron`, `authpriv`, `ftp`, `local0`, `local1`, `local2`, `local3`, `local4`, `local5`, `local6`, and `local7`; however, not all facilities are supported on all operating systems. How `syslog` handles messages sent to this facility is described in the `syslog.conf` man page. On a system which uses a very old version of `syslog`, which only uses two arguments to the `openlog()` function, this clause is silently ignored.

severity

  Grammar: `severity <log_severity>;`

  Blocks: logging.channel

  Tags: logging

  Defines the priority level of log messages.

  The `severity` clause works like `syslog`’s “priorities,” except that they can also be used when writing straight to a file rather than using `syslog`. Messages which are not at least of the severity level given are not selected for the channel; messages of higher severity levels are accepted.

  When using `syslog`, the `syslog.conf` priorities also determine what eventually passes through. For example, defining a channel facility and severity as `daemon` and `debug`, but only logging `daemon.warning` via `syslog.conf`, causes messages of severity `info` and `notice` to be dropped. If the situation were reversed, with `named` writing messages of only `warning` or higher, then `syslogd` would print all messages it received from the channel.

stderr

  Grammar: `stderr;`

  Blocks: logging.channel

  Tags: logging

  Directs the logging channel output to the server’s standard error stream.

  The `stderr` destination clause directs the channel to the server’s standard error stream. This is intended for use when the server is running as a foreground process, as when debugging a configuration, for example.

The server can supply extensive debugging information when it is in debugging mode. If the server’s global debug level is greater than zero, debugging mode is active. The global debug level is set either by starting the `named` server with the `-d` flag followed by a positive integer, or by running `rndc trace`. The global debug level can be set to zero, and debugging mode turned off, by running `rndc notrace`. All debugging messages in the server have a debug level; higher debug levels give more detailed output. Channels that indicate a specific debug severity get debugging output of level 3 or less any time the server is in debugging mode, regardless of the global debugging level:

    channel specific_debug_level {
        file "foo";
        severity debug 3;
    };

Channels with `dynamic` severity use the server’s global debug level to determine which messages to print.

print-time

  Grammar: `print-time ( iso8601 | iso8601-utc | local | <boolean> );`

  Blocks: logging.channel

  Tags: logging

  Specifies the time format for log messages.

  `print-time` can be set to `yes`, `no`, or a time format specifier, which may be one of `local`, `iso8601`, or `iso8601-utc`. If set to `no`, the date and time are not logged. If set to `yes` or `local`, the date and time are logged in a human-readable format, using the local time zone. If set to `iso8601`, the local time is logged in ISO 8601 format. If set to `iso8601-utc`, the date and time are logged in ISO 8601 format, with time zone set to UTC. The default is `no`.

  `print-time` may be specified for a `syslog` channel, but it is usually pointless since `syslog` also logs the date and time.

print-category

  Grammar: `print-category <boolean>;`

  Blocks: logging.channel

  Tags: logging

  Includes the category in log messages.

  If `print-category` is requested, then the category of the message is logged as well.

print-severity

  Grammar: `print-severity <boolean>;`

  Blocks: logging.channel

  Tags: logging

  Includes the severity in log messages.

  If `print-severity` is on, then the severity level of the message is logged. The `print-` options may be used in any combination, and are always printed in the following order: time, category, severity.

Here is an example where all three `print-` options are on:

`28-Feb-2000 15:05:32.863 general: notice: running`

buffered

  Grammar: `buffered <boolean>;`

  Blocks: logging.channel

  Tags: logging

  Controls flushing of log messages.

  If `buffered` has been turned on, the output to files is not flushed after each log entry. By default all log messages are flushed.

There are four predefined channels that are used for `named`’s default logging, as follows. If `named` is started with the `-L` option, then a fifth channel, `default_logfile`, is added. How they are used is described in `category`.

    channel default_syslog {
        // send to syslog's daemon facility
        syslog daemon;
        // only send priority info and higher
        severity info;
    };

    channel default_debug {
        // write to named.run in the working directory
        // Note: stderr is used instead of "named.run" if
        // the server is started with the '-g' option.
        file "named.run";
        // log at the server's current debug level
        severity dynamic;
    };

    channel default_stderr {
        // writes to stderr
        stderr;
        // only send priority info and higher
        severity info;
    };

    channel null {
       // toss anything sent to this channel
       null;
    };

    channel default_logfile {
        // this channel is only present if named is
        // started with the -L option, whose argument
        // provides the file name
        file "...";
        // log at the server's current debug level
        severity dynamic;
    };

The `default_debug` channel has the special property that it only produces output when the server’s debug level is non-zero. It normally writes to a file called `named.run` in the server’s working directory.

For security reasons, when the `-u` command-line option is used, the `named.run` file is created only after `named` has changed to the new UID, and any debug output generated while `named` is starting - and still running as root - is discarded. To capture this output, run the server with the `-L` option to specify a default logfile, or the `-g` option to log to standard error which can be redirected to a file.

Once a channel is defined, it cannot be redefined. The built-in channels cannot be altered directly, but the default logging can be modified by pointing categories at defined channels.

#### 8.2.10.2. The `category` Phrase

There are many categories, so desired logs can be sent anywhere while unwanted logs are ignored. If a list of channels is not specified for a category, log messages in that category are sent to the `default` category instead. If no default category is specified, the following “default default” is used:

    category default { default_syslog; default_debug; };

If `named` is started with the `-L` option, the default category is:

    category default { default_logfile; default_debug; };

As an example, let’s say a user wants to log security events to a file, but also wants to keep the default logging behavior. They would specify the following:

    channel my_security_channel {
        file "my_security_file";
        severity info;
    };
    category security {
        my_security_channel;
        default_syslog;
        default_debug;
    };

To discard all messages in a category, specify the `null` channel:

    category xfer-out { null; };
    category notify { null; };

category

  Grammar: `category <string> { <string>; ... }; // may occur multiple times`

  Blocks: logging

  Tags: logging

  Specifies the type of data logged to a particular channel.

The following are the available categories and brief descriptions of the types of log information they contain. More categories may be added in future BIND releases.

`client`

  Processing of client requests.

`cname`

  Name servers that are skipped for being a CNAME rather than A/AAAA records.

`config`

  Configuration file parsing and processing.

`database`

  Messages relating to the databases used internally by the name server to store zone and cache data.

`default`

  Logging options for those categories where no specific configuration has been defined.

`dispatch`

  Dispatching of incoming packets to the server modules where they are to be processed.

`dnssec`

  DNSSEC and TSIG protocol processing.

`dnstap`

  The `dnstap` DNS traffic capture system.

`edns-disabled`

  Log queries that have been forced to use plain DNS due to timeouts. This is often due to the remote servers not being RFC 1034-compliant (not always returning FORMERR or similar to EDNS queries and other extensions to the DNS when they are not understood). In other words, this is targeted at servers that fail to respond to DNS queries that they don’t understand.

  Note: the log message can also be due to packet loss. Before reporting servers for non-RFC 1034 compliance they should be re-tested to determine the nature of the non-compliance. This testing should prevent or reduce the number of false-positive reports.

  Note: eventually `named` will have to stop treating such timeouts as due to RFC 1034 non-compliance and start treating it as plain packet loss. Falsely classifying packet loss as due to RFC 1034 non-compliance impacts DNSSEC validation, which requires EDNS for the DNSSEC records to be returned.

`general`

  A catch-all for many things that still are not classified into categories.

`lame-servers`

  Misconfigurations in remote servers, discovered by BIND 9 when trying to query those servers during resolution.

`network`

  Network operations.

`notify`

  The NOTIFY protocol.

`nsid`

  NSID options received from upstream servers.

`queries`

  The locations where queries should be logged.

  At startup, specifying the category `queries` also enables query logging unless the `querylog` option has been specified.

  The query log entry first reports a client object identifier in @0x<hexadecimal-number> format. Next, it reports the client’s IP address and port number, and the query name, class, and type. Next, it reports whether the Recursion Desired flag was set (+ if set, - if not set), whether the query was signed (S), whether EDNS was in use along with the EDNS version number (E(#)), whether TCP was used (T), whether DO (DNSSEC Ok) was set (D), whether CD (Checking Disabled) was set (C), whether a valid DNS Server COOKIE was received (V), and whether a DNS COOKIE option without a valid Server COOKIE was present (K). After this, the destination address the query was sent to is reported. Finally, if any CLIENT-SUBNET option was present in the client query, it is included in square brackets in the format [ECS address/source/scope].

      client @0x7f91b8005490 127.0.0.1#62536 (www.example.com): query: www.example.com IN AAAA +E(0)K (127.0.0.1)
      client @0x7f91b4007400 ::1#62537 (www.example.net): query: www.example.net IN AAAA +E(0)K (::1)

  The first part of this log message, showing the client address/port number and query name, is repeated in all subsequent log messages related to the same query.

`query-errors`

  Information about queries that resulted in some failure.

`rate-limit`

  Start, periodic, and final notices of the rate limiting of a stream of responses that are logged at `info` severity in this category. These messages include a hash value of the domain name of the response and the name itself, except when there is insufficient memory to record the name for the final notice. The final notice is normally delayed until about one minute after rate limiting stops. A lack of memory can hurry the final notice, which is indicated by an initial asterisk (*). Various internal events are logged at debug level 1 and higher.

  Rate limiting of individual requests is logged in the `query-errors` category.

`resolver`

  DNS resolution, such as the recursive lookups performed on behalf of clients by a caching name server.

`responses`

  The locations where query response summaries should be logged.

`rpz`

  Information about errors in response policy zone files, rewritten responses, and, at the highest `debug` levels, mere rewriting attempts.

`rpz-passthru`

  Information about RPZ PASSTHRU policy activity. This category allows pre-approved policy activity to be logged into a dedicated channel.

`security`

  Approval and denial of requests.

`serve-stale`

  Indication of whether a stale answer is used following a resolver failure.

`spill`

  Queries that have been terminated, either by dropping or responding with SERVFAIL, as a result of a fetchlimit quota being exceeded.

`sslkeylog`

  TLS pre-master secrets (for debugging purposes).

`trust-anchor-telemetry`

  `trust-anchor-telemetry` requests received by `named`.

`unmatched`

  Messages that `named` was unable to determine the class of, or for which there was no matching `view`. A one-line summary is also logged to the `client` category. This category is best sent to a file or stderr; by default it is sent to the `null` channel.

`update`

  Dynamic updates.

`update-security`

  Approval and denial of update requests.

`xfer-in`

  Zone transfers the server is receiving.

`xfer-out`

  Zone transfers the server is sending.

`zoneload`

  Loading of zones and creation of automatic empty zones.

#### 8.2.10.3. The `query-errors` Category

The `query-errors` category is used to indicate why and how specific queries resulted in responses which indicate an error. Normally, these messages are logged at `debug` logging levels; note, however, that if query logging is active, some are logged at `info`. The logging levels are described below:

At `debug` level 1 or higher - or at `info` when query logging is active - each response with the rcode of SERVFAIL is logged as follows:

`client 127.0.0.1#61502: query failed (SERVFAIL) for www.example.com/IN/AAAA at query.c:3880`

This means an error resulting in SERVFAIL was detected at line 3880 of source file `query.c`. Log messages of this level are particularly helpful in identifying the cause of SERVFAIL for an authoritative server.

At `debug` level 2 or higher, detailed context information about recursive resolutions that resulted in SERVFAIL is logged. The log message looks like this:

    fetch completed at resolver.c:2970 for www.example.com/A
    in 10.000183: timed out/success [domain:example.com,
    referral:2,restart:7,qrysent:8,timeout:5,lame:0,quota:0,neterr:0,
    badresp:1,adberr:0,findfail:0,valfail:0]

The first part before the colon shows that a recursive resolution for AAAA records of www.example.com completed in 10.000183 seconds, and the final result that led to the SERVFAIL was determined at line 2970 of source file `resolver.c`.

The next part shows the detected final result and the latest result of DNSSEC validation. The latter is always “success” when no validation attempt was made. In this example, this query probably resulted in SERVFAIL because all name servers are down or unreachable, leading to a timeout in 10 seconds. DNSSEC validation was probably not attempted.

The last part, enclosed in square brackets, shows statistics collected for this particular resolution attempt. The `domain` field shows the deepest zone that the resolver reached; it is the zone where the error was finally detected. The meaning of the other fields is summarized in the following list.

`referral`

  The number of referrals the resolver received throughout the resolution process. In the above `example.com` there are two.

`restart`

  The number of cycles that the resolver tried remote servers at the `domain` zone. In each cycle, the resolver sends one query (possibly resending it, depending on the response) to each known name server of the `domain` zone.

`qrysent`

  The number of queries the resolver sent at the `domain` zone.

`timeout`

  The number of timeouts the resolver received since the last response.

`lame`

  The number of lame servers the resolver detected at the `domain` zone. A server is detected to be lame either by an invalid response or as a result of lookup in BIND 9’s address database (ADB), where lame servers are cached.

`quota`

  The number of times the resolver was unable to send a query because it had exceeded the permissible fetch quota for a server.

`neterr`

  The number of erroneous results that the resolver encountered in sending queries at the `domain` zone. One common case is when the remote server is unreachable and the resolver receives an “ICMP unreachable” error message.

`badresp`

  The number of unexpected responses (other than `lame`) to queries sent by the resolver at the `domain` zone.

`adberr`

  Failures in finding remote server addresses of the``domain`` zone in the ADB. One common case of this is that the remote server’s name does not have any address records.

`findfail`

  Failures to resolve remote server addresses. This is a total number of failures throughout the resolution process.

`valfail`

  Failures of DNSSEC validation. Validation failures are counted throughout the resolution process (not limited to the `domain` zone), but should only happen in `domain`.

At `debug` level 3 or higher, the same messages as those at `debug` level 1 are logged for errors other than SERVFAIL. Note that negative responses such as NXDOMAIN are not errors, and are not logged at this debug level.

At `debug` level 4 or higher, the detailed context information logged at `debug` level 2 is logged for errors other than SERVFAIL and for negative responses such as NXDOMAIN.

### 8.2.11. `remote-servers` Block Grammar

remote-servers

  Grammar: `remote-servers <string> [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... }; // may occur multiple times`

  Blocks: topmost

  Tags: server

  Defines a list of servers to be used by primary and secondary zones.

This specifies a list that allows for a common set of servers to be easily used by multiple zones. The following options may reference to a list of remote servers: `parental-agents`, `primaries`, and `also-notify`.

A “parental agent” is a trusted DNS server that is queried to check whether DS records for a given zones are up-to-date.

A “primary server” is where a secondary server can request zone transfers from.

To force the zone transfer requests to be sent over TLS, use `tls` keyword, e.g. `primaries { 192.0.2.1 tls tls-configuration-name; };`, where `tls-configuration-name` refers to a previously defined `tls statement`.

Warning

Please note that TLS connections to primaries are not authenticated unless `remote-hostname` or `ca-file` are specified within the `tls statement` in use (see information on Strict TLS and Mutual TLS for more details). Not authenticated mode (Opportunistic TLS) provides protection from passive observers but does not protect from man-in-the-middle attacks on zone transfers.

### 8.2.12. `options` Block Grammar

options

  Grammar:

      options {
      	allow-new-zones <boolean>;
      	allow-notify { <address_match_element>; ... };
      	allow-proxy { <address_match_element>; ... }; // experimental
      	allow-proxy-on { <address_match_element>; ... }; // experimental
      	allow-query { <address_match_element>; ... };
      	allow-query-cache { <address_match_element>; ... };
      	allow-query-cache-on { <address_match_element>; ... };
      	allow-query-on { <address_match_element>; ... };
      	allow-recursion { <address_match_element>; ... };
      	allow-recursion-on { <address_match_element>; ... };
      	allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_element>; ... };
      	allow-update { <address_match_element>; ... };
      	allow-update-forwarding { <address_match_element>; ... };
      	also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      	answer-cookie <boolean>;
      	attach-cache <string>;
      	auth-nxdomain <boolean>;
      	automatic-interface-scan <boolean>;
      	avoid-v4-udp-ports { <portrange>; ... }; // deprecated
      	avoid-v6-udp-ports { <portrange>; ... }; // deprecated
      	bindkeys-file <quoted_string>; // test only
      	blackhole { <address_match_element>; ... };
      	catalog-zones { zone <string> [ default-primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... } ] [ zone-directory <quoted_string> ] [ in-memory <boolean> ] [ min-update-interval <duration> ]; ... };
      	check-dup-records ( fail | warn | ignore );
      	check-integrity <boolean>;
      	check-mx ( fail | warn | ignore );
      	check-mx-cname ( fail | warn | ignore );
      	check-names ( primary | master | secondary | slave | response ) ( fail | warn | ignore ); // may occur multiple times
      	check-sibling <boolean>;
      	check-spf ( warn | ignore );
      	check-srv-cname ( fail | warn | ignore );
      	check-svcb <boolean>;
      	check-wildcard <boolean>;
      	clients-per-query <integer>;
      	cookie-algorithm ( siphash24 );
      	cookie-secret <string>; // may occur multiple times
      	deny-answer-addresses { <address_match_element>; ... } [ except-from { <string>; ... } ];
      	deny-answer-aliases { <string>; ... } [ except-from { <string>; ... } ];
      	dialup ( notify | notify-passive | passive | refresh | <boolean> ); // deprecated
      	directory <quoted_string>;
      	disable-algorithms <string> { <string>; ... }; // may occur multiple times
      	disable-ds-digests <string> { <string>; ... }; // may occur multiple times
      	disable-empty-zone <string>; // may occur multiple times
      	dns64 <netprefix> {
      		break-dnssec <boolean>;
      		clients { <address_match_element>; ... };
      		exclude { <address_match_element>; ... };
      		mapped { <address_match_element>; ... };
      		recursive-only <boolean>;
      		suffix <ipv6_address>;
      	}; // may occur multiple times
      	dns64-contact <string>;
      	dns64-server <string>;
      	dnskey-sig-validity <integer>; // obsolete
      	dnsrps-enable <boolean>;
      	dnsrps-library <quoted_string>;
      	dnsrps-options { <unspecified-text> };
      	dnssec-accept-expired <boolean>;
      	dnssec-dnskey-kskonly <boolean>; // obsolete
      	dnssec-loadkeys-interval <integer>;
      	dnssec-must-be-secure <string> <boolean>; // may occur multiple times, deprecated
      	dnssec-policy <string>;
      	dnssec-secure-to-insecure <boolean>; // obsolete
      	dnssec-update-mode ( maintain | no-resign ); // obsolete
      	dnssec-validation ( yes | no | auto );
      	dnstap { ( all | auth | client | forwarder | resolver | update ) [ ( query | response ) ]; ... };
      	dnstap-identity ( <quoted_string> | none | hostname );
      	dnstap-output ( file | unix ) <quoted_string> [ size ( unlimited | <size> ) ] [ versions ( unlimited | <integer> ) ] [ suffix ( increment | timestamp ) ];
      	dnstap-version ( <quoted_string> | none );
      	dual-stack-servers [ port <integer> ] { ( <quoted_string> [ port <integer> ] | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ); ... };
      	dump-file <quoted_string>;
      	edns-udp-size <integer>;
      	empty-contact <string>;
      	empty-server <string>;
      	empty-zones-enable <boolean>;
      	fetch-quota-params <integer> <fixedpoint> <fixedpoint> <fixedpoint>;
      	fetches-per-server <integer> [ ( drop | fail ) ];
      	fetches-per-zone <integer> [ ( drop | fail ) ];
      	flush-zones-on-shutdown <boolean>;
      	forward ( first | only );
      	forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };
      	fstrm-set-buffer-hint <integer>;
      	fstrm-set-flush-timeout <integer>;
      	fstrm-set-input-queue-size <integer>;
      	fstrm-set-output-notify-threshold <integer>;
      	fstrm-set-output-queue-model ( mpsc | spsc );
      	fstrm-set-output-queue-size <integer>;
      	fstrm-set-reopen-interval <duration>;
      	geoip-directory ( <quoted_string> | none );
      	heartbeat-interval <integer>; // deprecated
      	hostname ( <quoted_string> | none );
      	http-listener-clients <integer>;
      	http-port <integer>;
      	http-streams-per-connection <integer>;
      	https-port <integer>;
      	interface-interval <duration>;
      	ipv4only-contact <string>;
      	ipv4only-enable <boolean>;
      	ipv4only-server <string>;
      	ixfr-from-differences ( primary | master | secondary | slave | <boolean> );
      	keep-response-order { <address_match_element>; ... }; // obsolete
      	key-directory <quoted_string>;
      	lame-ttl <duration>;
      	listen-on [ port <integer> ] [ proxy <string> ] [ tls <string> ] [ http <string> ] { <address_match_element>; ... }; // may occur multiple times
      	listen-on-v6 [ port <integer> ] [ proxy <string> ] [ tls <string> ] [ http <string> ] { <address_match_element>; ... }; // may occur multiple times
      	lmdb-mapsize <sizeval>;
      	managed-keys-directory <quoted_string>;
      	masterfile-format ( raw | text );
      	masterfile-style ( full | relative );
      	match-mapped-addresses <boolean>;
      	max-cache-size ( default | unlimited | <sizeval> | <percentage> );
      	max-cache-ttl <duration>;
      	max-clients-per-query <integer>;
      	max-ixfr-ratio ( unlimited | <percentage> );
      	max-journal-size ( default | unlimited | <sizeval> );
      	max-ncache-ttl <duration>;
      	max-query-count <integer>;
      	max-query-restarts <integer>;
      	max-records <integer>;
      	max-records-per-type <integer>;
      	max-recursion-depth <integer>;
      	max-recursion-queries <integer>;
      	max-refresh-time <integer>;
      	max-retry-time <integer>;
      	max-rsa-exponent-size <integer>;
      	max-stale-ttl <duration>;
      	max-transfer-idle-in <integer>;
      	max-transfer-idle-out <integer>;
      	max-transfer-time-in <integer>;
      	max-transfer-time-out <integer>;
      	max-types-per-name <integer>;
      	max-udp-size <integer>;
      	max-validation-failures-per-fetch <integer>; // experimental
      	max-validations-per-fetch <integer>; // experimental
      	max-zone-ttl ( unlimited | <duration> ); // deprecated
      	memstatistics <boolean>;
      	memstatistics-file <quoted_string>;
      	message-compression <boolean>;
      	min-cache-ttl <duration>;
      	min-ncache-ttl <duration>;
      	min-refresh-time <integer>;
      	min-retry-time <integer>;
      	min-transfer-rate-in <integer> <integer>;
      	minimal-any <boolean>;
      	minimal-responses ( no-auth | no-auth-recursive | <boolean> );
      	multi-master <boolean>;
      	new-zones-directory <quoted_string>;
      	no-case-compress { <address_match_element>; ... };
      	nocookie-udp-size <integer>;
      	notify ( explicit | master-only | primary-only | <boolean> );
      	notify-defer <integer>;
      	notify-delay <integer>;
      	notify-rate <integer>;
      	notify-source ( <ipv4_address> | * );
      	notify-source-v6 ( <ipv6_address> | * );
      	notify-to-soa <boolean>;
      	nsec3-test-zone <boolean>; // test only
      	nta-lifetime <duration>;
      	nta-recheck <duration>;
      	nxdomain-redirect <string>;
      	parental-source ( <ipv4_address> | * );
      	parental-source-v6 ( <ipv6_address> | * );
      	pid-file ( <quoted_string> | none );
      	port <integer>;
      	preferred-glue <string>;
      	prefetch <integer> [ <integer> ];
      	provide-ixfr <boolean>;
      	qname-minimization ( strict | relaxed | disabled | off );
      	query-source [ address ] ( <ipv4_address> | * | none );
      	query-source-v6 [ address ] ( <ipv6_address> | * | none );
      	querylog <boolean>;
      	rate-limit {
      		all-per-second <integer>;
      		errors-per-second <integer>;
      		exempt-clients { <address_match_element>; ... };
      		ipv4-prefix-length <integer>;
      		ipv6-prefix-length <integer>;
      		log-only <boolean>;
      		max-table-size <integer>;
      		min-table-size <integer>;
      		nodata-per-second <integer>;
      		nxdomains-per-second <integer>;
      		qps-scale <integer>;
      		referrals-per-second <integer>;
      		responses-per-second <integer>;
      		slip <integer>;
      		window <integer>;
      	};
      	recursing-file <quoted_string>;
      	recursion <boolean>;
      	recursive-clients <integer>;
      	request-expire <boolean>;
      	request-ixfr <boolean>;
      	request-nsid <boolean>;
      	require-server-cookie <boolean>;
      	resolver-query-timeout <integer>;
      	resolver-use-dns64 <boolean>;
      	response-padding { <address_match_element>; ... } block-size <integer>;
      	response-policy { zone <string> [ add-soa <boolean> ] [ log <boolean> ] [ max-policy-ttl <duration> ] [ min-update-interval <duration> ] [ policy ( cname | disabled | drop | given | no-op | nodata | nxdomain | passthru | tcp-only <quoted_string> ) ] [ recursive-only <boolean> ] [ nsip-enable <boolean> ] [ nsdname-enable <boolean> ] [ ede <string> ]; ... } [ add-soa <boolean> ] [ break-dnssec <boolean> ] [ max-policy-ttl <duration> ] [ min-update-interval <duration> ] [ min-ns-dots <integer> ] [ nsip-wait-recurse <boolean> ] [ nsdname-wait-recurse <boolean> ] [ qname-wait-recurse <boolean> ] [ recursive-only <boolean> ] [ nsip-enable <boolean> ] [ nsdname-enable <boolean> ] [ dnsrps-enable <boolean> ] [ dnsrps-options { <unspecified-text> } ];
      	responselog <boolean>;
      	reuseport <boolean>;
      	root-key-sentinel <boolean>;
      	rrset-order { [ class <string> ] [ type <string> ] [ name <quoted_string> ] <string> <string>; ... };
      	secroots-file <quoted_string>;
      	send-cookie <boolean>;
      	serial-query-rate <integer>;
      	serial-update-method ( date | increment | unixtime );
      	server-id ( <quoted_string> | none | hostname );
      	servfail-ttl <duration>;
      	session-keyalg <string>;
      	session-keyfile ( <quoted_string> | none );
      	session-keyname <string>;
      	sig-signing-nodes <integer>;
      	sig-signing-signatures <integer>;
      	sig-signing-type <integer>;
      	sig-validity-interval <integer> [ <integer> ]; // obsolete
      	sig0checks-quota <integer>; // experimental
      	sig0checks-quota-exempt { <address_match_element>; ... }; // experimental
      	sig0key-checks-limit <integer>;
      	sig0message-checks-limit <integer>;
      	sortlist { <address_match_element>; ... }; // deprecated
      	stale-answer-client-timeout ( disabled | off | <integer> );
      	stale-answer-enable <boolean>;
      	stale-answer-ttl <duration>;
      	stale-cache-enable <boolean>;
      	stale-refresh-time <duration>;
      	startup-notify-rate <integer>;
      	statistics-file <quoted_string>;
      	synth-from-dnssec <boolean>;
      	tcp-advertised-timeout <integer>;
      	tcp-clients <integer>;
      	tcp-idle-timeout <integer>;
      	tcp-initial-timeout <integer>;
      	tcp-keepalive-timeout <integer>;
      	tcp-listen-queue <integer>;
      	tcp-receive-buffer <integer>;
      	tcp-send-buffer <integer>;
      	tkey-domain <quoted_string>;
      	tkey-gssapi-credential <quoted_string>;
      	tkey-gssapi-keytab <quoted_string>;
      	tls-port <integer>;
      	transfer-format ( many-answers | one-answer );
      	transfer-message-size <integer>;
      	transfer-source ( <ipv4_address> | * );
      	transfer-source-v6 ( <ipv6_address> | * );
      	transfers-in <integer>;
      	transfers-out <integer>;
      	transfers-per-ns <integer>;
      	trust-anchor-telemetry <boolean>;
      	try-tcp-refresh <boolean>;
      	udp-receive-buffer <integer>;
      	udp-send-buffer <integer>;
      	update-check-ksk <boolean>; // obsolete
      	update-quota <integer>;
      	use-v4-udp-ports { <portrange>; ... }; // deprecated
      	use-v6-udp-ports { <portrange>; ... }; // deprecated
      	v6-bias <integer>;
      	validate-except { <string>; ... };
      	version ( <quoted_string> | none );
      	zero-no-soa-ttl <boolean>;
      	zero-no-soa-ttl-cache <boolean>;
      	zone-statistics ( full | terse | none | <boolean> );
      };

  Blocks: topmost

  Tags: server

  Defines global options to be used by BIND 9.

This is the grammar of the `options` statement in the `named.conf` file:

### 8.2.13. `options` Block Definition and Usage

The `options` statement sets up global options to be used by BIND. This statement may appear only once in a configuration file. If there is no `options` statement, an options block with each option set to its default is used.

attach-cache

  Grammar: `attach-cache <string>;`

  Blocks: options, view

  Tags: view

  Allows multiple views to share a single cache database.

  This option allows multiple views to share a single cache database. Each view has its own cache database by default, but if multiple views have the same operational policy for name resolution and caching, those views can share a single cache to save memory, and possibly improve resolution efficiency, by using this option.

  The `attach-cache` option may also be specified in `view` statements, in which case it overrides the global `attach-cache` option.

  The `cache_name` specifies the cache to be shared. When the `named` server configures views which are supposed to share a cache, it creates a cache with the specified name for the first view of these sharing views. The rest of the views simply refer to the already-created cache.

  One common configuration to share a cache is to allow all views to share a single cache. This can be done by specifying `attach-cache` as a global option with an arbitrary name.

  Another possible operation is to allow a subset of all views to share a cache while the others retain their own caches. For example, if there are three views A, B, and C, and only A and B should share a cache, specify the `attach-cache` option as a view of A (or B)’s option, referring to the other view name:

      view "A" {
        // this view has its own cache
        ...
      };
      view "B" {
        // this view refers to A's cache
        attach-cache "A";
      };
      view "C" {
        // this view has its own cache
        ...
      };

  Views that share a cache must have the same policy on configurable parameters that may affect caching. The current implementation requires the following configurable options be consistent among these views: `check-names`, `dnssec-accept-expired`, `dnssec-validation`, `max-cache-ttl`, `max-ncache-ttl`, `max-stale-ttl`, `max-cache-size`, `min-cache-ttl`, `min-ncache-ttl`, and `zero-no-soa-ttl`.

  Note that there may be other parameters that may cause confusion if they are inconsistent for different views that share a single cache. For example, if these views define different sets of forwarders that can return different answers for the same question, sharing the answer does not make sense or could even be harmful. It is the administrator’s responsibility to ensure that configuration differences in different views do not cause disruption with a shared cache.

directory

  Grammar key-store: `directory <string>;`

  Grammar options: `directory <quoted_string>;`

  Blocks: key-store, options

  Tags: server

  Sets the server’s working directory.

  This sets the working directory of the server. Any non-absolute pathnames in the configuration file are taken as relative to this directory. The default location for most server output files (e.g., `named.run`) is this directory. If a directory is not specified, the working directory defaults to `"."`, the directory from which the server was started. The directory specified should be an absolute path, and must be writable by the effective user ID of the `named` process.

  The option takes effect only at the time that the configuration option is parsed; if other files are being included before or after specifying the new `directory`, the `directory` option must be listed before any other directive (like `include`) that can work with relative files. The safest way to include files is to use absolute file names.

dnstap

  Grammar: `dnstap { ( all | auth | client | forwarder | resolver | update ) [ ( query | response ) ]; ... };`

  Blocks: options, view

  Tags: logging

  Enables logging of `dnstap` messages.

  `dnstap` is a fast, flexible method for capturing and logging DNS traffic. Developed by Robert Edmonds at Farsight Security, Inc., and supported by multiple DNS implementations, `dnstap` uses `libfstrm` (a lightweight high-speed framing library; see https://github.com/farsightsec/fstrm) to send event payloads which are encoded using Protocol Buffers (`libprotobuf-c`, a mechanism for serializing structured data developed by Google, Inc.; see https://protobuf.dev).

  To enable `dnstap` at compile time, the `fstrm` and `protobuf-c` libraries must be available, and BIND must be configured with `--enable-dnstap`.

  The `dnstap` option is a bracketed list of message types to be logged. These may be set differently for each view. Supported types are `client`, `auth`, `resolver`, `forwarder`, and `update`. Specifying type `all` causes all `dnstap` messages to be logged, regardless of type.

  Each type may take an additional argument to indicate whether to log `query` messages or `response` messages; if not specified, both queries and responses are logged.

  Example: To log all authoritative queries and responses, recursive client responses, and upstream queries sent by the resolver, use:

      dnstap {
        auth;
        client response;
        resolver query;
      };

  Note

  In the default configuration, the dnstap output for recursive resolver traffic does not include the IP addresses used by server-side sockets. This is caused by the fact that unless the query source address is explicitly set, these sockets are bound to wildcard IP addresses and determining the specific IP address used by each of them requires issuing a system call (i.e. incurring a performance penalty).

  Logged `dnstap` messages can be parsed using the `dnstap-read` utility (see dnstap-read - print dnstap data in human-readable form for details).

  For more information on `dnstap`, see https://dnstap.info.

  The `fstrm` library has a number of tunables that are exposed in `named.conf`, and can be modified if necessary to improve performance or prevent loss of data. These are:

  fstrm-set-buffer-hint

    Grammar: `fstrm-set-buffer-hint <integer>;`

    Blocks: options

    Tags: logging

    Sets the number of accumulated bytes in the output buffer before forcing a buffer flush.

    The indicates the threshold number of bytes to accumulate in the output buffer before forcing a buffer flush. The minimum is 1024, the maximum is 65536, and the default is 8192.

  fstrm-set-flush-timeout

    Grammar: `fstrm-set-flush-timeout <integer>;`

    Blocks: options

    Tags: logging

    Sets the number of seconds that unflushed data remains in the output buffer.

    This is the number of seconds to allow unflushed data to remain in the output buffer. The minimum is 1 second, the maximum is 600 seconds (10 minutes), and the default is 1 second.

  fstrm-set-output-notify-threshold

    Grammar: `fstrm-set-output-notify-threshold <integer>;`

    Blocks: options

    Tags: logging

    Sets the number of outstanding queue entries allowed on an input queue before waking the I/O thread.

    This indicates the number of outstanding queue entries to allow on an input queue before waking the I/O thread. The minimum is 1 and the default is 32.

  fstrm-set-output-queue-model

    Grammar: `fstrm-set-output-queue-model ( mpsc | spsc );`

    Blocks: options

    Tags: logging

    Sets the queuing semantics to use for queue objects.

    This sets the queuing semantics to use for queue objects. The default is `mpsc` (multiple producer, single consumer); the other option is `spsc` (single producer, single consumer).

  fstrm-set-input-queue-size

    Grammar: `fstrm-set-input-queue-size <integer>;`

    Blocks: options

    Tags: logging

    Sets the number of queue entries to allocate for each input queue.

    This is the number of queue entries to allocate for each input queue. This value must be a power of 2. The minimum is 2, the maximum is 16384, and the default is 512.

  fstrm-set-output-queue-size

    Grammar: `fstrm-set-output-queue-size <integer>;`

    Blocks: options

    Tags: logging

    Sets the number of queue entries allocated for each output queue.

    This specifies the number of queue entries to allocate for each output queue. The minimum is 2, the maximum is system-dependent and based on `IOV_MAX`, and the default is 64.

  fstrm-set-reopen-interval

    Grammar: `fstrm-set-reopen-interval <duration>;`

    Blocks: options

    Tags: logging

    Sets the number of seconds to wait between attempts to reopen a closed output stream.

    This sets the number of seconds to wait between attempts to reopen a closed output stream. The minimum is 1 second, the maximum is 600 seconds (10 minutes), and the default is 5 seconds. For convenience, TTL-style time-unit suffixes may be used to specify the value.

  Note that all of the above minimum, maximum, and default values are set by the `libfstrm` library, and may be subject to change in future versions of the library. See the `libfstrm` documentation for more information.

dnstap-output

  Grammar: `dnstap-output ( file | unix ) <quoted_string> [ size ( unlimited | <size> ) ] [ versions ( unlimited | <integer> ) ] [ suffix ( increment | timestamp ) ];`

  Blocks: options

  Tags: logging

  Configures the path to which the `dnstap` frame stream is sent.

  This configures the path to which the `dnstap` frame stream is sent if `dnstap` is enabled at compile time and active.

  The first argument is either `file` or `unix`, indicating whether the destination is a file or a Unix domain socket. The second argument is the path of the file or socket. (Note: when using a socket, `dnstap` messages are only sent if another process such as `fstrm_capture` (provided with `libfstrm`) is listening on the socket.)

  If the first argument is `file`, then up to three additional options can be added: `size` indicates the size to which a `dnstap` log file can grow before being rolled to a new file; `versions` specifies the number of rolled log files to retain; and `suffix` indicates whether to retain rolled log files with an incrementing counter as the suffix (`increment`) or with the current timestamp (`timestamp`). These are similar to the `size`, `versions`, and `suffix` options in a `logging` channel. The default is to allow `dnstap` log files to grow to any size without rolling.

  `dnstap-output` can only be set globally in `options`. Currently, it can only be set once while `named` is running; once set, it cannot be changed by `rndc reload` or `rndc reconfig`.

dnstap-identity

  Grammar: `dnstap-identity ( <quoted_string> | none | hostname );`

  Blocks: options

  Tags: logging

  Specifies an `identity` string to send in `dnstap` messages.

  This specifies an `identity` string to send in `dnstap` messages. If set to `hostname`, which is the default, the server’s hostname is sent. If set to `none`, no identity string is sent.

dnstap-version

  Grammar: `dnstap-version ( <quoted_string> | none );`

  Blocks: options

  Tags: logging

  Specifies a `version` string to send in `dnstap` messages.

  This specifies a `version` string to send in `dnstap` messages. The default is the version number of the BIND release. If set to `none`, no version string is sent.

geoip-directory

  Grammar: `geoip-directory ( <quoted_string> | none );`

  Blocks: options

  Tags: server

  Specifies the directory containing GeoIP database files.

  When `named` is compiled using the MaxMind GeoIP2 geolocation API, this specifies the directory containing GeoIP database files. By default, the option is set based on the prefix used to build the `libmaxminddb` module; for example, if the library is installed in `/usr/local/lib`, then the default `geoip-directory` is `/usr/local/share/GeoIP`. See `acl` for details about `geoip` ACLs.

key-directory

  Grammar: `key-directory <quoted_string>;`

  Blocks: options, view, zone (primary, secondary)

  Tags: dnssec

  Indicates the directory where public and private DNSSEC key files are found.

  This is the directory where the public and private DNSSEC key files should be found when performing a dynamic update of secure zones, if different than the current working directory. (Note that this option has no effect on the paths for files containing non-DNSSEC keys, such as `rndc.key`, or `session.key`.)

lmdb-mapsize

  Grammar: `lmdb-mapsize <sizeval>;`

  Blocks: options, view

  Tags: server

  Sets a maximum size for the memory map of the new-zone database in LMDB database format.

  When `named` is built with liblmdb, this option sets a maximum size for the memory map of the new-zone database (NZD) in LMDB database format. This database is used to store configuration information for zones added using `rndc addzone`. Note that this is not the NZD database file size, but the largest size that the database may grow to.

  Because the database file is memory-mapped, its size is limited by the address space of the `named` process. The default of 32 megabytes was chosen to be usable with 32-bit `named` builds. The largest permitted value is 1 terabyte. Given typical zone configurations without elaborate ACLs, a 32 MB NZD file ought to be able to hold configurations of about 100,000 zones.

managed-keys-directory

  Grammar: `managed-keys-directory <quoted_string>;`

  Blocks: options

  Tags: dnssec

  Specifies the directory in which to store the files that track managed DNSSEC keys.

  This specifies the directory in which to store the files that track managed DNSSEC keys (i.e., those configured using the `initial-key` or `initial-ds` keywords in a `trust-anchors` statement). By default, this is the working directory. The directory must be writable by the effective user ID of the `named` process.

  If `named` is not configured to use views, managed keys for the server are tracked in a single file called `managed-keys.bind`. Otherwise, managed keys are tracked in separate files, one file per view; each file name is the view name (or, if it contains characters that are incompatible with use as a file name, the SHA256 hash of the view name), followed by the extension `.mkeys`.

  (Note: in earlier releases, file names for views always used the SHA256 hash of the view name. To ensure compatibility after upgrading, if a file using the old name format is found to exist, it is used instead of the new format.)

max-ixfr-ratio

  Grammar: `max-ixfr-ratio ( unlimited | <percentage> );`

  Blocks: options, view, zone (mirror, primary, secondary)

  Tags: transfer

  Sets the maximum size for IXFR responses to zone transfer requests.

  This sets the size threshold (expressed as a percentage of the size of the full zone) beyond which `named` chooses to use an AXFR response rather than IXFR when answering zone transfer requests. See Incremental Zone Transfers (IXFR).

  The minimum value is `1%`. The keyword `unlimited` disables ratio checking and allows IXFRs of any size. The default is `100%`.

new-zones-directory

  Grammar: `new-zones-directory <quoted_string>;`

  Blocks: options, view

  Tags: zone

  Specifies the directory where configuration parameters are stored for zones added by `rndc addzone`.

  This specifies the directory in which to store the configuration parameters for zones added via `rndc addzone`. By default, this is the working directory. If set to a relative path, it is relative to the working directory. The directory must be writable by the effective user ID of the `named` process.

qname-minimization

  Grammar: `qname-minimization ( strict | relaxed | disabled | off );`

  Blocks: options, view

  Tags: query

  Controls QNAME minimization behavior in the BIND 9 resolver.

  When this is set to `strict`, BIND follows the QNAME minimization algorithm to the letter, as specified in RFC 7816.

  Setting this option to `relaxed` causes BIND to fall back to normal (non-minimized) query mode when it receives either NXDOMAIN or other unexpected responses (e.g., SERVFAIL, improper zone cut, REFUSED) to a minimized query.

  In `relaxed` mode `named` makes NS queries for `<domain>` as it walks down the tree.

  `disabled` disables QNAME minimization completely. `off` is a synonym for `disabled`.

  The current default is `relaxed`, but it may be changed to `strict` in a future release.

tkey-gssapi-keytab

  Grammar: `tkey-gssapi-keytab <quoted_string>;`

  Blocks: options

  Tags: security

  Sets the KRB5 keytab file to use for GSS-TSIG updates.

  This is the KRB5 keytab file to use for GSS-TSIG updates. If this option is set and `tkey-gssapi-credential` is not set, updates are allowed with any key matching a principal in the specified keytab.

tkey-gssapi-credential

  Grammar: `tkey-gssapi-credential <quoted_string>;`

  Blocks: options

  Tags: security

  Sets the security credential for authentication keys requested by the GSS-TSIG protocol.

  This is the security credential with which the server should authenticate keys requested by the GSS-TSIG protocol. Currently only Kerberos 5 authentication is available; the credential is a Kerberos principal which the server can acquire through the default system key file, normally `/etc/krb5.keytab`. The location of the keytab file can be overridden using the `tkey-gssapi-keytab` option. Normally this principal is of the form `DNS/server.domain`. To use GSS-TSIG, `tkey-domain` must also be set if a specific keytab is not set with `tkey-gssapi-keytab`.

tkey-domain

  Grammar: `tkey-domain <quoted_string>;`

  Blocks: options

  Tags: security

  Sets the domain appended to the names of all shared keys generated with `TKEY`.

  This domain is appended to the names of all shared keys generated with `TKEY`. When a client requests a `TKEY` exchange, it may or may not specify the desired name for the key. If present, the name of the shared key is `client-specified part` + `tkey-domain`. Otherwise, the name of the shared key is `random hex digits` + `tkey-domain`. In most cases, the `domainname` should be the server’s domain name, or an otherwise nonexistent subdomain like `_tkey.domainname`. If using GSS-TSIG, this variable must be defined, unless a specific keytab is indicated using `tkey-gssapi-keytab`.

dump-file

  Grammar: `dump-file <quoted_string>;`

  Blocks: options

  Tags: logging

  Indicates the pathname of the file where the server dumps the database after `rndc dumpdb`.

  This is the pathname of the file the server dumps the database to, when instructed to do so with `rndc dumpdb`. If not specified, the default is `named_dump.db`.

memstatistics-file

  Grammar: `memstatistics-file <quoted_string>;`

  Blocks: options

  Tags: logging

  Sets the pathname of the file where the server writes memory usage statistics on exit.

  This is the pathname of the file the server writes memory usage statistics to on exit. If not specified, the default is `named.memstats`.

pid-file

  Grammar: `pid-file ( <quoted_string> | none );`

  Blocks: options

  Tags: server

  Specifies the pathname of the file where the server writes its process ID.

  This is the pathname of the file the server writes its process ID in. If not specified, the default is `/run/named.pid`. The PID file is used by programs that send signals to the running name server. Specifying `pid-file none` disables the use of a PID file; no file is written and any existing one is removed. Note that `none` is a keyword, not a filename, and therefore is not enclosed in double quotes.

recursing-file

  Grammar: `recursing-file <quoted_string>;`

  Blocks: options

  Tags: server

  Specifies the pathname of the file where the server dumps queries that are currently recursing via `rndc recursing`.

  This is the pathname of the file where the server dumps the queries that are currently recursing, when instructed to do so with `rndc recursing`. If not specified, the default is `named.recursing`.

statistics-file

  Grammar: `statistics-file <quoted_string>;`

  Blocks: options

  Tags: logging, server

  Specifies the pathname of the file where the server appends statistics, when using `rndc stats`.

  This is the pathname of the file the server appends statistics to, when instructed to do so using `rndc stats`. If not specified, the default is `named.stats` in the server’s current directory. The format of the file is described in The Statistics File.

bindkeys-file

  Grammar: `bindkeys-file <quoted_string>; // test only`

  Blocks: options

  Tags: dnssec

  Specifies the pathname of a file to override the built-in trusted keys provided by `named`.

  This is the pathname of a file to override the built-in trusted keys provided by `named`. See the discussion of `dnssec-validation` for details. This is intended for server testing.

secroots-file

  Grammar: `secroots-file <quoted_string>;`

  Blocks: options

  Tags: dnssec

  Specifies the pathname of the file where the server dumps security roots, when using `rndc secroots`.

  This is the pathname of the file the server dumps security roots to, when instructed to do so with `rndc secroots`. If not specified, the default is `named.secroots`.

session-keyfile

  Grammar: `session-keyfile ( <quoted_string> | none );`

  Blocks: options

  Tags: security

  Specifies the pathname of the file where a TSIG session key is written, when generated by `named` for use by `nsupdate -l`.

  This is the pathname of the file into which to write a TSIG session key generated by `named` for use by `nsupdate -l`. If not specified, the default is `/run/session.key`. (See Dynamic Update Policies, and in particular the discussion of the `update-policy` statement’s `local` option, for more information about this feature.)

session-keyname

  Grammar: `session-keyname <string>;`

  Blocks: options

  Tags: security

  Specifies the key name for the TSIG session key.

  This is the key name to use for the TSIG session key. If not specified, the default is `local-ddns`.

session-keyalg

  Grammar: `session-keyalg <string>;`

  Blocks: options

  Tags: security

  Specifies the algorithm to use for the TSIG session key.

  This is the algorithm to use for the TSIG session key. Valid values are hmac-sha1, hmac-sha224, hmac-sha256, hmac-sha384, hmac-sha512, and hmac-md5. If not specified, the default is hmac-sha256.

port

  Grammar: `port <integer>;`

  Blocks: options

  Tags: server, query

  Specifies the UDP/TCP port number the server uses to receive and send DNS protocol traffic.

  This is the UDP/TCP port number the server uses to receive and send DNS protocol traffic. The default is 53. This option is mainly intended for server testing; a server using a port other than 53 is not able to communicate with the global DNS.

tls-port

  Grammar: `tls-port <integer>;`

  Blocks: options

  Tags: server, query

  Specifies the TCP port number the server uses to receive and send DNS-over-TLS protocol traffic.

  This is the TCP port number the server uses to receive and send DNS-over-TLS protocol traffic. The default is 853.

https-port

  Grammar: `https-port <integer>;`

  Blocks: options

  Tags: server, query

  Specifies the TCP port number the server uses to receive and send DNS-over-HTTPS protocol traffic.

  This is the TCP port number the server uses to receive and send DNS-over-HTTPS protocol traffic. The default is 443.

http-port

  Grammar: `http-port <integer>;`

  Blocks: options

  Tags: server, query

  Specifies the TCP port number the server uses to receive and send unencrypted DNS traffic via HTTP.

  This is the TCP port number the server uses to receive and send unencrypted DNS traffic via HTTP (a configuration that may be useful when encryption is handled by third-party software or by a reverse proxy).

http-listener-clients

  Grammar: `http-listener-clients <integer>;`

  Blocks: options

  Tags: server

  Limits the number of active concurrent connections on a per-listener basis.

  This sets a hard limit on the number of active concurrent connections on a per-listener basis. The default value is 300; setting it to 0 removes the quota.

http-streams-per-connection

  Grammar: `http-streams-per-connection <integer>;`

  Blocks: options

  Tags: server

  Limits the number of active concurrent HTTP/2 streams on a per-connection basis.

  This sets a hard limit on the number of active concurrent HTTP/2 streams on a per-connection basis. The default value is 100; setting it to 0 removes the limit. Once the limit is exceeded, the server finishes the HTTP session.

preferred-glue

  Grammar: `preferred-glue <string>;`

  Blocks: options, view

  Tags: query

  Controls the order of glue records in an A or AAAA response.

  If specified, the listed type (A or AAAA) is emitted before other glue in the additional section of a query response. The default is to prefer A records when responding to queries that arrived via IPv4, and AAAA when responding to queries that arrived via IPv6.

disable-algorithms

  Grammar: `disable-algorithms <string> { <string>; ... }; // may occur multiple times`

  Blocks: options, view

  Tags: dnssec

  Disables DNSSEC algorithms from a specified zone.

  This disables the specified DNSSEC algorithms at and below the specified name. Multiple `disable-algorithms` statements are allowed. Only the best-match `disable-algorithms` clause is used to determine the algorithms.

  If all supported algorithms are disabled, the zones covered by the `disable-algorithms` setting are treated as insecure.

  Configured trust anchors in `trust-anchors` (or `managed-keys` or `trusted-keys`) that match a disabled algorithm are ignored and treated as if they were not configured.

disable-ds-digests

  Grammar: `disable-ds-digests <string> { <string>; ... }; // may occur multiple times`

  Blocks: options, view

  Tags: dnssec, zone

  Disables DS digest types from a specified zone.

  This disables the specified DS digest types at and below the specified name. Multiple `disable-ds-digests` statements are allowed. Only the best-match `disable-ds-digests` clause is used to determine the digest types.

  If all supported digest types are disabled, the zones covered by `disable-ds-digests` are treated as insecure.

dnssec-must-be-secure

  Warning

  This option is deprecated and will be removed in a future version of BIND.

  Grammar: `dnssec-must-be-secure <string> <boolean>; // may occur multiple times, deprecated`

  Blocks: options, view

  Tags: deprecated

  Defines hierarchies that must or may not be secure (signed and validated).

  This option is deprecated and will be removed in a future release.

  This specifies hierarchies which must be or may not be secure (signed and validated). If `yes`, then `named` only accepts answers if they are secure. If `no`, then normal DNSSEC validation applies, allowing insecure answers to be accepted. The specified domain must be defined as a trust anchor, for instance in a `trust-anchors` statement, or `dnssec-validation auto` must be active.

dns64

  Grammar:

      dns64 <netprefix> {
      	break-dnssec <boolean>;
      	clients { <address_match_element>; ... };
      	exclude { <address_match_element>; ... };
      	mapped { <address_match_element>; ... };
      	recursive-only <boolean>;
      	suffix <ipv6_address>;
      }; // may occur multiple times

  Blocks: options, view

  Tags: query

  Instructs `named` to return mapped IPv4 addresses to AAAA queries when there are no AAAA records.

  This directive instructs `named` to return mapped IPv4 addresses to AAAA queries when there are no AAAA records. It is intended to be used in conjunction with a NAT64. Each `dns64` defines one DNS64 prefix. Multiple DNS64 prefixes can be defined.

  Compatible IPv6 prefixes have lengths of 32, 40, 48, 56, 64, and 96, per RFC 6052. Bits 64..71 inclusive must be zero, with the most significant bit of the prefix in position 0.

  In addition, a reverse IP6.ARPA zone is created for the prefix to provide a mapping from the IP6.ARPA names to the corresponding IN-ADDR.ARPA names using synthesized CNAMEs.

  dns64-server

    Grammar: `dns64-server <string>;`

    Blocks: options, view

    Tags: server

    Specifies the name of the server for `dns64` zones.

  dns64-contact

    Grammar: `dns64-contact <string>;`

    Blocks: options, view

    Tags: server

    Specifies the name of the contact for `dns64` zones.

    `dns64-server` and `dns64-contact` can be used to specify the name of the server and contact for the zones. These can be set at the view/options level but not on a per-prefix basis.

    `dns64` will also cause IPV4ONLY.ARPA to be created if not explicitly disabled using `ipv4only-enable`.

  clients

    Grammar: `clients { <address_match_element>; ... };`

    Blocks: options.dns64, view.dns64

    Tags: query

    Specifies an access control list (ACL) of clients that are affected by a given `dns64` directive.

    Each `dns64` supports an optional `clients` ACL that determines which clients are affected by this directive. If not defined, it defaults to `any;`.

  mapped

    Grammar: `mapped { <address_match_element>; ... };`

    Blocks: options.dns64, view.dns64

    Tags: query

    Specifies an access control list (ACL) of IPv4 addresses that are to be mapped to the corresponding A RRset in `dns64`.

    Each `dns64` block supports an optional `mapped` ACL that selects which IPv4 addresses are to be mapped in the corresponding A RRset. If not defined, it defaults to `any;`.

  exclude

    Grammar: `exclude { <address_match_element>; ... };`

    Blocks: options.dns64, view.dns64

    Tags: query

    Allows a list of IPv6 addresses to be ignored if they appear in a domain name’s AAAA records in `dns64`.

    Normally, DNS64 does not apply to a domain name that owns one or more AAAA records; these records are simply returned. The optional `exclude` ACL allows specification of a list of IPv6 addresses that are ignored if they appear in a domain name’s AAAA records; DNS64 is applied to any A records the domain name owns. If not defined, `exclude` defaults to ::ffff:0.0.0.0/96.

  suffix

    Grammar: `suffix <ipv6_address>;`

    Blocks: options.dns64, view.dns64

    Tags: query

    Defines trailing bits for mapped IPv4 address bits in `dns64`.

    An optional `suffix` can also be defined to set the bits trailing the mapped IPv4 address bits. By default these bits are set to `::`. The bits matching the prefix and mapped IPv4 address must be zero.

  recursive-only

    Grammar: `recursive-only <boolean>;`

    Blocks: options.dns64, view.dns64

    Tags: query

    Toggles whether `dns64` synthesis occurs only for recursive queries.

    If `recursive-only` is set to `yes`, the DNS64 synthesis only happens for recursive queries. The default is `no`.

  break-dnssec

    Grammar: `break-dnssec <boolean>;`

    Blocks: options.dns64, view.dns64

    Tags: query

    Enables `dns64` synthesis even if the validated result would cause a DNSSEC validation failure.

    If `break-dnssec` is set to `yes`, the DNS64 synthesis happens even if the result, if validated, would cause a DNSSEC validation failure. If this option is set to `no` (the default), the DO is set on the incoming query, and there are RRSIGs on the applicable records, then synthesis does not happen.

      acl rfc1918 { 10/8; 192.168/16; 172.16/12; };

      dns64 64:FF9B::/96 {
          clients { any; };
          mapped { !rfc1918; any; };
          exclude { 64:FF9B::/96; ::ffff:0000:0000/96; };
          suffix ::;
      };

resolver-use-dns64

  Grammar: `resolver-use-dns64 <boolean>;`

  Blocks: options, view

  Tags: server

  Specifies whether to apply DNS64 mappings when sending queries.

  If `resolver-use-dns64` is set to `yes`, then the IPv4-to-IPv6 address transformations specified by the `dns64` option are applied to IPv4 server addresses to which recursive queries are sent. This allows a server to perform lookups via a NAT64 connection; queries that would have been sent via IPv4 are instead sent to mapped IPv6 addresses. The default is `no`.

ipv4only-enable

  Grammar: `ipv4only-enable <boolean>;`

  Blocks: options, view

  Tags: query

  Enables automatic IPv4 zones if a `dns64` block is configured.

  This enables or disables automatic zones `ipv4only.arpa`, `170.0.0.192.in-addr.arpa`, and `171.0.0.192.in-addr.arpa`.

  By default these zones are loaded if `dns64` is configured.

ipv4only-server

  Grammar: `ipv4only-server <string>;`

  Blocks: options, view

  Tags: server, query

  Specifies the name of the server for the IPV4ONLY.ARPA zone created by `dns64`.

ipv4only-contact

  Grammar: `ipv4only-contact <string>;`

  Blocks: options, view

  Tags: server

  Specifies the contact for the IPV4ONLY.ARPA zone created by `dns64`.

  `ipv4only-server` and `ipv4only-contact` can be used to specify the name of the server and contact for the IPV4ONLY.ARPA zone created by `dns64`.

dnssec-loadkeys-interval

  Grammar: `dnssec-loadkeys-interval <integer>;`

  Blocks: options, view, zone (primary, secondary)

  Tags: dnssec

  Sets the frequency of automatic checks of the DNSSEC key repository.

  When a zone is configured with `dnssec-policy;`, its key repository must be checked periodically to see whether the next step of a key rollover is due. The `dnssec-loadkeys-interval` option sets the default interval of key repository checks, in minutes, in case the next key event cannot be calculated (e.g. because a DS record needs to be published).

  The default is `60` (1 hour), the minimum is `1` (1 minute), and the maximum is `1440` (24 hours); any higher value is silently reduced.

`dnssec-policy`

> This specifies which key and signing policy (KASP) should be used for this zone. This is a string referring to a `dnssec-policy` block. The default is `none`.

dnssec-update-mode

  Grammar: `dnssec-update-mode ( maintain | no-resign ); // obsolete`

  Blocks: options, view, zone (primary, secondary)

  Tags: obsolete

  This option no longer has any effect.

nta-lifetime

  Grammar: `nta-lifetime <duration>;`

  Blocks: options, view

  Tags: dnssec

  Specifies the lifetime, in seconds, for negative trust anchors added via `rndc nta`.

  This specifies the default lifetime, in seconds, for negative trust anchors added via `rndc nta`.

  A negative trust anchor selectively disables DNSSEC validation for zones that are known to be failing because of misconfiguration, rather than an attack. When data to be validated is at or below an active NTA (and above any other configured trust anchors), `named` aborts the DNSSEC validation process and treats the data as insecure rather than bogus. This continues until the NTA’s lifetime has elapsed. NTAs persist across `named` restarts.

  For convenience, TTL-style time-unit suffixes can be used to specify the NTA lifetime in seconds, minutes, or hours. It also accepts ISO 8601 duration formats.

  `nta-lifetime` defaults to one hour; it cannot exceed one week.

nta-recheck

  Grammar: `nta-recheck <duration>;`

  Blocks: options, view

  Tags: dnssec

  Specifies the time interval for checking whether negative trust anchors added via `rndc nta` are still necessary.

  This specifies how often to check whether negative trust anchors added via `rndc nta` are still necessary.

  A negative trust anchor is normally used when a domain has stopped validating due to operator error; it temporarily disables DNSSEC validation for that domain. In the interest of ensuring that DNSSEC validation is turned back on as soon as possible, `named` periodically sends a query to the domain, ignoring negative trust anchors, to find out whether it can now be validated. If so, the negative trust anchor is allowed to expire early.

  Validity checks can be disabled for an individual NTA by using `rndc nta -f`, or for all NTAs by setting `nta-recheck` to zero.

  For convenience, TTL-style time-unit suffixes can be used to specify the NTA recheck interval in seconds, minutes, or hours. It also accepts ISO 8601 duration formats.

  The default is five minutes. It cannot be longer than `nta-lifetime`, which cannot be longer than a week.

max-zone-ttl

  Warning

  This option is deprecated and will be removed in a future version of BIND.

  Grammar dnssec-policy: `max-zone-ttl <duration>;`

  Grammar options, view, zone (primary, redirect): `max-zone-ttl ( unlimited | <duration> ); // deprecated`

  Blocks: dnssec-policy, options, view, zone (primary, redirect)

  Tags: deprecated

  Specifies a maximum permissible time-to-live (TTL) value, in seconds.

  This should now be configured as part of `dnssec-policy`. Use of this option in `options`, `view`, and `zone` blocks is a fatal error if `dnssec-policy` has also been configured for the same zone. In zones without `dnssec-policy`, this option is deprecated, and will be rendered non-operational in a future release.

  `max-zone-ttl` specifies a maximum permissible TTL value in seconds. For convenience, TTL-style time-unit suffixes may be used to specify the maximum value. When a zone file is loaded, any record encountered with a TTL higher than `max-zone-ttl` causes the zone to be rejected.

  This is needed in DNSSEC-maintained zones because when rolling to a new DNSKEY, the old key needs to remain available until RRSIG records have expired from caches. The `max-zone-ttl` option guarantees that the largest TTL in the zone is no higher than the set value.

  When used in `options`, `view` and `zone` blocks, setting `max-zone-ttl` to zero is equivalent to “unlimited”.

stale-answer-ttl

  Grammar: `stale-answer-ttl <duration>;`

  Blocks: options, view

  Tags: query

  Specifies the time to live (TTL) to be returned on stale answers, in seconds.

  This specifies the TTL to be returned on stale answers. The default is 30 seconds. The minimum allowed is 1 second; a value of 0 is updated silently to 1 second.

  For stale answers to be returned, they must be enabled, either in the configuration file using `stale-answer-enable` or via `rndc serve-stale on`.

serial-update-method

  Grammar: `serial-update-method ( date | increment | unixtime );`

  Blocks: options, view, zone (primary)

  Tags: zone

  Specifies the update method to be used for the zone serial number in the SOA record.

  Zones configured for dynamic DNS may use this option to set the update method to be used for the zone serial number in the SOA record.

  With the default setting of `serial-update-method increment;`, the SOA serial number is incremented by one each time the zone is updated.

  When set to `serial-update-method unixtime;`, the SOA serial number is set to the number of seconds since the Unix epoch, unless the serial number is already greater than or equal to that value, in which case it is simply incremented by one.

  When set to `serial-update-method date;`, the new SOA serial number is the current date in the form “YYYYMMDD”, followed by two zeroes, unless the existing serial number is already greater than or equal to that value, in which case it is incremented by one.

zone-statistics

  Grammar: `zone-statistics ( full | terse | none | <boolean> );`

  Blocks: options, view, zone (mirror, primary, redirect, secondary, static-stub, stub)

  Tags: zone, logging

  Controls the level of statistics gathered for all zones.

  If `full`, the server collects statistical data on all zones, unless specifically turned off on a per-zone basis by specifying `zone-statistics terse` or `zone-statistics none` in the `zone` statement. The statistical data includes, for example, DNSSEC signing operations and the number of authoritative answers per query type. The default is `terse`, providing minimal statistics on zones (including name and current serial number, but not query type counters), and also information about the currently ongoing incoming zone transfers.

  These statistics may be accessed via the `statistics-channel` or using `rndc stats`, which dumps them to the file listed in the `statistics-file`. See also The Statistics File.

  For backward compatibility with earlier versions of BIND 9, the `zone-statistics` option can also accept `yes` or `no`; `yes` has the same meaning as `full`. As of BIND 9.10, `no` has the same meaning as `none`; previously, it was the same as `terse`.

#### 8.2.13.1. Boolean Options

automatic-interface-scan

  Grammar: `automatic-interface-scan <boolean>;`

  Blocks: options

  Tags: server

  Controls the automatic rescanning of network interfaces when addresses are added or removed.

  If `yes` and supported by the operating system, this automatically rescans network interfaces when the interface addresses are added or removed. The default is `yes`. This configuration option does not affect the time-based `interface-interval` option; it is recommended to set the time-based `interface-interval` to 0 when the operator confirms that automatic interface scanning is supported by the operating system.

  The `automatic-interface-scan` implementation uses routing sockets for the network interface discovery; therefore, the operating system must support the routing sockets for this feature to work.

allow-new-zones

  Grammar: `allow-new-zones <boolean>;`

  Blocks: options, view

  Tags: server, zone

  Controls the ability to add zones at runtime via `rndc addzone`.

  If `yes`, then zones can be added at runtime via `rndc addzone`. The default is `no`.

  Newly added zones’ configuration parameters are stored so that they can persist after the server is restarted. The configuration information is saved in a file called `viewname.nzf` (or, if `named` is compiled with liblmdb, in an LMDB database file called `viewname.nzd`). “viewname” is the name of the view, unless the view name contains characters that are incompatible with use as a file name, in which case a cryptographic hash of the view name is used instead.

  Configurations for zones added at runtime are stored either in a new-zone file (NZF) or a new-zone database (NZD), depending on whether `named` was linked with liblmdb at compile time. See rndc - name server control utility for further details about `rndc addzone`.

auth-nxdomain

  Grammar: `auth-nxdomain <boolean>;`

  Blocks: options, view

  Tags: query

  Controls whether BIND, acting as a resolver, provides authoritative NXDOMAIN (domain does not exist) answers.

  If `yes`, then the `AA` bit is always set on NXDOMAIN responses, even if the server is not actually authoritative. The default is `no`.

memstatistics

  Grammar: `memstatistics <boolean>;`

  Blocks: options

  Tags: server, logging

  Controls whether memory statistics are written to the file specified by `memstatistics-file` at exit.

  This writes memory statistics to the file specified by `memstatistics-file` at exit. The default is `no` unless `-m record` is specified on the command line, in which case it is `yes`.

dialup

  Warning

  This option is deprecated and will be removed in a future version of BIND.

  Grammar: `dialup ( notify | notify-passive | passive | refresh | <boolean> ); // deprecated`

  Blocks: options, view, zone (primary, secondary, stub)

  Tags: deprecated

  Concentrates zone maintenance so that all transfers take place once every `heartbeat-interval`, ideally during a single call.

  This option is deprecated and will be removed in a future release.

  If `yes`, then the server treats all zones as if they are doing zone transfers across a dial-on-demand dialup link, which can be brought up by traffic originating from this server. Although this setting has different effects according to zone type, it concentrates the zone maintenance so that everything happens quickly, once every `heartbeat-interval`, ideally during a single call. It also suppresses some normal zone maintenance traffic. The default is `no`.

  If specified in the `view` and `zone` statements, the `dialup` option overrides the global `dialup` option.

  If the zone is a primary zone, the server sends out a NOTIFY request to all the secondaries (default). This should trigger the zone serial number check in the secondary (providing it supports NOTIFY), allowing the secondary to verify the zone while the connection is active. The set of servers to which NOTIFY is sent can be controlled by `notify` and `also-notify`.

  If the zone is a secondary or stub zone, the server suppresses the regular “zone up to date” (refresh) queries and only performs them when the `heartbeat-interval` expires, in addition to sending NOTIFY requests.

  Finer control can be achieved by using `notify`, which only sends NOTIFY messages; `notify-passive`, which sends NOTIFY messages and suppresses the normal refresh queries; `refresh`, which suppresses normal refresh processing and sends refresh queries when the `heartbeat-interval` expires; and `passive`, which disables normal refresh processing.

  dialup mode | normal refresh | heart-beat refresh | heart-beat notify
  `no` (default) | yes | no | no
  `yes` | no | yes | yes
  `notify` | yes | no | yes
  `refresh` | no | yes | no
  `passive` | no | no | no
  `notify-passive` | no | no | yes

  Note that normal NOTIFY processing is not affected by `dialup`.

flush-zones-on-shutdown

  Grammar: `flush-zones-on-shutdown <boolean>;`

  Blocks: options

  Tags: zone

  Controls whether pending zone writes are flushed when the name server exits.

  When the name server exits upon receiving SIGTERM, flush or do not flush any pending zone writes. The default is `flush-zones-on-shutdown no`.

root-key-sentinel

  Grammar: `root-key-sentinel <boolean>;`

  Blocks: options, view

  Tags: server

  Controls whether BIND 9 responds to root key sentinel probes.

  If `yes`, the server responds to root key sentinel probes as described in RFC 8509:. The default is `yes`.

reuseport

  Grammar: `reuseport <boolean>;`

  Blocks: options

  Tags: server

  Enables kernel load-balancing of sockets.

  This option enables kernel load-balancing of sockets on systems which support it, including Linux (SO_REUSEPORT) and FreeBSD (SO_REUSEPORT_LB). This instructs the kernel to distribute incoming socket connections among the networking threads based on a hashing scheme. For more information, see the receive network flow classification options (`rx-flow-hash`) section in the `ethtool` manual page. The default is `yes`.

  Enabling `reuseport` significantly increases general throughput when incoming traffic is distributed uniformly onto the threads by the operating system. However, in cases where a worker thread is busy with a long-lasting operation, such as processing a Response Policy Zone (RPZ) or Catalog Zone update or an unusually large zone transfer, incoming traffic that hashes onto that thread may be delayed. On servers where these events occur frequently, it may be preferable to disable socket load-balancing so that other threads can pick up the traffic that would have been sent to the busy thread.

  Note: this option can only be set when `named` first starts. Changes will not take effect during reconfiguration; the server must be restarted.

message-compression

  Grammar: `message-compression <boolean>;`

  Blocks: options, view

  Tags: query

  Controls whether DNS name compression is used in responses to regular queries.

  If `yes`, DNS name compression is used in responses to regular queries (not including AXFR or IXFR, which always use compression). Setting this option to `no` reduces CPU usage on servers and may improve throughput. However, it increases response size, which may cause more queries to be processed using TCP; a server with compression disabled is out of compliance with RFC 1123 Section 6.1.3.2. The default is `yes`.

minimal-responses

  Grammar: `minimal-responses ( no-auth | no-auth-recursive | <boolean> );`

  Blocks: options, view

  Tags: query

  Controls whether the server only adds records to the authority and additional data sections when they are required (e.g. delegations, negative responses). This improves server performance.

  This option controls the addition of records to the authority and additional sections of responses. Such records may be included in responses to be helpful to clients; for example, MX records may have associated address records included in the additional section, obviating the need for a separate address lookup. However, adding these records to responses is not mandatory and requires additional database lookups, causing extra latency when marshalling responses.

  Responses to DNSKEY, DS, CDNSKEY, and CDS requests will never have optional additional records added. Responses to NS requests will always have additional section processing.

  `minimal-responses` takes one of four values:

  - `no`: the server is as complete as possible when generating responses.

  - `yes`: the server only adds records to the authority and additional sections when such records are required by the DNS protocol (for example, when returning delegations or negative responses). This provides the best server performance but may result in more client queries.

  - `no-auth`: the server omits records from the authority section except when they are required, but it may still add records to the additional section.

  - `no-auth-recursive`: the same as `no-auth` when recursion is requested in the query (RD=1), or the same as `no` if recursion is not requested.

  `no-auth` and `no-auth-recursive` are useful when answering stub clients, which usually ignore the authority section. `no-auth-recursive` is meant for use in mixed-mode servers that handle both authoritative and recursive queries.

  The default is `no-auth-recursive`.

minimal-any

  Grammar: `minimal-any <boolean>;`

  Blocks: options, view

  Tags: query

  Controls whether the server replies with only one of the RRsets for a query name, when generating a positive response to a query of type ANY over UDP.

  If set to `yes`, the server replies with only one of the RRsets for the query name, and its covering RRSIGs if any, when generating a positive response to a query of type ANY over UDP, instead of replying with all known RRsets for the name. Similarly, a query for type RRSIG is answered with the RRSIG records covering only one type. This can reduce the impact of some kinds of attack traffic, without harming legitimate clients. (Note, however, that the RRset returned is the first one found in the database; it is not necessarily the smallest available RRset.) Additionally, `minimal-responses` is turned on for these queries, so no unnecessary records are added to the authority or additional sections. The default is `no`.

notify

  Grammar: `notify ( explicit | master-only | primary-only | <boolean> );`

  Blocks: options, view, zone (mirror, primary, secondary)

  Tags: transfer

  Controls whether `NOTIFY` messages are sent on zone changes.

  If set to `yes` (the default), DNS NOTIFY messages are sent when a zone the server is authoritative for changes; see using notify. The messages are sent to the servers listed in the zone’s NS records (except the primary server identified in the SOA MNAME field), and to any servers listed in the `also-notify` option.

  If set to `primary-only` (or the older keyword `master-only`), notifies are only sent for primary zones. If set to `explicit`, notifies are sent only to servers explicitly listed using `also-notify`. If set to `no`, no notifies are sent.

  The `notify` option may also be specified in the `zone` statement, in which case it overrides the `options notify` statement. It would only be necessary to turn off this option if it caused secondary zones to crash.

notify-to-soa

  Grammar: `notify-to-soa <boolean>;`

  Blocks: options, view, zone (primary, secondary)

  Tags: transfer

  Controls whether the name servers in the NS RRset are checked against the SOA MNAME.

  If `yes`, do not check the name servers in the NS RRset against the SOA MNAME. Normally a NOTIFY message is not sent to the SOA MNAME (SOA ORIGIN), as it is supposed to contain the name of the ultimate primary server. Sometimes, however, a secondary server is listed as the SOA MNAME in hidden primary configurations; in that case, the ultimate primary should be set to still send NOTIFY messages to all the name servers listed in the NS RRset.

recursion

  Grammar: `recursion <boolean>;`

  Blocks: options, view

  Tags: query

  Defines whether recursion and caching are allowed.

  If `yes`, and a DNS query requests recursion, then the server attempts to do all the work required to answer the query. If recursion is off and the server does not already know the answer, it returns a referral response. The default is `yes`. Note that setting `recursion no` does not prevent clients from getting data from the server’s cache; it only prevents new data from being cached as an effect of client queries. Caching may still occur as an effect of the server’s internal operation, such as NOTIFY address lookups.

request-nsid

  Grammar: `request-nsid <boolean>;`

  Blocks: options, server, view, view.server

  Tags: query

  Controls whether an empty EDNS(0) NSID (Name Server Identifier) option is sent with all queries to authoritative name servers during iterative resolution.

  If `yes`, then an empty EDNS(0) NSID (Name Server Identifier) option is sent with all queries to authoritative name servers during iterative resolution. If the authoritative server returns an NSID option in its response, then its contents are logged in the `nsid` category at level `info`. The default is `no`.

require-cookie

  Grammar: `require-cookie <boolean>;`

  Blocks: server, view.server

  Tags: query

  Controls whether responses without a server cookie are accepted.

  The `require-cookie` clause can be used to indicate that the remote server is known to support DNS COOKIE. Setting this option to `yes` causes `named` to always retry a request over TCP when it receives a UDP response without a DNS COOKIE from the remote server, even if UDP responses with DNS COOKIE have not been sent by this server before. This prevents spoofed answers from being accepted without a retry over TCP, when `named` has not yet determined whether the remote server supports DNS COOKIE. Setting this option to `no` (the default) causes `named` to rely on autodetection of DNS COOKIE support to determine when to retry a request over TCP.

  Note

  If a UDP response is signed using TSIG, `named` accepts it even if `require-cookie` is set to `yes` and the response does not contain a DNS COOKIE.

  The `send-cookie` clause determines whether the local server adds a COOKIE EDNS option to requests sent to the server. This overrides `send-cookie` set at the view or option level. The `named` server may determine that COOKIE is not supported by the remote server and not add a COOKIE EDNS option to requests.

require-server-cookie

  Grammar: `require-server-cookie <boolean>;`

  Blocks: options, view

  Tags: query

  Controls whether a valid server cookie is required before sending a full response to a UDP request.

  If `yes`, BIND requires a valid server cookie before sending a full response to a UDP request from a cookie-aware client. BADCOOKIE is sent if there is a bad or nonexistent server cookie.

  The default is `no`.

  Users wishing to test that DNS COOKIE clients correctly handle BADCOOKIE, or who are getting a lot of forged DNS requests with DNS COOKIES present, should set this to `yes`. Setting this to `yes` results in a reduced amplification effect in a reflection attack, as the BADCOOKIE response is smaller than a full response, while also requiring a legitimate client to follow up with a second query with the new, valid, cookie.

answer-cookie

  Grammar: `answer-cookie <boolean>;`

  Blocks: options

  Tags: query

  Controls whether COOKIE EDNS replies are sent in response to client queries.

  When set to the default value of `yes`, COOKIE EDNS options are sent when applicable in replies to client queries. If set to `no`, COOKIE EDNS options are not sent in replies. This can only be set at the global options level, not per-view.

  `answer-cookie no` is intended as a temporary measure, for use when `named` shares an IP address with other servers that do not yet support DNS COOKIE. A mismatch between servers on the same address is not expected to cause operational problems, but the option to disable COOKIE responses so that all servers have the same behavior is provided out of an abundance of caution. DNS COOKIE is an important security mechanism, and should not be disabled unless absolutely necessary.

send-cookie

  Grammar: `send-cookie <boolean>;`

  Blocks: options, server, view, view.server

  Tags: query

  Controls whether a COOKIE EDNS option is sent along with a query.

  If `yes`, a COOKIE EDNS option is sent along with the query. If the resolver has previously communicated with the server, the COOKIE returned in the previous transaction is sent. This is used by the server to determine whether the resolver has talked to it before. A resolver sending the correct COOKIE is assumed not to be an off-path attacker sending a spoofed-source query; the query is therefore unlikely to be part of a reflection/amplification attack, so resolvers sending a correct COOKIE option are not subject to response-rate limiting (RRL). Resolvers which do not send a correct COOKIE option may be limited to receiving smaller responses via the `nocookie-udp-size` option.

  The `named` server may determine that COOKIE is not supported by the remote server and not add a COOKIE EDNS option to requests.

  The default is `yes`.

stale-answer-enable

  Grammar: `stale-answer-enable <boolean>;`

  Blocks: options, view

  Tags: server, query

  Enables the returning of “stale” cached answers when the name servers for a zone are not answering.

  If `yes`, this option enables the returning of “stale” cached answers when the name servers for a zone are not answering and the `stale-cache-enable` option is also enabled. The default is not to return stale answers.

  Stale answers can also be enabled or disabled at runtime via `rndc serve-stale on` or `rndc serve-stale off`; these override the configured setting. `rndc serve-stale reset` restores the setting to the one specified in `named.conf`. Note that if stale answers have been disabled by `rndc`, they cannot be re-enabled by reloading or reconfiguring `named`; they must be re-enabled with `rndc serve-stale on`, or the server must be restarted.

  Information about stale answers is logged under the `serve-stale` log category.

stale-answer-client-timeout

  Grammar: `stale-answer-client-timeout ( disabled | off | <integer> );`

  Blocks: options, view

  Tags: server, query

  Defines the amount of time (in milliseconds) that `named` waits before attempting to answer a query with a stale RRset from cache.

  This option defines the amount of time (in milliseconds) that `named` waits before attempting to answer the query with a stale RRset from cache. If a stale answer is found, `named` continues the ongoing fetches, attempting to refresh the RRset in cache until the `resolver-query-timeout` interval is reached.

  This option is off by default, which is equivalent to setting it to `off` or `disabled`. It also has no effect if `stale-answer-enable` is disabled.

  The minimum value, `0`, causes a cached (stale) RRset to be immediately returned if it is available, while still attempting to refresh the data in cache.

  When this option is enabled, the only supported value in the current version of BIND 9 is `0`. Non-zero values generate a warning message and are treated as `0`.

stale-cache-enable

  Grammar: `stale-cache-enable <boolean>;`

  Blocks: options, view

  Tags: server, query

  Enables the retention of “stale” cached answers.

  If `yes`, enable the retaining of “stale” cached answers. Default `no`.

stale-refresh-time

  Grammar: `stale-refresh-time <duration>;`

  Blocks: options, view

  Tags: server, query

  Sets the time window for the return of “stale” cached answers before the next attempt to contact, if the name servers for a given zone are not responding.

  If the name servers for a given zone are not answering, this sets the time window for which `named` will promptly return “stale” cached answers for that RRSet being requested before a new attempt in contacting the servers is made. For convenience, TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.

  The default `stale-refresh-time` is 30 seconds, as RFC 8767 recommends that attempts to refresh to be done no more frequently than every 30 seconds. A value of zero disables the feature, meaning that normal resolution will take place first, if that fails only then `named` will return “stale” cached answers.

nocookie-udp-size

  Grammar: `nocookie-udp-size <integer>;`

  Blocks: options, view

  Tags: query

  Sets the maximum size of UDP responses that are sent to queries without a valid server COOKIE.

  This sets the maximum size of UDP responses that are sent to queries without a valid server COOKIE. A value below 128 is silently raised to 128. The default value is 4096, but the `max-udp-size` option may further limit the response size as the default for `max-udp-size` is 1232.

cookie-algorithm

  Grammar: `cookie-algorithm ( siphash24 );`

  Blocks: options

  Tags: server

  Sets the algorithm to be used when generating a server cookie.

  This sets the algorithm to be used when generating the server cookie. The default is “siphash24”, which is the only supported option, as the previously supported “aes” option has been removed.

cookie-secret

  Grammar: `cookie-secret <string>; // may occur multiple times`

  Blocks: options

  Tags: server

  Specifies a shared secret used for generating and verifying EDNS COOKIE options within an anycast cluster.

  If set, this is a shared secret used for generating and verifying EDNS COOKIE options within an anycast cluster. If not set, the system generates a random secret at startup. The shared secret is encoded as a hex string and needs to be 128 bits.

  If there are multiple secrets specified, the first one listed in `named.conf` is used to generate new server cookies. The others are only used to verify returned cookies.

response-padding

  Grammar: `response-padding { <address_match_element>; ... } block-size <integer>;`

  Blocks: options, view

  Tags: query

  Adds an EDNS Padding option to encrypted messages, to reduce the chance of guessing the contents based on size.

  The EDNS Padding option is intended to improve confidentiality when DNS queries are sent over an encrypted channel, by reducing the variability in packet sizes. If a query:

  1. contains an EDNS Padding option,

  2. includes a valid server cookie or uses TCP,

  3. is not signed using TSIG or SIG(0), and

  4. is from a client whose address matches the specified ACL,

  then the response is padded with an EDNS Padding option to a multiple of `block-size` bytes. If these conditions are not met, the response is not padded.

  If `block-size` is 0 or the ACL is `none;`, this feature is disabled and no padding occurs; this is the default. If `block-size` is greater than 512, a warning is logged and the value is truncated to 512. Block sizes are ordinarily expected to be powers of two (for instance, 128), but this is not mandatory.

trust-anchor-telemetry

  Grammar: `trust-anchor-telemetry <boolean>;`

  Blocks: options, view

  Tags: dnssec

  Instructs `named` to send specially formed queries once per day to domains for which trust anchors have been configured.

  This causes `named` to send specially formed queries once per day to domains for which trust anchors have been configured via, e.g., `trust-anchors` or `dnssec-validation auto`.

  The query name used for these queries has the form `_ta-xxxx(-xxxx)(...).<domain>`, where each “xxxx” is a group of four hexadecimal digits representing the key ID of a trusted DNSSEC key. The key IDs for each domain are sorted smallest to largest prior to encoding. The query type is NULL.

  By monitoring these queries, zone operators are able to see which resolvers have been updated to trust a new key; this may help them decide when it is safe to remove an old one.

  The default is `yes`.

provide-ixfr

  Grammar: `provide-ixfr <boolean>;`

  Blocks: options, server, view, view.server

  Tags: transfer

  Controls whether a primary responds to an incremental zone request (IXFR) or only responds with a full zone transfer (AXFR).

  The `provide-ixfr` clause determines whether the local server, acting as primary, responds with an incremental zone transfer when the given remote server, a secondary, requests it. If set to `yes`, incremental transfer is provided whenever possible. If set to `no`, all transfers to the remote server are non-incremental.

request-ixfr

  Grammar: `request-ixfr <boolean>;`

  Blocks: options, server, view, zone (mirror, secondary), view.server

  Tags: transfer

  Controls whether a secondary requests an incremental zone transfer (IXFR) or a full zone transfer (AXFR).

  The `request-ixfr` statement determines whether the local server, acting as a secondary, requests incremental zone transfers from the given remote server, a primary.

  IXFR requests to servers that do not support IXFR automatically fall back to AXFR. Therefore, there is no need to manually list which servers support IXFR and which ones do not; the global default of `yes` should always work. The purpose of the `provide-ixfr` and `request-ixfr` statements is to make it possible to disable the use of IXFR even when both primary and secondary claim to support it: for example, if one of the servers is buggy and crashes or corrupts data when IXFR is used.

  It may also be set in the zone block; if set there, it overrides the global or view setting for that zone. It may also be set in the `server` block.

request-expire

  Grammar: `request-expire <boolean>;`

  Blocks: options, server, view, zone (mirror, secondary), view.server

  Tags: transfer, query

  Specifies whether the local server requests the EDNS EXPIRE value, when acting as a secondary.

  The `request-expire` statement determines whether the local server, when acting as a secondary, requests the EDNS EXPIRE value. The EDNS EXPIRE value indicates the remaining time before the zone data expires and needs to be refreshed. This is used when a secondary server transfers a zone from another secondary server; when transferring from the primary, the expiration timer is set from the EXPIRE field of the SOA record instead. The default is `yes`.

match-mapped-addresses

  Grammar: `match-mapped-addresses <boolean>;`

  Blocks: options

  Tags: server

  Allows IPv4-mapped IPv6 addresses to match address-match list entries for corresponding IPv4 addresses.

  If `yes`, then an IPv4-mapped IPv6 address matches any address-match list entries that match the corresponding IPv4 address.

  This option was introduced to work around a kernel quirk in some operating systems that causes IPv4 TCP connections, such as zone transfers, to be accepted on an IPv6 socket using mapped addresses. This caused address-match lists designed for IPv4 to fail to match. However, `named` now solves this problem internally. The use of this option is discouraged.

ixfr-from-differences

  Grammar zone (mirror, primary, secondary): `ixfr-from-differences <boolean>;`

  Grammar options, view: `ixfr-from-differences ( primary | master | secondary | slave | <boolean> );`

  Blocks: options, view, zone (mirror, primary, secondary)

  Tags: transfer

  Controls how IXFR transfers are calculated.

  When `yes` and the server loads a new version of a primary zone from its zone file or receives a new version of a secondary file via zone transfer, it compares the new version to the previous one and calculates a set of differences. The differences are then logged in the zone’s journal file so that the changes can be transmitted to downstream secondaries as an incremental zone transfer.

  By allowing incremental zone transfers to be used for non-dynamic zones, this option saves bandwidth at the expense of increased CPU and memory consumption at the primary server. In particular, if the new version of a zone is completely different from the previous one, the set of differences is of a size comparable to the combined size of the old and new zone versions, and the server needs to temporarily allocate memory to hold this complete difference set.

  `ixfr-from-differences` also accepts `primary` and `secondary` at the view and options levels, which causes `ixfr-from-differences` to be enabled for all primary or secondary zones, respectively. It is off for all zones by default.

  Note: if inline signing is enabled for a zone, the user-provided `ixfr-from-differences` setting is ignored for that zone.

multi-master

  Grammar: `multi-master <boolean>;`

  Blocks: options, view, zone (mirror, secondary, stub)

  Tags: transfer

  Controls whether serial number mismatch errors are logged.

  This should be set when there are multiple primary servers for a zone and the addresses refer to different machines. If `yes`, `named` does not log when the serial number on the primary is less than what `named` currently has. The default is `no`.

dnssec-validation

  Grammar: `dnssec-validation ( yes | no | auto );`

  Blocks: options, view

  Tags: dnssec

  Enables DNSSEC validation in `named`.

  This option enables DNSSEC validation in `named`.

  If set to `auto`, DNSSEC validation is enabled and a default trust anchor for the DNS root zone is used. This trust anchor is provided as part of BIND and is kept up-to-date using Dynamic Trust Anchor Management key management. Adding an explicit static key using the `trust-anchors` statement, with a `static-key` anchor type (or using the deprecated `trusted-keys` statement) for the root zone, is not supported with the `auto` setting and is treated as a configuration error.

  If set to `yes`, DNSSEC validation is enabled, but a trust anchor must be manually configured using a `trust-anchors` statement (or the `managed-keys` or `trusted-keys` statements, both deprecated). If `trust-anchors` is not configured, it is a configuration error. If `trust-anchors` does not include a valid root key, then validation does not take place for names which are not covered by any of the configured trust anchors.

  If set to `no`, DNSSEC validation is disabled. (Note: the resolver will still set the DO bit in outgoing queries to indicate that it can accept DNSSEC responses, even if `dnssec-validation` is disabled.)

  The default is `auto`, unless BIND is built with `configure --disable-auto-validation`, in which case the default is `yes`.

  The default root trust anchor is compiled into `named` and is current as of the release date. If the root key changes, a running BIND server detects this and rolls smoothly to the new key. However, newly installed servers will be unable to start validation, and BIND must be upgraded to a newer version.

validate-except

  Grammar: `validate-except { <string>; ... };`

  Blocks: options, view

  Tags: dnssec

  Specifies a list of domain names at and beneath which DNSSEC validation should not be performed.

  This specifies a list of domain names at and beneath which DNSSEC validation should not be performed, regardless of the presence of a trust anchor at or above those names. This may be used, for example, when configuring a top-level domain intended only for local use, so that the lack of a secure delegation for that domain in the root zone does not cause validation failures. (This is similar to setting a negative trust anchor except that it is a permanent configuration, whereas negative trust anchors expire and are removed after a set period of time.)

dnssec-accept-expired

  Grammar: `dnssec-accept-expired <boolean>;`

  Blocks: options, view

  Tags: dnssec

  Instructs BIND 9 to accept expired DNSSEC signatures when validating.

  This accepts expired signatures when verifying DNSSEC signatures. The default is `no`. Setting this option to `yes` leaves `named` vulnerable to replay attacks.

querylog

  Grammar: `querylog <boolean>;`

  Blocks: options

  Tags: logging, server

  Specifies whether query logging should be active when `named` first starts.

  Query logging provides a complete log of all incoming queries and all query errors. This provides more insight into the server’s activity, but with a cost to performance which may be significant on heavily loaded servers.

  The `querylog` option specifies whether query logging should be active when `named` first starts. If `querylog` is not specified, then query logging is determined by the presence of the logging category `queries`. Please note that `rndc reconfig` and `rndc reload` have no effect on this option, so it cannot be changed once the server is running. However, query logging can be activated at runtime using the command `rndc querylog on`, or deactivated with `rndc querylog off`.

responselog

  Grammar: `responselog <boolean>;`

  Blocks: options

  Tags: logging, server

  Specifies whether response logging should be active when `named` first starts.

  Response logging complements `querylog` by logging the rcode of previous queries along with the queries’ name, type and class.

  Response logging can also be activated at runtime using the command `rndc responselog on`, or deactivated with `rndc responselog off`.

check-names

  Grammar zone (hint, mirror, primary, secondary, stub): `check-names ( fail | warn | ignore );`

  Grammar options, view: `check-names ( primary | master | secondary | slave | response ) ( fail | warn | ignore ); // may occur multiple times`

  Blocks: options, view, zone (hint, mirror, primary, secondary, stub)

  Tags: query, server

  Restricts the character set and syntax of certain domain names in primary files and/or DNS responses received from the network.

  This option is used to restrict the character set and syntax of certain domain names in primary files and/or DNS responses received from the network. The default varies according to usage area. For `type primary` zones the default is `fail`. For `type secondary` zones the default is `warn`. For answers received from the network (`response`), the default is `ignore`.

  The rules for legal hostnames and mail domains are derived from RFC 952 and RFC 821 as modified by RFC 1123.

  `check-names` applies to the owner names of A, AAAA, and MX records. It also applies to the domain names in the RDATA of NS, SOA, MX, and SRV records. It further applies to the RDATA of PTR records where the owner name indicates that it is a reverse lookup of a hostname (the owner name ends in IN-ADDR.ARPA, IP6.ARPA, or IP6.INT).

check-dup-records

  Grammar: `check-dup-records ( fail | warn | ignore );`

  Blocks: options, view, zone (primary)

  Tags: dnssec, query

  Checks primary zones for records that are treated as different by DNSSEC but are semantically equal in plain DNS.

  This checks primary zones for records that are treated as different by DNSSEC but are semantically equal in plain DNS. The default is to `warn`. Other possible values are `fail` and `ignore`.

check-mx

  Grammar: `check-mx ( fail | warn | ignore );`

  Blocks: options, view, zone (primary)

  Tags: zone

  Checks whether an MX record appears to refer to an IP address.

  This checks whether the MX record appears to refer to an IP address. The default is to `warn`. Other possible values are `fail` and `ignore`.

check-wildcard

  Grammar: `check-wildcard <boolean>;`

  Blocks: options, view, zone (primary)

  Tags: zone

  Checks for non-terminal wildcards.

  This option is used to check for non-terminal wildcards. The use of non-terminal wildcards is almost always as a result of a lack of understanding of the wildcard-matching algorithm (RFC 1034). This option affects primary zones. The default (`yes`) is to check for non-terminal wildcards and issue a warning.

check-integrity

  Grammar: `check-integrity <boolean>;`

  Blocks: options, view, zone (primary)

  Tags: zone

  Performs post-load zone integrity checks on primary zones.

  This performs post-load zone integrity checks on primary zones. It checks that MX and SRV records refer to address (A or AAAA) records and that glue address records exist for delegated zones. For MX and SRV records, only in-zone hostnames are checked (for out-of-zone hostnames, use `named-checkzone`). For NS records, only names below top-of-zone are checked (for out-of-zone names and glue consistency checks, use `named-checkzone`). DS records not at delegations are rejected. The default is `yes`.

  The use of the SPF record to publish Sender Policy Framework is deprecated, as the migration from using TXT records to SPF records was abandoned. Enabling this option also checks that a TXT Sender Policy Framework record exists (starts with “v=spf1”) if there is an SPF record. Warnings are emitted if the TXT record does not exist; they can be suppressed with `check-spf`.

check-mx-cname

  Grammar: `check-mx-cname ( fail | warn | ignore );`

  Blocks: options, view, zone (primary)

  Tags: zone

  Sets the response to MX records that refer to CNAMEs.

  If `check-integrity` is set, `named` fails, warns, or ignores MX records that refer to CNAMEs. The default is to `warn`.

check-srv-cname

  Grammar: `check-srv-cname ( fail | warn | ignore );`

  Blocks: options, view, zone (primary)

  Tags: zone

  Sets the response to SRV records that refer to CNAMEs.

  If `check-integrity` is set, `named` fails, warns, or ignores SRV records that refer to CNAMEs. The default is to `warn`.

check-sibling

  Grammar: `check-sibling <boolean>;`

  Blocks: options, view, zone (primary)

  Tags: zone

  Specifies whether to check for sibling glue when performing integrity checks.

  This option instructs BIND to also check that sibling glue exists, when performing integrity checks. The default is `yes`.

check-spf

  Grammar: `check-spf ( warn | ignore );`

  Blocks: options, view, zone (primary)

  Tags: zone

  Specifies whether to check for a TXT Sender Policy Framework record, if an SPF record is present.

  If `check-integrity` is set, `named` checks whether there is a TXT Sender Policy Framework record present (starts with “v=spf1”), if there is an SPF record present. The default is `warn`.

check-svcb

  Grammar: `check-svcb <boolean>;`

  Blocks: options, view, zone (primary)

  Tags: zone

  Specifies whether to perform additional checks on SVCB records.

  If `yes`, `named` checks that SVCB records that start with a `_dns` label prefixed by an optional `_<port>` label (e.g. `_443._dns.ns1.example`) have an `alpn` parameter, and that the `dohpath` parameter exists when the `alpn` indicates that it should be present. The default is `yes`.

zero-no-soa-ttl

  Grammar: `zero-no-soa-ttl <boolean>;`

  Blocks: options, view, zone (mirror, primary, secondary)

  Tags: zone, query, server

  Specifies whether to set the time to live (TTL) of the SOA record to zero, when returning authoritative negative responses to SOA queries.

  If `yes`, when returning authoritative negative responses to SOA queries, `named` sets the TTL of the SOA record returned in the authority section to zero. The default is `yes`.

zero-no-soa-ttl-cache

  Grammar: `zero-no-soa-ttl-cache <boolean>;`

  Blocks: options, view

  Tags: zone, query, server

  Sets the time to live (TTL) to zero when caching a negative response to an SOA query.

  If `yes`, this option instructs BIND to set the TTL to zero when caching a negative response to an SOA query. The default is `no`.

update-check-ksk

  Grammar: `update-check-ksk <boolean>; // obsolete`

  Blocks: options, view, zone (primary, secondary)

  Tags: obsolete

  This option no longer has any effect.

dnssec-dnskey-kskonly

  Grammar: `dnssec-dnskey-kskonly <boolean>; // obsolete`

  Blocks: options, view, zone (primary, secondary)

  Tags: obsolete

  This option no longer has any effect.

try-tcp-refresh

  Grammar: `try-tcp-refresh <boolean>;`

  Blocks: options, view, zone (mirror, secondary)

  Tags: transfer

  Specifies that BIND 9 should attempt to refresh a zone using TCP if UDP queries fail.

  If `yes`, BIND tries to refresh the zone using TCP if UDP queries fail. The default is `yes`.

dnssec-secure-to-insecure

  Grammar: `dnssec-secure-to-insecure <boolean>; // obsolete`

  Blocks: options, view, zone (primary)

  Tags: obsolete

  This option no longer has any effect.

synth-from-dnssec

  Grammar: `synth-from-dnssec <boolean>;`

  Blocks: options, view

  Tags: dnssec

  Enables support for RFC 8198, Aggressive Use of DNSSEC-Validated Cache.

  This option enables support for RFC 8198, Aggressive Use of DNSSEC-Validated Cache. It allows the resolver to send a smaller number of queries when resolving queries for DNSSEC-signed domains by synthesizing answers from cached NSEC and other RRsets that have been proved to be correct using DNSSEC. The default is `yes`.

  Note

  DNSSEC validation must be enabled for this option to be effective. This initial implementation only covers synthesis of answers from NSEC records; synthesis from NSEC3 is planned for the future. This will also be controlled by `synth-from-dnssec`.

#### 8.2.13.2. Forwarding

The forwarding facility can be used to create a large site-wide cache on a few servers, reducing traffic over links to external name servers. It can also be used to allow queries by servers that do not have direct access to the Internet, but that wish to look up exterior names anyway. Forwarding occurs only on those queries for which the server is not authoritative and does not have the answer in its cache.

forward

  Grammar: `forward ( first | only );`

  Blocks: options, view, zone (forward, primary, secondary, static-stub, stub)

  Tags: query

  Allows or disallows fallback to recursion if forwarding has failed; it is always used in conjunction with the `forwarders` statement.

  This option is only meaningful if the forwarders list is not empty. A value of `first` is the default and causes the server to query the forwarders first; if that does not answer the question, the server then looks for the answer itself. If `only` is specified, the server only queries the forwarders.

forwarders

  Grammar: `forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };`

  Blocks: options, view, zone (forward, primary, secondary, static-stub, stub)

  Tags: query

  Defines one or more hosts to which queries are forwarded.

  This specifies a list of IP addresses to which queries are forwarded. The default is the empty list (no forwarding). Each address in the list can be associated with an optional port number and a TLS transport. A default port number and a TLS transport can be set for the entire list.

  If a TLS configuration is specified, `named` uses DNS-over-TLS (DoT) connections when connecting to the specified IP address(es), via the TLS configuration referenced by the `tls` statement.

Forwarding can also be configured on a per-domain basis, allowing for the global forwarding options to be overridden in a variety of ways. Particular domains can be set to use different forwarders, or have a different `forward only/first` behavior, or not forward at all; see `zone`.

#### 8.2.13.3. Dual-stack Servers

Dual-stack servers are used as servers of last resort, to work around problems in reachability due to the lack of support for either IPv4 or IPv6 on the host machine.

dual-stack-servers

  Grammar: `dual-stack-servers [ port <integer> ] { ( <quoted_string> [ port <integer> ] | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ); ... };`

  Blocks: options, view

  Tags: server

  Specifies host names or addresses of machines with access to both IPv4 and IPv6 transports.

  This specifies host names or addresses of machines with access to both IPv4 and IPv6 transports. If a hostname is used, the server must be able to resolve the name using only the transport it has. If the machine is dual-stacked, the `dual-stack-servers` parameter has no effect unless access to a transport has been disabled on the command line (e.g., `named -4`).

#### 8.2.13.4. Access Control

Access to the server can be restricted based on the IP address of the requesting system. See Address Match Lists for details on how to specify IP address lists.

allow-notify

  Grammar: `allow-notify { <address_match_element>; ... };`

  Blocks: options, view, zone (mirror, secondary)

  Tags: transfer

  Defines an `address_match_list` that is allowed to send `NOTIFY` messages for the zone, in addition to addresses defined in the `primaries` option for the zone.

  This ACL specifies which hosts may send NOTIFY messages to inform this server of changes to zones for which it is acting as a secondary server. This is only applicable for secondary zones (i.e., `type secondary` or `slave`).

  If this option is set in `view` or `options`, it is globally applied to all secondary zones. If set in the `zone` statement, the global value is overridden.

  If not specified, the default is to process NOTIFY messages only from the configured `primaries` for the zone. `allow-notify` can be used to expand the list of permitted hosts, not to reduce it.

allow-proxy

  Warning

  This option is experimental and subject to change.

  Grammar: `allow-proxy { <address_match_element>; ... }; // experimental`

  Blocks: options, view

  Tags: server

  Defines an `address_match_list` for the client addresses allowed to send PROXYv2 headers.

  The default `address_match_list` is none, which means that no client is allowed to do that by default for security reasons, as the PROXYv2 protocol provides an easy way to spoof both source and destination addresses.

  This `address_match_list` is primarily meant to have addresses and subnets of the proxies that are allowed to send PROXYv2 headers to BIND. In most cases, we do not recommend setting this `address_match_list` to be very permissive; in particular, we recommend against setting it to any, especially in cases when PROXYv2 headers can be accepted on publicly available networking interfaces.

  The specified option is the only option that matches against real peer addresses when PROXYv2 headers are used. Most of the options that work with peer addresses use the ones extracted from PROXYv2 headers.

  See also: `allow-proxy-on`.

allow-proxy-on

  Warning

  This option is experimental and subject to change.

  Grammar: `allow-proxy-on { <address_match_element>; ... }; // experimental`

  Blocks: options, view

  Tags: server

  Defines an `address_match_list` for the interface addresses allowed to accept PROXYv2 headers. The option is mostly intended for multi-homed configurations.

  The default `address_match_list` is any, which means that accepting PROXYv2 is allowed on any interface.

  The option is useful in cases when a user needs to have precise control over which interfaces allow PROXYv2, as it is the only option that matches against real interface addresses when PROXYv2 headers are used. Most options that work with interface addresses use the ones extracted from PROXYv2 headers.

  It may be desirable to first set `allow-proxy`.

allow-query

  Grammar: `allow-query { <address_match_element>; ... };`

  Blocks: options, view, zone (mirror, primary, redirect, secondary, static-stub, stub)

  Tags: query

  Specifies which hosts (an IP address list) are allowed to send queries to this resolver.

  `allow-query` may also be specified in the `zone` statement, in which case it overrides the `options allow-query` statement. If not specified, the default is to allow queries from all hosts.

  Note

  `allow-query-cache` is used to specify access to the cache.

allow-query-on

  Grammar: `allow-query-on { <address_match_element>; ... };`

  Blocks: options, view, zone (mirror, primary, redirect, secondary, static-stub, stub)

  Tags: query

  Specifies which local addresses (an IP address list) are allowed to send queries to this resolver. This option is used in multi-homed configurations.

  This makes it possible, for instance, to allow queries on internal-facing interfaces but disallow them on external-facing ones, without necessarily knowing the internal network’s addresses.

  Note that `allow-query-on` is only checked for queries that are permitted by `allow-query`. A query must be allowed by both ACLs, or it is refused.

  `allow-query-on` may also be specified in the `zone` statement, in which case it overrides the `options allow-query-on` statement.

  If not specified, the default is to allow queries on all addresses.

  Note

  `allow-query-cache` is used to specify access to the cache.

allow-query-cache

  Grammar: `allow-query-cache { <address_match_element>; ... };`

  Blocks: options, view

  Tags: query

  Specifies which hosts (an IP address list) can access this server’s cache and thus effectively controls recursion.

  This option defines an address_match_list of IP address(es) which are allowed to issue queries that access the local cache. Without access to the local cache, recursive queries are effectively useless so, in effect, this statement (or its default) controls recursive behavior. This statement’s default setting depends on:

  1. If `recursion no;` present, it defaults to `allow-query-cache {none;};`. No local cache access permitted.

  2. If `recursion yes;` (default), then, if `allow-recursion` is present, it defaults to the value of `allow-recursion`. Local cache access is permitted to the same address_match_list as `allow-recursion`.

  3. If `recursion yes;` (default), then, if `allow-recursion` is not present, it defaults to `allow-query-cache {localnets; localhost;};`. Local cache access is permitted to address_match_list localnets and localhost IP addresses only.

allow-query-cache-on

  Grammar: `allow-query-cache-on { <address_match_element>; ... };`

  Blocks: options, view

  Tags: query

  Specifies which hosts (from an IP address list) can access this server’s cache. It is used on servers with multiple interfaces.

  This specifies which local addresses can send answers from the cache. If `allow-query-cache-on` is not set, then `allow-recursion-on` is used if set. Otherwise, the default is to allow cache responses to be sent from any address. Note: both `allow-query-cache` and `allow-query-cache-on` must be satisfied before a cache response can be sent; a client that is blocked by one cannot be allowed by the other.

allow-recursion

  Grammar: `allow-recursion { <address_match_element>; ... };`

  Blocks: options, view

  Tags: query

  Defines an `address_match_list` of clients that are allowed to perform recursive queries.

  This specifies which hosts are allowed to make recursive queries through this server. BIND checks to see if the following parameters are set, in order: `allow-query-cache` and `allow-query`. If neither of those parameters is set, the default (localnets; localhost;) is used.

allow-recursion-on

  Grammar: `allow-recursion-on { <address_match_element>; ... };`

  Blocks: options, view

  Tags: query, server

  Specifies which local addresses can accept recursive queries.

  This specifies which local addresses can accept recursive queries. If `allow-recursion-on` is not set, then `allow-query-cache-on` is used if set; otherwise, the default is to allow recursive queries on all addresses. Any client permitted to send recursive queries can send them to any address on which `named` is listening. Note: both `allow-recursion` and `allow-recursion-on` must be satisfied before recursion is allowed; a client that is blocked by one cannot be allowed by the other.

allow-update

  Grammar: `allow-update { <address_match_element>; ... };`

  Blocks: options, view, zone (primary)

  Tags: transfer

  Defines an `address_match_list` of hosts that are allowed to submit dynamic updates for primary zones.

  This provides a simple access control list. When set in the `zone` statement for a primary zone, this specifies which hosts are allowed to submit dynamic DNS updates to that zone. The default is to deny updates from all hosts.

  Note that allowing updates based on the requestor’s IP address is insecure; see Dynamic Update Security for details.

  In general, this option should only be set at the `zone` level. While a default value can be set at the `options` or `view` level and inherited by zones, this could lead to some zones unintentionally allowing updates.

  Updates are written to the zone’s filename that is set in `file`.

allow-update-forwarding

  Grammar: `allow-update-forwarding { <address_match_element>; ... };`

  Blocks: options, view, zone (mirror, secondary)

  Tags: transfer

  Defines an `address_match_list` of hosts that are allowed to submit dynamic updates to a secondary server for transmission to a primary.

  When set in the `zone` statement for a secondary zone, this specifies which hosts are allowed to submit dynamic DNS updates and have them be forwarded to the primary. The default is `{ none; }`, which means that no update forwarding is performed.

  To enable update forwarding, specify `allow-update-forwarding { any; };` in the `zone` statement. Specifying values other than `{ none; }` or `{ any; }` is usually counterproductive; the responsibility for update access control should rest with the primary server, not the secondary.

  Note that enabling the update forwarding feature on a secondary server may expose primary servers to attacks if they rely on insecure IP-address-based access control; see Dynamic Update Security for more details.

  In general this option should only be set at the `zone` level. While a default value can be set at the `options` or `view` level and inherited by zones, this can lead to some zones unintentionally forwarding updates.

allow-transfer

  Grammar: `allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_element>; ... };`

  Blocks: options, view, zone (mirror, primary, secondary)

  Tags: transfer

  Defines an `address_match_list` of hosts that are allowed to transfer the zone information from this server.

  This specifies which hosts are allowed to receive zone transfers from the server. `allow-transfer` may also be specified in the `zone` statement, in which case it overrides the `allow-transfer` statement set in `options` or `view`.

  Transport-level limitations can also be specified. In particular, zone transfers can be restricted to a specific port and/or DNS transport protocol by using the options port and `transport`. Either option can be specified; if both are used, both constraints must be satisfied in order for the transfer to be allowed. Zone transfers are currently only possible via the TCP and TLS transports.

  For example: `allow-transfer port 853 transport tls { any; };` allows outgoing zone transfers to any host using the TLS transport over port 853.

  If `allow-transfer` is not specified, then the default is `none`; outgoing zone transfers are disabled.

Warning

Please note that incoming TLS connections are not authenticated at the TLS level by default. Please use TSIG to authenticate requestors or consider implementing Mutual TLS authentication.

blackhole

  Grammar: `blackhole { <address_match_element>; ... };`

  Blocks: options

  Tags: query

  Defines an `address_match_list` of hosts to ignore. The server will neither respond to queries from nor send queries to these addresses.

  This specifies a list of addresses which the server does not accept queries from or or cannot use to resolve a query. Queries from these addresses are not responded to. The default is `none`.

no-case-compress

  Grammar: `no-case-compress { <address_match_element>; ... };`

  Blocks: options, view

  Tags: server

  Specifies a list of addresses that require case-insensitive compression in responses.

  This specifies a list of addresses which require responses to use case-insensitive compression. This ACL can be used when `named` needs to work with clients that do not comply with the requirement in RFC 1034 to use case-insensitive name comparisons when checking for matching domain names.

  If left undefined, the ACL defaults to `none`: case-sensitive compression is used for all clients. If the ACL is defined and matches a client, case is ignored when compressing domain names in DNS responses sent to that client.

  This can result in slightly smaller responses; if a response contains the names “example.com” and “example.COM”, case-insensitive compression treats the second one as a duplicate. It also ensures that the case of the query name exactly matches the case of the owner names of returned records, rather than matches the case of the records entered in the zone file. This allows responses to exactly match the query, which is required by some clients due to incorrect use of case-sensitive comparisons.

  Case-insensitive compression is always used in AXFR and IXFR responses, regardless of whether the client matches this ACL.

  There are circumstances in which `named` does not preserve the case of owner names of records: if a zone file defines records of different types with the same name, but the capitalization of the name is different (e.g., “www.example.com/A” and “WWW.EXAMPLE.COM/AAAA”), then all responses for that name use the first version of the name that was used in the zone file. This limitation may be addressed in a future release. However, domain names specified in the rdata of resource records (i.e., records of type NS, MX, CNAME, etc.) always have their case preserved unless the client matches this ACL.

resolver-query-timeout

  Grammar: `resolver-query-timeout <integer>;`

  Blocks: options, view

  Tags: query

  Specifies the length of time, in milliseconds, that a resolver attempts to resolve a recursive query before failing.

  This is the amount of time, in milliseconds, that the resolver spends attempting to resolve a recursive query before failing. The default is `10000`, the minimum is `301`, and the maximum is `30000`. Setting it to `0` results in the default being used.

  This value was originally specified in seconds. Values less than or equal to 300 are treated as seconds and converted to milliseconds before applying the above limits.

#### 8.2.13.5. Interfaces

The interfaces, ports, and protocols that the server can use to answer queries may be specified using the `listen-on` and `listen-on-v6` options.

listen-on

  Grammar: `listen-on [ port <integer> ] [ proxy <string> ] [ tls <string> ] [ http <string> ] { <address_match_element>; ... }; // may occur multiple times`

  Blocks: options

  Tags: server

  Specifies the IPv4 addresses on which a server listens for DNS queries.

listen-on-v6

  Grammar: `listen-on-v6 [ port <integer> ] [ proxy <string> ] [ tls <string> ] [ http <string> ] { <address_match_element>; ... }; // may occur multiple times`

  Blocks: options

  Tags: server

  Specifies the IPv6 addresses on which a server listens for DNS queries.

  The `listen-on` and `listen-on-v6` statements can each take an optional port, PROXYv2 support switch, TLS configuration identifier, and/or HTTP configuration identifier, in addition to an address_match_list.

  The address_match_list in `listen-on` specifies the IPv4 addresses on which the server will listen. (IPv6 addresses are ignored, with a logged warning.) The server listens on all interfaces allowed by the address match list. If no `listen-on` is specified, the default is to listen for standard DNS queries on port 53 of all IPv4 interfaces.

  `listen-on-v6` takes an address_match_list of IPv6 addresses. The server listens on all interfaces allowed by the address match list. If no `listen-on-v6` is specified, the default is to listen for standard DNS queries on port 53 of all IPv6 interfaces.

  When specified, the PROXYv2 support switch `proxy` allows the enabling of PROXYv2 protocol support. The PROXYv2 protocol provides the means for passing connection information, such as a client’s source and destination addresses and ports, across multiple layers of NAT or TCP/UDP proxies to back-end servers. The addresses passed by the PROXYv2 protocol are then used, instead of the peer and interface addresses provided by the operating system.

  The `proxy` switch can have the following values:

  - `plain` - accept plain PROXYv2 headers. This is the only valid option for transports that do not employ encryption. In the case of transports that employ encryption, this value instructs BIND that PROXYv2 headers are sent without encryption before the TLS handshake. In that case, only PROXYv2 headers are not encrypted.

  - `encrypted` - accept encrypted PROXYv2 headers. This value instructs BIND that PROXYv2 headers are sent encrypted immediately after the TLS handshake. The option is valid only for transports that employ encryption; encrypted PROXYv2 headers cannot be sent via unencrypted transports.

  Please consult the documentation of any proxying front-end software to decide which value should be used. If in doubt, use `plain` for encrypted transports, especially for DNS-over-HTTPS (DoH), but DNS-specific software is likely to need `encrypted`.

  It should be noted that when PROXYv2 is enabled on a listener, it loses the ability to accept regular DNS queries without associated PROXYv2 headers.

  In some cases, PROXYv2 headers might not contain usable source and destination addresses. In particular, this can happen when the headers use the `LOCAL` command, or headers use address types that are unspecified or unsupported by BIND. If otherwise correct, such headers are accepted by BIND and the real endpoint addresses are used in these cases.

  The PROXYv2 protocol is designed to be extensible and can carry additional information in the form of type-length-values (TLVs). Many of the types are defined in the protocol specification, and for some of these, BIND does a reasonable amount of validation in order to detect and reject ill-formed or hand-crafted headers. Apart from that, this additional data, while accepted, is not currently used by BIND for anything else.

  By default, no client is allowed to send queries that contain PROXYv2 protocol headers, even when support for the protocol is enabled in a `listen-on` statement. Users who are interested in enabling the PROXYv2 protocol support may also want to look at the `allow-proxy` and `allow-proxy-on` options, to adjust the corresponding ACLs.

  If a TLS configuration is specified, `named` will listen for DNS-over-TLS (DoT) connections, using the key and certificate specified in the referenced `tls` statement. If the name `ephemeral` is used, an ephemeral key and certificate created for the currently running `named` process will be used.

  If an HTTP configuration is specified, `named` listens for DNS-over-HTTPS (DoH) connections using the HTTP endpoint specified in the referenced `http` statement. If the name `default` is used, then `named` listens for connections at the default endpoint, `/dns-query`.

  Use of an `http` specification requires `tls` to be specified as well. If an unencrypted connection is desired (for example, on load-sharing servers behind a reverse proxy), `tls none` may be used.

  If a port number is not specified, the default is 53 for standard DNS, 853 for DNS over TLS, 443 for DNS over HTTPS, and 80 for DNS over HTTP (unencrypted). These defaults may be overridden using the `port`, `tls-port`, `https-port`, and `http-port` options.

  Multiple `listen-on` statements are allowed. For example:

      listen-on { 5.6.7.8; };
      listen-on port 1234 { !1.2.3.4; 1.2/16; };
      listen-on port 8853 tls ephemeral { 4.3.2.1; };
      listen-on port 8453 tls ephemeral http myserver { 8.7.6.5; };
      listen-on port 5300 proxy plain { !1.2.3.4; 1.2/16; };
      listen-on port 8953 proxy encrypted tls ephemeral { 4.3.2.1; };
      listen-on port 8553 proxy plain tls ephemeral http myserver { 8.7.6.5; };

  The first two lines instruct the name server to listen for standard DNS queries on port 53 of the IP address 5.6.7.8 and on port 1234 of an address on the machine in net 1.2 that is not 1.2.3.4. The third line instructs the server to listen for DNS-over-TLS connections on port 8853 of the IP address 4.3.2.1 using the ephemeral key and certifcate. The fourth line enables DNS-over-HTTPS connections on port 8453 of address 8.7.6.5, using the ephemeral key and certificate, and the HTTP endpoint or endpoints configured in an `http` statement with the name `myserver`.

  Multiple `listen-on-v6` options can be used. For example:

      listen-on-v6 { any; };
      listen-on-v6 port 1234 { !2001:db8::/32; any; };
      listen-on-v6 port 8853 tls example-tls { 2001:db8::100; };
      listen-on-v6 port 8453 tls example-tls http default { 2001:db8::100; };
      listen-on-v6 port 8000 tls none http myserver { 2001:db8::100; };
      listen-on-v6 port 53000 proxy plain { !2001:db8::/32; any; };
      listen-on-v6 port 8953 proxy encrypted tls example-tls { 2001:db8::100; };
      listen-on-v6 port 8553 proxy plain tls example-tls http default { 2001:db8::100; };

  The first two lines instruct the name server to listen for standard DNS queries on port 53 of any IPv6 addresses, and on port 1234 of IPv6 addresses that are not in the prefix 2001:db8::/32. The third line instructs the server to listen for for DNS-over-TLS connections on port 8853 of the address 2001:db8::100, using a TLS key and certificate specified in the a `tls` statement with the name `example-tls`. The fourth instructs the server to listen for DNS-over-HTTPS connections, again using `example-tls`, on the default HTTP endpoint. The fifth line, in which the `tls` parameter is set to `none`, instructs the server to listen for unencrypted DNS queries over HTTP at the endpoint specified in `myserver`..

  To instruct the server not to listen on any IPv6 addresses, use:

      listen-on-v6 { none; };

#### 8.2.13.6. Query Address

query-source

  Grammar options, view: `query-source [ address ] ( <ipv4_address> | * | none );`

  Grammar server, view.server: `query-source [ address ] ( <ipv4_address> | * );`

  Blocks: options, server, view, view.server

  Tags: query

  Controls the IPv4 address from which queries are issued. If none, then no IPv4 address would be used to issue the query and therefore only IPv6 servers are queried.

query-source-v6

  Grammar options, view: `query-source-v6 [ address ] ( <ipv6_address> | * | none );`

  Grammar server, view.server: `query-source-v6 [ address ] ( <ipv6_address> | * );`

  Blocks: options, server, view, view.server

  Tags: query

  Controls the IPv6 address from which queries are issued. If none, then no IPv6 address would be used to issue the query and therefore only IPv4 servers are quried.

  If the server does not know the answer to a question, it queries other name servers. `query-source` specifies the address and port used for such queries. For queries sent over IPv6, there is a separate `query-source-v6` option. If `address` is `*` (asterisk) or is omitted, a wildcard IP address (`INADDR_ANY`) is used.

  The defaults of the `query-source` and `query-source-v6` options are:

      query-source address * port *;
      query-source-v6 address * port *;

  Note

  `port` configuration is deprecated. A warning will be logged when this parameter is used.

  Note

  The address specified in the `query-source` option is used for both UDP and TCP queries, but the port applies only to UDP queries. TCP queries always use a random unprivileged port.

use-v4-udp-ports

  Warning

  This option is deprecated and will be removed in a future version of BIND.

  Grammar: `use-v4-udp-ports { <portrange>; ... }; // deprecated`

  Blocks: options

  Tags: deprecated

  Specifies a list of ports that are valid sources for UDP/IPv4 messages.

use-v6-udp-ports

  Warning

  This option is deprecated and will be removed in a future version of BIND.

  Grammar: `use-v6-udp-ports { <portrange>; ... }; // deprecated`

  Blocks: options

  Tags: deprecated

  Specifies a list of ports that are valid sources for UDP/IPv6 messages.

  These statements, which are deprecated and will be removed in a future release, specify a list of IPv4 and IPv6 UDP ports that are used as source ports for UDP messages.

  If port is `*` or is omitted, a random port number from a pre-configured range is selected and used for each query. The port range(s) are specified in the `use-v4-udp-ports` (for IPv4) and `use-v6-udp-ports` (for IPv6) options.

  If `use-v4-udp-ports` or `use-v6-udp-ports` is unspecified, `named` checks whether the operating system provides a programming interface to retrieve the system’s default range for ephemeral ports. If such an interface is available, `named` uses the corresponding system default range; otherwise, it uses its own defaults:

      use-v4-udp-ports { range 1024 65535; };
      use-v6-udp-ports { range 1024 65535; };

avoid-v4-udp-ports

  Warning

  This option is deprecated and will be removed in a future version of BIND.

  Grammar: `avoid-v4-udp-ports { <portrange>; ... }; // deprecated`

  Blocks: options

  Tags: deprecated

  Specifies the range(s) of ports to be excluded from use as sources for UDP/IPv4 messages.

avoid-v6-udp-ports

  Warning

  This option is deprecated and will be removed in a future version of BIND.

  Grammar: `avoid-v6-udp-ports { <portrange>; ... }; // deprecated`

  Blocks: options

  Tags: deprecated

  Specifies the range(s) of ports to be excluded from use as sources for UDP/IPv6 messages.

  These statements, which are deprecated and will be removed in a future release, indicate ranges of port numbers to exclude from those specified in the `avoid-v4-udp-ports` and `avoid-v6-udp-ports` options, respectively.

  The defaults of the `avoid-v4-udp-ports` and `avoid-v6-udp-ports` options are:

      avoid-v4-udp-ports {};
      avoid-v6-udp-ports {};

  For example, with the following configuration:

      use-v6-udp-ports { range 32768 65535; };
      avoid-v6-udp-ports { 40000; range 50000 60000; };

  UDP ports of IPv6 messages sent from `named` are in one of the following ranges: 32768 to 39999, 40001 to 49999, or 60001 to 65535.

  `avoid-v4-udp-ports` and `avoid-v6-udp-ports` can be used to prevent `named` from choosing as its random source port a port that is blocked by a firewall or that is used by other applications; if a query went out with a source port blocked by a firewall, the answer would not pass through the firewall and the name server would have to query again. Note: the desired range can also be represented only with `use-v4-udp-ports` and `use-v6-udp-ports`, and the `avoid-` options are redundant in that sense; they are provided for backward compatibility and to possibly simplify the port specification.

  Note

  Make sure the ranges are sufficiently large for security. A desirable size depends on several parameters, but we generally recommend it contain at least 16384 ports (14 bits of entropy). Note also that the system’s default range when used may be too small for this purpose, and that the range may even be changed while `named` is running; the new range is automatically applied when `named` is reloaded. Explicit configuration of `use-v4-udp-ports` and `use-v6-udp-ports` is encouraged, so that the ranges are sufficiently large and are reasonably independent from the ranges used by other applications.

  Note

  The operational configuration where `named` runs may prohibit the use of some ports. For example, Unix systems do not allow `named`, if run without root privilege, to use ports less than 1024. If such ports are included in the specified (or detected) set of query ports, the corresponding query attempts will fail, resulting in resolution failures or delay. It is therefore important to configure the set of ports that can be safely used in the expected operational environment.

  Warning

  Specifying a single port is discouraged, as it removes a layer of protection against spoofing errors.

  Warning

  The configured port must not be the same as the listening port.

  Note

  See also `transfer-source`, `notify-source` and `parental-source`.

#### 8.2.13.7. Zone Transfers

BIND has mechanisms in place to facilitate zone transfers and set limits on the amount of load that transfers place on the system. The following options apply to zone transfers.

also-notify

  Grammar: `also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };`

  Blocks: options, view, zone (mirror, primary, secondary)

  Tags: transfer

  Defines one or more hosts that are sent `NOTIFY` messages when zone changes occur.

  This option defines a global list of IP addresses of name servers that are also sent NOTIFY messages whenever a fresh copy of the zone is loaded, in addition to the servers listed in the zone’s NS records. This helps to ensure that copies of the zones quickly converge on stealth servers. Optionally, a port may be specified with each `also-notify` address to send the notify messages to a port other than the default of 53. An optional TSIG key can also be specified with each address to cause the notify messages to be signed; this can be useful when sending notifies to multiple views. In place of explicit addresses, one or more named `primaries` lists can be used.

  If an `also-notify` list is given in a `zone` statement, it overrides the `options also-notify` statement. When a `zone notify` statement is set to `no`, the IP addresses in the global `also-notify` list are not sent NOTIFY messages for that zone. The default is the empty list (no global notification list).

min-transfer-rate-in

  Grammar: `min-transfer-rate-in <integer> <integer>;`

  Blocks: options, view, zone (mirror, secondary, stub)

  Tags: transfer

  Specifies the minimum traffic rate below which inbound zone transfers are terminated.

  Inbound zone transfers running slower than the given amount of bytes in the given amount of minutes are terminated. This option takes two non-zero integer values. A check is performed periodically every time the configured time interval passes. The default value is `10240 5`, i.e. 10240 bytes in 5 minutes. The maximum time value is 28 days (40320 minutes).

max-transfer-time-in

  Grammar: `max-transfer-time-in <integer>;`

  Blocks: options, view, zone (mirror, secondary, stub)

  Tags: transfer

  Specifies the number of minutes after which inbound zone transfers are terminated.

  Inbound zone transfers running longer than this many minutes are terminated. The default is 120 minutes (2 hours). The maximum value is 28 days (40320 minutes).

max-transfer-idle-in

  Grammar: `max-transfer-idle-in <integer>;`

  Blocks: options, view, zone (mirror, secondary, stub)

  Tags: transfer

  Specifies the number of minutes after which inbound zone transfers making no progress are terminated.

  Inbound zone transfers making no progress in this many minutes are terminated. The default is 60 minutes (1 hour). The maximum value is 28 days (40320 minutes).

  Note

  Inbound zone transfers are also affected by `tcp-idle-timeout`; `max-transfer-idle-in` closes the inbound zone transfer if there is no complete AXFR or no complete IXFR chunk. `tcp-idle-timeout` closes the connection if there is no progress on the TCP level.

max-transfer-time-out

  Grammar: `max-transfer-time-out <integer>;`

  Blocks: options, view, zone (mirror, primary, secondary)

  Tags: transfer

  Specifies the number of minutes after which outbound zone transfers are terminated.

  Outbound zone transfers running longer than this many minutes are terminated. The default is 120 minutes (2 hours). The maximum value is 28 days (40320 minutes).

max-transfer-idle-out

  Grammar: `max-transfer-idle-out <integer>;`

  Blocks: options, view, zone (mirror, primary, secondary)

  Tags: transfer

  Specifies the number of minutes after which outbound zone transfers making no progress are terminated.

  Outbound zone transfers making no progress in this many minutes are terminated. The default is 60 minutes (1 hour). The maximum value is 28 days (40320 minutes).

notify-rate

  Grammar: `notify-rate <integer>;`

  Blocks: options

  Tags: transfer, zone

  Specifies the rate at which NOTIFY requests are sent during normal zone maintenance operations.

  This specifies the rate at which NOTIFY requests are sent during normal zone maintenance operations. (NOTIFY requests due to initial zone loading are subject to a separate rate limit; see below.) The default is 20 per second. The lowest possible rate is one per second; when set to zero, it is silently raised to one.

primaries

  Grammar: `primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };`

  Blocks: zone (mirror, redirect, secondary, stub)

  Tags: transfer, zone

  Defines one or more servers that zone transfer can be requested from.

  This specifies a list of one or more IP addresses of primary servers that the secondary contacts to update its copy of the zone. Primaries list elements can also be names of `remote-servers` blocks.

  By default, transfers are made from port 53 on the servers; this can be changed for all servers by specifying a port number before the list of IP addresses, or on a per-server basis after the IP address. Authentication to the primary can also be done with per-server TSIG keys.

startup-notify-rate

  Grammar: `startup-notify-rate <integer>;`

  Blocks: options

  Tags: transfer, zone

  Specifies the rate at which NOTIFY requests are sent when the name server is first starting, or when new zones have been added.

  This is the rate at which NOTIFY requests are sent when the name server is first starting up, or when zones have been newly added to the name server. The default is 20 per second. The lowest possible rate is one per second; when set to zero, it is silently raised to one.

serial-query-rate

  Grammar: `serial-query-rate <integer>;`

  Blocks: options

  Tags: transfer

  Defines an upper limit on the number of queries per second issued by the server, when querying the SOA RRs used for zone transfers.

  Secondary servers periodically query primary servers to find out if zone serial numbers have changed. Each such query uses a minute amount of the secondary server’s network bandwidth. To limit the amount of bandwidth used, BIND 9 limits the rate at which queries are sent. The value of the `serial-query-rate` option, an integer, is the maximum number of queries sent per second. The default is 20 per second. The lowest possible rate is one per second; when set to zero, it is silently raised to one.

transfer-format

  Grammar: `transfer-format ( many-answers | one-answer );`

  Blocks: options, server, view, view.server

  Tags: transfer

  Controls whether multiple records can be packed into a message during zone transfers.

  Zone transfers can be sent using two different formats, `one-answer` and `many-answers`. The `transfer-format` option is used on the primary server to determine which format it sends. `one-answer` uses one DNS message per resource record transferred. `many-answers` packs as many resource records as possible into one message. `many-answers` is more efficient; the default is `many-answers`. `transfer-format` may be overridden on a per-server basis by using the `server` block.

transfer-message-size

  Grammar: `transfer-message-size <integer>;`

  Blocks: options

  Tags: transfer

  Limits the uncompressed size of DNS messages used in zone transfers over TCP.

  This is an upper bound on the uncompressed size of DNS messages used in zone transfers over TCP. If a message grows larger than this size, additional messages are used to complete the zone transfer. (Note, however, that this is a hint, not a hard limit; if a message contains a single resource record whose RDATA does not fit within the size limit, a larger message will be permitted so the record can be transferred.)

  Valid values are between 512 and 65535 octets; any values outside that range are adjusted to the nearest value within it. The default is `20480`, which was selected to improve message compression; most DNS messages of this size will compress to less than 16536 bytes. Larger messages cannot be compressed as effectively, because 16536 is the largest permissible compression offset pointer in a DNS message.

  This option is mainly intended for server testing; there is rarely any benefit in setting a value other than the default.

transfers-in

  Grammar: `transfers-in <integer>;`

  Blocks: options

  Tags: transfer

  Limits the number of concurrent inbound zone transfers.

  This is the maximum number of inbound zone transfers that can run concurrently. The default value is `10`. Increasing `transfers-in` may speed up the convergence of secondary zones, but it also may increase the load on the local system.

transfers-out

  Grammar: `transfers-out <integer>;`

  Blocks: options

  Tags: transfer

  Limits the number of concurrent outbound zone transfers.

  This is the maximum number of outbound zone transfers that can run concurrently. Zone transfer requests in excess of the limit are refused. The default value is `10`.

transfers-per-ns

  Grammar: `transfers-per-ns <integer>;`

  Blocks: options

  Tags: transfer

  Limits the number of concurrent inbound zone transfers from a remote server.

  This is the maximum number of inbound zone transfers that can concurrently transfer from a given remote name server. The default value is `2`. Increasing `transfers-per-ns` may speed up the convergence of secondary zones, but it also may increase the load on the remote name server. `transfers-per-ns` may be overridden on a per-server basis by using the `transfers` phrase of the `server` statement.

transfer-source

  Grammar: `transfer-source ( <ipv4_address> | * );`

  Blocks: options, server, view, zone (mirror, secondary, stub), view.server

  Tags: transfer

  Defines which local IPv4 address(es) are bound to TCP connections used to fetch zones transferred inbound by the server.

  `transfer-source` determines which local address is bound to IPv4 TCP connections used to fetch zones transferred inbound by the server. It also determines the source IPv4 address, and optionally the UDP port, used for the refresh queries and forwarded dynamic updates. If not set, it defaults to a system-controlled value which is usually the address of the interface “closest to” the remote end. This address must appear in the remote end’s `allow-transfer` option for the zone being transferred, if one is specified. This statement sets the `transfer-source` for all zones, but can be overridden on a per-view or per-zone basis by including a `transfer-source` statement within the `view` or `zone` block in the configuration file.

  Note

  `port` configuration is deprecated. A warning will be logged when this parameter is used.

  Warning

  Specifying a single port is discouraged, as it removes a layer of protection against spoofing errors.

  Warning

  The configured port must not be the same as the listening port.

transfer-source-v6

  Grammar: `transfer-source-v6 ( <ipv6_address> | * );`

  Blocks: options, server, view, zone (mirror, secondary, stub), view.server

  Tags: transfer

  Defines which local IPv6 address(es) are bound to TCP connections used to fetch zones transferred inbound by the server.

  This option is the same as `transfer-source`, except zone transfers are performed using IPv6.

notify-source

  Grammar: `notify-source ( <ipv4_address> | * );`

  Blocks: options, server, view, zone (mirror, primary, secondary), view.server

  Tags: transfer

  Defines the IPv4 address (and optional port) to be used for outgoing `NOTIFY` messages.

  `notify-source` determines which local source address, and optionally UDP port, is used to send NOTIFY messages. This address must appear in the secondary server’s `primaries` zone clause or in an `allow-notify` clause. This statement sets the `notify-source` for all zones, but can be overridden on a per-zone or per-view basis by including a `notify-source` statement within the `zone` or `view` block in the configuration file.

  Note

  `port` configuration is deprecated. A warning will be logged when this parameter is used.

  Warning

  Specifying a single port is discouraged, as it removes a layer of protection against spoofing errors.

  Warning

  The configured port must not be the same as the listening port.

notify-source-v6

  Grammar: `notify-source-v6 ( <ipv6_address> | * );`

  Blocks: options, server, view, zone (mirror, primary, secondary), view.server

  Tags: transfer

  Defines the IPv6 address (and optional port) to be used for outgoing `NOTIFY` messages.

  This option acts like `notify-source`, but applies to `NOTIFY` messages sent to IPv6 addresses.

#### 8.2.13.8. Server Resource Limits

The following options set limits on the server’s resource consumption that are enforced internally by the server rather than by the operating system.

max-journal-size

  Grammar: `max-journal-size ( default | unlimited | <sizeval> );`

  Blocks: options, view, zone (mirror, primary, secondary)

  Tags: transfer

  Controls the size of journal files.

  This sets a maximum size for each journal file (see The Journal File), expressed in bytes or, if followed by an optional unit suffix (‘k’, ‘m’, or ‘g’), in kilobytes, megabytes, or gigabytes. When the journal file approaches the specified size, some of the oldest transactions in the journal are automatically removed. The largest permitted value is 2 gigabytes. Very small values are rounded up to 4096 bytes. It is possible to specify `unlimited`, which also means 2 gigabytes. If the limit is set to `default` or left unset, the journal is allowed to grow up to twice as large as the zone. (There is little benefit in storing larger journals.)

  This option may also be set on a per-zone basis.

max-records

  Grammar: `max-records <integer>;`

  Blocks: options, view, zone (mirror, primary, redirect, secondary, static-stub, stub)

  Tags: zone, server

  Sets the maximum number of records permitted in a zone.

  This sets the maximum number of records permitted in a zone. The default is zero, which means the maximum is unlimited.

max-records-per-type

  Grammar: `max-records-per-type <integer>;`

  Blocks: options, view, zone (mirror, primary, redirect, secondary, static-stub, stub)

  Tags: server

  Sets the maximum number of records that can be stored in an RRset.

  This sets the maximum number of resource records that can be stored in an RRset in a database. When configured in `options` or `view`, it controls the cache database; it also sets the default value for zone databases, which can be overridden by setting it at the `zone` level.

  If set to a positive value, any attempt to cache, or to add to a zone an RRset with more than the specified number of records, will result in a failure. If set to 0, there is no cap on RRset size. The default is 100.

max-types-per-name

  Grammar: `max-types-per-name <integer>;`

  Blocks: options, view, zone (mirror, primary, redirect, secondary, static-stub, stub)

  Tags: server

  Sets the maximum number of RR types that can be stored for an owner name.

  This sets the maximum number of resource record types that can be stored for a single owner name in a database. When configured in `options` or `view`, it controls the cache database and sets the default value for zone databases, which can be overridden by setting it at the `zone` level.

  An RR type and its corresponding signature are counted as two types. So, for example, a signed node containing A and AAAA records has four types: A, RRSIG(A), AAAA, and RRSIG(AAAA).

  The behavior is slightly different for zone and cache databases:

  In a zone, if `max-types-per-name` is set to a positive number, any attempt to add a new resource record set to a name that already has the specified number of types will fail.

  In a cache, if `max-types-per-name` is set to a positive number, an attempt to add a new resource record set to a name that already has the specified number of types will temporarily succeed, so that the query can be answered. However, the newly added RRset will immediately be purged.

  Certain high-priority types, including SOA, CNAME, DNSKEY, and their corresponding signatures, are always cached. If `max-types-per-name` is set to a very low value, then it may be ignored to allow high-priority types to be cached.

  When `max-types-per-name` is set to 0, there is no cap on the number of RR types. The default is 100.

recursive-clients

  Grammar: `recursive-clients <integer>;`

  Blocks: options

  Tags: query

  Specifies the maximum number of concurrent recursive queries the server can perform.

  This sets the maximum number (a “hard quota”) of simultaneous recursive lookups the server performs on behalf of clients. The default is `1000`. Because each recursing client uses a fair bit of memory (on the order of 20 kilobytes), the value of the `recursive-clients` option may have to be decreased on hosts with limited memory.

  `recursive-clients` defines a “hard quota” limit for pending recursive clients; when more clients than this are pending, new incoming requests are not accepted, and for each incoming request a previous pending request is dropped.

  A “soft quota” is also set. When this lower quota is exceeded, incoming requests are accepted, but for each one, a pending request is dropped. If `recursive-clients` is greater than 1000, the soft quota is set to `recursive-clients` minus 100; otherwise it is set to 90% of `recursive-clients`.

tcp-clients

  Grammar: `tcp-clients <integer>;`

  Blocks: options

  Tags: server

  Specifies the maximum number of simultaneous client TCP connections accepted by the server.

  This is the maximum number of simultaneous client TCP connections that the server accepts. The default is `150`.

clients-per-query

  Grammar: `clients-per-query <integer>;`

  Blocks: options, view

  Tags: server

  Sets the initial minimum number of simultaneous recursive clients accepted by the server for any given query before the server drops additional clients.

  This sets the initial value (minimum) number of simultaneous recursive clients for any given query (<qname,qtype,qclass>) that the server accepts before dropping additional clents. `named` attempts to self-tune this value and changes are logged. The default value is 10.

  The chosen value should reflect how many queries come in for a given name in the time it takes to resolve that name.

max-clients-per-query

  Grammar: `max-clients-per-query <integer>;`

  Blocks: options, view

  Tags: server

  Sets the maximum number of simultaneous recursive clients accepted by the server for any given query before the server drops additional clients.

  This sets the maximum number of simultaneous recursive clients for any given query (<qname,qtype,qclass>) that the server accepts before dropping additional clients.

  If the number of queries exceeds `clients-per-query`, `named` assumes that it is dealing with a non-responsive zone and drops additional queries. If it gets a response after dropping queries, it raises the estimate, up to a limit of `max-clients-per-query`. The estimate is then lowered after 20 minutes if it has remained unchanged.

  If `max-clients-per-query` is set to zero, there is no upper bound, other than that imposed by `recursive-clients`. If the option is set to a lower value than `clients-per-query`, the value is adjusted to `clients-per-query`.

  If `clients-per-query` is set to zero, `max-clients-per-query` no longer applies and there is no upper bound, other than that imposed by `recursive-clients`.

max-validations-per-fetch

  Warning

  This option is experimental and subject to change.

  Grammar: `max-validations-per-fetch <integer>; // experimental`

  Blocks: options, view

  Tags: server

  Sets the maximum number of DNSSEC validations that can happen in a single fetch.

  This is an experimental setting that defines the maximum number of DNSSEC validations that can happen in a single resolver fetch. The default is 16.

max-validation-failures-per-fetch

  Warning

  This option is experimental and subject to change.

  Grammar: `max-validation-failures-per-fetch <integer>; // experimental`

  Blocks: options, view

  Tags: server

  Sets the maximum number of DNSSEC validation failures that can happen in a single fetch.

  This is an experimental setting that defines the maximum number of DNSSEC validation failures that can happen in a single resolver fetch. The default is 1.

fetches-per-zone

  Grammar: `fetches-per-zone <integer> [ ( drop | fail ) ];`

  Blocks: options, view

  Tags: server, query

  Sets the maximum number of simultaneous iterative queries allowed to any one domain before the server blocks new queries for data in or beneath that zone.

  This sets the maximum number of simultaneous iterative queries to any one domain that the server permits before blocking new queries for data in or beneath that zone. This value should reflect how many fetches would normally be sent to any one zone in the time it would take to resolve them. It should be smaller than `recursive-clients`.

  When many clients simultaneously query for the same name and type, the clients are all attached to the same fetch, up to the `max-clients-per-query` limit, and only one iterative query is sent. However, when clients are simultaneously querying for different names or types, multiple queries are sent and `max-clients-per-query` is not effective as a limit.

  Optionally, this value may be followed by the keyword `drop` or `fail`, indicating whether queries which exceed the fetch quota for a zone are dropped with no response, or answered with SERVFAIL. The default is `drop`.

  If `fetches-per-zone` is set to zero, there is no limit on the number of fetches per query and no queries are dropped. The default is zero.

  The current list of active fetches can be dumped by running `rndc recursing`. The list includes the number of active fetches for each domain and the number of queries that have been passed (allowed) or dropped (spilled) as a result of the `fetches-per-zone` limit. (Note: these counters are not cumulative over time; whenever the number of active fetches for a domain drops to zero, the counter for that domain is deleted, and the next time a fetch is sent to that domain, it is recreated with the counters set to zero.)

  Note

  Fetches generated automatically in the result of `prefetch` are exempt from this quota.

fetches-per-server

  Grammar: `fetches-per-server <integer> [ ( drop | fail ) ];`

  Blocks: options, view

  Tags: server, query

  Sets the maximum number of simultaneous iterative queries allowed to be sent by a server to an upstream name server before the server blocks additional queries.

  This sets the maximum number of simultaneous iterative queries that the server allows to be sent to a single upstream name server before blocking additional queries. This value should reflect how many fetches would normally be sent to any one server in the time it would take to resolve them. It should be smaller than `recursive-clients`.

  Optionally, this value may be followed by the keyword `drop` or `fail`, indicating whether queries are dropped with no response or answered with SERVFAIL, when all of the servers authoritative for a zone are found to have exceeded the per-server quota. The default is `fail`.

  If `fetches-per-server` is set to zero, there is no limit on the number of fetches per query and no queries are dropped. The default is zero.

  The `fetches-per-server` quota is dynamically adjusted in response to detected congestion. As queries are sent to a server and either are answered or time out, an exponentially weighted moving average is calculated of the ratio of timeouts to responses. If the current average timeout ratio rises above a “high” threshold, then `fetches-per-server` is reduced for that server. If the timeout ratio drops below a “low” threshold, then `fetches-per-server` is increased. The `fetch-quota-params` options can be used to adjust the parameters for this calculation.

  Note

  Fetches generated automatically in the result of `prefetch` are exempt from this quota, but they are included in the quota calculations.

fetch-quota-params

  Grammar: `fetch-quota-params <integer> <fixedpoint> <fixedpoint> <fixedpoint>;`

  Blocks: options, view

  Tags: server, query

  Sets the parameters for dynamic resizing of the `fetches-per-server` quota in response to detected congestion.

  This sets the parameters to use for dynamic resizing of the `fetches-per-server` quota in response to detected congestion.

  The first argument is an integer value indicating how frequently to recalculate the moving average of the ratio of timeouts to responses for each server. The default is 100, meaning that BIND recalculates the average ratio after every 100 queries have either been answered or timed out.

  The remaining three arguments represent the “low” threshold (defaulting to a timeout ratio of 0.1), the “high” threshold (defaulting to a timeout ratio of 0.3), and the discount rate for the moving average (defaulting to 0.7). A higher discount rate causes recent events to weigh more heavily when calculating the moving average; a lower discount rate causes past events to weigh more heavily, smoothing out short-term blips in the timeout ratio. These arguments are all fixed-point numbers with precision of 1/100; at most two places after the decimal point are significant.

max-cache-size

  Grammar: `max-cache-size ( default | unlimited | <sizeval> | <percentage> );`

  Blocks: options, view

  Tags: server

  Sets the maximum amount of memory to use for an individual cache database and its associated metadata.

  This sets the maximum amount of memory to use for an individual cache database and its associated metadata, in bytes or percentage of total physical memory. By default, each view has its own separate cache, which means the total amount of memory required for cache data is the sum of the cache database sizes for all views (unless the `attach-cache` option is used).

  When the amount of data in a cache database reaches the configured limit, `named` starts purging non-expired records (following an LRU-based strategy).

  The default size limit for each individual cache is:

  > - 90% of physical memory for views with `recursion` set to `yes` (the default), or

  > - 2 MB for views with `recursion` set to `no`.

  Any positive value smaller than 2 MB is ignored and reset to 2 MB. The keyword `unlimited`, or the value `0`, places no limit on the cache size; records are then purged from the cache only when they expire (according to their TTLs).

  Note

  For configurations which define multiple views with separate caches and recursion enabled, it is recommended to set `max-cache-size` appropriately for each view, as using the default value of that option (90% of physical memory for each individual cache) may lead to memory exhaustion over time.

  Note

  `max-cache-size` does not work reliably for a maximum amount of memory of 100 MB or lower.

  Upon startup and reconfiguration, caches with a limited size preallocate a small amount of memory (less than 1% of `max-cache-size` for a given view). This preallocation serves as an optimization to eliminate extra latency introduced by resizing internal cache structures.

  On systems where detection of the amount of physical memory is not supported, percentage-based values fall back to `unlimited`. Note that the amount of physical memory available is only detected on startup, so `named` does not adjust the cache size limits if the amount of physical memory is changed at runtime.

tcp-listen-queue

  Grammar: `tcp-listen-queue <integer>;`

  Blocks: options

  Tags: server

  Sets the listen-queue depth.

  This sets the listen-queue depth. The default and minimum is 10. If the kernel supports the accept filter “dataready”, this also controls how many TCP connections are queued in kernel space waiting for some data before being passed to accept. Non-zero values less than 10 are silently raised. A value of 0 may also be used; on most platforms this sets the listen-queue length to a system-defined default value.

tcp-initial-timeout

  Grammar: `tcp-initial-timeout <integer>;`

  Blocks: options

  Tags: server, query

  Sets the amount of time (in milliseconds) that the server waits on a new TCP connection for the first message from the client.

  This sets the amount of time, in units of 100 milliseconds, that the server waits on a new TCP connection for the first message from the client. The default is 300 (30 seconds), the minimum is 25 (2.5 seconds), and the maximum is 1200 (two minutes). Values above the maximum or below the minimum are adjusted with a logged warning. (Note: this value must be greater than the expected round-trip delay time; otherwise, no client will ever have enough time to submit a message.) This value can be updated at runtime by using `rndc tcp-timeouts`.

tcp-idle-timeout

  Grammar: `tcp-idle-timeout <integer>;`

  Blocks: options

  Tags: query

  Sets the amount of time (in milliseconds) that the server waits on an idle TCP connection before closing it, if the EDNS TCP keepalive option is not in use.

  This sets the amount of time, in units of 100 milliseconds, that the server waits on an idle TCP connection before closing it, when the client is not using the EDNS TCP keepalive option. The default is 300 (30 seconds), the maximum is 1200 (two minutes), and the minimum is 1 (one-tenth of a second). Values above the maximum or below the minimum are adjusted with a logged warning. See `tcp-keepalive-timeout` for clients using the EDNS TCP keepalive option. This value can be updated at runtime by using `rndc tcp-timeouts`.

tcp-keepalive-timeout

  Grammar: `tcp-keepalive-timeout <integer>;`

  Blocks: options

  Tags: query

  Sets the amount of time (in milliseconds) that the server waits on an idle TCP connection before closing it, if the EDNS TCP keepalive option is in use.

  This sets the amount of time, in units of 100 milliseconds, that the server waits on an idle TCP connection before closing it, when the client is using the EDNS TCP keepalive option. The default is 300 (30 seconds), the maximum is 65535 (about 1.8 hours), and the minimum is 1 (one-tenth of a second). Values above the maximum or below the minimum are adjusted with a logged warning. This value may be greater than `tcp-idle-timeout` because clients using the EDNS TCP keepalive option are expected to use TCP connections for more than one message. This value can be updated at runtime by using `rndc tcp-timeouts`.

tcp-advertised-timeout

  Grammar: `tcp-advertised-timeout <integer>;`

  Blocks: options

  Tags: query

  Sets the timeout value (in milliseconds) that the server sends in responses containing the EDNS TCP keepalive option.

  This sets the timeout value, in units of 100 milliseconds, that the server sends in responses containing the EDNS TCP keepalive option, which informs a client of the amount of time it may keep the session open. The default is 300 (30 seconds), the maximum is 65535 (about 1.8 hours), and the minimum is 0, which signals that the clients must close TCP connections immediately. Ordinarily this should be set to the same value as `tcp-keepalive-timeout`. This value can be updated at runtime by using `rndc tcp-timeouts`.

update-quota

  Grammar: `update-quota <integer>;`

  Blocks: options

  Tags: server

  Specifies the maximum number of concurrent DNS UPDATE messages that can be processed by the server.

  This is the maximum number of simultaneous DNS UPDATE messages that the server will accept, for updating local authoritative zones or forwarding to a primary server. The default is `100`.

sig0checks-quota

  Warning

  This option is experimental and subject to change.

  Grammar: `sig0checks-quota <integer>; // experimental`

  Blocks: options

  Tags: server

  Specifies the maximum number of concurrent SIG(0) signature checks that can be processed by the server.

  This is the maximum number of simultaneous SIG(0)-signed messages that the server accepts. If the quota is reached, then `named` answers with a status code of REFUSED. The value of `0` disables the quota. The default is `1`.

sig0checks-quota-exempt

  Warning

  This option is experimental and subject to change.

  Grammar: `sig0checks-quota-exempt { <address_match_element>; ... }; // experimental`

  Blocks: options

  Tags: server

  Exempts specific clients or client groups from SIG(0) signature checking quota.

  DNS clients can be exempted from the SIG(0) signature checking quota with the `sig0checks-quota-exempt` clause, using their IP and/or network addresses. The default value is an empty list.

  Example:

      sig0checks-quota-exempt {
          10.0.0.0/8;
          2001:db8::100;
      };

sig0key-checks-limit

  Grammar: `sig0key-checks-limit <integer>;`

  Blocks: options, view

  Tags: server

  Specifies the maximum number of SIG(0) keys to consider when trying to verify a message.

  This is the maximum number of keys to consider for a SIG(0)-signed message when trying to verify it. `named` will parse the candidate keys and check whether their key tag and algorithm matches with the expected one before trying to verify the signature. If the limit is reached the message verification fails. The value of `0` disables the limitation. The default is `16`.

sig0message-checks-limit

  Grammar: `sig0message-checks-limit <integer>;`

  Blocks: options, view

  Tags: server

  Specifies the maximum number of matching SIG(0) keys to try to verify a message.

  This is the maximum number of keys which (when correctly parsed and matched against the expected key tag and algorithm) `named` uses to verify a SIG(0)-signed message. If the limit is reached the message verification fails. The value of `0` disables the limitation. The default is `2`.

#### 8.2.13.9. Periodic Task Intervals

heartbeat-interval

  Warning

  This option is deprecated and will be removed in a future version of BIND.

  Grammar: `heartbeat-interval <integer>; // deprecated`

  Blocks: options

  Tags: deprecated

  Sets the interval at which the server performs zone maintenance tasks for all zones marked as `dialup`.

  The server performs zone maintenance tasks for all zones marked as `dialup` whenever this interval expires. The default is 60 minutes. Reasonable values are up to 1 day (1440 minutes). The maximum value is 28 days (40320 minutes). If set to 0, no zone maintenance for these zones occurs.

  This option is deprecated and will be removed in a future release.

interface-interval

  Grammar: `interface-interval <duration>;`

  Blocks: options

  Tags: server

  Sets the interval at which the server scans the network interface list.

  The server scans the network interface list on every interval as specified by `interface-interval`.

  If set to 0, interface scanning only occurs when the configuration file is loaded, or when `automatic-interface-scan` is enabled and supported by the operating system. After the scan, the server begins listening for queries on any newly discovered interfaces (provided they are allowed by the `listen-on` configuration), and stops listening on interfaces that have gone away. For convenience, TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.

  The default is 60 minutes (1 hour); the maximum value is 28 days.

#### 8.2.13.10. The `sortlist` Statement

The response to a DNS query may consist of multiple resource records (RRs) forming a resource record set (RRset). The name server normally returns the RRs within the RRset in an indeterminate order (but see the `rrset-order` statement in RRset Ordering). The client resolver code should rearrange the RRs as appropriate: that is, using any addresses on the local net in preference to other addresses. However, not all resolvers can do this or are correctly configured. When a client is using a local server, the sorting can be performed in the server, based on the client’s address. This only requires configuring the name servers, not all the clients.

sortlist

  Warning

  This option is deprecated and will be removed in a future version of BIND.

  Grammar: `sortlist { <address_match_element>; ... }; // deprecated`

  Blocks: options, view

  Tags: query, deprecated

  Controls the ordering of RRs returned to the client, based on the client’s IP address.

  This option is deprecated and will be removed in a future release.

  The `sortlist` statement (see below) takes an address_match_list and interprets it in a special way. Each top-level statement in the `sortlist` must itself be an explicit address_match_list with one or two elements. The first element (which may be an IP address, an IP prefix, an ACL name, or a nested address_match_list) of each top-level list is checked against the source address of the query until a match is found. When the addresses in the first element overlap, the first rule to match is selected.

  Once the source address of the query has been matched, if the top-level statement contains only one element, the actual primitive element that matched the source address is used to select the address in the response to move to the beginning of the response. If the statement is a list of two elements, then the second element is interpreted as a topology preference list. Each top-level element is assigned a distance, and the address in the response with the minimum distance is moved to the beginning of the response.

  In the following example, any queries received from any of the addresses of the host itself get responses preferring addresses on any of the locally connected networks. Next most preferred are addresses on the 192.168.1/24 network, and after that either the 192.168.2/24 or 192.168.3/24 network, with no preference shown between these two networks. Queries received from a host on the 192.168.1/24 network prefer other addresses on that network to the 192.168.2/24 and 192.168.3/24 networks. Queries received from a host on the 192.168.4/24 or the 192.168.5/24 network only prefer other addresses on their directly connected networks.

    sortlist {
        // IF the local host
        // THEN first fit on the following nets
        { localhost;
        { localnets;
            192.168.1/24;
            { 192.168.2/24; 192.168.3/24; }; }; };
        // IF on class C 192.168.1 THEN use .1, or .2 or .3
        { 192.168.1/24;
        { 192.168.1/24;
            { 192.168.2/24; 192.168.3/24; }; }; };
        // IF on class C 192.168.2 THEN use .2, or .1 or .3
        { 192.168.2/24;
        { 192.168.2/24;
            { 192.168.1/24; 192.168.3/24; }; }; };
        // IF on class C 192.168.3 THEN use .3, or .1 or .2
        { 192.168.3/24;
        { 192.168.3/24;
            { 192.168.1/24; 192.168.2/24; }; }; };
        // IF .4 or .5 THEN prefer that net
        { { 192.168.4/24; 192.168.5/24; };
        };
    };

The following example illustrates reasonable behavior for the local host and hosts on directly connected networks. Responses sent to queries from the local host favor any of the directly connected networks. Responses sent to queries from any other hosts on a directly connected network prefer addresses on that same network. Responses to other queries are not sorted.

    sortlist {
           { localhost; localnets; };
           { localnets; };
    };

#### 8.2.13.11. RRset Ordering

Note

While alternating the order of records in a DNS response between subsequent queries is a known load distribution technique, certain caveats apply (mostly stemming from caching) which usually make it a suboptimal choice for load balancing purposes when used on its own.

rrset-order

  Grammar: `rrset-order { [ class <string> ] [ type <string> ] [ name <quoted_string> ] <string> <string>; ... };`

  Blocks: options, view

  Tags: query

  Defines the order in which equal RRs (RRsets) are returned.

  The `rrset-order` statement permits configuration of the ordering of the records in a multiple-record response. See also: `sortlist`.

  Each rule in an `rrset-order` statement is defined as follows:

      [class <class_name>] [type <type_name>] [name "<domain_name>"] order <ordering>

  The default qualifiers for each rule are:

  > - If no `class` is specified, the default is `ANY`.

  > - If no `type` is specified, the default is `ANY`.

  > - If no `name` is specified, the default is `*` (asterisk).

  <domain_name> only matches the name itself, not any of its subdomains. To make a rule match all subdomains of a given name, a wildcard name (`*.<domain_name>`) must be used. Note that `*.<domain_name>` does not match `<domain_name>` itself; to specify RRset ordering for a name and all of its subdomains, two separate rules must be defined: one for `<domain_name>` and one for `*.<domain_name>`.

  The legal values for `<ordering>` are:

  `fixed`

    Records are returned in the order they are defined in the zone file.

    This value is deprecated and will be removed in a future release.

  Note

  The `fixed` option is only available if BIND is configured with `--enable-fixed-rrset` at compile time.

  `random`

    Records are returned in a random order.

  `cyclic`

    Records are returned in a cyclic round-robin order, rotating by one record per query.

  `none`

    Records are returned in the order they were retrieved from the database. This order is indeterminate, but remains consistent as long as the database is not modified.

  The default RRset order used depends on whether any `rrset-order` statements are present in the configuration file used by `named`:

  > - If no `rrset-order` statement is present in the configuration file, the implicit default is to return all records in `random` order.

  > - If any `rrset-order` statements are present in the configuration file, but no ordering rule specified in these statements matches a given RRset, the default order for that RRset is `none`.

  Note that if multiple `rrset-order` statements are present in the configuration file (at both the `options` and `view` levels), they are not combined; instead, the more-specific one (`view`) replaces the less-specific one (`options`).

  If multiple rules within a single `rrset-order` statement match a given RRset, the first matching rule is applied.

  Example:

      rrset-order {
          type A name "foo.isc.org" order random;
          type AAAA name "foo.isc.org" order cyclic;
          name "bar.isc.org" order fixed;
          name "*.bar.isc.org" order random;
          name "*.baz.isc.org" order cyclic;
      };

  With the above configuration, the following RRset ordering is used:

  QNAME | QTYPE | RRset Order
  --- | --- | ---
  `foo.isc.org` | `A` | `random`
  `foo.isc.org` | `AAAA` | `cyclic`
  `foo.isc.org` | `TXT` | `none`
  `sub.foo.isc.org` | all | `none`
  `bar.isc.org` | all | `fixed`
  `sub.bar.isc.org` | all | `random`
  `baz.isc.org` | all | `none`
  `sub.baz.isc.org` | all | `cyclic`

#### 8.2.13.12. Tuning

lame-ttl

  Grammar: `lame-ttl <duration>;`

  Blocks: options, view

  Tags: server

  Sets the resolver’s lame cache.

  This is always set to 0. More information is available in the security advisory for CVE-2021-25219.

servfail-ttl

  Grammar: `servfail-ttl <duration>;`

  Blocks: options, view

  Tags: server

  Sets the length of time (in seconds) that a SERVFAIL response is cached.

  This sets the number of seconds to cache a SERVFAIL response due to DNSSEC validation failure or other general server failure. If set to `0`, SERVFAIL caching is disabled. The SERVFAIL cache is not consulted if a query has the CD (Checking Disabled) bit set; this allows a query that failed due to DNSSEC validation to be retried without waiting for the SERVFAIL TTL to expire.

  The maximum value is `30` seconds; any higher value is silently reduced. The default is `1` second.

min-ncache-ttl

  Grammar: `min-ncache-ttl <duration>;`

  Blocks: options, view

  Tags: server

  Specifies the minimum retention time (in seconds) for storage of negative answers in the server’s cache.

  To reduce network traffic and increase performance, the server stores negative answers. `min-ncache-ttl` is used to set a minimum retention time for these answers in the server, in seconds. For convenience, TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.

  The default `min-ncache-ttl` is `0` seconds. `min-ncache-ttl` cannot exceed 90 seconds and is truncated to 90 seconds if set to a greater value.

min-cache-ttl

  Grammar: `min-cache-ttl <duration>;`

  Blocks: options, view

  Tags: server

  Specifies the minimum time (in seconds) that the server caches ordinary (positive) answers.

  This sets the minimum time for which the server caches ordinary (positive) answers, in seconds. For convenience, TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.

  The default `min-cache-ttl` is `0` seconds. `min-cache-ttl` cannot exceed 90 seconds and is truncated to 90 seconds if set to a greater value.

max-ncache-ttl

  Grammar: `max-ncache-ttl <duration>;`

  Blocks: options, view

  Tags: server

  Specifies the maximum retention time (in seconds) for storage of negative answers in the server’s cache.

  To reduce network traffic and increase performance, the server stores negative answers. `max-ncache-ttl` is used to set a maximum retention time for these answers in the server, in seconds. For convenience, TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.

  The default `max-ncache-ttl` is 10800 seconds (3 hours). `max-ncache-ttl` cannot exceed 7 days and is silently truncated to 7 days if set to a greater value.

max-cache-ttl

  Grammar: `max-cache-ttl <duration>;`

  Blocks: options, view

  Tags: server

  Specifies the maximum time (in seconds) that the server caches ordinary (positive) answers.

  This sets the maximum time for which the server caches ordinary (positive) answers, in seconds. For convenience, TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.

  The default `max-cache-ttl` is 604800 (one week). A value of zero may cause all queries to return SERVFAIL, because of lost caches of intermediate RRsets (such as NS and glue AAAA/A records) in the resolution process.

max-stale-ttl

  Grammar: `max-stale-ttl <duration>;`

  Blocks: options, view

  Tags: server

  Specifies the maximum time that the server retains records past their normal expiry, to return them as stale records.

  If retaining stale RRsets in cache is enabled, and returning of stale cached answers is also enabled, `max-stale-ttl` sets the maximum time for which the server retains records past their normal expiry to return them as stale records, when the servers for those records are not reachable. The default is 1 day. The minimum allowed is 1 second; a value of 0 is updated silently to 1 second.

  For stale answers to be returned, the retaining of them in cache must be enabled via the configuration option `stale-cache-enable`, and returning cached answers must be enabled, either in the configuration file using the `stale-answer-enable` option or by calling `rndc serve-stale on`.

  When `stale-cache-enable` is set to `no`, setting the `max-stale-ttl` has no effect; the value of `max-stale-ttl` is `0` in such a case.

sig-validity-interval

  Grammar: `sig-validity-interval <integer> [ <integer> ]; // obsolete`

  Blocks: options, view, zone (primary, secondary)

  Tags: obsolete

  This option no longer has any effect.

dnskey-sig-validity

  Grammar: `dnskey-sig-validity <integer>; // obsolete`

  Blocks: options, view, zone (primary, secondary)

  Tags: obsolete

  This option no longer has any effect.

sig-signing-nodes

  Grammar: `sig-signing-nodes <integer>;`

  Blocks: options, view, zone (primary, secondary)

  Tags: dnssec

  Specifies the maximum number of nodes to be examined in each quantum, when signing a zone with a new DNSKEY.

  This specifies the maximum number of nodes to be examined in each quantum, when signing a zone with a new DNSKEY. The default is `100`.

sig-signing-signatures

  Grammar: `sig-signing-signatures <integer>;`

  Blocks: options, view, zone (primary, secondary)

  Tags: dnssec

  Specifies the threshold for the number of signatures that terminates processing a quantum, when signing a zone with a new DNSKEY.

  This specifies a threshold number of signatures that terminates processing a quantum, when signing a zone with a new DNSKEY. The default is `10`.

sig-signing-type

  Grammar: `sig-signing-type <integer>;`

  Blocks: options, view, zone (primary, secondary)

  Tags: dnssec

  Specifies a private RDATA type to use when generating signing-state records.

  This specifies a private RDATA type to be used when generating signing-state records. The default is `65534`.

  This parameter may be removed in a future version, once there is a standard type.

  Signing-state records are used internally by `named` to track the current state of a zone-signing process, i.e., whether it is still active or has been completed. The records can be inspected using the command `rndc signing -list zone`. Once `named` has finished signing a zone with a particular key, the signing-state record associated with that key can be removed from the zone by running `rndc signing -clear keyid/algorithm zone`. To clear all of the completed signing-state records for a zone, use `rndc signing -clear all zone`.

min-refresh-time

  Grammar: `min-refresh-time <integer>;`

  Blocks: options, view, zone (mirror, secondary, stub)

  Tags: transfer

  Limits the zone refresh interval to no more often than the specified value, in seconds.

  This option controls the server’s behavior on refreshing a zone (querying for SOA changes). Usually, the SOA refresh values for the zone are used; however, these values are set by the primary, giving secondary server administrators little control over their contents.

  This option allows the administrator to set a minimum refresh time in seconds per-zone, per-view, or globally. This option is valid for secondary and stub zones, and clamps the SOA refresh time to the specified value.

  The default is 300 seconds.

max-refresh-time

  Grammar: `max-refresh-time <integer>;`

  Blocks: options, view, zone (mirror, secondary, stub)

  Tags: transfer

  Limits the zone refresh interval to no less often than the specified value, in seconds.

  This option controls the server’s behavior on refreshing a zone (querying for SOA changes). Usually, the SOA refresh values for the zone are used; however, these values are set by the primary, giving secondary server administrators little control over their contents.

  This option allows the administrator to set a maximum refresh time in seconds per-zone, per-view, or globally. This option is valid for secondary and stub zones, and clamps the SOA refresh time to the specified value.

  The default is 2419200 seconds (4 weeks).

min-retry-time

  Grammar: `min-retry-time <integer>;`

  Blocks: options, view, zone (mirror, secondary, stub)

  Tags: transfer

  Limits the zone refresh retry interval to no more often than the specified value, in seconds.

  This option controls the server’s behavior on retrying failed zone transfers. Usually, the SOA retry values for the zone are used; however, these values are set by the primary, giving secondary server administrators little control over their contents.

  This option allows the administrator to set a minimum retry time in seconds per-zone, per-view, or globally. This option is valid for secondary and stub zones, and clamps the SOA retry time to the specified value.

  The default is 500 seconds.

max-retry-time

  Grammar: `max-retry-time <integer>;`

  Blocks: options, view, zone (mirror, secondary, stub)

  Tags: transfer

  Limits the zone refresh retry interval to no less often than the specified value, in seconds.

  This option controls the server’s behavior on retrying failed zone transfers. Usually, the SOA retry values for the zone are used; however, these values are set by the primary, giving secondary server administrators little control over their contents.

  This option allows the administrator to set a maximum retry time in seconds per-zone, per-view, or globally. This option is valid for secondary and stub zones, and clamps the SOA retry time to the specified value.

  The default is 1209600 seconds (2 weeks).

edns-udp-size

  Grammar: `edns-udp-size <integer>;`

  Blocks: options, server, view, view.server

  Tags: query

  Sets the maximum advertised EDNS UDP buffer size to control the size of packets received from authoritative servers in response to recursive queries.

  This sets the maximum advertised EDNS UDP buffer size, in bytes, to control the size of packets received from authoritative servers in response to recursive queries. Valid values are 512 to 4096; values outside this range are silently adjusted to the nearest value within it. The default value is 1232.

  The usual reason for setting `edns-udp-size` to a non-default value is to get UDP answers to pass through broken firewalls that block fragmented packets and/or block UDP DNS packets that are greater than 512 bytes.

  When `named` first queries a remote server, it advertises a UDP buffer size of 1232.

  Query timeouts observed for any given server affect the buffer size advertised in queries sent to that server. Depending on observed packet dropping patterns, the query is retried over TCP. Per-server EDNS statistics are only retained in memory for the lifetime of a given server’s ADB entry.

  According to measurements taken by multiple parties, the default value should not be causing the fragmentation. As most of the Internet “core” is able to cope with IP message sizes between 1400-1500 bytes, the 1232 size was chosen as a conservative minimal number that could be changed by the DNS operator to a estimated path MTU, minus the estimated header space. In practice, the smallest MTU witnessed in the operational DNS community is 1500 octets, the Ethernet maximum payload size, so a useful default for the maximum DNS/UDP payload size on reliable networks would be 1432.

  Any server-specific `edns-udp-size` setting has precedence over all the above rules, i.e. configures a static value for a given `server` block.

max-udp-size

  Grammar: `max-udp-size <integer>;`

  Blocks: options, server, view, view.server

  Tags: query

  Sets the maximum EDNS UDP message size sent by `named`.

  This sets the maximum EDNS UDP message size that `named` sends, in bytes. Valid values are 512 to 4096; values outside this range are silently adjusted to the nearest value within it. The default value is 1232.

  This value applies to responses sent by a server; to set the advertised buffer size in queries, see `edns-udp-size`.

  The usual reason for setting `max-udp-size` to a non-default value is to allow UDP answers to pass through broken firewalls that block fragmented packets and/or block UDP packets that are greater than 512 bytes. This is independent of the advertised receive buffer (`edns-udp-size`).

  Setting this to a low value encourages additional TCP traffic to the name server.

masterfile-format

  Grammar: `masterfile-format ( raw | text );`

  Blocks: options, view, zone (mirror, primary, redirect, secondary, stub)

  Tags: zone, server

  Specifies the file format of zone files.

  This specifies the file format of zone files (see Additional File Formats for details). The default value is `text`, which is the standard textual representation, except for secondary zones, in which the default value is `raw`. Files in formats other than `text` are typically expected to be generated by the `named-compilezone` tool, or dumped by `named`.

  Note that when a zone file in a format other than `text` is loaded, `named` may omit some of the checks which are performed for a file in `text` format. For example, `check-names` only applies when loading zones in `text` format. Zone files in `raw` format should be generated with the same check level as that specified in the `named` configuration file.

  When configured in `options`, this statement sets the `masterfile-format` for all zones, but it can be overridden on a per-zone or per-view basis by including a `masterfile-format` statement within the `zone` or `view` block in the configuration file.

masterfile-style

  Grammar: `masterfile-style ( full | relative );`

  Blocks: options, view, zone (mirror, primary, redirect, secondary, stub)

  Tags: server

  Specifies the format of zone files during a dump, when the `masterfile-format` is `text`.

  This specifies the formatting of zone files during dump, when the `masterfile-format` is `text`. This option is ignored with any other `masterfile-format`.

  When set to `relative`, records are printed in a multi-line format, with owner names expressed relative to a shared origin. When set to `full`, records are printed in a single-line format with absolute owner names. The `full` format is most suitable when a zone file needs to be processed automatically by a script. The `relative` format is more human-readable, and is thus suitable when a zone is to be edited by hand. The default is `relative`.

max-query-count

  Grammar: `max-query-count <integer>;`

  Blocks: options, view

  Tags: server, query

  Sets the maximum number of iterative queries while servicing a recursive query.

  This sets the maximum number of iterative queries that may be sent by a resolver while looking up a single name. If more queries than this need to be sent before an answer is reached, then recursion is terminated and a SERVFAIL response is returned to the client. The default is `200`.

max-recursion-depth

  Grammar: `max-recursion-depth <integer>;`

  Blocks: options, view

  Tags: server

  Sets the maximum number of levels of recursion permitted at any one time while servicing a recursive query.

  This sets the maximum number of levels of recursion that are permitted at any one time while servicing a recursive query. Resolving a name may require looking up a name server address, which in turn requires resolving another name, etc.; if the number of recursions exceeds this value, the recursive query is terminated and returns SERVFAIL. The default is 7.

max-recursion-queries

  Grammar: `max-recursion-queries <integer>;`

  Blocks: options, view

  Tags: server, query

  Sets the maximum number of iterative queries while servicing a recursive query.

  This sets the maximum number of iterative queries that may be sent by a resolver while looking up a single name. If more queries than this need to be sent before an answer is reached, then recursion is terminated and a SERVFAIL response is returned to the client. (Note: if the answer is a CNAME, then the subsequent lookup for the target of the CNAME is counted separately.) The default is 50.

max-query-restarts

  Grammar: `max-query-restarts <integer>;`

  Blocks: options, view

  Tags: server, query

  Sets the maximum number of chained CNAMEs to follow

  This sets the maximum number of successive CNAME targets to follow when resolving a client query, before terminating the query to avoid a CNAME loop. Valid values are 1 to 255. The default is 11.

notify-defer

  Grammar: `notify-defer <integer>;`

  Blocks: options, view, zone (mirror, primary, secondary)

  Tags: transfer, zone

  Sets the defer time (in seconds) before sending NOTIFY messages for a zone.

  This sets the delay, in seconds, to wait before sending a set of NOTIFY messages for a zone. Whenever a NOTIFY message is ready to be sent, sending will be deferred for this duration. This can be useful, for example, when for some operation needs a catalog zone is updated with new member zones before these member zones are actually ready to be tranferred. The delay can be tuned for the catalog zone to an amount of time after which the member zones are usually known to become ready. The default is 0 seconds.

  Warning

  This option is not to be confused with the `notify-delay` option.

  Note

  An implicit `rndc notify` command for a zone overrides the effects of this option.

  Note

  This options is ignored for notifies sent during the `dialup` process.

notify-delay

  Grammar: `notify-delay <integer>;`

  Blocks: options, view, zone (mirror, primary, secondary)

  Tags: transfer, zone

  Sets the delay (in seconds) between sending sets of NOTIFY messages for a zone.

  This sets the delay, in seconds, between sending sets of NOTIFY messages for a zone. Whenever a NOTIFY message is sent for a zone, a timer will be set for this duration. If the zone is updated again before the timer expires, the NOTIFY for that update will be postponed. The default is 5 seconds.

  The overall rate at which NOTIFY messages are sent for all zones is controlled by `notify-rate`.

  Warning

  This option is not to be confused with the `notify-defer` option.

max-rsa-exponent-size

  Grammar: `max-rsa-exponent-size <integer>;`

  Blocks: options

  Tags: dnssec, query

  Sets the maximum RSA exponent size (in bits) when validating.

  This sets the maximum RSA exponent size, in bits, that is accepted when validating. Valid values are 35 to 4096 bits. The default, zero, is also accepted and is equivalent to 4096.

prefetch

  Grammar: `prefetch <integer> [ <integer> ];`

  Blocks: options, view

  Tags: query

  Specifies the “trigger” time-to-live (TTL) value at which prefetch of the current query takes place.

  When a query is received for cached data which is to expire shortly, `named` can refresh the data from the authoritative server immediately, ensuring that the cache always has an answer available.

  `prefetch` specifies the “trigger” TTL value at which prefetch of the current query takes place; when a cache record with an equal or lower TTL value is encountered during query processing, it is refreshed. Valid trigger TTL values are 1 to 10 seconds. Values larger than 10 seconds are silently reduced to 10. Setting a trigger TTL to zero causes prefetch to be disabled. The default trigger TTL is `2`.

  An optional second argument specifies the “eligibility” TTL: the smallest original TTL value that is accepted for a record to be eligible for prefetching. The eligibility TTL must be at least six seconds longer than the trigger TTL; if not, `named` silently adjusts it upward. The default eligibility TTL is `9`.

v6-bias

  Grammar: `v6-bias <integer>;`

  Blocks: options, view

  Tags: server, query

  Indicates the number of milliseconds of preference to give to IPv6 name servers.

  When determining the next name server to try, this indicates by how many milliseconds to prefer IPv6 name servers. The default is `50` milliseconds.

tcp-receive-buffer

  Grammar: `tcp-receive-buffer <integer>;`

  Blocks: options

  Tags: server

  Sets the operating system’s receive buffer size for TCP sockets.

udp-receive-buffer

  Grammar: `udp-receive-buffer <integer>;`

  Blocks: options

  Tags: server

  Sets the operating system’s receive buffer size for UDP sockets.

  These options control the operating system’s receive buffer sizes (`SO_RCVBUF`) for TCP and UDP sockets, respectively. Buffering at the operating system level can prevent packet drops during brief load spikes, but if the buffer size is set too high, a running server could get clogged with outstanding queries that have already timed out. The default is `0`, which means the operating system’s default value should be used. The minimum configurable value is `4096`; any nonzero value lower than that is silently raised. The maximum value is determined by the kernel, and values exceeding the maximum are silently reduced.

tcp-send-buffer

  Grammar: `tcp-send-buffer <integer>;`

  Blocks: options

  Tags: server

  Sets the operating system’s send buffer size for TCP sockets.

udp-send-buffer

  Grammar: `udp-send-buffer <integer>;`

  Blocks: options

  Tags: server

  Sets the operating system’s send buffer size for UDP sockets.

  These options control the operating system’s send buffer sizes (`SO_SNDBUF`) for TCP and UDP sockets, respectively. Buffering at the operating system level can prevent packet drops during brief load spikes, but if the buffer size is set too high, a running server could get clogged with outstanding queries that have already timed out. The default is `0`, which means the operating system’s default value should be used. The minimum configurable value is `4096`; any nonzero value lower than that is silently raised. The maximum value is determined by the kernel, and values exceeding the maximum are silently reduced.

#### 8.2.13.13. Built-in Server Information Zones

The server provides some helpful diagnostic information through a number of built-in zones under the pseudo-top-level-domain `bind` in the `CHAOS` class. These zones are part of a built-in view (see `view`) of class `CHAOS`, which is separate from the default view of class `IN`. Most global configuration options (`allow-query`, etc.) apply to this view, but some are locally overridden: `notify`, `recursion`, and `allow-new-zones` are always set to `no`, and `rate-limit` is set to allow three responses per second.

To disable these zones, use the options below or hide the built-in `CHAOS` view by defining an explicit view of class `CHAOS` that matches all clients.

version

  Grammar: `version ( <quoted_string> | none );`

  Blocks: options

  Tags: server

  Specifies the version number of the server to return in response to a `version.bind` query.

  This is the version the server should report via a query of the name `version.bind` with type `TXT` and class `CHAOS`. The default is the real version number of this server. Specifying `version none` disables processing of the queries.

  Setting `version` to any value (including `none`) also disables queries for `authors.bind TXT CH`.

hostname

  Grammar: `hostname ( <quoted_string> | none );`

  Blocks: options

  Tags: server

  Specifies the hostname of the server to return in response to a `hostname.bind` query.

  This is the hostname the server should report via a query of the name `hostname.bind` with type `TXT` and class `CHAOS`. This defaults to the hostname of the machine hosting the name server, as found by the `gethostname()` function. The primary purpose of such queries is to identify which of a group of anycast servers is actually answering the queries. Specifying `hostname none;` disables processing of the queries.

server-id

  Grammar: `server-id ( <quoted_string> | none | hostname );`

  Blocks: options

  Tags: server

  Specifies the ID of the server to return in response to a `ID.SERVER` query.

  This is the ID the server should report when receiving a Name Server Identifier (NSID) query, or a query of the name `ID.SERVER` with type `TXT` and class `CHAOS`. The primary purpose of such queries is to identify which of a group of anycast servers is actually answering the queries. Specifying `server-id none;` disables processing of the queries. Specifying `server-id hostname;` causes `named` to use the hostname as found by the `gethostname()` function. The default `server-id` is `none`.

#### 8.2.13.14. Built-in Empty Zones

The `named` server has some built-in empty zones, for SOA and NS records only. These are for zones that should normally be answered locally and for which queries should not be sent to the Internet’s root servers. The official servers that cover these namespaces return NXDOMAIN responses to these queries. In particular, these cover the reverse namespaces for addresses from RFC 1918, RFC 4193, RFC 5737, and RFC 6598. They also include the reverse namespace for the IPv6 local address (locally assigned), IPv6 link local addresses, the IPv6 loopback address, and the IPv6 unknown address.

The server attempts to determine whether a built-in zone already exists or is active (covered by a forward-only forwarding declaration), and does not create an empty zone if either is true.

The current list of empty zones is:

- 10.IN-ADDR.ARPA

- 16.172.IN-ADDR.ARPA

- 17.172.IN-ADDR.ARPA

- 18.172.IN-ADDR.ARPA

- 19.172.IN-ADDR.ARPA

- 20.172.IN-ADDR.ARPA

- 21.172.IN-ADDR.ARPA

- 22.172.IN-ADDR.ARPA

- 23.172.IN-ADDR.ARPA

- 24.172.IN-ADDR.ARPA

- 25.172.IN-ADDR.ARPA

- 26.172.IN-ADDR.ARPA

- 27.172.IN-ADDR.ARPA

- 28.172.IN-ADDR.ARPA

- 29.172.IN-ADDR.ARPA

- 30.172.IN-ADDR.ARPA

- 31.172.IN-ADDR.ARPA

- 168.192.IN-ADDR.ARPA

- 64.100.IN-ADDR.ARPA

- 65.100.IN-ADDR.ARPA

- 66.100.IN-ADDR.ARPA

- 67.100.IN-ADDR.ARPA

- 68.100.IN-ADDR.ARPA

- 69.100.IN-ADDR.ARPA

- 70.100.IN-ADDR.ARPA

- 71.100.IN-ADDR.ARPA

- 72.100.IN-ADDR.ARPA

- 73.100.IN-ADDR.ARPA

- 74.100.IN-ADDR.ARPA

- 75.100.IN-ADDR.ARPA

- 76.100.IN-ADDR.ARPA

- 77.100.IN-ADDR.ARPA

- 78.100.IN-ADDR.ARPA

- 79.100.IN-ADDR.ARPA

- 80.100.IN-ADDR.ARPA

- 81.100.IN-ADDR.ARPA

- 82.100.IN-ADDR.ARPA

- 83.100.IN-ADDR.ARPA

- 84.100.IN-ADDR.ARPA

- 85.100.IN-ADDR.ARPA

- 86.100.IN-ADDR.ARPA

- 87.100.IN-ADDR.ARPA

- 88.100.IN-ADDR.ARPA

- 89.100.IN-ADDR.ARPA

- 90.100.IN-ADDR.ARPA

- 91.100.IN-ADDR.ARPA

- 92.100.IN-ADDR.ARPA

- 93.100.IN-ADDR.ARPA

- 94.100.IN-ADDR.ARPA

- 95.100.IN-ADDR.ARPA

- 96.100.IN-ADDR.ARPA

- 97.100.IN-ADDR.ARPA

- 98.100.IN-ADDR.ARPA

- 99.100.IN-ADDR.ARPA

- 100.100.IN-ADDR.ARPA

- 101.100.IN-ADDR.ARPA

- 102.100.IN-ADDR.ARPA

- 103.100.IN-ADDR.ARPA

- 104.100.IN-ADDR.ARPA

- 105.100.IN-ADDR.ARPA

- 106.100.IN-ADDR.ARPA

- 107.100.IN-ADDR.ARPA

- 108.100.IN-ADDR.ARPA

- 109.100.IN-ADDR.ARPA

- 110.100.IN-ADDR.ARPA

- 111.100.IN-ADDR.ARPA

- 112.100.IN-ADDR.ARPA

- 113.100.IN-ADDR.ARPA

- 114.100.IN-ADDR.ARPA

- 115.100.IN-ADDR.ARPA

- 116.100.IN-ADDR.ARPA

- 117.100.IN-ADDR.ARPA

- 118.100.IN-ADDR.ARPA

- 119.100.IN-ADDR.ARPA

- 120.100.IN-ADDR.ARPA

- 121.100.IN-ADDR.ARPA

- 122.100.IN-ADDR.ARPA

- 123.100.IN-ADDR.ARPA

- 124.100.IN-ADDR.ARPA

- 125.100.IN-ADDR.ARPA

- 126.100.IN-ADDR.ARPA

- 127.100.IN-ADDR.ARPA

- 0.IN-ADDR.ARPA

- 127.IN-ADDR.ARPA

- 254.169.IN-ADDR.ARPA

- 2.0.192.IN-ADDR.ARPA

- 100.51.198.IN-ADDR.ARPA

- 113.0.203.IN-ADDR.ARPA

- 255.255.255.255.IN-ADDR.ARPA

- 0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA

- 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA

- 8.B.D.0.1.0.0.2.IP6.ARPA

- D.F.IP6.ARPA

- 8.E.F.IP6.ARPA

- 9.E.F.IP6.ARPA

- A.E.F.IP6.ARPA

- B.E.F.IP6.ARPA

- EMPTY.AS112.ARPA

- HOME.ARPA

- RESOLVER.ARPA

Empty zones can be set at the view level and only apply to views of class IN. Disabled empty zones are only inherited from options if there are no disabled empty zones specified at the view level. To override the options list of disabled zones, disable the root zone at the view level. For example:

    disable-empty-zone ".";

If using the address ranges covered here, reverse zones covering the addresses should already be in place. In practice this appears to not be the case, with many queries being made to the infrastructure servers for names in these spaces. So many, in fact, that sacrificial servers had to be deployed to channel the query load away from the infrastructure servers.

Note

The real parent servers for these zones should disable all empty zones under the parent zone they serve. For the real root servers, this is all built-in empty zones. This enables them to return referrals to deeper in the tree.

empty-server

  Grammar: `empty-server <string>;`

  Blocks: options, view

  Tags: server, zone

  Specifies the server name in the returned SOA record for empty zones.

  This specifies the server name that appears in the returned SOA record for empty zones. If none is specified, the zone’s name is used.

empty-contact

  Grammar: `empty-contact <string>;`

  Blocks: options, view

  Tags: server, zone

  Specifies the contact name in the returned SOA record for empty zones.

  This specifies the contact name that appears in the returned SOA record for empty zones. If none is specified, “.” is used.

empty-zones-enable

  Grammar: `empty-zones-enable <boolean>;`

  Blocks: options, view

  Tags: server, zone

  Enables or disables all empty zones.

  This enables or disables all empty zones. By default, they are enabled.

disable-empty-zone

  Grammar: `disable-empty-zone <string>; // may occur multiple times`

  Blocks: options, view

  Tags: server, zone

  Disables individual empty zones.

  This disables individual empty zones. By default, none are disabled. This option can be specified multiple times.

#### 8.2.13.15. Content Filtering

deny-answer-addresses

  Grammar: `deny-answer-addresses { <address_match_element>; ... } [ except-from { <string>; ... } ];`

  Blocks: options, view

  Tags: query

  Rejects A or AAAA records if the corresponding IPv4 or IPv6 addresses match a given `address_match_list`.

  BIND 9 provides the ability to filter out responses from external DNS servers containing certain types of data in the answer section. Specifically, it can reject address (A or AAAA) records if the corresponding IPv4 or IPv6 addresses match the given address_match_list of the `deny-answer-addresses` option.

  In the address_match_list of the `deny-answer-addresses` option, only ip_address and netprefix are meaningful; any server_key is silently ignored.

deny-answer-aliases

  Grammar: `deny-answer-aliases { <string>; ... } [ except-from { <string>; ... } ];`

  Blocks: options, view

  Tags: query

  Rejects CNAME or DNAME records if the “alias” name matches a given list of `domain_name` elements.

  BIND can also reject CNAME or DNAME records if the “alias” name (i.e., the CNAME alias or the substituted query name due to DNAME) matches the given list of domain_name elements of the `deny-answer-aliases` option, where “match” means the alias name is a subdomain of one of the listed domain names. If the optional list is specified in the `except-from` argument, records whose query name matches the list are accepted regardless of the filter setting. Likewise, if the alias name is a subdomain of the corresponding zone, the `deny-answer-aliases` filter does not apply; for example, even if “example.com” is specified for `deny-answer-aliases`,

      www.example.com. CNAME xxx.example.com.

  returned by an “example.com” server is accepted.

If a response message is rejected due to filtering, the entire message is discarded without being cached and a SERVFAIL error is returned to the client.

This filtering is intended to prevent “DNS rebinding attacks,” in which an attacker, in response to a query for a domain name the attacker controls, returns an IP address within the user’s own network or an alias name within the user’s own domain. A naive web browser or script could then serve as an unintended proxy, allowing the attacker to get access to an internal node of the local network that could not be externally accessed otherwise. See the paper available at https://dl.acm.org/doi/10.1145/1315245.1315298 for more details about these attacks.

For example, with a domain named “example.net” and an internal network using an IPv4 prefix 192.0.2.0/24, an administrator might specify the following rules:

    deny-answer-addresses { 192.0.2.0/24; } except-from { "example.net"; };
    deny-answer-aliases { "example.net"; };

If an external attacker let a web browser in the local network look up an IPv4 address of “attacker.example.com”, the attacker’s DNS server would return a response like this:

    attacker.example.com. A 192.0.2.1

in the answer section. Since the rdata of this record (the IPv4 address) matches the specified prefix 192.0.2.0/24, this response would be ignored.

On the other hand, if the browser looked up a legitimate internal web server “www.example.net” and the following response were returned to the BIND 9 server:

    www.example.net. A 192.0.2.2

it would be accepted, since the owner name “www.example.net” matches the `except-from` element, “example.net”.

Note that this is not really an attack on the DNS per se. In fact, there is nothing wrong with having an “external” name mapped to an “internal” IP address or domain name from the DNS point of view; it might actually be provided for a legitimate purpose, such as for debugging. As long as the mapping is provided by the correct owner, it either is not possible or does not make sense to detect whether the intent of the mapping is legitimate within the DNS. The “rebinding” attack must primarily be protected at the application that uses the DNS. For a large site, however, it may be difficult to protect all possible applications at once. This filtering feature is provided only to help such an operational environment; turning it on is generally discouraged unless there is no other choice and the attack is a real threat to applications.

Care should be particularly taken if using this option for addresses within 127.0.0.0/8. These addresses are obviously “internal,” but many applications conventionally rely on a DNS mapping from some name to such an address. Filtering out DNS records containing this address spuriously can break such applications.

#### 8.2.13.16. Response Policy Zone (RPZ) Rewriting

BIND 9 includes a limited mechanism to modify DNS responses for requests analogous to email anti-spam DNS rejection lists. Responses can be changed to deny the existence of domains (NXDOMAIN), deny the existence of IP addresses for domains (NODATA), or contain other IP addresses or data.

response-policy

  Grammar: `response-policy { zone <string> [ add-soa <boolean> ] [ log <boolean> ] [ max-policy-ttl <duration> ] [ min-update-interval <duration> ] [ policy ( cname | disabled | drop | given | no-op | nodata | nxdomain | passthru | tcp-only <quoted_string> ) ] [ recursive-only <boolean> ] [ nsip-enable <boolean> ] [ nsdname-enable <boolean> ] [ ede <string> ]; ... } [ add-soa <boolean> ] [ break-dnssec <boolean> ] [ max-policy-ttl <duration> ] [ min-update-interval <duration> ] [ min-ns-dots <integer> ] [ nsip-wait-recurse <boolean> ] [ nsdname-wait-recurse <boolean> ] [ qname-wait-recurse <boolean> ] [ recursive-only <boolean> ] [ nsip-enable <boolean> ] [ nsdname-enable <boolean> ] [ dnsrps-enable <boolean> ] [ dnsrps-options { <unspecified-text> } ];`

  Blocks: options, view

  Tags: server, query, zone, security

  Specifies response policy zones for the view or among global options.

  Response policy zones are named in the `response-policy` option for the view, or among the global options if there is no `response-policy` option for the view. Response policy zones are ordinary DNS zones containing RRsets that can be queried normally if allowed. It is usually best to restrict those queries with something like `allow-query { localhost; };`.

  A `response-policy` option can support multiple policy zones. To maximize performance, a radix tree is used to quickly identify response policy zones containing triggers that match the current query. This imposes an upper limit of 64 on the number of policy zones in a single `response-policy` option; more than that is a configuration error.

Rules encoded in response policy zones are processed after those defined in Access Control. All queries from clients which are not permitted access to the resolver are answered with a status code of REFUSED, regardless of configured RPZ rules.

Five policy triggers can be encoded in RPZ records.

`RPZ-CLIENT-IP`

  IP records are triggered by the IP address of the DNS client. Client IP address triggers are encoded in records that have owner names that are subdomains of `rpz-client-ip`, relativized to the policy zone origin name, and that encode an address or address block. IPv4 addresses are represented as `prefixlength.B4.B3.B2.B1.rpz-client-ip`. The IPv4 prefix length must be between 1 and 32. All four bytes - B4, B3, B2, and B1 - must be present. B4 is the decimal value of the least significant byte of the IPv4 address as in IN-ADDR.ARPA.

  IPv6 addresses are encoded in a format similar to the standard IPv6 text representation, `prefixlength.W8.W7.W6.W5.W4.W3.W2.W1.rpz-client-ip`. Each of W8,…,W1 is a one- to four-digit hexadecimal number representing 16 bits of the IPv6 address as in the standard text representation of IPv6 addresses, but reversed as in IP6.ARPA. (Note that this representation of IPv6 addresses is different from IP6.ARPA, where each hex digit occupies a label.) All 8 words must be present except when one set of consecutive zero words is replaced with `.zz.`, analogous to double colons (::) in standard IPv6 text encodings. The IPv6 prefix length must be between 1 and 128.

`QNAME`

  QNAME policy records are triggered by query names of requests and targets of CNAME records resolved to generate the response. The owner name of a QNAME policy record is the query name relativized to the policy zone.

`RPZ-IP`

  IP triggers are IP addresses in an A or AAAA record in the ANSWER section of a response. They are encoded like client-IP triggers, except as subdomains of `rpz-ip`.

`RPZ-NSDNAME`

  NSDNAME triggers match names of authoritative servers for the query name, a parent of the query name, a CNAME for the query name, or a parent of a CNAME. They are encoded as subdomains of `rpz-nsdname`, relativized to the RPZ origin name. NSIP triggers match IP addresses in A and AAAA RRsets for domains that can be checked against NSDNAME policy records. The `nsdname-enable` phrase turns NSDNAME triggers off or on for a single policy zone or for all zones.

  If authoritative name servers for the query name are not yet known, `named` recursively looks up the authoritative servers for the query name before applying an RPZ-NSDNAME rule, which can cause a processing delay. To speed up processing at the cost of precision, the `nsdname-wait-recurse` option can be used; when set to `no`, RPZ-NSDNAME rules are only applied when authoritative servers for the query name have already been looked up and cached. If authoritative servers for the query name are not in the cache, the RPZ-NSDNAME rule is ignored, but the authoritative servers for the query name are looked up in the background and the rule is applied to subsequent queries. The default is `yes`, meaning RPZ-NSDNAME rules are always applied, even if authoritative servers for the query name need to be looked up first.

`RPZ-NSIP`

  NSIP triggers match the IP addresses of authoritative servers. They are encoded like IP triggers, except as subdomains of `rpz-nsip`. NSDNAME and NSIP triggers are checked only for names with at least `min-ns-dots` dots. The default value of `min-ns-dots` is 1, to exclude top-level domains. The `nsip-enable` phrase turns NSIP triggers off or on for a single policy zone or for all zones.

  If a name server’s IP address is not yet known, `named` recursively looks up the IP address before applying an RPZ-NSIP rule, which can cause a processing delay. To speed up processing at the cost of precision, the `nsip-wait-recurse` option can be used; when set to `no`, RPZ-NSIP rules are only applied when a name server’s IP address has already been looked up and cached. If a server’s IP address is not in the cache, the RPZ-NSIP rule is ignored, but the address is looked up in the background and the rule is applied to subsequent queries. The default is `yes`, meaning RPZ-NSIP rules are always applied, even if an address needs to be looked up first.

The query response is checked against all response policy zones, so two or more policy records can be triggered by a response. Because DNS responses are rewritten according to at most one policy record, a single record encoding an action (other than `DISABLED` actions) must be chosen. Triggers, or the records that encode them, are chosen for rewriting in the following order:

1. Choose the triggered record in the zone that appears first in the response-policy option.

2. Prefer CLIENT-IP to QNAME to IP to NSDNAME to NSIP triggers in a single zone.

3. Among NSDNAME triggers, prefer the trigger that matches the smallest name under the DNSSEC ordering.

4. Among IP or NSIP triggers, prefer the trigger with the longest prefix.

5. Among triggers with the same prefix length, prefer the IP or NSIP trigger that matches the smallest IP address.

When the processing of a response is restarted to resolve DNAME or CNAME records and a policy record set has not been triggered, all response policy zones are again consulted for the DNAME or CNAME names and addresses.

RPZ record sets are any types of DNS record, except DNAME or DNSSEC, that encode actions or responses to individual queries. Any of the policies can be used with any of the triggers. For example, while the `TCP-only` policy is commonly used with `client-IP` triggers, it can be used with any type of trigger to force the use of TCP for responses with owner names in a zone.

`PASSTHRU`

  The auto-acceptance policy is specified by a CNAME whose target is `rpz-passthru`. It causes the response to not be rewritten and is most often used to “poke holes” in policies for CIDR blocks.

`DROP`

  The auto-rejection policy is specified by a CNAME whose target is `rpz-drop`. It causes the response to be discarded. Nothing is sent to the DNS client.

`TCP-Only`

  The “slip” policy is specified by a CNAME whose target is `rpz-tcp-only`. It changes UDP responses to short, truncated DNS responses that require the DNS client to try again with TCP. It is used to mitigate distributed DNS reflection attacks.

`NXDOMAIN`

  The “domain undefined” response is encoded by a CNAME whose target is the root domain (.).

`NODATA`

  The empty set of resource records is specified by a CNAME whose target is the wildcard top-level domain (`*.`). It rewrites the response to NODATA or ANCOUNT=0.

`Local Data`

  A set of ordinary DNS records can be used to answer queries. Queries for record types not in the set are answered with NODATA.

  A special form of local data is a CNAME whose target is a wildcard such as *.example.com. It is used as if an ordinary CNAME after the asterisk (*) has been replaced with the query name. This special form is useful for query logging in the walled garden’s authoritative DNS server.

All of the actions specified in all of the individual records in a policy zone can be overridden with a `policy` clause in the `response-policy` option. An organization using a policy zone provided by another organization might use this mechanism to redirect domains to its own walled garden.

`GIVEN`

  The placeholder policy says “do not override but perform the action specified in the zone.”

`DISABLED`

  The testing override policy causes policy zone records to do nothing but log what they would have done if the policy zone were not disabled. The response to the DNS query is written (or not) according to any triggered policy records that are not disabled. Disabled policy zones should appear first, because they are often not logged if a higher-precedence trigger is found first.

`PASSTHRU`; `DROP`; `TCP-Only`; `NXDOMAIN`; `NODATA`

  These settings each override the corresponding per-record policy.

`CNAME domain`

  This causes all RPZ policy records to act as if they were “cname domain” records.

By default, the actions encoded in a response policy zone are applied only to queries that ask for recursion (RD=1). That default can be changed for a single policy zone, or for all response policy zones in a view, with a `recursive-only no` clause. This feature is useful for serving the same zone files both inside and outside an RFC 1918 cloud and using RPZ to delete answers that would otherwise contain RFC 1918 values on the externally visible name server or view.

Also by default, RPZ actions are applied only to DNS requests that either do not request DNSSEC metadata (DO=0) or when no DNSSEC records are available for the requested name in the original zone (not the response policy zone). This default can be changed for all response policy zones in a view with a `break-dnssec yes` clause. In that case, RPZ actions are applied regardless of DNSSEC. The name of the clause option reflects the fact that results rewritten by RPZ actions cannot verify.

No DNS records are needed for a QNAME or Client-IP trigger; the name or IP address itself is sufficient, so in principle the query name need not be recursively resolved. However, not resolving the requested name can leak the fact that response policy rewriting is in use, and that the name is listed in a policy zone, to operators of servers for listed names. To prevent that information leak, by default any recursion needed for a request is done before any policy triggers are considered. Because listed domains often have slow authoritative servers, this behavior can cost significant time. The `qname-wait-recurse no` option overrides the default and enables that behavior when recursion cannot change a non-error response. The option does not affect QNAME or client-IP triggers in policy zones listed after other zones containing IP, NSIP, and NSDNAME triggers, because those may depend on the A, AAAA, and NS records that would be found during recursive resolution. It also does not affect DNSSEC requests (DO=1) unless `break-dnssec yes` is in use, because the response would depend on whether RRSIG records were found during resolution. Using this option can cause error responses such as SERVFAIL to appear to be rewritten, since no recursion is being done to discover problems at the authoritative server.

dnsrps-enable

  Grammar: `dnsrps-enable <boolean>;`

  Blocks: options, view

  Tags: server, security

  Turns on the DNS Response Policy Service (DNSRPS) interface.

  The `dnsrps-enable yes` option turns on the DNS Response Policy Service (DNSRPS) interface, if it has been compiled in `named` using `configure --enable-dnsrps`.

dnsrps-library

  Grammar: `dnsrps-library <quoted_string>;`

  Blocks: options

  Tags: server, security

  Specifies the path to the DNS Response Policy Service (DNSRPS) provider library.

  This option specifies the path to the DNSRPS provider library. Typically this library is detected when building with `configure --enable-dnsrps` and does not need to be specified in `named.conf`; the option exists to override the default library for testing purposes.

dnsrps-options

  Grammar: `dnsrps-options { <unspecified-text> };`

  Blocks: options, view

  Tags: server, security

  Provides additional RPZ configuration settings, which are passed to the DNS Response Policy Service (DNSRPS) provider library.

  The block provides additional RPZ configuration settings, which are passed through to the DNSRPS provider library. Multiple DNSRPS settings in an `dnsrps-options` string should be separated with semi-colons (;). The DNSRPS provider library is passed a configuration string consisting of the `dnsrps-options` text, concatenated with settings derived from the `response-policy` statement.

  Note: the `dnsrps-options` text should only include configuration settings that are specific to the DNSRPS provider. For example, the DNSRPS provider from Farsight Security takes options such as `dnsrpzd-conf`, `dnsrpzd-sock`, and `dnzrpzd-args` (for details of these options, see the `librpz` documentation). Other RPZ configuration settings could be included in `dnsrps-options` as well, but if `named` were switched back to traditional RPZ by setting `dnsrps-enable` to “no”, those options would be ignored.

The TTL of a record modified by RPZ policies is set from the TTL of the relevant record in the policy zone. It is then limited to a maximum value. The `max-policy-ttl` clause changes the maximum number of seconds from its default of 5. For convenience, TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.

For example, an administrator might use this option statement:

    response-policy { zone "badlist"; };

and this zone statement:

    zone "badlist" {type primary; file "primary/badlist"; allow-query {none;}; };

with this zone file:

    $TTL 1H
    @                       SOA LOCALHOST. named-mgr.example.com (1 1h 15m 30d 2h)
                NS  LOCALHOST.

    ; QNAME policy records.  There are no periods (.) after the owner names.
    nxdomain.domain.com     CNAME   .               ; NXDOMAIN policy
    *.nxdomain.domain.com   CNAME   .               ; NXDOMAIN policy
    nodata.domain.com       CNAME   *.              ; NODATA policy
    *.nodata.domain.com     CNAME   *.              ; NODATA policy
    bad.domain.com          A       10.0.0.1        ; redirect to a walled garden
                AAAA    2001:2::1
    bzone.domain.com        CNAME   garden.example.com.

    ; do not rewrite (PASSTHRU) OK.DOMAIN.COM
    ok.domain.com           CNAME   rpz-passthru.

    ; redirect x.bzone.domain.com to x.bzone.domain.com.garden.example.com
    *.bzone.domain.com      CNAME   *.garden.example.com.

    ; IP policy records that rewrite all responses containing A records in 127/8
    ;       except 127.0.0.1
    8.0.0.0.127.rpz-ip      CNAME   .
    32.1.0.0.127.rpz-ip     CNAME   rpz-passthru.

    ; NSDNAME and NSIP policy records
    ns.domain.com.rpz-nsdname   CNAME   .
    48.zz.2.2001.rpz-nsip       CNAME   .

    ; auto-reject and auto-accept some DNS clients
    112.zz.2001.rpz-client-ip    CNAME   rpz-drop.
    8.0.0.0.127.rpz-client-ip    CNAME   rpz-drop.

    ; force some DNS clients and responses in the example.com zone to TCP
    16.0.0.1.10.rpz-client-ip   CNAME   rpz-tcp-only.
    example.com                 CNAME   rpz-tcp-only.
    *.example.com               CNAME   rpz-tcp-only.

Response policy zones can be configured to set an Extended DNS Error (EDE) code on the responses which have been modified by the response policy:

    response-policy { zone "badlist" ede filtered; };

The following settings are supported for the `ede` option:

`none`

  No Extended DNS Error code is set (default).

`forged`

  Extended DNS Error code 4 - Forged Answer.

`blocked`

  Extended DNS Error code 15 - Blocked.

`censored`

  Extended DNS Error code 16 - Censored.

`filtered`

  Extended DNS Error code 17 - Filtered.

`prohibited`

  Extended DNS Error code 18 - Prohibited.

See RFC 8914 for more information about the Extended DNS Error codes.

RPZ can affect server performance. Each configured response policy zone requires the server to perform one to four additional database lookups before a query can be answered. For example, a DNS server with four policy zones, each with all four kinds of response triggers (QNAME, IP, NSIP, and NSDNAME), requires a total of 17 times as many database lookups as a similar DNS server with no response policy zones. A BIND 9 server with adequate memory and one response policy zone with QNAME and IP triggers might achieve a maximum queries-per-second (QPS) rate about 20% lower. A server with four response policy zones with QNAME and IP triggers might have a maximum QPS rate about 50% lower.

Responses rewritten by RPZ are counted in the `RPZRewrites` statistics.

The `log` clause can be used to optionally turn off rewrite logging for a particular response policy zone. By default, all rewrites are logged.

The `add-soa` option controls whether the RPZ’s SOA record is added to the section for traceback of changes from this zone. This can be set at the individual policy zone level or at the response-policy level. The default is `yes`.

Updates to RPZ zones are processed asynchronously; if there is more than one update pending they are bundled together. If an update to a RPZ zone (for example, via IXFR) happens less than `min-update-interval` seconds after the most recent update, the changes are not carried out until this interval has elapsed. The default is `60` seconds. For convenience, TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.

#### 8.2.13.17. Response Rate Limiting

rate-limit

  Grammar:

      rate-limit {
      	all-per-second <integer>;
      	errors-per-second <integer>;
      	exempt-clients { <address_match_element>; ... };
      	ipv4-prefix-length <integer>;
      	ipv6-prefix-length <integer>;
      	log-only <boolean>;
      	max-table-size <integer>;
      	min-table-size <integer>;
      	nodata-per-second <integer>;
      	nxdomains-per-second <integer>;
      	qps-scale <integer>;
      	referrals-per-second <integer>;
      	responses-per-second <integer>;
      	slip <integer>;
      	window <integer>;
      };

  Blocks: options, view

  Tags: query

  Controls excessive UDP responses, to prevent BIND 9 from being used to amplify reflection denial-of-service (DoS) attacks.

  Excessive, almost-identical UDP responses can be controlled by configuring a `rate-limit` clause in an `options` or `view` statement. This mechanism keeps authoritative BIND 9 from being used to amplify reflection denial-of-service (DoS) attacks. Short BADCOOKIE errors or truncated (TC=1) responses can be sent to provide rate-limited responses to legitimate clients within a range of forged, attacked IP addresses. Legitimate clients react to dropped responses by retrying, to BADCOOKIE errors by including a server cookie when retrying, and to truncated responses by switching to TCP.

  This mechanism is intended for authoritative DNS servers. It can be used on recursive servers, but can slow applications such as SMTP servers (mail receivers) and HTTP clients (web browsers) that repeatedly request the same domains. When possible, closing “open” recursive servers is better.

  Response-rate limiting uses a “credit” or “token bucket” scheme. Each combination of identical response and client has a conceptual “account” that earns a specified number of credits every second. A prospective response debits its account by one. Responses are dropped or truncated while the account is negative.

  window

    Grammar: `window <integer>;`

    Blocks: options.rate-limit, view.rate-limit

    Tags: query

    Specifies the length of time during which responses are tracked.

    Responses are tracked within a rolling window of time which defaults to 15 seconds, but which can be configured with the `window` option to any value from 1 to 3600 seconds (1 hour). The account cannot become more positive than the per-second limit or more negative than `window` times the per-second limit. When the specified number of credits for a class of responses is set to 0, those responses are not rate-limited.

  ipv4-prefix-length

    Grammar: `ipv4-prefix-length <integer>;`

    Blocks: options.rate-limit, view.rate-limit

    Tags: server

    Specifies the prefix lengths of IPv4 address blocks.

  ipv6-prefix-length

    Grammar: `ipv6-prefix-length <integer>;`

    Blocks: options.rate-limit, view.rate-limit

    Tags: server

    Specifies the prefix lengths of IPv6 address blocks.

    The notions of “identical response” and “DNS client” for rate limiting are not simplistic. All responses to an address block are counted as if to a single client. The prefix lengths of address blocks are specified with `ipv4-prefix-length` (default 24) and `ipv6-prefix-length` (default 56).

  responses-per-second

    Grammar: `responses-per-second <integer>;`

    Blocks: options.rate-limit, view.rate-limit

    Tags: query

    Limits the number of non-empty responses for a valid domain name and record type.

    All non-empty responses for a valid domain name (qname) and record type (qtype) are identical and have a limit specified with `responses-per-second` (default 0 or no limit). All valid wildcard domain names are interpreted as the zone’s origin name concatenated to the “*” name.

  nodata-per-second

    Grammar: `nodata-per-second <integer>;`

    Blocks: options.rate-limit, view.rate-limit

    Tags: query

    Limits the number of empty (NODATA) responses for a valid domain name.

    All empty (NODATA) responses for a valid domain, regardless of query type, are identical. Responses in the NODATA class are limited by `nodata-per-second` (default `responses-per-second`).

  nxdomains-per-second

    Grammar: `nxdomains-per-second <integer>;`

    Blocks: options.rate-limit, view.rate-limit

    Tags: query

    Limits the number of undefined subdomains for a valid domain name.

    Requests for any and all undefined subdomains of a given valid domain result in NXDOMAIN errors, and are identical regardless of query type. They are limited by `nxdomains-per-second` (default `responses-per-second`). This controls some attacks using random names, but can be relaxed or turned off (set to 0) on servers that expect many legitimate NXDOMAIN responses, such as from anti-spam rejection lists.

  referrals-per-second

    Grammar: `referrals-per-second <integer>;`

    Blocks: options.rate-limit, view.rate-limit

    Tags: query

    Limits the number of referrals or delegations to a server for a given domain.

    Referrals or delegations to the server of a given domain are identical and are limited by `referrals-per-second` (default `responses-per-second`).

  Responses generated from local wildcards are counted and limited as if they were for the parent domain name. This controls flooding using random.wild.example.com.

  All requests that result in DNS errors other than NXDOMAIN, such as SERVFAIL and FORMERR, are identical regardless of requested name (qname) or record type (qtype). This controls attacks using invalid requests or distant, broken authoritative servers.

  errors-per-second

    Grammar: `errors-per-second <integer>;`

    Blocks: options.rate-limit, view.rate-limit

    Tags: server

    Limits the number of errors for a valid domain name and record type.

    By default the limit on errors is the same as the `responses-per-second` value, but it can be set separately with `errors-per-second`.

  slip

    Grammar: `slip <integer>;`

    Blocks: options.rate-limit, view.rate-limit

    Tags: query

    Sets the number of “slipped” responses to minimize the use of forged source addresses for an attack.

    Many attacks using DNS involve UDP requests with forged source addresses. Rate limiting prevents the use of BIND 9 to flood a network with responses to requests with forged source addresses, but could let a third party block responses to legitimate requests. There is a mechanism that can answer some legitimate requests from a client whose address is being forged in a flood. Setting `slip` to 2 (its default) causes every other UDP request without a valid server cookie to be answered with a small response. The small size and reduced frequency, and resulting lack of amplification, of “slipped” responses make them unattractive for reflection DoS attacks. `slip` must be between 0 and 10. A value of 0 does not “slip”; no small responses are sent due to rate limiting. Rather, all responses are dropped. A value of 1 causes every response to slip; values between 2 and 10 cause every nth response to slip.

    If the request included a client cookie, then a “slipped” response is a BADCOOKIE error with a server cookie, which allows a legitimate client to include the server cookie to be exempted from the rate limiting when it retries the request. If the request did not include a cookie, then a “slipped” response is a truncated (TC=1) response, which prompts a legitimate client to switch to TCP and thus be exempted from the rate limiting. Some error responses, including REFUSED and SERVFAIL, cannot be replaced with truncated responses and are instead leaked at the `slip` rate.

    (Note: dropped responses from an authoritative server may reduce the difficulty of a third party successfully forging a response to a recursive resolver. The best security against forged responses is for authoritative operators to sign their zones using DNSSEC and for resolver operators to validate the responses. When this is not an option, operators who are more concerned with response integrity than with flood mitigation may consider setting `slip` to 1, causing all rate-limited responses to be truncated rather than dropped. This reduces the effectiveness of rate-limiting against reflection attacks.)

  qps-scale

    Grammar: `qps-scale <integer>;`

    Blocks: options.rate-limit, view.rate-limit

    Tags: query

    Tightens defenses during DNS attacks by scaling back the ratio of the current query-per-second rate.

    When the approximate query-per-second rate exceeds the `qps-scale` value, the `responses-per-second`, `errors-per-second`, `nxdomains-per-second`, and `all-per-second` values are reduced by the ratio of the current rate to the `qps-scale` value. This feature can tighten defenses during attacks. For example, with `qps-scale 250; responses-per-second 20;` and a total query rate of 1000 queries/second for all queries from all DNS clients including via TCP, then the effective responses/second limit changes to (250/1000)*20, or 5. Responses to requests that included a valid server cookie, and responses sent via TCP, are not limited but are counted to compute the query-per-second rate.

  exempt-clients

    Grammar: `exempt-clients { <address_match_element>; ... };`

    Blocks: options.rate-limit, view.rate-limit

    Tags: query

    Exempts specific clients or client groups from rate limiting.

    Communities of DNS clients can be given their own parameters or no rate limiting by putting `rate-limit` statements in `view` statements instead of in the global `option` statement. A `rate-limit` statement in a view replaces, rather than supplements, a `rate-limit` statement among the main options.

    DNS clients within a view can be exempted from rate limits with the `exempt-clients` clause.

  all-per-second

    Grammar: `all-per-second <integer>;`

    Blocks: options.rate-limit, view.rate-limit

    Tags: query

    Limits UDP responses of all kinds.

    UDP responses of all kinds can be limited with the `all-per-second` phrase. This rate limiting is unlike the rate limiting provided by `responses-per-second`, `errors-per-second`, and `nxdomains-per-second` on a DNS server, which are often invisible to the victim of a DNS reflection attack. Unless the forged requests of the attack are the same as the legitimate requests of the victim, the victim’s requests are not affected. Responses affected by an `all-per-second` limit are always dropped; the `slip` value has no effect. An `all-per-second` limit should be at least 4 times as large as the other limits, because single DNS clients often send bursts of legitimate requests. For example, the receipt of a single mail message can prompt requests from an SMTP server for NS, PTR, A, and AAAA records as the incoming SMTP/TCP/IP connection is considered. The SMTP server can need additional NS, A, AAAA, MX, TXT, and SPF records as it considers the SMTP `Mail From` command. Web browsers often repeatedly resolve the same names that are duplicated in HTML <IMG> tags in a page. `all-per-second` is similar to the rate limiting offered by firewalls but is often inferior. Attacks that justify ignoring the contents of DNS responses are likely to be attacks on the DNS server itself. They usually should be discarded before the DNS server spends resources making TCP connections or parsing DNS requests, but that rate limiting must be done before the DNS server sees the requests.

  max-table-size

    Grammar: `max-table-size <integer>;`

    Blocks: options.rate-limit, view.rate-limit

    Tags: server

    Sets the maximum size of the table used to track requests and rate-limit responses.

  min-table-size

    Grammar: `min-table-size <integer>;`

    Blocks: options.rate-limit, view.rate-limit

    Tags: query

    Sets the minimum size of the table used to track requests and rate-limit responses.

    The maximum size of the table used to track requests and rate-limit responses is set with `max-table-size`. Each entry in the table is between 40 and 80 bytes. The table needs approximately as many entries as the number of requests received per second. The default is 20,000. To reduce the cold start of growing the table, `min-table-size` (default 500) can set the minimum table size. Enable `rate-limit` category logging to monitor expansions of the table and inform choices for the initial and maximum table size.

  log-only

    Grammar: `log-only <boolean>;`

    Blocks: options.rate-limit, view.rate-limit

    Tags: logging, query

    Tests rate-limiting parameters without actually dropping any requests.

    Use `log-only yes` to test rate-limiting parameters without actually dropping any requests.

  Responses dropped by rate limits are included in the `RateDropped` and `QryDropped` statistics. Responses that are truncated by rate limits are included in `RateSlipped` and `RespTruncated`.

#### 8.2.13.18. NXDOMAIN Redirection

`named` supports NXDOMAIN redirection via two methods:

- `Redirect zone`

- Redirect namespace

With either method, when `named` gets an NXDOMAIN response it examines a separate namespace to see if the NXDOMAIN response should be replaced with an alternative response.

With a redirect zone (`zone "." { type redirect; };`), the data used to replace the NXDOMAIN is held in a single zone which is not part of the normal namespace. All the redirect information is contained in the zone; there are no delegations.

nxdomain-redirect

  Grammar: `nxdomain-redirect <string>;`

  Blocks: options, view

  Tags: query

  Appends the specified suffix to the original query name, when replacing an NXDOMAIN with a redirect namespace.

  With a redirect namespace (`option { nxdomain-redirect <suffix> };`), the data used to replace the NXDOMAIN is part of the normal namespace and is looked up by appending the specified suffix to the original query name. This roughly doubles the cache required to process NXDOMAIN responses, as both the original NXDOMAIN response and the replacement data (or an NXDOMAIN indicating that there is no replacement) must be stored.

If both a redirect zone and a redirect namespace are configured, the redirect zone is tried first.

### 8.2.14. `server` Block Grammar

server

  Grammar:

      server <netprefix> {
      	bogus <boolean>;
      	edns <boolean>;
      	edns-udp-size <integer>;
      	edns-version <integer>;
      	keys <server_key>;
      	max-udp-size <integer>;
      	notify-source ( <ipv4_address> | * );
      	notify-source-v6 ( <ipv6_address> | * );
      	padding <integer>;
      	provide-ixfr <boolean>;
      	query-source [ address ] ( <ipv4_address> | * );
      	query-source-v6 [ address ] ( <ipv6_address> | * );
      	request-expire <boolean>;
      	request-ixfr <boolean>;
      	request-nsid <boolean>;
      	require-cookie <boolean>;
      	send-cookie <boolean>;
      	tcp-keepalive <boolean>;
      	tcp-only <boolean>;
      	transfer-format ( many-answers | one-answer );
      	transfer-source ( <ipv4_address> | * );
      	transfer-source-v6 ( <ipv6_address> | * );
      	transfers <integer>;
      }; // may occur multiple times

  Blocks: topmost, view

  Tags: server

  Defines characteristics to be associated with a remote name server.

### 8.2.15. `server` Block Definition and Usage

The `server` statement defines characteristics to be associated with a remote name server. If a prefix length is specified, then a range of servers is covered. Only the most specific server clause applies, regardless of the order in `named.conf`.

The `server` statement can occur at the top level of the configuration file or inside a `view` statement. If a `view` statement contains one or more `server` statements, only those apply to the view and any top-level ones are ignored. If a view contains no `server` statements, any top-level `server` statements are used as defaults.

bogus

  Grammar: `bogus <boolean>;`

  Blocks: server, view.server

  Tags: server

  Allows a remote server to be ignored.

  If a remote server is giving out bad data, marking it as bogus prevents further queries to it. The default value of `bogus` is `no`.

edns

  Grammar: `edns <boolean>;`

  Blocks: server, view.server

  Tags: server

  Controls the use of the EDNS0 (RFC 2671) feature.

  The `edns` clause determines whether the local server attempts to use EDNS when communicating with the remote server. The default is `yes`.

edns-version

  Grammar: `edns-version <integer>;`

  Blocks: server, view.server

  Tags: server

  Sets the maximum EDNS VERSION that is sent to the server(s) by the resolver.

  The `edns-version` option sets the maximum EDNS VERSION that is sent to the server(s) by the resolver. The actual EDNS version sent is still subject to normal EDNS version-negotiation rules (see RFC 6891), the maximum EDNS version supported by the server, and any other heuristics that indicate that a lower version should be sent. This option is intended to be used when a remote server reacts badly to a given EDNS version or higher; it should be set to the highest version the remote server is known to support. Valid values are 0 to 255; higher values are silently adjusted. This option is not needed until higher EDNS versions than 0 are in use.

padding

  Grammar: `padding <integer>;`

  Blocks: server, view.server

  Tags: server

  Adds EDNS Padding options to outgoing messages to increase the packet size.

  The option adds EDNS Padding options to outgoing messages, increasing the packet size to a multiple of the specified block size. Valid block sizes range from 0 (the default, which disables the use of EDNS Padding) to 512 bytes. Larger values are reduced to 512, with a logged warning. Note: this option is not currently compatible with no TSIG or SIG(0), as the EDNS OPT record containing the padding would have to be added to the packet after it had already been signed.

tcp-only

  Grammar: `tcp-only <boolean>;`

  Blocks: server, view.server

  Tags: server

  Sets the transport protocol to TCP.

  The option sets the transport protocol to TCP. The default is to use the UDP transport and to fallback on TCP only when a truncated response is received.

tcp-keepalive

  Grammar: `tcp-keepalive <boolean>;`

  Blocks: server, view.server

  Tags: server

  Adds EDNS TCP keepalive to messages sent over TCP.

  The option adds EDNS TCP keepalive to messages sent over TCP. Note that currently idle timeouts in responses are ignored.

transfers

  Grammar: `transfers <integer>;`

  Blocks: server, view.server

  Tags: server

  Limits the number of concurrent inbound zone transfers from a server.

  `transfers` is used to limit the number of concurrent inbound zone transfers from the specified server. If no `transfers` clause is specified, the limit is set according to the `transfers-per-ns` option.

keys

  Blocks: dnssec-policy, server, view.server

  Tags: server, security

  Specifies one or more `server_key` s to be used with a remote server.

  Warning

  This option is not to be confused with `keys` in the `dnssec-policy` specification. Although statements with the same name exist in both contexts, they refer to fundamentally incompatible concepts.

  In the context of a `server` block, the option identifies a server_key defined by the `key` statement, to be used for transaction security (see TSIG) when talking to the remote server. When a request is sent to the remote server, a request signature is generated using the key specified here and appended to the message. A request originating from the remote server is not required to be signed by this key.

  Only a single key per server is currently supported.

It is possible to override the following values defined in `view` and `options` blocks:

> - `edns-udp-size`

> - `max-udp-size`

> - `notify-source-v6`

> - `notify-source`

> - `provide-ixfr`

> - `query-source-v6`

> - `query-source`

> - `request-expire`

> - `request-ixfr`

> - `request-nsid`

> - `require-cookie`

> - `send-cookie`

> - `transfer-format`

> - `transfer-source-v6`

> - `transfer-source`

### 8.2.16. `statistics-channels` Block Grammar

statistics-channels

  Grammar:

      statistics-channels {
      	inet ( <ipv4_address> | <ipv6_address> | * ) [ port ( <integer> | * ) ] [ allow { <address_match_element>; ... } ]; // may occur multiple times
      }; // may occur multiple times

  Blocks: topmost

  Tags: logging

  Specifies the communication channels to be used by system administrators to access statistics information on the name server.

### 8.2.17. `statistics-channels` Block Definition and Usage

The `statistics-channels` statement declares communication channels to be used by system administrators to get access to statistics information on the name server.

This statement is intended to be flexible to support multiple communication protocols in the future, but currently only HTTP access is supported. It requires that BIND 9 be compiled with libxml2 and/or json-c (also known as libjson0); the `statistics-channels` statement is still accepted even if it is built without the library, but any HTTP access fails with an error.

An `inet` control channel is a TCP socket listening at the specified port on the specified ip_address, which can be an IPv4 or IPv6 address. An ip_address of `*` (asterisk) is interpreted as the IPv4 wildcard address; connections are accepted on any of the system’s IPv4 addresses. To listen on the IPv6 wildcard address, use an ip_address of `::`.

If no port is specified, port 80 is used for HTTP channels. The asterisk (`*`) cannot be used for port.

Attempts to open a statistics channel are restricted by the optional `allow` clause. Connections to the statistics channel are permitted based on the address_match_list. If no `allow` clause is present, `named` accepts connection attempts from any address. Since the statistics may contain sensitive internal information, the source of connection requests must be restricted appropriately so that only trusted parties can access the statistics channel.

Gathering data exposed by the statistics channel locks various subsystems in `named`, which could slow down query processing if statistics data is requested too often.

An issue in the statistics channel would be considered a security issue only if it could be exploited by unprivileged users circumventing the access control list. In other words, any issue in the statistics channel that could be used to access information unavailable otherwise, or to crash `named`, is not considered a security issue if it can be avoided through the use of a secure configuration.

If no `statistics-channels` statement is present, `named` does not open any communication channels.

The statistics are available in various formats and views, depending on the URI used to access them. For example, if the statistics channel is configured to listen on 127.0.0.1 port 8888, then the statistics are accessible in XML format at http://127.0.0.1:8888/ or http://127.0.0.1:8888/xml. A CSS file is included, which can format the XML statistics into tables when viewed with a stylesheet-capable browser, and into charts and graphs using the Google Charts API when using a JavaScript-capable browser.

Broken-out subsets of the statistics can be viewed at http://127.0.0.1:8888/xml/v3/status (server uptime and last reconfiguration time), http://127.0.0.1:8888/xml/v3/server (server and resolver statistics), http://127.0.0.1:8888/xml/v3/zones (zone statistics), http://127.0.0.1:8888/xml/v3/xfrins (incoming zone transfer statistics), http://127.0.0.1:8888/xml/v3/net (network status and socket statistics), http://127.0.0.1:8888/xml/v3/mem (memory manager statistics), and http://127.0.0.1:8888/xml/v3/traffic (traffic sizes).

The full set of statistics can also be read in JSON format at http://127.0.0.1:8888/json, with the broken-out subsets at http://127.0.0.1:8888/json/v1/status (server uptime and last reconfiguration time), http://127.0.0.1:8888/json/v1/server (server and resolver statistics), http://127.0.0.1:8888/json/v1/zones (zone statistics), http://127.0.0.1:8888/json/v1/xfrins (incoming zone transfer statistics), http://127.0.0.1:8888/json/v1/net (network status and socket statistics), http://127.0.0.1:8888/json/v1/mem (memory manager statistics), and http://127.0.0.1:8888/json/v1/traffic (traffic sizes).

### 8.2.18. `tls` Block Grammar

tls

  Grammar:

      tls <string> {
      	ca-file <quoted_string>;
      	cert-file <quoted_string>;
      	cipher-suites <string>;
      	ciphers <string>;
      	dhparam-file <quoted_string>;
      	key-file <quoted_string>;
      	prefer-server-ciphers <boolean>;
      	protocols { <string>; ... };
      	remote-hostname <quoted_string>;
      	session-tickets <boolean>;
      }; // may occur multiple times

  Blocks: topmost

  Tags: security

  Configures a TLS connection.

### 8.2.19. `tls` Block Definition and Usage

The `tls` statement is used to configure a TLS connection; this configuration can then be referenced by a `listen-on` or `listen-on-v6` statement to cause `named` to listen for incoming requests via TLS, or in the `primaries` statement for a zone of `type secondary` to cause zone transfer requests to be sent via TLS.

`tls` can only be set at the top level of `named.conf`.

The following options can be specified in a `tls` statement:

key-file

  Grammar: `key-file <quoted_string>;`

  Blocks: tls

  Tags: server, security

  Specifies the path to a file containing the private TLS key for a connection.

  > This indicates the path to a file containing the private TLS key to be used for the connection.

cert-file

  Grammar: `cert-file <quoted_string>;`

  Blocks: tls

  Tags: server, security

  Specifies the path to a file containing the TLS certificate for a connection.

  > This indicates the path to a file containing the TLS certificate to be used for the connection.

ca-file

  Grammar: `ca-file <quoted_string>;`

  Blocks: tls

  Tags: server, security

  Specifies the path to a file containing TLS certificates for trusted CA authorities, used to verify remote peer certificates.

  > This indicates the path to a file containing trusted CA authorities’ TLS certificates, used to verify remote peer certificates. Specifying this option enables verification of remote peer certificates. For incoming connections, specifying this option makes BIND require a valid TLS certificate from a client. In the case of outgoing connections, if `remote-hostname` is not specified, the remote server IP address is used instead.

dhparam-file

  Grammar: `dhparam-file <quoted_string>;`

  Blocks: tls

  Tags: server, security

  Specifies the path to a file containing Diffie-Hellman parameters, for enabling cipher suites.

  > This indicates the path to a file containing Diffie-Hellman parameters, which is needed to enable the cipher suites depending on the Diffie-Hellman ephemeral key exchange (DHE). Having these parameters specified is essential for enabling perfect forward secrecy capable ciphers in TLSv1.2.

remote-hostname

  Grammar: `remote-hostname <quoted_string>;`

  Blocks: tls

  Tags: security

  Specifies the expected hostname in the TLS certificate of the remote server.

  > This specifies the expected hostname in the TLS certificate of the remote server. This option enables a remote server certificate verification. If `ca-file` is not specified, then the platform-specific certificates store is used for verification. This option is used when connecting to a remote peer only and, thus, is ignored when `tls` statements are referenced by `listen-on` or `listen-on-v6` statements.

protocols

  Grammar: `protocols { <string>; ... };`

  Blocks: tls

  Tags: security

  Specifies the allowed versions of the TLS protocol.

  > This specifies the allowed versions of the TLS protocol. TLS version 1.2 and higher are supported, depending on the cryptographic library in use. Multiple versions may be specified (e.g. `protocols { TLSv1.2; TLSv1.3; };`).

cipher-suites

  Grammar: `cipher-suites <string>;`

  Blocks: tls

  Tags: security

  Specifies a list of allowed cipher suites in the order of preference for TLSv1.3 only.

  > This option defines allowed cipher suites, such as `TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:TLS_AES_128_GCM_SHA256`. The string must be formed according to the rules specified in the OpenSSL documentation (see https://docs.openssl.org/1.1.1/man1/ciphers/, section “TLS v1.3 cipher suites” for details).

ciphers

  Grammar: `ciphers <string>;`

  Blocks: tls

  Tags: security

  Specifies a list of allowed ciphers in the order of preference for TLSv1.2 only.

  > This option defines allowed ciphers, such as `HIGH:!aNULL:!MD5:!SHA1:!SHA256:!SHA384`. The string must be formed according to the rules specified in the OpenSSL documentation (see https://docs.openssl.org/1.1.1/man1/ciphers/ for details).

prefer-server-ciphers

  Grammar: `prefer-server-ciphers <boolean>;`

  Blocks: tls

  Tags: server, security

  Specifies that server ciphers should be preferred over client ones.

  > This option specifies that server ciphers should be preferred over client ones.

session-tickets

  Grammar: `session-tickets <boolean>;`

  Blocks: tls

  Tags: security

  Enables or disables session resumption through TLS session tickets.

  > This option enables or disables session resumption through TLS session tickets, as defined in RFC 5077. Disabling the stateless session tickets might be required in the cases when forward secrecy is needed, or the TLS certificate and key pair is planned to be used across multiple BIND instances.

Warning

TLS configuration is subject to change and incompatible changes might be introduced in the future. Users of TLS are encouraged to carefully read release notes when upgrading.

The options described above are used to control different aspects of TLS functioning. Thus, most of them have no well-defined default values, as these depend on the cryptographic library version in use and system-wide cryptographic policy. On the other hand, by specifying the needed options one could have a uniform configuration deployable across a range of platforms.

An example of privacy-oriented, perfect forward secrecy enabled configuration can be found below. It can be used as a starting point.

    tls local-tls {
        key-file "/path/to/key.pem";
        cert-file "/path/to/fullchain_cert.pem";
        dhparam-file "/path/to/dhparam.pem";
        ciphers "HIGH:!kRSA:!aNULL:!eNULL:!RC4:!3DES:!MD5:!EXP:!PSK:!SRP:!DSS:!SHA1:!SHA256:!SHA384";
        prefer-server-ciphers yes;
        session-tickets no;
    };

A Diffie-Hellman parameters file can be generated using e.g. OpenSSL, like follows:

    openssl dhparam -out /path/to/dhparam.pem <3072_or_4096>

It is important to ensure that the file is generated on a machine with enough entropy from external sources (e.g. the local computer should be fine, the remote virtual machine or server might not be). These files do not contain any sensitive data and can be shared if required.

There are two built-in TLS connection configurations: `ephemeral`, which uses a temporary key and certificate created for the current `named` session only, and `none`, which can be used when setting up an HTTP listener with no encryption.

The main motivation behind the existence of the `ephemeral` configuration is to aid in testing. Since trusted certificate authorities do not issue the certificates associated with this configuration, these certificates will never be trusted by any clients that verify TLS certificates; they provide encryption of the traffic but no authentication of the transmission channel. That might be enough in the case of deployment in a controlled environment.

It should be noted that on reconfiguration, the `ephemeral` TLS key and the certificate are recreated, and all TLS certificates and keys, as well as associated data, are reloaded from the disk. In that case, listening sockets associated with TLS remain intact.

Note that performing a reconfiguration can cause a short interruption in BIND’s ability to process inbound client packets. The length of interruption is environment- and configuration-specific. A good example of when reconfiguration is necessary is when TLS keys and certificates are updated on the disk.

BIND supports the following TLS authentication mechanisms described in RFC 9103, Section 9.3: Opportunistic TLS, Strict TLS, and Mutual TLS.

Opportunistic TLS provides encryption for data but does not provide any authentication for the channel. This mode is the default and is used whenever the `remote-hostname` and `ca-file` options are not set in `tls` statements in use. RFC 9103 allows optional fallback to clear-text DNS in the cases when TLS is not available; however, BIND intentionally does not support that fallback, to protect from unexpected data leaks due to misconfiguration. Both BIND and its complementary tools either successfully establish a secure channel via TLS when instructed to do so, or fail to establish a connection otherwise.

Strict TLS provides server authentication via a pre-configured hostname for outgoing connections. This mechanism offers both channel confidentiality and channel authentication (of the server). In order to achieve Strict TLS, one needs to use `remote-hostname` and, optionally, `ca-file` options in the `tls` statements used for establishing outgoing connections (e.g. the ones used to download zone from primaries via TLS). Providing any of the mentioned options will enable server authentication. If `remote-hostname` is provided but `ca-file` is missing, then the platform-specific certificate authority certificates are used for authentication. The set roughly corresponds to the one used by WEB-browsers to authenticate HTTPS hosts. On the other hand, if `ca-file` is provided but `remote-hostname` is missing, then the remote side’s IP address is used instead.

Mutual TLS is an extension to Strict TLS that provides channel confidentiality and mutual channel authentication. It builds up upon the clients offering client certificates when establishing connections and them doing the server authentication as in the case of Strict TLS. The server verifies the provided client certificates and accepts the TLS connection in case of successful verification or rejects it otherwise. In order to instruct the server to require and verify client TLS certificates, one needs to specify the `ca-file` option in `tls` configurations used to configure server listeners. The provided file must contain certificate authority certificates used to issue client certificates. In most cases, one should build one’s own TLS certificate authority specifically to issue client certificates and include the certificate authority certificate into the file.

For authenticating zone transfers over TLS, Mutual TLS might be considered a standalone solution, while Strict TLS paired with TSIG-based authentication and, optionally, IP-based access lists, might be considered acceptable for most practical purposes. Mutual TLS has the advantage of not requiring TSIG and thus, not having security issues related to shared cryptographic secrets.

### 8.2.20. `http` Block Grammar

http

  Grammar:

      http <string> {
      	endpoints { <quoted_string>; ... };
      	listener-clients <integer>;
      	streams-per-connection <integer>;
      }; // may occur multiple times

  Blocks: topmost

  Tags: server, query

  Configures HTTP endpoints on which to listen for DNS-over-HTTPS (DoH) queries.

### 8.2.21. `http` Block Definition and Usage

The `http` statement is used to configure HTTP endpoints on which to listen for DNS-over-HTTPS (DoH) queries. This configuration can then be referenced by a `listen-on` or `listen-on-v6` statement to cause `named` to listen for incoming requests over HTTPS.

`http` can only be set at the top level of `named.conf`.

The following options can be specified in an `http` statement:

endpoints

  Grammar: `endpoints { <quoted_string>; ... };`

  Blocks: http

  Tags: server, query

  Specifies a list of HTTP query paths on which to listen.

  > This specifies a list of HTTP query paths on which to listen. This is the portion of an RFC 3986-compliant URI following the hostname; it must be an absolute path, beginning with “/”. The default value is `"/dns-query"`, if omitted.

listener-clients

  Grammar: `listener-clients <integer>;`

  Blocks: http

  Tags: server, query

  Specifies a per-listener quota for active connections.

  > This option specifies a per-listener quota for active connections.

streams-per-connection

  Grammar: `streams-per-connection <integer>;`

  Blocks: http

  Tags: server, query

  Specifies the maximum number of concurrent HTTP/2 streams over an HTTP/2 connection.

  > This option specifies the hard limit on the number of concurrent HTTP/2 streams over an HTTP/2 connection.

Any of the options above could be omitted. In such a case, a global value specified in the `options` statement is used (see `http-listener-clients`, `http-streams-per-connection`.

For example, the following configuration enables DNS-over-HTTPS queries on all local addresses:

    http local {
        endpoints { "/dns-query"; };
    };

    options {
        ....
        listen-on tls ephemeral http local { any; };
        listen-on-v6 tls ephemeral http local { any; };
    };

### 8.2.22. `trust-anchors` Block Grammar

trust-anchors

  Grammar: `trust-anchors { <string> ( static-key | initial-key | static-ds | initial-ds ) <integer> <integer> <integer> <quoted_string>; ... }; // may occur multiple times`

  Blocks: topmost, view

  Tags: dnssec

  Defines DNSSEC trust anchors.

### 8.2.23. `trust-anchors` Block Definition and Usage

The `trust-anchors` statement defines DNSSEC trust anchors. DNSSEC is described in DNSSEC.

A trust anchor is defined when the public key or public key digest for a non-authoritative zone is known but cannot be securely obtained through DNS, either because it is the DNS root zone or because its parent zone is unsigned. Once a key or digest has been configured as a trust anchor, it is treated as if it has been validated and proven secure.

The resolver attempts DNSSEC validation on all DNS data in subdomains of configured trust anchors. Validation below specified names can be temporarily disabled by using `rndc nta`, or permanently disabled with the `validate-except` option.

All keys listed in `trust-anchors`, and their corresponding zones, are deemed to exist regardless of what parent zones say. Only keys configured as trust anchors are used to validate the DNSKEY RRset for the corresponding name. The parent’s DS RRset is not used.

`trust-anchors` may be set at the top level of `named.conf` or within a view. If it is set in both places, the configurations are additive; keys defined at the top level are inherited by all views, but keys defined in a view are only used within that view.

The `trust-anchors` statement can contain multiple trust-anchor entries, each consisting of a domain name, followed by an “anchor type” keyword indicating the trust anchor’s format, followed by the key or digest data.

If the anchor type is `static-key` or `initial-key`, it is followed with the key’s flags, protocol, and algorithm, plus the Base64 representation of the public key data. This is identical to the text representation of a DNSKEY record. Spaces, tabs, newlines, and carriage returns are ignored in the key data, so the configuration may be split into multiple lines.

If the anchor type is `static-ds` or `initial-ds`, it is followed with the key tag, algorithm, digest type, and the hexadecimal representation of the key digest. This is identical to the text representation of a DS record. Spaces, tabs, newlines, and carriage returns are ignored.

Trust anchors configured with the `static-key` or `static-ds` anchor types are immutable, while keys configured with `initial-key` or `initial-ds` can be kept up-to-date automatically, without intervention from the resolver operator. (`static-key` keys are identical to keys configured using the deprecated `trusted-keys` statement.)

Suppose, for example, that a zone’s key-signing key was compromised, and the zone owner had to revoke and replace the key. A resolver which had the original key configured using `static-key` or `static-ds` would be unable to validate this zone any longer; it would reply with a SERVFAIL response code. This would continue until the resolver operator had updated the `trust-anchors` statement with the new key.

If, however, the trust anchor had been configured using `initial-key` or `initial-ds` instead, the zone owner could add a “stand-by” key to the zone in advance. `named` would store the stand-by key, and when the original key was revoked, `named` would be able to transition smoothly to the new key. It would also recognize that the old key had been revoked and cease using that key to validate answers, minimizing the damage that the compromised key could do. This is the process used to keep the ICANN root DNSSEC key up-to-date.

Whereas `static-key` and `static-ds` trust anchors continue to be trusted until they are removed from `named.conf`, an `initial-key` or `initial-ds` is only trusted once: for as long as it takes to load the managed key database and start the RFC 5011 key maintenance process.

It is not possible to mix static with initial trust anchors for the same domain name.

The first time `named` runs with an `initial-key` or `initial-ds` configured in `named.conf`, it fetches the DNSKEY RRset directly from the zone apex, and validates it using the trust anchor specified in `trust-anchors`. If the DNSKEY RRset is validly signed by a key matching the trust anchor, then it is used as the basis for a new managed-keys database.

From that point on, whenever `named` runs, it sees the `initial-key` or `initial-ds` listed in `trust-anchors`, checks to make sure RFC 5011 key maintenance has already been initialized for the specified domain, and if so, simply moves on. The key specified in the `trust-anchors` statement is not used to validate answers; it is superseded by the key or keys stored in the managed-keys database.

The next time `named` runs after an `initial-key` or `initial-ds` has been removed from the `trust-anchors` statement (or changed to a `static-key` or `static-ds`), the corresponding zone is removed from the managed-keys database, and RFC 5011 key maintenance is no longer used for that domain.

In the current implementation, the managed-keys database is stored as a master-format zone file.

On servers which do not use views, this file is named `managed-keys.bind`. When views are in use, there is a separate managed-keys database for each view; the filename is the view name (or, if a view name contains characters which would make it illegal as a filename, a hash of the view name), followed by the suffix `.mkeys`.

When the key database is changed, the zone is updated. As with any other dynamic zone, changes are written into a journal file, e.g., `managed-keys.bind.jnl` or `internal.mkeys.jnl`. Changes are committed to the primary file as soon as possible afterward, usually within 30 seconds. Whenever `named` is using automatic key maintenance, the zone file and journal file can be expected to exist in the working directory. (For this reason, among others, the working directory should be always be writable by `named`.)

If the `dnssec-validation` option is set to `auto`, `named` automatically sets up an `initial-key` for the root zone. This initializing key is built into `named` and is current as of the release date. When the root zone key changes, a running server detects the change and rolls to the new key; however, newly installed servers being run for the first time will need to be on a recent-enough version of BIND to have been built with the current key.

### 8.2.24. `dnssec-policy` Block Grammar

dnssec-policy

  Grammar options, view, zone (primary, secondary): `dnssec-policy <string>;`

  Grammar topmost:

      dnssec-policy <string> {
      	cdnskey <boolean>;
      	cds-digest-types { <string>; ... };
      	dnskey-ttl <duration>;
      	inline-signing <boolean>;
      	keys { ( csk | ksk | zsk ) [ key-directory | key-store <string> ] lifetime <duration_or_unlimited> algorithm <string> [ tag-range <integer> <integer> ] [ <integer> ]; ... };
      	max-zone-ttl <duration>;
      	nsec3param [ iterations <integer> ] [ optout <boolean> ] [ salt-length <integer> ];
      	offline-ksk <boolean>;
      	parent-ds-ttl <duration>;
      	parent-propagation-delay <duration>;
      	publish-safety <duration>;
      	purge-keys <duration>;
      	retire-safety <duration>;
      	signatures-jitter <duration>;
      	signatures-refresh <duration>;
      	signatures-validity <duration>;
      	signatures-validity-dnskey <duration>;
      	zone-propagation-delay <duration>;
      }; // may occur multiple times

  Blocks: topmost, options, view, zone (primary, secondary)

  Tags: dnssec

  Defines a key and signing policy (KASP) for zones.

### 8.2.25. `dnssec-policy` Block Definition and Usage

The `dnssec-policy` statement defines a key and signing policy (KASP) for zones.

A KASP determines how one or more zones are signed with DNSSEC. For example, it specifies how often keys should roll, which cryptographic algorithms to use, and how often RRSIG records need to be refreshed. Multiple key and signing policies can be configured with unique policy names.

A policy for a zone is selected using a `dnssec-policy` statement in the `zone` block, specifying the name of the policy that should be used.

There are three built-in policies:

  - `default`, which uses the default policy;

  - `insecure`, to be used when the zone should be unsigned gracefully; and

  - `none`, which means no DNSSEC policy (the same as not selecting `dnssec-policy` at all; the zone is not signed).

Keys are not shared among zones, which means that one set of keys per zone is generated even if they have the same policy. If multiple views are configured with different versions of the same zone, each separate version uses the same set of signing keys.

If the expected key files that were previously observed have gone missing or are inaccessible, key management is halted. This will prevent rollovers from being started if there is a temporary file access issue. If his problem is permanent it will eventually lead to expired signatures in your zone. Note that if the key files are missing or inaccessible during `named` startup, BIND 9 will try to generate new keys according to the DNSSEC policy, because it has no cached information about existing keys yet.

The `dnssec-policy` statement requires dynamic DNS to be set up, or `inline-signing` to be enabled (which is the default for DNSSEC zones).

If `inline-signing` is enabled, this means that a signed version of the zone is maintained separately and is written out to a different file on disk (the zone’s filename plus a `.signed` extension).

If `inline-signing` is disabled, the zone needs to be configured with an `update-policy` or `allow-update`. In such a case, the DNSSEC records are written to the filename set in the original zone’s `file`.

Key rollover timing is computed for each key according to the key lifetime defined in the KASP. The lifetime may be modified by zone TTLs and propagation delays, to prevent validation failures. When a key reaches the end of its lifetime, `named` generates and publishes a new key automatically, then deactivates the old key and activates the new one; finally, the old key is retired according to a computed schedule.

Zone-signing key (ZSK) rollovers require no operator input. Key-signing key (KSK) and combined-signing key (CSK) rollovers require action to be taken to submit a DS record to the parent. Rollover timing for KSKs and CSKs is adjusted to take into account delays in processing and propagating DS updates.

The policy `default` causes the zone to be signed with a single combined-signing key (CSK) using the algorithm ECDSAP256SHA256; this key has an unlimited lifetime. This policy can be displayed using the command `named -C`.

Note

The default signing policy may change in future releases. This could require changes to a signing policy when upgrading to a new version of BIND. Check the release notes carefully when upgrading to be informed of such changes. To prevent policy changes on upgrade, use an explicitly defined `dnssec-policy`, rather than `default`.

If a `dnssec-policy` statement is modified and the server restarted or reconfigured, `named` attempts to change the policy smoothly from the old one to the new. For example, if the key algorithm is changed, then a new key is generated with the new algorithm, and the old algorithm is retired when the existing key’s lifetime ends.

Note

Rolling to a new policy while another key rollover is already in progress is not yet supported, and may result in unexpected behavior.

The following options can be specified in a `dnssec-policy` statement:

cdnskey

  Grammar: `cdnskey <boolean>;`

  Blocks: dnssec-policy

  Tags: dnssec

  Specifies whether a CDNSKEY record should be published during KSK rollover.

  > When set to the default value of `yes`, a CDNSKEY record is published during KSK rollovers when the DS of the successor key may be submitted to the parent.

cds-digest-types

  Grammar: `cds-digest-types { <string>; ... };`

  Blocks: dnssec-policy

  Tags: dnssec

  Specifies the digest types to use for CDS resource records.

  > This indicates the digest types to use when generating CDS resource records. The default is SHA-256 only.

dnskey-ttl

  Grammar: `dnskey-ttl <duration>;`

  Blocks: dnssec-policy

  Tags: dnssec

  Specifies the time-to-live (TTL) for DNSKEY resource records.

  > This indicates the TTL to use when generating DNSKEY resource records. The default is 1 hour (3600 seconds).

inline-signing
  tags:

    dnssec

  short:

    Specifies whether BIND 9 maintains a separate signed version of a zone.

  If `yes`, BIND 9 maintains a separate signed version of the zone. An unsigned zone is transferred in or loaded from disk and the signed version of the zone is served with, possibly, a different serial number. The signed version of the zone is stored in a file that is the zone’s filename (set in `file`) with a `.signed` extension.

  This behavior is enabled by default.

keys
  tags:

    dnssec

  short:

    Specifies the type of keys to be used for DNSSEC signing.

    This is a list specifying the algorithms and roles to use when generating keys and signing the zone. Entries in this list do not represent specific DNSSEC keys, which may be changed on a regular basis, but the roles that keys play in the signing policy. For example, configuring a KSK of algorithm RSASHA256 ensures that the DNSKEY RRset always includes a key-signing key for that algorithm.

    Here is an example (for illustration purposes only) of some possible entries in a `keys` list:

        keys {
            ksk key-directory lifetime unlimited algorithm rsasha256 2048;
            zsk lifetime 30d algorithm 8 tag-range 0 32767;
            csk key-store "hsm" lifetime P6MT12H3M15S algorithm ecdsa256;
        };

    This example specifies that three keys should be used in the zone. The first token determines which role the key plays in signing RRsets. If set to `ksk`, then this is a key-signing key; it has the KSK flag set and is only used to sign DNSKEY, CDS, and CDNSKEY RRsets. If set to `zsk`, this is a zone-signing key; the KSK flag is unset, and the key signs all RRsets except DNSKEY, CDS, and CDNSKEY. If set to `csk`, the key has the KSK flag set and is used to sign all RRsets.

    An optional second token determines where the key is stored. The two available options are `key-store <string>` and `key-directory`.

    When using `key-store`, the referenced `key-store` describes how the key should be be stored. This can be as a file, or it can be inside a PKCS#11 token.

    When using `key-directory`, the key is stored in the zone’s configured `key-directory`. This is also the default.

    When using `tag-range`, valid key tags for managed keys are restricted to this range [`tag-min` `tag-max`]. The optional `tag-range` is intended to be used in multi-signer scenarios. The default is unlimited ([0..65535]).

    The `lifetime` parameter specifies how long a key may be used before rolling over. For convenience, TTL-style time-unit suffixes can be used to specify the key lifetime. It also accepts ISO 8601 duration formats.

    In the example above, the first key has an unlimited lifetime, the second key may be used for 30 days, and the third key has a rather peculiar lifetime of 6 months, 12 hours, 3 minutes, and 15 seconds. A lifetime of 0 seconds is the same as `unlimited`.

    Note that the lifetime of a key may be extended if retiring it too soon would cause validation failures. The key lifetime must be longer than the time it takes to do a rollover; that is, the lifetime must be more than the publication interval (which is the sum of `dnskey-ttl`, `publish-safety`, and `zone-propagation-delay`). It must also be more than the retire interval (which is the sum of `max-zone-ttl`, `retire-safety`, `zone-propagation-delay`, and signing delay (`signatures-validity` minus `signatures-refresh`) for ZSKs, and the sum of `parent-ds-ttl`, `retire-safety`, and `parent-propagation-delay` for KSKs and CSKs). BIND 9 treats a key lifetime that is too short as an error.

    The `algorithm` parameter specifies the key’s algorithm, expressed either as a string (“rsasha256”, “ecdsa384”, etc.) or as a decimal number. An optional second parameter specifies the key’s size in bits. If it is omitted, as shown in the example for the second and third keys, an appropriate default size for the algorithm is used. Each KSK/ZSK pair must have the same algorithm. A CSK combines the functionality of a ZSK and a KSK.

Note

When changing the `key-directory` or the `key-store`, BIND will be unable to find existing key files. Be sure to copy key files to the new directory before changing the path used in the configuration file. This is also true when changing to a built-in policy, e.g. to `insecure`. In this specific case, the existing key files should be moved to the zone’s `key-directory` from the new configuration.

offline-ksk

  Grammar: `offline-ksk <boolean>;`

  Blocks: dnssec-policy

  Tags: dnssec

  Specifies whether the DNSKEY, CDS, and CDNSKEY RRsets are being signed offline.

  > If enabled, BIND 9 does not generate signatures for the DNSKEY, CDS, and CDNSKEY RRsets. Instead, the signed DNSKEY, CDS and CDNSKEY RRsets are looked up from Signed Key Response (SKR) files.

  > Any existing DNSKEY, CDS, and CDNSKEY RRsets in the unsigned version of the zone are filtered and replaced with RRsets from the SKR file.

  > This feature is off by default. Configuring `offline-ksk` in conjunction with a CSK is a configuration error.

purge-keys

  Grammar: `purge-keys <duration>;`

  Blocks: dnssec-policy

  Tags: dnssec

  Specifies the amount of time after which DNSSEC keys that have been deleted from the zone can be removed from disk.

  > This is the amount of time after which DNSSEC keys that have been deleted from the zone can be removed from disk. If a key still determined to have presence (for example in some resolver cache), `named` will not remove the key files.

  > The default is `P90D` (90 days). Set this option to `0` to never purge deleted keys.

publish-safety

  Grammar: `publish-safety <duration>;`

  Blocks: dnssec-policy

  Tags: dnssec

  Increases the amount of time between when keys are published and when they become active, to allow for unforeseen events.

  > This is a margin that is added to the pre-publication interval in rollover timing calculations, to give some extra time to cover unforeseen events. This increases the time between when keys are published and when they become active. The default is `PT1H` (1 hour).

retire-safety

  Grammar: `retire-safety <duration>;`

  Blocks: dnssec-policy

  Tags: dnssec

  Increases the amount of time a key remains published after it is no longer active, to allow for unforeseen events.

  > This is a margin that is added to the post-publication interval in rollover timing calculations, to give some extra time to cover unforeseen events. This increases the time a key remains published after it is no longer active. The default is `PT1H` (1 hour).

signatures-jitter

  Grammar: `signatures-jitter <duration>;`

  Blocks: dnssec-policy

  Tags: dnssec

  Specifies a range for signature expirations.

  > To prevent all signatures from expiring at the same moment, BIND 9 may vary the validity interval of individual signatures. The validity of a newly generated signature is in the range between `signatures-validity` (maximum) and `signatures-validity`, minus `signatures-jitter` (minimum). The default jitter is 12 hours, and the configured value must be lower than both `signatures-validity` and `signatures-validity-dnskey`.

signatures-refresh

  Grammar: `signatures-refresh <duration>;`

  Blocks: dnssec-policy

  Tags: dnssec

  Specifies how frequently an RRSIG record is refreshed.

  > This determines how frequently an RRSIG record needs to be refreshed. The signature is renewed when the time until the expiration time is less than the specified interval. The default is `P5D` (5 days), meaning signatures that expire in 5 days or sooner are refreshed. The `signatures-refresh` value must be less than 90% of the minimum value of `signatures-validity` and `signatures-validity-dnskey`.

signatures-validity

  Grammar: `signatures-validity <duration>;`

  Blocks: dnssec-policy

  Tags: dnssec

  Indicates the validity period of an RRSIG record.

  > This indicates the validity period of an RRSIG record (subject to inception offset and jitter). The default is `P2W` (2 weeks).

  > The `signatures-validity` should be at least several multiples of the SOA expire interval, to allow for reasonable interaction between the various timer and expiry dates.

signatures-validity-dnskey

  Grammar: `signatures-validity-dnskey <duration>;`

  Blocks: dnssec-policy

  Tags: dnssec

  Indicates the validity period of DNSKEY records.

  > This is similar to `signatures-validity`, but for DNSKEY records. The default is `P2W` (2 weeks).

max-zone-ttl
  tags:

    zone, query

  short:

    Specifies a maximum permissible time-to-live (TTL) value, in seconds.

  This specifies the maximum permissible TTL value for the zone. When a zone file is loaded, any record encountered with a TTL higher than `max-zone-ttl` causes the zone to be rejected.

  This ensures that when rolling to a new DNSKEY, the old key will remain available until RRSIG records have expired from caches. The `max-zone-ttl` option guarantees that the largest TTL in the zone is no higher than a known and predictable value.

  The default value `PT24H` (24 hours). A value of zero is treated as if the default value were in use.

nsec3param

  Grammar: `nsec3param [ iterations <integer> ] [ optout <boolean> ] [ salt-length <integer> ];`

  Blocks: dnssec-policy

  Tags: dnssec

  Specifies the use of NSEC3 instead of NSEC, and sets NSEC3 parameters.

  > Use NSEC3 instead of NSEC, and optionally set the NSEC3 parameters.

  > Here is an example of an `nsec3` configuration:

  >     nsec3param iterations 0 optout no salt-length 0;

  > The default is to use NSEC. The `iterations`, `optout`, and `salt-length` parts are optional, but if not set, the values in the example above are the default NSEC3 parameters. Note that the specific salt string is not specified by the user; `named` creates a salt of the indicated length.

  > Warning

  > Do not use extra iterations, salt, and opt-out unless their implications are fully understood. A higher number of iterations causes interoperability problems and opens servers to CPU-exhausting DoS attacks. See RFC 9276.

zone-propagation-delay

  Grammar: `zone-propagation-delay <duration>;`

  Blocks: dnssec-policy

  Tags: dnssec, zone

  Sets the propagation delay from the time a zone is first updated to when the new version of the zone is served by all secondary servers.

  > This is the expected propagation delay from the time when a zone is first updated to the time when the new version of the zone is served by all secondary servers. The default is `PT5M` (5 minutes).

parent-ds-ttl

  Grammar: `parent-ds-ttl <duration>;`

  Blocks: dnssec-policy

  Tags: dnssec

  Sets the time to live (TTL) of the DS RRset used by the parent zone.

  > This is the TTL of the DS RRset that the parent zone uses. The default is `P1D` (1 day).

parent-propagation-delay

  Grammar: `parent-propagation-delay <duration>;`

  Blocks: dnssec-policy

  Tags: dnssec, zone

  Sets the propagation delay from the time the parent zone is updated to when the new version is served by all of the parent zone’s name servers.

  > This is the expected propagation delay from the time when the parent zone is updated to the time when the new version is served by all of the parent zone’s name servers. The default is `PT1H` (1 hour).

#### 8.2.25.1. Automated KSK Rollovers

BIND has mechanisms in place to facilitate automated KSK rollovers. It publishes CDS and CDNSKEY records that can be used by the parent zone to publish or withdraw the zone’s DS records. BIND will query the parental agents to see if the new DS is actually published before withdrawing the old DNSSEC key.

> Note

> The DS response is not validated so it is recommended to set up a trust relationship with the parental agent. For example, use TSIG to authenticate the parental agent, or point to a validating resolver.

parental-agents

  Grammar: `parental-agents [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };`

  Blocks: zone (primary, secondary)

  Tags: dnssec

  This specifies a list of one or more IP addresses of parental agents that are used to query the zone’s DS records during a KSK rollover. The list of parental agents can also contain the names of `remote-servers` blocks.

  By default, DS queries are sent from port 53 on the servers; this can be changed for all servers by specifying a port number before the list of IP addresses, or on a per-server basis after the IP address. Authentication to the primary can also be done with per-server TSIG keys.

The following options apply to DS queries sent to `parental-agents`:

checkds

  Grammar: `checkds ( explicit | <boolean> );`

  Blocks: zone (primary, secondary)

  Tags: dnssec

  Controls whether `DS` queries are sent to parental agents.

  If set to `yes`, DS queries are sent when a KSK rollover is in progress. The queries are sent to the servers listed in the parent zone’s NS records. This is the default if there are no `parental-agents` configured for the zone.

  If set to `explicit`, DS queries are sent only to servers explicitly listed using `parental-agents`. This is the default if there are parental agents configured.

  If set to `no`, no DS queries are sent. Users should manually run `rndc dnssec -checkds` with the appropriate parameters, to signal that specific DS records are published and/or withdrawn.

parental-source

  Grammar: `parental-source ( <ipv4_address> | * );`

  Blocks: options, view, zone (primary, secondary)

  Tags: dnssec

  Specifies which local IPv4 source address is used to send parental DS queries.

  `parental-source` determines which local source address, and optionally UDP port, is used to send parental DS queries. This statement sets the `parental-source` for all zones, but can be overridden on a per-zone or per-view basis by including a `parental-source` statement within the `zone` or `view` block in the configuration file.

  Note

  `port` configuration is deprecated. A warning will be logged when this parameter is used.

  Warning

  Specifying a single port is discouraged, as it removes a layer of protection against spoofing errors.

  Warning

  The configured port must not be the same as the listening port.

parental-source-v6

  Grammar: `parental-source-v6 ( <ipv6_address> | * );`

  Blocks: options, view, zone (primary, secondary)

  Tags: dnssec

  Specifies which local IPv6 source address is used to send parental DS queries.

  This option acts like `parental-source`, but applies to parental DS queries sent to IPv6 addresses.

### 8.2.26. `managed-keys` Block Grammar

managed-keys

  Warning

  This option is deprecated and will be removed in a future version of BIND.

  Grammar: `managed-keys { <string> ( static-key | initial-key | static-ds | initial-ds ) <integer> <integer> <integer> <quoted_string>; ... }; // may occur multiple times, deprecated`

  Blocks: topmost, view

  Tags: deprecated

### 8.2.27. `managed-keys` Block Definition and Usage

The `managed-keys` statement has been deprecated in favor of `trust-anchors` with the `initial-key` keyword.

### 8.2.28. `trusted-keys` Block Grammar

trusted-keys

  Warning

  This option is deprecated and will be removed in a future version of BIND.

  Grammar: `trusted-keys { <string> <integer> <integer> <integer> <quoted_string>; ... }; // may occur multiple times, deprecated`

  Blocks: topmost, view

  Tags: deprecated

### 8.2.29. `trusted-keys` Block Definition and Usage

The `trusted-keys` statement has been deprecated in favor of `trust-anchors` with the `static-key` keyword.

### 8.2.30. `view` Block Grammar

view

  Grammar:

      view <string> [ <class> ] {
      	allow-new-zones <boolean>;
      	allow-notify { <address_match_element>; ... };
      	allow-proxy { <address_match_element>; ... }; // experimental
      	allow-proxy-on { <address_match_element>; ... }; // experimental
      	allow-query { <address_match_element>; ... };
      	allow-query-cache { <address_match_element>; ... };
      	allow-query-cache-on { <address_match_element>; ... };
      	allow-query-on { <address_match_element>; ... };
      	allow-recursion { <address_match_element>; ... };
      	allow-recursion-on { <address_match_element>; ... };
      	allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_element>; ... };
      	allow-update { <address_match_element>; ... };
      	allow-update-forwarding { <address_match_element>; ... };
      	also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      	attach-cache <string>;
      	auth-nxdomain <boolean>;
      	catalog-zones { zone <string> [ default-primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... } ] [ zone-directory <quoted_string> ] [ in-memory <boolean> ] [ min-update-interval <duration> ]; ... };
      	check-dup-records ( fail | warn | ignore );
      	check-integrity <boolean>;
      	check-mx ( fail | warn | ignore );
      	check-mx-cname ( fail | warn | ignore );
      	check-names ( primary | master | secondary | slave | response ) ( fail | warn | ignore ); // may occur multiple times
      	check-sibling <boolean>;
      	check-spf ( warn | ignore );
      	check-srv-cname ( fail | warn | ignore );
      	check-svcb <boolean>;
      	check-wildcard <boolean>;
      	clients-per-query <integer>;
      	deny-answer-addresses { <address_match_element>; ... } [ except-from { <string>; ... } ];
      	deny-answer-aliases { <string>; ... } [ except-from { <string>; ... } ];
      	dialup ( notify | notify-passive | passive | refresh | <boolean> ); // deprecated
      	disable-algorithms <string> { <string>; ... }; // may occur multiple times
      	disable-ds-digests <string> { <string>; ... }; // may occur multiple times
      	disable-empty-zone <string>; // may occur multiple times
      	dlz <string> {
      		database <string>;
      		search <boolean>;
      	}; // may occur multiple times
      	dns64 <netprefix> {
      		break-dnssec <boolean>;
      		clients { <address_match_element>; ... };
      		exclude { <address_match_element>; ... };
      		mapped { <address_match_element>; ... };
      		recursive-only <boolean>;
      		suffix <ipv6_address>;
      	}; // may occur multiple times
      	dns64-contact <string>;
      	dns64-server <string>;
      	dnskey-sig-validity <integer>; // obsolete
      	dnsrps-enable <boolean>;
      	dnsrps-options { <unspecified-text> };
      	dnssec-accept-expired <boolean>;
      	dnssec-dnskey-kskonly <boolean>; // obsolete
      	dnssec-loadkeys-interval <integer>;
      	dnssec-must-be-secure <string> <boolean>; // may occur multiple times, deprecated
      	dnssec-policy <string>;
      	dnssec-secure-to-insecure <boolean>; // obsolete
      	dnssec-update-mode ( maintain | no-resign ); // obsolete
      	dnssec-validation ( yes | no | auto );
      	dnstap { ( all | auth | client | forwarder | resolver | update ) [ ( query | response ) ]; ... };
      	dual-stack-servers [ port <integer> ] { ( <quoted_string> [ port <integer> ] | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ); ... };
      	dyndb <string> <quoted_string> { <unspecified-text> }; // may occur multiple times
      	edns-udp-size <integer>;
      	empty-contact <string>;
      	empty-server <string>;
      	empty-zones-enable <boolean>;
      	fetch-quota-params <integer> <fixedpoint> <fixedpoint> <fixedpoint>;
      	fetches-per-server <integer> [ ( drop | fail ) ];
      	fetches-per-zone <integer> [ ( drop | fail ) ];
      	forward ( first | only );
      	forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };
      	ipv4only-contact <string>;
      	ipv4only-enable <boolean>;
      	ipv4only-server <string>;
      	ixfr-from-differences ( primary | master | secondary | slave | <boolean> );
      	key <string> {
      		algorithm <string>;
      		secret <string>;
      	}; // may occur multiple times
      	key-directory <quoted_string>;
      	lame-ttl <duration>;
      	lmdb-mapsize <sizeval>;
      	managed-keys { <string> ( static-key | initial-key | static-ds | initial-ds ) <integer> <integer> <integer> <quoted_string>; ... }; // may occur multiple times, deprecated
      	masterfile-format ( raw | text );
      	masterfile-style ( full | relative );
      	match-clients { <address_match_element>; ... };
      	match-destinations { <address_match_element>; ... };
      	match-recursive-only <boolean>;
      	max-cache-size ( default | unlimited | <sizeval> | <percentage> );
      	max-cache-ttl <duration>;
      	max-clients-per-query <integer>;
      	max-ixfr-ratio ( unlimited | <percentage> );
      	max-journal-size ( default | unlimited | <sizeval> );
      	max-ncache-ttl <duration>;
      	max-query-count <integer>;
      	max-query-restarts <integer>;
      	max-records <integer>;
      	max-records-per-type <integer>;
      	max-recursion-depth <integer>;
      	max-recursion-queries <integer>;
      	max-refresh-time <integer>;
      	max-retry-time <integer>;
      	max-stale-ttl <duration>;
      	max-transfer-idle-in <integer>;
      	max-transfer-idle-out <integer>;
      	max-transfer-time-in <integer>;
      	max-transfer-time-out <integer>;
      	max-types-per-name <integer>;
      	max-udp-size <integer>;
      	max-validation-failures-per-fetch <integer>; // experimental
      	max-validations-per-fetch <integer>; // experimental
      	max-zone-ttl ( unlimited | <duration> ); // deprecated
      	message-compression <boolean>;
      	min-cache-ttl <duration>;
      	min-ncache-ttl <duration>;
      	min-refresh-time <integer>;
      	min-retry-time <integer>;
      	min-transfer-rate-in <integer> <integer>;
      	minimal-any <boolean>;
      	minimal-responses ( no-auth | no-auth-recursive | <boolean> );
      	multi-master <boolean>;
      	new-zones-directory <quoted_string>;
      	no-case-compress { <address_match_element>; ... };
      	nocookie-udp-size <integer>;
      	notify ( explicit | master-only | primary-only | <boolean> );
      	notify-defer <integer>;
      	notify-delay <integer>;
      	notify-source ( <ipv4_address> | * );
      	notify-source-v6 ( <ipv6_address> | * );
      	notify-to-soa <boolean>;
      	nsec3-test-zone <boolean>; // test only
      	nta-lifetime <duration>;
      	nta-recheck <duration>;
      	nxdomain-redirect <string>;
      	parental-source ( <ipv4_address> | * );
      	parental-source-v6 ( <ipv6_address> | * );
      	plugin ( query ) <string> [ { <unspecified-text> } ]; // may occur multiple times
      	preferred-glue <string>;
      	prefetch <integer> [ <integer> ];
      	provide-ixfr <boolean>;
      	qname-minimization ( strict | relaxed | disabled | off );
      	query-source [ address ] ( <ipv4_address> | * | none );
      	query-source-v6 [ address ] ( <ipv6_address> | * | none );
      	rate-limit {
      		all-per-second <integer>;
      		errors-per-second <integer>;
      		exempt-clients { <address_match_element>; ... };
      		ipv4-prefix-length <integer>;
      		ipv6-prefix-length <integer>;
      		log-only <boolean>;
      		max-table-size <integer>;
      		min-table-size <integer>;
      		nodata-per-second <integer>;
      		nxdomains-per-second <integer>;
      		qps-scale <integer>;
      		referrals-per-second <integer>;
      		responses-per-second <integer>;
      		slip <integer>;
      		window <integer>;
      	};
      	recursion <boolean>;
      	request-expire <boolean>;
      	request-ixfr <boolean>;
      	request-nsid <boolean>;
      	require-server-cookie <boolean>;
      	resolver-query-timeout <integer>;
      	resolver-use-dns64 <boolean>;
      	response-padding { <address_match_element>; ... } block-size <integer>;
      	response-policy { zone <string> [ add-soa <boolean> ] [ log <boolean> ] [ max-policy-ttl <duration> ] [ min-update-interval <duration> ] [ policy ( cname | disabled | drop | given | no-op | nodata | nxdomain | passthru | tcp-only <quoted_string> ) ] [ recursive-only <boolean> ] [ nsip-enable <boolean> ] [ nsdname-enable <boolean> ] [ ede <string> ]; ... } [ add-soa <boolean> ] [ break-dnssec <boolean> ] [ max-policy-ttl <duration> ] [ min-update-interval <duration> ] [ min-ns-dots <integer> ] [ nsip-wait-recurse <boolean> ] [ nsdname-wait-recurse <boolean> ] [ qname-wait-recurse <boolean> ] [ recursive-only <boolean> ] [ nsip-enable <boolean> ] [ nsdname-enable <boolean> ] [ dnsrps-enable <boolean> ] [ dnsrps-options { <unspecified-text> } ];
      	root-key-sentinel <boolean>;
      	rrset-order { [ class <string> ] [ type <string> ] [ name <quoted_string> ] <string> <string>; ... };
      	send-cookie <boolean>;
      	serial-update-method ( date | increment | unixtime );
      	server <netprefix> {
      		bogus <boolean>;
      		edns <boolean>;
      		edns-udp-size <integer>;
      		edns-version <integer>;
      		keys <server_key>;
      		max-udp-size <integer>;
      		notify-source ( <ipv4_address> | * );
      		notify-source-v6 ( <ipv6_address> | * );
      		padding <integer>;
      		provide-ixfr <boolean>;
      		query-source [ address ] ( <ipv4_address> | * );
      		query-source-v6 [ address ] ( <ipv6_address> | * );
      		request-expire <boolean>;
      		request-ixfr <boolean>;
      		request-nsid <boolean>;
      		require-cookie <boolean>;
      		send-cookie <boolean>;
      		tcp-keepalive <boolean>;
      		tcp-only <boolean>;
      		transfer-format ( many-answers | one-answer );
      		transfer-source ( <ipv4_address> | * );
      		transfer-source-v6 ( <ipv6_address> | * );
      		transfers <integer>;
      	}; // may occur multiple times
      	servfail-ttl <duration>;
      	sig-signing-nodes <integer>;
      	sig-signing-signatures <integer>;
      	sig-signing-type <integer>;
      	sig-validity-interval <integer> [ <integer> ]; // obsolete
      	sig0key-checks-limit <integer>;
      	sig0message-checks-limit <integer>;
      	sortlist { <address_match_element>; ... }; // deprecated
      	stale-answer-client-timeout ( disabled | off | <integer> );
      	stale-answer-enable <boolean>;
      	stale-answer-ttl <duration>;
      	stale-cache-enable <boolean>;
      	stale-refresh-time <duration>;
      	synth-from-dnssec <boolean>;
      	transfer-format ( many-answers | one-answer );
      	transfer-source ( <ipv4_address> | * );
      	transfer-source-v6 ( <ipv6_address> | * );
      	trust-anchor-telemetry <boolean>;
      	trust-anchors { <string> ( static-key | initial-key | static-ds | initial-ds ) <integer> <integer> <integer> <quoted_string>; ... }; // may occur multiple times
      	trusted-keys { <string> <integer> <integer> <integer> <quoted_string>; ... }; // may occur multiple times, deprecated
      	try-tcp-refresh <boolean>;
      	update-check-ksk <boolean>; // obsolete
      	v6-bias <integer>;
      	validate-except { <string>; ... };
      	zero-no-soa-ttl <boolean>;
      	zero-no-soa-ttl-cache <boolean>;
       	zone <string> [ <class> ] {
      		in-view <string>;
      	};
      	zone <string> [ <class> ] {
      		type forward;
      		forward ( first | only );
      		forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };
      	};
      	zone <string> [ <class> ] {
      		type hint;
      		check-names ( fail | warn | ignore );
      		file <quoted_string>;
      	};
      	zone <string> [ <class> ] {
      		type mirror;
      		allow-notify { <address_match_element>; ... };
      		allow-query { <address_match_element>; ... };
      		allow-query-on { <address_match_element>; ... };
      		allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_element>; ... };
      		allow-update-forwarding { <address_match_element>; ... };
      		also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      		check-names ( fail | warn | ignore );
      		database <string>;
      		file <quoted_string>;
      		ixfr-from-differences <boolean>;
      		journal <quoted_string>;
      		masterfile-format ( raw | text );
      		masterfile-style ( full | relative );
      		max-ixfr-ratio ( unlimited | <percentage> );
      		max-journal-size ( default | unlimited | <sizeval> );
      		max-records <integer>;
      		max-records-per-type <integer>;
      		max-refresh-time <integer>;
      		max-retry-time <integer>;
      		max-transfer-idle-in <integer>;
      		max-transfer-idle-out <integer>;
      		max-transfer-time-in <integer>;
      		max-transfer-time-out <integer>;
      		max-types-per-name <integer>;
      		min-refresh-time <integer>;
      		min-retry-time <integer>;
      		min-transfer-rate-in <integer> <integer>;
      		multi-master <boolean>;
      		notify ( explicit | master-only | primary-only | <boolean> );
      		notify-defer <integer>;
      		notify-delay <integer>;
      		notify-source ( <ipv4_address> | * );
      		notify-source-v6 ( <ipv6_address> | * );
      		primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      		request-expire <boolean>;
      		request-ixfr <boolean>;
      		transfer-source ( <ipv4_address> | * );
      		transfer-source-v6 ( <ipv6_address> | * );
      		try-tcp-refresh <boolean>;
      		zero-no-soa-ttl <boolean>;
      		zone-statistics ( full | terse | none | <boolean> );
      	};
      	zone <string> [ <class> ] {
      		type primary;
      		allow-query { <address_match_element>; ... };
      		allow-query-on { <address_match_element>; ... };
      		allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_element>; ... };
      		allow-update { <address_match_element>; ... };
      		also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      		check-dup-records ( fail | warn | ignore );
      		check-integrity <boolean>;
      		check-mx ( fail | warn | ignore );
      		check-mx-cname ( fail | warn | ignore );
      		check-names ( fail | warn | ignore );
      		check-sibling <boolean>;
      		check-spf ( warn | ignore );
      		check-srv-cname ( fail | warn | ignore );
      		check-svcb <boolean>;
      		check-wildcard <boolean>;
      		checkds ( explicit | <boolean> );
      		database <string>;
      		dialup ( notify | notify-passive | passive | refresh | <boolean> ); // deprecated
      		dlz <string>;
      		dnskey-sig-validity <integer>; // obsolete
      		dnssec-dnskey-kskonly <boolean>; // obsolete
      		dnssec-loadkeys-interval <integer>;
      		dnssec-policy <string>;
      		dnssec-secure-to-insecure <boolean>; // obsolete
      		dnssec-update-mode ( maintain | no-resign ); // obsolete
      		file <quoted_string>;
      		forward ( first | only );
      		forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };
      		inline-signing <boolean>;
      		ixfr-from-differences <boolean>;
      		journal <quoted_string>;
      		key-directory <quoted_string>;
      		masterfile-format ( raw | text );
      		masterfile-style ( full | relative );
      		max-ixfr-ratio ( unlimited | <percentage> );
      		max-journal-size ( default | unlimited | <sizeval> );
      		max-records <integer>;
      		max-records-per-type <integer>;
      		max-transfer-idle-out <integer>;
      		max-transfer-time-out <integer>;
      		max-types-per-name <integer>;
      		max-zone-ttl ( unlimited | <duration> ); // deprecated
      		notify ( explicit | master-only | primary-only | <boolean> );
      		notify-defer <integer>;
      		notify-delay <integer>;
      		notify-source ( <ipv4_address> | * );
      		notify-source-v6 ( <ipv6_address> | * );
      		notify-to-soa <boolean>;
      		nsec3-test-zone <boolean>; // test only
      		parental-agents [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      		parental-source ( <ipv4_address> | * );
      		parental-source-v6 ( <ipv6_address> | * );
      		serial-update-method ( date | increment | unixtime );
      		sig-signing-nodes <integer>;
      		sig-signing-signatures <integer>;
      		sig-signing-type <integer>;
      		sig-validity-interval <integer> [ <integer> ]; // obsolete
      		update-check-ksk <boolean>; // obsolete
      		update-policy ( local | { ( deny | grant ) <string> ( 6to4-self | external | krb5-self | krb5-selfsub | krb5-subdomain | krb5-subdomain-self-rhs | ms-self | ms-selfsub | ms-subdomain | ms-subdomain-self-rhs | name | self | selfsub | selfwild | subdomain | tcp-self | wildcard | zonesub ) [ <string> ] <rrtypelist>; ... } );
      		zero-no-soa-ttl <boolean>;
      		zone-statistics ( full | terse | none | <boolean> );
      	};
      	zone <string> [ <class> ] {
      		type redirect;
      		allow-query { <address_match_element>; ... };
      		allow-query-on { <address_match_element>; ... };
      		dlz <string>;
      		file <quoted_string>;
      		masterfile-format ( raw | text );
      		masterfile-style ( full | relative );
      		max-records <integer>;
      		max-records-per-type <integer>;
      		max-types-per-name <integer>;
      		max-zone-ttl ( unlimited | <duration> ); // deprecated
      		primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      		zone-statistics ( full | terse | none | <boolean> );
      	};
      	zone <string> [ <class> ] {
      		type secondary;
      		allow-notify { <address_match_element>; ... };
      		allow-query { <address_match_element>; ... };
      		allow-query-on { <address_match_element>; ... };
      		allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_element>; ... };
      		allow-update-forwarding { <address_match_element>; ... };
      		also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      		check-names ( fail | warn | ignore );
      		checkds ( explicit | <boolean> );
      		database <string>;
      		dialup ( notify | notify-passive | passive | refresh | <boolean> ); // deprecated
      		dlz <string>;
      		dnskey-sig-validity <integer>; // obsolete
      		dnssec-dnskey-kskonly <boolean>; // obsolete
      		dnssec-loadkeys-interval <integer>;
      		dnssec-policy <string>;
      		dnssec-update-mode ( maintain | no-resign ); // obsolete
      		file <quoted_string>;
      		forward ( first | only );
      		forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };
      		inline-signing <boolean>;
      		ixfr-from-differences <boolean>;
      		journal <quoted_string>;
      		key-directory <quoted_string>;
      		masterfile-format ( raw | text );
      		masterfile-style ( full | relative );
      		max-ixfr-ratio ( unlimited | <percentage> );
      		max-journal-size ( default | unlimited | <sizeval> );
      		max-records <integer>;
      		max-records-per-type <integer>;
      		max-refresh-time <integer>;
      		max-retry-time <integer>;
      		max-transfer-idle-in <integer>;
      		max-transfer-idle-out <integer>;
      		max-transfer-time-in <integer>;
      		max-transfer-time-out <integer>;
      		max-types-per-name <integer>;
      		min-refresh-time <integer>;
      		min-retry-time <integer>;
      		min-transfer-rate-in <integer> <integer>;
      		multi-master <boolean>;
      		notify ( explicit | master-only | primary-only | <boolean> );
      		notify-defer <integer>;
      		notify-delay <integer>;
      		notify-source ( <ipv4_address> | * );
      		notify-source-v6 ( <ipv6_address> | * );
      		notify-to-soa <boolean>;
      		nsec3-test-zone <boolean>; // test only
      		parental-agents [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      		parental-source ( <ipv4_address> | * );
      		parental-source-v6 ( <ipv6_address> | * );
      		primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      		request-expire <boolean>;
      		request-ixfr <boolean>;
      		sig-signing-nodes <integer>;
      		sig-signing-signatures <integer>;
      		sig-signing-type <integer>;
      		sig-validity-interval <integer> [ <integer> ]; // obsolete
      		transfer-source ( <ipv4_address> | * );
      		transfer-source-v6 ( <ipv6_address> | * );
      		try-tcp-refresh <boolean>;
      		update-check-ksk <boolean>; // obsolete
      		zero-no-soa-ttl <boolean>;
      		zone-statistics ( full | terse | none | <boolean> );
      	};
      	zone <string> [ <class> ] {
      		type static-stub;
      		allow-query { <address_match_element>; ... };
      		allow-query-on { <address_match_element>; ... };
      		forward ( first | only );
      		forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };
      		max-records <integer>;
      		max-records-per-type <integer>;
      		max-types-per-name <integer>;
      		server-addresses { ( <ipv4_address> | <ipv6_address> ); ... };
      		server-names { <string>; ... };
      		zone-statistics ( full | terse | none | <boolean> );
      	};
      	zone <string> [ <class> ] {
      		type stub;
      		allow-query { <address_match_element>; ... };
      		allow-query-on { <address_match_element>; ... };
      		check-names ( fail | warn | ignore );
      		database <string>;
      		dialup ( notify | notify-passive | passive | refresh | <boolean> ); // deprecated
      		file <quoted_string>;
      		forward ( first | only );
      		forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };
      		masterfile-format ( raw | text );
      		masterfile-style ( full | relative );
      		max-records <integer>;
      		max-records-per-type <integer>;
      		max-refresh-time <integer>;
      		max-retry-time <integer>;
      		max-transfer-idle-in <integer>;
      		max-transfer-time-in <integer>;
      		max-types-per-name <integer>;
      		min-refresh-time <integer>;
      		min-retry-time <integer>;
      		min-transfer-rate-in <integer> <integer>;
      		multi-master <boolean>;
      		primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      		transfer-source ( <ipv4_address> | * );
      		transfer-source-v6 ( <ipv6_address> | * );
      		zone-statistics ( full | terse | none | <boolean> );
      	};

      	zone-statistics ( full | terse | none | <boolean> );
      }; // may occur multiple times

  Blocks: topmost

  Tags: view

  Allows a name server to answer a DNS query differently depending on who is asking.

    view view_name [ class ] {
        match-clients { address_match_list } ;
        match-destinations { address_match_list } ;
        match-recursive-only <boolean> ;
      [ view_option ; ... ]
      [ zone_statement ; ... ]
    } ;

### 8.2.31. `view` Block Definition and Usage

The `view` statement is a powerful feature of BIND 9 that lets a name server answer a DNS query differently depending on who is asking. It is particularly useful for implementing split DNS setups without having to run multiple servers.

match-clients

  Grammar: `match-clients { <address_match_element>; ... };`

  Blocks: view

  Tags: view

  Specifies a view of DNS namespace for a given subset of client IP addresses.

match-destinations

  Grammar: `match-destinations { <address_match_element>; ... };`

  Blocks: view

  Tags: view

  Specifies a view of DNS namespace for a given subset of destination IP addresses.

  Each `view` statement defines a view of the DNS namespace that is seen by a subset of clients. A client matches a view if its source IP address matches the address_match_list of the view’s `match-clients` clause, and its destination IP address matches the address_match_list of the view’s `match-destinations` clause. If not specified, both `match-clients` and `match-destinations` default to matching all addresses. In addition to checking IP addresses, `match-clients` and `match-destinations` can also take the name of a TSIG `key`, which provides a mechanism for the client to select the view.

match-recursive-only

  Grammar: `match-recursive-only <boolean>;`

  Blocks: view

  Tags: view

  Specifies that only recursive requests can match this view of the DNS namespace.

  A view can also be specified as `match-recursive-only`, which means that only recursive requests from matching clients match that view. The order of the `view` statements is significant; a client request is resolved in the context of the first `view` that it matches.

Zones defined within a `view` statement are only accessible to clients that match the `view`. By defining a zone of the same name in multiple views, different zone data can be given to different clients: for example, “internal” and “external” clients in a split DNS setup.

Many of the options given in the `options` statement can also be used within a `view` statement, and then apply only when resolving queries with that view. When no view-specific value is given, the value in the `options` statement is used as a default. Also, zone options can have default values specified in the `view` statement; these view-specific defaults take precedence over those in the `options` statement.

Views are class-specific. If no class is given, class IN is assumed. Note that all non-IN views must contain a hint zone, since only the IN class has compiled-in default hints.

If there are no `view` statements in the config file, a default view that matches any client is automatically created in class IN. Any `zone` statements specified on the top level of the configuration file are considered to be part of this default view, and the `options` statement applies to the default view. If any explicit `view` statements are present, all `zone` statements must occur inside `view` statements.

Here is an example of a typical split DNS setup implemented using `view` statements:

    view "internal" {
          // This should match our internal networks.
          match-clients { 10.0.0.0/8; };

          // Provide recursive service to internal
          // clients only.
          recursion yes;

          // Provide a complete view of the example.com
          // zone including addresses of internal hosts.
          zone "example.com" {
            type primary;
            file "example-internal.db";
          };
    };

    view "external" {
          // Match all clients not matched by the
          // previous view.
          match-clients { any; };

          // Refuse recursive service to external clients.
          recursion no;

          // Provide a restricted view of the example.com
          // zone containing only publicly accessible hosts.
          zone "example.com" {
           type primary;
           file "example-external.db";
          };
    };

### 8.2.32. `zone` Block Grammar

zone

  Blocks: topmost, view

  Tags: zone

  Specifies the zone in a BIND 9 configuration.

### 8.2.33. `zone` Block Definition and Usage

#### 8.2.33.1. Zone Types

type

  Blocks: zone (forward, hint, mirror, primary, redirect, secondary, static-stub, stub)

  Tags: zone

  Specifies the kind of zone in a given configuration.

  The `type` keyword is required for the `zone` configuration unless it is an `in-view` configuration. Its acceptable values are: `primary` (or `master`), `secondary` (or `slave`), `mirror`, `hint`, `stub`, `static-stub`, `forward`, or `redirect`.

type primary

  Grammar:

      zone <string> [ <class> ] {
      	type primary;
      	allow-query { <address_match_element>; ... };
      	allow-query-on { <address_match_element>; ... };
      	allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_element>; ... };
      	allow-update { <address_match_element>; ... };
      	also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      	check-dup-records ( fail | warn | ignore );
      	check-integrity <boolean>;
      	check-mx ( fail | warn | ignore );
      	check-mx-cname ( fail | warn | ignore );
      	check-names ( fail | warn | ignore );
      	check-sibling <boolean>;
      	check-spf ( warn | ignore );
      	check-srv-cname ( fail | warn | ignore );
      	check-svcb <boolean>;
      	check-wildcard <boolean>;
      	checkds ( explicit | <boolean> );
      	database <string>;
      	dialup ( notify | notify-passive | passive | refresh | <boolean> ); // deprecated
      	dlz <string>;
      	dnskey-sig-validity <integer>; // obsolete
      	dnssec-dnskey-kskonly <boolean>; // obsolete
      	dnssec-loadkeys-interval <integer>;
      	dnssec-policy <string>;
      	dnssec-secure-to-insecure <boolean>; // obsolete
      	dnssec-update-mode ( maintain | no-resign ); // obsolete
      	file <quoted_string>;
      	forward ( first | only );
      	forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };
      	inline-signing <boolean>;
      	ixfr-from-differences <boolean>;
      	journal <quoted_string>;
      	key-directory <quoted_string>;
      	masterfile-format ( raw | text );
      	masterfile-style ( full | relative );
      	max-ixfr-ratio ( unlimited | <percentage> );
      	max-journal-size ( default | unlimited | <sizeval> );
      	max-records <integer>;
      	max-records-per-type <integer>;
      	max-transfer-idle-out <integer>;
      	max-transfer-time-out <integer>;
      	max-types-per-name <integer>;
      	max-zone-ttl ( unlimited | <duration> ); // deprecated
      	notify ( explicit | master-only | primary-only | <boolean> );
      	notify-defer <integer>;
      	notify-delay <integer>;
      	notify-source ( <ipv4_address> | * );
      	notify-source-v6 ( <ipv6_address> | * );
      	notify-to-soa <boolean>;
      	nsec3-test-zone <boolean>; // test only
      	parental-agents [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      	parental-source ( <ipv4_address> | * );
      	parental-source-v6 ( <ipv6_address> | * );
      	serial-update-method ( date | increment | unixtime );
      	sig-signing-nodes <integer>;
      	sig-signing-signatures <integer>;
      	sig-signing-type <integer>;
      	sig-validity-interval <integer> [ <integer> ]; // obsolete
      	update-check-ksk <boolean>; // obsolete
      	update-policy ( local | { ( deny | grant ) <string> ( 6to4-self | external | krb5-self | krb5-selfsub | krb5-subdomain | krb5-subdomain-self-rhs | ms-self | ms-selfsub | ms-subdomain | ms-subdomain-self-rhs | name | self | selfsub | selfwild | subdomain | tcp-self | wildcard | zonesub ) [ <string> ] <rrtypelist>; ... } );
      	zero-no-soa-ttl <boolean>;
      	zone-statistics ( full | terse | none | <boolean> );
      };

  Blocks: zone, view.zone

  Tags: zone

  Contains the main copy of the data for a zone.

  A primary zone has a master copy of the data for the zone and is able to provide authoritative answers for it. Type `master` is a synonym for `primary`.

type secondary

  Grammar:

      zone <string> [ <class> ] {
      	type secondary;
      	allow-notify { <address_match_element>; ... };
      	allow-query { <address_match_element>; ... };
      	allow-query-on { <address_match_element>; ... };
      	allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_element>; ... };
      	allow-update-forwarding { <address_match_element>; ... };
      	also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      	check-names ( fail | warn | ignore );
      	checkds ( explicit | <boolean> );
      	database <string>;
      	dialup ( notify | notify-passive | passive | refresh | <boolean> ); // deprecated
      	dlz <string>;
      	dnskey-sig-validity <integer>; // obsolete
      	dnssec-dnskey-kskonly <boolean>; // obsolete
      	dnssec-loadkeys-interval <integer>;
      	dnssec-policy <string>;
      	dnssec-update-mode ( maintain | no-resign ); // obsolete
      	file <quoted_string>;
      	forward ( first | only );
      	forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };
      	inline-signing <boolean>;
      	ixfr-from-differences <boolean>;
      	journal <quoted_string>;
      	key-directory <quoted_string>;
      	masterfile-format ( raw | text );
      	masterfile-style ( full | relative );
      	max-ixfr-ratio ( unlimited | <percentage> );
      	max-journal-size ( default | unlimited | <sizeval> );
      	max-records <integer>;
      	max-records-per-type <integer>;
      	max-refresh-time <integer>;
      	max-retry-time <integer>;
      	max-transfer-idle-in <integer>;
      	max-transfer-idle-out <integer>;
      	max-transfer-time-in <integer>;
      	max-transfer-time-out <integer>;
      	max-types-per-name <integer>;
      	min-refresh-time <integer>;
      	min-retry-time <integer>;
      	min-transfer-rate-in <integer> <integer>;
      	multi-master <boolean>;
      	notify ( explicit | master-only | primary-only | <boolean> );
      	notify-defer <integer>;
      	notify-delay <integer>;
      	notify-source ( <ipv4_address> | * );
      	notify-source-v6 ( <ipv6_address> | * );
      	notify-to-soa <boolean>;
      	nsec3-test-zone <boolean>; // test only
      	parental-agents [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      	parental-source ( <ipv4_address> | * );
      	parental-source-v6 ( <ipv6_address> | * );
      	primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      	request-expire <boolean>;
      	request-ixfr <boolean>;
      	sig-signing-nodes <integer>;
      	sig-signing-signatures <integer>;
      	sig-signing-type <integer>;
      	sig-validity-interval <integer> [ <integer> ]; // obsolete
      	transfer-source ( <ipv4_address> | * );
      	transfer-source-v6 ( <ipv6_address> | * );
      	try-tcp-refresh <boolean>;
      	update-check-ksk <boolean>; // obsolete
      	zero-no-soa-ttl <boolean>;
      	zone-statistics ( full | terse | none | <boolean> );
      };

  Blocks: zone, view.zone

  Tags: zone

  Contains a duplicate of the data for a zone that has been transferred from a primary server.

  A secondary zone is a replica of a primary zone. Type `slave` is a synonym for `secondary`. The `primaries` list specifies one or more IP addresses of primary servers that the secondary contacts to update its copy of the zone.

  A zone may refresh on timer or on receipt of a notify. If a valid notify is received where the notify carries a serial number larger than the one in the SOA currently served, then the secondary will schedule a zone refresh.

  A notify is considered valid if the sender is one of the servers in the NS RRset for the zone, has been explicitly allowed using an `allow-notify` clause, or is from an address listed in the primary servers clause.

  If no notifies have been received, the server will try to refresh the zone. The REFRESH field in the SOA record determines how long after the last zone update it should query the primaries for the SOA record. Again, if the SOA record contains a serial number larger than the one in the SOA currently served, a zone refresh is scheduled. If a notify is received while a refresh is in progress, the serial number of the notify is checked and if it is larger, another refresh for the zone is queued. There will at most be one zone refresh queued.

  The primary servers are queried in turn, `named` will move on to the next server in the list if either it is unable to get a valid response from the server it is currently querying, or the primary being queried returns the same or smaller SOA than the secondary is currently serving. On the first SOA received that has a serial bigger than the one currently served, `named` will initiate a zone transfer with that server. Once the zone transfer has been received and the zone has been updated, then this zone refresh is complete, and no other servers are tried.

  When receiving a notify, `named` does not first query the sender of the notify. It will continue with the next server in the list that transferred the zone, skipping over unreachable servers. A primary is considered unreachable if the secondary cannot get a response from the server. This state will be cached for 10 minutes, or until a notify is received from that address.

  Furthermore, a zone is refreshed when the secondary server is restarted, or when a `rndc refresh` command is received.

  If a file is specified, then the replica is written to this file whenever the zone is changed, and reloaded from this file on a server restart. Use of a file is recommended, since it often speeds server startup and eliminates a needless waste of bandwidth. Note that for large numbers (in the tens or hundreds of thousands) of zones per server, it is best to use a two-level naming scheme for zone filenames. For example, a secondary server for the zone `example.com` might place the zone contents into a file called `ex/example.com`, where `ex/` is just the first two letters of the zone name. (Most operating systems behave very slowly if there are 100,000 files in a single directory.)

type mirror

  Grammar:

      zone <string> [ <class> ] {
      	type mirror;
      	allow-notify { <address_match_element>; ... };
      	allow-query { <address_match_element>; ... };
      	allow-query-on { <address_match_element>; ... };
      	allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_element>; ... };
      	allow-update-forwarding { <address_match_element>; ... };
      	also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      	check-names ( fail | warn | ignore );
      	database <string>;
      	file <quoted_string>;
      	ixfr-from-differences <boolean>;
      	journal <quoted_string>;
      	masterfile-format ( raw | text );
      	masterfile-style ( full | relative );
      	max-ixfr-ratio ( unlimited | <percentage> );
      	max-journal-size ( default | unlimited | <sizeval> );
      	max-records <integer>;
      	max-records-per-type <integer>;
      	max-refresh-time <integer>;
      	max-retry-time <integer>;
      	max-transfer-idle-in <integer>;
      	max-transfer-idle-out <integer>;
      	max-transfer-time-in <integer>;
      	max-transfer-time-out <integer>;
      	max-types-per-name <integer>;
      	min-refresh-time <integer>;
      	min-retry-time <integer>;
      	min-transfer-rate-in <integer> <integer>;
      	multi-master <boolean>;
      	notify ( explicit | master-only | primary-only | <boolean> );
      	notify-defer <integer>;
      	notify-delay <integer>;
      	notify-source ( <ipv4_address> | * );
      	notify-source-v6 ( <ipv6_address> | * );
      	primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      	request-expire <boolean>;
      	request-ixfr <boolean>;
      	transfer-source ( <ipv4_address> | * );
      	transfer-source-v6 ( <ipv6_address> | * );
      	try-tcp-refresh <boolean>;
      	zero-no-soa-ttl <boolean>;
      	zone-statistics ( full | terse | none | <boolean> );
      };

  Blocks: zone, view.zone

  Tags: zone

  Contains a DNSSEC-validated duplicate of the main data for a zone.

  A mirror zone is similar to a zone of `type secondary`, except its data is subject to DNSSEC validation before being used in answers. Validation is applied to the entire zone during the zone transfer process, and again when the zone file is loaded from disk upon restarting `named`. If validation of a new version of a mirror zone fails, a retransfer is scheduled; in the meantime, the most recent correctly validated version of that zone is used until it either expires or a newer version validates correctly. If no usable zone data is available for a mirror zone, due to either transfer failure or expiration, traditional DNS recursion is used to look up the answers instead. Mirror zones cannot be used in a view that does not have recursion enabled.

  Answers coming from a mirror zone look almost exactly like answers from a zone of `type secondary`, with the notable exceptions that the AA bit (“authoritative answer”) is not set, and the AD bit (“authenticated data”) is.

  Mirror zones are intended to be used to set up a fast local copy of the root zone (see RFC 8806). A default list of primary servers for the IANA root zone is built into `named`, so its mirroring can be enabled using the following configuration:

      zone "." {
          type mirror;
      };

  Mirror zone validation always happens for the entire zone contents. This ensures that each version of the zone used by the resolver is fully self-consistent with respect to DNSSEC. For incoming mirror zone IXFRs, every revision of the zone contained in the IXFR sequence is validated independently, in the order in which the zone revisions appear on the wire. For this reason, it might be useful to force use of AXFR for mirror zones by setting `request-ixfr no;` for the relevant zone (or view). Other, more efficient zone verification methods may be added in the future.

  To make mirror zone contents persist between `named` restarts, use the `file` option.

  Mirroring a zone other than root requires an explicit list of primary servers to be provided using the `primaries` option (see `primaries` for details), and a key-signing key (KSK) for the specified zone to be explicitly configured as a trust anchor (see `trust-anchors`).

  When configuring NOTIFY for a mirror zone, only `notify no;` and `notify explicit;` can be used at the zone level; any other `notify` setting at the zone level is a configuration error. Using any other `notify` setting at the `options` or `view` level causes that setting to be overridden with `notify explicit;` for the mirror zone. The global default for the `notify` option is `yes`, so mirror zones are by default configured with `notify explicit;`.

  Outgoing transfers of mirror zones are disabled by default but may be enabled using `allow-transfer`.

  Note

  Use of this zone type with any zone other than the root should be considered experimental and may cause performance issues, especially for zones that are large and/or frequently updated.

type hint

  Grammar:

      zone <string> [ <class> ] {
      	type hint;
      	check-names ( fail | warn | ignore );
      	file <quoted_string>;
      };

  Blocks: zone, view.zone

  Tags: zone

  Contains the initial set of root name servers to be used at BIND 9 startup.

  The initial set of root name servers is specified using a hint zone. When the server starts, it uses the root hints to find a root name server and get the most recent list of root name servers. If no hint zone is specified for class IN, the server uses a compiled-in default set of root servers hints. Classes other than IN have no built-in default hints.

type stub

  Grammar:

      zone <string> [ <class> ] {
      	type stub;
      	allow-query { <address_match_element>; ... };
      	allow-query-on { <address_match_element>; ... };
      	check-names ( fail | warn | ignore );
      	database <string>;
      	dialup ( notify | notify-passive | passive | refresh | <boolean> ); // deprecated
      	file <quoted_string>;
      	forward ( first | only );
      	forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };
      	masterfile-format ( raw | text );
      	masterfile-style ( full | relative );
      	max-records <integer>;
      	max-records-per-type <integer>;
      	max-refresh-time <integer>;
      	max-retry-time <integer>;
      	max-transfer-idle-in <integer>;
      	max-transfer-time-in <integer>;
      	max-types-per-name <integer>;
      	min-refresh-time <integer>;
      	min-retry-time <integer>;
      	min-transfer-rate-in <integer> <integer>;
      	multi-master <boolean>;
      	primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      	transfer-source ( <ipv4_address> | * );
      	transfer-source-v6 ( <ipv6_address> | * );
      	zone-statistics ( full | terse | none | <boolean> );
      };

  Blocks: zone, view.zone

  Tags: zone

  Contains a duplicate of the NS records of a primary zone.

  A stub zone is similar to a secondary zone, except that it replicates only the NS records of a primary zone instead of the entire zone. Stub zones are not a standard part of the DNS; they are a feature specific to the BIND implementation.

  Stub zones can be used to eliminate the need for a glue NS record in a parent zone, at the expense of maintaining a stub zone entry and a set of name server addresses in `named.conf`. This usage is not recommended for new configurations, and BIND 9 supports it only in a limited way. If a BIND 9 primary, serving a parent zone, has child stub zones configured, all the secondary servers for the parent zone also need to have the same child stub zones configured.

  Stub zones can also be used as a way to force the resolution of a given domain to use a particular set of authoritative servers. For example, the caching name servers on a private network using RFC 1918 addressing may be configured with stub zones for `10.in-addr.arpa` to use a set of internal name servers as the authoritative servers for that domain.

type static-stub

  Grammar:

      zone <string> [ <class> ] {
      	type static-stub;
      	allow-query { <address_match_element>; ... };
      	allow-query-on { <address_match_element>; ... };
      	forward ( first | only );
      	forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };
      	max-records <integer>;
      	max-records-per-type <integer>;
      	max-types-per-name <integer>;
      	server-addresses { ( <ipv4_address> | <ipv6_address> ); ... };
      	server-names { <string>; ... };
      	zone-statistics ( full | terse | none | <boolean> );
      };

  Blocks: zone, view.zone

  Tags: zone

  Contains a duplicate of the NS records of a primary zone, but statically configured rather than transferred from a primary server.

  A static-stub zone is similar to a stub zone, with the following exceptions: the zone data is statically configured, rather than transferred from a primary server; and when recursion is necessary for a query that matches a static-stub zone, the locally configured data (name server names and glue addresses) is always used, even if different authoritative information is cached.

  Zone data is configured via the `server-addresses` and `server-names` zone options.

  The zone data is maintained in the form of NS and (if necessary) glue A or AAAA RRs internally, which can be seen by dumping zone databases with `rndc dumpdb -all`. The configured RRs are considered local configuration parameters rather than public data. Non-recursive queries (i.e., those with the RD bit off) to a static-stub zone are therefore prohibited and are responded to with REFUSED.

  Since the data is statically configured, no zone maintenance action takes place for a static-stub zone. For example, there is no periodic refresh attempt, and an incoming notify message is rejected with an rcode of NOTAUTH.

  Each static-stub zone is configured with internally generated NS and (if necessary) glue A or AAAA RRs.

type forward

  Grammar:

      zone <string> [ <class> ] {
      	type forward;
      	forward ( first | only );
      	forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };
      };

  Blocks: zone, view.zone

  Tags: zone

  Contains forwarding statements that apply to queries within a given domain.

  A forward zone is a way to configure forwarding on a per-domain basis. A `zone` statement of type `forward` can contain a `forward` and/or `forwarders` statement, which applies to queries within the domain given by the zone name. If no `forwarders` statement is present, or an empty list for `forwarders` is given, then no forwarding is done for the domain, canceling the effects of any forwarders in the `options` statement. Thus, to use this type of zone to change the behavior of the global `forward` option (that is, “forward first” to, then “forward only”, or vice versa), but use the same servers as set globally, re-specify the global forwarders.

type redirect

  Grammar:

      zone <string> [ <class> ] {
      	type redirect;
      	allow-query { <address_match_element>; ... };
      	allow-query-on { <address_match_element>; ... };
      	dlz <string>;
      	file <quoted_string>;
      	masterfile-format ( raw | text );
      	masterfile-style ( full | relative );
      	max-records <integer>;
      	max-records-per-type <integer>;
      	max-types-per-name <integer>;
      	max-zone-ttl ( unlimited | <duration> ); // deprecated
      	primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <server-list> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
      	zone-statistics ( full | terse | none | <boolean> );
      };

  Blocks: zone, view.zone

  Tags: zone

  Contains information to answer queries when normal resolution would return NXDOMAIN.

  Redirect zones are used to provide answers to queries when normal resolution would result in NXDOMAIN being returned. Only one redirect zone is supported per view. `allow-query` can be used to restrict which clients see these answers.

  If the client has requested DNSSEC records (DO=1) and the NXDOMAIN response is signed, no substitution occurs.

  To redirect all NXDOMAIN responses to 100.100.100.2 and 2001:ffff:ffff::100.100.100.2, configure a type `redirect` zone named “.”, with the zone file containing wildcard records that point to the desired addresses: `*. IN A 100.100.100.2` and `*. IN AAAA 2001:ffff:ffff::100.100.100.2`.

  As another example, to redirect all Spanish names (under .ES), use similar entries but with the names `*.ES.` instead of `*.`. To redirect all commercial Spanish names (under COM.ES), use wildcard entries called `*.COM.ES.`.

  Note that the redirect zone supports all possible types; it is not limited to A and AAAA records.

  If a redirect zone is configured with a `primaries` option, then it is transferred in as if it were a secondary zone. Otherwise, it is loaded from a file as if it were a primary zone.

  Because redirect zones are not referenced directly by name, they are not kept in the zone lookup table with normal primary and secondary zones. To reload a redirect zone, use `rndc reload -redirect`; to retransfer a redirect zone configured as a secondary, use `rndc retransfer -redirect`. When using `rndc reload` without specifying a zone name, redirect zones are reloaded along with other zones.

in-view

  Grammar zone, view.zone:

      zone <string> [ <class> ] {
      	in-view <string>;
      };

  Grammar zone (in-view): `in-view <string>;`

  Blocks: zone, zone (in-view), view.zone

  Tags: view, zone

  Specifies the view in which a given zone is defined.

  When using multiple views, a `type primary` or `type secondary` zone configured in one view can be referenced in a subsequent view. This allows both views to use the same zone without the overhead of loading it more than once. This is configured using a `zone` statement, with an `in-view` option specifying the view in which the zone is defined. A `zone` statement containing `in-view` does not need to specify a type, since that is part of the zone definition in the other view.

  See Multiple Views for more information.

#### 8.2.33.2. Class

The zone’s name may optionally be followed by a class. If a class is not specified, class `IN` (for `Internet`) is assumed. This is correct for the vast majority of cases.

The `hesiod` class is named for an information service from MIT’s Project Athena. It was used to share information about various systems databases, such as users, groups, printers, and so on. The keyword `HS` is a synonym for hesiod.

Another MIT development is Chaosnet, a LAN protocol created in the mid-1970s. Zone data for it can be specified with the `CHAOS` class.

#### 8.2.33.3. Zone Options

`allow-notify`

  See the description of `allow-notify` in Access Control.

`allow-query`

  See the description of `allow-query` in Access Control.

`allow-query-on`

  See the description of `allow-query-on` in Access Control.

`allow-transfer`

  See the description of `allow-transfer` in Access Control.

`allow-update`

  See the description of `allow-update` in Access Control.

`update-policy`

  This specifies a “Simple Secure Update” policy. See Dynamic Update Policies.

`allow-update-forwarding`

  See the description of `allow-update-forwarding` in Access Control.

`also-notify`

  This option is only meaningful if `notify` is active for this zone. The set of machines that receive a `DNS NOTIFY` message for this zone is made up of all the listed name servers (other than the primary) for the zone, plus any IP addresses specified with `also-notify`. A port may be specified with each `also-notify` address to send the notify messages to a port other than the default of 53. A TSIG key may also be specified to cause the `NOTIFY` to be signed by the given key. `also-notify` is not meaningful for stub zones. The default is the empty list.

`check-names`

  This option is used to restrict the character set and syntax of certain domain names in primary files and/or DNS responses received from the network. The default varies according to zone type. For `primary` zones the default is `fail`; for `secondary` zones the default is `warn`. It is not implemented for `hint` zones.

`check-mx`

  See the description of `check-mx` in Boolean Options.

`check-spf`

  See the description of `check-spf` in Boolean Options.

`check-wildcard`

  See the description of `check-wildcard` in Boolean Options.

`check-integrity`

  See the description of `check-integrity` in Boolean Options.

`check-sibling`

  See the description of `check-sibling` in Boolean Options.

`zero-no-soa-ttl`

  See the description of `zero-no-soa-ttl` in Boolean Options.

`update-check-ksk`

  See the description of `update-check-ksk` in Boolean Options.

`dnssec-loadkeys-interval`

  See the description of `dnssec-loadkeys-interval` in `options`.

`dnssec-update-mode`

  See the description of `dnssec-update-mode` in `options`.

`dnssec-dnskey-kskonly`

  See the description of `dnssec-dnskey-kskonly` in Boolean Options.

`try-tcp-refresh`

  See the description of `try-tcp-refresh` in Boolean Options.

database

  Grammar: `database <string>;`

  Blocks: dlz, zone (mirror, primary, secondary, stub), view.dlz

  Tags: zone

  Specifies the type of database to be used to store zone data.

  This specifies the type of database to be used to store the zone data. The string following the `database` keyword is interpreted as a list of whitespace-delimited words. The first word identifies the database type, and any subsequent words are passed as arguments to the database to be interpreted in a way specific to the database type.

  The default is `rbt`, BIND 9’s native in-memory red-black tree database. This database does not take arguments.

  Other values are possible if additional database drivers have been linked into the server. Some sample drivers are included with the distribution but none are linked in by default.

`dialup`

  See the description of `dialup` in Boolean Options.

file

  Grammar logging.channel: `file <quoted_string> [ versions ( unlimited | <integer> ) ] [ size <size> ] [ suffix ( increment | timestamp ) ];`

  Grammar zone (hint, mirror, primary, redirect, secondary, stub): `file <quoted_string>;`

  Blocks: zone (hint, mirror, primary, redirect, secondary, stub), logging.channel

  Tags: zone

  Specifies the zone’s filename.

  This sets the zone’s filename. In `primary`, `hint`, and `redirect` zones which do not have `primaries` defined, zone data is loaded from this file. In `secondary`, `mirror`, `stub`, and `redirect` zones which do have `primaries` defined, zone data is retrieved from another server and saved in this file. This option is not applicable to other zone types.

`forward`

  This option is only meaningful if the zone has a forwarders list. The `only` value causes the lookup to fail after trying the forwarders and getting no answer, while `first` allows a normal lookup to be tried.

`forwarders`

  This is used to override the list of global forwarders. If it is not specified in a zone of type `forward`, no forwarding is done for the zone and the global options are not used.

journal

  Grammar: `journal <quoted_string>;`

  Blocks: zone (mirror, primary, secondary)

  Tags: zone

  Allows the default journal’s filename to be overridden.

  This allows the default journal’s filename to be overridden. The default is the zone’s filename with “`.jnl`” appended. This is applicable to `primary` and `secondary` zones.

`max-ixfr-ratio`

  See the description of `max-ixfr-ratio` in `options`.

`max-journal-size`

  See the description of `max-journal-size` in Server Resource Limits.

`max-records`

  See the description of `max-records` in Server Resource Limits.

`min-transfer-rate-in`

  See the description of `min-transfer-rate-in` in Zone Transfers.

`max-transfer-time-in`

  See the description of `max-transfer-time-in` in Zone Transfers.

`max-transfer-idle-in`

  See the description of `max-transfer-idle-in` in Zone Transfers.

`max-transfer-time-out`

  See the description of `max-transfer-time-out` in Zone Transfers.

`max-transfer-idle-out`

  See the description of `max-transfer-idle-out` in Zone Transfers.

`notify`

  See the description of `notify` in Boolean Options.

`notify-delay`

  See the description of `notify-delay` in Tuning.

`notify-to-soa`

  See the description of `notify-to-soa` in Boolean Options.

`parental-agents`

  This option is only meaningful if the zone is DNSSEC signed. When performing a key rollover, BIND will query the parental agents to see if the new DS is actually published before withdrawing the old DNSSEC key.

`primaries`

  For secondary zones, these are the name servers to request zone transfers from.

`zone-statistics`

  See the description of `zone-statistics` in `options`.

server-addresses

  Grammar: `server-addresses { ( <ipv4_address> | <ipv6_address> ); ... };`

  Blocks: zone (static-stub)

  Tags: query, zone

  Specifies a list of IP addresses to which queries should be sent in recursive resolution for a static-stub zone.

  This option is only meaningful for static-stub zones. This is a list of IP addresses to which queries should be sent in recursive resolution for the zone. A non-empty list for this option internally configures the apex NS RR with associated glue A or AAAA RRs.

  For example, if “example.com” is configured as a static-stub zone with 192.0.2.1 and 2001:db8::1234 in a `server-addresses` option, the following RRs are internally configured:

      example.com. NS example.com.
      example.com. A 192.0.2.1
      example.com. AAAA 2001:db8::1234

  These records are used internally to resolve names under the static-stub zone. For instance, if the server receives a query for “www.example.com” with the RD bit on, the server initiates recursive resolution and sends queries to 192.0.2.1 and/or 2001:db8::1234.

server-names

  Grammar: `server-names { <string>; ... };`

  Blocks: zone (static-stub)

  Tags: zone

  Specifies a list of domain names of name servers that act as authoritative servers of a static-stub zone.

  This option is only meaningful for static-stub zones. This is a list of domain names of name servers that act as authoritative servers of the static-stub zone. These names are resolved to IP addresses when `named` needs to send queries to these servers. For this supplemental resolution to be successful, these names must not be a subdomain of the origin name of the static-stub zone. That is, when “example.net” is the origin of a static-stub zone, “ns.example” and “master.example.com” can be specified in the `server-names` option, but “ns.example.net” cannot; it is rejected by the configuration parser.

  A non-empty list for this option internally configures the apex NS RR with the specified names. For example, if “example.com” is configured as a static-stub zone with “ns1.example.net” and “ns2.example.net” in a `server-names` option, the following RRs are internally configured:

      example.com. NS ns1.example.net.
      example.com. NS ns2.example.net.

  These records are used internally to resolve names under the static-stub zone. For instance, if the server receives a query for “www.example.com” with the RD bit on, the server initiates recursive resolution, resolves “ns1.example.net” and/or “ns2.example.net” to IP addresses, and then sends queries to one or more of these addresses.

`sig-validity-interval`

  See the description of `sig-validity-interval` in Tuning.

`sig-signing-nodes`

  See the description of `sig-signing-nodes` in Tuning.

`sig-signing-signatures`

  See the description of `sig-signing-signatures` in Tuning.

`sig-signing-type`

  See the description of `sig-signing-type` in Tuning.

`transfer-source`

  See the description of `transfer-source` in Zone Transfers.

`transfer-source-v6`

  See the description of `transfer-source-v6` in Zone Transfers.

`notify-source`

  See the description of `notify-source` in Zone Transfers.

`notify-source-v6`

  See the description of `notify-source-v6` in Zone Transfers.

`min-refresh-time`; `max-refresh-time`; `min-retry-time`; `max-retry-time`

  See the descriptions in Tuning.

`ixfr-from-differences`

  See the description of `ixfr-from-differences` in Boolean Options. (Note that the `ixfr-from-differences` choices of `primary` and `secondary` are not available at the zone level.)

`key-directory`

  See the description of `key-directory` in `options`.

`serial-update-method`

  See the description of `serial-update-method` in `options`.

inline-signing

  Grammar: `inline-signing <boolean>;`

  Blocks: dnssec-policy, zone (primary, secondary)

  Tags: dnssec, zone

  Specifies whether BIND 9 maintains a separate signed version of a zone.

  The use of inline signing is determined by the `dnssec-policy` for the zone. If `inline-signing` is explicitly set to `yes` or `no` in `zone`, it overrides any value from `dnssec-policy`.

`multi-master`

  See the description of `multi-master` in Boolean Options.

`masterfile-format`

  See the description of `masterfile-format` in Tuning.

`max-zone-ttl`

  See the description of `max-zone-ttl` in `options`. The use of this option in `zone` blocks is deprecated and will be rendered non-operational in a future release.

#### 8.2.33.4. Dynamic Update Policies

BIND 9 supports two methods of granting clients the right to perform dynamic updates to a zone:

- `allow-update` - a simple access control list

- `update-policy` - fine-grained access control

In both cases, BIND 9 writes the updates to the zone’s filename set in `file`.

In the case of a DNSSEC zone where `inline-signing` is disabled, DNSSEC records are also written to the zone’s filename.

> Note

> The zone file can no longer be manually updated while `named` is running; it is now necessary to perform `rndc freeze`, edit, and then perform `rndc thaw`. Comments and formatting in the zone file are lost when dynamic updates occur.

update-policy

  Grammar: `update-policy ( local | { ( deny | grant ) <string> ( 6to4-self | external | krb5-self | krb5-selfsub | krb5-subdomain | krb5-subdomain-self-rhs | ms-self | ms-selfsub | ms-subdomain | ms-subdomain-self-rhs | name | self | selfsub | selfwild | subdomain | tcp-self | wildcard | zonesub ) [ <string> ] <rrtypelist>; ... } );`

  Blocks: zone (primary)

  Tags: transfer

  Sets fine-grained rules to allow or deny dynamic updates (DDNS), based on requester identity, updated content, etc.

  The `update-policy` clause allows more fine-grained control over which updates are allowed. It specifies a set of rules, in which each rule either grants or denies permission for one or more names in the zone to be updated by one or more identities. Identity is determined by the key that signed the update request, using either TSIG or SIG(0). In most cases, `update-policy` rules only apply to key-based identities. There is no way to specify update permissions based on the client source address.

  `update-policy` rules are only meaningful for zones of `type primary`, and are not allowed in any other zone type. It is a configuration error to specify both `allow-update` and `update-policy` at the same time.

  A pre-defined `update-policy` rule can be switched on with the command `update-policy local;`. `named` automatically generates a TSIG session key when starting and stores it in a file; this key can then be used by local clients to update the zone while `named` is running. By default, the session key is stored in the file `/run/session.key`, the key name is “local-ddns”, and the key algorithm is HMAC-SHA256. These values are configurable with the `session-keyfile`, `session-keyname`, and `session-keyalg` options, respectively. A client running on the local system, if run with appropriate permissions, may read the session key from the key file and use it to sign update requests. The zone’s update policy is set to allow that key to change any record within the zone. Assuming the key name is “local-ddns”, this policy is equivalent to:

      update-policy { grant local-ddns zonesub any; };

  with the additional restriction that only clients connecting from the local system are permitted to send updates.

  Note that only one session key is generated by `named`; all zones configured to use `update-policy local` accept the same key.

  The command `nsupdate -l` implements this feature, sending requests to localhost and signing them using the key retrieved from the session key file.

  Other rule definitions look like this:

      ( grant | deny ) identity ruletype  name   types

  Each rule grants or denies privileges. Rules are checked in the order in which they are specified in the `update-policy` statement. Once a message has successfully matched a rule, the operation is immediately granted or denied, and no further rules are examined. There are 16 types of rules; the rule type is specified by the `ruletype` field, and the interpretation of other fields varies depending on the rule type.

  In general, a rule is matched when the key that signed an update request matches the `identity` field, the name of the record to be updated matches the `name` field (in the manner specified by the `ruletype` field), and the type of the record to be updated matches the `types` field. Details for each rule type are described below.

  The `identity` field must be set to a fully qualified domain name. In most cases, this represents the name of the TSIG or SIG(0) key that must be used to sign the update request. If the specified name is a wildcard, it is subject to DNS wildcard expansion, and the rule may apply to multiple identities. When a TKEY exchange has been used to create a shared secret, the identity of the key used to authenticate the TKEY exchange is used as the identity of the shared secret. Some rule types use identities matching the client’s Kerberos principal (e.g, `"host/machine@REALM"`) or Windows realm (`machine$@REALM`).

  The `name` field also specifies a fully qualified domain name. This often represents the name of the record to be updated. Interpretation of this field is dependent on rule type.

  If no `types` are explicitly specified, then a rule matches all types except RRSIG, NS, SOA, NSEC, and NSEC3. Types may be specified by name, including `ANY`; ANY matches all types except NSEC and NSEC3, which can never be updated. Note that when an attempt is made to delete all records associated with a name, the rules are checked for each existing record type.

  If the type is immediately followed by a number in parentheses, that number is the maximum number of records of that type permitted to exist in the RRset after an update has been applied. For example, `PTR(1)` indicates that only one PTR record is allowed. If an attempt is made to add two PTR records in an update, the second one is silently discarded. If a PTR record already exists, both new records are silently discarded.

  If type ANY is specified with a limit, then that limit applies to all types that are not otherwise specified. For example, `A PTR(1) ANY(2)` indicates that an unlimited number of A records can exist, but only one PTR record, and no more than two of any other type.

  Typical use with a rule `grant * tcp-self . PTR(1);` in the zone 2.0.192.IN-ADDR.ARPA looks like this:

      nsupdate -v <<EOF
      local 192.0.2.1
      del 1.2.0.192.IN-ADDR.ARPA PTR
      add 1.2.0.192.IN-ADDR.ARPA 0 PTR EXAMPLE.COM
      send
      EOF

  The ruletype field has 18 values: `name`, `subdomain`, `zonesub`, `wildcard`, `self`, `selfsub`, `selfwild`, `ms-self`, `ms-selfsub`, `ms-subdomain`, `ms-subdomain-self-rhs`, `krb5-self`, `krb5-selfsub`, `krb5-subdomain`, `krb5-subdomain-self-rhs`, `tcp-self`, `6to4-self`, and `external`.

  `name`

    With exact-match semantics, this rule matches when the name being updated is identical to the contents of the `name` field.

  `subdomain`

    This rule matches when the name being updated is a subdomain of, or identical to, the contents of the `name` field.

  `zonesub`

    This rule is similar to subdomain, except that it matches when the name being updated is a subdomain of the zone in which the `update-policy` statement appears. This obviates the need to type the zone name twice, and enables the use of a standard `update-policy` statement in multiple zones without modification. When this rule is used, the `name` field is omitted.

  `wildcard`

    The `name` field is subject to DNS wildcard expansion, and this rule matches when the name being updated is a valid expansion of the wildcard.

  `self`

    This rule matches when the name of the record being updated matches the contents of the `identity` field. The `name` field is ignored. To avoid confusion, it is recommended that this field be set to the same value as the `identity` field or to “.” The `self` rule type is most useful when allowing one key per name to update, where the key has the same name as the record to be updated. In this case, the `identity` field can be specified as `*` (asterisk).

  `selfsub`

    This rule is similar to `self`, except that subdomains of `self` can also be updated.

  `selfwild`

    This rule is similar to `self`, except that only subdomains of `self` can be updated.

  `ms-self`

    When a client sends an UPDATE using a Windows machine principal (for example, `machine$@REALM`), this rule allows records with the absolute name of `machine.REALM` to be updated.

    The realm to be matched is specified in the `identity` field.

    The `name` field has no effect on this rule; it should be set to “.” as a placeholder.

    For example, `grant EXAMPLE.COM ms-self . A AAAA` allows any machine with a valid principal in the realm `EXAMPLE.COM` to update its own address records.

  `ms-selfsub`

    This is similar to `ms-self`, except it also allows updates to any subdomain of the name specified in the Windows machine principal, not just to the name itself.

  `ms-subdomain`

    When a client sends an UPDATE using a Windows machine principal (for example, `machine$@REALM`), this rule allows any machine in the specified realm to update any record in the zone or in a specified subdomain of the zone.

    The realm to be matched is specified in the `identity` field.

    The `name` field specifies the subdomain that may be updated. If set to “.” or any other name at or above the zone apex, any name in the zone can be updated.

    For example, if `update-policy` for the zone “example.com” includes `grant EXAMPLE.COM ms-subdomain hosts.example.com. AA AAAA`, any machine with a valid principal in the realm `EXAMPLE.COM` is able to update address records at or below `hosts.example.com`.

  `ms-subdomain-self-rhs`

    This rule is similar to `ms-subdomain`, with an additional restriction that PTR and SRV target names must match the name of the machine identified in the principal.

  `krb5-self`

    When a client sends an UPDATE using a Kerberos machine principal (for example, `host/machine@REALM`), this rule allows records with the absolute name of `machine` to be updated, provided it has been authenticated by REALM. This is similar but not identical to `ms-self`, due to the `machine` part of the Kerberos principal being an absolute name instead of an unqualified name.

    The realm to be matched is specified in the `identity` field.

    The `name` field has no effect on this rule; it should be set to “.” as a placeholder.

    For example, `grant EXAMPLE.COM krb5-self . A AAAA` allows any machine with a valid principal in the realm `EXAMPLE.COM` to update its own address records.

  `krb5-selfsub`

    This is similar to `krb5-self`, except it also allows updates to any subdomain of the name specified in the `machine` part of the Kerberos principal, not just to the name itself.

  `krb5-subdomain`

    This rule is identical to `ms-subdomain`, except that it works with Kerberos machine principals (i.e., `host/machine@REALM`) rather than Windows machine principals.

  `krb5-subdomain-self-rhs`

    This rule is similar to `krb5-subdomain`, with an additional restriction that PTR and SRV target names must match the name of the machine identified in the principal.

  `tcp-self`

    This rule allows updates that have been sent via TCP and for which the standard mapping from the client’s IP address into the `in-addr.arpa` and `ip6.arpa` namespaces matches the name to be updated. The `identity` field must match that name. The `name` field should be set to “.”. Note that, since identity is based on the client’s IP address, it is not necessary for update request messages to be signed.

    Note

    It is theoretically possible to spoof these TCP sessions.

  `6to4-self`

    This allows the name matching a 6to4 IPv6 prefix, as specified in RFC 3056, to be updated by any TCP connection from either the 6to4 network or from the corresponding IPv4 address. This is intended to allow NS or DNAME RRsets to be added to the `ip6.arpa` reverse tree.

    The `identity` field must match the 6to4 prefix in `ip6.arpa`. The `name` field should be set to “.”. Note that, since identity is based on the client’s IP address, it is not necessary for update request messages to be signed.

    In addition, if specified for an `ip6.arpa` name outside of the `2.0.0.2.ip6.arpa` namespace, the corresponding /48 reverse name can be updated. For example, TCP/IPv6 connections from 2001:DB8:ED0C::/48 can update records at `C.0.D.E.8.B.D.0.1.0.0.2.ip6.arpa`.

    Note

    It is theoretically possible to spoof these TCP sessions.

  `external`

    This rule allows `named` to defer the decision of whether to allow a given update to an external daemon.

    The method of communicating with the daemon is specified in the `identity` field, the format of which is “`local:`path”, where “path” is the location of a Unix-domain socket. (Currently, “local” is the only supported mechanism.)

    Requests to the external daemon are sent over the Unix-domain socket as datagrams with the following format:

        Protocol version number (4 bytes, network byte order, currently 1)
        Request length (4 bytes, network byte order)
        Signer (null-terminated string)
        Name (null-terminated string)
        TCP source address (null-terminated string)
        Rdata type (null-terminated string)
        Key (null-terminated string)
        TKEY token length (4 bytes, network byte order)
        TKEY token (remainder of packet)

    The daemon replies with a four-byte value in network byte order, containing either 0 or 1; 0 indicates that the specified update is not permitted, and 1 indicates that it is.

    Warning

    The external daemon must not delay communication. This policy is evaluated synchronously; any wait period negatively affects `named` performance.

#### 8.2.33.5. Multiple Views

When multiple views are in use, a zone may be referenced by more than one of them. Often, the views contain different zones with the same name, allowing different clients to receive different answers for the same queries. At times, however, it is desirable for multiple views to contain identical zones. The `in-view` zone option provides an efficient way to do this; it allows a view to reference a zone that was defined in a previously configured view. For example:

    view internal {
        match-clients { 10/8; };

        zone example.com {
        type primary;
        file "example-external.db";
        };
    };

    view external {
        match-clients { any; };

        zone example.com {
        in-view internal;
        };
    };

An `in-view` option cannot refer to a view that is configured later in the configuration file.

A `zone` statement which uses the `in-view` option may not use any other options, with the exception of `forward` and `forwarders`. (These options control the behavior of the containing view, rather than change the zone object itself.)

Zone-level ACLs (e.g., allow-query, allow-transfer), and other configuration details of the zone, are all set in the view the referenced zone is defined in. Be careful to ensure that ACLs are wide enough for all views referencing the zone.

An `in-view` zone cannot be used as a response policy zone.

An `in-view` zone is not intended to reference a `forward` zone.

## 8.3. Statements

BIND 9 supports many hundreds of statements; finding the right statement to control a specific behavior or solve a particular problem can be a daunting task. To simplify the task for users, all statements have been assigned one or more tags. Tags are designed to group together statements that have broadly similar functionality; thus, for example, all statements that control the handling of queries or of zone transfers are respectively tagged under query and transfer.

DNSSEC Tag Statements are those that relate to or control DNSSEC.

Logging Tag Statements relate to or control logging, and typically only appear in a logging block.

Query Tag Statements relate to or control queries.

Security Tag Statements relate to or control security features.

Server Tag Statements relate to or control server behavior, and typically only appear in a server block.

Transfer Tag Statements relate to or control zone transfers.

View Tag Statements relate to or control view selection criteria, and typically only appear in a view block.

Zone Tag Statements relate to or control zone behavior, and typically only appear in a zone block.

Deprecated Tag Statements are those that are now deprecated, but are included here for historical reference.

The following table lists all statements permissible in `named.conf`, with their associated tags; the next section groups the statements by tag. Please note that these sections are a work in progress.

Statement | Description | Tags
--- | --- | ---
acl | Assigns a symbolic name to an address match list. | server
algorithm | Defines the algorithm to be used in a key clause. | security
all-per-second | Limits UDP responses of all kinds. | query
allow-new-zones | Controls the ability to add zones at runtime via `rndc addzone`. | server, zone
allow-notify | Defines an `address_match_list` that is allowed to send `NOTIFY` messages for the zone, in addition to addresses defined in the `primaries` option for the zone. | transfer
allow-proxy | Defines an `address_match_list` for the client addresses allowed to send PROXYv2 headers. | server
allow-proxy-on | Defines an `address_match_list` for the interface addresses allowed to accept PROXYv2 headers. The option is mostly intended for multi-homed configurations. | server
allow-query | Specifies which hosts (an IP address list) are allowed to send queries to this resolver. | query
allow-query-cache | Specifies which hosts (an IP address list) can access this server's cache and thus effectively controls recursion. | query
allow-query-cache-on | Specifies which hosts (from an IP address list) can access this server's cache. It is used on servers with multiple interfaces. | query
allow-query-on | Specifies which local addresses (an IP address list) are allowed to send queries to this resolver. This option is used in multi-homed configurations. | query
allow-recursion | Defines an `address_match_list` of clients that are allowed to perform recursive queries. | query
allow-recursion-on | Specifies which local addresses can accept recursive queries. | query, server
allow-transfer | Defines an `address_match_list` of hosts that are allowed to transfer the zone information from this server. | transfer
allow-update | Defines an `address_match_list` of hosts that are allowed to submit dynamic updates for primary zones. | transfer
allow-update-forwarding | Defines an `address_match_list` of hosts that are allowed to submit dynamic updates to a secondary server for transmission to a primary. | transfer
also-notify | Defines one or more hosts that are sent `NOTIFY` messages when zone changes occur. | transfer
answer-cookie | Controls whether COOKIE EDNS replies are sent in response to client queries. | query
attach-cache | Allows multiple views to share a single cache database. | view
auth-nxdomain | Controls whether BIND, acting as a resolver, provides authoritative NXDOMAIN (domain does not exist) answers. | query
automatic-interface-scan | Controls the automatic rescanning of network interfaces when addresses are added or removed. | server
avoid-v4-udp-ports | Specifies the range(s) of ports to be excluded from use as sources for UDP/IPv4 messages. | deprecated
avoid-v6-udp-ports | Specifies the range(s) of ports to be excluded from use as sources for UDP/IPv6 messages. | deprecated
bindkeys-file | Specifies the pathname of a file to override the built-in trusted keys provided by `named`. | dnssec
blackhole | Defines an `address_match_list` of hosts to ignore. The server will neither respond to queries from nor send queries to these addresses. | query
bogus | Allows a remote server to be ignored. | server
break-dnssec | Enables `dns64` synthesis even if the validated result would cause a DNSSEC validation failure. | query
buffered | Controls flushing of log messages. | logging
ca-file | Specifies the path to a file containing TLS certificates for trusted CA authorities, used to verify remote peer certificates. | server, security
catalog-zones | Configures catalog zones in `named.conf`. | zone
category | Specifies the type of data logged to a particular channel. | logging
cdnskey | Specifies whether a CDNSKEY record should be published during KSK rollover. | dnssec
cds-digest-types | Specifies the digest types to use for CDS resource records. | dnssec
cert-file | Specifies the path to a file containing the TLS certificate for a connection. | server, security
channel | Defines a stream of data that can be independently logged. | logging
check-dup-records | Checks primary zones for records that are treated as different by DNSSEC but are semantically equal in plain DNS. | dnssec, query
check-integrity | Performs post-load zone integrity checks on primary zones. | zone
check-mx | Checks whether an MX record appears to refer to an IP address. | zone
check-mx-cname | Sets the response to MX records that refer to CNAMEs. | zone
check-names | Restricts the character set and syntax of certain domain names in primary files and/or DNS responses received from the network. | query, server
check-sibling | Specifies whether to check for sibling glue when performing integrity checks. | zone
check-spf | Specifies whether to check for a TXT Sender Policy Framework record, if an SPF record is present. | zone
check-srv-cname | Sets the response to SRV records that refer to CNAMEs. | zone
check-svcb | Specifies whether to perform additional checks on SVCB records. | zone
check-wildcard | Checks for non-terminal wildcards. | zone
checkds | Controls whether `DS` queries are sent to parental agents. | dnssec
cipher-suites | Specifies a list of allowed cipher suites in the order of preference for TLSv1.3 only. | security
ciphers | Specifies a list of allowed ciphers in the order of preference for TLSv1.2 only. | security
clients | Specifies an access control list (ACL) of clients that are affected by a given `dns64` directive. | query
clients-per-query | Sets the initial minimum number of simultaneous recursive clients accepted by the server for any given query before the server drops additional clients. | server
controls | Specifies control channels to be used to manage the name server. | server
cookie-algorithm | Sets the algorithm to be used when generating a server cookie. | server
cookie-secret | Specifies a shared secret used for generating and verifying EDNS COOKIE options within an anycast cluster. | server
database | Specifies the type of database to be used to store zone data. | zone
deny-answer-addresses | Rejects A or AAAA records if the corresponding IPv4 or IPv6 addresses match a given `address_match_list`. | query
deny-answer-aliases | Rejects CNAME or DNAME records if the "alias" name matches a given list of `domain_name` elements. | query
dhparam-file | Specifies the path to a file containing Diffie-Hellman parameters, for enabling cipher suites. | server, security
dialup | Concentrates zone maintenance so that all transfers take place once every `heartbeat-interval`, ideally during a single call. | deprecated
directory | Sets the server's working directory. | server
disable-algorithms | Disables DNSSEC algorithms from a specified zone. | dnssec
disable-ds-digests | Disables DS digest types from a specified zone. | dnssec, zone
disable-empty-zone | Disables individual empty zones. | server, zone
dlz | Configures a Dynamically Loadable Zone (DLZ) database in `named.conf`. | zone
dns64 | Instructs `named` to return mapped IPv4 addresses to AAAA queries when there are no AAAA records. | query
dns64-contact | Specifies the name of the contact for `dns64` zones. | server
dns64-server | Specifies the name of the server for `dns64` zones. | server
dnskey-sig-validity |  | obsolete
dnskey-ttl | Specifies the time-to-live (TTL) for DNSKEY resource records. | dnssec
dnsrps-enable | Turns on the DNS Response Policy Service (DNSRPS) interface. | server, security
dnsrps-library | Specifies the path to the DNS Response Policy Service (DNSRPS) provider library. | server, security
dnsrps-options | Provides additional RPZ configuration settings, which are passed to the DNS Response Policy Service (DNSRPS) provider library. | server, security
dnssec-accept-expired | Instructs BIND 9 to accept expired DNSSEC signatures when validating. | dnssec
dnssec-dnskey-kskonly |  | obsolete
dnssec-loadkeys-interval | Sets the frequency of automatic checks of the DNSSEC key repository. | dnssec
dnssec-must-be-secure | Defines hierarchies that must or may not be secure (signed and validated). | deprecated
dnssec-policy | Defines a key and signing policy (KASP) for zones. | dnssec
dnssec-secure-to-insecure |  | obsolete
dnssec-update-mode |  | obsolete
dnssec-validation | Enables DNSSEC validation in `named`. | dnssec
dnstap | Enables logging of `dnstap` messages. | logging
dnstap-identity | Specifies an `identity` string to send in `dnstap` messages. | logging
dnstap-output | Configures the path to which the `dnstap` frame stream is sent. | logging
dnstap-version | Specifies a `version` string to send in `dnstap` messages. | logging
dual-stack-servers | Specifies host names or addresses of machines with access to both IPv4 and IPv6 transports. | server
dump-file | Indicates the pathname of the file where the server dumps the database after `rndc dumpdb`. | logging
dyndb | Configures a DynDB database in `named.conf`. | zone
edns | Controls the use of the EDNS0 (RFC 2671) feature. | server
edns-udp-size | Sets the maximum advertised EDNS UDP buffer size to control the size of packets received from authoritative servers in response to recursive queries. | query
edns-version | Sets the maximum EDNS VERSION that is sent to the server(s) by the resolver. | server
empty-contact | Specifies the contact name in the returned SOA record for empty zones. | server, zone
empty-server | Specifies the server name in the returned SOA record for empty zones. | server, zone
empty-zones-enable | Enables or disables all empty zones. | server, zone
endpoints | Specifies a list of HTTP query paths on which to listen. | server, query
errors-per-second | Limits the number of errors for a valid domain name and record type. | server
exclude | Allows a list of IPv6 addresses to be ignored if they appear in a domain name's AAAA records in `dns64`. | query
exempt-clients | Exempts specific clients or client groups from rate limiting. | query
fetch-quota-params | Sets the parameters for dynamic resizing of the `fetches-per-server` quota in response to detected congestion. | server, query
fetches-per-server | Sets the maximum number of simultaneous iterative queries allowed to be sent by a server to an upstream name server before the server blocks additional queries. | server, query
fetches-per-zone | Sets the maximum number of simultaneous iterative queries allowed to any one domain before the server blocks new queries for data in or beneath that zone. | server, query
file | Specifies the zone's filename. | zone
flush-zones-on-shutdown | Controls whether pending zone writes are flushed when the name server exits. | zone
forward | Allows or disallows fallback to recursion if forwarding has failed; it is always used in conjunction with the `forwarders` statement. | query
forwarders | Defines one or more hosts to which queries are forwarded. | query
fstrm-set-buffer-hint | Sets the number of accumulated bytes in the output buffer before forcing a buffer flush. | logging
fstrm-set-flush-timeout | Sets the number of seconds that unflushed data remains in the output buffer. | logging
fstrm-set-input-queue-size | Sets the number of queue entries to allocate for each input queue. | logging
fstrm-set-output-notify-threshold | Sets the number of outstanding queue entries allowed on an input queue before waking the I/O thread. | logging
fstrm-set-output-queue-model | Sets the queuing semantics to use for queue objects. | logging
fstrm-set-output-queue-size | Sets the number of queue entries allocated for each output queue. | logging
fstrm-set-reopen-interval | Sets the number of seconds to wait between attempts to reopen a closed output stream. | logging
geoip-directory | Specifies the directory containing GeoIP database files. | server
heartbeat-interval | Sets the interval at which the server performs zone maintenance tasks for all zones marked as `dialup`. | deprecated
hostname | Specifies the hostname of the server to return in response to a `hostname.bind` query. | server
http | Configures HTTP endpoints on which to listen for DNS-over-HTTPS (DoH) queries. | server, query
http-listener-clients | Limits the number of active concurrent connections on a per-listener basis. | server
http-port | Specifies the TCP port number the server uses to receive and send unencrypted DNS traffic via HTTP. | server, query
http-streams-per-connection | Limits the number of active concurrent HTTP/2 streams on a per-connection basis. | server
https-port | Specifies the TCP port number the server uses to receive and send DNS-over-HTTPS protocol traffic. | server, query
in-view | Specifies the view in which a given zone is defined. | view, zone
inet | Specifies a TCP socket as a control channel. | server
inline-signing | Specifies whether BIND 9 maintains a separate signed version of a zone. | dnssec, zone
interface-interval | Sets the interval at which the server scans the network interface list. | server
ipv4-prefix-length | Specifies the prefix lengths of IPv4 address blocks. | server
ipv4only-contact | Specifies the contact for the IPV4ONLY.ARPA zone created by `dns64`. | server
ipv4only-enable | Enables automatic IPv4 zones if a `dns64` block is configured. | query
ipv4only-server | Specifies the name of the server for the IPV4ONLY.ARPA zone created by `dns64`. | server, query
ipv6-prefix-length | Specifies the prefix lengths of IPv6 address blocks. | server
ixfr-from-differences | Controls how IXFR transfers are calculated. | transfer
journal | Allows the default journal's filename to be overridden. | zone
key | Defines a shared secret key for use with TSIG or the command channel. | security
key-directory | Indicates the directory where public and private DNSSEC key files are found. | dnssec
key-file | Specifies the path to a file containing the private TLS key for a connection. | server, security
key-store | Configures a DNSSEC key store. | dnssec
keys | Specifies one or more `server_key` s to be used with a remote server. | server, security
lame-ttl | Sets the resolver's lame cache. | server
listen-on | Specifies the IPv4 addresses on which a server listens for DNS queries. | server
listen-on-v6 | Specifies the IPv6 addresses on which a server listens for DNS queries. | server
listener-clients | Specifies a per-listener quota for active connections. | server, query
lmdb-mapsize | Sets a maximum size for the memory map of the new-zone database in LMDB database format. | server
log-only | Tests rate-limiting parameters without actually dropping any requests. | logging, query
logging | Configures logging options for the name server. | logging
managed-keys |  | deprecated
managed-keys-directory | Specifies the directory in which to store the files that track managed DNSSEC keys. | dnssec
mapped | Specifies an access control list (ACL) of IPv4 addresses that are to be mapped to the corresponding A RRset in `dns64`. | query
masterfile-format | Specifies the file format of zone files. | zone, server
masterfile-style | Specifies the format of zone files during a dump, when the `masterfile-format` is `text`. | server
match-clients | Specifies a view of DNS namespace for a given subset of client IP addresses. | view
match-destinations | Specifies a view of DNS namespace for a given subset of destination IP addresses. | view
match-mapped-addresses | Allows IPv4-mapped IPv6 addresses to match address-match list entries for corresponding IPv4 addresses. | server
match-recursive-only | Specifies that only recursive requests can match this view of the DNS namespace. | view
max-cache-size | Sets the maximum amount of memory to use for an individual cache database and its associated metadata. | server
max-cache-ttl | Specifies the maximum time (in seconds) that the server caches ordinary (positive) answers. | server
max-clients-per-query | Sets the maximum number of simultaneous recursive clients accepted by the server for any given query before the server drops additional clients. | server
max-ixfr-ratio | Sets the maximum size for IXFR responses to zone transfer requests. | transfer
max-journal-size | Controls the size of journal files. | transfer
max-ncache-ttl | Specifies the maximum retention time (in seconds) for storage of negative answers in the server's cache. | server
max-query-count | Sets the maximum number of iterative queries while servicing a recursive query. | server, query
max-query-restarts | Sets the maximum number of chained CNAMEs to follow | server, query
max-records | Sets the maximum number of records permitted in a zone. | zone, server
max-records-per-type | Sets the maximum number of records that can be stored in an RRset. | server
max-recursion-depth | Sets the maximum number of levels of recursion permitted at any one time while servicing a recursive query. | server
max-recursion-queries | Sets the maximum number of iterative queries while servicing a recursive query. | server, query
max-refresh-time | Limits the zone refresh interval to no less often than the specified value, in seconds. | transfer
max-retry-time | Limits the zone refresh retry interval to no less often than the specified value, in seconds. | transfer
max-rsa-exponent-size | Sets the maximum RSA exponent size (in bits) when validating. | dnssec, query
max-stale-ttl | Specifies the maximum time that the server retains records past their normal expiry, to return them as stale records. | server
max-table-size | Sets the maximum size of the table used to track requests and rate-limit responses. | server
max-transfer-idle-in | Specifies the number of minutes after which inbound zone transfers making no progress are terminated. | transfer
max-transfer-idle-out | Specifies the number of minutes after which outbound zone transfers making no progress are terminated. | transfer
max-transfer-time-in | Specifies the number of minutes after which inbound zone transfers are terminated. | transfer
max-transfer-time-out | Specifies the number of minutes after which outbound zone transfers are terminated. | transfer
max-types-per-name | Sets the maximum number of RR types that can be stored for an owner name. | server
max-udp-size | Sets the maximum EDNS UDP message size sent by `named`. | query
max-validation-failures-per-fetch | Sets the maximum number of DNSSEC validation failures that can happen in a single fetch. | server
max-validations-per-fetch | Sets the maximum number of DNSSEC validations that can happen in a single fetch. | server
max-zone-ttl | Specifies a maximum permissible time-to-live (TTL) value, in seconds. | deprecated
memstatistics | Controls whether memory statistics are written to the file specified by `memstatistics-file` at exit. | server, logging
memstatistics-file | Sets the pathname of the file where the server writes memory usage statistics on exit. | logging
message-compression | Controls whether DNS name compression is used in responses to regular queries. | query
min-cache-ttl | Specifies the minimum time (in seconds) that the server caches ordinary (positive) answers. | server
min-ncache-ttl | Specifies the minimum retention time (in seconds) for storage of negative answers in the server's cache. | server
min-refresh-time | Limits the zone refresh interval to no more often than the specified value, in seconds. | transfer
min-retry-time | Limits the zone refresh retry interval to no more often than the specified value, in seconds. | transfer
min-table-size | Sets the minimum size of the table used to track requests and rate-limit responses. | query
min-transfer-rate-in | Specifies the minimum traffic rate below which inbound zone transfers are terminated. | transfer
minimal-any | Controls whether the server replies with only one of the RRsets for a query name, when generating a positive response to a query of type ANY over UDP. | query
minimal-responses | Controls whether the server only adds records to the authority and additional data sections when they are required (e.g. delegations, negative responses). This improves server performance. | query
multi-master | Controls whether serial number mismatch errors are logged. | transfer
new-zones-directory | Specifies the directory where configuration parameters are stored for zones added by `rndc addzone`. | zone
no-case-compress | Specifies a list of addresses that require case-insensitive compression in responses. | server
nocookie-udp-size | Sets the maximum size of UDP responses that are sent to queries without a valid server COOKIE. | query
nodata-per-second | Limits the number of empty (NODATA) responses for a valid domain name. | query
notify | Controls whether `NOTIFY` messages are sent on zone changes. | transfer
notify-defer | Sets the defer time (in seconds) before sending NOTIFY messages for a zone. | transfer, zone
notify-delay | Sets the delay (in seconds) between sending sets of NOTIFY messages for a zone. | transfer, zone
notify-rate | Specifies the rate at which NOTIFY requests are sent during normal zone maintenance operations. | transfer, zone
notify-source | Defines the IPv4 address (and optional port) to be used for outgoing `NOTIFY` messages. | transfer
notify-source-v6 | Defines the IPv6 address (and optional port) to be used for outgoing `NOTIFY` messages. | transfer
notify-to-soa | Controls whether the name servers in the NS RRset are checked against the SOA MNAME. | transfer
nsec3param | Specifies the use of NSEC3 instead of NSEC, and sets NSEC3 parameters. | dnssec
nta-lifetime | Specifies the lifetime, in seconds, for negative trust anchors added via `rndc nta`. | dnssec
nta-recheck | Specifies the time interval for checking whether negative trust anchors added via `rndc nta` are still necessary. | dnssec
null | Causes all messages sent to the logging channel to be discarded. | logging
nxdomain-redirect | Appends the specified suffix to the original query name, when replacing an NXDOMAIN with a redirect namespace. | query
nxdomains-per-second | Limits the number of undefined subdomains for a valid domain name. | query
offline-ksk | Specifies whether the DNSKEY, CDS, and CDNSKEY RRsets are being signed offline. | dnssec
options | Defines global options to be used by BIND 9. | server
padding | Adds EDNS Padding options to outgoing messages to increase the packet size. | server
parent-ds-ttl | Sets the time to live (TTL) of the DS RRset used by the parent zone. | dnssec
parent-propagation-delay | Sets the propagation delay from the time the parent zone is updated to when the new version is served by all of the parent zone's name servers. | dnssec, zone
parental-agents |  | dnssec
parental-source | Specifies which local IPv4 source address is used to send parental DS queries. | dnssec
parental-source-v6 | Specifies which local IPv6 source address is used to send parental DS queries. | dnssec
pid-file | Specifies the pathname of the file where the server writes its process ID. | server
pkcs11-uri |  | dnssec, pkcs11
plugin | Configures plugins in `named.conf`. | server
port | Specifies the UDP/TCP port number the server uses to receive and send DNS protocol traffic. | server, query
prefer-server-ciphers | Specifies that server ciphers should be preferred over client ones. | server, security
preferred-glue | Controls the order of glue records in an A or AAAA response. | query
prefetch | Specifies the "trigger" time-to-live (TTL) value at which prefetch of the current query takes place. | query
primaries | Defines one or more servers that zone transfer can be requested from. | transfer, zone
print-category | Includes the category in log messages. | logging
print-severity | Includes the severity in log messages. | logging
print-time | Specifies the time format for log messages. | logging
protocols | Specifies the allowed versions of the TLS protocol. | security
provide-ixfr | Controls whether a primary responds to an incremental zone request (IXFR) or only responds with a full zone transfer (AXFR). | transfer
publish-safety | Increases the amount of time between when keys are published and when they become active, to allow for unforeseen events. | dnssec
purge-keys | Specifies the amount of time after which DNSSEC keys that have been deleted from the zone can be removed from disk. | dnssec
qname-minimization | Controls QNAME minimization behavior in the BIND 9 resolver. | query
qps-scale | Tightens defenses during DNS attacks by scaling back the ratio of the current query-per-second rate. | query
query-source | Controls the IPv4 address from which queries are issued. If none, then no IPv4 address would be used to issue the query and therefore only IPv6 servers are queried. | query
query-source-v6 | Controls the IPv6 address from which queries are issued. If none, then no IPv6 address would be used to issue the query and therefore only IPv4 servers are quried. | query
querylog | Specifies whether query logging should be active when `named` first starts. | logging, server
rate-limit | Controls excessive UDP responses, to prevent BIND 9 from being used to amplify reflection denial-of-service (DoS) attacks. | query
recursing-file | Specifies the pathname of the file where the server dumps queries that are currently recursing via `rndc recursing`. | server
recursion | Defines whether recursion and caching are allowed. | query
recursive-clients | Specifies the maximum number of concurrent recursive queries the server can perform. | query
recursive-only | Toggles whether `dns64` synthesis occurs only for recursive queries. | query
referrals-per-second | Limits the number of referrals or delegations to a server for a given domain. | query
remote-hostname | Specifies the expected hostname in the TLS certificate of the remote server. | security
remote-servers | Defines a list of servers to be used by primary and secondary zones. | server
request-expire | Specifies whether the local server requests the EDNS EXPIRE value, when acting as a secondary. | transfer, query
request-ixfr | Controls whether a secondary requests an incremental zone transfer (IXFR) or a full zone transfer (AXFR). | transfer
request-nsid | Controls whether an empty EDNS(0) NSID (Name Server Identifier) option is sent with all queries to authoritative name servers during iterative resolution. | query
require-cookie | Controls whether responses without a server cookie are accepted. | query
require-server-cookie | Controls whether a valid server cookie is required before sending a full response to a UDP request. | query
resolver-query-timeout | Specifies the length of time, in milliseconds, that a resolver attempts to resolve a recursive query before failing. | query
resolver-use-dns64 | Specifies whether to apply DNS64 mappings when sending queries. | server
response-padding | Adds an EDNS Padding option to encrypted messages, to reduce the chance of guessing the contents based on size. | query
response-policy | Specifies response policy zones for the view or among global options. | server, query, zone, security
responselog | Specifies whether response logging should be active when `named` first starts. | logging, server
responses-per-second | Limits the number of non-empty responses for a valid domain name and record type. | query
retire-safety | Increases the amount of time a key remains published after it is no longer active, to allow for unforeseen events. | dnssec
reuseport | Enables kernel load-balancing of sockets. | server
root-key-sentinel | Controls whether BIND 9 responds to root key sentinel probes. | server
rrset-order | Defines the order in which equal RRs (RRsets) are returned. | query
search | Specifies whether a Dynamically Loadable Zone (DLZ) module is queried for an answer to a query name. | query
secret | Defines a Base64-encoded string to be used as the secret by the algorithm. | security
secroots-file | Specifies the pathname of the file where the server dumps security roots, when using `rndc secroots`. | dnssec
send-cookie | Controls whether a COOKIE EDNS option is sent along with a query. | query
serial-query-rate | Defines an upper limit on the number of queries per second issued by the server, when querying the SOA RRs used for zone transfers. | transfer
serial-update-method | Specifies the update method to be used for the zone serial number in the SOA record. | zone
server | Defines characteristics to be associated with a remote name server. | server
server-addresses | Specifies a list of IP addresses to which queries should be sent in recursive resolution for a static-stub zone. | query, zone
server-id | Specifies the ID of the server to return in response to a `ID.SERVER` query. | server
server-names | Specifies a list of domain names of name servers that act as authoritative servers of a static-stub zone. | zone
servfail-ttl | Sets the length of time (in seconds) that a SERVFAIL response is cached. | server
session-keyalg | Specifies the algorithm to use for the TSIG session key. | security
session-keyfile | Specifies the pathname of the file where a TSIG session key is written, when generated by `named` for use by `nsupdate -l`. | security
session-keyname | Specifies the key name for the TSIG session key. | security
session-tickets | Enables or disables session resumption through TLS session tickets. | security
severity | Defines the priority level of log messages. | logging
sig-signing-nodes | Specifies the maximum number of nodes to be examined in each quantum, when signing a zone with a new DNSKEY. | dnssec
sig-signing-signatures | Specifies the threshold for the number of signatures that terminates processing a quantum, when signing a zone with a new DNSKEY. | dnssec
sig-signing-type | Specifies a private RDATA type to use when generating signing-state records. | dnssec
sig-validity-interval |  | obsolete
sig0checks-quota | Specifies the maximum number of concurrent SIG(0) signature checks that can be processed by the server. | server
sig0checks-quota-exempt | Exempts specific clients or client groups from SIG(0) signature checking quota. | server
sig0key-checks-limit | Specifies the maximum number of SIG(0) keys to consider when trying to verify a message. | server
sig0message-checks-limit | Specifies the maximum number of matching SIG(0) keys to try to verify a message. | server
signatures-jitter | Specifies a range for signature expirations. | dnssec
signatures-refresh | Specifies how frequently an RRSIG record is refreshed. | dnssec
signatures-validity | Indicates the validity period of an RRSIG record. | dnssec
signatures-validity-dnskey | Indicates the validity period of DNSKEY records. | dnssec
slip | Sets the number of "slipped" responses to minimize the use of forged source addresses for an attack. | query
sortlist | Controls the ordering of RRs returned to the client, based on the client's IP address. | query, deprecated
stale-answer-client-timeout | Defines the amount of time (in milliseconds) that `named` waits before attempting to answer a query with a stale RRset from cache. | server, query
stale-answer-enable | Enables the returning of "stale" cached answers when the name servers for a zone are not answering. | server, query
stale-answer-ttl | Specifies the time to live (TTL) to be returned on stale answers, in seconds. | query
stale-cache-enable | Enables the retention of "stale" cached answers. | server, query
stale-refresh-time | Sets the time window for the return of "stale" cached answers before the next attempt to contact, if the name servers for a given zone are not responding. | server, query
startup-notify-rate | Specifies the rate at which NOTIFY requests are sent when the name server is first starting, or when new zones have been added. | transfer, zone
statistics-channels | Specifies the communication channels to be used by system administrators to access statistics information on the name server. | logging
statistics-file | Specifies the pathname of the file where the server appends statistics, when using `rndc stats`. | logging, server
stderr | Directs the logging channel output to the server's standard error stream. | logging
streams-per-connection | Specifies the maximum number of concurrent HTTP/2 streams over an HTTP/2 connection. | server, query
suffix | Defines trailing bits for mapped IPv4 address bits in `dns64`. | query
synth-from-dnssec | Enables support for RFC 8198, Aggressive Use of DNSSEC-Validated Cache. | dnssec
syslog | Directs the logging channel to the system log. | logging
tcp-advertised-timeout | Sets the timeout value (in milliseconds) that the server sends in responses containing the EDNS TCP keepalive option. | query
tcp-clients | Specifies the maximum number of simultaneous client TCP connections accepted by the server. | server
tcp-idle-timeout | Sets the amount of time (in milliseconds) that the server waits on an idle TCP connection before closing it, if the EDNS TCP keepalive option is not in use. | query
tcp-initial-timeout | Sets the amount of time (in milliseconds) that the server waits on a new TCP connection for the first message from the client. | server, query
tcp-keepalive | Adds EDNS TCP keepalive to messages sent over TCP. | server
tcp-keepalive-timeout | Sets the amount of time (in milliseconds) that the server waits on an idle TCP connection before closing it, if the EDNS TCP keepalive option is in use. | query
tcp-listen-queue | Sets the listen-queue depth. | server
tcp-only | Sets the transport protocol to TCP. | server
tcp-receive-buffer | Sets the operating system's receive buffer size for TCP sockets. | server
tcp-send-buffer | Sets the operating system's send buffer size for TCP sockets. | server
tkey-domain | Sets the domain appended to the names of all shared keys generated with `TKEY`. | security
tkey-gssapi-credential | Sets the security credential for authentication keys requested by the GSS-TSIG protocol. | security
tkey-gssapi-keytab | Sets the KRB5 keytab file to use for GSS-TSIG updates. | security
tls | Configures a TLS connection. | security
tls-port | Specifies the TCP port number the server uses to receive and send DNS-over-TLS protocol traffic. | server, query
transfer-format | Controls whether multiple records can be packed into a message during zone transfers. | transfer
transfer-message-size | Limits the uncompressed size of DNS messages used in zone transfers over TCP. | transfer
transfer-source | Defines which local IPv4 address(es) are bound to TCP connections used to fetch zones transferred inbound by the server. | transfer
transfer-source-v6 | Defines which local IPv6 address(es) are bound to TCP connections used to fetch zones transferred inbound by the server. | transfer
transfers | Limits the number of concurrent inbound zone transfers from a server. | server
transfers-in | Limits the number of concurrent inbound zone transfers. | transfer
transfers-out | Limits the number of concurrent outbound zone transfers. | transfer
transfers-per-ns | Limits the number of concurrent inbound zone transfers from a remote server. | transfer
trust-anchor-telemetry | Instructs `named` to send specially formed queries once per day to domains for which trust anchors have been configured. | dnssec
trust-anchors | Defines DNSSEC trust anchors. | dnssec
trusted-keys |  | deprecated
try-tcp-refresh | Specifies that BIND 9 should attempt to refresh a zone using TCP if UDP queries fail. | transfer
type | Specifies the kind of zone in a given configuration. | zone
type forward | Contains forwarding statements that apply to queries within a given domain. | zone
type hint | Contains the initial set of root name servers to be used at BIND 9 startup. | zone
type mirror | Contains a DNSSEC-validated duplicate of the main data for a zone. | zone
type primary | Contains the main copy of the data for a zone. | zone
type redirect | Contains information to answer queries when normal resolution would return NXDOMAIN. | zone
type secondary | Contains a duplicate of the data for a zone that has been transferred from a primary server. | zone
type static-stub | Contains a duplicate of the NS records of a primary zone, but statically configured rather than transferred from a primary server. | zone
type stub | Contains a duplicate of the NS records of a primary zone. | zone
udp-receive-buffer | Sets the operating system's receive buffer size for UDP sockets. | server
udp-send-buffer | Sets the operating system's send buffer size for UDP sockets. | server
unix | Specifies a Unix domain socket as a control channel. | obsolete
update-check-ksk |  | obsolete
update-policy | Sets fine-grained rules to allow or deny dynamic updates (DDNS), based on requester identity, updated content, etc. | transfer
update-quota | Specifies the maximum number of concurrent DNS UPDATE messages that can be processed by the server. | server
use-v4-udp-ports | Specifies a list of ports that are valid sources for UDP/IPv4 messages. | deprecated
use-v6-udp-ports | Specifies a list of ports that are valid sources for UDP/IPv6 messages. | deprecated
v6-bias | Indicates the number of milliseconds of preference to give to IPv6 name servers. | server, query
validate-except | Specifies a list of domain names at and beneath which DNSSEC validation should not be performed. | dnssec
version | Specifies the version number of the server to return in response to a `version.bind` query. | server
view | Allows a name server to answer a DNS query differently depending on who is asking. | view
window | Specifies the length of time during which responses are tracked. | query
zero-no-soa-ttl | Specifies whether to set the time to live (TTL) of the SOA record to zero, when returning authoritative negative responses to SOA queries. | zone, query, server
zero-no-soa-ttl-cache | Sets the time to live (TTL) to zero when caching a negative response to an SOA query. | zone, query, server
zone | Specifies the zone in a BIND 9 configuration. | zone
zone-propagation-delay | Sets the propagation delay from the time a zone is first updated to when the new version of the zone is served by all secondary servers. | dnssec, zone
zone-statistics | Controls the level of statistics gathered for all zones. | zone, logging

## 8.4. Statements by Tag

These tables group the various statements permissible in `named.conf` by their corresponding tag.

### 8.4.1. DNSSEC Tag Statements

Statement | Description
--- | ---
bindkeys-file | Specifies the pathname of a file to override the built-in trusted keys provided by `named`.
cdnskey | Specifies whether a CDNSKEY record should be published during KSK rollover.
cds-digest-types | Specifies the digest types to use for CDS resource records.
check-dup-records | Checks primary zones for records that are treated as different by DNSSEC but are semantically equal in plain DNS.
checkds | Controls whether `DS` queries are sent to parental agents.
disable-algorithms | Disables DNSSEC algorithms from a specified zone.
disable-ds-digests | Disables DS digest types from a specified zone.
dnskey-ttl | Specifies the time-to-live (TTL) for DNSKEY resource records.
dnssec-accept-expired | Instructs BIND 9 to accept expired DNSSEC signatures when validating.
dnssec-loadkeys-interval | Sets the frequency of automatic checks of the DNSSEC key repository.
dnssec-policy | Defines a key and signing policy (KASP) for zones.
dnssec-validation | Enables DNSSEC validation in `named`.
inline-signing | Specifies whether BIND 9 maintains a separate signed version of a zone.
key-directory | Indicates the directory where public and private DNSSEC key files are found.
key-store | Configures a DNSSEC key store.
managed-keys-directory | Specifies the directory in which to store the files that track managed DNSSEC keys.
max-rsa-exponent-size | Sets the maximum RSA exponent size (in bits) when validating.
nsec3param | Specifies the use of NSEC3 instead of NSEC, and sets NSEC3 parameters.
nta-lifetime | Specifies the lifetime, in seconds, for negative trust anchors added via `rndc nta`.
nta-recheck | Specifies the time interval for checking whether negative trust anchors added via `rndc nta` are still necessary.
offline-ksk | Specifies whether the DNSKEY, CDS, and CDNSKEY RRsets are being signed offline.
parent-ds-ttl | Sets the time to live (TTL) of the DS RRset used by the parent zone.
parent-propagation-delay | Sets the propagation delay from the time the parent zone is updated to when the new version is served by all of the parent zone's name servers.
parental-agents |
parental-source | Specifies which local IPv4 source address is used to send parental DS queries.
parental-source-v6 | Specifies which local IPv6 source address is used to send parental DS queries.
pkcs11-uri |
publish-safety | Increases the amount of time between when keys are published and when they become active, to allow for unforeseen events.
purge-keys | Specifies the amount of time after which DNSSEC keys that have been deleted from the zone can be removed from disk.
retire-safety | Increases the amount of time a key remains published after it is no longer active, to allow for unforeseen events.
secroots-file | Specifies the pathname of the file where the server dumps security roots, when using `rndc secroots`.
sig-signing-nodes | Specifies the maximum number of nodes to be examined in each quantum, when signing a zone with a new DNSKEY.
sig-signing-signatures | Specifies the threshold for the number of signatures that terminates processing a quantum, when signing a zone with a new DNSKEY.
sig-signing-type | Specifies a private RDATA type to use when generating signing-state records.
signatures-jitter | Specifies a range for signature expirations.
signatures-refresh | Specifies how frequently an RRSIG record is refreshed.
signatures-validity | Indicates the validity period of an RRSIG record.
signatures-validity-dnskey | Indicates the validity period of DNSKEY records.
synth-from-dnssec | Enables support for RFC 8198, Aggressive Use of DNSSEC-Validated Cache.
trust-anchor-telemetry | Instructs `named` to send specially formed queries once per day to domains for which trust anchors have been configured.
trust-anchors | Defines DNSSEC trust anchors.
validate-except | Specifies a list of domain names at and beneath which DNSSEC validation should not be performed.
zone-propagation-delay | Sets the propagation delay from the time a zone is first updated to when the new version of the zone is served by all secondary servers.

### 8.4.2. Logging Tag Statements

Statement | Description
--- | ---
buffered | Controls flushing of log messages.
category | Specifies the type of data logged to a particular channel.
channel | Defines a stream of data that can be independently logged.
dnstap | Enables logging of `dnstap` messages.
dnstap-identity | Specifies an `identity` string to send in `dnstap` messages.
dnstap-output | Configures the path to which the `dnstap` frame stream is sent.
dnstap-version | Specifies a `version` string to send in `dnstap` messages.
dump-file | Indicates the pathname of the file where the server dumps the database after `rndc dumpdb`.
fstrm-set-buffer-hint | Sets the number of accumulated bytes in the output buffer before forcing a buffer flush.
fstrm-set-flush-timeout | Sets the number of seconds that unflushed data remains in the output buffer.
fstrm-set-input-queue-size | Sets the number of queue entries to allocate for each input queue.
fstrm-set-output-notify-threshold | Sets the number of outstanding queue entries allowed on an input queue before waking the I/O thread.
fstrm-set-output-queue-model | Sets the queuing semantics to use for queue objects.
fstrm-set-output-queue-size | Sets the number of queue entries allocated for each output queue.
fstrm-set-reopen-interval | Sets the number of seconds to wait between attempts to reopen a closed output stream.
log-only | Tests rate-limiting parameters without actually dropping any requests.
logging | Configures logging options for the name server.
memstatistics | Controls whether memory statistics are written to the file specified by `memstatistics-file` at exit.
memstatistics-file | Sets the pathname of the file where the server writes memory usage statistics on exit.
null | Causes all messages sent to the logging channel to be discarded.
print-category | Includes the category in log messages.
print-severity | Includes the severity in log messages.
print-time | Specifies the time format for log messages.
querylog | Specifies whether query logging should be active when `named` first starts.
responselog | Specifies whether response logging should be active when `named` first starts.
severity | Defines the priority level of log messages.
statistics-channels | Specifies the communication channels to be used by system administrators to access statistics information on the name server.
statistics-file | Specifies the pathname of the file where the server appends statistics, when using `rndc stats`.
stderr | Directs the logging channel output to the server's standard error stream.
syslog | Directs the logging channel to the system log.
zone-statistics | Controls the level of statistics gathered for all zones.

### 8.4.3. Query Tag Statements

Statement | Description
--- | ---
all-per-second | Limits UDP responses of all kinds.
allow-query | Specifies which hosts (an IP address list) are allowed to send queries to this resolver.
allow-query-cache | Specifies which hosts (an IP address list) can access this server's cache and thus effectively controls recursion.
allow-query-cache-on | Specifies which hosts (from an IP address list) can access this server's cache. It is used on servers with multiple interfaces.
allow-query-on | Specifies which local addresses (an IP address list) are allowed to send queries to this resolver. This option is used in multi-homed configurations.
allow-recursion | Defines an `address_match_list` of clients that are allowed to perform recursive queries.
allow-recursion-on | Specifies which local addresses can accept recursive queries.
answer-cookie | Controls whether COOKIE EDNS replies are sent in response to client queries.
auth-nxdomain | Controls whether BIND, acting as a resolver, provides authoritative NXDOMAIN (domain does not exist) answers.
blackhole | Defines an `address_match_list` of hosts to ignore. The server will neither respond to queries from nor send queries to these addresses.
break-dnssec | Enables `dns64` synthesis even if the validated result would cause a DNSSEC validation failure.
check-dup-records | Checks primary zones for records that are treated as different by DNSSEC but are semantically equal in plain DNS.
check-names | Restricts the character set and syntax of certain domain names in primary files and/or DNS responses received from the network.
clients | Specifies an access control list (ACL) of clients that are affected by a given `dns64` directive.
deny-answer-addresses | Rejects A or AAAA records if the corresponding IPv4 or IPv6 addresses match a given `address_match_list`.
deny-answer-aliases | Rejects CNAME or DNAME records if the "alias" name matches a given list of `domain_name` elements.
dns64 | Instructs `named` to return mapped IPv4 addresses to AAAA queries when there are no AAAA records.
edns-udp-size | Sets the maximum advertised EDNS UDP buffer size to control the size of packets received from authoritative servers in response to recursive queries.
endpoints | Specifies a list of HTTP query paths on which to listen.
exclude | Allows a list of IPv6 addresses to be ignored if they appear in a domain name's AAAA records in `dns64`.
exempt-clients | Exempts specific clients or client groups from rate limiting.
fetch-quota-params | Sets the parameters for dynamic resizing of the `fetches-per-server` quota in response to detected congestion.
fetches-per-server | Sets the maximum number of simultaneous iterative queries allowed to be sent by a server to an upstream name server before the server blocks additional queries.
fetches-per-zone | Sets the maximum number of simultaneous iterative queries allowed to any one domain before the server blocks new queries for data in or beneath that zone.
forward | Allows or disallows fallback to recursion if forwarding has failed; it is always used in conjunction with the `forwarders` statement.
forwarders | Defines one or more hosts to which queries are forwarded.
http | Configures HTTP endpoints on which to listen for DNS-over-HTTPS (DoH) queries.
http-port | Specifies the TCP port number the server uses to receive and send unencrypted DNS traffic via HTTP.
https-port | Specifies the TCP port number the server uses to receive and send DNS-over-HTTPS protocol traffic.
ipv4only-enable | Enables automatic IPv4 zones if a `dns64` block is configured.
ipv4only-server | Specifies the name of the server for the IPV4ONLY.ARPA zone created by `dns64`.
listener-clients | Specifies a per-listener quota for active connections.
log-only | Tests rate-limiting parameters without actually dropping any requests.
mapped | Specifies an access control list (ACL) of IPv4 addresses that are to be mapped to the corresponding A RRset in `dns64`.
max-query-count | Sets the maximum number of iterative queries while servicing a recursive query.
max-query-restarts | Sets the maximum number of chained CNAMEs to follow
max-recursion-queries | Sets the maximum number of iterative queries while servicing a recursive query.
max-rsa-exponent-size | Sets the maximum RSA exponent size (in bits) when validating.
max-udp-size | Sets the maximum EDNS UDP message size sent by `named`.
message-compression | Controls whether DNS name compression is used in responses to regular queries.
min-table-size | Sets the minimum size of the table used to track requests and rate-limit responses.
minimal-any | Controls whether the server replies with only one of the RRsets for a query name, when generating a positive response to a query of type ANY over UDP.
minimal-responses | Controls whether the server only adds records to the authority and additional data sections when they are required (e.g. delegations, negative responses). This improves server performance.
nocookie-udp-size | Sets the maximum size of UDP responses that are sent to queries without a valid server COOKIE.
nodata-per-second | Limits the number of empty (NODATA) responses for a valid domain name.
nxdomain-redirect | Appends the specified suffix to the original query name, when replacing an NXDOMAIN with a redirect namespace.
nxdomains-per-second | Limits the number of undefined subdomains for a valid domain name.
port | Specifies the UDP/TCP port number the server uses to receive and send DNS protocol traffic.
preferred-glue | Controls the order of glue records in an A or AAAA response.
prefetch | Specifies the "trigger" time-to-live (TTL) value at which prefetch of the current query takes place.
qname-minimization | Controls QNAME minimization behavior in the BIND 9 resolver.
qps-scale | Tightens defenses during DNS attacks by scaling back the ratio of the current query-per-second rate.
query-source | Controls the IPv4 address from which queries are issued. If none, then no IPv4 address would be used to issue the query and therefore only IPv6 servers are queried.
query-source-v6 | Controls the IPv6 address from which queries are issued. If none, then no IPv6 address would be used to issue the query and therefore only IPv4 servers are quried.
rate-limit | Controls excessive UDP responses, to prevent BIND 9 from being used to amplify reflection denial-of-service (DoS) attacks.
recursion | Defines whether recursion and caching are allowed.
recursive-clients | Specifies the maximum number of concurrent recursive queries the server can perform.
recursive-only | Toggles whether `dns64` synthesis occurs only for recursive queries.
referrals-per-second | Limits the number of referrals or delegations to a server for a given domain.
request-expire | Specifies whether the local server requests the EDNS EXPIRE value, when acting as a secondary.
request-nsid | Controls whether an empty EDNS(0) NSID (Name Server Identifier) option is sent with all queries to authoritative name servers during iterative resolution.
require-cookie | Controls whether responses without a server cookie are accepted.
require-server-cookie | Controls whether a valid server cookie is required before sending a full response to a UDP request.
resolver-query-timeout | Specifies the length of time, in milliseconds, that a resolver attempts to resolve a recursive query before failing.
response-padding | Adds an EDNS Padding option to encrypted messages, to reduce the chance of guessing the contents based on size.
response-policy | Specifies response policy zones for the view or among global options.
responses-per-second | Limits the number of non-empty responses for a valid domain name and record type.
rrset-order | Defines the order in which equal RRs (RRsets) are returned.
search | Specifies whether a Dynamically Loadable Zone (DLZ) module is queried for an answer to a query name.
send-cookie | Controls whether a COOKIE EDNS option is sent along with a query.
server-addresses | Specifies a list of IP addresses to which queries should be sent in recursive resolution for a static-stub zone.
slip | Sets the number of "slipped" responses to minimize the use of forged source addresses for an attack.
sortlist | Controls the ordering of RRs returned to the client, based on the client's IP address.
stale-answer-client-timeout | Defines the amount of time (in milliseconds) that `named` waits before attempting to answer a query with a stale RRset from cache.
stale-answer-enable | Enables the returning of "stale" cached answers when the name servers for a zone are not answering.
stale-answer-ttl | Specifies the time to live (TTL) to be returned on stale answers, in seconds.
stale-cache-enable | Enables the retention of "stale" cached answers.
stale-refresh-time | Sets the time window for the return of "stale" cached answers before the next attempt to contact, if the name servers for a given zone are not responding.
streams-per-connection | Specifies the maximum number of concurrent HTTP/2 streams over an HTTP/2 connection.
suffix | Defines trailing bits for mapped IPv4 address bits in `dns64`.
tcp-advertised-timeout | Sets the timeout value (in milliseconds) that the server sends in responses containing the EDNS TCP keepalive option.
tcp-idle-timeout | Sets the amount of time (in milliseconds) that the server waits on an idle TCP connection before closing it, if the EDNS TCP keepalive option is not in use.
tcp-initial-timeout | Sets the amount of time (in milliseconds) that the server waits on a new TCP connection for the first message from the client.
tcp-keepalive-timeout | Sets the amount of time (in milliseconds) that the server waits on an idle TCP connection before closing it, if the EDNS TCP keepalive option is in use.
tls-port | Specifies the TCP port number the server uses to receive and send DNS-over-TLS protocol traffic.
v6-bias | Indicates the number of milliseconds of preference to give to IPv6 name servers.
window | Specifies the length of time during which responses are tracked.
zero-no-soa-ttl | Specifies whether to set the time to live (TTL) of the SOA record to zero, when returning authoritative negative responses to SOA queries.
zero-no-soa-ttl-cache | Sets the time to live (TTL) to zero when caching a negative response to an SOA query.

### 8.4.4. Security Tag Statements

Statement | Description
--- | ---
algorithm | Defines the algorithm to be used in a key clause.
ca-file | Specifies the path to a file containing TLS certificates for trusted CA authorities, used to verify remote peer certificates.
cert-file | Specifies the path to a file containing the TLS certificate for a connection.
cipher-suites | Specifies a list of allowed cipher suites in the order of preference for TLSv1.3 only.
ciphers | Specifies a list of allowed ciphers in the order of preference for TLSv1.2 only.
dhparam-file | Specifies the path to a file containing Diffie-Hellman parameters, for enabling cipher suites.
dnsrps-enable | Turns on the DNS Response Policy Service (DNSRPS) interface.
dnsrps-library | Specifies the path to the DNS Response Policy Service (DNSRPS) provider library.
dnsrps-options | Provides additional RPZ configuration settings, which are passed to the DNS Response Policy Service (DNSRPS) provider library.
key | Defines a shared secret key for use with TSIG or the command channel.
key-file | Specifies the path to a file containing the private TLS key for a connection.
keys | Specifies one or more `server_key` s to be used with a remote server.
prefer-server-ciphers | Specifies that server ciphers should be preferred over client ones.
protocols | Specifies the allowed versions of the TLS protocol.
remote-hostname | Specifies the expected hostname in the TLS certificate of the remote server.
response-policy | Specifies response policy zones for the view or among global options.
secret | Defines a Base64-encoded string to be used as the secret by the algorithm.
session-keyalg | Specifies the algorithm to use for the TSIG session key.
session-keyfile | Specifies the pathname of the file where a TSIG session key is written, when generated by `named` for use by `nsupdate -l`.
session-keyname | Specifies the key name for the TSIG session key.
session-tickets | Enables or disables session resumption through TLS session tickets.
tkey-domain | Sets the domain appended to the names of all shared keys generated with `TKEY`.
tkey-gssapi-credential | Sets the security credential for authentication keys requested by the GSS-TSIG protocol.
tkey-gssapi-keytab | Sets the KRB5 keytab file to use for GSS-TSIG updates.
tls | Configures a TLS connection.

### 8.4.5. Server Tag Statements

Statement | Description
--- | ---
acl | Assigns a symbolic name to an address match list.
allow-new-zones | Controls the ability to add zones at runtime via `rndc addzone`.
allow-proxy | Defines an `address_match_list` for the client addresses allowed to send PROXYv2 headers.
allow-proxy-on | Defines an `address_match_list` for the interface addresses allowed to accept PROXYv2 headers. The option is mostly intended for multi-homed configurations.
allow-recursion-on | Specifies which local addresses can accept recursive queries.
automatic-interface-scan | Controls the automatic rescanning of network interfaces when addresses are added or removed.
bogus | Allows a remote server to be ignored.
ca-file | Specifies the path to a file containing TLS certificates for trusted CA authorities, used to verify remote peer certificates.
cert-file | Specifies the path to a file containing the TLS certificate for a connection.
check-names | Restricts the character set and syntax of certain domain names in primary files and/or DNS responses received from the network.
clients-per-query | Sets the initial minimum number of simultaneous recursive clients accepted by the server for any given query before the server drops additional clients.
controls | Specifies control channels to be used to manage the name server.
cookie-algorithm | Sets the algorithm to be used when generating a server cookie.
cookie-secret | Specifies a shared secret used for generating and verifying EDNS COOKIE options within an anycast cluster.
dhparam-file | Specifies the path to a file containing Diffie-Hellman parameters, for enabling cipher suites.
directory | Sets the server's working directory.
disable-empty-zone | Disables individual empty zones.
dns64-contact | Specifies the name of the contact for `dns64` zones.
dns64-server | Specifies the name of the server for `dns64` zones.
dnsrps-enable | Turns on the DNS Response Policy Service (DNSRPS) interface.
dnsrps-library | Specifies the path to the DNS Response Policy Service (DNSRPS) provider library.
dnsrps-options | Provides additional RPZ configuration settings, which are passed to the DNS Response Policy Service (DNSRPS) provider library.
dual-stack-servers | Specifies host names or addresses of machines with access to both IPv4 and IPv6 transports.
edns | Controls the use of the EDNS0 (RFC 2671) feature.
edns-version | Sets the maximum EDNS VERSION that is sent to the server(s) by the resolver.
empty-contact | Specifies the contact name in the returned SOA record for empty zones.
empty-server | Specifies the server name in the returned SOA record for empty zones.
empty-zones-enable | Enables or disables all empty zones.
endpoints | Specifies a list of HTTP query paths on which to listen.
errors-per-second | Limits the number of errors for a valid domain name and record type.
fetch-quota-params | Sets the parameters for dynamic resizing of the `fetches-per-server` quota in response to detected congestion.
fetches-per-server | Sets the maximum number of simultaneous iterative queries allowed to be sent by a server to an upstream name server before the server blocks additional queries.
fetches-per-zone | Sets the maximum number of simultaneous iterative queries allowed to any one domain before the server blocks new queries for data in or beneath that zone.
geoip-directory | Specifies the directory containing GeoIP database files.
hostname | Specifies the hostname of the server to return in response to a `hostname.bind` query.
http | Configures HTTP endpoints on which to listen for DNS-over-HTTPS (DoH) queries.
http-listener-clients | Limits the number of active concurrent connections on a per-listener basis.
http-port | Specifies the TCP port number the server uses to receive and send unencrypted DNS traffic via HTTP.
http-streams-per-connection | Limits the number of active concurrent HTTP/2 streams on a per-connection basis.
https-port | Specifies the TCP port number the server uses to receive and send DNS-over-HTTPS protocol traffic.
inet | Specifies a TCP socket as a control channel.
interface-interval | Sets the interval at which the server scans the network interface list.
ipv4-prefix-length | Specifies the prefix lengths of IPv4 address blocks.
ipv4only-contact | Specifies the contact for the IPV4ONLY.ARPA zone created by `dns64`.
ipv4only-server | Specifies the name of the server for the IPV4ONLY.ARPA zone created by `dns64`.
ipv6-prefix-length | Specifies the prefix lengths of IPv6 address blocks.
key-file | Specifies the path to a file containing the private TLS key for a connection.
keys | Specifies one or more `server_key` s to be used with a remote server.
lame-ttl | Sets the resolver's lame cache.
listen-on | Specifies the IPv4 addresses on which a server listens for DNS queries.
listen-on-v6 | Specifies the IPv6 addresses on which a server listens for DNS queries.
listener-clients | Specifies a per-listener quota for active connections.
lmdb-mapsize | Sets a maximum size for the memory map of the new-zone database in LMDB database format.
masterfile-format | Specifies the file format of zone files.
masterfile-style | Specifies the format of zone files during a dump, when the `masterfile-format` is `text`.
match-mapped-addresses | Allows IPv4-mapped IPv6 addresses to match address-match list entries for corresponding IPv4 addresses.
max-cache-size | Sets the maximum amount of memory to use for an individual cache database and its associated metadata.
max-cache-ttl | Specifies the maximum time (in seconds) that the server caches ordinary (positive) answers.
max-clients-per-query | Sets the maximum number of simultaneous recursive clients accepted by the server for any given query before the server drops additional clients.
max-ncache-ttl | Specifies the maximum retention time (in seconds) for storage of negative answers in the server's cache.
max-query-count | Sets the maximum number of iterative queries while servicing a recursive query.
max-query-restarts | Sets the maximum number of chained CNAMEs to follow
max-records | Sets the maximum number of records permitted in a zone.
max-records-per-type | Sets the maximum number of records that can be stored in an RRset.
max-recursion-depth | Sets the maximum number of levels of recursion permitted at any one time while servicing a recursive query.
max-recursion-queries | Sets the maximum number of iterative queries while servicing a recursive query.
max-stale-ttl | Specifies the maximum time that the server retains records past their normal expiry, to return them as stale records.
max-table-size | Sets the maximum size of the table used to track requests and rate-limit responses.
max-types-per-name | Sets the maximum number of RR types that can be stored for an owner name.
max-validation-failures-per-fetch | Sets the maximum number of DNSSEC validation failures that can happen in a single fetch.
max-validations-per-fetch | Sets the maximum number of DNSSEC validations that can happen in a single fetch.
memstatistics | Controls whether memory statistics are written to the file specified by `memstatistics-file` at exit.
min-cache-ttl | Specifies the minimum time (in seconds) that the server caches ordinary (positive) answers.
min-ncache-ttl | Specifies the minimum retention time (in seconds) for storage of negative answers in the server's cache.
no-case-compress | Specifies a list of addresses that require case-insensitive compression in responses.
options | Defines global options to be used by BIND 9.
padding | Adds EDNS Padding options to outgoing messages to increase the packet size.
pid-file | Specifies the pathname of the file where the server writes its process ID.
plugin | Configures plugins in `named.conf`.
port | Specifies the UDP/TCP port number the server uses to receive and send DNS protocol traffic.
prefer-server-ciphers | Specifies that server ciphers should be preferred over client ones.
querylog | Specifies whether query logging should be active when `named` first starts.
recursing-file | Specifies the pathname of the file where the server dumps queries that are currently recursing via `rndc recursing`.
remote-servers | Defines a list of servers to be used by primary and secondary zones.
resolver-use-dns64 | Specifies whether to apply DNS64 mappings when sending queries.
response-policy | Specifies response policy zones for the view or among global options.
responselog | Specifies whether response logging should be active when `named` first starts.
reuseport | Enables kernel load-balancing of sockets.
root-key-sentinel | Controls whether BIND 9 responds to root key sentinel probes.
server | Defines characteristics to be associated with a remote name server.
server-id | Specifies the ID of the server to return in response to a `ID.SERVER` query.
servfail-ttl | Sets the length of time (in seconds) that a SERVFAIL response is cached.
sig0checks-quota | Specifies the maximum number of concurrent SIG(0) signature checks that can be processed by the server.
sig0checks-quota-exempt | Exempts specific clients or client groups from SIG(0) signature checking quota.
sig0key-checks-limit | Specifies the maximum number of SIG(0) keys to consider when trying to verify a message.
sig0message-checks-limit | Specifies the maximum number of matching SIG(0) keys to try to verify a message.
stale-answer-client-timeout | Defines the amount of time (in milliseconds) that `named` waits before attempting to answer a query with a stale RRset from cache.
stale-answer-enable | Enables the returning of "stale" cached answers when the name servers for a zone are not answering.
stale-cache-enable | Enables the retention of "stale" cached answers.
stale-refresh-time | Sets the time window for the return of "stale" cached answers before the next attempt to contact, if the name servers for a given zone are not responding.
statistics-file | Specifies the pathname of the file where the server appends statistics, when using `rndc stats`.
streams-per-connection | Specifies the maximum number of concurrent HTTP/2 streams over an HTTP/2 connection.
tcp-clients | Specifies the maximum number of simultaneous client TCP connections accepted by the server.
tcp-initial-timeout | Sets the amount of time (in milliseconds) that the server waits on a new TCP connection for the first message from the client.
tcp-keepalive | Adds EDNS TCP keepalive to messages sent over TCP.
tcp-listen-queue | Sets the listen-queue depth.
tcp-only | Sets the transport protocol to TCP.
tcp-receive-buffer | Sets the operating system's receive buffer size for TCP sockets.
tcp-send-buffer | Sets the operating system's send buffer size for TCP sockets.
tls-port | Specifies the TCP port number the server uses to receive and send DNS-over-TLS protocol traffic.
transfers | Limits the number of concurrent inbound zone transfers from a server.
udp-receive-buffer | Sets the operating system's receive buffer size for UDP sockets.
udp-send-buffer | Sets the operating system's send buffer size for UDP sockets.
update-quota | Specifies the maximum number of concurrent DNS UPDATE messages that can be processed by the server.
v6-bias | Indicates the number of milliseconds of preference to give to IPv6 name servers.
version | Specifies the version number of the server to return in response to a `version.bind` query.
zero-no-soa-ttl | Specifies whether to set the time to live (TTL) of the SOA record to zero, when returning authoritative negative responses to SOA queries.
zero-no-soa-ttl-cache | Sets the time to live (TTL) to zero when caching a negative response to an SOA query.

### 8.4.6. Transfer Tag Statements

Statement | Description
--- | ---
allow-notify | Defines an `address_match_list` that is allowed to send `NOTIFY` messages for the zone, in addition to addresses defined in the `primaries` option for the zone.
allow-transfer | Defines an `address_match_list` of hosts that are allowed to transfer the zone information from this server.
allow-update | Defines an `address_match_list` of hosts that are allowed to submit dynamic updates for primary zones.
allow-update-forwarding | Defines an `address_match_list` of hosts that are allowed to submit dynamic updates to a secondary server for transmission to a primary.
also-notify | Defines one or more hosts that are sent `NOTIFY` messages when zone changes occur.
ixfr-from-differences | Controls how IXFR transfers are calculated.
max-ixfr-ratio | Sets the maximum size for IXFR responses to zone transfer requests.
max-journal-size | Controls the size of journal files.
max-refresh-time | Limits the zone refresh interval to no less often than the specified value, in seconds.
max-retry-time | Limits the zone refresh retry interval to no less often than the specified value, in seconds.
max-transfer-idle-in | Specifies the number of minutes after which inbound zone transfers making no progress are terminated.
max-transfer-idle-out | Specifies the number of minutes after which outbound zone transfers making no progress are terminated.
max-transfer-time-in | Specifies the number of minutes after which inbound zone transfers are terminated.
max-transfer-time-out | Specifies the number of minutes after which outbound zone transfers are terminated.
min-refresh-time | Limits the zone refresh interval to no more often than the specified value, in seconds.
min-retry-time | Limits the zone refresh retry interval to no more often than the specified value, in seconds.
min-transfer-rate-in | Specifies the minimum traffic rate below which inbound zone transfers are terminated.
multi-master | Controls whether serial number mismatch errors are logged.
notify | Controls whether `NOTIFY` messages are sent on zone changes.
notify-defer | Sets the defer time (in seconds) before sending NOTIFY messages for a zone.
notify-delay | Sets the delay (in seconds) between sending sets of NOTIFY messages for a zone.
notify-rate | Specifies the rate at which NOTIFY requests are sent during normal zone maintenance operations.
notify-source | Defines the IPv4 address (and optional port) to be used for outgoing `NOTIFY` messages.
notify-source-v6 | Defines the IPv6 address (and optional port) to be used for outgoing `NOTIFY` messages.
notify-to-soa | Controls whether the name servers in the NS RRset are checked against the SOA MNAME.
primaries | Defines one or more servers that zone transfer can be requested from.
provide-ixfr | Controls whether a primary responds to an incremental zone request (IXFR) or only responds with a full zone transfer (AXFR).
request-expire | Specifies whether the local server requests the EDNS EXPIRE value, when acting as a secondary.
request-ixfr | Controls whether a secondary requests an incremental zone transfer (IXFR) or a full zone transfer (AXFR).
serial-query-rate | Defines an upper limit on the number of queries per second issued by the server, when querying the SOA RRs used for zone transfers.
startup-notify-rate | Specifies the rate at which NOTIFY requests are sent when the name server is first starting, or when new zones have been added.
transfer-format | Controls whether multiple records can be packed into a message during zone transfers.
transfer-message-size | Limits the uncompressed size of DNS messages used in zone transfers over TCP.
transfer-source | Defines which local IPv4 address(es) are bound to TCP connections used to fetch zones transferred inbound by the server.
transfer-source-v6 | Defines which local IPv6 address(es) are bound to TCP connections used to fetch zones transferred inbound by the server.
transfers-in | Limits the number of concurrent inbound zone transfers.
transfers-out | Limits the number of concurrent outbound zone transfers.
transfers-per-ns | Limits the number of concurrent inbound zone transfers from a remote server.
try-tcp-refresh | Specifies that BIND 9 should attempt to refresh a zone using TCP if UDP queries fail.
update-policy | Sets fine-grained rules to allow or deny dynamic updates (DDNS), based on requester identity, updated content, etc.

### 8.4.7. View Tag Statements

Statement | Description
--- | ---
attach-cache | Allows multiple views to share a single cache database.
in-view | Specifies the view in which a given zone is defined.
match-clients | Specifies a view of DNS namespace for a given subset of client IP addresses.
match-destinations | Specifies a view of DNS namespace for a given subset of destination IP addresses.
match-recursive-only | Specifies that only recursive requests can match this view of the DNS namespace.
view | Allows a name server to answer a DNS query differently depending on who is asking.

### 8.4.8. Zone Tag Statements

Statement | Description
--- | ---
allow-new-zones | Controls the ability to add zones at runtime via `rndc addzone`.
catalog-zones | Configures catalog zones in `named.conf`.
check-integrity | Performs post-load zone integrity checks on primary zones.
check-mx | Checks whether an MX record appears to refer to an IP address.
check-mx-cname | Sets the response to MX records that refer to CNAMEs.
check-sibling | Specifies whether to check for sibling glue when performing integrity checks.
check-spf | Specifies whether to check for a TXT Sender Policy Framework record, if an SPF record is present.
check-srv-cname | Sets the response to SRV records that refer to CNAMEs.
check-svcb | Specifies whether to perform additional checks on SVCB records.
check-wildcard | Checks for non-terminal wildcards.
database | Specifies the type of database to be used to store zone data.
disable-ds-digests | Disables DS digest types from a specified zone.
disable-empty-zone | Disables individual empty zones.
dlz | Configures a Dynamically Loadable Zone (DLZ) database in `named.conf`.
dyndb | Configures a DynDB database in `named.conf`.
empty-contact | Specifies the contact name in the returned SOA record for empty zones.
empty-server | Specifies the server name in the returned SOA record for empty zones.
empty-zones-enable | Enables or disables all empty zones.
file | Specifies the zone's filename.
flush-zones-on-shutdown | Controls whether pending zone writes are flushed when the name server exits.
in-view | Specifies the view in which a given zone is defined.
inline-signing | Specifies whether BIND 9 maintains a separate signed version of a zone.
journal | Allows the default journal's filename to be overridden.
masterfile-format | Specifies the file format of zone files.
max-records | Sets the maximum number of records permitted in a zone.
new-zones-directory | Specifies the directory where configuration parameters are stored for zones added by `rndc addzone`.
notify-defer | Sets the defer time (in seconds) before sending NOTIFY messages for a zone.
notify-delay | Sets the delay (in seconds) between sending sets of NOTIFY messages for a zone.
notify-rate | Specifies the rate at which NOTIFY requests are sent during normal zone maintenance operations.
parent-propagation-delay | Sets the propagation delay from the time the parent zone is updated to when the new version is served by all of the parent zone's name servers.
primaries | Defines one or more servers that zone transfer can be requested from.
response-policy | Specifies response policy zones for the view or among global options.
serial-update-method | Specifies the update method to be used for the zone serial number in the SOA record.
server-addresses | Specifies a list of IP addresses to which queries should be sent in recursive resolution for a static-stub zone.
server-names | Specifies a list of domain names of name servers that act as authoritative servers of a static-stub zone.
startup-notify-rate | Specifies the rate at which NOTIFY requests are sent when the name server is first starting, or when new zones have been added.
type | Specifies the kind of zone in a given configuration.
type forward | Contains forwarding statements that apply to queries within a given domain.
type hint | Contains the initial set of root name servers to be used at BIND 9 startup.
type mirror | Contains a DNSSEC-validated duplicate of the main data for a zone.
type primary | Contains the main copy of the data for a zone.
type redirect | Contains information to answer queries when normal resolution would return NXDOMAIN.
type secondary | Contains a duplicate of the data for a zone that has been transferred from a primary server.
type static-stub | Contains a duplicate of the NS records of a primary zone, but statically configured rather than transferred from a primary server.
type stub | Contains a duplicate of the NS records of a primary zone.
zero-no-soa-ttl | Specifies whether to set the time to live (TTL) of the SOA record to zero, when returning authoritative negative responses to SOA queries.
zero-no-soa-ttl-cache | Sets the time to live (TTL) to zero when caching a negative response to an SOA query.
zone | Specifies the zone in a BIND 9 configuration.
zone-propagation-delay | Sets the propagation delay from the time a zone is first updated to when the new version of the zone is served by all secondary servers.
zone-statistics | Controls the level of statistics gathered for all zones.

### 8.4.9. Deprecated Tag Statements

Statement | Description
--- | ---
avoid-v4-udp-ports | Specifies the range(s) of ports to be excluded from use as sources for UDP/IPv4 messages.
avoid-v6-udp-ports | Specifies the range(s) of ports to be excluded from use as sources for UDP/IPv6 messages.
dialup | Concentrates zone maintenance so that all transfers take place once every `heartbeat-interval`, ideally during a single call.
dnssec-must-be-secure | Defines hierarchies that must or may not be secure (signed and validated).
heartbeat-interval | Sets the interval at which the server performs zone maintenance tasks for all zones marked as `dialup`.
managed-keys |
max-zone-ttl | Specifies a maximum permissible time-to-live (TTL) value, in seconds.
sortlist | Controls the ordering of RRs returned to the client, based on the client's IP address.
trusted-keys |
use-v4-udp-ports | Specifies a list of ports that are valid sources for UDP/IPv4 messages.
use-v6-udp-ports | Specifies a list of ports that are valid sources for UDP/IPv6 messages.

## 8.5. BIND 9 Statistics

BIND 9 maintains lots of statistics information and provides several interfaces for users to access those statistics. The available statistics include all statistics counters that are meaningful in BIND 9, and other information that is considered useful.

The statistics information is categorized into the following sections:

Incoming Requests

  The number of incoming DNS requests for each OPCODE.

Incoming Queries

  The number of incoming queries for each RR type.

Outgoing Queries

  The number of outgoing queries for each RR type sent from the internal resolver, maintained per view.

Incoming Zone Transfers

  Information about in-progress incoming zone transfers.

  This section describes the information that can be seen in the HTML table about in-progress incoming zone transfers. It lists the meaning, units, and possible range of values of each column, and the key/attribute/element name (in parentheses) for the JSON and XML output formats.

  `Zone Name` (`name`)

    Text string. This is the name of the zone being transferred, as specified in the `zone` declaration on this server.

  `Zone Type` (`type`)

    Text string. This is the type of zone being transferred, as specified in the `zone` declaration on this server. Possible values are: `secondary`, `stub`, `redirect`, and `mirror`.

  `Local Serial` (`serial`)

    32-bit unsigned Integer. This is the current (old) serial number of the zone being transferred. It comes from the SOA record held on the current server.

  `Remote Serial` (`remoteserial`)

    32-bit unsigned Integer. This is the new serial number of the zone being transferred. It comes from the SOA record held on the primary server from which the zone is being transferred.

  `IXFR` (`ixfr`)

    Boolean. This says whether the transfer is incremental (using IXFR) or full (using AXFR). Possible values are: `Yes` and `No`.

  `State` (`state`)

    Text string. This is the current state of the transfer for this zone. Possible values and their meanings are:

    > `Needs Refresh`

    >   The zone needs a refresh, but the process has not started yet; this can be due to different factors, like the retry interval of the zone.

    > `Pending`

    >   The zone is flagged for a refresh, but the process is currently in the queue and will start shortly, or is in a waiting state because of rate-limiting; see `serial-query-rate`. The `Duration (s)` timer starts before entering this state.

    > `Refresh SOA`

    >   BIND is sending a refresh SOA query to get the zone serial number and will then initiate a zone transfer, if necessary. If this step is successful, the `SOA Query` and `Got SOA` states are skipped. Otherwise, the zone transfer procedure can still be initiated, and the SOA request will be attempted using the same transport as the zone transfer. The `Duration (s)` timer restarts before entering this state, and for each attempted connection (note that in UDP mode there can be several retries during one “connection” attempt).

    > `Deferred`

    >   The zone is going to be refreshed, but the process was deferred due to quota; see `transfers-in` and `transfers-per-ns`. The `Duration (s)` timer restarts before entering this state.

    > `SOA Query`

    >   BIND is sending an SOA query to get the zone serial number and will then follow with a zone transfer, if necessary. The `Duration (s)` timer restarts before entering this state.

    > `Got SOA`

    >   An answer for the SOA query from the previous step is received, initiating a transfer.

    > `Zone Transfer Request`

    >   BIND is waiting for the zone transfer to start. The `Duration (s)` timer restarts before entering this state.

    > `First Data`

    >   BIND is waiting for the first data record of the transfer.

    > `Receiving IXFR Data`

    >   BIND is receiving data for an IXFR type incremental zone transfer.

    > `Finalizing IXFR`

    >   BIND is finalizing an IXFR type incremental zone transfer.

    > `Receiving AXFR Data`

    >   BIND is receiving data for an AXFR type zone transfer.

    > `Finalizing AXFR`

    >   BIND is finalizing an AXFR type zone transfer.

    Note

    State names can change between BIND versions.

  `Additional Refresh Queued` (`refreshqueued`)

    Boolean. This shows that the zone is flagged for a refresh. This can be set to `Yes` either when the zone transfer is still in one of the pending states (see the description of the `State` column), or when the transfer is in a running state, but the zone was marked for another refresh again (e.g. because of “notify” request from a primary server). Possible values are: `Yes` and `No`.

  `Local Address` (`localaddr`)

    IP address (IPv4 or IPv6, as appropriate) and port number. This shows the source address used to establish the connection for the transfer.

  `Remote Address` (`remoteaddr`)

    IP address (IPv4 or IPv6, as appropriate) and port number. This shows the destination address used to establish the connection for the transfer.

  `SOA Transport` (`soatransport`)

    Text string. This is the transport protocol in use for the SOA query. Note that this value can potentially change during the process. For example, when the transfer is in the `Refresh SOA` state, the `SOA Transport` of the ongoing query can be shown as `UDP`. If that query fails or times out, it then can be retried using another transport, or the transfer process can be initiated in “SOA before” mode, where the SOA query will be attempted using the same transport as the zone transfer. See the description of the `State` field for more information. Possible values are: `UDP`, `TCP`, `TLS`, and `None`.

  `Transport` (`transport`)

    Text string. This is the transport protocol in use for the transfer. Possible values are: `TCP` and `TLS`.

  `TSIG Key Name` (`tsigkeyname`)

    Text string. This is the name of the TSIG key specified for use with this zone in the `zone` declaration (if any).

  `Duration (s)` (`duration`)

    64-bit unsigned Integer. This is the time, in seconds, that the current major state of the transfer process has been running so far. The timer starts after the refresh SOA request is queued (before the `Pending` state), and then restarts several times during the process to indicate the duration of the current major state. See the descriptions of the different states to find out the states before which this timer restarts.

  `Messages Received` (`nmsg`)

    64-bit unsigned Integer. This is the number of DNS messages received. It does not include transport overheads, such as TCP ACK.

  `Records Received` (`nrecs`)

    64-bit unsigned Integer. This is the number of individual RRs received so far. If an address record has, for example, five addresses associated with the same name, it counts as five RRs.

  `Bytes Received` (`nbytes`)

    64-bit unsigned Integer. This is the number of usable bytes of DNS data. It does not include transport overhead.

  `Transfer Rate (B/s)` (`rate`)

    64 bit unsigned Integer. This is the average zone transfer rate in bytes-per-second during the latest full interval that is configured by the `min-transfer-rate-in` configuration option. If no such interval has passed yet, then the overall average rate is reported instead.

  Note

  Depending on the current state of the transfer, some of the values may be empty or set to `-` (meaning “not available”). Also, in the case of the JSON output format, the corresponding keys can be missing or values can be set to `NULL`. For example, it is unknown whether a transfer is using AXFR or IXFR until the first data is received (see the description of the `State` column).

Name Server Statistics

  Statistics counters for incoming request processing.

Zone Maintenance Statistics

  Statistics counters regarding zone maintenance operations, such as zone transfers.

Resolver Statistics

  Statistics counters for name resolutions performed in the internal resolver, maintained per view.

Cache DB RRsets

  Statistics counters related to cache contents, maintained per view.

  The “NXDOMAIN” counter is the number of names that have been cached as nonexistent. Counters named for RR types indicate the number of active RRsets for each type in the cache database.

  If an RR type name is preceded by an exclamation point (!), it represents the number of records in the cache which indicate that the type does not exist for a particular name; this is also known as “NXRRSET”. If an RR type name is preceded by a hash mark (#), it represents the number of RRsets for this type that are present in the cache but whose TTLs have expired; these RRsets may only be used if stale answers are enabled. If an RR type name is preceded by a tilde (~), it represents the number of RRsets for this type that are present in the cache database but are marked for garbage collection; these RRsets cannot be used.

Socket I/O Statistics

  Statistics counters for network-related events.

A subset of Name Server Statistics is collected and shown per zone for which the server has the authority, when `zone-statistics` is set to `full` (or `yes`), for backward compatibility. See the description of `zone-statistics` in `options` for further details.

These statistics counters are shown with their zone and view names. The view name is omitted when the server is not configured with explicit views.

There are currently two user interfaces to get access to the statistics. One is in plain-text format, dumped to the file specified by the `statistics-file` configuration option; the other is remotely accessible via a statistics channel when the `statistics-channels` statement is specified in the configuration file.

### 8.5.1. The Statistics File

The text format statistics dump begins with a line, like:

`+++ Statistics Dump +++ (973798949)`

The number in parentheses is a standard Unix-style timestamp, measured in seconds since January 1, 1970. Following that line is a set of statistics information, which is categorized as described above. Each section begins with a line, like:

`++ Name Server Statistics ++`

Each section consists of lines, each containing the statistics counter value followed by its textual description; see below for available counters. For brevity, counters that have a value of 0 are not shown in the statistics file.

The statistics dump ends with the line where the number is identical to the number in the beginning line; for example:

`--- Statistics Dump --- (973798949)`

### 8.5.2. Statistics Counters

The following lists summarize the statistics counters that BIND 9 provides. For each counter, the abbreviated symbol name is given; these symbols are shown in the statistics information accessed via an HTTP statistics channel. The description of the counter is also shown in the statistics file but, in this document, may be slightly modified for better readability.

#### 8.5.2.1. Name Server Statistics Counters

`Requestv4`

  This indicates the number of IPv4 requests received. Note: this also counts non-query requests.

`Requestv6`

  This indicates the number of IPv6 requests received. Note: this also counts non-query requests.

`ReqEdns0`

  This indicates the number of requests received with EDNS(0).

`ReqBadEDN SVer`

  This indicates the number of requests received with an unsupported EDNS version.

`ReqTSIG`

  This indicates the number of requests received with TSIG.

`ReqSIG0`

  This indicates the number of requests received with SIG(0).

`ReqBadSIG`

  This indicates the number of requests received with an invalid (TSIG or SIG(0)) signature.

`ReqTCP`

  This indicates the number of TCP requests received.

`AuthQryRej`

  This indicates the number of rejected authoritative (non-recursive) queries.

`RecQryRej`

  This indicates the number of rejected recursive queries.

`XfrRej`

  This indicates the number of rejected zone transfer requests.

`UpdateRej`

  This indicates the number of rejected dynamic update requests.

`Response`

  This indicates the number of responses sent.

`RespTruncated`

  This indicates the number of truncated responses sent.

`RespEDNS0`

  This indicates the number of responses sent with EDNS(0).

`RespTSIG`

  This indicates the number of responses sent with TSIG.

`RespSIG0`

  This indicates the number of responses sent with SIG(0).

`QrySuccess`

  This indicates the number of queries that resulted in a successful answer, meaning queries which return a NOERROR response with at least one answer RR. This corresponds to the `success` counter of previous versions of BIND 9.

`QryAuthAns`

  This indicates the number of queries that resulted in an authoritative answer.

`QryNoauthAns`

  This indicates the number of queries that resulted in a non-authoritative answer.

`QryReferral`

  This indicates the number of queries that resulted in a referral answer. This corresponds to the `referral` counter of previous versions of BIND 9.

`QryNxrrset`

  This indicates the number of queries that resulted in NOERROR responses with no data. This corresponds to the `nxrrset` counter of previous versions of BIND 9.

`QrySERVFAIL`

  This indicates the number of queries that resulted in SERVFAIL.

`QryFORMERR`

  This indicates the number of queries that resulted in FORMERR.

`QryNXDOMAIN`

  This indicates the number of queries that resulted in NXDOMAIN. This corresponds to the `nxdomain` counter of previous versions of BIND 9.

`QryRecursion`

  This indicates the number of queries that caused the server to perform recursion in order to find the final answer. This corresponds to the `recursion` counter of previous versions of BIND 9.

`QryDuplicate`

  This indicates the number of queries which the server attempted to recurse but for which it discovered an existing query with the same IP address, port, query ID, name, type, and class already being processed. This corresponds to the `duplicate` counter of previous versions of BIND 9.

`QryDropped`

  This indicates the number of recursive queries dropped by the server as a result of configured limits. These limits include the settings of the `fetches-per-zone`, `fetches-per-server`, `clients-per-query`, and `max-clients-per-query` options, as well as the `rate-limit` option. This corresponds to the `dropped` counter of previous versions of BIND 9.

`QryFailure`

  This indicates the number of query failures. This corresponds to the `failure` counter of previous versions of BIND 9. Note: this counter is provided mainly for backward compatibility with previous versions; normally, more fine-grained counters such as `AuthQryRej` and `RecQryRej` that would also fall into this counter are provided, so this counter is not of much interest in practice.

`QryNXRedir`

  This indicates the number of queries that resulted in NXDOMAIN that were redirected.

`QryNXRedirRLookup`

  This indicates the number of queries that resulted in NXDOMAIN that were redirected and resulted in a successful remote lookup.

`XfrReqDone`

  This indicates the number of requested and completed zone transfers.

`UpdateReqFwd`

  This indicates the number of forwarded update requests.

`UpdateRespFwd`

  This indicates the number of forwarded update responses.

`UpdateFwdFail`

  This indicates the number of forwarded dynamic updates that failed.

`UpdateDone`

  This indicates the number of completed dynamic updates.

`UpdateFail`

  This indicates the number of failed dynamic updates.

`UpdateBadPrereq`

  This indicates the number of dynamic updates rejected due to a prerequisite failure.

`UpdateQuota`

  This indicates the number of times a dynamic update or update forwarding request was rejected because the number of pending requests exceeded `update-quota`.

`RateDropped`

  This indicates the number of responses dropped due to rate limits.

`RateSlipped`

  This indicates the number of responses truncated by rate limits.

`RPZRewrites`

  This indicates the number of response policy zone rewrites.

#### 8.5.2.2. Zone Maintenance Statistics Counters

`NotifyOutv4`

  This indicates the number of IPv4 notifies sent.

`NotifyOutv6`

  This indicates the number of IPv6 notifies sent.

`NotifyInv4`

  This indicates the number of IPv4 notifies received.

`NotifyInv6`

  This indicates the number of IPv6 notifies received.

`NotifyRej`

  This indicates the number of incoming notifies rejected.

`SOAOutv4`

  This indicates the number of IPv4 SOA queries sent.

`SOAOutv6`

  This indicates the number of IPv6 SOA queries sent.

`AXFRReqv4`

  This indicates the number of requested IPv4 AXFRs.

`AXFRReqv6`

  This indicates the number of requested IPv6 AXFRs.

`IXFRReqv4`

  This indicates the number of requested IPv4 IXFRs.

`IXFRReqv6`

  This indicates the number of requested IPv6 IXFRs.

`XfrSuccess`

  This indicates the number of successful zone transfer requests.

`XfrFail`

  This indicates the number of failed zone transfer requests.

#### 8.5.2.3. Resolver Statistics Counters

`Queryv4`

  This indicates the number of IPv4 queries sent.

`Queryv6`

  This indicates the number of IPv6 queries sent.

`Responsev4`

  This indicates the number of IPv4 responses received.

`Responsev6`

  This indicates the number of IPv6 responses received.

`NXDOMAIN`

  This indicates the number of NXDOMAINs received.

`SERVFAIL`

  This indicates the number of SERVFAILs received.

`FORMERR`

  This indicates the number of FORMERRs received.

`OtherError`

  This indicates the number of other errors received.

`EDNS0Fail`

  This indicates the number of EDNS(0) query failures.

`Mismatch`

  This indicates the number of mismatched responses received, meaning the DNS ID, response’s source address, and/or the response’s source port does not match what was expected. (The port must be 53 or as defined by the `port` option.) This may be an indication of a cache poisoning attempt.

`Truncated`

  This indicates the number of truncated responses received.

`Lame`

  This indicates the number of lame delegations received.

`Retry`

  This indicates the number of query retries performed.

`QueryAbort`

  This indicates the number of queries aborted due to quota control.

`QuerySockFail`

  This indicates the number of failures in opening query sockets. One common reason for such failures is due to a limitation on file descriptors.

`QueryCurUDP`

  This indicates the number of UDP queries in progress.

`QueryCurTCP`

  This indicates the number of TCP queries in progress.

`QueryTimeout`

  This indicates the number of query timeouts.

`GlueFetchv4`

  This indicates the number of IPv4 NS address fetches invoked.

`GlueFetchv6`

  This indicates the number of IPv6 NS address fetches invoked.

`GlueFetchv4Fail`

  This indicates the number of failed IPv4 NS address fetches.

`GlueFetchv6Fail`

  This indicates the number of failed IPv6 NS address fetches.

`ValAttempt`

  This indicates the number of attempted DNSSEC validations.

`ValOk`

  This indicates the number of successful DNSSEC validations.

`ValNegOk`

  This indicates the number of successful DNSSEC validations on negative information.

`ValFail`

  This indicates the number of failed DNSSEC validations.

`QryRTTnn`

  This provides a frequency table on query round-trip times (RTTs). Each `nn` specifies the corresponding frequency. In the sequence of `nn_1`, `nn_2`, …, `nn_m`, the value of `nn_i` is the number of queries whose RTTs are between `nn_(i-1)` (inclusive) and `nn_i` (exclusive) milliseconds. For the sake of convenience, we define `nn_0` to be 0. The last entry should be represented as `nn_m+`, which means the number of queries whose RTTs are equal to or greater than `nn_m` milliseconds.

`NumFetch`

  This indicates the number of active fetches.

`BucketSize`

  This indicates the number of the resolver’s internal buckets (a static number).

`REFUSED`

  This indicates the number of REFUSED responses received.

`ClientCookieOut`

  This indicates the number of COOKIE messages sent to an authoritative server with only a client cookie.

`ServerCookieOut`

  This indicates the number of COOKIE messages sent to an authoritative server with both a client and a cached server cookie.

`CookieIn`

  This indicates the number of COOKIE replies received from an authoritative server.

`CookieClientOk`

  This indicates the number of correctly formed COOKIE client responses received.

`BadEDNSVersion`

  This indicates the number of bad EDNS version replies received.

`BadCookieRcode`

  This indicates the number of BADCOOKIE response codes received from an authoritative server.

`ZoneQuota`

  This indicates the number of queries spilled for exceeding the `fetches-per-zone` quota.

`ServerQuota`

  This indicates the number of queries spilled for exceeding the `fetches-per-server` quota.

`ClientQuota`

  This indicates the number of queries spilled for exceeding the `clients-per-query` quota.

`NextItem`

  This indicates the number of times the server waited for the next item after receiving an invalid response.

`Priming`

  This indicates the number of priming fetches performed by the resolver.

#### 8.5.2.4. Socket I/O Statistics Counters

Socket I/O statistics counters are defined per socket type, which are `UDP4` (UDP/IPv4), `UDP6` (UDP/IPv6), `TCP4` (TCP/IPv4), and `TCP6` (TCP/IPv6). In the following list, `<TYPE>` represents a socket type. Not all counters are available for all socket types; exceptions are noted in the descriptions.

`<TYPE>Open`

  This indicates the number of sockets opened successfully.

`<TYPE>OpenFail`

  This indicates the number of failures to open sockets.

`<TYPE>Close`

  This indicates the number of closed sockets.

`<TYPE>BindFail`

  This indicates the number of failures to bind sockets.

`<TYPE>ConnFail`

  This indicates the number of failures to connect sockets.

`<TYPE>Conn`

  This indicates the number of connections established successfully.

`<TYPE>AcceptFail`

  This indicates the number of failures to accept incoming connection requests. This counter does not apply to the `UDP` type.

`<TYPE>Accept`

  This indicates the number of incoming connections successfully accepted. This counter does not apply to the `UDP` type.

`<TYPE>SendErr`

  This indicates the number of errors in socket send operations.

`<TYPE>RecvErr`

  This indicates the number of errors in socket receive operations, including errors of send operations on a connected UDP socket, notified by an ICMP error message.