BIND 9.3.2 - Chapter 6

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Administrator Reference Manual
 · Configuration Reference

• Configuration File Elements
• Address Match Lists
• Comment Syntax
• Configuration File Grammar
• acl Statement Grammar
• acl Statement Definition and Usage
• controls Statement Grammar
• controls Statement Definition and Usage
• include Statement Grammar
• include Statement Definition and Usage
• key Statement Grammar
• key Statement Definition and Usage
• logging Statement Grammar
• logging Statement Definition and Usage
• lwres Statement Grammar
• lwres Statement Definition and Usage
• masters Statement Grammar
• masters Statement Definition and Usage
• options Statement Grammar
• options Statement Definition and Usage
• server Statement Grammar
• server Statement Definition and Usage
• trusted-keys Statement Grammar
• trusted-keys Statement Definition and Usage
• view Statement Grammar
• view Statement Definition and Usage
• zone Statement Grammar
• zone Statement Definition and Usage
• Zone File
• Types of Resource Records and When to Use Them
• Discussion of MX Records
• Setting TTLs
• Inverse Mapping in IPv4
• Other Zone File Directives
• BIND Master File Extension: the $GENERATE Directive

BIND 9 configuration is broadly similar to BIND 8; however, there are a few new areas of configuration, such as views. BIND 8 configuration files should work with few alterations in BIND 9, although more complex configurations should be reviewed to check if they can be more efficiently implemented using the new features found in BIND 9.

BIND 4 configuration files can be converted to the new format using the shell script contrib/named-bootconf/named-bootconf.sh.

Configuration File Elements

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

Address Match Lists

Syntax

address_match_list = address_match_list_element ; [ address_match_list_element; ... ]
address_match_list_element = [ ! ] (ip_address [/length] | key key_id | acl_name | { address_match_list } )

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:

• an IP address (IPv4 or IPv6)
• an IP prefix (in `/' notation)
• a key ID, as defined by the key statement
• 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 list is traversed in order until an element matches. 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-query, allow-transfer, allow-update, allow-update-forwarding, and blackhole all use address match lists this. Similarly, the listen-on option will cause the server to not accept queries on any of the machine's addresses which do not match the list.

Because of the first-match aspect of the algorithm, 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 will match 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 having 1.2.3.13 blocked by the negation but all other 1.2.3.* hosts fall through.

Comment Syntax

The BIND 9 comment syntax allows for comments to appear anywhere that white space 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.

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

Definition and Usage

Comments may appear 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, if you prefer) comments start with the character # (number 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

You cannot use the semicolon (`;') character to start a comment such as you would in a zone file. The semicolon indicates the end of a configuration statement.

Configuration File Grammar

A BIND 9 configuration consists of statements and comments. Statements end with a semicolon. Statements and comments are the only elements that can appear without enclosing braces. Many statements contain a block of sub-statements, which are also terminated with a semicolon.

The following statements are supported:

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

acl Statement Grammar

acl acl-name {
   address_match_list
};

acl Statement Definition and Usage

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

Note that an address match list's name must be defined with acl before it can be used elsewhere; no forward references are allowed.

The following ACLs are built-in:

controls Statement Grammar

controls {
   inet ( ip_addr | * ) [ port ip_port ] allow { address_match_list }
      keys { key_list };
   [ inet ...; ]
};

controls Statement Definition and Usage

The controls statement declares control channels to be used by system administrators to control 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.

An inet control channel is a TCP socket listening at the specified ip_port on the specified ip_addr, which can be an IPv4 or IPv6 address. An ip_addr of * is interpreted as the IPv4 wildcard address; connections will be accepted on any of the system's IPv4 addresses. To listen on the IPv6 wildcard address, use an ip_addr of ::. If you will only use rndc 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. "*" cannot be used for ip_port.

The ability to issue commands over the control channel is restricted by the allow and keys clauses. Connections to the control channel are permitted based on the address_match_list. This is for simple IP address based filtering only; any key_id elements of the address_match_list are ignored.

The primary authorization mechanism of the command channel is the key_list, which contains a list of key_ids. Each key_id in the key_list is authorized to execute commands over the control channel. See Remote Name Daemon Control application in the section called “Administrative Tools”) for information about configuring keys in rndc.

If no controls statement is present, named will set 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 will attempt to load the command channel key from the file rndc.key in /etc (or whatever sysconfdir was specified as when BIND was built). To create a rndc.key file, run rndc-confgen -a.

The rndc.key feature was created to ease the transition of systems from BIND 8, which did not have digital signatures on its command channel messages and thus did not have a keys clause. It makes it possible to use an existing BIND 8 configuration file in BIND 9 unchanged, and still have rndc work the same way ndc worked in BIND 8, simply by executing the command rndc-confgen -a after BIND 9 is installed.

Since the rndc.key feature is only intended to allow the backward-compatible usage of BIND 8 configuration files, this feature does not have a high degree of configurability. You cannot easily change the key name or the size of the secret, so you should make a rndc.conf with your own key if you wish to change those things. The rndc.key file also has its permissions set such that only the owner of the file (the user that named is running as) can access it. If you desire greater flexibility in allowing other users to access rndc commands then you need to create an rndc.conf and make it group readable by a group that contains the users who should have access.

The UNIX control channel type of BIND 8 is not supported in BIND 9, and is not expected to be added in future releases. If it is present in the controls statement from a BIND 8 configuration file, it is ignored and a warning is logged.

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

include Statement Grammar

include filename;

include Statement Definition and Usage

The include statement inserts the specified file at the point where the include statement is encountered. The include statement 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.

key Statement Grammar

key key_id {
   algorithm string;
   secret string;
};

key Statement Definition and Usage

The key statement defines a shared secret key for use with TSIG (see the section called “TSIG”) or the command channel (see the section called “controls Statement Definition and Usage”).

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 (see the section called “controls Statement Definition and Usage”) must be defined at the top level.

The key_id, also known as the key name, is a domain name uniquely identifying 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.

The algorithm_id is a string that specifies a security/authentication algorithm. The only algorithm currently supported with TSIG authentication is hmac-md5. The secret_string is the secret to be used by the algorithm, and is treated as a base-64 encoded string.

logging Statement Grammar

logging {
   [ channel channel_name {
     ( file path name
          [ versions ( number | unlimited ) ]
          [ size size spec ]
        | syslog syslog_facility
        | stderr
        | null );
     [ severity (critical | error | warning | notice |
        info | debug [ level ] | dynamic ); ]
     [ print-category yes or no; ]
     [ print-severity yes or no; ]
     [ print-time yes or no; ]
   }; ]
   [ category category_name {
     channel_name ; [ channel_name ; ... ]
   }; ]
   ...
};

logging Statement 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 are wanted. If there is no logging statement, the logging configuration will be:

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

In BIND 9, the logging configuration is only established when the entire configuration file has been parsed. In BIND 8, it was established as soon as the logging statement was parsed. When the server is starting 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.

The channel Phrase

All log output goes to one or more channels; you can make as many of them as you want.

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

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

The file destination clause directs the channel to a disk file. It can include limitations both on how large the file is allowed to become, and how many versions of the file will be saved each time the file is opened.

If you use the versions log file option, then named will retain that many backup versions of the file by renaming them when opening. For example, if you choose to keep 3 old versions of the file lamers.log then just before it is opened lamers.log.1 is renamed to lamers.log.2, lamers.log.0 is renamed to lamers.log.1, and lamers.log is renamed to lamers.log.0. You can say versions unlimited to not limit the number of versions. If a size option is associated with the log file, then renaming is only done when the file being opened exceeds the indicated size. No backup versions are kept by default; any existing log file is simply appended.

The size option for files is used to limit log growth. If the file ever exceeds the size, then named will stop writing to the file unless it has a versions option associated with it. If backup versions are kept, the files are rolled as described above and a new one begun. If there is no versions option, no more data will be 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.

Example usage of the size and versions options:

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

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 will handle messages sent to this facility is described in the syslog.conf man page. If you have a system which uses a very old version of syslog that only uses two arguments to the openlog() function, then this clause is silently ignored.

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

If you are using syslog, then the syslog.conf priorities will 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 will cause 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.

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, for example when debugging a configuration.

The server can supply extensive debugging information when it is in debugging mode. If the server's global debug level is greater than zero, then debugging mode will be 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 ndc notrace. All debugging messages in the server have a debug level, and higher debug levels give more detailed output. Channels that specify a specific debug severity, for example:

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

will get debugging output of level 3 or less any time the server is in debugging mode, regardless of the global debugging level. Channels with dynamic severity use the server's global debug level to determine what messages to print.

If print-time has been turned on, then the date and time will be logged. print-time may be specified for a syslog channel, but is usually pointless since syslog also prints the date and time. If print-category is requested, then the category of the message will be logged as well. Finally, if print-severity is on, then the severity level of the message will be logged. The print- options may be used in any combination, and will always be 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

There are four predefined channels that are used for named's default logging as follows. How they are used is described in the section called “The category Phrase”.

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

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

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

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

The default_debug channel has the special property that it only produces output when the server's debug level is nonzero. It normally writes to a file 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 up and still running as root is discarded. If you need to capture this output, you must run the server with the "-g" option and redirect standard error to a file.

Once a channel is defined, it cannot be redefined. Thus you cannot alter the built-in channels directly, but you can modify the default logging by pointing categories at channels you have defined.

The category Phrase

There are many categories, so you can send the logs you want to see wherever you want, without seeing logs you don't want. If you don't specify a list of channels for a category, then log messages in that category will be sent to the default category instead. If you don't specify a default category, the following "default default" is used:

category default { default_syslog; default_debug; };

As an example, let's say you want to log security events to a file, but you also want keep the default logging behavior. You'd 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; };

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.

lwres Statement Grammar

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

lwres {
 [ listen-on { ip_addr [port ip_port] ; [ ip_addr [port ip_port] ; ... ] }; ]
 [ view view_name; ]
 [ search { domain_name ; [ domain_name ; ... ] }; ]
 [ ndots number; ]
};

lwres Statement Definition and Usage

The lwres statement configures the name server to also act as a lightweight resolver server, see the section called “Running a Resolver Daemon”. There may be be multiple lwres statements configuring lightweight resolver servers with different properties.

The listen-on statement specifies a list of addresses (and ports) that this instance of a lightweight resolver daemon should accept requests on. If no port is specified, port 921 is used. If this statement is omitted, requests will be accepted on 127.0.0.1, port 921.

The view statement binds this instance of a lightweight resolver daemon to a view in the DNS namespace, so that the response will be constructed in the same manner as a normal DNS query matching this view. If this statement is omitted, the default view is used, and if there is no default view, an error is triggered.

The search statement is equivalent to the search statement in /etc/resolv.conf. It provides a list of domains which are appended to relative names in queries.

The ndots statement is equivalent to the ndots statement in /etc/resolv.conf. It indicates the minimum number of dots in a relative domain name that should result in an exact match lookup before search path elements are appended.

masters Statement Grammar

masters name [port ip_port] { ( masters_list | ip_addr [port ip_port] [key key] ) ; [...] } ;

masters Statement Definition and Usage

masters lists allow for a common set of masters to be easily used by multiple stub and slave zones.

options Statement Grammar

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

options {
 [ version version_string; ]
 [ hostname hostname_string; ]
 [ server-id server_id_string; ]
 [ directory path_name; ]
 [ key-directory path_name; ]
 [ named-xfer path_name; ]
 [ tkey-domain domainname; ]
 [ tkey-dhkey key_name key_tag; ]
 [ dump-file path_name; ]
 [ memstatistics-file path_name; ]
 [ pid-file path_name; ]
 [ statistics-file path_name; ]
 [ zone-statistics yes_or_no; ]
 [ auth-nxdomain yes_or_no; ]
 [ deallocate-on-exit yes_or_no; ]
 [ dialup dialup_option; ]
 [ fake-iquery yes_or_no; ]
 [ fetch-glue yes_or_no; ]
 [ flush-zones-on-shutdown yes_or_no; ]
 [ has-old-clients yes_or_no; ]
 [ host-statistics yes_or_no; ]
 [ host-statistics-max number; ]
 [ minimal-responses yes_or_no; ]
 [ multiple-cnames yes_or_no; ]
 [ notify yes_or_no | explicit; ]
 [ recursion yes_or_no; ]
 [ rfc2308-type1 yes_or_no; ]
 [ use-id-pool yes_or_no; ]
 [ maintain-ixfr-base yes_or_no; ]
 [ dnssec-enable yes_or_no; ]
 [ dnssec-lookaside domain trust-anchor domain; ]
 [ dnssec-must-be-secure domain yes_or_no; ]
 [ forward ( only | first ); ]
 [ forwarders { [ ip_addr [port ip_port] ; ... ] }; ]
 [ dual-stack-servers [port ip_port] { ( domain_name [port ip_port] | ip_addr [port ip_port] ) ; ... }; ]
 [ check-names ( master | slave | response )( warn | fail | ignore ); ]
 [ allow-notify { address_match_list }; ]
 [ allow-query { address_match_list }; ]
 [ allow-transfer { address_match_list }; ]
 [ allow-recursion { address_match_list }; ]
 [ allow-update-forwarding { address_match_list }; ]
 [ allow-v6-synthesis { address_match_list }; ]
 [ blackhole { address_match_list }; ]
 [ avoid-v4-udp-ports { port_list }; ]
 [ avoid-v6-udp-ports { port_list }; ]
 [ listen-on [ port ip_port ] { address_match_list }; ]
 [ listen-on-v6 [ port ip_port ] { address_match_list }; ]
 [ query-source [ address ( ip_addr | * ) ] [ port ( ip_port | * ) ]; ]
 [ query-source-v6 [ address ( ip_addr | * ) ] [ port ( ip_port | * ) ]; ]
 [ max-transfer-time-in number; ]
 [ max-transfer-time-out number; ]
 [ max-transfer-idle-in number; ]
 [ max-transfer-idle-out number; ]
 [ tcp-clients number; ]
 [ recursive-clients number; ]
 [ serial-query-rate number; ]
 [ serial-queries number; ]
 [ tcp-listen-queue number; ]
 [ transfer-format ( one-answer | many-answers ); ]
 [ transfers-in number; ]
 [ transfers-out number; ]
 [ transfers-per-ns number; ]
 [ transfer-source (ip4_addr | *) [port ip_port] ; ]
 [ transfer-source-v6 (ip6_addr | *) [port ip_port] ; ]
 [ alt-transfer-source (ip4_addr | *) [port ip_port] ; ]
 [ alt-transfer-source-v6 (ip6_addr | *) [port ip_port] ; ]
 [ use-alt-transfer-source yes_or_no; ]
 [ notify-source (ip4_addr | *) [port ip_port] ; ]
 [ notify-source-v6 (ip6_addr | *) [port ip_port] ; ]
 [ also-notify { ip_addr [port ip_port] ; [ ip_addr [port ip_port] ; ... ] }; ]
 [ max-ixfr-log-size number; ]
 [ max-journal-size size_spec; ]
 [ coresize size_spec ; ]
 [ datasize size_spec ; ]
 [ files size_spec ; ]
 [ stacksize size_spec ; ]
 [ cleaning-interval number; ]
 [ heartbeat-interval number; ]
 [ interface-interval number; ]
 [ statistics-interval number; ]
 [ topology { address_match_list }];
 [ sortlist { address_match_list }];
 [ rrset-order { order_spec ; [ order_spec ; ... ] ] };
 [ lame-ttl number; ]
 [ max-ncache-ttl number; ]
 [ max-cache-ttl number; ]
 [ sig-validity-interval number ; ]
 [ min-roots number; ]
 [ use-ixfr yes_or_no ; ]
 [ provide-ixfr yes_or_no; ]
 [ request-ixfr yes_or_no; ]
 [ treat-cr-as-space yes_or_no ; ]
 [ min-refresh-time number ; ]
 [ max-refresh-time number ; ]
 [ min-retry-time number ; ]
 [ max-retry-time number ; ]
 [ port ip_port; ]
 [ additional-from-auth yes_or_no ; ]
 [ additional-from-cache yes_or_no ; ]
 [ random-device path_name ; ]
 [ max-cache-size size_spec ; ]
 [ match-mapped-addresses yes_or_no; ]
 [ preferred-glue ( A | AAAA | NONE ); ]
 [ edns-udp-size number; ]
 [ root-delegation-only [ exclude { namelist } ] ; ]
 [ querylog yes_or_no ; ]
 [ disable-algorithms domain { algorithm; [ algorithm; ] }; ]
};

options Statement 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 will be used.

options {
 root-delegation-only exclude { "de"; "lv"; "us"; "museum"; };
};

Boolean Options

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 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.

Forwarding can also be configured on a per-domain basis, allowing for the global forwarding options to be overridden in a variety of ways. You can set particular domains to use different forwarders, or have a different forward only/first behavior, or not forward at all, see the section called “zone Statement Grammar”.

Dual-stack Servers

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

Access Control

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

Interfaces

The interfaces and ports that the server will answer queries from may be specified using the listen-on option. listen-on takes an optional port, and an address_match_list. The server will listen on all interfaces allowed by the address match list. If a port is not specified, port 53 will be used.

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; };

will enable the name server on port 53 for 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.

If no listen-on is specified, the server will listen on port 53 on all interfaces.

The listen-on-v6 option is used to specify the interfaces and the ports on which the server will listen for incoming queries sent using IPv6.

When

{ any; }

is specified as the address_match_list for the listen-on-v6 option, the server does not bind a separate socket to each IPv6 interface address as it does for IPv4 if the operating system has enough API support for IPv6 (specifically if it conforms to RFC 3493 and RFC 3542). Instead, it listens on the IPv6 wildcard address. If the system only has incomplete API support for IPv6, however, the behavior is the same as that for IPv4.

A list of particular IPv6 addresses can also be specified, in which case the server listens on a separate socket for each specified address, regardless of whether the desired API is supported by the system.

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

listen-on-v6 { any; };
listen-on-v6 port 1234 { !2001:db8::/32; any; };

will enable the name server on port 53 for any IPv6 addresses (with a single wildcard socket), and on port 1234 of IPv6 addresses that is not in the prefix 2001:db8::/32 (with separate sockets for each matched address.)

To make the server not listen on any IPv6 address, use

listen-on-v6 { none; };

If no listen-on-v6 option is specified, the server will not listen on any IPv6 address.

Query Address

If the server doesn't know the answer to a question, it will query other name servers. query-source specifi