BIND 9 - named.conf reference





acl_name The name of an address_match_list as defined by the acl statement.
address_match_list A list of one or more ip_addr, ip_prefix, key_id, or acl_name elements.
domain_name A quoted string which will be used as a DNS name, for example "my.test.domain".
dotted_decimal One or more integers valued 0 through 255 separated only by dots (`.'), such as 123, 45.67 or
ip4_addr An IPv4 address with exactly four elements in dotted_decimal notation.
ip6_addr An IPv6 address, such as fe80::200:f8ff:fe01:9742.
ip_addr An ip4_addr or ip6_addr.
ip_port An IP port number. number is limited to 0 through 65535, with values below 1024 typically restricted to root-owned processes. In some cases an asterisk (`*') character can be used as a placeholder to select a random high-numbered port.
ip_prefix An IP network specified as an ip_addr, followed by a slash (`/') and then the number of bits in the netmask. Trailing zeros in a ip_addr may omitted. For example, 127/8 is the network with netmask and is network with netmask
key_id A domain_name representing the name of a shared key, to be used for transaction security.
key_list A list of one or more key_ids, separated by semicolons and ending with a semicolon.
number A non-negative integer with an entire range limited by the range of a C language signed integer (2,147,483,647 on a machine with 32 bit integers). Its acceptable value might further be limited by the context in which it is used.
path_name A quoted string which will be used as a pathname, such as zones/master/my.test.domain.
size_spec A number, the word unlimited, or the word default. The maximum value of size_spec is that of unsigned long integers on the machine. An unlimited size_spec requests unlimited use, or the maximum available amount. A default size_spec uses the limit that was in force when the server was started. A number 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. Integer storage overflow is currently silently ignored during conversion of scaled values, resulting in values less than intended, possibly even negative. Using unlimited is the best way to safely set a really large number.
yes_or_no Either yes or no. The words true and false are also accepted, as are the numbers 1 and 0.
dialup_option One of yes, no, notify, notify-passive, refresh or passive. When used in a zone, notify-passive, refresh, and passive are restricted to slave and stub zones.


Address Match Lists



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 to define priorities for querying other nameservers and to set the addresses on which named will listen for queries. The elements which constitute an address match list can be any of the following:

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 as a topology, 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 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.

When used with the topology clause, a non-negated match returns a distance based on its position on the list (the closer the match is to the start of the list, the shorter the distance is between it and the server). A negated match will be assigned the maximum distance from the server. If there is no match, the address will get a distance which is further than any non-negated list element, and closer than any negated element.

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; !; the element is completely useless because the algorithm will match any lookup for to the 1.2.3/24 element. Using !; 1.2.3/24 fixes that problem by having 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 C, C++, or shell/perl constructs.



/* 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 substatements, which are also terminated with a semicolon.

The following statements 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.
include includes a file.
key specifies key information for use in authentication and authorization using TSIG.
logging specifies what the server logs, and where the log messages are sent.
options controls global server configuration options and sets defaults for other statements.
server sets certain configuration options on a per-server basis.
trusted-keys defines trusted DNSSEC keys.
view defines a view.
zone defines a zone.

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


acl Statement Grammar

acl acl-name { 


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:

any Matches all hosts.
none Matches no hosts.
localhost Matches the IP addresses of all interfaces on the system.
localnets Matches any host on a network for which the system has an interface.


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 affect the operation of the local nameserver. These control channels are used by the rndc utility to send commands to and retrieve non-DNS results from a nameserver.

An inet control channel is a TCP/IP socket accessible to the Internet, created at the specified ip_port on the specified ip_addr. If no port is specified, port 953 is used by default. "*" 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 permissions in address_match_list. key_id members of the address_match_list are ignored, and instead are interpreted independently based the key_list. Each key_id in the key_list is allowed to be used to authenticate commands and responses given over the control channel by digitally signing each message between the server and a command client (See Remote Name Daemon Control application in Section All commands to the control channel must be signed by one of its specified keys to be honored.

The UNIX control channel type of BIND 8 is not supported in BIND 9.0.0, and is not expected to be added in future releases. If it is present in the controls statement from a BIND 8 configuration file, a non-fatal warning will be logged.


include Statement Grammar

include filename;


include Statement Definition and Usage

The include statement inserts the specified file at the point that 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 a nameserver.


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.

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 nameserver. 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"; };

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.

The size option for files is simply a hard ceiling on log growth. If the file ever exceeds the size, then named will not write anything more to it until the file is reopened; exceeding the size does not automatically trigger a reopen. The default behavior is not to limit the size of the file.

If you use the version 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. No rolled versions are kept by default; any existing log file is simply appended. The unlimited keyword is synonymous with 99 in current BIND releases.

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. 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.

Note: the latter method is not yet implemented

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 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 Section

channel "default_syslog" {
    syslog daemon;			// end to syslog's daemon
					// facility
    severity info;			// only send priority info
					// and higher
channel "default_debug" {
    file "";			// write to in
					// the working directory
					// Note: stderr is used instead
					// of ""
					// if the server is started
					// with the '-f' option.
    severity dynamic;			// log at the server's
					// current debug level
channel "default_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 in the server's working directory.

For security reasons, when the "-u" command line option is used, the 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, 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" {
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.

default The default category defines the logging options for those categories where no specific configuration has been defined.
general The catch-all. Many things still aren't classified into categories, and they all end up here.
database Messages relating to the databases used internally by the name server to store zone and cache data.
security Approval and denial of requests.
config Configuration file parsing and processing.
resolver DNS resolution, such as the recursive lookups performed on behalf of clients by a caching name server.
xfer-in Zone transfers the server is receiving.
xfer-out Zone transfers the server is sending.
notify The NOTIFY protocol.
client Processing of client requests.
network Network operations.
update Dynamic updates.
queries Queries.
dispatch Dispatching of incoming packets to the server modules where they are to be processed.
dnssec DNSSEC and TSIG protocol processing.
lame-servers Lame servers. These are misconfigurations in remote servers, discovered by BIND 9 when trying to query those servers during resolution.


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 ; [ ip_addr ; ... ] }; ]
    [ ndots number; ]


lwres Statement Definition and Usage

The lwres statement configures the name server to also act as a lightweight resolver server. 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 this statement is omitted, requests will be accepted on, port 53.

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.


options Statement Grammar

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

options {
    [ version version_string; ]
    [ 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; ]
    [ has-old-clients yes_or_no; ]
    [ host-statistics 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; ]
    [ forward ( only | first ); ]
    [ forwarders { [ in_addr ; [ in_addr ; ... ] ] }; ]
    [ 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 }; ]
    [ blackhole { address_match_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 | * ) ]; ]
    [ 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-queries 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] ; ]
    [ 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; ]
    [ 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 ; ]
    [ 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 ; ]


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 more than one occurrence is found, the first occurrence determines the actual options used, and a warning will be generated. If there is no options statement, an options block with each option set to its default will be used.

version The version the server should report via a query of name version.bind in class chaos. The default is the real version number of this server.
directory The working directory of the server. Any non-absolute pathnames in the configuration file will be taken as relative to this directory. The default location for most server output files (e.g. 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.
named-xfer This option is obsolete. It was used in BIND 8 to specify the pathname to the named-xfer program. In BIND 9, no separate named-xfer program is needed; its functionality is built into the name server.
tkey-domain The domain 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 will be "client specified part" + "tkey-domain". Otherwise, the name of the shared key will be "random hex digits" + "tkey-domain". In most cases, the domainname should be the server's domain name.
tkey-dhkey The Diffie-Hellman key used by the server to generate shared keys with clients using the Diffie-Hellman mode of TKEY. The server must be able to load the public and private keys from files in the working directory. In most cases, the keyname should be the server's host name.
dump-file 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 The pathname of the file the server writes memory usage statistics to on exit. If not specified, the default is named.memstats. Note: Not yet implemented in BIND 9.
pid-file The pathname of the file the server writes its process ID in. If not specified, the default is operating system dependent, but is usually /var/run/ or /etc/ The pid-file is used by programs that want to send signals to the running nameserver.
statistics-file 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 Section
port The UDP/TCP port number the server uses for receiving and sending DNS protocol traffic. The default is 53. This option is mainly intended for server testing; a server using a port other than 53 will not be able to communicate with the global DNS. The port option should be placed at the beginning of the options block, before any other options that take port numbers or IP addresses, to ensure that the port value takes effect for all addresses used by the server.


Boolean Options

auth-nxdomain If yes, then the AA bit is always set on NXDOMAIN responses, even if the server is not actually authoritative. The default is no; this is a change from BIND 8. If you are using very old DNS software, you may need to set it to yes.
deallocate-on-exit This option was used in BIND 8 to enable checking for memory leaks on exit. BIND 9 ignores the option and always performs the checks.
dialup 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. This has different effects according to zone type and concentrates the zone maintenance so that it all happens in a short interval, once every heartbeat-interval and hopefully during the one call. It also suppresses some of the normal zone maintenance traffic. The default is no.

The dialup option may also be specified in the view and zone statements, in which case it overrides the global dialup option.

If the zone is a master zone then the server will send out a NOTIFY request to all the slaves. This will trigger the zone serial number check in the slave (providing it supports NOTIFY) allowing the slave to verify the zone while the connection is active.

If the zone is a slave or stub zone, then the server will suppress the regular "zone up to date" (refresh) queries and only perform 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 send refresh queries when the heartbeat-interval expires and passive which just disables normal refresh processing.

fake-iquery In BIND 8, this option was used to enable simulating the obsolete DNS query type IQUERY. BIND 9 never does IQUERY simulation.
fetch-glue This option is obsolete. In BIND 8, fetch-glue yes caused the server to attempt to fetch glue resource records it didn't have when constructing the additional data section of a response. This is now considered a bad idea and BIND 9 never does it.
has-old-clients This option was incorrectly implemented in BIND 8, and is ignored by BIND 9. To achieve the intended effect of has-old-clients yes, specify the two separate options auth-nxdomain yes and rfc2308-type1 no instead.
host-statistics In BIND 8, this enables keeping of statistics for every host that the nameserver interacts with. Not implemented in BIND 9.
maintain-ixfr-base This option is obsolete. It was used in BIND 8 to determine whether a transaction log was kept for Incremental Zone Transfer. BIND 9 maintains a transaction log whenever possible. If you need to disable outgoing incremental zone transfers, use provide-ixfr no.
multiple-cnames This option was used in BIND 8 to allow a domain name to allow multiple CNAME records in violation of the DNS standards. BIND 9.1 always strictly enforces the CNAME rules both in master files and dynamic updates.
notify If yes (the default), DNS NOTIFY messages are sent when a zone the server is authoritative for changes. The messages are sent to the servers listed in the zone's NS records (except the master server identified in the SOA MNAME field), and to any servers listed in the also-notify option. If explicit, notifies are sent only to servers explicitly listed using also-notify. If 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 slaves to crash.
recursion If yes, and a DNS query requests recursion, then the server will attempt to do all the work required to answer the query. If recursion is off and the server does not already know the answer, it will return 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 the server's internal operation, such as NOTIFY address lookups. See also fetch-glue above.
rfc2308-type1 Setting this to yes will cause the server to send NS records along with the SOA record for negative answers. The default is no. Not yet implemented in BIND 9.
use-id-pool This option is obsolete. BIND 9 always allocates query IDs from a pool.
zone-statistics If yes, the server will, by default, collect statistical data on all zones in the server. These statistics may be accessed using rndc stats, which will dump them to the file listed in the statistics-file. See also Section
use-ixfr This option is obsolete. If you need to disable IXFR to a particular server or servers see the information on the provide-ixfr option in Section 6.2.16. See also Section 4.2. treat-cr-as-space This option was used in BIND 8 to make the server treat carriage return ("\r") characters the same way as a space or tab character, to facilitate loading of zone files on a UNIX system that were generated on an NT or DOS machine. In BIND 9, both UNIX "\n" and NT/DOS "\r\n" newlines are always accepted, and the option is ignored.
These options control the server's behavior on refreshing a zone (querying for SOA changes) or retrying failed transfers. Usually the SOA values for the zone are used, but these values are set by the master, giving slave server administrators little control over their contents. These options allow the administrator to set a minimum and maximum refresh and retry time either per-zone, per-view, or per-server. These options are valid for master, slave and stub zones, and clamp the SOA refresh and retry times to the specified values.
These options control the behavior of an authoritative server when answering queries which have additional data, or when following CNAME and DNAME chains.

When both of these options are set to yes (the default) and a query is being answered from authoritative data (a zone configured into the server), the additional data section of the reply will be filled in using data from other authoritative zones and from the cache. In some situations this is undesirable, such as when there is concern over the correctness of the cache, or in servers where slave zones may be added and modified by untrusted third parties. Also, avoiding the search for this additional data will speed up server operations at the possible expense of additional queries to resolve what would otherwise be provided in the additional section.

For example, if a query asks for an MX record for host, and the record found is "MX 10", normally the address records (A, A6, and AAAA) for will be provided as well, if known. Setting these options to no disables this behavior.

These options are intended for use in authoritative-only servers, or in authoritative-only views. In other words, they should only be set to no if the option recursion no; has also been specified. Setting them to no in a recursive server will have unexpected side effects such as causing recursion to not function.

Specifying additional-from-cache no actually disables the use of the cache not only for additional data lookups but also when looking up the answer. This is usually the desired behavior in an authoritative-only server where the correctness of the cached data is an issue.

When a name server is non-recursively queried for a name that is not below the apex of any served zone, it normally answers with an "upwards referral" to the root servers or the servers of some other known parent of the query name. Since the data in an upwards referral comes from the cache, the server will not be able to provide upwards referrals when additional-from-cache no has been specified. Instead, it will respond to such queries with REFUSED. This should not cause any problems since upwards referrals are not required for the resolution process.



The forwarding facility can be used to create a large site-wide cache on a few servers, reducing traffic over links to external nameservers. 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.

forward This option is only meaningful if the forwarders list is not empty. A value of first, the default, causes the server to query the forwarders first, and if that doesn't answer the question the server will then look for the answer itself. If only is specified, the server will only query the forwarders.
forwarders Specifies the IP addresses to be used for forwarding. The default is the empty list (no forwarding).
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.


Access Control

Access to the server can be restricted based on the IP address of the requesting system. See Section 6.1.1 for details on how to specify IP address lists.

allow-notify Specifies which hosts are allowed to notify slaves of a zone change in addition to the zone masters. allow-notify may also be specified in the zone statement, in which case it overrides the options allow-notify statement. It is only meaningful for a slave zone. If not specified, the default is to process notify messages only from a zone's master.
allow-query Specifies which hosts are allowed to ask ordinary questions. 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.
allow-recursion Specifies which hosts are allowed to make recursive queries through this server. If not specified, the default is to allow recursive queries from all hosts. Note that disallowing recursive queries for a host does not prevent the host from retrieving data that is already in the server's cache.
allow-transfer 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 options allow-transfer statement. If not specified, the default is to allow transfers from all hosts.
blackhole Specifies a list of addresses that the server will not accept queries from or use to resolve a query. Queries from these addresses will not be responded to. The default is none.



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 {; }; listen-on port 1234 { !; 1.2/16; }; will enable the nameserver on port 53 for the IP address, and on port 1234 of an address on the machine in net 1.2 that is not 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 ports on which the server will listen for incoming queries sent using IPv6. The server does not bind a separate socket to each IPv6 interface address as it does for IPv4. Instead, it always listens on the IPv6 wildcard address. Therefore, the only values allowed for the address_match_list argument to the listen-on-v6 statement are { any; } and { none;} Multiple listen-on-v6 options can be used to listen on multiple ports: listen-on-v6 port 53 { any; }; listen-on-v6 port 1234 { any; }; To make the server not listen on any IPv6 address, use listen-on-v6 { none; }; If no listen-on-v6 statement 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 nameservers. 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 * or is omitted, a wildcard IP address (INADDR_ANY) will be used. If port is * or is omitted, a random unprivileged port will be used. The defaults are query-source address * port *; query-source-v6 address * port * Note: query-source currently applies only to UDP queries; TCP queries always use a wildcard IP address and a random unprivileged port.


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 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 will quickly converge on stealth servers. If an also-notify list is given in a zone statement, it will override the options also-notify statement. When a zone notify statement is set to no, the IP addresses in the global also-notify list will not be sent NOTIFY messages for that zone. The default is the empty list (no global notification list).
max-transfer-time-in Inbound zone transfers running longer than this many minutes will be terminated. The default is 120 minutes (2 hours).
max-transfer-idle-in Inbound zone transfers making no progress in this many minutes will be terminated. The default is 60 minutes (1 hour).
max-transfer-time-out Outbound zone transfers running longer than this many minutes will be terminated. The default is 120 minutes (2 hours).
max-transfer-idle-out Outbound zone transfers making no progress in this many minutes will be terminated. The default is 60 minutes (1 hour).
serial-queries Slave servers will periodically query master servers to find out if zone serial numbers have changed. Each such query uses a minute amount of the slave server's network bandwidth, but more importantly each query uses a small amount of memory in the slave server while waiting for the master server to respond. In BIND 8, the serial-queries option set the maximum number of concurrent serial-number queries allowed to be outstanding at any given time. BIND 9 does not limit the number of outstanding serial queries and ignores the The serial-queries option; instead, it limits the rate at which the queries are sent. The maximum rate is currently fixed at 20 queries per second but may become configurable in a future release.
transfer-format Zone transfers can be sent using two different formats, one-answer and many-answers. The transfer-format option is used on the master 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 a message. many-answers is more efficient, but is only supported by relatively new slave servers, such as BIND 9, BIND 8.x and patched versions of BIND 4.9.5. The default is many-answers. transfer-format may be overridden on a per-server basis by using the server statement.
transfers-in The maximum number of inbound zone transfers that can be running concurrently. The default value is 10. Increasing transfers-in may speed up the convergence of slave zones, but it also may increase the load on the local system.
transfers-out The maximum number of outbound zone transfers that can be running concurrently. Zone transfer requests in excess of the limit will be refused. The default value is 10.
transfers-per-ns The maximum number of inbound zone transfers that can be concurrently transferring from a given remote nameserver. The default value is 2. Increasing transfers-per-ns may speed up the convergence of slave zones, but it also may increase the load on the remote nameserver. transfers-per-ns may be overridden on a per-server basis by using the transfers phrase of the server statement.
transfer-source transfer-source determines which local address will be 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 will usually be 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.
transfer-source-v6 The same as transfer-source, except zone transfers are performed using IPv6.
notify-source notify-source determines which local source address, and optionally UDP port, will be used to send NOTIFY messages. This address must appear in the slave server's masters 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 / per-view basis by including a notify-source statement within the zone or view block in the configuration file.
notify-source-v6 Like notify-source, but applies to notify messages sent to IPv6 addresses.


Resource Limits

The server's usage of many system resources can be limited. Some operating systems don't support some of the limits. On such systems, a warning will be issued if the unsupported limit is used. Some operating systems don't support limiting resources.

Scaled values are allowed when specifying resource limits. For example, 1G can be used instead of 1073741824 to specify a limit of one gigabyte. unlimited requests unlimited use, or the maximum available amount. default uses the limit that was in force when the server was started. See the description of size_spec in Section 6.1.

coresize The maximum size of a core dump. The default is default.
datasize The maximum amount of data memory the server may use. The default is default.
files The maximum number of files the server may have open concurrently. The default is unlimited.
max-ixfr-log-size This option is obsolete; it is accepted and ignored for BIND 8 compatibility.
recursive-clients The maximum number of simultaneous recursive lookups the server will perform on behalf of clients. The default is 1000.
stacksize The maximum amount of stack memory the server may use. The default is default.
tcp-clients The maximum number of simultaneous client TCP connections that the server will accept. The default is 100.


Periodic Task Intervals

cleaning-interval The server will remove expired resource records from the cache every cleaning-interval minutes. The default is 60 minutes. If set to 0, no periodic cleaning will occur.
heartbeat-interval The server will perform 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). If set to 0, no zone maintenance for these zones will occur.
interface-interval The server will scan the network interface list every interface-interval minutes. The default is 60 minutes. If set to 0, interface scanning will only occur when the configuration file is loaded. After the scan, listeners will be started on any new interfaces (provided they are allowed by the listen-on configuration). Listeners on interfaces that have gone away will be cleaned up.
statistics-interval Nameserver statistics will be logged every statistics-interval minutes. The default is 60. If set to 0, no statistics will be logged. Note: Not yet implemented in BIND9.



All other things being equal, when the server chooses a nameserver to query from a list of nameservers, it prefers the one that is topologically closest to itself. The topology statement takes an address_match_list and interprets it in a special way. Each top-level list element is assigned a distance. Non-negated elements get a distance based on their position in the list, where the closer the match is to the start of the list, the shorter the distance is between it and the server. A negated match will be assigned the maximum distance from the server. If there is no match, the address will get a distance which is further than any non-negated list element, and closer than any negated element. For example,

topology {
    { 1.2/16; 3/8; };
will prefer servers on network 10 the most, followed by hosts on network (netmask and network 3, with the exception of hosts on network 1.2.3 (netmask, which is preferred least of all. The default topology is topology { localhost; localnets; }; Note: The topology option is not yet implemented in BIND 9.


The sortlist Statement

The response to a DNS query may consist of multiple resource records (RRs) forming a resource records set (RRset). The name server will normally return the RRs within the RRset in an indeterminate order (but see the rrset-order statement in Section 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 nameservers, not all the clients.

The sortlist statement (see below) takes an address_match_list and interprets it even more specifically than the topology statement does (Section 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.

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 treated the same as the address_match_list in a topology statement. 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 will 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 will 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 will only prefer other addresses on their directly connected networks.

sortlist {
    { localhost;				   // IF   the local host
        { localnets;				   // THEN first fit on the
            192.168.1/24;			   //   following nets
            { 192.168.2/24; 192.168.3/24; }; }; };
    { 192.168.1/24;				   // IF   on class C 192.168.1
        { 192.168.1/24;				   // THEN use .1, or .2 or .3
            { 192.168.2/24; 192.168.3/24; }; }; };
    { 192.168.2/24;				   // IF   on class C 192.168.2
        { 192.168.2/24;				   // THEN use .2, or .1 or .3
            { 192.168.1/24; 192.168.3/24; }; }; };
    { 192.168.3/24;				   // IF   on class C 192.168.3
        { 192.168.3/24;				   // THEN use .3, or .1 or .2
            { 192.168.1/24; 192.168.2/24; }; }; };
    { { 192.168.4/24; 192.168.5/24; };		   // if .4 or .5, prefer that net
The following example will give reasonable behavior for the local host and hosts on directly connected networks. It is similar to the behavior of the address sort in BIND 4.9.x. Responses sent to queries from the local host will favor any of the directly connected networks. Responses sent to queries from any other hosts on a directly connected network will prefer addresses on that same network. Responses to other queries will not be sorted.

sortlist {
           { localhost; localnets; };
           { localnets; };


RRset Ordering

When multiple records are returned in an answer it may be useful to configure the order of the records placed into the response. The rrset-order statement permits configuration of the ordering of the records in a multiple record response. See also the sortlist statement, Section

An order_spec is defined as follows:

[ class class_name ][ type type_name ][ name "domain_name"]
      order ordering
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 "*". The legal values for ordering are:

fixed Records are returned in the order they are defined in the zone file.
random Records are returned in some random order.
cyclic Records are returned in a round-robin order.
For example:

rrset-order {
   class IN type A name "" order random;
   order cyclic;
will cause any responses for type A records in class IN that have "" as a suffix, to always be returned in random order. All other records are returned in cyclic order.

If multiple rrset-order statements appear, they are not combined . the last one applies.

If no rrset-order statement is specified, then a default one of:

rrset-order { class ANY type ANY name "*" order cyclic ; };
is used. Note: The rrset-order statement is not yet implemented in BIND 9. BIND 9 currently supports only a "random-cyclic" ordering, where the server randomly chooses a starting point within the RRset and returns the records in order starting at that point, wrapping around the end of the RRset if necessary.



lame-ttl Sets the number of seconds to cache a lame server indication. 0 disables caching. (This is NOT recommended.) Default is 600 (10 minutes). Maximum value is 1800 (30 minutes).
max-ncache-ttl 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. The default max-ncache-ttl is 10800 seconds (3 hours). max-ncache-ttl cannot exceed 7 days and will be silently truncated to 7 days if set to a greater value.
max-cache-ttl max-cache-ttl sets the maximum time for which the server will cache ordinary (positive) answers. The default is one week (7 days).
min-roots The minimum number of root servers that is required for a request for the root servers to be accepted. Default is 2. Note: Not yet implemented in BIND 9.
sig-validity-interval Specifies the number of days into the future when DNSSEC signatures automatically generated as a result of dynamic updates (Section 4.1) will expire. The default is 30 days. The signature inception time is unconditionally set to one hour before the current time to allow for a limited amount of clock skew.


The Statistics File

The statistics file generated by BIND 9 is similar, but not identical, to that generated by BIND 8.

The statistics dump begins with the line +++ Statistics Dump +++ (973798949), where the number in parentheses is a standard Unix-style timestamp, measured as seconds since January 1, 1970. Following that line are a series of lines containing a counter type, the value of the counter, optionally a zone name, and optionally a view name. The lines without view and zone listed are global statistics for the entire server. Lines with a zone and view name for the given view and zone (the view name is omitted for the default view). The statistics dump ends with the line --- Statistics Dump --- (973798949), where the number is identical to the number in the beginning line.

The following statistics counters are maintained:

success The number of successful queries made to the server or zone. A successful query is defined as query which returns a NOERROR response other than a referral response.
referral The number of queries which resulted in referral responses.
nxrrset The number of queries which resulted in NOERROR responses with no data.
nxdomain The number of queries which resulted in NXDOMAIN responses.
recursion The number of queries which caused the server to perform recursion in order to find the final answer.
failure The number of queries which resulted in a failure response other than those above.


server Statement Grammar

server ip_addr {
    [ bogus yes_or_no ; ]
    [ provide-ixfr yes_or_no ; ]
    [ request-ixfr yes_or_no ; ]
    [ transfers number ; ]
    [ transfer-format ( one-answer | many-answers ) ; ]]
    [ keys { string ; [ string ; [...]] } ; ]


server Statement Definition and Usage

The server statement defines the characteristics to be associated with a remote nameserver.

If you discover that a remote server is giving out bad data, marking it as bogus will prevent further queries to it. The default value of bogus is no.

The provide-ixfr clause determines whether the local server, acting as master, will respond with an incremental zone transfer when the given remote server, a slave, requests it. If set to yes, incremental transfer will be provided whenever possible. If set to no, all transfers to the remote server will be nonincremental. If not set, the value of the provide-ixfr option in the global options block is used as a default.

The request-ixfr clause determines whether the local server, acting as a slave, will request incremental zone transfers from the given remote server, a master. If not set, the value of the request-ixfr option in the global options block is used as a default.

IXFR requests to servers that do not support IXFR will 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 clauses is to make it possible to disable the use of IXFR even when both master and slave claim to support it, for example if one of the servers is buggy and crashes or corrupts data when IXFR is used.

The server supports two zone transfer methods. The first, one-answer, uses one DNS message per resource record transferred. many-answers packs as many resource records as possible into a message. many-answers is more efficient, but is only known to be understood by BIND 9, BIND 8.x, and patched versions of BIND 4.9.5. You can specify which method to use for a server with the transfer-format option. If transfer-format is not specified, the transfer-format specified by the options statement will be used.

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.

The keys clause is used to identify a key_id defined by the key statement, to be used for transaction security when talking to the remote server. The key statement must come before the server statement that references it. When a request is sent to the remote server, a request signature will be 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.

Although the grammar of the keys clause allows for multiple keys, only a single key per server is currently supported.


trusted-keys Statement Grammar

trusted-keys {
    string number number number string ;
    [ string number number number string ; [...]]


trusted-keys Statement Definition and Usage

The trusted-keys statement defines DNSSEC security roots. DNSSEC is described in Section 4.7. A security root is defined when the public key for a non-authoritative zone is known, but cannot be securely obtained through DNS, either because it is the DNS root zone or its parent zone is unsigned. Once a key has been configured as a trusted key, it is treated as if it had been validated and proven secure. The resolver attempts DNSSEC validation on all DNS data in subdomains of a security root.

The trusted-keys statement can contain multiple key entries, each consisting of the key's domain name, flags, protocol, algorithm, and the base-64 representation of the key data.


view Statement Grammar

view view_name [class] {
      match-clients { address_match_list } ;
      [ view_option; ...]
      [ zone-statistics yes_or_no ; ]
      [ zone_statement; ...]


view Statement Definition and Usage

The view statement is a powerful new 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.

Each view statement defines a view of the DNS namespace that will be seen by those clients whose IP addresses match the address_match_list of the view's match-clients clause. The order of the view statements is significant-a client query will be resolved in the context of the first view whose match-clients list matches the client's IP address.

Zones defined within a view statement will be only be 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, and any zone statements specified on the top level of the configuration file are considered to be part of this 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 {; };
               // Provide recursive service to internal clients only.
      recursion yes;
               // Provide a complete view of the zone
               // including addresses of internal hosts.
      zone "" {
            type master;
            file "example-internal.db";
view "external" {
      match-clients { any; };
               // Refuse recursive service to external clients.
      recursion no;
               // Provide a restricted view of the zone
               // containing only publicly accessible hosts.
      zone "" {
           type master;
           file "example-external.db";


zone Statement Grammar

zone zone_name [class] [{ 
    type ( master | slave | hint | stub | forward ) ;
    [ allow-notify { address_match_list } ; ]
    [ allow-query { address_match_list } ; ]
    [ allow-transfer { address_match_list } ; ]
    [ allow-update { address_match_list } ; ]
    [ update-policy { update_policy_rule [...] } ; ]
    [ allow-update-forwarding { address_match_list } ; ]
    [ also-notify { ip_addr [port ip_port] ; [ ip_addr [port ip_port] ; ... ] }; ]
    [ check-names (warn|fail|ignore) ; ]
    [ dialup dialup_option ; ]
    [ file string ; ]
    [ forward (only|first) ; ]
    [ forwarders { [ ip_addr ; [ ip_addr ; [...]]] } ; ]
    [ ixfr-base string ; ]
    [ ixfr-tmp-file string ; ]
    [ maintain-ixfr-base yes_or_no ; ]
    [ masters [port ip_port] { ip_addr [port ip_port] [key key]; [...] } ; ]
    [ max-ixfr-log-size number ; ]
    [ max-transfer-idle-in number ; ]
    [ max-transfer-idle-out number ; ]
    [ max-transfer-time-in number ; ]
    [ max-transfer-time-out number ; ]
    [ notify yes_or_no | explicit ; ]
    [ pubkey number number number string ; ]
    [ transfer-source  ip4_addr(| *) [port ip_port] ; ]
    [ transfer-source-v6  ip6_addr(| *) [port ip_port] ; ]
    [ notify-source  ip4_addr(| *) [port ip_port] ; ]
    [ notify-source-v6  ip6_addr(| *) [port ip_port] ; ]
    [ zone-statistics yes_or_no ; ]
    [ sig-validity-interval number ; ]
    [ database string ; ]


zone Statement Definition and Usage


Zone Types



In general class can now be omitted from a zone's definition. It is now inherited for the enclosing view or if there is no explicit view, from the default view which is IN (for Internet).

The hesiod class is named for an information service from MIT's Project Athena. It is 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.


Zone Options

master The server has a master copy of the data for the zone and will be able to provide authoritative answers for it.
slave A slave zone is a replica of a master zone. The masters list specifies one or more IP addresses of master servers that the slave contacts to update its copy of the zone. 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 master can also be done with per-server TSIG keys. If a file is specified, then the replica will be 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 start-up 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 file names. For example, a slave server for the zone might place the zone contents into a file called ex/ where ex/ is just the first two letters of the zone name. (Most operating systems behave very slowly if you put 100K files into a single directory.)
stub A stub zone is similar to a slave zone, except that it replicates only the NS records of a master 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 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. In BIND 4/8, zone transfers of a parent zone included the NS records from stub children of that zone. This meant that, in some cases, users could get away with configuring child stubs only in the master server for the parent zone. BIND 9 never mixes together zone data from different zones in this way. Therefore, if a BIND 9 master serving a parent zone has child stub zones configured, all the slave servers for the parent zone also need to have the same child stub zones configured.

Stub zones can also be used as a way of forcing 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 RFC2157 addressing may be configured with stub zones for to use a set of internal name servers as the authoritative servers for that domain.

forward 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 will apply 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 will be done for the domain, cancelling the effects of any forwarders in the options statement. Thus if you want 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 want to use the same servers as set globally) you need to respecify the global forwarders.
hint The initial set of root nameservers is specified using a "hint zone". When the server starts up, it uses the root hints to find a root nameserver and get the most recent list of root nameservers. 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 defaults hints.
allow-notify See the description of allow-notify in Section
allow-query See the description of allow-query in Section
allow-transfer See the description of allow-transfer in Section
allow-update Specifies which hosts are allowed to submit Dynamic DNS updates for master zones. The default is to deny updates from all hosts.
update-policy Specifies a "Simple Secure Update" policy. See Section
allow-update-forwarding Specifies which hosts are allowed to submit Dynamic DNS updates to slave zones to be forwarded to the master. The default is { none; }, which means that no update forwarding will be performed. To enable update forwarding, specify allow-update-forwarding { any; };. Specifying values other than { none; } or { any; } is usually counterproductive, since the responsibility for update access control should rest with the master server, not the slaves.

Note that enabling the update forwarding feature on a slave server may expose master servers relying on insecure IP address based access control to attacks.

also-notify Only meaningful if notify is active for this zone. The set of machines that will receive a DNS NOTIFY message for this zone is made up of all the listed nameservers (other than the primary master) 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. also-notify is not meaningful for stub zones. The default is the empty list.
check-names This option was used in BIND 8 to restrict the character set of domain names in master files and/or DNS responses received from the netowrk. BIND 9 does not restrict the character set of domain names and does not implement the check-names option.
database Specify the type of database to be used for storing 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 Section
forward 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 would allow a normal lookup to be tried.
forwarders 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; the global options are not used.
ixfr-base Was used in BIND 8 to specify the name of the transaction log (journal) file for dynamic update and IXFR. BIND 9 ignores the option and constructs the name of the journal file by appending ".jnl" to the name of the zone file.
ixfr-tmp-file Was an undocumented optino in BIND 8. Ignored in BIND 9.
max-transfer-time-in See the description of max-transfer-time-in in Section
max-transfer-idle-in See the description of max-transfer-idle-in in Section
max-transfer-time-out See the description of max-transfer-time-out in Section
max-transfer-idle-out See the description of max-transfer-idle-out in Section
notify See the description of notify in Section
pubkey In BIND 8, this option was intended for specifying a public zone key for verification of signatures in DNSSEC signed zones when they are loaded from disk. BIND 9 does not verify signatures on loading and ignores the option.
zone-statistics If yes, the server will keep statistical information for this zone, which can be dumped to the statistics-file defined in the server options.
sig-validity-interval See the description of sig-validity-interval in Section
transfer-source See the description of transfer-source in Section
transfer-source-v6 See the description of transfer-source-v6 in Section
notify-source See the description of notify-source in Section
notify-source-v6 See the description of notify-source-v6 in Section


Dynamic Update Policies

BIND 9 supports two alternative methods of granting clients the right to perform dynamic updates to a zone, configured by the allow-update and update-policy option, respectively.

The allow-update clause works the same way as in previous versions of BIND. It grants given clients the permission to update any record of any name in the zone.

The update-policy clause is new in BIND 9 and allows more fine-grained control over what updates are allowed. A set of rules is specified, where each rule either grants or denies permissions for one or more names to be updated by one or more identities. If the dynamic update request message is signed (that is, it includes either a TSIG or SIG(0) record), the identity of the signer can be determined.

Rules are specified in the update-policy zone option, and are only meaningful for master zones. When the update-policy statement is present, it is a configuration error for the allow-update statement to be present. The update-policy statement only examines the signer of a message; the source address is not relevant.

This is how a rule definition looks:

( grant | deny ) identity nametype name [ types ]

Each rule grants or denies privileges. Once a message has successfully matched a rule, the operation is immediately granted or denied and no further rules are examined. A rule is matched when the signer matches the identity field, the name matches the name field, and the type is specified in the type field.

The identity field specifies a name or a wildcard name. The nametype field has 4 values: name, subdomain, wildcard, and self

name Matches when the updated name is the same as the name in the name field.
subdomain Matches when the updated name is a subdomain of the name in the name field (which includes the name itself).
wildcard Matches when the updated name is a valid expansion of the wildcard name in the name field.
self Matches when the updated name is the same as the message signer. The name field is ignored.

If no types are specified, the rule matches all types except SIG, NS, SOA, and NXT. Types may be specified by name, including "ANY" (ANY matches all types except NXT, which can never be updated).