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Files Reference

named.conf File Format for TCP/IP


Defines the configuration and behavior of the named daemon.


The /etc/named.conf file is the default configuration file for the named8 and named9 server. If the named daemon is started without specifying an alternate file, the named daemon reads this file for information on how to set up the local name server.

The format of the named.conf file will be different depending on which version of the named server is configured. File format information for both named8 and named9 can be found below.

The named daemon reads the configuration file only when the named daemon starts or when the named daemon receives an SRC refresh command or a SIGHUP signal.

The data in the named.conf file specifies general configuration characteristics for the name server, defines each zone for which the name server is responsible (its zones of authority), and provides further config information per zone, possibly including the source DOMAIN database file for the zone.

Any database files referenced in the named.conf file must be in Standard Resource Record Format. These data files can have any name and any directory path. However, for convenience in maintaining the named database, they are generally given names in the following form: /etc/named.extension. The general format of named data files is described in DOMAIN Data File, DOMAIN Reverse Data File, DOMAIN Cache File, and DOMAIN Local File.

Format of the named.conf file when configuring named8


Comments in the named.conf file can begin with a # (pound sign) or // (two forward slashes), or can be enclosed in the C-style comment characters, e.g., /* comment text */.

Configuration options are lines of text beginning with a keyword, possibly including some option text or a list, and ending in a ; (semicolon).

The named.conf file is organized into stanzas. Each stanza is an enclosed set of configuration options that define either general characteristics of the daemon or a zone configuration. Certain stanza definitions are allowed only at the top-level, therefore nesting these stanzas is not allowed. The current top-level configuration stanza keywords are: acl, key, logging, options, server, and zone.

Further configuration information can be incorporated into the conf file via the include keyword. This keyword directs the daemon to insert the contents of the indicated file into the current position of the include directive.

Access Control List (ACL) Definition

acl acl-name {
    [ access-element; ... ]

Defines an access control list to be referenced thoughout the configuration file byacl-name. Multiple acl definitions can exist within one configuration file provided that each acl-name is unique. Additionally, four default access control lists are defined:

Option Values Explanation
access-element IP-address
Defines a source as allowed or disallowed. Multiple access-elements are allowed inside the acl stanza.

Each element can be an IP address in dot notation (e.g., an IP prefix in CIDR or slash notation (e.g., 9.3.149/24) or a reference to another access control list (e.g., localhost).

Additionally, each element indicates whether the element is allowed or disallowed access via an ! (exclamation point) modifier prepended to the element.

For example:

acl hostlist1 {

When the access control list " hostlist1" is referenced in the configuration, it implies to allow access from any host whose IP address begins with 9.3.149 and to disallow access from the internet host

Key Definition

key key-name {
    algorithm alg-id;
    secret secret-string;

Defines an algorithm and shared secret key to be referenced in a server stanza and used for authentication by that name server. This feature is included for future use and is currently unused in the name server.

Option Values Explanation
algorithm alg-id string A quoted-string that defines the type of security algorithm that will be used when interpreting the secret string. None are defined at this time.
secret secret-string string A quoted-string that is used by the algorithm to authenticate the host.

Logging Configuration

logging {

    [ channel channel-name {
       ( file file-name
             [ versions ( num-vers | unlimited ) ]
             [ size size-value ]
       | syslog ( kern | user | mail | daemon |
                  syslog | lpr | news | uucp )
       | null );
       [ print-category ( yes | no ); ]
       [ print-severity ( yes | no ); ]
       [ print-time ( yes | no ); ]
      }; ... ]
    [ category category-name {
          [ channel-reference; ... ]
      }; ... ]

In this newest version of the name server, the logging facility has been greatly improved to allow for much reconfiguration of the default logging mechanism. The logging stanza is used to define logging output channels and to associate the predefined logging categories with either the predefined or user-defined logging output channels.

When no logging stanza is included in the conf file, the name server still logs messages and errors just as it has in previous releases. Informational and some critical messages will be logged through the syslog daemon facility, and debug and other esoteric information will be logged to the named.run file when the global debug level (set with the -d command-line option) is non-zero.

Option Values Explanation
channel Defines an output channel to be referenced later by the channel-name identifier. An output channel specifies a destination for output messages to be sent as well as some formatting information to be used when writing the output message. More than one output channel can be defined provided that each channel-identifier is unique. Also, each output channel can be referenced from multiple logging categories.

There are four predefined output channels:

  • default_syslog sends "info" and higher severity messages to syslog's "daemon" facility
  • default_debug writes debug messages to the named.run file as specified by the global debug level
  • default_stderr writes "info" and higher severity messages to stderr
  • null discards all messages
file file-name string Defines an output channel as one that logs messages to an output file. The file used for output is specified with the file-name string. Additionally, the file option allows for controlling how many versions of the output file should be kept, and what size limit the output file should never exceed.

The file, syslog, and null output paths are mutually exclusive.

versions num-versions
Specifies the number of old output files that should be kept. When an output file is reopened, rather than replacing a possible existing output file, the existing output file will be saved as an old output file with a .value extension. Using the num-versions value, one can limit the number of old output files to be kept. However, specifying the unlimited keyword indicates to continually accumulate old output file versions. By default, no old versions of any log file are kept.
size size-value Specifies the maximum size of the log file used by this channel. By default, the size is unlimited. However, when a size is configured, once size-value bytes are written to the file, nothing more will be written until the file is reopened.

Accepted values for size-value include the word "unlimited" and numbers with k, m, or g modifiers specifying kilobytes, megabytes, and gigabytes respectively. For example, 1000k and 1m indicate one thousand kilobytes and one megabyte respectively.

syslog kern
Defines an output channel as one that redirects its messages to the syslog service. The supported value keywords correspond to facilities logged by the syslog service.

Ultimately, the syslog service will define which received messages will be logged through the service, therefore, if definining a channel to redirect its messages to the syslog service's user facility would not result in any visibly logged messages if the syslog service is not configured to output messages from this facility.

For more information concerning the syslog service, see the syslogd daemon.

The file, syslog, and null output paths are mutually exclusive.

null Defines an output channel through which all messages will be discarded. All other output channel options are invalid for an output channel whose output path is null.
severity critical
debug [ level ]
Sets a threshold of message severities to be logged through the output channel. While these severity definitions are similar to those used by the syslog service, for the name server they also control output through file path channels. Messages must meet or exceed the severity level to be logged through the output channel. The dynamic severity specifies that the name server's global debug level (specified when the daemon is invoked with the -d flag) controls which messages pass through the output channel.

Also, the debug severity can specify a level modifier which is an upper threshold for debug messages whenever the name server has debugging enabled at any level. A lower debug level indicates less information is to be logged through the channel. It is not necessary for the global debug level to meet or exceed the debug level value.

If used with the syslog output path, the syslog facility will ultimately control what severities are logged through the syslog service. For example, if the syslog service is configured to only log daemon.info messages, and the name server is configured to channel all debug messages to the syslog service, the syslog service will filter the messages from its output path.

print-category yes
Controls the format of the output message when it is sent through the output path. Regardless of which, how many, or in which order these options are listed inside the channel stanza, the message will be prepended with the the text in a time, category, severity order.

The following is an example of a message with all three print- options enabled:

28-Apr-1997 15:05:32.863 default: notice: Ready to answer queries.

By default, no extra text will be prepended to an output message.

Note that when the syslog service logs messages, it also prepends the date and time information to the text of the message. Thus, enabling print-time on a channel that uses the syslog output path would result in the syslog service logging a message with two dates prepended to it.

print-severity yes
print-time yes
category The category keyword defines a stanza which associates a logging or messaging category with predefined or user-defined output channels.

By default, the following categories are defined:

category default { default_syslog; default_debug; };
category panic { default_syslog; default_debug; };
category-name default
The category-name specifies which logging category is to be associated with the listed channel-references. This results in any output text generated by the name server daemon for that logging category to be redirected through each of the channel-references listed.

The default category defines all messages that are not listed in one of the specific categories listed. Also, the insist and panic categories are associated with messages that define a fatal inconsistency in the name server's state. The remaining categories define messages that are generated when handling specific functions of the name server. For example, the update category is used when logging errors or messages specific to the handling of a dynamic zone update, and the parser category is used when logging errors or messages during the parsing of the conf file.

channel-reference References a channel-name identifier defined previously in the logging configuration stanza. Therefore, every message associated with the defined category-name will be logged through each of the defined channel-references.

Global Options

options {
    [ directory path-string; ]
    [ named-xfer path-string; ]
    [ dump-file path-string; ]
    [ pid-file path-string; ]
    [ statistics-file path-string; ]
    [ auth-nxdomain ( yes | no ); ]
    [ fake-iquery ( yes | no ); ]
    [ fetch-glue ( yes | no ); ]
    [ multiple-cnames ( yes | no ); ]
    [ notify ( yes | no ); ]
    [ recursion ( yes | no ); ]
    [ forward ( only | first ); ]
    [ forwarders { ipaddr; [...] }; ]
    [ check-names
       ( master|slave|response )
       ( warn|fail|ignore ); ]
    [ allow-query { access-element; [...] }; ]
    [ allow-transfer { access-element; [...] ); ]
    [ listen-on [ port port-num ] { access-element; [...] }; ... ]
    [ query-source [ address ( ipaddr|* ) ] [ port ( port|* ) ]; ]
    [ max-transfer-time-in seconds; ]
    [ transfer-format ( one-answer | many-answers ); ]
    [ transfers-in value; ]
    [ transfers-out value; ]
    [ transfers-per-ns value; ]
    [ coresize size-value; ]
    [ datasize size-value; ]
    [ files size-value; ]
    [ stacksize size-value; ]
    [ clean-interval value; ]
    [ interface-interval value; ]
    [ statistics-interval value; ]
    [ topology { access-element; [...] }; ]

Defines many globally available options to to modify basic characteristics of the name server.

Because some of the options in this configuration stanza may modify the behavior in how the named daemon will read and interpret later sections of the named file, it is highly recommended that the options stanza be the first stanza listed in the configuration file.

Option Values Default Explanation
directory path-string "." Indicates the directory from which all relative paths will be anchored. The path-string parameter must be a quoted string. For example, to indicate that all zone files will exist in the "/usr/local/named/data" without listing each file in the zone definitions, specify the global option directory as:
options {

named-xfer path-string "/usr/sbin/named-xfer" Specifies the path and executable name of the named-xfer command used for inbound zone transfers. The path-string parameter must be a quoted string.
dump-file path-string "/usr/tmp/named_dump.db" Specifies a filename to which the database in memory will be dumped whenever the named daemon receives a SIGINT signal.
pid-file path-string "/etc/named.pid" Specifies the file in which the named daemon will write its PID value.
statistics-file path-string "/usr/tmp/named.stats" Specifies the file to which the name server will append operating statistics when it receives the SIGILL signal.
auth-nxdomain yes
yes Controls whether the server should respond authoritatively when returning an NXDOMAIN response.
fake-iquery yes
no Controls whether the server should respond to the obsolete IQUERY requests.
fetch-glue yes
yes Controls whether the server should search for "glue" records to include in the additional section of a query response.
multiple-cnames yes
no Controls whether the server will allow multiple CNAME records for one domain name in any of its zone databases. This practice is discouraged but an option remains for backwards compatibility.
notify yes
yes Controls whether the name server will send NOTIFY messages to its slave servers upon realization of zone changes. Because the slave servers will almost immediately respond to the NOTIFY message with a request for zone transfer, this limits the amount of time that the databases are out of synchronization in the master and slave relationship.
recursion yes
yes Controls whether the server will attempt to resolve names outside of its domains on behalf of the client. If set to no, the name server will return a referral to the client in order for the client to continue searching for the name. Used with the fetch-glue option, one can contain the amount of data that grows in the name server's memory cache.
forward only
first Controls how forwarding is used when forwarding is enabled. When set to first, the name server will attempt to search for a name whenever the forwarded host does not provide an answer. However, when set to only, the name server will not attempt this extra work.
forwarders ipaddr (empty list) Enables the use of query forwarding when defining a Forwarding Name Server. The ipaddr parameter list specifies the hosts to which the query should be forwarded when it cannot be resolved from the local database. Each ipaddr is an internet address in standard dot notation.
check-names master ignore
master warn
master fail
slave ignore
slave warn
slave fail
response ignore
response warn
response fail
master fail
slave warn
response ignore
Controls how the name server will handle non-RFC compliant host names and domain names through each of its operation domains.

The master keyword specifies how to handle malformed names in a master zone file.
The slave keyword specifies how to handle malformed names received from a master server.
The response keyword specifies how to handle malformed names received in response to a query.

ignore directs the server to ignore any malformed names and continue normal processing.
warn directs the server to warn the administrator through logging, but to continue normal processing.
fail directs the server to reject the name entirely. For the responses to queries, this implies that the server will return a REFUSED message to the original query host.

allow-query access-element any Limits the range of querying hosts allowed to access the system. Each access-element is specified in the same manner as in the acl stanza defined earlier.
allow-transfer access-element any Limits the range of querying hosts that are requesting zone transfers. Each access-element is specified in the same manner as in the acl stanza defined earlier.
listen-on port port-num
port 53 { localhost; } Limits the interfaces available to the name server daemon and controls which port to use to listen for queries. By default, the name server uses all interfaces on the system and listens on port 53. Additionally, multiple listen-on definitions are allowed within the options stanza.

Each access element is specified in the same manner as in the acl stanza defined earlier. The following example limits the name server to using only the interface with address

listen-on port 53 {; };
query-source address ipaddr
address *
port port
port *
address * port * Modifies the default address and port from which queries will originate.
max-transfer-time-in seconds 120 Specifies the maximum amount of time an inbound zone transfer will be allowed to run before it is aborted. This is used to control an event in which a child process of the name server does not execute or terminate properly.
transfer-format one-answer
one-answer Controls the method in which full zone transfers will be sent to requestors. The one-answer method uses one packet per zone resource record while many-answers will insert as many resource records into one packet as possible. While the many-answers method is more efficient, it is only understood by the newest revisions of the name server. This option can be overridden in the server stanza to specify the method on a per name server basis.
transfers-in value 10 Specifies the maximum number of concurrent inbound zone transfers. While this will limit the amount of time each slave zone is out of synchronization with the master's database, because each inbound transfer runs in a separate child process, increasing the value may also increase the load on the slave server.
transfers-out value N/A Specifies the maximum number of concurrent outbound zone transfers for the name server. This option is currently unused in the server, but will be available at a later time.
transfers-per-ns value 2 Specifies the maximum amount of concurrent zone transfers from a specific remote name server. While this will limit the amount of time each slave zone is out of synchronization with the master's database, increasing this value may increase the load on the remote master server.
coresize size-value default Configures some process specific values for the daemon.

The default values or those inherited by the system and by the system's resources.

Each size-value can be specified as a number or as a number followed by the k, m, and g modifiers indicating kilobytes, megabytes, and gigabytes respectively.

datasize size-value default
files value unlimited
stacksize size-value default
clean-interval minutes 60 Controls the intervals for the periodic maintenance tasks of the name server.

The clean-interval specifies how frequently the server will remove expired resource records from the cache. The interface-interval specifies how frequently the server will rescan for interfaces in the system. The statistics-interval specifies how frequently the name server will output statistics data.

A minutes value of zero indicates that the service task should only run when the configuration file is reread.

interface-interval minutes 60
statistics-interval minutes 60
cleandb-time time N/A Specifies a time of day in which the database will be scanned and any dynamic records whose set of SIG resource records are all expired will be removed. For a dynamic zone which has update-security set to presecured, only the expired SIG KEY will remain.

The default is to never perform this scan. Instead, the expired records will remain until the name is queried.

time is specified as HH:MM in a 24-hour format.

topology access-element localhost; localnets; Specifies a search order to use to find a preference in a list of addresses corresponding to a name server. Whenever a query is forwarded or a query must be made to another name server, it may be necessary to choose an address from a list of available addresses.

Each access-element, while seemingly similar to those specified in an acl stanza, is interpretted by its position in the list. The first elements in the list are preferred more than those following them. Negated elements (those specified with the ! (exclamation point) modifier) are considered least desirable.

Server Specific Options

server ipaddr
    [ bogus ( yes | no ); ]
    [ transfers value;
    [ transfer-format ( one-answer |
many-answers ); ]

Modifies the behavior in which the remote name server matching the specified ipaddr IP address should be treated.

Option Values Explanation
bogus yes
Indicates that the name server identified by the stanza should not be used again. The default value is no.
transfers value Overrides the globally available option transfers-per-ns. Specifies a maximum value for the number of concurrent inbound zone transfers from the foreign name server identified by the stanza.
transfer-format one-answer
Overrides the globally available option transfer-format to a specific value for the specified server. The transfer-format option indicates to the name server how to form its outbound full zone transfers. By default, the value is inherited from the options stanza (where it defaults to one-answer). one-answer specifies that only one resource record can be sent per packet during the zone transfer, whereas many-answers indicates to entirely fill the outbound packet with resource records. The many-answers format is only available in the newest revisions of the name server.

Zone Definition

zone domain-string [ class ] {
    type ( hint | stub | slave | master );
    [ file path-string; ]
    [ masters { ipaddr; [...] }; ]
    [ check-names ( warn | fail | ignore ); ]
    [ allow-update { access-element; [...] }; ]
    [ update-security ( unsecured | presecured | controlled ); ]
    [ allow-query { access-element; [...] }; ]
    [ allow-transfer { access-element; [...] }; ]
    [ max-transfer-time-in seconds; ]
    [ notify ( yes | no ); ]
    [ also-notify { ipaddr; [...] }; ]
    [ dont-notify { ipaddr; [...] }; ]
    [ notify-delaytime seconds; ]
    [ notify-retrytime seconds; ]
    [ notify-retrycount value; ]
    [ dump-interval seconds; ]
    [ incr-interval seconds; ]
    [ deferupdcnt value; ]
    [ key-xfer ( yes | no ); ]
    [ timesync ( yes | no ); ]
    [ timesync-xfer ( yes | no ); ]
    [ save-backups ( yes | no ); ]
    [ ixfr-directory path-string; ]
    [ separate-dynamic ( yes | no ); ]

The zone stanza is used to define a zone, its type, possible location of data, and operating parameters. The domain-string is a quoted string specifying the zone, where "." is used to specify the root zone. The class paramter specifies the class of the zone as either in, hs, hesiod, or chaos. By default, the class is assumed to be IN.

Option Values Default Explanation
type hint
N/A Defines the type of the zone. hint zones, previously regarded as cache zones, only describe a source for information not contained in the other defined zones. A stub zone is one similar to a slave zone. While the slave zone replicates the entire database of its master, the stub zone only replicates the NS resource records. The master zone maintains a database on disk.

Based upon the selection of zone type, some of the other options are required while others may be impertinent. Zones of type hint and master require the file option, while zones of type slave and stub require the masters option. Additionally, the only other option available to a hint zone is the check-names option.

file path-string N/A Specifies the location for the source of data specific to the zone. This parameter is only optional for stub and slave zones, where its inclusion indicates that a locally saved copy of the remote zone can be kept. The path-string parameter is a quoted string which can specify the file name either non-relative or relative to the options stanza's directory. If the path is intended to be specified relative to the server root, the options stanza must be specified before the zone stanza.
masters ipaddr N/A Specifies a list of sources that will be referenced for a slave or stub zone to retrieve its data. This option is not valid for any other type of zone, and must be included for either of these two types.
check-names warn
Overrides the check-names option in the global options stanza. The default value is inherited from the options stanza, where its default is fail for master zones and warn for slave zones.
allow-update access-element none Indicates from what source addresses a zone will accept dynamic updates. access-elements are specified in the same manner as they are for the acl stanza. Because of the inherint insecurity of a dynamic update, this value defaults to none. If no update-security is specified, dynamic updates should be limited to a specific set of secured machines.
update-security unsecured
unsecured Valid only when the allow-update option specifies at least one source address, update-security defines what type of secured update mechanism the zone will use. The current zone update security method is a non-standard two-key method, but is compatible with previous releases of the name server.

presecured indicates that a zone will only accept updates for which names and resource records already exist, unless the update is signed by the zone's authorizing key. Normally, this means that the zone must be prepopulated with the names and records it is to maintain. controlled specifies a zone in which names can be added to the database without the signature of the zone's authorizing key, but existing records cannot be modified without being signed by the KEY resource record's corresponding private key.

Note that a proper presecured or controlled zone must contain a zone KEY resource record.

See the TCP/IP Name Resolution for more information regarding zone update security.

allow-query access-element Overrides the globally available option allow-query. This option's default is inherited from the global options stanza, where its default is any.
allow-transfer access-element Overrides the globally available option allow-transfer. This option's default is inherited from the global options stanza, where its default is any.
max-transfer-time-in seconds Overrides the globally available option max-transfer-time-in. This option's default is inherited from the global options stanza, where its default is 120.
notify yes
Overrides the globally available option notify. This option's default is inherited from the global options stanza, where its default is yes.
also-notify ipaddr N/A The default NOTIFY mechanism will notify slave servers of a change in the DOMAIN database in order to limit the amount of time that the slave server retains a zone out of synchronization with the master server. The also-notify option allows for the addition of addresses to submit the notifications.
dont-notify ipaddr N/A Specifies a list of IP addresses to be removed from the default list of NOTIFY recipients. This option is useful if a name server is known to be problematic when receiving NOTIFY requests.
notify-delaytime seconds 30 Specifies an estimated time of delay between notifications to multiple name servers. Because the receipt of a NOTIFY message usually triggers the prompt request for a zone transfer, this option can tune to latency in which each server will respond with the request for the modified zone.

The real value used will be randomized between the specified number of seconds and twice this value.

notify-retrytime seconds 60 Specifies the number of seconds in which the name server will wait to retransmit a NOTIFY message which has gone unresponded.
notify-retrycount value 3 Specifies the maximum number of tries that the name server will attempt to send unanswered NOTIFY messages to other name servers.
dump-interval seconds 3600 Specifies an interval in which the name server will rewrite a dynamic zone to the zone file. In the interim, all updates and other transactions will be logged in the transaction log file for performance reasons. Aside from this periodic zone dump, the transaction log file is only discarded and the zone is only dumped when the name server is properly shut down.

This option is only valid for zones in which the allow-update option specifies at least one valid accessor.

The transaction log file name is the zone file name with an appended ".log" extension.
incr-interval seconds 300 Specifies an interval in which the name server will accept dynamic updates while not increasing the zone's SOA record's serial level. Because a change in the zone SOA record will instantiate a NOTIFY message, limiting this occurrence will limit the amount of zone transfer requests at the expense of minimal zone differences between a dynamic master server and its slave.

This option is only valid for zones in which the allow-update option specifies at least one valid accessor.

deferupdcnt value 100 Specifies a threshold value for the number of properly applied updates received during one incr-interval interval. If more than value updates are realized during the interval, the name server will modify the zone SOA serial level and subsequently NOTIFY each of the slave servers. Use this value to limit the database replication inconsistencies in an environment where dynamic zone updates occur infrequently but in large magnitude.

This option is only valid for zones in which the allow-update option specifies at least one valid accessor.

key-xfer yes
yes Specifies whether the server should transmit KEY resource records during a zone transfer. In a very controlled environment where KEY queries will only be made to the master name server, setting this option to no will save zone transfer time and improve performance.
timesync yes
yes Specifies that a name server should calculate the true expiration time of a SIG resource record using its own clock rather than relying on the expiration time set by a possible update source. This removes the inconsistencies involved when dynamic zone updaters have their system clocks misaligned from the name server host. Because enabling this option modifies the output and interpretation of a SIG resource record in a DOMAIN database file, disabling this option may be required when manually transfering a DOMAIN database file to another name server.
timesync-xfer yes
yes Specifies which SIG resource record expiration time will be transfered during a zone transfer. Enabling this option is only valid when the timesync option is enabled.
ixfr-directory path-string Specifies a directory in which temporary data files will be contained for use with this zone. The datafiles contain incremental zone changes and are essential to the proper use of the Incremental Zone Transfer (IXFR) method. Because these files are created and destroyed dynamically by the name server, one should not specify a globally-writable directory. Additionally, the directory specified must be unique from other ixfr-directory options specified in other zones.

The default value for this directory is derived from the zone's file name or domain name. By default, a directory is created in an "ixfrdata" directory within the name server's default directory. Contained in this directory will be subdirectory matching the base name of the zone's file name or domain name.

It is not necessary to specify this option for the proper behavior of the IXFR feature.

save-backups yes
no To properly calculate an incremental zone difference between server invocations, it is necessary to determine the zone database differences prior to the shutdown of the server and after the loading of the server. By enabling this option, a backup of the zone file will be written and read upon loading of the name server to determine any zone differences.

While enabling this option is necessary to use the IXFR transfer method after a stop and restart transition of the name server, it is not necessary to realize incremental zone differences when a zone file is modified and signalled to reload via the SRC refresh command or SIGHUP signal.

separate-dynamic yes
no Instructs the name server to retain $INCLUDE references in a dynamic zone when the DOMAIN database file is written to disk. The behavior of this feature implies that resource records that can be modified through the dynamic update mechanism exist in the DOMAIN database file referenced by the file option, while other resource records that should not be modified through the dynamic update mechanism be contained in files included (through the $INCLUDE directive) by the DOMAIN database file.


The following examples show the some of the various ways to use configure a simple named.conf file. In these examples, two networks are represented: abc and xyz.

Network abc consists of:

Network xyz consists of:

  1. The /etc/named.conf file for gobi.abc, the master name server for network abc, contains these entries:

    # conf file for abc master server - gobi.abc
    server {
    transfer-format many-answers;

    zone "abc" in {
    type master;
    file "/etc/named.abcdata";
    allow-update { localhost; };

    zone "201.9.192.in-addr.arpa" in {
    type master;
    file "/etc/named.abcrev";
    allow-update { localhost; };

    zone "0.0.127.in-addr.arpa" in {
    type master;
    file "/etc/named.abclocal";
  2. The /etc/named.conf file for kalahari.xyz, the master name server for network xyz, contains these entries:

    # conf file for abc master server - kalahari.xyz
    acl xyz-slaves {;

    options {
    directory "/etc";
    allow-transfer { xyz-slaves; localhost; };

    zone "xyz" in {
    type master;
    file "named.xyzdata";

    zone "9.160.in-addr.arpa" in {
    type master;
    file "named.xyxrev";

    zone "0.0.127.in-addr.arpa" in {
    type master;
    file "named.xyzlocal";
  3. The /etc/named.conf file for sandy, the slave name server for networks abc and xyz, contains the following entries:

    # conf file for slave server for abc and xyz - sandy
    options {
    directory "/etc";

    zone "abc" in {
    type slave;
    masters {; };
    file "named.abcdata.bak";

    zone "xyz" in {
    type slave;
    masters {; };
    file "named.xyzdata.bak";

    zone "201.9.192.in-addr.arpa" in {
    type slave;
    masters {; };

    zone "9.160.in-addr.arpa" in {
    type slave;
    masters {; };

    zone "0.0.127.in-addr.arpa" in {
    type master;
    file "named.local";
  4. The /etc/named.conf file for sahara, a hint name server for the network xyz, contains the following entries:

    # conf file for hint server for xyz - sahara
    zone "." in {
    type hint;
    file "/etc/named.ca";

    zone "0.0.127.in-addr.arpa" in {
    type master;
    file "/etc/named.local";

Format of the named.conf file when configuring named9


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 IPv4 addresses of all network interfaces on the system.
localnets Matches any host on an IPv4 network for which the system has an interface.

The localhost and localnets ACLs do not currently support IPv6 (that is, localhost does not match the host's IPv6 addresses, and localnets does not match the host's attached IPv6 networks) due to the lack of a standard method of determining the complete set of local IPv6 addresses for a host.

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 . All commands to the control channel must be signed by one of its specified keys to be honored.

If no controls statement is present, named9 will set up a default control channel listening on the loopback address and its IPv6 counterpart ::1. In this case, and also when the controls statement is present but does not have a keys clause, named9 will attempt to load the command channel key from the /etc/rndc.key file in (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-keygen -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. If it is present in the controls statement from a BIND 8 configuration file, it is ignored and a warning is 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 statement can occur at the top level of the configuration file or inside a view statement. Keys defined in top-level key statements can be used in all views. Keys intended for use in a controls statement must be defined at the top level.

The 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 "unmatched" { "null"; };
     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.

If you use the versions log file option, then named9 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 named9 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. 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 named9 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 named9 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 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- ptions 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 named9's default logging as follows.

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" {              // 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 named9run in the server's working directory.

For security reasons, when the -u command line option is used, the named9run file is created only after named9 has changed to the new UID, and any debug output generated while named9 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" {

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.

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.
unmatched Messages that named was unable to determine the class of or for which there was no matching view. A one line summary is also logged to the client category. This category is best sent to a file or stderr, by default it is sent to the null channel.
network Network operations.
update Dynamic updates.
queries Queries. Using the category queries will enable query logging.
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.

options Statement Grammar

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; ]
    [ 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; ]
    [ forward ( only | first ); ]
    [ forwarders { ip_addr [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-v6-synthesis { 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-query-rate 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 ; ]
    [ 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; ]

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.

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.
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. named.run) is this directory. If a directory is not specified, the working directory defaults to ".," the directory from which the server was started. The directory specified should be an absolute path.
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.
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.
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.
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.
The pathname of the file the server writes memory usage statistics to on exit. If not specified, the default is named.memstats.
Not yet implemented in BIND 9.
The pathname of the file the server writes its process ID in. If not specified, the default is /var/run/named.pid. The pid-file is used by programs that want to send signals to the running nameserver.
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 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 source of entropy to be used by the server. Entropy is primarily needed for DNSSEC operations, such as TKEY transactions and dynamic update of signed zones. This options specifies the device (or file) from which to read entropy. If this is a file, operations requiring entropy will fail when the file has been exhausted. If not specified, the default value is /dev/random (or equivalent) when present, and none otherwise. The random-device option takes effect during the initial configuration load at server startup time and is ignored on subsequent reloads.

Boolean Options

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.
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.
If yes, 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-intervaland 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; and refresh, which suppresses normal refresh processing and send refresh queries when the heartbeat-interval expires and passive which just disables normal refresh processing.

In BIND 8, this option was used to enable simulating the obsolete DNS query type IQUERY. BIND 9 never does IQUERY simulation.
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 bad practice, and BIND 9 never does it.
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.
In BIND 8, this enables keeping of statistics for every host that the nameserver interacts with. It is not implemented in BIND 9.
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.
If yes, then when generating responses the server will only add records to the authority and additional data sections when they are required. This may improve the performance of the server. The default is no.
This option was used in BIND 8 to allow a domain name to allow multiple CNAME records in violation of the DNS standards. BIND 9.2 strictly enforces the CNAME rules both in master files and dynamic updates.
If yes (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.

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.
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.
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.
This option is obsolete. BIND 9 always allocates query IDs from a pool.
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 The Statistics File.
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 server Statement Definition and Usage.
See the description of provide-ixfr in server Statement Definition and Usage.
See the description of request-ixfr in server Statement Definition and Usage.
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 a Windows NT or DOS machine. In BIND 9, both UNIX "\n" and NT/DOS "\r\n" newlines are always accepted, and the option is ignored.
additional-from-auth, additional-from-cache
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 (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 foo.example.com, and the record found is "MX 10 mail.example.net", normally the address records for mail.example.net 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. Attempts to set them to no without also specifying recursion no; will cause the server to ignore the options and log a warning message.

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.

If yes, then an IPv4-mapped IPv6 address will match any address match list entries that match the corresponding IPv4 address. Enabling this option is sometimes useful on IPv6-enabled Linux systems, to work around a kernel quirk that causes IPv4 TCP connections such as zone transfers to be accepted on an IPv6 socket using mapped addresses, causing address match lists designed for IPv4 to fail to match. The use of this option for any other purpose is discouraged.


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.

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.
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. See zone Statement Grammar.

Access Control

Access to the server can be restricted based on the IP address of the requesting system.

Specifies which hosts are allowed to notify slaves of a zone change in addition to the zone masters. The allow-notify option 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.
Specifies which hosts are allowed to ask ordinary questions. The allow-query option 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.
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.
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.
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; };

This 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.

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. 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 as follows:

query-source address * port *;
query-source-v6 address * port *
The address specified in the query-source option is used for both UDP and TCP queries, but the port applies only to UDP queries. TCP queries always use a random unprivileged port.

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.

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).
Inbound zone transfers running longer than this many minutes will be terminated. The default is 120 minutes (2 hours).
Inbound zone transfers making no progress in this many minutes will be terminated. The default is 60 minutes (1 hour).
Outbound zone transfers running longer than this many minutes will be terminated. The default is 120 minutes (2 hours).
Outbound zone transfers making no progress in this many minutes will be terminated. The default is 60 minutes (1 hour).
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. To limit the amount of bandwidth used, BIND 9 limits the rate at which queries are sent. The value of the serial-query-rate option, an integer, is the maximum number of queries sent per second. The default is 20.
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 serial-queries option. Instead, it limits the rate at which the queries are sent as defined using the serial-query-rate option.
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.
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.
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.
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 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.
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.

Operating System Resource Limits

The server's usage of many system resources can be limited. Scaled values are allowed when specifying resource limits. For example, 1G can be used instead of 1073741824 to specify a limit of one gigabyte. The unlimited option requests unlimited use, or the maximum available amount. The default option uses the limit that was in force when the server was started.

The following options set operating system resource limits for the name server process. Some operating systems don't support some or any of the limits. On such systems, a warning will be issued if the unsupported limit is used.

The maximum size of a core dump. The default is default.
The maximum amount of data memory the server may use. The default is default. This is a hard limit on server memory usage. If the server attempts to allocate memory in excess of this limit, the allocation will fail, which may in turn leave the server unable to perform DNS service. Therefore, this option is rarely useful as a way of limiting the amount of memory used by the server, but it can be used to raise an operating system data size limit that is too small by default. If you wish to limit the amount of memory used by the server, use the max-cache-size and recursive-clients options instead.
The maximum number of files the server may have open concurrently. The default is unlimited.
The maximum amount of stack memory the server may use. The default is default.

Server Resource Limits

The following options set limits on the server's resource consumption that are enforced internally by the server rather than the operating system.

This option is obsolete; it is accepted and ignored for BIND 8 compatibility.

The maximum number of simultaneous recursive lookups the server will perform on behalf of clients. The default is 1000. Because each recursing client uses a fair bit of memory, on the order of 20 kilobytes, the value of the recursive-clients option may have to be decreased on hosts with limited memory.


The maximum number of simultaneous client TCP connections that the server will accept. The default is 100.


The maximum amount of memory to use for the server's cache, in bytes. When the amount of data in the cache reaches this limit, the server will cause records to expire prematurely so that the limit is not exceeded. In a server with multiple views, the limit applies separately to the cache of each view. The default is unlimited, meaning that records are purged from the cache only when their TTLs expire.

Periodic Task Intervals


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.


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.


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.


Nameserver statistics will be logged every statistics-interval minutes. The default is 60. If set to 0, no statistics will be logged.

Not yet implemented in BIND 9.


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; };
The topology option is not 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 RRset Ordering). The client resolver code should rearrange the RRs as appropriate, that is, using any addresses on the local net in preference to other addresses. However, not all resolvers can do this or are correctly configured. When a client is using a local server the sorting can be performed in the server, based on the client's address. This only requires configuring the 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 (Topology). 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, The sortlist Statement.

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:


Records are returned in the order they are defined in the zone file.


Records are returned in some random order.


Records are returned in a round-robin order.

For example:

rrset-order {
   class IN type A name "host.example.com" order random;
   order cyclic;

will cause any responses for type A records in class IN that have " host.example.com" 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.

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.



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).

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 sets the maximum time for which the server will cache ordinary (positive) answers. The default is one week (7 days).
The minimum number of root servers that is required for a request for the root servers to be accepted. Default is 2.
Not yet implemented in BIND 9.

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.

min-refresh-time, max-refresh-time, min-retry-time, max-retry-time

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.

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:


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.


The number of queries which resulted in referral responses.


The number of queries which resulted in NOERROR responses with no data.


The number of queries which resulted in NXDOMAIN responses.


The number of queries which caused the server to perform recursion in order to find the final answer.


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 ; ]
    [ edns yes_or_no ; ]
    [ transfers number ; ]
    [ transfer-format ( one-answer | many-answers ) ; ]]
    [ keys { string ; [ string ; [...]] } ; ]

server Statement Definition and Usage

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

The server statement can occur at the top level of the configuration file or inside a view statement. If a view statement contains one or more server statements, only those apply to the view and any top-level ones are ignored. If a view contains no server statements, any top-level server statements are used as defaults.

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 view or 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 view or 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 edns clause determines whether the local server will attempt to use EDNS when communicating with the remote server. The default is yes.

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. 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 } ;
      match-destinations { address_match_list } ;
      match-recursive-only { yes_or_no } ;
      [ view_option; ...]
      [ zone-statistics yes_or_no ; ]
      [ zone_statement; ...]

6.2.20. 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 a subset of clients. A client matches a view if its source IP address matches the address_match_list of the view's match-clients clause and its destination IP address matches the address_match_list of the view's match-destinations clause. If not specified, both match-clients and match-destinations default to matching all addresses. A view can also be specified as match-recursive-only, which means that only recursive requests from matching clients will match that view. The order of the view statements is significant -- a client request will be resolved in the context of the first view that it matches.

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 example.com zone
               // including addresses of internal hosts.
      zone "example.com" {
            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 example.com zone
               // containing only publicly accessible hosts.
      zone "example.com" {
           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 [port ip_port] ; [ ip_addr [port ip_port] ; ... ] }; ]
    [ 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 ; ]
    [ min-refresh-time number ; ]
    [ max-refresh-time number ; ]
    [ min-retry-time number ; ]
    [ max-retry-time number ; ]


zone Statement Definition and Usage

Zone Types


The server has a master copy of the data for the zone and will be able to provide authoritative answers for it.


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 example.com might place the zone contents into a file called ex/example.com where ex/ is just the first two letters of the zone name. (Most operating systems behave very slowly if you put 100K files into a single directory.)


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 10.in-addr.arpa to use a set of internal name servers as the authoritative servers for that domain.


A "forward zone" is a way to configure forwarding on a per-domain basis. A zone statement of type forward can contain a forward and/or forwarders statement, which 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, canceling 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.


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.


The zone's name may optionally be followed by a class. If a class is not specified, class IN (for Internet), is assumed. This is correct for the vast majority of cases.

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

See the description of allow-notify in Access Control.


See the description of allow-query in Access Control.


See the description of allow-transfer in Access Control.


Specifies which hosts are allowed to submit Dynamic DNS updates for master zones. The default is to deny updates from all hosts.


Specifies a "Simple Secure Update" policy. See Dynamic Update Policies.


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.


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.


This option was used in BIND 8 to restrict the character set of domain names in master files or DNS responses received from the network. BIND 9 does not restrict the character set of domain names and does not implement the check-names option.


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.


See the description of dialup in Boolean Options.


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.


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.


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.


Was an undocumented option in BIND 8. Ignored in BIND 9.


See the description of max-transfer-time-in in Zone Transfers.


See the description of max-transfer-idle-in in Zone Transfers.


See the description of max-transfer-time-out in Zone Transfers.


See the description of max-transfer-idle-out in Zone Transfers.


See the description of notify in Boolean Options.


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.


If yes, the server will keep statistical information for this zone, which can be dumped to the statistics-file defined in the server options.


See the description of sig-validity-interval in Tuning.


See the description of transfer-source in Zone Transfers


See the description of notify-source in Zone Transfers

min-refresh-time, max-refresh-time, min-retry-time, max-retry-time

See the description in Tuning.

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


Matches when the updated name is the same as the name in the name field.


Matches when the updated name is a subdomain of the name in the name field (which includes the name itself).


Matches when the updated name is a valid expansion of the wildcard name in the name field.


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).

Zone File
DOMAIN Data File, DOMAIN Reverse Data File, DOMAIN Cache File, and DOMAIN Local
Types of Resource Records and When to Use Them

This section, largely borrowed from RFC 1034, describes the concept of a Resource Record (RR) and explains when each is used. Since the publication of RFC 1034, several new RRs have been identified and implemented in the DNS. These are also included.

Resource Records

A domain name identifies a node. Each node has a set of resource information, which may be empty. The set of resource information associated with a particular name is composed of separate RRs. The order of RRs in a set is not significant and need not be preserved by nameservers, resolvers, or other parts of the DNS. However, sorting of multiple RRs is permitted for optimization purposes, for example, to specify that a particular nearby server be tried first. See The sortlist Statement and RRset Ordering.

The components of a Resource Record are:

owner name

the domain name where the RR is found.


an encoded 16 bit value that specifies the type of the resource in this resource record. Types refer to abstract resources.


the time to live of the RR. This field is a 32 bit integer in units of seconds, and is primarily used by resolvers when they cache RRs. The TTL describes how long a RR can be cached before it should be discarded.


an encoded 16 bit value that identifies a protocol family or instance of a protocol.


the type and sometimes class-dependent data that describes the resource.

The following are types of valid RRs (some of these listed, although not obsolete, are experimental (x) or historical (h) and no longer in general use):


a host address.


an IPv6 address.


Obsolete format of IPv6 address


(x) location of AFS database servers. Experimental.


identifies the canonical name of an alias.


for delegation of reverse addresses. Replaces the domain name specified with another name to be looked up. Described in RFC 2672.


identifies the CPU and OS used by a host.


(x) representation of ISDN addresses. Experimental.


stores a public key associated with a DNS name.


(x) for storing GPS info. See RFC 1876. Experimental.


identifies a mail exchange for the domain. See RFC 974 for details.


the authoritative nameserver for the domain.


used in DNSSEC to securely indicate that RRs with an owner name in a certain name interval do not exist in a zone and indicate what RR types are present for an existing name. See RFC 2535 for details.


a pointer to another part of the domain name space.


(x) information on persons responsible for the domain. Experimental.


(x) route-through binding for hosts that do not have their own direct wide area network addresses. Experimental.


("signature") contains data authenticated in the secure DNS. See RFC 2535 for details.


identifies the start of a zone of authority.


information about well known network services (replaces WKS).


(h) information about which well known network services, such as SMTP, that a domain supports. Historical, replaced by newer RR SRV.


(x) representation of X.25 network addresses. Experimental.

The following classes of resource records are currently valid in the DNS:


the Internet system.

For information about other, older classes of RRs

RDATA is the type-dependent or class-dependent data that describes the resource:


for the IN class, a 32 bit IP address.


maps a domain name to an IPv6 address, with a provision for indirection for leading "prefix" bits.


a domain name.


provides alternate naming to an entire subtree of the domain name space, rather than to a single node. It causes some suffix of a queried name to be substituted with a name from the DNAME record's RDATA.


a 16 bit preference value (lower is better) followed by a host name willing to act as a mail exchange for the owner domain.


a fully qualified domain name.


a fully qualified domain name.


several fields.

The owner name is often implicit, rather than forming an integral part of the RR. For example, many nameservers internally form tree or hash structures for the name space, and chain RRs off nodes. The remaining RR parts are the fixed header (type, class, TTL) which is consistent for all RRs, and a variable part (RDATA) that fits the needs of the resource being described.

The meaning of the TTL field is a time limit on how long an RR can be kept in a cache. This limit does not apply to authoritative data in zones; it is also timed out, but by the refreshing policies for the zone. The TTL is assigned by the administrator for the zone where the data originates. While short TTLs can be used to minimize caching, and a zero TTL prohibits caching, the realities of Internet performance suggest that these times should be on the order of days for the typical host. If a change can be anticipated, the TTL can be reduced prior to the change to minimize inconsistency during the change, and then increased back to its former value following the change.

The data in the RDATA section of RRs is carried as a combination of binary strings and domain names. The domain names are frequently used as "pointers" to other data in the DNS.

Textual expression of RRs

RRs are represented in binary form in the packets of the DNS protocol, and are usually represented in highly encoded form when stored in a nameserver or resolver. In the examples provided in RFC 1034, a style similar to that used in master files was employed in order to show the contents of RRs. In this format, most RRs are shown on a single line, although continuation lines are possible using parentheses.

The start of the line gives the owner of the RR. If a line begins with a blank, then the owner is assumed to be the same as that of the previous RR. Blank lines are often included for readability.

Following the owner, we list the TTL, type, and class of the RR. Class and type use the mnemonics defined above, and TTL is an integer before the type field. In order to avoid ambiguity in parsing, type and class mnemonics are disjoint, TTLs are integers, and the type mnemonic is always last. The IN class and TTL values are often omitted from examples in the interests of clarity.

The resource data or RDATA section of the RR are given using knowledge of the typical representation for the data.

For example, we might show the RRs carried in a message as:












The MX RRs have an RDATA section which consists of a 16 bit number followed by a domain name. The address RRs use a standard IP address format to contain a 32 bit internet address.

This example shows six RRs, with two RRs at each of three domain names.

Similarly we might see:





MIT.EDU. 2420

This example shows two addresses for XX.LCS.MIT.EDU, each of a different class.

Discussion of MX Records

As described above, domain servers store information as a series of resource records, each of which contains a particular piece of information about a given domain name (which is usually, but not always, a host). The simplest way to think of a RR is as a typed pair of datum, a domain name matched with relevant data, and stored with some additional type information to help systems determine when the RR is relevant.

MX records are used to control delivery of email. The data specified in the record is a priority and a domain name. The priority controls the order in which email delivery is attempted, with the lowest number first. If two priorities are the same, a server is chosen randomly. If no servers at a given priority are responding, the mail transport agent will fall back to the next largest priority. Priority numbers do not have any absolute meaning -- they are relevant only respective to other MX records for that domain name. The domain name given is the machine to which the mail will be delivered. It must have an associated A record -- CNAME is not sufficient.

For a given domain, if there is both a CNAME record and an MX record, the MX record is in error, and will be ignored. Instead, the mail will be delivered to the server specified in the MX record pointed to by the CNAME.




















For example:

Mail delivery will be attempted to mail.example.com and mail2.example.com (in any order), and if neither of those succeed, delivery to mail.backup.org will be attempted.

Setting TTLs

The time to live of the RR field is a 32 bit integer represented in units of seconds, and is primarily used by resolvers when they cache RRs. The TTL describes how long a RR can be cached before it should be discarded. The following three types of TTL are currently used in a zone file.


The last field in the SOA is the negative caching TTL. This controls how long other servers will cache no-such-domain (NXDOMAIN) responses from you.

The maximum time for negative caching is 3 hours (3h).


The $TTL directive at the top of the zone file (before the SOA) gives a default TTL for every RR without a specific TTL set.


Each RR can have a TTL as the second field in the RR, which will control how long other servers can cache the it.

All of these TTLs default to units of seconds, though units can be explicitly specified, for example, 1h30m.

Inverse Mapping in IPv4

Reverse name resolution (that is, translation from IP address to name) is achieved by means of the in-addr.arpa domain and PTR records. Entries in the in-addr.arpa domain are made in least-to-most significant order, read left to right. This is the opposite order to the way IP addresses are usually written. Thus, a machine with an IP address of would have a corresponding in-addr.arpa name of This name should have a PTR resource record whose data field is the name of the machine or, optionally, multiple PTR records if the machine has more than one name. For example, in the [ example.com ] domain:




IN PTR foo.example.com.

The $ORIGIN lines in the examples are for providing context to the examples only-they do not necessarily appear in the actual usage. They are only used here to indicate that the example is relative to the listed origin.
Other Zone File Directives

The Master File Format was initially defined in RFC 1035 and has subsequently been extended. While the Master File Format itself is class independent all records in a Master File must be of the same class.

Master File Directives include $ORIGIN, $INCLUDE, and $TTL.

The $ORIGIN Directive

Syntax: $ORIGIN domain-name [ comment ]

$ORIGIN sets the domain name that will be appended to any unqualified records. When a zone is first read in there is an implicit $ORIGIN < zone-name> . The current $ORIGIN is appended to the domain specified in the $ORIGIN argument if it is not absolute.

$ORIGIN example.com.

is equivalent to

The $INCLUDE Directive

Syntax: $INCLUDE filename [ origin ] [ comment ]

Read and process the file filename as if it were included into the file at this point. If origin is specified the file is processed with $ORIGIN set to that value, otherwise the current $ORIGIN is used.

The origin and the current domain name revert to the values they had prior to the $INCLUDE once the file has been read.

RFC 1035 specifies that the current origin should be restored after an $INCLUDE, but it is silent on whether the current domain name should also be restored. BIND 9 restores both of them. This could be construed as a deviation from RFC 1035, a feature, or both.
The $TTL Directive

Syntax: $TTL default-ttl [ comment ]

Set the default Time To Live (TTL) for subsequent records with undefined TTLs. Valid TTLs are of the range 0-2147483647 seconds.

$TTL is defined in RFC 2308.

BIND Master File Extension: the $GENERATE Directive

Syntax: $GENERATE range lhs type rhs [ comment ]

$GENERATE is used to create a series of resource records that only differ from each other by an iterator. $GENERATE can be used to easily generate the sets of records required to support sub /24 reverse delegations described in RFC 2317: Classless IN-ADDR.ARPA delegation.

$GENERATE 1-127 $ CNAME $.0



This can be one of two forms: start-stop or start-stop/step. If the first form is used then step is set to 1. All of start, stop and step must be positive.


lhs describes the owner name of the resource records to be created. Any single $ symbols within the lhs side are replaced by the iterator value. To get a $ in the output you need to escape the $ using a backslash \, e.g. \$. The $ may optionally be followed by modifiers which change the offset from the interator, field width and base. Modifiers are introduced by a { immediately following the $ as ${offset[,width[,base]]}. e.g. ${-20,3,d} which subtracts 20 from the current value, prints the result as a decimal in a zero padded field of with 3. Available output forms are decimal (d), octal (o) and hexadecimal (x or X for uppercase). The default modifier is ${0,0,d}. If the lhs is not absolute, the current $ORIGIN is appended to the name.

For compatability with earlier versions $$ is still recognised a indicating a literal $ in the output.


At present the only supported types are PTR, CNAME, DNAME, A, AAAA and NS.


rhs is a domain name. It is processed similarly to lhs.

The $GENERATE directive is a BIND extension and not part of the standard zone file format.


/usr/samples/tcpip/named.conf Contains the sample named.conf file.

Related Information

The named daemon.

The syslogd daemon.

The DOMAIN cache file format, DOMAIN local file format, DOMAIN data file format, DOMAIN Reverse data file format, rc.tcpip file format.

Configuring a Primary Name Server and Naming for TCP/IP in AIX 5L Version 5.2 System Management Guide: Communications and Networks.

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