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     named.conf - configuration file for named(8)


     BIND 8 is much more configurable than previous release of BIND.  There
     are entirely new areas of configuration, such as access control lists and
     categorized logging.  Many options that previously applied to all zones
     can now be used selectively.  These features, plus a consideration of fu­
     ture configuration needs led to the creation of a new configuration file

   General Syntax

     A BIND 8 configuration consists of two general features, statements and
     comments.  All statements end with a semicolon.  Many statements can con­
     tain substatements, which are each also terminated with a semicolon.

     The following statements are supported:

       specifies what the server logs, and where the log messages are sent

       controls global server configuration options and sets defaults for oth­
       er statements

       defines a zone

       defines a named IP address matching list, for access control and other

       specifies key information for use in authentication and authorization

       defines DNSSEC keys that are preconfigured into the server and implic­
       itly trusted

       sets certain configuration options for individual remote servers

       declares control channels to be used by the ndc utility

     in C, C++, or shell/perl constructs.

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

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

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

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

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

     Shell-style (or perl-style, if you prefer) comments start with the char­
     acter # (hash or pound or number or octothorpe or whatever) and continue
     to the end of the physical line, like C++ comments.  For example:

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

     WARNING: you cannot use the ; (semicolon) character to start a comment
     such as you would in a zone file.  The semicolon indicates the end of a
     configuration statement, so whatever follows it will be interpreted as
     the start of the next statement.

   Converting from BIND 4.9.x

     BIND 4.9.x configuration files can be converted to the new format by us­
     ing src/bin/named/named-bootconf, a shell script that is part of the BIND
     8.2.x source kit.


     Described below are elements used throughout the BIND configuration file
     documentation.  Elements which are only associated with one statement are
     described only in the section describing that statement.

       One or more integers valued 0 through 255 separated only by dots
       (``.''), such as 123, 45.67 or

       A quoted string which will be used as a DNS name, for example

       A quoted string which will be used as a pathname, such as

       An IP address in with exactly four elements in dotted-decimal notation.

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

       An IP network specified in dotted-decimal form, followed by  ``/'' and
       then the number of bits in the netmask.  E.g.  127/8 is the network with netmask is network with

       A string representing the name of a shared key, to be used for transac­
       tion security.

       A non-negative integer with an entire range limited by the range of a C
       language signed integer (2,147,483,647 on a machine with 32 bit inte­
       gers).  Its acceptable value might further be limited by the context in
       which it is used.

       A number, the word unlimited, or the word default.

       The maximum value of size_spec is that of unsigned long integers on the
       machine.  unlimited requests unlimited use, or the maximum available
       amount.  default uses the limit that was in force when the server was

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



     address_match_list    = 1*address_match_element

     address_match_element = [ "!" ] ( address_match_list /
                                       ip_address / ip_prefix /
                                       acl_name / "key " key_id ) ";"

   Definition and Usage

     Address match lists are primarily used to determine access control for
     various server operations.  They are also used to define priorities for
     querying other nameservers and to set the addresses on which named will
     listen for queries.  The elements which constitute an address match list
     can be any of the following:

     ·   an ip-address (in dotted-decimal notation,

     ·   an ip-prefix (in the '/'-notation),

     ·   A key_id, as defined by the key statement,

     ·   the name of an address match list previously defined with the acl
         statement, or

     ·   another address_match_list.

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

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

     When a given IP address or prefix is compared to an address match list,
     the list is traversed in order until an element matches.  The interpreta­
     tion of a match depends on whether the list is being used for access con­
     trol, defining listen-on ports, or as a topology, and whether the element
     When used with the topology option, a non-negated match returns a dis­
     tance based on its position on the list (the closer the match is to the
     start of the list, the shorter the distance is between it and the serv­
     er).  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

     Because of the first-match aspect of the algorithm, an element that de­
     fines a subset of another element in the list should come before the
     broader element, regardless of whether either is negated.  For example,
           1.2.3/24; !
     the element is completely useless, because the algorithm will
     match any lookup for to the 1.2.3/24 element.  Using
           !; 1.2.3/24
     fixes that problem by having blocked by the negation but all
     other 1.2.3.* hosts fall through.



     logging {
       [ channel channel_name {
         ( file path_name
            [ versions ( number | unlimited ) ]
            [ size size_spec ]
          | syslog ( kern | user | mail | daemon | auth | syslog | lpr |
                     news | uucp | cron | authpriv | ftp |
                     local0 | local1 | local2 | local3 |
                     local4 | local5 | local6 | local7 )
          | 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; ... ]
       }; ]

   Definition and Usage

     The logging statement configures a wide variety of logging options for
     the nameserver.  Its channel phrase associates output methods, format op­
         logging {
             category default { default_syslog; default_debug; };
             category panic { default_syslog; default_stderr; };
             category packet { default_debug; };
             category eventlib { default_debug; };

     The logging configuration is established as soon as the logging statement
     is parsed.  If you want to redirect messages about processing of the en­
     tire configuration file, the logging statement must appear first.  Even
     if you do not redirect configuration file parsing messages, we recommend
     always putting the logging statement first so that this rule need not be
     consciously recalled if you ever do need want the parser's messages relo­

   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 clause that says whether messages
     selected for the channel go to a file, to a particular syslog facility,
     or are discarded.  It can optionally also limit the message severity lev­
     el that will be accepted by the channel (default is info), and whether to
     include a time stamp generated by named, the category name, or severity
     level.  The default is not to include any of those three.

     The word null as the destination option for the channel will cause all
     messages sent to it to be discarded; other options for the channel are

     The file clause can include limitations both on how large the file is al­
     lowed to become, and how many versions of the file will be saved each
     time the file is opened.

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

     If you use the version logfile option, then named will retain that many
     backup versions of the file by renaming them when opening.  For example,
     if you choose to keep 3 old versions of the file lamers.log then just be­
     fore it is opened lamers.log.1 is renamed to lames.log.2, lamers.log.0 is
     renamed to lamers.log.1, and lamers.log is renamed to lamers.log.0.  No
     rolled versions are kept by default; any existing log file is simply ap­
     pended.  The unlimited keyword is synonymous with 99 in current BIND re­
     facility is described in the syslog.conf(5) manual page.  If you have a
     system which uses a very old version of syslog that only uses two argu­
     ments 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 deter­
     mine what eventually passes through.  For example, defining a channel fa­
     cility and severity as daemon and debug but only logging daemon.warning
     via syslog.conf will cause messages of severity info and notice to be
     dropped.  If the situation were reversed, with named writing messages of
     only warning or higher, then syslogd would print all messages it received
     from the channel.

     The server can supply extensive debugging information when it is in de­
     bugging mode.  If the server's global debug level is greater than zero,
     then debugging mode will be active.  The global debug level is set either
     by starting the named server with the -d flag followed by a positive in­
     teger, or by sending the running server the SIGUSR1 signal (for example,
     by using ndc trace). The global debug level can be set to zero, and de­
     bugging mode turned off, by sending the server the SIGUSR2 signal (as
     with ndc notrace). All debugging messages in the server have a debug lev­
     el, and higher debug levels give more more detailed output.  Channels
     that specify a specific debug severity, e.g.

         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 point­
     less since syslog also prints the date and time.  If print-category is
     requested, then the category of the message will be logged as well.  Fi­
     nally, if print-severity is on, then the severity level of the message
     will be logged.  The print- options may be used in any combination, and
     will always be printed in the following order: time, category, severity.
     Here is an example where all three print- options are on:

         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
             file "<stderr>";     # this is illustrative only; there's currently
                                  # no way of specifying an internal file
                                  # descriptor in the configuration language.
             severity info;       # only send priority info and higher

         channel null {
             null;                # toss anything sent to this channel

     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 wher­
     ever 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 de­
     fault 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 fol­

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

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

         category lame-servers { null; };
         category cname { null; };

     The following categories are available:

       Low-level configuration file processing.

       A short log message is generated for every query the server receives.

       Messages like ``Lame server on ...''


       If the server has to shut itself down due to an internal problem, it
       will log the problem in this category as well as in the problem's na­
       tive category.  If you do not define the panic category, the following
       definition is used:
             category panic { default_syslog; default_stderr; };

       Dynamic updates.

       Negative caching.

       Zone transfers the server is receiving.

       Zone transfers the server is sending.

       All database operations.

       Debugging info from the event system.  Only one channel may be speci­
       fied for this category, and it must be a file channel.  If you do not
       define the eventlib category, the following definition is used:
             category eventlib { default_debug; };

       Messages like ``... points to a CNAME''.

       Approved/unapproved requests.

       Operating system problems.

       Internal consistency check failures.

       Periodic maintenance events.

       Zone loading messages.

       Messages arising from response checking, such as ``Malformed response
       ...'', ``wrong ans. name ...'', ``unrelated additional info ...'',
       ``invalid RR type ...'', and ``bad referral ...''.



     options {
       [ version version_string; ]
       [ directory path_name; ]
       [ named-xfer path_name; ]
       [ dump-file path_name; ]
       [ memstatistics-file path_name; ]
       [ pid-file path_name; ]
       [ statistics-file path_name; ]
       [ auth-nxdomain yes_or_no; ]
       [ deallocate-on-exit yes_or_no; ]
       [ dialup yes_or_no; ]
       [ fake-iquery yes_or_no; ]
       [ fetch-glue yes_or_no; ]
       [ has-old-clients yes_or_no; ]
       [ host-statistics yes_or_no; ]
       [ host-statistics-max number; ]
       [ multiple-cnames yes_or_no; ]
       [ notify yes_or_no; ]
       [ recursion yes_or_no; ]
       [ rfc2308-type1 yes_or_no; ]
                      [ port ( ip_port | * ) ] ; ]
       [ lame-ttl number; ]
       [ max-transfer-time-in number; ]
       [ max-ncache-ttl number; ]
       [ min-roots number; ]
       [ serial-queries number; ]
       [ transfer-format ( one-answer | many-answers ); ]
       [ transfers-in  number; ]
       [ transfers-out number; ]
       [ transfers-per-ns number; ]
       [ transfer-source ip_addr; ]
       [ maintain-ixfr-base yes_or_no; ]
       [ 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|fR }; ]
       [ rrset-order { order_spec ; [ order_spec ; ... [ [ };

   Definition and Usage

     The options statement sets up global options to be used by BIND. This
     statement may appear at only once in a configuration file; if more than
     one occurrence is found, the first occurrence determines the actual op­
     tions 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


       The version the server should report via the ndc command or via a query
       of name version.bind in class chaos. The default is the real version
       number of ths server, but some server operators prefer the string (
       surely you must be joking ).

       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 de­
       faults to ., the directory from which the server was started.  The di­
       default is named_dump.db.

       The pathname of the file the server writes memory usage statistics to
       on exit, if deallocate-on-exit is yes. If not specified, the default is

       The pathname of the file the server writes its process ID in.  If not
       specified, the default is operating system dependent, but is usually
       /var/run/named.pid or /etc/named.pid. The pid-file is used by programs
       like ndc that want to send signals to the running nameserver.

       The pathname of the file the server appends statistics to when it re­
       ceives SIGILL signal (from ndc stats). If not specified, the default is

   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 yes. Do not
       turn off auth-nxdomain unless you are sure you know what you are doing,
       as some older software won't like it.

       If yes, then when the server exits it will painstakingly deallocate ev­
       ery object it allocated, and then write a memory usage report to the
       memstatistics-file. The default is no, because it is faster to let the
       operating system clean up.  deallocate-on-exit is handy for detecting
       memory leaks.

       If yes, then the server treats all zones as if they are doing zone
       transfers across a dial on demand dialup link, which can be brought up
       by traffic originating from this server.  This has different effects
       according to zone type and concentrates the zone maintenance so that it
       all happens in a short interval, once every heartbeat-interval and
       hopefully during the one call.  It also suppresses some of the normal
       zone maintenance traffic.  The default is no. The dialup option may al­
       so be specified in the zone statement, in which case it overrides the
       options dialup statement.

       If the zone is a master then the server will send out NOTIFY request to
       all the slaves.  This will trigger the zone up to date checking in the
       The default is no.

       If yes (the default), the server will fetch ``glue'' resource records
       it doesn't have when constructing the additional data section of a re­
       sponse.  fetch-glue no can be used in conjunction with recursion no to
       prevent the server's cache from growing or becoming corrupted (at the
       cost of requiring more work from the client).

       Setting the option to yes, is equivalent to setting the following three
       options: auth-nxdomain yes ;, maintain-ixfr-base yes ;, and
       rfc2308-type1 no; has-old-clients with auth-nxdomain, maintain-ixfr-
       base, and rfc2308-type1 is order dependant.

       If yes, then statistics are kept for every host that the the nameserver
       interacts with.  The default is no. Note: turning on host-statistics
       can consume huge amounts of memory.

     IC host-statistics-max
       The maximum number of host records that will be kept.  When this limit
       is reached no new hosts will be added to the host statistics.  If the
       set to zero then there is no limit set.  The default value is zero.

       If yes, a IXFR database file is kept for all dynamicaly updated zones.
       This enables the server to answer IXFR queries which can speed up zone
       transfers enormously.  The default is no.

       If yes, then multiple CNAME resource records will be allowed for a do­
       main name.  The default is no. Allowing multiple CNAME records is
       against standards and is not recommended.  Multiple CNAME support is
       available because previous versions of BIND allowed multiple CNAME
       records, and these records have been used for load balancing by a num­
       ber of sites.

       If yes (the default), DNS NOTIFY messages are sent when a zone the
       server is authoritative for changes.  The use of NOTIFY speeds conver­
       gence between the master and its slaves.  Slave servers that receive a
       NOTIFY message and understand it will contact the master server for the
       zone and see if they need to do a zone transfer, and if they do, they
       will initiate it immediately.  The notify option may also be specified
       in the zone statement, in which case it overrides the options notify
       server using you as a forwarder that does not understand negative an­
       swers which contain both SOA and NS records or you have an old version
       of sendmail.  The correct fix is to upgrade the broken server or send­
       mail.  The default is no.

       If yes, the server will keep track of its own outstanding query ID's to
       avoid duplication and increase randomness.  This will result in 128KB
       more memory being consumed by the server.  The default is no.

       If yes, the server will treat CR characters the same way it treats a
       space or tab.  This may be necessary when loading zone files on a UNIX
       system that were generated on an NT or DOS machine.  The default is no.



     Defines a global list of IP addresses that also get sent NOTIFY messages
     whenever a fresh copy of the zone is loaded. 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 get sent NOTIFY
     messages for that zone.  The default is the empty list (no global notifi­
     cation list).


     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 ac­
     cess to the Internet, but wish to look up exterior names anyway.  For­
     warding occurs only on those queries for which the server is not authori­
     tative 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.

     Future versions of BIND 8 will provide a more powerful forwarding system.
     The syntax described above will continue to be supported.

   Name Checking

     The server can check domain names based upon their expected client con­
     texts.  For example, a domain name used as a hostname can be checked for
     compliance with the RFCs defining valid hostnames.

     Three checking methods are available:

       No checking is done.

       Names are checked against their expected client contexts.  Invalid
       names are logged, but processing continues normally.

       Names are checked against their expected client contexts.  Invalid
       names are logged, and the offending data is rejected.

     The server can check names three areas: master zone files, slave zone
     files, and in responses to queries the server has initiated.  If check-
     names response fail has been specified, and answering the client's ques­
     tion would require sending an invalid name to the client, the server will
     send a REFUSED response code to the client.

     The defaults are:

         check-names master fail;
         check-names slave warn;
         check-names response ignore;

     check-names may also be specified in the zone statement, in which case it
     overrides the options check-names statement.  When used in a zone state­
     ment, the area is not specified (because it can be deduced from the zone

   Access Control

     Access to the server can be restricted based on the IP address of the re­
     questing system or via shared secret keys.  See ADDRESS MATCH LISTS for
         specified, the default is to allow recursive queries from all hosts.

         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 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 al­
     lowed by the address match list.  If a port is not specified, port 53
     will be used.

     Multiple listen-on statements are allowed.  For example,

         listen-on {; };
         listen-on port 1234 { !; 1.2/16; };

     will enable the nameserver on port 53 for the IP address, and on
     port 1234 of an address on the machine in net 1.2 that is not

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

   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 unprivi­
     leged port will be used.  The default is
           query-source address * port *;

     Note: query-source currently applies only to UDP queries; TCP queries al­
     ways use a wildcard IP address and a random unprivileged port.

       The server supports two zone transfer methods.  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 ef­
       ficient, but is only known to be understood by BIND 8.1 and patched
       versions of BIND 4.9.5.  The default is one-answer. 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 con­
       currently.  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.

       This option will be used in the future to limit the number of concur­
       rent outbound zone transfers.  It is checked for syntax, but is other­
       wise ignored.

       The maximum number of inbound zone transfers ( named-xfer processes)
       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 the TCP
       connection used to fetch all zones transferred inbound by the server.
       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
       zones being transferred, if one is specified.  This statement sets the
       transfer-source for all zones, but can be overriden on a per-zone basis
       by includinga transfer-source statement within the zone block in the
       configuration file.

   Resource Limits

     The server's usage of many system resources can be limited.  Some operat­
     ing systems don't support some of the limits.  On such systems, a warning
     will be issued if the unsupported limit is used.  Some operating systems
     don't support limiting resources, and on these systems a
           set resource limits on this system
     message will be logged.

     Scaled values are allowed when specifying resource limits.  For example,
       The maximum amount of data memory the server may use.  The default val­
       ue is default.

       The maximum number of files the server may have open concurrently.  The
       default value is unlimited. Note that on some operating systems the
       server cannot set an unlimited value and cannot determine the maximum
       number of open files the kernel can support.  On such systems, choosing
       unlimited will cause the server to use the larger of the rlim_max from
       getrlimit(RLIMIT_NOFILE) and the value returned by
       sysconf(_SC_OPEN_MAX).  If the actual kernel limit is larger than this
       value, use limit files to specify the limit explicitly.

       The max-ixfr-log-size will be used in a future release of the server to
       limit the size of the transaction log kept for Incremental Zone Trans­

       The maximum amount of stack memory the server may use.  The default
       value is default.

   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
       dialup yes 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 inter­
       faces that have gone away will be cleaned up.

       Nameserver statistics will be logged every statistics-interval minutes.

     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

     The default topology is
           topology { localhost; localnets; };

   Resource Record sorting

     When returning multiple RRs, the nameserver will normally return them in
     Round Robin, i.e. after each request, the first RR is put to the end of
     the list.  As the order of RRs is not defined, this should not cause any

     The client resolver code should re-arrange the RRs as appropriate, i.e.
     using any addresses on the local net in preference to other addresses.
     However, not all resolvers can do this, or are not 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 takes an address match list and interprets it even
     more specially than the statement does.

     Each top level statement in the sortlist must itself be an explicit ad­
     dress match list with one or two elements. The first element (which may
     be an IP address, an IP prefix, an ACL name or 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, the second element is treated like 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

     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 behaviour 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 lo­
     cal 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 con­
     figure the order the records are placed into the response. For example
     the records for a zone might be configured to always be returned in the
     order they are defined in the zone file. Or perhaps a random shuffle of
     the records as they are returned is wanted. The rrset-order statement
     permits configuration of the ordering made of the records in a multiple
     record response. The default, if no ordering is defined, is a cyclic or­
     dering (round robin).

     An order_spec is defined as follows:

       [ class class_name ][ type type_name ][ name "FQDN" ] order ordering

     If no class is specified, the default is ANY. If no Ictype is specified,
     the default is ANY. If no name is specified, the default is "*".

         rrset-order {
             class IN type A name "rc.vix.com" order random;
             order cyclic;

     will cause any responses for type A records in class IN that have
     "rc.vix.com" as a suffix, to always be returned in random order. All oth­
     er records are returned in cyclic order.

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

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

         rrset-order { class ANY type ANY name "*" order cyclic ; };

     is used.


       Sets the number of seconds to cache a lame server indication.  0 dis­
       ables caching.  Default is 600 (10 minutes).  Maximum value is 1800 (30

       To reduce network traffic and increase performance the server store
       negative answers.  max-ncache-ttl is used to set a maximum retention
       time for these answers in the server is seconds.  The default max-
       ncache-ttl is 10800 seconds (3 hours).  max-ncache-ttl cannot exceed
       the maximum retention time for ordinary (positive) answers (7 days) and
       will be silently truncated to 7 days if set to a value which is greater
       that 7 days.

       The minimum number of root servers that is required for a request for
       the root servers to be accepted.  Default is 2.



     zone domain_name [ ( in | hs | hesiod | chaos ) ] {
       type master;
       file path_name;
       [ check-names ( warn | fail | ignore ); ]
       [ allow-update { address_match_list }; ]
       [ allow-query { address_match_list }; ]
       [ allow-transfer { address_match_list }; ]
       [ check-names ( warn | fail | ignore ); ]
       [ allow-update { address_match_list }; ]
       [ allow-query { address_match_list }; ]
       [ allow-transfer { address_match_list }; ]
       [ forward ( only | first ); ]
       [ forwarders { [ ip_addr ; [ ip_addr ; ... ] ] }; ]
       [ transfer-source ip_addr; ]
       [ max-transfer-time-in number; ]
       [ notify yes_or_no; ]
       [ also-notify { ip_addr; [ ip_addr; ... ] };
       [ pubkey number number number string; ]

     zone domain_name [ ( in | hs | hesiod | chaos ) ] {
       type forward;
       [ forward ( only | first ); ]
       [ forwarders { [ ip_addr ; [ ip_addr ; ... ] ] }; ]
       [ check-names ( warn | fail | ignore ); ]

     zone "." [ ( in | hs | hesiod | chaos ) ] {
       type hint;
       file path_name;
       [ check-names ( warn | fail | ignore ); ]

   Definition and Usage

     The zone statement is used to define how information about particular DNS
     zones is managed by the server.  There are five different 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 that the slave contacts to update its copy of
       the zone.  If a port is specified then checks to see if the zone is
       current and zone transfers will be done to the port given. If file is
       specified, then the replica will be written to the named file.  Use of
       the file clause is highly recommended, since it often speeds server
       startup and eliminates a needless waste of bandwidth.

       A stub zone is like a slave zone, except that it replicates only the NS
       records of a master zone instead of the entire zone.


       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 name­
       server and get the most recent list of root nameservers.

     Note: previous releases of BIND used the term primary for a master zone,
     secondary for a slave zone, and cache for a hint zone.


     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 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.  More information can be found at
     ftp://athena-dist.mit.edu/pub/ATHENA/usenix/athena_changes.PS.  The key­
     word hs is a synonym for hesiod.

     Another MIT development was CHAOSnet, a LAN protocol created in the
     mid-1970s.  It is still sometimes seen on LISP stations and other hard­
     ware in the AI community, and zone data for it can be specified with the
     chaos class.


       See the subsection on Name Checking in THE OPTIONS STATEMENT.

       See the description of allow-query in the Access Control subsection of

       Specifies which hosts are allowed to submit Dynamic DNS updates to the
       server.  The default is to deny updates from all hosts.

       See the description of allow-transfer in the Access Control subsection

       See the description of dialup in the Boolean Options subsection of THE

       See the description of notify in the Boolean Options subsection of the

       also-notify is 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 for the zone (other than the pri­
       mary master) plus any IP addresses specified with also-notify. also-
       notify is not meaningful for stub zones.  The default is the empty

       forward is only meaningful if the zone has a forwarders list. The only
       value causes the lookup to fail after trying the forwarders and getting
       no answer, while first would allow a normal lookup to be tried.

       The forwarders option in a zone is used to override the list of global
       forwarders.  If it is not specified in a zone of type forward, no for­
       warding is done for the zone; the global options are not used.

       The DNSSEC flags, protocol, and algorithm are specified, as well as a
       base-64 encoded string representing the key.



     acl name {

   Definition and Usage

     The acl statement creates a named 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.
       Allows the IP addresses of all interfaces on the system.

       Allows any host on a network for which the system has an interface.



     key key_id {
       algorithm algorithm_id;
       secret secret_string;

   Definition and Usage

     The key statement defines a key ID which can be used in a server state­
     ment to associate a method of authentication with a particular name serv­
     er that is more rigorous than simple IP address matching.  A key ID must
     be created with the key statement before it can be used in a server defi­
     nition or an address match list.

     The algorithm_id is a string that specifies a security/authentication al­
     gorithm.  secret_string is the secret to be used by the algorithm, and is
     treated as a base-64 encoded string.  It should go without saying, but
     probably can't, that if you have secret_string 's in your named.conf,
     then it should not be readable by anyone but the superuser.



     trusted-keys {
       [ domain_name flags protocol algorithm key; ]

   Definition and Usage

     The trusted-keys statement is for use with DNSSEC-style security, origi­
     nally specified in RFC 2065.  DNSSEC is meant to provide three distinct
     services: key distribution, data origin authentication, and transaction
     and request authentication.  A complete description of DNSSEC and its use
     is beyond the scope of this document, and readers interested in more in­
     formation should start with RFC 2065 and then continue with the Internet
     Drafts available at http://www.ietf.org/ids.by.wg/dnssec.html.

     Each trusted key is associated with a domain name.  Its attributes are
     server ip_addr {
       [ bogus yes_or_no; ]
       [ transfers number; ]
       [ transfer-format ( one-answer | many-answers ); ]
       [ keys { key_id [ key_id ... ] }; ]

   Definition and Usage

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

     If you discover that a server is giving out bad data, marking it as bogus
     will prevent further queries to it.  The default value of bogus is no.
     Marking a server as bogus will mark all other addresses for that server
     as bogus when a match is made when looking up a server's address by name.

     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 8.1 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

     The transfers will be used in a future release of the server to limit the
     number of concurrent in-bound zone transfers from the specified server.
     It is checked for syntax but is otherwise ignored.

     The keys clause is used to identify a key_id defined by the key state­
     ment, to be used for transaction security when talking to the remote
     server.  The key statememnt must come before the server statement that
     references it.

     The keys statement is intended for future use by the server.  It is
     checked for syntax but is otherwise ignored.



     controls {
       [ inet ip_addr
         port ip_port
         allow { address_match_list; }; ]
       [ unix path_name

     A unix control channel is a FIFO in the file system, and access to it is
     controlled by normal file system permissions.  It is created by named
     with the specified file mode bits (see chmod(1)),  user and group owner.
     Note that, unlike chmod, the mode bits specified for perm will normally
     have a leading 0 so the number is interpreted as octal.  Also note that
     the user and group ownership specified as owner and group must be given
     as numbers, not names.  It is recommended that the permissions be re­
     stricted to administrative personnel only, or else any user on the system
     might be able to manage the local name server.

     An inet control channel is a TCP/IP socket accessible to the Internet,
     created at the specified ip_port on the specified ip_addr. Modern telnet
     clients are capable of speaking directly to these sockets, and the con­
     trol protocol is ARPAnet-style text.  It is recommended that be
     the only ip_addr used, and this only if you trust all non-privileged
     users on the local host to manage your name server.



     include path_name;

   Definition and Usage

     The include statement inserts the specified file at the point that the
     include statement is encountered.  It cannot be used within another
     statement, though, so a line such as
           acl internal_hosts { include internal_hosts.acl; };
     is not allowed.

     Use include to break the configuration up into easily-managed chunks.
     For example:

     include "/etc/security/keys.bind";
     include "/etc/acls.bind";

     could be used at the top of a BIND configuration file in order to include
     any ACL or key information.

     Be careful not to type ``#include'', like you would in a C program, be­
     cause ``#'' is used to start a comment.


     The simplest configuration file that is still realistically useful is one
      * A simple BIND 8 configuration

     logging {
             category lame-servers { null; };
             category cname { null; };

     options {
             directory "/var/named";

     controls {
             inet * port 52 allow { any; };                  // a bad idea
             unix "/var/run/ndc" perm 0600 owner 0 group 0;  // the default

     zone "isc.org" in {
             type master;
             file "master/isc.org";

     zone "vix.com" in {
             type slave;
             file "slave/vix.com";
             masters {; };

     zone "0.0.127.in-addr.arpa" in {
             type master;
             file "master/127.0.0";

     zone "." in {
             type hint;
             file "root.cache";


       The BIND 8 named configuration file.


     named(8),  ndc(8)

4th Berkeley Distribution       January 7, 1999                             28

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