BIND Configuration File Guide -- options Statement

options {
  [ 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; ]
  [ fake-iquery yes_or_no; ]
  [ fetch-glue yes_or_no; ]
  [ host-statistics yes_or_no; ]
  [ multiple-cnames yes_or_no; ]
  [ notify yes_or_no; ]
  [ recursion yes_or_no; ]
  [ forward ( only | first ); ]
  [ forwarders { [ in_addr ; [ in_addr ; ... ] ] }; ]
  [ check-names ( master | slave | response ) ( warn | fail | ignore); ]
  [ allow-query { address_match_list }; ]
  [ allow-transfer { address_match_list }; ]
  [ listen-on [ port ip_port ] { address_match_list }; ]
  [ query-source [ address ( ip_addr | * ) ] [ port ( ip_port | * ) ] ; ]
  [ max-transfer-time-in number; ]
  [ transfer-format ( one-answer | many-answers ); ]
  [ transfers-in  number; ]
  [ transfers-out number; ]
  [ transfers-per-ns number; ]
  [ coresize size_spec ; ]
  [ datasize size_spec ; ]
  [ files size_spec ; ]
  [ stacksize size_spec ; ]
  [ cleaning-interval number; ]
  [ interface-interval number; ]
  [ statistics-interval number; ]
  [ topology { address_match_list }; ]
};

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 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.

Pathnames

directory

The working directory of the server. Any non-absolute pathnames in the configuration file will be taken as relative to this directory. The default location for most server output files (e.g. "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.

named-xfer

The pathname to the named-xfer program that the server uses for inbound zone transfers. If not specified, the default is system dependent (e.g. "/usr/sbin/named-xfer").

dump-file

The pathname of the file the server dumps the database to when it receives SIGINT signal (ndc dumpdb). If not specified, the default is "named_dump.db".

memstatistics-file

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

pid-file

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

statistics-file

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

auth-nxdomain

If yes, then the AA bit is always set on NXDOMAIN responses, even if the server is not actually authoritative. The default is 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.

deallocate-on-exit

If yes, then when the server exits it will painstakingly deallocate every 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.

fake-iquery

If yes, the server will simulate the obsolete DNS query type IQUERY. The default is no.

fetch-glue

If yes (the default), the server will fetch "glue" resource records it doesn't have when constructing the additional data section of a response. 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).

host-statistics

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.

multiple-cnames

If yes, then multiple CNAME resource records will be allowed for a domain 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 number of sites.

notify

If yes (the default), DNS NOTIFY messages are sent when a zone the server is authoritative for changes. The use of NOTIFY speeds convergence 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 statement.

recursion

If yes, and a DNS query requests recursion, then the server will attempt to do all the work required to answer the query. If recursion is not on, the server will return a referral to the client if it doesn't know the answer. The default is yes. See also fetch-glue above.

Forwarding

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

forward

This option is only meaningful if the forwarders list is not empty. A value of first, the default, causes the server to query the forwarders first, and if that doesn't answer the question the server will then look for the answer itself. If only is specified, the server will only query the forwarders.

forwarders

Specifies the IP addresses to be used for forwarding. The default is the empty list (no forwarding).

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 contexts. 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:

ignore

No checking is done.

warn

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

fail

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 question 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 statement, the area is not specified (because it can be deduced from the zone type).

Access Control

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

allow-query

Specifies which hosts are allowed to ask ordinary questions. allow-query may also be specified in the zone statement, in which case it overrides the options allow-query statement. If not specified, the default is to allow queries from all hosts.

allow-transfer

Specifies which hosts are allowed to receive zone transfers from the server. allow-transfer may also be specified in the zone statement, in which case it overrides the options allow-transfer statement. If not specified, the default is to allow transfers from all hosts.

Interfaces

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

Multiple listen-on statements are allowed. For example,

    listen-on { 5.6.7.8; };
    listen-on port 1234 { !1.2.3.4; 1.2/16; };

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 default is

    query-source address * port *;

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

Zone Transfers

max-transfer-time-in

Inbound zone transfers (named-xfer processes) running longer than this many minutes will be terminated. The default is 120 minutes (2 hours).

transfer-format

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 efficient, 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.

transfers-in

The maximum number of inbound zone transfers that can be running concurrently. The default value is 10. Increasing transfers-in may speed up the convergence of slave zones, but it also may increase the load on the local system.

transfers-out

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

transfers-per-ns

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.

Resource Limits

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

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

coresize

The maximum size of a core dump. The default is default.

datasize

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

files

The maximum number of files ther server may have open concurrently. The default is unlimited. Note: 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 for 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.

stacksize

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

Periodic Task Intervals

cleaning-interval

The server will remove expired resource records from the cache every cleaning-interval minutes. The default is 60 minutes. If set to 0, no periodic cleaning will occur.

interface-interval

The server will scan the network interface list every interface-interval minutes. The default is 60 minutes. If set to 0, interface scanning will only occur when the configuration file is loaded. After the scan, listeners will be started on any new interfaces (provided they are allowed by the listen-on configuration). Listeners on interfaces that have gone away will be cleaned up.

statistics-interval

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

Topology

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 {
        10/8;
        !1.2.3/24;
        { 1.2/16; 3/8; };
    };

will prefer servers on network 10 the most, followed by hosts on network 1.2.0.0 (netmask 255.255.0.0) and network 3, with the exception of hosts on network 1.2.3 (netmask 255.255.255.0), which is preferred least of all.

The default topology is

    topology { localhost; localnets; };