BIND options Statement

BIND Configuration File Guide - `options` Statement

Syntax

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; ]
  [ 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 }; ]
};

Definition and Use

The options statement sets up global options for BIND to use. This statement may appear only one time 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 nonabsolute pathnames in the configuration file will be taken as relative to this directory. The default location for most server output files (for example, 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 operating system dependent (for example, /usr/sbin/named-xfer).
dump-file: The pathname of the file the server dumps the database to when it receives the SIGINT signal. If not specified, the default is named_dump.db.
memstatistics-file: The pathname of the file the server writes memory usage statistics to when it exits, if deallocate-on-exit is yes. If not specified, the default is named.memstats.
pid-file: The pathname of the file into which the server writes its process ID. If not specified, the default is /var/run/named.pid. You use the pid file if you want to send signals to the running named daemon.
statistics-file: The pathname of the file the server appends statistics to when it receives the SIGILL signal. If not specified, the default is named.stats.

Boolean Options

auth-nxdomain: If yes, 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: some older software may be problematic.
deallocate-on-exit: If yes, when the server exits, it deallocates every object it allocated, and then writes a memory usage report to the memstatistics-file. The default is no, because it is faster to let the operating system clean up. The deallocate-on-exit option is useful 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 does not have when constructing the additional data section of a response. You can use the fetch-glue no option in conjunction with the recursion no option to prevent the server's cache from growing or becoming corrupted (at the cost of requiring more work from the client).
multiple-cnames: If yes, 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 to see if they need to do a zone transfer; 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, 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 does not know the answer. The default is yes. See also the fetch-glue option.

Forwarding

You can use the forwarding facility to create a large sitewide cache on a few servers, reducing traffic over links to external nameservers. You can also use it 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 meaningful only if the forwarders list is not empty. A value of first, the default, causes the server to query the forwarders first, and if that does not answer the question the server will then look for the answer itself. If only is specified, the server queries only the forwarders.
forwarders: Specifies the IP addresses to be used for forwarding. The default is the empty list (no forwarding).

Name Checking

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

The following 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 in three areas: master zone files, slave zone files, and in responses to queries the server has initiated. If you specify check-names response fail, 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 ignore;
    check-names slave ignore;
    check-names response ignore;

You can also specify the check-names option 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

You can restrict access to the server 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. You can also specify the allow-query option 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. You can also specify the allow-transfer option 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. The listen-on option 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 phrases 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 phrase is specified, the server listens on port 53 on all interfaces.

Query Address

If the server does not know the answer to a question, it will query other nameservers. The query-source option 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 the following zone transfer methods:

one-answer: Uses one DNS message per resource record transferred. This is the default.
many-answers: Packs as many resource records as possible into a message. This method is more efficient, but is only known to be understood by BIND 8.1 and patched versions of BIND 4.9.5.

You can override the transfer-format option 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 The transfers-per-ns option may speed up the convergence of slave zones, but it also may increase the load on the remote nameserver. You can override the transfers-per-ns option on a per-server basis by using the transfers option of the server statement.

Resource Limits

The server's usage of many system resources can be limited. Some operating systems do not support some of the limits and a warning will be generated if an unsupported limit is set in the configuration file.

Scaled values are allowed when specifying resource limits. For example, you can use 1G 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. 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 the server may have open concurrently. The default is unlimited.
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 occurs.
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 occurs only when the configuration file is loaded. After the scan, listeners will be started on any new interfaces (provided they are allowed by the listen-on configuration). Listeners on interfaces that have gone away will be cleaned up.
statistics-interval: Nameserver statistics will be logged every statistics-interval minutes. The default is 60. If set to 0, no statistics are logged.

Topology

Typically, 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. Nonnegated 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 that is farther than any nonnegated list element, and closer than any negated element.

The following example prefers 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:

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

The default topology is:

    topology { localhost; localnets; };

BIND Configuration File Guide - options Statement