RESOLV.CONF(5)            NetBSD File Formats Manual            RESOLV.CONF(5)

NAME
     resolv.conf -- resolver configuration file

DESCRIPTION
     The resolv.conf file specifies how the resolver(3) routines in the C
     library (which provide access to the Internet Domain Name System) should
     operate.  The resolver configuration file contains information that is
     read by the resolver routines the first time they are invoked by a
     process.  The file is designed to be human readable and contains a list
     of keywords with values that provide various types of resolver informa-
     tion.

     On a normally configured system this file should not be necessary.  The
     only name server to be queried will be on the local machine, the domain
     name is determined from the host name, and the domain search path is con-
     structed from the domain name.

     The different configuration options are:

     nameserver  IPv4 address (in dot notation) or IPv6 address (in
                 hex-and-colon notation) of a name server that the resolver
                 should query.  Scoped IPv6 address notation is accepted as
                 well (see inet6(4) for details).  Up to MAXNS (currently 3)
                 name servers may be listed, one per keyword.  If there are
                 multiple servers, the resolver library queries them in the
                 order listed.  If no nameserver entries are present, the
                 default is to use the name server on the local machine.  (The
                 algorithm used is to try a name server, and if the query
                 times out, try the next, until out of name servers, then
                 repeat trying all the name servers until a maximum number of
                 retries are made).

     domain      Local domain name.  Most queries for names within this domain
                 can use short names relative to the local domain.  If no
                 domain entry is present, the domain is determined from the
                 local host name returned by gethostname(3); the domain part
                 is taken to be everything after the first `.'.  Finally, if
                 the host name does not contain a domain part, the root domain
                 is assumed.

     lookup      This keyword is now ignored: its function has been superseded
                 by features of nsswitch.conf(5).

     search      Search list for host-name lookup.  The search list is nor-
                 mally determined from the local domain name; by default, it
                 begins with the local domain name, then successive parent
                 domains that have at least two components in their names.
                 This may be changed by listing the desired domain search path
                 following the search keyword with spaces or tabs separating
                 the names.  Most resolver queries will be attempted using
                 each component of the search path in turn until a match is
                 found.  Note that this process may be slow and will generate
                 a lot of network traffic if the servers for the listed
                 domains are not local, and that queries will time out if no
                 server is available for one of the domains.

                 The search list is currently limited to six domains with a
                 total of 1024 characters.

     sortlist    Sortlist allows addresses returned by gethostbyname to be
                 sorted.  A sortlist is specified by IP address netmask pairs.
                 The netmask is optional and defaults to the natural netmask
                 of the net.  The IP address and optional network pairs are
                 separated by slashes.  Up to 10 pairs may be specified, ie.

                 sortlist 130.155.160.0/255.255.240.0 130.155.0.0

     options     Options allows certain internal resolver variables to be mod-
                 ified.  The syntax is:

                 options option ...

                 where option is one of the following:

                 debug      enable debugging information, by setting RES_DEBUG
                            in _res.options (see resolver(3)).

                 edns0      attach OPT pseudo-RR for ENDS0 extension specified
                            in RFC 2671, to inform DNS server of our receive
                            buffer size.  The option will allow DNS servers to
                            take advantage of non-default receive buffer size,
                            and to send larger replies.  DNS query packets
                            with EDNS0 extension is not compatible with non-
                            EDNS0 DNS servers.  The option must be used only
                            when all the DNS servers listed in nameserver
                            lines are able to handle EDNS0 extension.

                 inet6      enable support for IPv6-only applications, by set-
                            ting RES_USE_INET6 in _res.options (see
                            resolver(3)).  The option is meaningful with cer-
                            tain kernel configuration only and use of this
                            option is discouraged.

                 insecure1  Do not require IP source address on the reply
                            packet to be equal to the servers' address.

                 insecure2  Do not check if the query section of the reply
                            packet is equal to that of the query packet.  For
                            testing purposes only.

                 ndots:n    sets a threshold for the number of dots which must
                            appear in a name given to res_query (see
                            resolver(3)) before an initial absolute query will
                            be made.  The default for n is 1, meaning that if
                            there are any dots in a name, the name will be
                            tried first as an absolute name before any search
                            list elements are appended to it.

     The domain and search keywords are mutually exclusive.  If more than one
     instance of these keywords is present, the last instance will override.

     The search keyword of a system's resolv.conf file can be overridden on a
     per-process basis by setting the environment variable LOCALDOMAIN to a
     space-separated list of search domains.

     The options keyword of a system's resolv.conf file can be amended on a
     per-process basis by setting the environment variable RES_OPTIONS to a
     space-separated list of resolver options as explained above.

     The keyword and value must appear on a single line, and the keyword (e.g.
     nameserver) must start the line.  The value follows the keyword, sepa-
     rated by white space.

FILES
     /etc/resolv.conf  The file resolv.conf resides in /etc.

SEE ALSO
     gethostbyname(3), resolver(3), nsswitch.conf(5), hostname(7), named(8)

     Name Server Operations Guide for BIND.

HISTORY
     The resolv.conf file format appeared in 4.3BSD.

NetBSD 5.1                     January 16, 1999                     NetBSD 5.1

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