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NetBSD 6.1.5 - man page for resolver (netbsd section 5)

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

     resolv.conf -- resolver configuration file

     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 information.

     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 constructed 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 algo-
		 rithm 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 maxi-
		 mum 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     lookup	 This keyword is now ignored: its function has been superseded by features of

     search	 Search list for host-name lookup.  The search list is normally 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 charac-

     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.


     options	 Options allows certain internal resolver variables to be modified.  The syntax

		 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 setting RES_USE_INET6
			    in _res.options (see resolver(3)).	The option is meaningful with
			    certain kernel configuration only and use of this option is discour-

		 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, separated by white space.

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

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

     Paul Vixie, Kevin J. Dunlap, and Michael J. Karels, Name Server Operations Guide for BIND,
     CSRG, Department of Electrical Engineering and Computer Sciences, University of California,
     Berkeley, Release 4.9.4, http://www.dns.net/dnsrd/docs/bog/bog.html, July 16, 1996.

     The resolv.conf file format appeared in 4.3BSD.

BSD					 August 21, 2010				      BSD

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