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RESOLVER(5)		  FreeBSD File Formats Manual		   RESOLVER(5)

     resolver -- resolver configuration	file


     The resolver is a set of routines in the C	library	(resolve(3)) that pro-
     vide access to the	Internet Domain	Name System.  The resolver configura-
     tion 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 hu-
     man 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 con-
     structed from the domain name.

     The different configuration directives are:

	      Internet address (in dot notation) of a name server that the
	      resolver should query.  Up to MAXNS (see _resolv.h_) 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 un-
	      til 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; the	domain part is taken to	be ev-
	      erything after the first `.'.  Finally, if the host name does
	      not contain a domain part, the root domain is assumed.

     search   Search list for host-name	lookup.	 The search list is normally
	      determined from the local	domain name; by	default, it contains
	      only the local domain name.  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 un-
	      til 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 256 characters.

	      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.	For example:


     options  Allows certain internal resolver variables to be modified.  The
	      syntax is
		    options option ...
	      where option is one of the following:

	      debug	sets RES_DEBUG in _res.options.

	      ndots:n	sets a threshold for the number	of dots	which must ap-
			pear 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 ab-
			solute name before any search list elements are	ap-
			pended to it.

			sets the amount	of time	the resolver will wait for a
			response from a	remote name server before retrying the
			query via a different name server.  Measured in	sec-
			onds, the default is RES_TIMEOUT (see _resolv.h_).

			sets the number	of times the resolver will send	a
			query to its name servers before giving	up and return-
			ing an error to	the calling application.  The default
			is RES_DFLRETRY	(see _resolv.h_).

	      rotate	sets RES_ROTATE	in _res.options, which causes round
			robin selection	of nameservers from among those
			listed.	 This has the effect of	spreading the query
			load among all listed servers, rather than having all
			clients	try the	first listed server first every	time.

			sets RES_NOCHECKNAME in	_res.options, which disables
			the modern BIND	checking of incoming host names	and
			mail names for invalid characters such as underscore
			(_), non-ASCII,	or control characters.

	      inet6	sets RES_USE_INET6 in _res.options.  This has the ef-
			fect of	trying a AAAA query before an A	query inside
			the gethostbyname function, and	of mapping IPv4	re-
			sponses	in IPv6	``tunnelled form'' if no AAAA records
			are found but an A record set exists.

			sets RES_NOTLDQUERY in _res.options.  This option
			causes res_nsearch() to	not attempt to resolve a un-
			qualified name as if it	were a top level domain	(TLD).
			This option can	cause problems if the site has "local-
			host" as a TLD rather than having localhost on one or
			more elements of the search list.  This	option has no
			effect if neither RES_DEFNAMES or RES_DNSRCH is	set.

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

     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 under

     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 _resolv.h_

     gethostbyname(3), hostname(7), resolver(3), resolver(5).  "Name Server
     Operations	Guide for BIND"

4th Berkeley Distribution      November	11, 1993     4th Berkeley Distribution


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