resolv+ - enhanced DNS resolver library
Resolv+ is a modified version of the standard Berkeley BIND host
resolver library. Enhancements include support for host lookups via
the Internet Domain Name System (DNS), the /etc/hosts file, and Sun's
Network Information Service (NIS).
The programmer interface to the resolv+ routines is identical to that
of the standard resolver library. For further information see the
appropriate manual pages.
As with the standard resolver library, the file /etc/resolv.conf must
be set up before the resolver can function. In addition, the file
/etc/host.conf contains configuration information specific to resolv+.
The host.conf file should contain one configuration keyword per line,
followed by appropriate configuration information. The keywords recognized
are order , trim , multi , nospoof , and reorder . Each keyword
is described seperately below.
order This keyword specifies how host lookups are to be performed. It
should be followed by one or more lookup methods, seperated by
commas. Valid methods are bind , hosts and nis .
trim This keyword may be listed more than once. Each time it should
be followed by a single domain name, with the leading dot. When
set, the resolv+ library will automatically trim the given
domain name from the end of any hostname resolved via DNS. This
is intended for use with local hosts and domains. (Related
note: trim will not affect hostnames gathered via NIS or the
hosts file. Care should be taken to insure that the first hostname
for each entry in the hosts file is fully qualified or nonqualified,
as appropriate for the local installation.)
multi Valid values are on and off . If set to "on," the resolv+
library will return all valid addresses for a host that appears
in the /etc/hosts file, instead of only the first. This is off
by default, as it may cause a substantial performance loss at
sites with large hosts files.
Valid values are on and off . If set to "on," the resolv+
library will attempt to prevent hostname spoofing to enhance the
security of rlogin and rsh. It works as follows: after performing
a host address lookup, resolv+ will perform a hostname
lookup for that address. If the two hostnames do not match, the
query will fail.
alert If this option is set to "on" and the nospoof option is also
set, resolv+ will log a warning of the error via the syslog
facility. The default value is off.
Valid values are on and off . If set to "on," resolv+ will
attempt to reorder host addresses so that local addresses (i.e.,
on the same subnet) are listed first when a gethostbyname() is
performed. Reordering is done for all lookup methods. The
default value is off.
ENVIRONMENT VARIABLES [Toc] [Back]
The following environment variables may be set to override resolv+'s
If set, it will override the default filename ("/etc/host.conf")
for the resolv+ configuration file.
If set, will override the "order" keyword in the host.conf file.
If set, will override the spoof check flag. Valid values are
"off" to disable checking, "warn" to enable checking and warning,
and "warn off" to enable checking but not warning.
If set, contains a list of domains to trim that will augment,
not supersede, the list in the host.conf file.
If set, contains a list of domains to trim that will override
those in the host.conf file.
If set, overrides the "multi" keyword in the host.conf file.
If set, overrides the "reorder" keyword in the host.conf file.
The original BIND resolver library comes from the University of California
at Berkeley's Computer Science Research Group. The original
resolv+ modifications were made by Bill Wisner <wisner@uunet.UU.NET>.
Bug fixes and enhancements were contributed by Patrick Gosling, Chris
Metcalf, John DiMarco and J. Porter Clark, John P. Rouillard, Dan
O'Neill and Tom Limoncelli.
resolver(3), resolver(5), hosts(5), hostname(7), named(8)
August 19, 1992 RESOLV+(8)
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