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resolv+
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1994-06-08
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RESOLV+(8) August 19, 1992
NAME
resolv+ - enhanced DNS resolver library
DESCRIPTION
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.
CONFIGURATION
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, (use nameserver to find the address/name)
hosts, (use /etc/hosts to find the address/name)
and
nis. (use NIS to find the address/name)
• 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 non-qualified, 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.
• nospoof
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.
• reorder
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
The following environment variables may be set to override resolv+'s
configured behavior:
RESOLV_HOST_CONF
If set, it will override the default filename ("/etc/host.conf") for
the resolv+ configuration file.
RESOLV_SERV_ORDER
If set, will override the "order" keyword in the host.conf file.
RESOLV_SPOOF_CHECK
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.
RESOLV_ADD_TRIM_DOMAINS
If set, contains a list of domains to trim that will augment, not
supersede, the list in the host.conf file.
RESOLV_OVERRIDE_TRIM_DOMAINS
If set, contains a list of domains to trim that will override those
in the host.conf file.
RESOLV_MULTI
If set, overrides the "multi" keyword in the host.conf file.
RESOLV_REORDER
If set, overrides the "reorder" keyword in the host.conf file.
FILES
/etc/host.conf,
/etc/hosts
BUGS
Quite possibly.
AUTHOR
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.
SEE ALSO
resolver(3), resolver(5), hosts(5), hostname(7), named(8)