RESOLV+(8)RESOLV+(8)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 Net‐
work 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 recog‐
nized 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 host- names 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-quali‐
fied, 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 perform‐
ing 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 warn‐
ing, 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 Cali‐
fornia 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 ALSOresolver(3), resolver(5), hosts(5), hostname(7), named(8)
August 19, 1992 RESOLV+(8)
