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RESOLV+

Section: Maintenance Commands (8)
Updated: August 19, 1992
Index

NAME

resolv+ - enhanced DNS resolver library

DESCRIPTION

Resolv+is a modified version of the standard BerkeleyBIND host resolver library. Enhancements include supportfor host lookups via the Internet Domain Name System(DNS), the/etc/hostsfile, and Sun's Network InformationService (NIS).

The programmer interface to the resolv+ routines is identicalto that of the standard resolver library. For further informationsee the appropriate manual pages.

CONFIGURATION

As with the standard resolver library, the file/etc/resolv.confmust be set up before the resolver can function.In addition, the file/etc/host.confcontains configuration information specific to resolv+.

Thehost.conffile should contain one configuration keyword per line,followed by appropriate configuration information.The keywords recognized areorder,trim,multi,nospoof,andreorder.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, seperatedby commas. Valid methods arebind,hostsandnis.
trim: This keyword may be listed more than once. Each time it shouldbe followed by a single domain name, with the leading dot.When set, the resolv+ library will automatically trim the given domainname from the end of any hostname resolved via DNS.This is intended for use with local hosts anddomains. (Related note: trim will not affect host-names gathered via NIS or the hosts file. Careshould be taken to insure that the first hostnamefor each entry in the hosts file is fully qualifiedor non-qualified, as appropriate for the localinstallation.)
multi: Valid values areonandoff.If set to "on," the resolv+ library will return all valid addressesfor a host that appears in the/etc/hostsfile, instead of only the first. This is off by default, as itmay cause a substantial performance loss at siteswith large hosts files.
nospoof: Valid values areonandoff.If set to "on," theresolv+ library will attempt to prevent hostnamespoofing to enhance the security ofrloginandrsh.It works as follows: after performing a hostaddress lookup, resolv+ will perform a hostnamelookup for that address. If the two hostnames donot match, the query will fail.
alert: If this option is set to "on" and thenospoofoption is also set, resolv+ will log a warning ofthe error via thesyslogfacility. The default value is off.
reorder: Valid values areonandoff.If set to "on," resolv+ will attempt to reorder host addresses sothat local addresses (i.e., on the same subnet) arelisted first when a gethostbyname() is performed.Reordering is done for all lookup methods. Thedefault value is off.

ENVIRONMENT VARIABLES

The following environment variables may be set to overrideresolv+'s configured behavior:

RESOLV_HOST_CONF: If set, it will override the default filename("/etc/host.conf") for the resolv+ configurationfile.
RESOLV_SERV_ORDER: If set, will override the "order" keyword in thehost.conf file.
RESOLV_SPOOF_CHECK: If set, will override the spoof check flag. Validvalues are "off" to disable checking, "warn" toenable checking and warning, and "warn off" toenable checking but not warning.
RESOLV_ADD_TRIM_DOMAINS: If set, contains a list of domains to trim thatwill augment, not supersede, the list in thehost.conf file.
RESOLV_OVERRIDE_TRIM_DOMAINS: If set, contains a list of domains to trim thatwill override those in the host.conf file.
RESOLV_MULTI: If set, overrides the "multi" keyword in thehost.conf file.
RESOLV_REORDER: If set, overrides the "reorder" keyword in thehost.conf file.

FILES

/etc/host.conf, /etc/hosts

BUGS

Quite possibly.

AUTHOR

The original BIND resolver library comes from the Universityof California at Berkeley's Computer Science Research Group.The original resolv+ modifications were made byBill Wisner <wisnerAATTuunet.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.

This document was created byman2html,using the manual pages.