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Section: Maintenance Commands (8)
Updated: August 19, 1992Index
resolv+ - enhanced DNS resolver library
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/hosts
file, 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.
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+.
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.
- 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.
- 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.)
- 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.
- 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.
- 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.
- 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.
The following environment variables may be set to overrideresolv+'s configured behavior:
- If set, it will override the default filename("/etc/host.conf") for the resolv+ configurationfile.
- If set, will override the "order" keyword in thehost.conf file.
- 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.
- If set, contains a list of domains to trim thatwill augment, not supersede, the list in thehost.conf file.
- If set, contains a list of domains to trim thatwill override those in the host.conf file.
- If set, overrides the "multi" keyword in thehost.conf file.
- If set, overrides the "reorder" keyword in thehost.conf file.
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.
- ENVIRONMENT VARIABLES
- SEE ALSO
This document was created byman2html,using the manual pages.