Книга: Fedora™ Unleashed, 2008 edition

Resolver Configuration

Resolver Configuration

The last step before running BIND is to set up the local resolver software. This involves configuring the /etc/hosts, /etc/resolv.conf, and /etc/nsswitch.conf files.

To avoid gratuitous network traffic, most UNIX resolvers still use a hosts-like text file named /etc/hosts to store the names and addresses of commonly used hosts. Each line in this file contains an IP address and a list of names for the host. Add entries to this file for any hosts you want to be able to resolve independently from DNS. If the entry is found in /etc/hosts, the resolver does not have to contact a DNS server to resolve the name, which reduces network traffic.

/etc/resolv.conf specifies the addresses of preferred nameservers and a list of domains relative to which unqualified names are resolved. You specify a nameserver with a line of the form nameserver 1.2.3.4 (where 1.2.3.4 is the address of the nameserver). You can use multiple nameserver lines (usually up to three). You can use a search line to specify a list of domains to search for unqualified names.

A search line such as search example.com example.net causes the resolver to attempt to resolve the unqualified name xyz, first as xyz.example.com, and then, if that fails, as xyz.example.net. Do not use too many domains in the search list because it slows down resolution.

A hosts: files dns line in /etc/nsswitch.conf causes the resolver to consult /etc/hosts before using the DNS during the course of a name lookup. This allows you to override the DNS by making temporary changes to /etc/hosts, which is especially useful during network testing. (Older resolvers might require an order hosts, bind line in the /etc/host.conf file instead.)

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