21.3. Caching-only name Server

Caching-only name servers are servers not authoritative for any domains except 0.0.127.in-addr.arpa, the localhost. A caching-only name server can look up names inside and outside your zone, as can primary and slave name servers. The difference is that when a caching-only name server initially looks up a name within your zone, it ends up asking one of the primary or slave names servers for your zone for the answer.

The necessary files to setup a simple caching name server are:

1. named.conf

2. db.127.0.0

3. db.cache

4. named script

To configure the /etc/named.conf file for a simple caching name server, use this for all servers that dont act as a master or slave name server. Setting up a simple caching server for local client machines will reduce the load on the network's primary server. Many users on dialup connections may use this configuration along with bind for such a purpose. Create the named.conf file, touch /etc/named.conf and add the following lines to the file:

options { directory "/var/named"; forwarders { 208.164.186.1; 208.164.186.2; }; forward only; }; // // a caching only nameserver config zone "." in { type hint; file "db.cache"; }; zone "0.0.127.in-addr.arpa" in { type master; file "db.127.0.0"; };

To configure the /var/named/db.127.0.0 file for a simple caching name server,you can use this configuration for all machines on your network that don't act as a master or slave name server. The db.127.0.0 file covers the loopback network. Create the following files in /var/named/, touch /var/named/db.127.0.0 and add the following lines in the file:

$TTL 345600 @ IN SOA localhost. root.localhost. ( 00 ; Serial 86400 ; Refresh 7200 ; Retry 2592000 ; Expire 345600 ) ; Minimum IN NS localhost. 1 IN PTR localhost.

Configure the /var/named/db.cache file for a simple caching name server before starting your DNS server. You must take a copy of db.cache file and copy this file to the /var/named/ directory. The db.cache tells your server where the servers for the root zone are.

Use the following commands on another Unix computer in your organization to query a new db.cache file for your DNS Server or pick one from your Red Hat Linux CD-ROM source distribution:

[root@deep]# dig @.aroot-servers.net . ns > db.cache

Don't forget to copy the db.cache file to the /var/named/ directory on your server where you're installing DNS server after retrieving it over the Internet.