Caching Name Server

Installing and configuring caching nameserver (named) on Linux (Centos5)

Advantage: Reduces the delay in domain name resolution drastically as the requests for frequently accessed websites are served from cache. Google for cache nameserver to learn more.

Installing caching-nameserver:

# yum install bind bind-utils caching-nameserver -y


Configuring caching-nameserver:

The main configuration file reside in /etc/named.conf

You can find configuration file by using the command

# rpm -qc bind


Not much need to be changed in this file, however if you want to cascade your ISP DNS servers as forwarder, then edit the named.conf and add forwarder directive under the 'options' section.

options {
        listen-on port 53 { 127.0.0.1; };
        listen-on-v6 port 53 { ::1; };
        directory       "/var/named";
        dump-file       "/var/named/data/cache_dump.db";
        statistics-file "/var/named/data/named_stats.txt";
        memstatistics-file "/var/named/data/named_mem_stats.txt";
        allow-query     { localhost; };
        recursion yes; // This option for enable caching
        max-cache-size 10m; //cache size of 10MB for dns
        cleaning-interval 15; // clean the cache every 15 min
    // Replace the IPs with the DNS of your ISP
   forwarders {
    192.168.0.240;
    8.8.8.8;};
};


Starting caching-nameserver:

# service named start

Or

# /etc/init.d/named start

To make named start every time you reboot your machine

# chkconfig --level 35 named on

Or

# setup


Go to "System services" and check named

Using caching-nameserver:

To use your caching-nameserver, add the following line to /etc/resolv.conf

nameserver 127.0.0.1

Now your system will use your own nameserver (in caching mode) for resolving all domain names

$ dig safesquid.com
Query time: 8 msec

First time the response time will be little high, next time the DNS query response will be served from local cache and will takes very little time

$ dig safesquid.com
$ Query time: 0 msec