Addition/Setup.Bind.As.Cache.DNS.Server

From iRedMail

Revision as of 08:39, 10 March 2010

Mission

To configure a caching nameserver on a iRedMail server itself.

Advantage

Reduces the delay in domain name resolution drastically as the requests for frequently accessed domain are served from cache.

Working

"named" gets a request for domain resolution.

It checks whether the request can be satisfied from cache. If the answer is in cache and not stale, the request is satisfied from cache itself saving a lot of time. If request can't be satisfied from cache, named queries the first parent. If it replies with the answer, then named will cache the response and subsequent requests for the same domain name will be satisfied from the cache. In case first parent fails to reply, named will query the second parent and so on.

How to install

We choose BIND which is the most common package on DNS server.

To check the package present or not on the system, just using

       rpm -qa |grep bind
       rpm -qa |grep caching-nameserver

by default on iRedMail server, the result is:

[root@mail ~]# rpm -qa |grep bind

ypbind-1.19-12.el5

bind-libs-9.3.6-4.P1.el5_4.2

bind-utils-9.3.6-4.P1.el5_4.2

the package we need on cache named server is

• bind

• bind-chroot

• bind-util

• caching-nameserver

If they are not present on your system, install using

       yum install caching-nameserver bind-chroot

all the components we need will be installed

How to configure

The main configuration file for named resides in /var/named/chroot/etc/named.caching-nameserver.conf which is also soft linked from /etc/named.caching-nameserver.conf . named configuration file supports C/C++ style comments.

Below is a configuration file for a machine for iRedMail localhost only. The comments inline explain what each option does.

Since the DNS cache server is for iRedMail local use only, so the IP listen and query is only for localhost. If you want to share the DNS caching for local network for any query, you need to modify the config file to your own.

The RED characters indicate that you need to enter by yourself.

       //
       // named.caching-nameserver.conf
       //
       // Provided by Red Hat caching-nameserver package to configure the
       // ISC BIND named(8) DNS server as a caching only nameserver
       // (as a localhost DNS resolver only).
       //
       // See /usr/share/doc/bind*/sample/ for example named configuration files.
       //
       // DO NOT EDIT THIS FILE - use system-config-bind or an editor
       // to create named.conf - edits to this file will be lost on
       // caching-nameserver package upgrade.
       //
               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";
               forward first;  //using external DNS if no reference on this server
               forwarders {
                       202.76.4.18;    // CPCNet DNS 
                       8.8.8.8;        // Google DNS
               };
       // Those options should be used carefully because they disable port
       // randomization
       // query-source    port 53;
       // query-source-v6 port 53;
       
               allow-query     { localhost; };
               allow-query-cache { localhost; };
       };
       logging {
               channel default_debug {
                       file "data/named.run";
                       severity dynamic;
               };
       };
       view localhost_resolver {
               match-clients      { localhost; };
               match-destinations { localhost; };
               recursion yes;
               include "/etc/named.rfc1912.zones";
       };