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

From iRedMail

Revision as of 08:55, 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 BOLD 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 you should use the DNS from your ISP
                       8.8.8.8;        // Google DNS here is the sample 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";
       };

To use your caching-nameserver, open /etc/resolv.conf file and add the following line to make all query carry on the local iRedMail only.

nameserver 127.0.0.1

Comment all other lines in the file, so that finally the file looks like

  # search yourdomain.com
  # nameserver 202.76.4.18
  # nameserver 8.8.8.8
  nameserver 127.0.0.1

save and restart the service:

  [root@mail ~]# service network restart

Now try to ping any domain and you will find that the server cannot resolve any domain name. That mean the domain only query itself the server itself.

To start the DNS caching service

  [root@mail ~]# service named start

and then check the log to see the service starting status log

[root@mail ~]# cat /var/log/messages

Mar 10 12:20:03 mail named[1522]: starting BIND 9.3.6-P1-RedHat-9.3.6-4.P1.el5_4.2 -u named -c /etc/named.caching-nameserver.conf -t /var/named/chroot
Mar 10 12:20:03 mail named[1522]: adjusted limit on open files from 1024 to 1048576
Mar 10 12:20:03 mail named[1522]: found 1 CPU, using 1 worker thread
Mar 10 12:20:03 mail named[1522]: using up to 4096 sockets
Mar 10 12:20:03 mail named[1522]: loading configuration from '/etc/named.caching-nameserver.conf'
Mar 10 12:20:03 mail named[1522]: using default UDP/IPv4 port range: [1024, 65535]
Mar 10 12:20:03 mail named[1522]: using default UDP/IPv6 port range: [1024, 65535]
Mar 10 12:20:03 mail named[1522]: listening on IPv6 interface lo, ::1#53
Mar 10 12:20:03 mail named[1522]: listening on IPv4 interface lo, 127.0.0.1#53
Mar 10 12:20:03 mail named[1522]: command channel listening on 127.0.0.1#953
Mar 10 12:20:03 mail named[1522]: command channel listening on ::1#953
Mar 10 12:20:03 mail named[1522]: the working directory is not writable
Mar 10 12:20:03 mail named[1522]: zone 0.in-addr.arpa/IN/localhost_resolver: loaded serial 42
Mar 10 12:20:03 mail named[1522]: zone 0.0.127.in-addr.arpa/IN/localhost_resolver: loaded serial 1997022700
Mar 10 12:20:03 mail named[1522]: zone 255.in-addr.arpa/IN/localhost_resolver: loaded serial 42
Mar 10 12:20:03 mail named[1522]: zone 0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa/IN/localhost_resolver: loaded serial  1997022700
Mar 10 12:20:03 mail named[1522]: zone localdomain/IN/localhost_resolver: loaded serial 42
Mar 10 12:20:03 mail named[1522]: zone localhost/IN/localhost_resolver: loaded serial 42

This mean the service is started successfully.

Now you can try to ping any domain without any problem.

To make the DNS caching service start automatically everytime system bootup, simply enter:

 [root@mail ~]#  chkconfig named on

Using caching-nameserver

Now your system will use your own nameserver (in caching mode) for resolving all domain names. To test if your nameserver use the following command

 [root@localhost ~]# dig fedora.co.in 

Now if you use that command for the second time, the resolution time will be around 2-3 milli seconds while first time it would be around 400-700 milli seconds.

Example Below is two subsequent runs of dig for fedora.co.in . Notice the Query time.

 [root@bordeaux SPECS]# dig fedora.co.in

 ; <<>> DiG 9.3.6-P1-RedHat-9.3.6-4.P1.el5_4.2 <<>> fedora.co.in
 ;; global options:  printcmd
 ;; Got answer:
 ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 43694
 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 4, ADDITIONAL: 9
 
 ;; QUESTION SECTION:
 ;fedora.co.in.                  IN      A
 
 ;; ANSWER SECTION:
 fedora.co.in.           18199   IN      A       174.136.1.134
 
 ;; AUTHORITY SECTION:
 fedora.co.in.           31974   IN      NS      ns4.webcomindia.com.
 fedora.co.in.           31974   IN      NS      ns1.webcomindia.com.
 fedora.co.in.           31974   IN      NS      ns2.webcomindia.com.
 fedora.co.in.           31974   IN      NS      ns3.webcomindia.com.
 
 ;; ADDITIONAL SECTION:
 ns1.webcomindia.com.    31976   IN      A       67.15.47.189
 ns1.webcomindia.com.    31976   IN      A       67.15.253.220
 ns1.webcomindia.com.    31976   IN      A       67.15.253.251
 ns3.webcomindia.com.    31976   IN      A       67.15.253.252
 ns3.webcomindia.com.    31976   IN      A       67.15.47.188
 ns3.webcomindia.com.    31976   IN      A       67.15.253.219
 ns4.webcomindia.com.    166378  IN      A       66.249.5.122
 ns4.webcomindia.com.    166378  IN      A       66.249.5.25
 ns4.webcomindia.com.    166378  IN      A       66.249.5.105
 
 ;; Query time: 531 msec
 ;; SERVER: 127.0.0.1#53(127.0.0.1)
 ;; WHEN: Wed Mar 10 15:18:56 2010
 ;; MSG SIZE  rcvd: 277

The query time is long at the first time.

Enter the command again and then you will see the query time is greatly reduced that mean the caching service running successfully.