DNS Installation and configuration in Centos

The DNS resolves hostname into ip address and vice versa. For example if we type http://www.google.com in browser, the DNS server translates the domain name into its corresponding ip address. So it makes us easy to remember the domain names instead of its ip address.

Setup primary Master DNS Server

Step 1:

yum install bind* -y

Step 2:

Configure DNS Server

The main configuration of the DNS will look like below.

[root@ns1 ~]# vi /etc/named.conf
//
// named.conf
//
// Provided by Red Hat bind 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.
//
options {
      listen-on port 53 { 127.0.0.1; 192.168.198.140;};                      ## Master DNS IP ##
      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     { any; 192.168.198.0/24; };                      ## IP Range ##
      allow-transfer    { localhost; 192.168.198.141; };                        ## Slave DNS IP ## 
      recursion yes;
      dnssec-enable yes;
      dnssec-validation yes;
      dnssec-lookaside auto;
      /* Path to ISC DLV key */
      bindkeys-file "/etc/named.iscdlv.key";
      managed-keys-directory "/var/named/dynamic";
};
logging {
        channel default_debug {
                file "data/named.run";
                severity dynamic;
        };
};
zone "." IN {
      type hint;
      file "named.ca";
};
zone  "example.com" IN {
      type master;
      file "fwd.example.com";
      allow-update { none; };
};
zone  "198.168.192.in-addr.arpa" IN {
      type master;
      file "rev.example.com";
      allow-update { none; };
};
include "/etc/named.rfc1912.zones";
include "/etc/named.root.key";


Step 3:

Create Zone files

Now we should create forward and reverse zone files which we mentioned in the ‘/etc/named.conf’ file.

Create Forward Zone:

[root@masterdns ~]# vi /var/named/fwd.example.com
$TTL 86400
@   IN  SOA     ns1.example.com. root.example.com. (
        2011071001  ;Serial
        3600        ;Refresh
        1800        ;Retry
        604800      ;Expire
        86400       ;Minimum TTL
)
@     IN  NS      ns1.example.com.
@     IN  NS          ns2.example.com.
           
ns1     IN  A       192.168.198.140
ns2   IN  A     192.168.198.141

Create Reverse Zone:

[root@masterdns ~]# vi /var/named/rev.example.com
$TTL 86400
@   IN  SOA     ns1.example.com. root.example.com. (
        2011071001  ;Serial
        3600        ;Refresh
        1800        ;Retry
        604800      ;Expire
        86400       ;Minimum TTL
)
@     IN  NS      ns1.example.com.
@     IN  NS      ns2.example.com.
ns1   IN  A           192.168.198.140
ns2   IN  A           192.168.198.141
200     IN  PTR     ns1.example.com.
201   IN  PTR         ns2.example.com.


Step 4:

Start the bind service

[root@ns1 ~]# service named start
Generating /etc/rndc.key:                                  [  OK  ]
Starting named:                                            [  OK  ]
[root@ns1 ~]# chkconfig named on

Step 5:

Allow DNS Server through iptables

Add the lines shown below in ‘/etc/sysconfig/iptables’ file. This will allow all clients to access the DNS server.

-A INPUT -p udp -m state --state NEW --dport 53 -j ACCEPT
-A INPUT -p tcp -m state --state NEW --dport 53 -j ACCEPT

Then,

Restart iptables to save the changes

[root@ns1 ~]# service iptables restart




Test syntax errors of DNS configuration and zone files:

Checking DNS Config file

[root@ns1 ~]# named-checkconf /etc/named.conf
[root@ns2 ~]# named-checkconf /etc/named.rfc1912.zones

Checking zone files

[root@ns1 ~]# named-checkzone example.com /var/named/fwd.example.com
[root@ns2 ~]# named-checkzone example.com /var/named/rev.example.com


Test DNS Server

[root@ns1 ~]# dig ns1.example.com

[root@ns2 ~]# dig -x 192.168.198.140





Setup Secondary(Slave) DNS Server

Step 1:

[root@ns2 ~]# yum install bind* -y

Step 2:

Configure Slave DNS Server

[root@ns2 ~]# vi /etc/named.conf
//
// named.conf
//
// Provided by Red Hat bind 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.
//
options {
      listen-on port 53 { 127.0.0.1; 192.168.198.141; };                    ## NS2 DNS IP ##     
      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; 192.168.198.0/24; };                     ## IP Range ##  
      recursion yes;
      dnssec-enable yes;
      dnssec-validation yes;
      dnssec-lookaside auto;
      /* Path to ISC DLV key */
      bindkeys-file "/etc/named.iscdlv.key";
      managed-keys-directory "/var/named/dynamic";
};
logging {
        channel default_debug {
                file "data/named.run";
                severity dynamic;
        };
};
zone "." IN {
      type hint;
      file "named.ca";
};
zone  "example.com" IN {
      type slave;
      file "slaves/example.fwd";
      masters { 192.168.1.140; };
};
zone  "198.168.192.in-addr.arpa" IN {
      type slave;
      file "slaves/example.rev";
      masters { 192.168.1.140; };
};
include "/etc/named.rfc1912.zones";
include "/etc/named.root.key";

Step 3:

Start the DNS Service

[root@ns2 ~]# service named start
Generating /etc/rndc.key:                                  [  OK  ]
Starting named:                                            [  OK  ]
[root@ns2 ~]# chkconfig named on


Now the forward and reverse zones are automatically replicated from Master DNS server to Slave DNS server.
The forward and reverse zones are automatically replicated from Master DNS. Now check the zone files whether the correct zone files are replicated or not.


Step 4:

Add the DNS Server details to all systems

[root@slavedns ~]# vi /etc/resolv.conf
# Generated by NetworkManager
search example.com
nameserver 192.168.198.140
nameserver 192.168.198.141
nameserver 8.8.8.8

Step 5:

Test DNS Server

[root@ns2 ~]# dig ns2.example.com
[root@ns2 ~]# dig ns1.example.com