Multiple DNS server configuration

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Different DNS for different zone

It is possible for an organization to have many internal DNS servers serving different domains. Assume the domains to be example.com and example.org. Now if a client requests example.com DNS server for example.org address resolution then the request may be resolved as a public request, because example.com server will treat example.org same as yahoo.com or google.co.in. To ensure that such requests also get resolved locally both example.com and example.org servers should have both example.org and example.com zones. Now example.com server should have following entry in its 'named.conf' file:

        zone "example.org." {
                type forward;
                forwarders { <IP>; };
        };

where <IP> should be IP address of example.org DNS server which would resolve all example.org requests.

Different DNS for sub-zone

To delegate a sub-zone to a different DNS appropriate records have to be entered in the zone file of parent zone. This can be done as follows:

$ORIGIN <sub-zone>.
@    IN   NS   ns1.<sub-zone>.
     IN   NS   ns2.<sub-zone>.
ns1  IN   A    A.B.C.D.
ns2  IN   A    P.Q.R.S

Steps learned from http://stackoverflow.com/questions/15338232/how-to-forward-a-subzone

Subzone in same DNS

To create a sub-zone in same DNS use following at end after all current zone entries are complete:

$ORIGIN admin.sbarjatiya.com.
@       IN      MX      10 smtp.admin.sbarjatiya.com.
smtp    IN      A      172.19.4.126
imap    IN      A      172.19.4.126
pop3    IN      A      172.19.4.126
rcube   IN      A      172.19.4.127

Primary and secondary DNS servers

Primary server zone configuration

Multiple DNS servers are most commonly created for backup so that if primary server is down secondary server can resolve all queries. To configure a primary server zone use:

zone "sbarjatiya.com."
{
type master;
file "sbarjatiya.com.forward";
allow-transfer {192.168.2.114; 127.0.0.1; };
also-notify {192.168.2.114; };
allow-update {};
};

and replace 192.168.2.114 with actual secondary server IP. Multiple secondary servers can also be specified.

Secondary server zone configuration

To configure a secondary server zone use:

zone "sbarjatiya.com."
{
type slave;
file "sbarjatiya.com.forward";
masters {192.168.2.106; };
allow-notify {192.168.2.106; };
allow-transfer {127.0.0.1; };
};

and replace 192.168.2.106 with actual primary server IP. Multiple primary servers can also be specified.

Editing zone records

To edit zone records use following steps:

1. Log into primary server
2. Edit zone file
3. Use commands:

   rndc freeze sbarjatiya.com
   rndc reload sbarjatiya.com
   rndc thaw sbarjatiya.com

4. Verify new serial number is reflected in primary server

   dig -t AXFR sbarjatiya.com @127.0.0.1

5. Verify new serial number is reflected in secondary server using same dig command.

Steps learned from http://jon.netdork.net/2008/08/21/bind-dynamic-zones-and-updates/

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