Reverse zone files have a mapping from IP address to hostnames. They can be considered as mirrors to the primary zone files. The file lists the IP address first and then the name. This was used in earlier days to reject a service to some clients if they were not able to ping the domain in reverse. Now, this is used to stop e-mail spam by verifying the origins of an e-mail.

First, we create a reverse zone file for our server and put the entry into the named.conf file.

zone "162.240.10.in-addr.arpa" {
type master;
file "pri.162.240.10.in-addr.arpa";
};

The numbers in the IP address follow a pattern. They are in the reverse order. Our server ubuntuserver.org is in the 10.240.162 net and it is reversed to get 162.240.10. Note that the domain in-addr-arpa is used by all reverse lookups as the top-level domain. Let's look at a sample reverse zone file now.

We name our file pri.162.240.10.in-addr.arpa and the file will be in the same directory where our primary zone file was....