11.6. Reverse Zone

The format of the reverse lookup file (used to resolve an IP address to its corresponding host name ) is similar to the following:

 @     IN     SOA    ns.sitename.com root.sitename.com (                     1 ; serial                     28800 ; refresh                     7200 ; retry                     604800 ; expire                     86400 ; ttl                     ) IN    NS     localhost. 1     PTR    servername.com. 2     PTR    mail.servername.com.

You already know the purpose of the larger part of the file and only need to consider the last two records. These map IP addresses to their corresponding host names . Don't forget that the file is responsible for the 190.12.10.* network. The asterisk is replaced with the number from the first field, and the name corresponding to this IP address is given in the last field. The file defines the following mappings:

190.12.10.1 = servername.com.
190.12.10.2 = mail.servername.com.

It is mandatory that symbolic names end with a period.

You can find additional information concerning DNS in the RFC1035, RFC1712, and RFC1706 documents.