Configuring reverse resolution initially requires configuring a DNS server for a specific domain.
In the case of a /24 IPv4 block, for example, 10.0.0/24, a domain name must be configured for 0.0.10.in-addr.arpa.
If a DNS server running BIND (Berkeley Internet Name Domain) software developed by Internet Systems Consortium (ISC) in a Unix environment, the configuration would include the steps described below.
Creation of a general configuration file containing the following lines (in addition to any other lines of code needed for the proper operation of the server):
The lines above specify the zone for which this is the authoritative server, the type of server (master or slave) and the name of the file that will contain the information about the zone.
The file can have any name. In this example, we used a name based on the name of the zone we are configuring.
The next step is to create a file to contain the information about the zone. The name of this file must be the same name specified in the server's general configuration. In the example, the name is 0.0.10.in-addr.arpa.db.
Basically, this file will contain the following information:
0.0.10.in-addr.arpa. IN SOA ns.example.org root.example.org (
1 ; serial
3600 ; refresh
3600 ; retry
3600 ; expire
900) ; minimum
0.0.10.in-addr.arpa. IN NS ns.example.org.
1 IN PTR host1.example.org.
2 IN PTR host2.example.org.
The lines above specify the name of the zone that is being configured and its RR (Resources Records), for example, the SOA (Start of Authority), which specifies the authoritative server for this zone.
The information between brackets is used for organizing the synchronization of secondary servers (slaves).
This is followed by information on the DNS servers for the zone, which may be more than one.
Finally, the most interesting information in the case of reverse resolution, which is the name assigned to each IP address that is part of the block.
The Resource Record PTR specifies a pointer between the address and the corresponding name. For example, IP address 192.0.2.1 is associated with the name host1.example.or.