Configuring IPv4 address blocks

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

In a DNS server running Berkeley Internet Name Domain (BIND) software developed by Internet Systems Consortiom (ISC) in a Unix environment, this configuration would require 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):

zone ""{

type master;

file "";


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

Basically, this file will contain the following information: IN SOA (

1 ; serial

3600 ; refresh

3600 ; retry

3600 ; expire

900) ; minimum IN NS



The lines above specify the name of the zone that is being configured and its Resource Records (RR). For example, the Start of Authority (SOA) which specifies the authoritative server for this zone.

The information between brackets is used to organize the synchronization of secondary servers (slaves).

This is followed by information on the one or more DNS servers for the zone.

Finally, the file includes the most interesting information from the point of view of reverse resolution, i.e., the name associated with each IP address in the block.

Resource Record PTR specifies a pointer between the address and the corresponding name. For example, IP address is associated with the name host1.example.or.