A reverse translation is the mapping of an IP address to a domain name. We already know that a record defining the mapping of an IP address to a domain name is a pointer record (PTR). Some programs such as ftp, traceroute, etc., use reverse translation. If a reverse record for a domain name is missing in DNS, some services such as FTP might refuse to work properly. Therefore, it is very important not to forget about PTR records and thus about reverse domains.

A reverse domain is always created and delegated for an entire IP address network. For example for a network 194.149.177, a reverse domain 177.149.194 in-addr.arpa must be created and delegated in DNS. A reverse domain has no connection to a forward domain. Domain names of various domains can coexist, and often do so, within one reverse domain.

The types of reverse domains are derived from the extent of the used network. The user makes use of 256 IP addresses of a C class or a subnetwork of a C class...