Technical Library

Domain Name System

Introduction

Integration

Pointer (PTR) records are used in the in-addr.arpa (reverse) domain files for address-to-name mappings for the A records. PTR records are established for the canonical host names only. An alias name will not have a PTR record associated with it.

They are used to convert IP-addresses to host names. Sometimes, the reverse domains get ignored, or forgotten. Although things may seem to be running smoothly, you cannot forget the reverse domain. Many programs, such as FTP, use the reverse domains to track who is using their service. Without a reverse mapping, connection may be refused.

The format of the PTR records is:

The components of the PTR record are described below.

reverse-name

This is the name in the in-addr.arpa domain. Basically, it is created by taking the IP-address of the associated host, and reversing its octets, then tacking in-addr.arpa onto the end of it. Examples of PTR records can be found in the named.rev file.

host

This is the fully qualified domain name of the computer whose address is specified in the reverse-name field. This must be a fully qualified domain name, because the name cannot be relative to the current in-addr.arpa domain.