With a forward DNS lookup, the DNS is queried for the IP address of a certain hostname. A reverse DNS is exactly what you’d expect. It’s where the hostname of a certain IP address is queried. Basically, a reverse DNS lookup returns the hostname of an IP address.

Reverse DNS is mainly used to track the origin of a website visitor, the origin of an e-mail message, etc. It is usually not as critical as the classic DNS, visitors will reach the website even without the presence of reverse DNS for the IP of the web server or the IP of the visitor

Reverse DNS operates by creating a reverse DNS zone in which DNS PTR records (for Pointer Record) will be configured.

• Classic DNS: Record A: we know the name of a site and we want to obtain its IP address.
• Reverse DNS PTR: we know an IP address and we want to retrieve the name of the site.

The resolution system is constructed in a similar way to the classic resolution. To perform DNS resolution, the IP address to be queried is configured in the reverse zone with the suffix ‘.arpa’ and points to the required destination.

For example, the reverse DNS entry for IP “1.2.3.4” would be a PTR-record for “4.3.2.1.in-addr.arpa”.