Reverse DNS (Domain Name System)
Reverse DNS is used to map the domain name associated with an IP address. It is the reverse of Domain Name System.
It consists of a Reverse DNS Lookup Tool which requires the IP address which has a host name. Once you enter the IP address into the rDNS Lookup Tool, you get domain name associate with its respective IP. Though it is not as necessary as forward DNS is but having a rDNS is a guarantee that we will not face any problem with SMTP server or network backup systems.
Reverse DNS Uses
It is one of the basic requirements for running some internet protocols.
It could also be used for determining whether the IP address of an incoming mail matches to an authenticated domain name and to label it as junk if not.
The rDNS can also block the spam.
It is one of the techniques email servers use to identify that the sending server is not a malicious spammer.
A forward-confirmed reverse DNS verification is a form of validation which shows relationship between the domain owner and server owner that has been given an IP.
Reverse DNS records-
For instance, if we write www.test.com then it will direct the browser to 23.25.02.12 . This is the forward DNS and usually done with an A record.
Whereas for the Reverse DNS a PTR record is used. PTR record is stored in a zone called .in-addr.arpa.
One who owns the block of IP addresses is the administrator of this zone. To add a PTR record to the IP address you need to contact your ISP as usually the owner of IP address is the ISP.