Reverse DNS (rDNS) is Something That All Network Engineers and DNS Administrators Working in an ISP Environment Must be Conversant With
In the usual DNS process, domain names are mapped to IP addresses, and when you run a DNS query, it returns the associated IP address, and this is known as “forward DNS resolution”, and this is what most network engineers are used to.
Today I want to discuss the unusual, the opposite of “forward DNS resolution”; where an IP address is looked up against its designated domain name and this technique is known as “Reverse DNS lookup” and can also be referred to as “Reverse delegation”.
Reverse delegation is essential for the integrity and security of internet communications, allowing for verification and authentication of IP addresses in various network services, particularly email services that need to verify the domain associated with an incoming IP address while performing anti-spam checks.
If you work in an ISP environment, you probably have come across requests from clients asking you to configure reserve delegation for the public IP address you assigned to them, this is most likely that they are using that IP on their email servers and are having issues with their emails being dropped or marked as spam.
