How does rDNS (Reverse DNS) work?

After you set up your Forward DNS and add your DNS records, it is a great idea to set up a rDNS (Reverse DNS)! When you try to send an email from the domain, you will probably notice a problem. Your emails will go missing or to the SPAM folder. And this is something nobody wants for their business. So, now let’s explain a little bit more about rDNS (Reverse DNS).

What is rDNS?

Reverse DNS is also known as rDNS. It has the opposite purpose to a Forward DNS, which is to map IP addresses to hostnames. The main reason for using the Reverse DNS is to implement a way to verify the IP addresses and prove that they are related to a particular domain name. It is mainly necessary when we are talking about the verification of mail servers or other services. 

It lets you create a Reverse DNS zone, where you can add PTR records and use them as confirmation that the IP addresses and the domain name matches.

In short, let’s put it this way:

In Forward DNS, a domain name is pointing to an IP address where it is hosted.

In Revere DNS, An IP address is pointing to a domain name to verify it belongs to it.  

Master Reverse Zone

To be able to use Reverse DNS, you will need to create a Master Reverse Zone. IP addresses should be written in reverse. The rDNS can work both with IPv4 addresses as well as IPv6 addresses. Also, later you can add the PTR DNS record. The Master Reverse Zone will be the place where the PTR record can exist. 

PTR record

PTR record, also known as pointer record, produces the mapping we need: IP address to hostname. 

For each PTR record, you will need an A or AAAA record. 

You will need the PTR records and the Reverse Zone to verify the outgoing mail servers. During the process, there will be a check of both the PTR records and the A records. 

You have to make sure that your DNS records are set up appropriately. Your emails will most probably go to the spam folders if they are not arranged correctly. 

Slave Reverse Zone

If you want, you can create a Slave Reverse Zone. It is just a copy of the Master. A Slave Zone is always read-only. You can make changes only in the Master Reverse Zone. 

Slave Reverse Zone can serve you for providing redundancy or faster response if it is in a DNS server closer to the users. 

How to check your Reverse DNS?

You can check your Reverse DNS by examining the IP addresses and see if they lead to the hostname. There is a simple way to do it. On most of the OSes (Linux, macOS, Windows, etc.), you only have to use the Nslookup command:

nslookup 192.168.1.2

Just replace the IP address, in this example, is 192.168.1.2, with the one you want to verify. In this case, it is an IPv4 address, but that doesn’t mean that you can’t put in an IPv6 address too. 

So now you know how simple and easy it is.