Reverse DNS and PTR record

What is Reverse DNS?

You probably know already what is a forward DNS. It links the hostname/domain to the IP address. Now think from the opposite direction. Reverse DNS, also known as rDNS is doing the mirror action, using the IP address to find the hostname/domain. You might be surprised that this is actually needed, but it has significant application. It is very useful for e-mail verifications B2B and troubleshooting.

ReverseDNS

 

Imagine this situation, you don’t have a reverse DNS set up, but you are sending a very important e-mail to another company. They have a mail server with Anti-Spam protection. It will check if you have rDNS and if you are missing it, your message will go directly to the spam bin. This protection reduces the phishing significantly by putting straight into the spam, all e-mails that have IPs that don’t correspond to IPs of the domains they say they come from.

All devices, connected to the internet have their IP addresses. This makes it easy to do a reverse DNS lookup and see who is it on the other side. For this purpose, you will need a PTR record.

PTR record

PTR is short of a pointer, it is straightforward, by checking the IP address, you get to the hostname/domain.

For every A record, there should be a PTR record. It is opposite to how the DNS works, instead of writing the domain and getting to the A record, you start with the IP address and get the domain name.

What is the purpose of PTR records?

The answer is verification. They create trust, matching the IP addresses with the hostname/domain. They are essential for any outgoing mail server; without them, all the e-mails will get rejected and go straight to the spam. Missing PTR or mismatching A Record means problems.

They can be used as business lead generators. You can trace back different IPs, which have visited your website and see which companies are on the other side. This way you know that they have interest in you. You can provide this information to your sales team, and they can take it from there.

Create PTR record

The first step is to create a Reverse DNS zone; you can do that from the Control Panel, add a new zone and click on the Master Reverse DNS zone. This zone is directly related to the size of your IP network. For example in IPv4/24 network, you will have 255 IP addresses. In the network 192.168.1.0/24, all the available IPs will be from 192.168.1.1 to 192.168.1.255, and the reverse DNS zone will have this format 1.168.192.in-addr.arpa

Now in this reverse zone, we can add PTR records that match each IP from the network. You just add a new record; this will be for the first IP 192.168.1.1

 

Type: PTR

Host: 1

Points to: hostname1.example.com

 

The PTR records will look like this in the Control Panel:

Host:    Type:    Points to:    TTL

1.1.168.192.in-addr.arpa    PTR    hostname1.example.com    1 Hour

Then, make sure that there is a matching A record. Each PTR must have one.

For more information on how to create PTR record including a video tutorial, visit this page.

The last step is to change the name servers of your reverse zone at your IP provider or ask them to do it. A configured NS records at the IP provider must point to the name servers listed in your Control Panel.

Conclusion

As you can see, rDNS is is critical for business success. You can use Reverse DNS zones from ClouDNS for both IPv4 and IPv6 networks. You can check our prices here and start a 30-day free trial, no credit card required.

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