What Is a DNS PTR Record & What Is It Used For?

A pointer (PTR) record resolves an IP address (made up of numbers and decimals) into a domain name (such as okta.com).

The act of translating an IP address into a domain name is known as a reverse lookup in the Domain Name System (DNS).

Let us explain how this process works.

What does a DNS PTR record do?

Every computer has a unique IP address, per the DNS that powers the internet. You may never know your IP address, but no other computer can reach you without it.

Connected devices use IP addresses exclusively. But if you know the IP address, you may want to know the formal domain name too.

Enter the DNS PTR tool.

Use the DNS PTR tool to perform a reverse lookup and translate the numbers into a web address you can both read and understand.

Why do you need PTR records?

As we mentioned, the average computer user has no need for a DNS PTR record. But there are many reasons for security experts to use the tool.

You might use PTR records for:

• Validation. Some email servers won't accept notes from servers that don't have PTR records set up properly. Attending to this step is a little like proving that you have pure intentions.

• Safety. Just as you need PTR records to validate your outgoing email, you should expect your communication partners to do the same.

• Investigation. Some systems store only IP addresses, not domain names. You might need PTR records to understand where traffic originates.

DNS PTR records are stored under the IP address with ".in-addr.arpa" added in IPv4, and they're stored under the IPv6 address, converted into four-bit sections with ".ip6.arpa" added in IPv6.

What does a DNS PTR record look like?

An example could help you understand just how these systems work. Try a tool like this.

The DNS is critical to effective internet communication. But understanding the terminology takes time and a bit of practice. Check out our blog post for more DNS details.

References

What Is an IP Address and What Can It Reveal About You? (May 2015). Insider.

How to Set Up Reverse DNS and PTR Records. (June 2013). Computerworld.

Reverse DNS Lookup and PTR Query. DNS Insiders.