What is PTR? How is PTR different from DNS?

A PTR record is a type of Domain Name System (DNS) record that maps an IP address to a domain with a hostname, and is the exact opposite of an A record, where the domain name refers to the IP address. Because of its purpose, a PTR record is sometimes referred to as a reverse DNS record. Using an IP address, you can get the domain or hostname associated with it. A record must exist for every PTR record.

Why are PTR records and where are they used?

PTR records provide more confidence that a given hostname or domain is associated with an IP address. PTR records must be present for outgoing mail servers, as many mail servers do a reverse DNS lookup for the IP address that is trying to connect to them, and if not, most mail providers reject or mark as spam messages received by mail servers without valid reverse configuration. DNS records (missing PTR record or mismatch with A record for hostname).

How to check the PTR of a record?

There are several ways to check for a PTR record. The easiest of them is to use special tools, where you do not need to perform any additional actions, just enter in the required field, for example, domain or IP, select the type of record and the program automatically displays the result.

The entries can also be checked in the console (we are considering Linux) for this there are special utilities: dig and nslookup. To get started, you need to make sure that the packages with the appropriate commands are installed. In most cases, this is the bind-utils package, for installation we use the package manager of our Linux distribution.

To display the PTR record in the console, set nslookup -type = ptr IP, where the type of DNS record is indicated after the -type switch; similarly, you can use it to search for other records.