A PTR (Pointer) record is a type of DNS (Domain Name System) record that maps an IP address to a domain name. Unlike other DNS record types that associate domain names with IP addresses, a PTR record performs the reverse mapping by associating an IP address with a domain name.

PTR records are primarily used in reverse DNS (rDNS) lookups. Reverse DNS is a technique that allows you to look up the domain name associated with a given IP address. It can be useful for various purposes, such as verifying the authenticity of email servers, troubleshooting network connectivity issues, and implementing security measures.

Here’s an example to illustrate the usage of a PTR record:

Let’s say you have an IP address, such as 192.0.2.123, and you want to find the domain name associated with it. In order to perform a reverse DNS lookup, a PTR record must be set up for the IP address. The PTR record would contain the IP address in reverse order (e.g., 123.2.0.192) and the corresponding domain name. When a reverse DNS lookup is performed on the IP address, the DNS resolver checks the PTR record and returns the associated domain name, if available.

PTR records are commonly used for email servers to verify the hostname associated with the IP address from which an email originates. Many email servers perform reverse DNS lookups to check if the domain in the reverse lookup matches the domain in the sender’s email address. This helps prevent spam and fraudulent email activity.

It’s worth noting that setting up PTR records typically requires coordination with your internet service provider (ISP) or the organization responsible for managing your IP address range. They have control over the reverse DNS zone corresponding to the IP address range and can assist in creating and managing PTR records.

PTR records are specific to IPv4 addresses. For IPv6 addresses, the equivalent record type is called PTR6 or IP6.ARPA records.