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Overview

A DNS domain names (domain names) is with IP addresses connect it. The DNS PTR record, otherwise known as the pointer record, provides the domain name associated with the IP address. A DNS PTR record is the exact opposite of an "A" record, which specifies the IP address associated with a domain name. 

When a user tries to access a domain name in their browser, in the background DNS search occurs where the system is associated with the domain name IP addresses looking for And the DNS PTR records are stored in the in reverse DNS lookups is used (reverse DNS lookup), which is exactly the reverse of the normal DNS lookup process: it is a query that starts with an IP address and looks for the domain name associated with it.

Each PTR record must have an "A" record in the domain name zone.

 

 

Storage of PTR records

The way PTR records are stored is different for IPv4 and IPv6 networks, so we mention them separately.

For IPv4 networks

While the DNS "A" records are under that domain name in zone files are stored, whereas DNS PTR records are stored under the IP address - reversed and adding ".in-addr.arpa". For example, the PTR record for IP address 1.2.3.4 is stored under "4.3.2.1.in-addr.arpa".

The "in-addr.arpa" element is added because PTR records are stored in the DNS top-level .arpa domain. .arpa is a domain mostly used to manage network infrastructure and was the first top-level domain name defined for the Internet. (The name "arpa" dates back to the earliest days of the Internet: it was named after the Advanced Research Projects Agency (ARPA), which created ARPANET, an important precursor to the Internet.)

in-addr.arpa is a namespace in the .arpa domain that is used for reverse DNS lookups in IPv4 networks.

For IPv6 networks

IPv6 addresses are structured differently from IPv4 addresses, and IPv6 PTR records exist in a different namespace within the .arpa domain. IPv6 PTR records are stored under the IPv6 address, inverted and converted into four-bit sections (as opposed to 8-bit sections as in IPv4), plus ".ip6.arpa".

 

Main uses of PTR records

PTR records are used in reverse DNS lookups; Common uses for reverse DNA include:

Anti-spam

Spam filters use reverse DNS to check the domain names of email addresses and determine whether the associated IP addresses are indeed used by legitimate email servers.

PTR records therefore provide confidence that a given hostname or domain is connected to an IP address. PTR records are mandatory for outgoing mail servers, as most mail providers reject or mark as spam incoming messages without a valid reverse DNS configuration (missing PTR or mismatched hostname "A" record). This has now become standard, so to speak, as all mail providers try to keep spam out of their customers' inboxes. Proper reverse DNS configuration is always a good solution to avoid possible email filtering.

Troubleshooting email delivery problems

Because spam filters perform these checks, email delivery problems can be caused by a misconfigured or missing PTR record. If a domain does not have a PTR record, or if the PTR record contains the wrong domain, email services may refuse to accept all email from that domain.

Logging

In many cases, syslogs only store IP addresses, so using a reverse DNS lookup, these can be converted to domain names for the logs, which are easier for humans to read.

 

Set PTR record

The PTR record is set by the IP address maintainer. Thus, if we operate a web server and set the PTR record required for the fixed IP address assigned to it, in that case, first create an "A" record in the DNS zone of our domain name, which contains our host name and IP address. If this is available and the changes have been updated by the name servers, so the host name can be "pinged" from the outside, then we ask our hosting provider to set this record for us. Many hosting providers also provide a suitable interface for this, so the PTR record can be set there as well. Please contact our service provider for information on this matter.