DNS - PTR record (Pointer)

1 - About

A PTR record is a DNS record with the pointer type (PTR type) .

It's used to permits or set up a reverse lookup where an ip address as input gives you its domain name.

Only the owner of the IP can set a reverse record, not the owner of the domain. Therefore if you want to set a PTR record:
  • for a server, you need to do it at your server provider
  • for your internet connection, you need to ask it to your telecom provider

2.1 - Authentication

A PTR record is important because it's a part of request authentication on the Internet.

ie when a server got a request from an IP, it performs:

If they don't match, the request is classified as bad.

For instance:

3 - Format

The PTR records are stored within the .arpa top-level domain.

3.1 - Ipv4


142.175.106.72.in-addr.arpa. 86400 IN    PTR     name.apex.domain

where:

  • 142.175.106.72 is the IP
  • in-addr.arpa is the namespace (for Ipv4) where the records are stored. ie in the arpa domain

3.2 - Ipv6

IPv6 PTR records are stored under the IPv6 address, reversed and converted into four-bit sections (as opposed to 8-bit sections, as in IPv4), plus “.ip6.arpa”.

4 - Server provider

You Server provider should give you an interface to create it for a host

Example ovh on the cloud planel:


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