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What are reverse (PTR) records? Why do I need them?
Posted by admin on 11 September 2009 09:40 PM
A PTR record is the reverse of an A record. That is, it gives an IP address to a hostname, rather than vice versa. Given an IP address of the form 69.65.30.20, the usual form for a PTR record is this:

20.30.65.69.in-addr.arpa. PTR host.name.

Note that, in certain special cases (classless subnet reverse zones), the name of the record may be different.

Because the naming rule of PTR records, they are almost always organized into separate zones, called reverse zones. For example, a typical reverse zone for a class C subnet would be named “30.65.69.in-addr.arpa.”, where again, the letters at the beginning stand for the octets of the subnet address 69.65.30.0/24.

A reverse zone typically corresponds to a subnet, not a domain name, and a PTR record corresponds to a particular IP address, not an A record.
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