easyDNS Tutorial - Reverse DNS

Section One • A note about IPs

One of the differences between DNS and reverse DNS is in how each segment of the address is used to find the right information.

For a domain name the most general part of the name goes at the end. So for www.example.com, ".com" is where the search would begin for the information for the more specific levels of the domain. Once the ".com" servers are found the machines look for where to find info on "example.com", and from there find "www.example.com".

For an IP address however, the most general part of the address appears at the beginning of the address, so for 192.168.24.5, 192 is the most general and 5 the most specific, and you have to start at the value to the left rather than the right to find where to begin.

For this reason when you perform a reverse DNS lookup, you reverse the sections of the IP, called octets, and add in-addr.arpa to let the system know you're doing a reverse lookup.

So the reverse DNS of 192.168.24.5 would be looked up as follows:
5.24.168.192.in-addr.arpa

5.24.168.192.in-addr.arpa is known as "in-addr.arpa" notation.

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