In standard DNS queries, a domain name will resolve to an IP address. Reverse DNS is the opposite of this, resolving IP addresses to a domain name.

Reverse DNS can be used to log web traffic by domain name for site statistics, or prevent SPAM by verifying that an e-mail was truly sent from the domain name listed in the e-mail header.

To test Reverse DNS, we’ll use the command prompt:

Click Start -> Run…

Type “cmd” to bring up the command prompt

For a standard DNS query, type “nslookup www.google.com” in the command prompt (note, any domain name can replace www.google.com). In the returned results, we see the “name” listed as the domain typed above and the “address” it resolves to. Results:

Now, to test Reverse DNS, we’ll type in the IP address we wish to test rather then a domain name. For example, if we want to test Reverse DNS for the IP address 209.85.165.104, we would type “nslookup 209.85.165.104”. The results are as follows:

Now the DNS lookup has returned a domain name for the IP address we provided, www.google.com.