Forward DNS

An Internet domain name is used to find an IP address in a forward DNS search. To discover a domain name, a reverse DNS lookup uses an Internet IP address. When you type a Web site's address into your browser (the address is technically known as the Uniform Resource Locator or URL), it is sent to a nearby router, which does a forward DNS query in a routing table to get the IP address. Because most users conceive in terms of domain names rather than IP addresses, forward DNS (which stands for domain name system) lookups are more popular. However, you can come across a Web page with a URL that has the domain name component represented as an IP address (sometimes called a dot address) and want to be able to see its domain name. An Internet facility that lets you do either forward or reverse DNS lookup yourself is called nslookup. It comes with some operating systems or you can download the program and install it on your computer.

Reverse DNS

A DNS query for the domain name associated with a specific IP address is known as a reverse DNS lookup. This achieves the inverse of the more often used forward DNS lookup, which queries the DNS system for an IP address.

The Internet Engineering Task Force (IETF) recommends that every domain be able to do reverse DNS lookups, however, this is not a hard requirement because reverse lookups are not required for the usual operation of the Internet. As a result, reverse DNS lookups aren't widely used.