The Domain Name System (DNS) connects many kinds of information with domain names. This allows it to act as a kind of directory for the internet, converting the URL's that we see for websites every day, such as www.example.org, into IP addresses such as 188.8.131.52, that are required for the proper function of networking.
The DNS also holds additional data, for example the registry of mail exchange servers, which receives the email for a given domain. The DNS provides a worldwide redirection service that is entirely keyword-based, so that it has now become a vital element of internet usage.
Of course, in addition to the translation of IP address to domain name and back, the DNS is also responsible for assigning internet names to organizations (or their various concerns) with the numerical IP address, completely independent of the physical routing systems. The DNS then maps the assigned IP addresses so that they are connected to the relevant domain names.
This allows both an IP address and a hyperlink or URL to be used interchangeably, though clearly URLs are much easier for people to remember than many different long strands of numbers.
Just as for a telephone number, you could perform a cell phone lookup , the DNS allows you to perform a reverse DNS lookup, which permits you to use an IP address, and locate the relevant host information or domain information that is associated with that IP address.
There are many different reasons for which you'd want to perform a reverse DNS lookup, primarily for the security of your computer. In cases such as unrecognizable emails, reverse DNS lookups give you the ability to look up the domain name or hosting service related to the IP address where the email originated. This may help you to decide whether you have received a desirable email, or if it is simply another case of spam.
Furthermore, reverse DNS lookups can be used to create a whitelist screener or authenticator, which is effective enough to take out the majority of spam emails that would come in, as it is able to identify zombie computers used by most spam emailers.
Martin Verite is a freelance reporter and technologist who enjoys covering the telecommunications industry.