DNS — Domain Name System

Every website you visit lives on a computer somewhere, and that computer is found using a number called an IP address (for example, 192.0.2.10). Numbers like that are hard for people to remember, so instead we type friendly names like example.com. DNS (Domain Name System) is the service that turns those human-friendly names into the numeric addresses computers actually use to find each other.

Computers identify each other by numbers, but people think in names. Without DNS you'd have to know and type the exact numeric address of every site you wanted to visit — and those numbers can change whenever a site moves to a new server. DNS sits in the middle so you only ever have to remember the name, while the number is looked up fresh each time. We dig into this more in the Need for DNS lesson.

Here's the whole idea in one breath: you type a name, your device asks a special helper server to find the matching IP address, that helper hunts it down and hands it back, and your browser then connects to that address to load the page. The step-by-step version — with every server involved — is covered in Domain Name Resolution.

No single computer stores the address of every website in the world — that would be impossible to manage. Instead, DNS is organized as a tree, and a lookup works its way down it. At the top sit the root servers, which point to the servers for each ending like .com or .org. Those in turn point to the specific server that holds the real answer for one domain. Here's that hierarchy from top to bottom:

The rest of this topic builds up DNS one piece at a time — first the what and why, then the servers that do the work, then the records they store, and finally caching and privacy. Use the map below to jump around, or read straight through.