Internet protocols

The internet is a worldwide network of networks that lets computers communicate using a shared set of rules called protocols. The foundation is the TCP/IP suite: the Internet Protocol (IP) gives every connected device a numerical address and routes packets of data toward it, while the Transmission Control Protocol (TCP) breaks information into packets, ensures they arrive in order, and re-sends any that are lost. Together they let data travel reliably across many intermediate networks between source and destination.

Because numerical IP addresses are hard to remember, the Domain Name System (DNS) translates human-friendly names, such as a website's domain, into the addresses computers use. A URL (uniform resource locator) builds on this by specifying not just the host but the protocol to use and the path to a particular resource, which is how a browser knows exactly what to request and from where. These addressing systems make the vast network navigable.

Many familiar services run on top of these protocols. The World Wide Web is delivered by web servers that respond to browser requests with pages and other resources. Email moves between mail servers using its own protocols for sending and retrieving messages. Other building blocks include data formats such as XML for structured information, CGI and APIs for programs to exchange data, cookies for remembering state between page visits, and port numbers that let a single machine run many services at once. All of this rests on the addressing and packet delivery that TCP/IP provides.

Frequently asked questions

What does DNS do?

The Domain Name System translates human-readable names, such as a website's domain, into the numerical IP addresses that computers use to locate each other on the internet.

What is a URL?

A URL is a uniform resource locator that identifies a resource on the internet, specifying the protocol to use, the host, and the path to the particular page or file requested.

What are port numbers for?

Port numbers let a single computer run many network services at once by directing each connection to the correct program, for example separating web traffic from email.