HTML & XHTML: The Definitive Guide, 6th Edition

Talking the Internet Talk

Every computer connected to the Internet (even a beat-up old Apple II) has a unique address: a number whose format is defined by the Internet Protocol (IP), the standard that defines how messages are passed from one machine to another on the Net. An IP address is made up of four numbers, each less than 256, joined together by periods, such as 192.12.248.73 and 131.58.97.254.

While computers deal only with numbers, people prefer names. For this reason, most computers also have names bestowed upon them. By current estimates, there are hundreds of millions, if not billions, of devices on the Net, so it would be very difficult to come up with that many unique names, let alone keep track of them all. Instead, the Internet is a network of networks, and is divided into groups known as domains, which are further divided into one or more subdomains. So, while you might choose a very common name for your computer, it becomes unique when you append, like surnames, all of the machine's domain names as a period-separated suffix, creating a fully qualified domain name.

This naming stuff is easier than it sounds. For example, the fully qualified domain name www.oreilly.com translates to a machine named "www" that's part of the domain known as "oreilly," which, in turn, is part of the commercial (com) branch of the Internet. Other branches of the Internet include educational institutions (edu), nonprofit organizations (org), the U.S. government (gov), and Internet service ...