Your Internet Consultant - The FAQs of Life Online

3.6. What is the domain name system?

The computers on the Internet need a way to translate site names to their corresponding numerical addresses. The Internet has a sort of phone book for Internet hosts: a computer can look up another system's name and find out its address. This isn't as simple as it sounds. Millions of hosts on the Internet makes for a really thick phone book, even an electronic one. Also, what would happen if two computers on the Internet had the same name? Which address is the right one? Computers don't like ambiguity like that.

When the Internet was much smaller than it is today, the task of maintaining the Internet's address book was simple. The Network Information Center (or NIC) maintained a registry of Internet sites. The document, called a hosts file, was distributed periodically to every site on the Internet. As you can imagine, those blissful days have gone the way of the Dodo bird. As the Internet grew, maintenance and distribution of a huge hosts file became unmanageable.

The Domain Name Service (also known as the Domain Name System, or DNS) is the replacement of the obsolete hosts file. It is a method to administer Internet system names by giving each organization responsibility for maintaining the names at that site. This scheme eliminates the dependence on a centrally-maintained file that translates host names to addresses.

There is no longer a centralized list of sites. Instead, each organization keeps track of its own computers on the Internet. Humboldt State University keeps track of only its machines; Fred's Internet and Venetian Blind Company keeps track of its own. If a user at HSU needs to know something about one of Fred's computers, it sends out a query across the Internet that Fred's computer answers. That, in a nutshell, is the domain name system.

Note: If you've never heard of MX Records, they're the little guys with the baseball mitts that catch the queries about a specific domain and field them.

If the system administrator at HSU's College of Natural Resources and Sciences computer lab wants to plug another computer into the Internet, he doesn't need approval from anyone at the Network Information Center, and he doesn't have to wait for someone to add the new machine to a hosts file. With the Domain Name System, he can do all of this himself.

Note: The IP addresses cannot be assigned randomly, although the NIC still doles out IP address blocks. Before putting any computer on the Internet, an organization must get a block of addresses from the Network Information Center. How many addresses you get depends on how many your organization needs. The smallest is a "class C" address (for instance, 137.150.188.*) which gives the organization room to put 254 computers on the Net. A "class B" address (137.150.*.*) for larger organizations explodes the limit to 64,516 hosts. Finally, those with "class A" addresses (137.*.*.*) have access to whopping 16 million number combinations.

Similarly, if someone at that school decided to start a new group (like journalism) and put three computers in that group (we'll call them murrow, rather, and hearst) they can do that without anyone's permission. So, full names of the computers at that school would be

As long as there are never two computers in one domain with the same name, or two domains with the same name, everything goes swimmingly. If every system administrator makes sure that the names he assigns are unique at his site, there can be no conflicting names to confuse the situation. Given the preceding example, the following host names could be valid additions to the Internet:

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