If we had to remember the IP addresses of all of the Web sites we visit every day, we would all go nuts. Human beings just are not that good at remembering strings of numbers. We are good at remembering words, however, and that is where domain names come in. You probably have hundreds of domain names stored in your head. For example:
www.google.com – a typical name.
www.yahoo.com – the world’s best-known name.
www.mit.edu – a popular EDU name.
Encarta.msn.com – a Web server that does not start with www.
www.bbc.co.uk – a name using four parts rather than three
ftp.microsoft.com – an FTP server rather than a Web server.
The COM, EDU and UK portions of these domain names are called the top-level domain or first-level domain. There are several hundred top-level domain names, including COM, EDU, GOV, MIL, NET, ORG and INT, as well as unique two-letter combinations for every county.
Within every top-level domain there is a huge list of second-level domains. For example, in the COM first-level domain, you’ve got:
Google
Yahoo
msn
Microsoft
Plus millions of others…
Every name in the COM top-level domain must be unique, but there can be duplication across domains. For example, google.com and google.org are completely different machines. In the case of bbc.co.uk, it is a third-level domain. Up to 127 levels are possible, although more than four is rare.
The left-most word, such as www is the host name. It specifies the name of a specific machine (with a specific IP address) in a domain. A given domain can potentially contain millions of host names as long as they are all unique within that domain.
Because all of the names in a given domain need to be unique, there has to be a single entity that controls the list and makes sure no duplicates arise. For example, the COM domain cannot contain any duplicates names, and a company called Network Solution is in charge of maintaining this list. When you register a domain name, it goes through one of several dozen registrars who work with Network Solutions to add names to the list. Network Solutions, in turn, keeps a central database known as whose database that contains information about the owner and name servers for each domain. If you go to the who is form, you can find information about any domain currently in existence.
While it is important to have a central authority keeping track of the database of names in the COM (and other) top-level domain, you would not want to centralize the database of all of the information in the COM domain. For example, Microsoft has hundreds of thousands of IP addresses and host names.
Microsoft wants to maintain its own domain name server for the microsoft.com domain. Similarly, Great Britain probably wants to administrate the auk top-level domain, and Australia probably wants to administrate the au domain, and so on, for this reason, the DNS system is a distributed database. Microsoft is completely responsible for dealing with the name server for microsoft.com – it maintains the machines that implement its part of the DNS system, and Microsoft can change the database for its domain whenever it wants to because it owns its domain name servers.
Every domain has a domain name server somewhere that handles its requests, and there is a person maintaining the records in that DNS. This is one of the most amazing parts of the DNS system – it is completely distributed throughout the world on millions of machines administered by millions of people, yet it behaves like a single integrated database!
Structure Of Root Name Server Worldwide
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