DNS is the Domain Name Service or System. When a computer wishes to communicate with another, using the TCP/IP protocol, it needs to know its IP address. We humans prefer to use names so we specify to the computer that we want to connect to www.microsoft.com, say. The computer needs some way to translate that name to an IP Address, and that is the function of the DNS.

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How does DNS work?

Every Domain must have a Name Server specified (in fact, by convention, there should be at least two). Now taking the above example, www.microsoft.com is part of the microsoft.com domain, which is itself part of the com domain. The com domain is in turn part of the root domain. And just as the microsoft.com domain has a name server which knows all about its domain, so the com domain has a name server which knows all about its domain. In particular it knows where to find the microsoft.com name servers. Similarly, the root name server (rather, servers, for there are about 12 of them) knows where to find the com domain name servers.

Written down, this may seem a bit complicated but it is in fact very simple. If our name server doesn't know the IP address of www.microsoft.com, it refers the request to one of the root servers, which refers it to the com domain server, which refers it to the microsoft.com name server, which sends the answer back. Our name server passes it back your computer which can then send its message to microsoft and start pulling in that 50Mb upgrade to Internet Explorer.

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