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A DNS server provides 'name resolution service' which means that DNS servers resolve names into IP addresses or vice versa. DNS servers are also called name servers. Every computer on the Internet has a unique IP addresses (a series of four decimal numbers from 0 to 255 separated by dots). A DNS server is used to 'resolve' a name into an IP address (or vice versa).

A local DNS server which performs domain name lookup is usually located on the network to which your computer is attached. If you are using an Internet Service Provider (ISP), your DNS server is at your ISP. If you are using the network at your college or your office, you probably have a local DNS server somewhere near you at the server room.

When you are on your computer, you will at some point type in the name of a computer somewhere on your local network or on the Internet. Your resolver software running on your computer looks in its local cache. If it does not find an answer, it sends that computer name to a DNS server. Whenever your DNS server runs into a name it doesn't recognize (something it hasn't looked up yet), it goes to a pre-configured list of root DNS servers to look it up. The local DNS server will send a query to a root server. The root server will respond with a list of servers who have been delegated the responsibility of resolving the requested domain name. Your local DNS server then sends another query to those 'authoritative' servers, and usually gets an answer.

Whenver a DNS server is responsible for a domain, its referred to as the authoritative server because it is the authority on that domain. To decrease the workload, DNS servers also cache answers (and negative answers) as does the local resolver on the client host. Entries in both the DNS server cache and your computer's resolver cache time out and are removed from the cache eventually. DNS servers who provide answers but are not responsible for a domain are called non-authoritative servers.

Your local DNS administrator is responsible for putting the names and IP addresses of all the computers and devices on your network into the local DNS server. This is what makes that server an authoritative server. The DNS administrator is also responsible for making sure your domain name is registered with an accredited Internet domain name registrar (Internet domains only).

NOTE: A DNS 'domain' is an entirely different concept from a Windows NT 'domain' or a Unix NIS/NIS+ domain. These different domains have nothing to do with each other. Even an Windows Active Directory 'domain' is different and is NOT the same thing as DNS. Active Directory stores AD domain information in DNS in special folders with names that start with an underscore. The underscore character is illegal in DNS domain names.


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