(Domain Name System) A system for converting host names and domain names into IP addresses on the Internet or on local networks that use the TCP/IP protocol. For example, when a Web site address is given to the DNS either by typing a URL in a browser or behind the scenes from one application to another, DNS servers return the IP address of the server associated with that name.
In this hypothetical example, www.company.com would be converted into the IP address 204.0.8.51. Without DNS, you would have to type the four numbers and dots into your browser to retrieve the Web site, which, of course, you can do. Try finding the IP of a favorite Web site and type in the dotted number instead of the domain name! See IP address.
A Hierarchy of Servers
The DNS system is a hierarchy of database servers that start with the root servers for all the top level domains (.com, .net, etc.). The root servers point to the "authoritative" servers located in ISPs and in companies that turn the host names into IP addresses; the process known as "name resolution." Using the example www.company.com, COMPANY.COM is the domain name, and WWW is the host name. The domain name is the organization's identity on the Web, and the host name is the name of the Web server within that domain (see WWW). See DNS records, zone file, reverse DNS, DDNS, HOSTS file, mDNS, ping, root server and WINS.
Turning a URL in a Web browser into an IP address can take numerous queries. This is a simplified diagram because the original requester actually talks to each name server in turn, and there can be more name servers in between. A request can also be satisfied from a DNS cache along the way and not need to reach the authoritative server.
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