DNS is the naming service provided by the Internet for TCP/IP networks. DNS was developed so that machines on the network could be identified with common names instead of Internet addresses. DNS performs naming between hosts within your local administrative domain and across domain boundaries.
The collection of networked machines that use DNS are referred to as the DNS namespace. The DNS namespace can be divided into a hierarchy of domains. A DNS domain is a group of machines. Each domain is supported by two or more name servers, a principal server and one or more secondary servers. Each server implements DNS by running the in.named daemon. On the client's side, DNS is implemented through the “resolver.” The resolver's function is to resolve users' queries. The resolver queries a name server, which then returns either the requested information or a referral to another server.