DNS defined

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

DNS defined

DNS is an abbreviation for Domain Name System, a system for naming computers and network services that is organized into a hierarchy of domains. DNS naming is used in TCP/IP networks, such as the Internet, to locate computers and services through user-friendly names. When a user enters a DNS name in an application, DNS services can resolve the name to other information associated with the name, such as an IP address.

For example, most users prefer a friendly name such as example.microsoft.com to locate a computer such as a mail or Web server on a network. A friendly name can be easier to learn and remember. However, computers communicate over a network by using numeric addresses. To make the use of network resources easier, name systems such as DNS provide a way to map the user-friendly name for a computer or service to its numeric address.

The following figure shows a basic use of DNS, which is finding the IP address of a computer based on its name.

Example of DNS forward lookup

In this example, a client computer queries a DNS server, asking for the IP address of a computer configured to use host-a.example.microsoft.com as its DNS domain name. Because the DNS server is able to answer the query based on its local database, it replies with an answer containing the requested information, which is a host (A) resource record that contains the IP address information for host-a.example.microsoft.com.

The example shows a simple DNS query between a single client and DNS server. In practice, DNS queries can be more involved than this and include additional steps not shown here. For more information, see How DNS query works.


  • For additional background information about other DNS concepts, see Understanding DNS.