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What Is DNS?

Applies To: Windows Server 2008

Domain Name System (DNS) is one of the industry-standard suite of protocols that comprise TCP/IP. Windows Server® 2008 DNS is implemented using two software components: the DNS server and the DNS client (or resolver). Both components are run as background service applications.

Network resources are identified by numeric IP addresses, but these IP addresses are difficult for network users to remember. The DNS database contains records that map user-friendly alphanumeric names for network resources to the IP address used by those resources for communication. In this way, DNS acts as a mnemonic device, making network resources easier to remember for network users.

The Windows Server 2008 DNS Server and DNS Client services use the DNS protocol that is included in the TCP/IP protocol suite. DNS is part of the application layer of the TCP/IP reference model.

DNS in TCP/IP

DNS in TCP/IP

For more information and to view logical diagrams illustrating how DNS fits with other Windows Server 2008 technologies, see the topics in How DNS Works.

By default, Windows Server 2008 DNS is used for all name resolution in a Windows Server 2008 network. In the most typical scenario, when a Windows Server 2008 network user specifies the name of a network host or an internet DNS domain name, the DNS Client service running on the Windows Server 2008 computer of the user contacts a DNS server to resolve the name to an IP address.

Windows Server 2008 Active Directory Domain Services (AD DS) uses DNS as its domain controller location mechanism. When any of the principal Active Directory operations is performed, such as authentication, updating, or searching, computers running Windows Server 2008 use DNS to locate Active Directory domain controllers and these domain controllers use DNS to locate each other. For example, when a network user with an Active Directory user account logs in to an Active Directory domain, the user’s computer uses DNS to locate a domain controller for the Active Directory domain to which the user wants to log in. For more information about integrating DNS and Active Directory, see How DNS Works.

The earlier method of name resolution for a Windows network was Windows Internet Name Service (WINS). DNS is different from WINS in that DNS is a hierarchical namespace and WINS is a flat namespace. Clients and applications that rely on NetBIOS names continue to use WINS for name resolution. Because Windows Server 2008 DNS is WINS-aware, a combination of both DNS and WINS can be used in a mixed environment to achieve maximum efficiency in locating various network services and resources.

For Windows Server 2008 DNS, the DHCP service provides default support to register and update information for legacy DHCP clients in DNS zones. Legacy clients typically include other Microsoft TCP/IP client computers that were released prior to Windows 2000. The Windows Server 2008 DNS-DHCP integration enables a DHCP client that is unable to dynamically update DNS resource records directly to have this information updated in DNS forward and reverse lookup zones by the DHCP server.

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