A server that is used to resolve host names or fully qualified domain names (FQDNs) into IP addresses on a TCP/IP network. A DNS server, which is also called a name server, accomplishes this by accepting DNS queries from DNS clients and by performing DNS queries among other DNS servers, depending on how the servers have been configured.
Microsoft Windows 2000 Server can function as a DNS server and is managed using an administrative tool, DNS console, which is a snap-in for the Microsoft Management Console (MMC). Windows NT Server can also function as a DNS server and is managed using an administrative tool, DNS Manager.
Windows 2000 DNS servers include additional capabilities not supported by their Windows NT counterparts, such as dynamic update, which allows DNS servers to update their DNS database files automatically using Dynamic Host Configuration Protocol (DHCP).
Another feature of Windows 2000 is tight integration of DNS and Active Directory. For example, when a Windows 2000 client needs to locate a Windows 2000 domain controller, the NetLogon service uses the DNS server’s support for the SRV (service) resource record to allow registration of domain controllers in the local DNS namespace.
DNS servers can provide a simple means of load balancing connections to heavily used file or application servers such as Internet Information Services (IIS). The method is called Round Robin DNS, and it works as its name implies. Say you have three Web servers hosting identical content and you want to load balance incoming Hypertext Transfer Protocol (HTTP) requests across these servers. You can create three A records in the DNS zone file, each with the same host name but different IP addresses, one IP address for each Web server, as shown in this example:
When a DNS client requests resolution of the name www.northwind.microsoft.com into its IP address, the DNS server returns all three IP addresses (.33, .34, .35), and the client chooses the first address (.33) and sends the HTTP request to the Web server associated with this address. The next time the DNS server receives the same name resolution request, it rotates the IP addresses in round-robin fashion (.34, .35, .33) and returns them to the client. The client picks the first address, which is now .34. This way, each DNS name resolution returns a different IP address and the load is balanced between the Web servers.
The drawback to using Round Robin DNS is that if a server fails, DNS will continue to return the address of the failed server.