DNS is a service that takes the user-friendly names of the Internet and looks up their associated IP addresses. Active Directory uses DNS in the same way, looking up servers and services for users and applications. Because DNS is a hierarchical naming system, all Internet names exist within one of many available namespaces. One particularly familiar root namespace is the .com domain. The purpose of this hierarchy is to ensure that all names within a given namespace are unique. This way, when you connect to Microsoft.com, you know that you are connecting to the Microsoft.com owned by Microsoft, and not a Microsoft.com owned by some other company. Another function of DNS is to send you an IP address based on the service you want, rather than the machine name you want. Say that you send e-mail to an address in another company. Your mail server doesn t have to know the host name of the destination mail server to get its IP address. Instead, it asks DNS, Who is the mail server for that domain? DNS answers with an IP address, and your e-mail is sent.

Within your enterprise, DNS operates in much the same way; looking up IPs and helping people get access to the resources they need. On your network, there are many different servers and services. Fortunately, dynamic update allows your servers to update DNS tables on their own, advertising their services automatically as you install them and move them...