As you learned in Chapter 2, authentication is the process by which a computer validates the identity of a user or another computer. Authentication is a core functionality of any network operating system, including Windows Server 2003. Windows Server 2003 actually supports several complete authentication protocols: LAN Manager, NT LAN Manager Versions 1 and 2, and Kerberos. In this chapter, I'll introduce you to the two main types of protocols, explain how they're used and configured, and discuss why you might want to use one over the other.