In an open network computing environment, a work station cannot be trusted to identify its users correctly to network services. Kerberos provides an alternative approach whereby a trusted third-party authentication service is used to verify user's identities. This paper gives an overview of the Kerberos authentication protocol framework. The paper describes the protocols used by clients, servers and Kerberos to achieve authentication. It also describes the management and replication of database required. Kerberos is a computer network authentication protocol, which allows nodes communicating over a non-secure network to provide their identity to one another in a secure manner. It provides mutual authentication - both the user and the server verify each other's identity.