MCI WorldCom Advanced Networks The Network Access Server is the initial entry point to a network for the majority of users of network services. It is the first device in the network to provide services to an end user, and acts as a gateway for all further services. As such, its importance to users and ser- vice providers alike is paramount. However, the concept of a Network Access Server has grown up over the years without being formally defined or analyzed. This document offers a framework for the defini- tion and analysis of a modern Network Access Server.