A network access server (NAS) is a single point of access to a remote resource.
A NAS concentrates dial-in and dial-out user communications. An access server may have a mixture of analog and digital interfaces and support hundreds of simultaneous users. A NAS consists of a communications processor that connects asynchronous devices to a LAN or WAN through network and terminal emulation software. It performs both synchronous and asynchronous routing of supported protocols.
The NAS is meant to act as a gateway to guard access to a protected resource. This can be anything from a telephone network, to printers, to the Internet. A client connects to the NAS. The NAS then connects to another resource asking whether the client's supplied credentials are valid. Based on that answer the NAS then allows or disallows access to the protected resource.
NASs are almost exclusively used with authentication, authorization, and accounting (AAA) servers. Of the AAA protocols available, RADIUS tends to be the most widely used.
Every time a user tries to obtain network access, that request is made to a Network Access Server or NAS. These NASes are commonly located at an ISP, and provide dial-up access or broadband services. The NAS may also be a wireless Access Point (AP), at an Internet cafe or airport.
The role of the NAS is to act as the gateway between the user and the RADIUS server.[1]
