Network access server

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.

The above translates into different implementations for different uses. Here are some examples.

Although not required, NASs are almost exclusively used with (AAA) servers. Of the AAA protocols available, RADIUS tends to be the most widely used. The base protocol extends RADIUS services by providing error handling and inter-domain communications. This protocol is used in networks like the IP Multimedia Subsystem (IMS).

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