A general name for a server at an Internet service provider (ISP) that a dial-up client connects to in order to establish a Point-to-Point Protocol (PPP) connection. Network access servers (NAS’s) provide dial-up entry points for PPP clients to connect to the Internet.
They can also be used to tunnel through the Internet to establish a virtual private network (VPN) using the Point-to-Point Tunneling Protocol (PPTP). Another name for a NAS is a point of presence (POP) server.
The NAS is typically responsible for authenticating the dial-up client’s credentials and negotiating flow control and error correction. NAS’s can be general-purpose server computers running specialized NAS software such as Internet Connection Services for Microsoft Remote Access Service (RAS), or they can simply be routers with support for a built-in PPP connection, which are often called access servers.
Graphic N-3. Network access server (NAS).