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9-2 User’s Reference Guide

Transit Internetwork

Virtual Private Network

Logical

Equivalent

Unlike the phone company, private and public computer networks can use more than one protocol to carry your information over the wires. Two such protocols are in common use for tunnelling, Point-to-Point Tunnelling Protocol (PPTP) and Ascend Tunnel Management Protocol (ATMP). The Netopia Router can use either one.

■Point-to-Point Tunneling Protocol (PPTP) is an extension of Point-to-Point Protocol (PPP) and uses a client and server model. Netopia’s PPTP implementation is compatible with Microsoft’s and can function as either the client (PAC) or the server (PNS). As a client, a Netopia R-series router can provide all users on a LAN with secure access over the Internet to the resources of another LAN by setting up a tunnel with a Windows NT server running Remote Access Services (RAS) or with another Netopia Router. As a server, a Netopia R-series router can provide remote users a secure connection to the resources of the LAN over a dial-up, cable, DSL, or any other type of Internet access. Because PPTP can create a VPN tunnel using the Dial-Up Networking (DUN) (see “Dial-Up Networking for VPN” on page 9-10)utility built into Windows 95, 98, or NT, no additional client software is required.

■Ascend Tunnel Management Protocol (ATMP) is the protocol that is implemented in many Ascend routers. ATMP is a simple protocol for connecting nodes and/or networks together over the Internet via a tunnel. ATMP encapsulates IP or other user data without PPP headers within General Routing Encapsulation (GRE) protocol over IP. ATMP is more efficient than PPTP for network-to-network tunnels.

When used to initiate the tunnelled connection, the Netopia Router is called a PPTP Access Concentrator (PAC, in PPTP language), or a foreign agent (in ATMP language). When used to answer the tunnelled connection, the Netopia Router is called a PPTP Network Server (PNS, in PPTP language) or a home agent (in ATMP language).

In either case, the Netopia Router wraps, or encapsulates, information that one end of the tunnel exchanges with the other, in a wrapper called General Routing Encapsulation (GRE), at one end of the tunnel, and unwraps, or decapsulates, it at the other end.