User`s guide

Configuring IP Routing
Ascend Tunnel Management Protocol (ATMP)
Pipeline User’s Guide Preliminary January 30, 1998 2-37
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Ascend Tunnel Management Protocol (ATMP)
Virtual private networks can include the Pipeline as a Home Agent ATMP end
point in implementations where the Pipeline operates in router mode.
Using a Pipeline in a virtual private network
Virtual private networks provide low-cost remote access to private LANs via the
Internet. The tunnel to the private corporate network might be from an ISP,
enabling mobile nodes to dial into a corporate network, or between two corporate
networks that access one another through a low-cost Internet connection.
Ascend Tunnel Management Protocol (ATMP) uses a UDP/IP session between
two units to build a tunnel for encapsulated packets. It puts the packets in
standard Generic Routing Encapsulation (GRE), as described in RFC 1701. In
effect, the tunnel collapses the Internet cloud and provides what looks like direct
access to a home network. The packets must be routed (IPX or IP).
Foreign and home agents
ATMP tunnels work between two Ascend units. One of the units acts as a foreign
agent (typically a local ISP) and one as a home agent (which can access the home
network). A mobile node dials into the foreign agent, which establishes a cross-
Internet IP session with the home agent. The foreign agent then requests an
ATMP tunnel on top of the IP session. The foreign agent must use RADIUS to
authenticate mobile nodes dial-ins.
The home agent is the terminating part of the tunnel, where most of the ATMP
intelligence resides. This agent must be able to communicate with the home
network (the destination network for mobile nodes) through a direct connection,
another router, or across a nailed connection.
The home agent may communicate with the home network through a direct
connection, another router, or across a nailed connection. When it relies on