Foreign Agent Considerations

The foreign agent plays a mostly passive role in Mobile IP registration. A foreign agent adds all registered mobile nodes to its visitor table. It relays registration requests between mobile nodes and home agents, and, when it provides the care-of address, de-encapsulates datagrams for delivery to the mobile node. It also sends periodic agent advertisement messages to advertise its presence.

If reverse tunnels are supported, the foreign agent establishes appropriate routes to reverse tunnel all the data packets from the mobile node for a correspondent node. A foreign agent that supports reverse tunnels advertises that the reverse tunnel is supported for registration. Given the local policy, the foreign agent can deny a registration request when the reverse tunnel flag is not set. Also, the foreign agent can only distinguish two different mobile nodes with the same IP address when the mobile nodes visit on two different advertising interfaces.