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Chapter 10. Mobile IP > Reverse Tunneling

10.3. Reverse Tunneling

In some environments, routers examine not only the destination IP address, but also the source IP address, when making a decision about how to forward a packet. This processing allows the router to make some attempts to filter out spoofed packets. However, in mobile IP, the source IP address of a packet sent by the mobile node may be unexpected within the context of the foreign network and may be discarded by a router. This undesirable problem is overcome by tunneling packets from the mobile node back to the home agent, and having the home agent forward them from there. This process, known as reverse tunneling, effectively reverses the path of packets that are sent to the mobile node.

Ideally, reverse tunnels would be established by the mobile nodes; however, this only works if the mobile node is colocated with the care-of address. If a foreign agent is used to provide the care-of address, the reverse tunnel is managed by the foreign agent. There are two options:


  

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