1. Mobile IP Neil Tang 11/12/2008
CS440 Computer Networks

2. Overview Mobility Problem Home/Foreign Agents
The Forwarding Procedure and Tunneling
Route Optimization
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3. Mobility Problem
Mobility Problem: a host previously connected to a network is attached to another network now.
A Trivial Solution: Get a new IP address using DHCP.
Problems Related to the DHCP Solution: What if there is a mobile node which might detach itself to a network and attach to another one very frequently?
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4. Home/Foreign Agents
Home Agent: a router in the home network of the mobile hosts.
Foreign Agent: a router in the network to which the mobile node is attached.
Both agents periodically announce their presence using advertisement messages
A mobile host will register with the foreign agent when it attach itself to a foreign network. The foreign agent will contacts its home agent providing its IP address as the care-of-address.
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5. The Forwarding Procedure
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6. Tunneling Home agent Foreign agent CS440 Computer Networks IP header,
Destination =
IP payload
Destination = R1 R2
Internetwork
Network 1
Network 2
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7. Mobile IP
The home agent will impersonate the mobile host using a technique called proxy ARP, in which a message including the IP address of the mobile host and the hardware address of the home agent will be broadcast to the home network.
How about the traffic in another direction?
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8. Route Optimization
The route for packet forwarding is suboptimal. The most extreme case is that the sender and the mobile node are in the same network. This is referred as triangle routing problem.
The home agent can send a binding update to the sender. Then the sender will store it in its cache and forward the packet to the foreign agent directly next time.
The foreign agent will send back a binding warning message to the sender when the mobile node leaves its network.
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