Scalable support for transparent mobile host internetworking

One-line summary: Mobile IP is IP with an extra level of indirection.

Overview/Main Points

• Basic Mobile IP: Each mobile host (MH) has a home agent (HA) that acts as a location registry, maintaining the binding from the MH's home address and its foreign care-of-address. Each time the MH moves, this binding is updated. Correspondent hosts (CH's) address messages with the MH's home address; the HA forwards this message to the MH via IP tunneling or encapsulation. MH's gain their care-of-addresses by contacting a foreign agent; the foreign agent assigns the care-of-address and updates the MH's binding by contacting the HA. MD-5 checksums of messages + a secret key + a nonce are used to verify these updates.
• Location caching: Correspondent hosts or intermediate routers may cache MH's care-of-addresses. Explicit feedback messages from HA's must be used to both provide and invalidate these care-of-addresses; care-of-addresses have lifetimes that can help to purge old cached values.
• Foreign-agent handoff: When a MH changes its care-of-address, a forwarding pointer can be left at the old foreign agent so that in-flight messages are not dropped. (This is an extension to the basic mobile IP protocol; since messages are IP datagrams, it is alright to drop them.)
• Scalability: The mobile IP specification scales well. The home network/agent maintains bindings only for its own mobile hosts. Similarly, foreign networks/agents only need to accept and forward messages for MH's under their care. The rest of the internet does not need to maintain extra state, do extra work (except for the dog-leg delivery route), or be modified to behave correctly.

Relevance

Flaws

• The paper itself has little or no flaws; it accurately and clearly describes the Mobile IP spec. The basic Mobile IP's spec has the flaw of the dogleg route and the extra header overhead for IP encapsulation.