How Mobile IP Works
ByIn brief, Mobile IP routing works as follows. Packets destined to a mobile node are routed first to its home network; a network identified by the network prefix of the mobile node’s (permanent) home address. At the home network, the mobile node’s home agent intercepts such packets and tunnels them to the mobile node’s most recently reported care-of address. At the endpoint of the tunnel, the inner packets are de-capsulated and delivered to the mobile node. In the reverse direction, packets sourced by mobile nodes are routed to their destination using standard IP routing mechanisms.
Before getting into more detail, it is a good idea to frame the discussion by setting some terminology. Mobile IP introduces the following functional entities:
Mobile node (MN): A host or router that changes its point of attachment from one network or sub-network to another, without changing its IP address. A mobile node can continue to communicate with other Internet nodes at any location using its (constant) IP address.
Home agent (HA): A router on a mobile node’s home network which delivers datagram’s to departed mobile nodes, and maintains current location information for each.
Foreign agent (FA): A router on a mobile node’s visited network which cooperates with the home agent to complete the delivery of datagram’s to the mobile node while it is away from home.
A mobile node has a home address, which is a long-term IP address on its home network. When away from its home network, a care-of address is associated with the mobile node and reflects the mobile node’s current point of attachment. The mobile node uses its home address as the source address of all IP datagram’s it sends, except where otherwise required for certain registration request datagram’s.