Mobile IP uses which mechanism to maintain session continuity?

Concept: Mobile IP keeps a mobile node reachable at a single permanent home address while it roams across different networks. It relies on a Home Agent (HA) on the home network and a Foreign Agent (FA) or co-located care-of address on the visited network; the mobile node registers its current care-of address (CoA) with its home agent whenever it moves.

Application: Applying this to the mobile node's movement:

1. The mobile node moves to a foreign network and obtains a care-of address there (via the foreign agent or another local mechanism).

2. It sends a registration message to its home agent, binding its permanent home address to this new care-of address.

3. The home agent intercepts datagrams addressed to the mobile node's home address and encapsulates each one inside an outer IP packet addressed to the current care-of address — this is IP tunneling.

4. The tunnel endpoint decapsulates the packet and delivers the original datagram to the mobile node at its present location.

5. When the node moves again and re-registers a new care-of address, the home agent tears down the old tunnel and dynamically establishes a new one to the updated location, so the session continues without interruption from the correspondent host's point of view.

Cross-check: None of the other mechanisms redirect traffic toward a node's changing point of attachment: filtering packets against rule sets controls access, not location; switching between proxy servers changes which intermediary relays a request, not where the destination physically is; and compressing routing-table entries only shrinks table size. Only repeatedly re-establishing a tunnel to the node's latest care-of address preserves an ongoing session across moves — the mechanism offered as "Dynamic tunneling".