As a Mobile Node roams from network to network, it is essential that binding update messages are transmitted to that node’s Home Agent and Correspondent Nodes as soon as possible, in order to facilitate a fast handoff. Mobile Nodes therefore cannot rely on the soft state timeout mechanism used in binding caches to refresh stale bindings maintained by Correspondent Nodes (typical binding lifetimes are of the order of minutes). An additional data structure, the binding update list, is therefore kept by Mobile Nodes, which maintains state on any Correspondent Nodes or Home Agents.

The binding update list contains one entry for every Correspondent Node or Home Agent to which a binding update has been sent. List entries contain information such as the address and time at which the binding update was transmitted, the state of any unacknowledged updates, the lifetime of the binding, a Home Agent flag, and the sequence number of the last transmission. Binding list entries are garbage collected from the binding update list as the respective binding expires.

The maintenance of the binding update list allows for significantly faster handoff performance. After a handoff has been detected and autoconfiguration has been completed, the binding update list is traversed, and a binding update message transmitted to every node contained within the list, thereby updating the binding caches of any active Correspondent Nodes.