5.5 Route Optimization 521
Binding Update message for de-registration from a mobile node but it does not have a corre-
sponding binding cache entry, it will reply to the mobile node with a Binding Acknowledgment
message with status code 133. When a mobile node which has returned home receives a Bind-
ing Acknowledgment message with status code 133, the mobile node should consider that the
acknowledgment message has been lost and complete the de-registration procedure.
A mobile node may de-register its address from its home agent even when it does not return
to home (for example, when the mobile node stops its mobility function on a foreign network).
In this case, a similar procedure is used to de-register the address. The Binding Update message
sent ...