> IPv4 and NAT require maintaining a lot of state at critical intermediate routers. I'm sure we've all experienced (perhaps regularly) a NAT'ing router losing state because of a reboot, state tables overflowing, or similar hiccups.
As far as I can see, that state is not very important for the mobile IP design describe in the article. A router reboot or other hiccups are handled more or less the same way as an address change (there is a temporary connectivity loss, and when it's restored, you create a new mapping on the Y server between the existing connection, identified by the same old uuid, and the new external/internal addresses/ports of the client X).