MobileIPv6 has many optimizations relying on some minimal MobileIPv6 processing done by the correspondent node. During the course of the IETF standards work for IPv6 and MobileIP, the requirement that any IPv6 correspondent must implement some MobileIP functionality was dropped from required to optional. The previous sections explain MobileIPv6 with the assumption that the correspondent node is MobileIPv6 aware. This section describes the differences when a correspondent node is not MobileIPv6 aware.
A mobileIP node implementation manages its interaction using a cache which includes a list of correspondent nodes, home agents, states of bindings, etc. This cache is also used to handle the case when some of its correspondent nodes are not implementing MobileIP.
A correspondent node that is not implementing mobileIPv6 does not understand or use the mobileIP messaging, such as binding updates, home address destination option and return routability messages.
Section 11.5.2 describes the process where the mobile node registers with the correspondent node by starting the return routability procedure, described in Section 11.8.2. Without prior knowledge of the correspondent node, the mobile node starts the return routability procedure by sending the Home test Init (HoTI) and Care-of Test Init (CoTI) messages to the correspondent node. When the correspondent node does not understand these mobileIP ...