The IP-level mobility support protocol for host mobility is Mobile IPv6 and is specified in [RFC 3775]. The current version, Mobile IPv6, has evolved from the IPv4 version. Figure B-1 depicts the generic environment for Mobile IPv6.
Figure B-1 - Mobile IP Operation The basic operation is that a Mobile Node moves from its Home Network to a Foreign Network. When this occurs the Mobile Node interacts with its Home Agent (HA), which has its permanent Home Address (HoA), to provide it with its new address, called a Care-Of Address (CoA) associated with an Access Router, on a Foreign Network. The interaction (1) occurs with a Binding Update and Binding Acknowledgement Exchange. At this point a Correspondent Node (CN) can communicate with the Mobile Node through the Home Agent, essentially by tunneling traffic through the Home Agent (2). One this has occurred, IPv6 has a feature called route optimization such that the Binding Update and Binding Acknowledgement may be exchanged between the Mobile Node and the Correspondent Node to enable direct communications (3) between the Correspondent Node and Mobile Node rather than tunneling.