The current Mobile IPv6 and Network Mobility (NEMO) specifications support IPv6 only. This specification extends those standards to allow the registration of IPv4 addresses and prefixes, respectively, and the transport of both IPv4 and IPv6 packets over the tunnel to the home agent. This specification also allows the mobile node to roam over both IPv6 and IPv4, including the case where Network Address Translation is present on the path between the mobile node and its home agent. [STANDARDS-TRACK]