Mobile IPv6 (MIPv6) is a protocol developed as a subset of Internet Protocol version 6 (IPv6) to support mobile connections. MIPv6 is an update of the IETF (Internet Engineering Task Force) Mobile IP standard (RFC 2002) designed to authenticate mobile devices (known as mobile nodes) using IPv6 addresses.
In traditional IP routing, IP addresses represent a topology. Routing mechanisms rely on the assumption that each network node will always have the same point of attachment to the Internet, and that each node's IP address identifies the network link where it is connected. In this routing scheme, if you disconnect a mobile device from the Internet and want to reconnect through a different network, you have to configure the device with a new IP address, and the appropriate netmask and default router. Otherwise, routing protocols have no means of delivering datagrams (packets), because the device's network address doesn't contain the necessary information about the node's network point of attachment to the Internet.
MIPv6 allows a mobile node to transparently maintain connections while moving from one subnet to another. Each device is identified by its home address although it may be connecting to through another network. When connecting through a foreign network, a mobile device sends its location information to a home agent, which intercepts packets intended for the device and tunnels them to the current location.
The IETF has since proposed an enhancement to MIPv6, Hierarchical MIPv6 (HMIPv6).