5.2 Mobile IPv6 Overview

Mobile IPv6 adds the mobility function to IPv6. Mobile IPv6 is specified in [RFC3775] and [RFC3776]. An IPv6 host which supports the Mobile IPv6 function can move around the IPv6 Internet(*). The host which supports Mobile IPv6 can change its point of attachment to the IPv6 Internet whenever it wants. If a host does not support Mobile IPv6, all the existing connections on the host are terminated when it changes its point of attachment. A connection between two nodes is maintained by the pairing of the source address and the destination address. Since the IPv6 address of an IPv6 node is assigned based on the prefix of the network, the assigned address on a given network becomes invalid when the host leaves that network and attaches itself to another network. The reason for this problem came from the nature of IP addresses. An IP address has two meanings, one is the identifier of the node, and the other is the location information of the node. It would not be a big problem as long as IP nodes do not move around the Internet frequently, because, in that case, the location information would not change frequently and we could use location information as the identifier of a node. However, recent progress of communication technologies and small computers made it possible for IP nodes to move around. It is getting harder and harder to treat location information as an identifier, because the location information frequently changes.