TABLE OF CONTENTS When a mobile node attaches to a network, it must detect whether or not it has moved. There are several pieces of information which can be used to detect the movement of a node. The Mobile IPv6 specification talks about a basic movement detection method which uses Neighbor Unreachability Detection of a default router of a mobile node. As described in the Neighbor Discovery specification, an IPv6 node keeps a list of default routers on the attached network. If the routers become unreachable, it can be assumed that the node is attached to a different network.
When performing Neighbor Unreachability Detection for default routers, we need to take care of one thing. The Neighbor Unreachability Detection is done by sending a Neighbor Solicitation message to the target router. Usually, the address of the target router is a link-local address, since a normal Router Advertisement does not contain the global address of the router. A node usually does not know the global address of routers. However, a link-local address is unique only on a single link. This means that even if a mobile node moves from one network to another network, the mobile node may not be able to detect the unreachability of the default router if routers on the different links use the same link-local address. A mobile node needs to utilize other information as much as possible.
One of the other pieces of information which can be used for the unreachability detection is a global address...
