IPv6 default router preferences

The command ipv6 nd ra router-preference {high | medium | low} provides an extension to the Neighbor Discovery Router Advertisement messages for communicating default router preferences from routers to hosts. The extension improves the ability of hosts to pick the appropriate router for an off-link destination. In network topologies, where the host has multiple routers on its Default Router list, the choice of router for an off-link destination is critical for making the communication more efficient. For example, one router may provide much better performance than another for a destination while choosing a wrong router may result in failure to communicate.