IPv6 router advertisement preference improves the ability of IPv6 hosts to select an appropriate router for a remote destination.
An IPv6 host uses the preference value in an advertisement to determine the default router to use to reach a destination. A preference value can be low, medium, or high.
device# configuration terminal
device(config)# interface ethernet 0/1
device(conf-if-eth-0/1)# ipv6 nd router-preference medium