Router redirection
With multiple routers on a VLAN, if the default (first-hop) router for an IPv6-enabled VLAN on the switch determines that there is a better first-hop router for reaching a given remote destination, the default router can redirect the switch to use that other router as the default one. For further information on routing IPv6 traffic, see the documentation provided for the IPv6 router.
For related information, see RFC 2461: "Neighbor Discovery for IP Version 6."