Please implement the Router Advertisement Guard on switching and bridging.
More information:
https://tools.ietf.org/html/rfc6105
https://tools.ietf.org/html/rfc7113
http://forum.mikrotik.com/t/ipv6-router-advertisement-packet-filtering-in-switched-network/135848/1
This is an important security feature: https://www.google.com/search?q=IPv6+Router+Advertisement+Guard