About Cluster Active-Active Routing for IPv6 Addresses

With cluster active-active routing two cluster peers act as forwarding proxies for each other’s destination MAC addresses. This works for IPv4 as well as IPv6 traffic.

But if the two routers try to communicate with each other, packets may not route correctly on the network.

In particular, in case of the Neighbor Discovery function IPv6 uses ICMPv6 packets (instead of L2 ARP packets, as in the case of IPv4). Therefore, when one cluster node PN-0 sends a Neighbor Solicitation message to its peer, the other node PN-1 responds with a Neighbor Advertisement message with the destination IP address of the requester (PN-0). When transmitted by PN-1 the Neighbor Advertisement message will have both the destination IP and the destination MAC address of the peer PN-0. Since both nodes act as forwarding proxies for each other, the destination MAC address of the peer will be matched by the hardware of PN-1 and the packet will be routed (back to the CPU of PN-1) without reaching its correct destination (i.e., PN-0). This behavior would therefore break the Neighbor Discovery function of IPv6.

To obviate this problem, NetVisor OS adds a host route in hardware that matches the link-local IPv6 address of the cluster peer. 

This host route entry properly routes packets such as Neighbor Advertisement messages to their destination.