Solicited Node Multicast

The solicited node multicast address is used by NDP instead of using broadcast

Solicited Node Multicast

Every time we configure an IPv6 unicast address on an interface, the interface also joins a solicited-node multicast group.

The IP of the group can vary, but it will always start with ff02::1:ff. It selects the last 24-bits of the address based on the unicast address on the interface.

The IPv6 device takes the last 24-bits of the unicast address and uses them as the last 24-bits of the solicited-node multicast address.

By doing this, any device that knows a router’s IP can send a multicast message to it. Why would we want to do that?

Think about learning a MAC to IPv6 binding. In this case, a device knows the IP, but not the MAC. It can easily take the last 24-bits of the IP address and use them to work out what the solicited-node multicast address is.

It can then multicast a Neighbour Solicitation message to this group. Remember, IPv6 does not use broadcast.