To what multicast address are NDP Neighbor Solicitation (NS) messages sent?

Neighbor Solicitation (NS) messages in the context of the Neighbor Discovery Protocol (NDP) for IPv6 are specifically sent to the multicast address FF02::1, which is the all-nodes multicast address. This address allows a node to reach all nodes on the local link.

When a device needs to determine the link-layer address of another device on the same local subnet, it broadcasts an NS message to this multicast address. All nodes that receive the message can process it and respond if they are the target of the solicitation. This facilitates the resolution of link-layer addresses, which is vital for IPv6 communication on a local network.

The other options refer to different multicast addresses that serve other purposes in IPv6 networking. For example, FF02::2 is used for all routers on the local network segment. Since the question specifically asks about Neighbor Solicitation messages, the multicast address corresponding to this function is clearly FF02::1, making it the correct answer.