SolicitedNode

SolicitedNode refers to the solicited-node multicast mechanism used in IPv6 Neighbor Discovery. It designates a special multicast address associated with a specific unicast or anycast IPv6 address. The solicited-node address is used to reach the intended neighbor on a local link for address resolution and related Neighbor Discovery operations, while limiting unnecessary traffic on the network.

The solicited-node multicast address is formed by taking the last 24 bits of the target IPv6 address and inserting them into the prefix ff02::1:ffXX:XXXX, where XX:XXXX represent those last 24 bits in hexadecimal. This address is scoped to the local link (link-local multicast) and is not routable beyond the immediate network segment.

Usage in Neighbor Discovery: When a node needs to determine the link-layer address corresponding to an IPv6 address, it sends a Neighbor Solicitation message to the target’s solicited-node multicast address. The node that owns the target IPv6 address responds with a Neighbor Advertisement containing the necessary link-layer information. This mechanism reduces broadcast load by confining queries to a smaller multicast group rather than to all nodes on the link. It also supports the Duplicate Address Detection process during address autoconfiguration.

Scope and security: The solicited-node multicast address is restricted to the local link, so requests do not traverse routers. However, Neighbor Discovery traffic can be abused in some attack scenarios, such as spoofing or amplification. Mitigations include ND rate limiting, appropriate firewall rules, and defense-in-depth measures on the local network.

See also: IPv6, Neighbor Discovery Protocol, Multicast, Duplicate Address Detection.