Solicited-node multicast address
A solicited-node multicast address is an IPv6 multicast address used by the Neighbor Discovery Protocol to determine the link layer address associated with a given IPv6 address, which is also used to check if an address is already being used by the local-link or not, through a process called DAD (Duplicate Address Detection). The solicited-node multicast addresses are generated from the host's IPv6 unicast or anycast address, and each interface must have a solicited-node multicast address associated with it.
A solicited-node address is created by taking the least-significant 24 bits of an unicast or anycast address and appending them to the prefix ff02::1:ff00:0/104.[1]
Example
Assume a host with an unicast/anycast IPv6 address of 2001:db8::2aa:ff:fe28:9c5a. Its solicited-node multicast address will be ff02::1:ff28:9c5a.
2001:db8::2aa:ff:fe28:9c5a IPv6 unicast/anycast address (compressed notation) 2001:0db8:0000:0000:02aa:00ff:fe28:9c5a IPv6 unicast/anycast address (uncompressed notation) -- ---- The least-significant 24 bits ff02::1:ff00:0/104 Solicited-node multicast address prefix (compressed notation) ff02:0000:0000:0000:0000:0001:ff00:0000/104 Solicited-node multicast address prefix (uncompressed notation) ---- ---- ---- ---- ---- ---- -- The most-significant 104 bits ff02:0000:0000:0000:0000:0001:ff28:9c5a Solicited-node multicast address (uncompressed notation) ff02::1:ff28:9c5a Solicited-node multicast address (compressed notation)
Solicited-node multicast MAC address
A solicited-node multicast MAC address is an
It is created by taking the least-significant 24 bits of a solicited-node multicast address and appending them to the prefix 33:33:FF:xx:xx:xx.[2]
Example
Assume a host with a solicited-node multicast address of ff02::1:ff28:9c5a. Its solicited-node multicast MAC address will be 33:33:FF:28:9C:5A.
ff02::1:ff28:9c5a Solicited-node multicast address -- ---- The least-significant 24 bits 33:33:FF:xx:xx:xx Solicited-node multicast MAC address prefix 33:33:FF:28:9C:5A Solicited-node multicast MAC address -- -- -- The least-significant 24 bits
Efficiency compared to IPv4 and ARP
Solicited-node multicast addresses are used with IPv6 neighbor discovery to provide the same function as the
Since a solicited-node multicast address is a function of the last 24 bits of an IPv6 unicast/anycast address, the number of hosts that are subscribed to each solicited-node multicast address is very small. This number would typically be one, but there could be a few because the mapping function is not a 1:1 mapping, like for example if the same host bear the same last 24 bits of their IPv6 address (2001:db8:1::55 and 2001:db8:2::55 has the same solicited-node multicast address). This means that a host should not need to be interrupted as often to neighbor solicitation requests, compared to ARP in IPv4.
References
- . Updated by: RFC 5952, RFC 6052, RFC 7136, RFC 7346, RFC 7371, RFC 8064.
- ^ "IPv6 Real-Time Usage of IEEE 802.16: Problem Statement". www.ietf.org. Retrieved 2024-02-20.