Solicited-Node Multicast Address ff02::1:ff00:0/104
Understand solicited-node multicast addresses in IPv6. Learn how ff02::1:ffXX:XXXX is derived from a unicast address for efficient neighbor discovery.
Detailed Explanation
Solicited-Node Multicast Addresses
A solicited-node multicast address has the prefix:
ff02:0000:0000:0000:0000:0001:ff00:0000/104
For a specific unicast address like 2001:db8::1234:5678, the solicited-node address is:
ff02::1:ff34:5678
How It Is Derived
The last 24 bits of the unicast address are appended to the fixed prefix ff02::1:ff:
- Take the unicast address:
2001:0db8:0000:0000:0000:0000:1234:5678 - Extract the last 24 bits:
34:5678 - Append to prefix:
ff02::1:ff+34:5678=ff02::1:ff34:5678
Why It Exists
In IPv4, ARP uses broadcast to resolve MAC addresses, which interrupts every host on the subnet. IPv6 replaces this with Neighbor Solicitation sent to the solicited-node multicast address. Since only hosts whose addresses share the same last 24 bits receive the message, network interruptions are drastically reduced.
Expanded Form
ff02:0000:0000:0000:0000:0001:ff34:5678
Every IPv6 unicast address automatically joins its corresponding solicited-node multicast group on each interface.
Use Case
Solicited-node multicast is fundamental to IPv6 Neighbor Discovery. It is used in Neighbor Solicitation messages for address resolution (replacing ARP), Duplicate Address Detection (DAD), and Network Unreachability Detection (NUD).