IPv6 Solicited-Node Multicast

Compute solicited-node multicast addresses from IPv6 unicast for Neighbor Discovery Protocol

Purpose: Solicited-node multicast addresses enable efficient IPv6 Neighbor Discovery by targeting specific network nodes instead of all nodes.
Format: ff02::1:ffXX:XXXX where XX:XXXX are the last 24 bits of the unicast address.
Usage: Used in NDP Neighbor Solicitation messages for address resolution and duplicate address detection.

Quick Examples
Enter any valid IPv6 unicast address in any format (compressed or full)

Solicited-Node Calculation

Unicast Address
2001:0db8:0000:0000:0000:0000:1234:5678
Solicited-Node Multicast
ff02:0000:0000:0000:0000:0001:ff45:5678

Calculation Steps

1
1. Take the last 24 bits of the unicast address: 1234:5678 → 45678
2
2. Prepend the solicited-node multicast prefix: ff02::1:ff
3
3. Insert the 24 bits: ff02::1:ff45:5678
4
4. Result: ff02:0000:0000:0000:0000:0001:ff45:5678

Technical Details

Last 24 bits: 45678
Multicast prefix: ff02::1:ff
Address scope: Link-local multicast (ff02)
Multicast flag: Well-known (0)

What is NDP?

Neighbor Discovery Protocol (NDP) is IPv6's equivalent to IPv4's ARP. It's used for address resolution, router discovery, and duplicate address detection on local network segments.

Why Solicited-Node?

Instead of broadcasting to all nodes (like ARP), IPv6 uses solicited-node multicast to efficiently target only nodes that might have the specific address, reducing network traffic.

Address Collision

Multiple unicast addresses can map to the same solicited-node multicast address. This is acceptable since nodes will ignore solicitations for addresses they don't own.

Multicast Membership

Every IPv6 node automatically joins the solicited-node multicast group for each of its unicast addresses, enabling it to receive neighbor solicitations.