Multicast All Nodes Address ff02::1
Expand the IPv6 multicast all-nodes address ff02::1. Learn about multicast scope levels and how ff02::1 is used in neighbor discovery.
Multicast
Detailed Explanation
All-Nodes Multicast Address
The address ff02::1 expands to:
ff02:0000:0000:0000:0000:0000:0000:0001
Multicast Address Structure
IPv6 multicast addresses start with ff (binary 11111111), followed by flags and scope:
| Byte | Bits | Value | Meaning |
|---|---|---|---|
| ff | 8 | 0xff | Multicast prefix |
| 0 | 4 | 0x0 | Flags (no special flags) |
| 2 | 4 | 0x2 | Scope: Link-Local |
| ::1 | 112 | 1 | Group ID: All Nodes |
Scope Values
The scope nibble (2 in this case) determines the reach:
| Value | Scope | Reach |
|---|---|---|
| 1 | Interface-Local | Same interface only |
| 2 | Link-Local | Same network segment |
| 4 | Admin-Local | Administratively defined |
| 5 | Site-Local | Same site |
| 8 | Organization | Same organization |
| e | Global | Internet-wide |
How It Is Used
When a router or host sends a packet to ff02::1, every IPv6-enabled node on the local link receives it. This is used in:
- Router Advertisements: Routers periodically multicast their presence
- Neighbor Discovery: Finding other hosts on the link
- Duplicate Address Detection: Checking if an address is already in use
Use Case
Network engineers use ff02::1 in Neighbor Discovery Protocol (NDP), Router Advertisement (RA) messages, and for network diagnostics like sending multicast pings (ping6 ff02::1%eth0) to discover all IPv6 hosts on a link.