This article directory
1. Structure of IPv6 multicast address
An IPv6 multicast address is composed of a fixed 8-bit address prefix FF::/8, a 4-bit flag, a 4-bit multicast scope and a 112-bit multicast group identifier (group ID).
-
FF::/8
The highest 8 bits of an IPv6 multicast address are always FF. -
Flag
This field: Indicates whether the multicast address is "permanent" (an address assigned by IANA) or "temporary" (a temporary multicast group created by the user). Under normal circumstances, the upper 3 bits are always 0, and the remaining lower 1 bit means "permanent" when it is 0, and "temporary" when it is 1. -
Multicast range
This field consists of 4 bits, which defines the range type of the multicast address, as shown in the following table:
| binary value | hexadecimal value | Range definition for multicast |
|---|---|---|
| 0001 | 1 | local interface |
| 0010 | 2 | local link |
| 0011 | 3 | local subnet |
| 0100 | 4 | local management |
| 0101 | 5 | local site |
| 1000 | 8 | organization |
| 1110 | E | worldwide |
2. Special reserved addresses and reserved multicast addresses
- In addition to the following three special addresses that have been introduced before:
| special address | significance |
|---|---|
| ::/128 | Interface does not specify an address |
| ::/0 | default route |
| ::1/128 | loopback address |
-
Reserved multicast addresses for routing protocols
The table below summarizes the reserved multicast addresses used by the interior routing protocols
| multicast address | use |
|---|---|
| FF02::5 | OSPFv3 |
| FF02::6 | OSPFv3 Designated Routers |
| FF02::9 | RIPng |
| FF02::A | EIGRP |
- Reserve multicast addresses for routers/nodes
| multicast address | multicast scope |
|---|---|
| FF01::1 | All nodes of this interface |
| FF01::2 | All routing nodes on this interface |
| FF02::1 | Link-local all nodes |
| FF02::2 | Link-local all routing nodes |
| FF05::2 | All routing nodes at the local site |
After the IPv6 host is started, there is no need to configure an IPv6 address. The host uses EUI-64-based stateless auto-configuration of its own IPv6 address, and then communicates with available hosts/routers on the segment through these addresses. NDP automatically completes the address configuration process through the above-mentioned multicast address.