Multicast addresses provide one-to-many communication
Multicast addresses provide one-to-many communication.
An IPv6 multicast address identifies a group of nodes.
The scope is built into the multicast address structure.
The system uses a multicast address to send traffic to multiple destinations. In this situation traffic experiences less delay with a multicast address than it would with Unicast address.
The following figure shows the format of an IPv6 multicast address.
A value of FF (11111111) in the 8 high-order bits of an IPv6 address indicates that the address is an IP multicast address.
The Multicast IPv6 Prefix is FF00::/8 (RFC3513).
The 4-bit flags field indicates whether the group is permanent or transient. The first 3 bits are reserved and the 4th bit represents the Transient flag. Currently only the Transient (T) flag is defined. A T flag set to 0 specifies a permanently assigned multicast address. A T flag set to 1 specifies a transient address.
The 112 bit group ID identifies the multicast group.
An example of a multicast address is FF01:0:0:0:0:0:0:101
The 4-bit scope field within the group ID specifies the multicast traffic scope.
1 - node-local
2 - link-local
3 - subnet local
4 - admin local
5 - site-local – not supported
8 - organization-local
B - community-local
E - global
All-nodes addresses look like this:
FF01::1 (Node Local), FF02::1 (Link Local)
All-routers addresses look like this:
FF01::2 (Node Local), FF02::2 (Link Local)
A solicited node or host address looks like this:
FF02::1:FF1E:8329.
In this case the MAC is 00-02-B3-1E-83-29 and the IPv6 address is fe80::202:B3FF:FE1E:8329.
The following table lists some well-known multicast IPv6 addresses
Name |
Address |
---|---|
All Nodes |
FF02:0:0:0:0:0:0:1 |
All Routers |
FF02:0:0:0:0:0:0:2 |
OSPFIGP |
FF02:0:0:0:0:0:0:5 |
OSPFIGP Designated Routers |
FF02:0:0:0:0:0:0:6 |
All PIM Routers |
FF02:0:0:0:0:0:0:D |
VRRP |
FF02:0:0:0:0:0:0:12 |
All MLDv2–capable routers |
FF02:0:0:0:0:0:0:16 |
All DHCP agents |
FF02:0:0:0:0:0:0:2 |
Solicited Node address |
FF02::1:FF00:0000/104 |