Multicast Addresses

Unicast addresses are one-to-one.

• One source to one destination.

Broadcast addresses are one-to-all.

• One source to all destinations (within the subnet).

Multicast addresses are one-to-many.

• One source to multiple destinations (that have joined the specific multicast group).

IPv6 uses the range FF00::/8 for multicast. (FF00:: to FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)

IPv6 doesn't use broadcast (there is no 'broadcast address' in IPv6!).

Important addresses

Pupose	IPv6 Address	IPv4 Address
All nodes/hosts (functions like broadcast)	FF02::1	224.0.0.1
All routers	FF02::2	224.0.0.2
All OSPF routers	FF02::5	224.0.0.5
All OSPF DRs/BDRs	FF02::6	224.0.0.6
All RIP routers	FF02::9	224.0.0.9
All EIGRP routers	FF02::A	224.0.0.10

Scopes

IPv6 defines multiple multicast 'scopes' which indicate how far the packet should be forwarded.

The addresses in the previous slide all use the 'link-local' scope (FF02), which stays in the local subnet.

IPv6 multicast scopes:

• Interface-local (FF01): the packet doesn't leave the local device. Can be used to send traffic to a service within the local device.

• Link-local (FF02): The packet remains in the local subnet. Routers will not route the packet between subnets.

• Site-local (FF05): The packet can be forwarded by routers. Should be limited to a single physical location (not forwarded over a WAN).

• Organization-local (FF08): Wider in scope than site-local (an entire company/organization).

• Global (FF0E): No boundaries. Possible to be routed over the internet.