Ubuntu - Networking - IPv6 - Unicast, anycast, multicast - IPv6 multicast

IPv6 multicast works by nodes joining multicast groups by sending Multicast Listener Discovery (MLD) report messages.

NOTE: A node is an interface enabled for IPv6.

Router is any node that forwards IPv6 packets that are not expressly addressed to it.
Host is any node that is not a router.

Multicast groups are not constrained by local or global (network) geography.

Whether the host is on the local network or on the internet, as long as it is signaling to join a multicast group, it can receive multicast packets sent to that group.

Any host can be a sender, whether it is part of the multicast group or not.