optimise IP multicast

[rade]

Currently weave implements IP multicast in terms of broadcast, i.e. multicast packets are always sent to all peers. That is sub-optimal.

Weave does observe IGMP and hence could build up knowledge about which peers contain receivers for specific multicast groups, and then use that knowledge to route packets to just those peers.

[inercia]

I think you would need some kind of distributed database for doing IGMP snooping. Weave would need to detect IGMP join/leave requests and broadcast this information by updating the list of peers subscribed to each multicast group in the database (note that simple gossip updates would not be enough in this case as order is important). Then Weave would then detect all multicast traffic and translate it to unicast...

[rade]

@inercia

order is important

how do ordinary igmp-aware routers handle that?

[inercia]

I don't know the particular details, but I'd guess that routers detect join/leave messages in ports, serialize that information for updating some kind of multicast forwarding table, and use that table for controlling what multicast traffic is forwarded. I think a distributed router would need to do that serialization in the join/leave information detected in the virtual ports...

[greenpau]

@inercia 👍

[erandu]

Do you have any update on getting the multicast optimized ?