[RFC] Multicast and IPv6 Link Local Addresses

[Dan Lüdtke]

Hi everyone,

I am very excited that we have this discussion, as I am one of those IPv6-first/IPv6-only guys who like poking the topic.
I try to keep it short:

- Scalability: I agree with what George said. Broadcast does not scale nicely, and IPv6 multicast is intended to help scaling things by reaching exactly the node that need to get a copy of a particular packet. Downgrading IPv6 multicast to broadcast hurts scalability and I for one, would rather not see multicast in WireGuard if it does not scale. I am afraid it would be counterproductive to the goal of having a widely accepted and used protocol.

- Multicast is not the everyday use case, so if multicast requires an extra knob or an extra option, that would be fine I guess. I am in favor of intentionally enabling multicast. I am still wrapping my head around static vs. dynamic (read: magic) configuration of multicast addresses and groups. Will let you know once I end up with something worth sharing. In the meantime, I think "solicited node multicast addresses/groups" are the one thing that comes with the least amount of trouble. Especially if IPv6 LL addressing is also there.

- IPv6 link-local addressing: For me it is a perfect example for "the right amount of magic". It would make (at least my) life so much easier. Filling the neighbor cache would require WireGuard to provide (simulated or real) solicited node multicast addresses routing, right? Or is it feasible to fill the neighbor cache based on the peer configuration? The last thing sounds wrong to me.

So much for my first thoughts.

Cheers,

Dan