[RFC] Multicast and IPv6 Link Local Addresses

Juliusz Chroboczek jch at irif.fr
Sat Apr 8 19:15:04 CEST 2017

> - 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.

Not necessarily.  IPv6 link-local multicast replaces IPv4 link-local
broadcast.  Implementing link-local multicast as broadcast, while
suboptimal, is good enough to get IPv6 to work.

> - Multicast is not the everyday use case,

That's IPv4 thinking.  In IPv6, multicast is a basic, compulsory part of
the protocol.  A number of very basic IPv6 protocols fail to work if
link-local multicast is not functional.

See the IPv6 over NMBA (MARS, not LANE) specification for the kind of
horrors that are required to work around link layers that don't support

> - 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?

Yes, IPv6 neighbour discovery is one of those protocols that rely on
link-local multicast.

-- Juliusz

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