Re: [quicwg/base-drafts] Client connection IDs are broken (#2844)

[Kazuho Oku <[e-mail]>]

@DavidSchinazi Thank you for opening the issue. I agree that this is a design issue that needs to be fixed.

> Therefore we have two protocol features that are at odds with one another:
> (1) server can share port and use zero-length CIDs (which prohibits migration)
> (2) client can share port and use non-zero-length CIDs
> 
> We can't have both (1) and (2) because the client wanting to do (2) doesn't know if the server will do (1) or not.
> (snip)
> For client connection IDs to be useful in QUIC, I think we should ban zero-length connection IDs when you're multiplexing multiple connections on a local IP + port.

Agreed.

IIRC, the introduction of client CID was a deliberate action to allow multiple QUIC connections be coalesced on a 5-tuple. I think the reason (1) exists is simply because we did not notice that there is a conflict. Based on that, I think we should adjust (1) to allow (2) to happen.

Allowing a client use one (or few) UDP packets to handle many QUIC connections has benefits. It helps code reuse (because servers are designed to use one port for many connections) and also has performance benefits (because you can use one system call to read / write packets belonging to many connections).

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