Re: [quicwg/base-drafts] Specify DCID of 0-RTT packets (#2398)

[Martin Thomson <[e-mail]>]

The point that keeps coming up in this context (I'm sure I've typed the same response elsewhere...) is that the timescales over which connection IDs are stable is likely far less than the timescale over which attempting 0-RTT is possible.  That is, you might attempt 0-RTT up to a week later, but the server cluster you hit might be in a configuration so different that the connection ID you got 5 or 6 days ago doesn't route to the same node.

That said, for those server configurations that are more stable, this isn't a terrible idea.  If this were discretionary, say as an extension, then it might be useful for ensuring that 0-RTT attempts are routed to the right destination.

But anything that does this sort of targeting could also create a nice targeted DoS vector.  Connect to the same server multiple times over the course of a week.  Then, when it's go time, send that server 0-RTT using all the collected connection IDs that route directly to it.

Marking v2, not editorial.

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