Re: [quicwg/base-drafts] amplification attack using Retry and VN triggered by coalesced Initial packets (#2259)

[MikkelFJ <[e-mail]>]

@DavidSchinazi even if there is no strict ordering, there is still coordination. And reading you text verbatim you also require the first Reset / VN triggering packet to win.

For the sake of argument assume packets were coalesced in the general case. A single preprocessor locates packet boundaries and pushes each packet to a queue handled by several processing units which picks a packet whenever it is available for processing. Suddenly one of these processors wants to emit a Reset. It then has to signal all other processors that they should stop doing what they are doing if they happen to be processing the same datagram. Furthermore, the processor must figure out if there is another processor also wanting to send a VN or Reset on the same datagram, and if so, if it is earlier in the datagram such that the correct winner can be identified.

In praxis such complexity would not be implemented as long as coalescing only happens during handshake, but it illustrates that ordering constraints are difficult when introducing concurrency in processing.

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