Re: [quicwg/base-drafts] Which DCID do Handshake retransmissions use? (#3348)

Mike Bishop <> Wed, 15 January 2020 21:23 UTC

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From: Mike Bishop <>
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Subject: Re: [quicwg/base-drafts] Which DCID do Handshake retransmissions use? (#3348)
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> @ianswett: The part about what to do with DCID changes is underspecified. From the part of the spec you quote -- "Any additional changes are not permitted; if subsequent packets of those types include a different Source Connection ID, they MUST be discarded." -- it's not clear what these additional changes are limited to. I _think_ the intent was for all long-form packets, but that's certainly not clear here.

"of those types" => Retry or Initial, since that's what it was talking about.  That's trying to avoid the case where the server statelessly generates a new Retry (or Initial, in the rare case that would be stateless) with a second SCID upon receiving a retransmission or duplication of the client's Initial.  But it doesn't say anything about the server issuing new CIDs via an NCID frame in 1-RTT before the handshake is confirmed.

I think (a) or (b) would be fine; the server is clearly intending to accept the other CID if it issued it, but could conceivably use separate logic for long-header versus short-header routing.

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