Re: [quicwg/base-drafts] Confused about Fixed Bit in Version Negotiation Packet (#2995)

Martin Thomson <> Fri, 13 September 2019 07:44 UTC

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From: Martin Thomson <>
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Subject: Re: [quicwg/base-drafts] Confused about Fixed Bit in Version Negotiation Packet (#2995)
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>  If Client must ignore the value(including Fixed Bit), why server should set Fixed Bit?

Because this might allow us - in future - to depend on that behaviour.  We might assign semantics to a non-zero value.  A client that doesn't understand that bit will continue to consume the packet and ignore the semantic difference.  If servers set the value any way they please, then we can't.  (It's a SHOULD, so we won't be able to rely on it exclusively, but we might still be able to do something with it.  That said, I consider it a write-off, but this is a general protocol design hygiene matter.)

My proposal for this issue is to do nothing.  This is a little complex, but I don't think that the required behaviour is unclear in any way.

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