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Re: [tsvwg] UDP options and header-data split (zero copy)

Joseph Touch <touch@strayalpha.com> Mon, 02 August 2021 01:13 UTC

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From: Joseph Touch <touch@strayalpha.com>
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Date: Sun, 01 Aug 2021 18:12:53 -0700
Cc: Michael Tuexen <michael.tuexen@lurchi.franken.de>, tsvwg <tsvwg@ietf.org>
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To: Tom Herbert <tom@herbertland.com>
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Subject: Re: [tsvwg] UDP options and header-data split (zero copy)
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> On Aug 1, 2021, at 5:41 PM, Tom Herbert <tom@herbertland.com> wrote:
> 
> 
> 
> On Sun, Aug 1, 2021, 3:48 PM Joseph Touch <touch@strayalpha.com <mailto:touch@strayalpha.com>> wrote:
> Hi, Tom,
> 
> > On Aug 1, 2021, at 3:39 PM, Tom Herbert <tom@herbertland.com <mailto:tom@herbertland.com>> wrote:
> > 
> > There is also RFC9000:
> > 
> > "QUIC assumes a minimum IP packet size of at least 1280 bytes.  This
> > is the IPv6 minimum size [IPv6] and is also supported by most modern
> > IPv4 networks.  
> 
> Hmm. Seems like they completely overlooked IP source fragmentation support and 1500B reassembly...
> 
> No IP fragmentation in QUIC. DF bit is always set.

RFC 9000 talks about DF being set for IPv4, but that’s the default for IPv6 (no on-path fragmentation).

It does say "no fragmentation at the IP layer”, which presumably also prohibits IP source fragmentation, though it’s not at all clear why, other than to avoid black-holing through NAT. DF being set in IPv4 is critical to RFC1191 path MTU discovery, but that does not prohibit use of source fragmentation as long as DF is set. 

However, that does not prevent use of UDP fragmentation - which would both be opaque to avoiding IP fragmentation and QUIC, as well as would traverse NATs because of the replicated UDP header in UDP fragments.

Joe

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