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Re: [tsvwg] UDP Options: on forcing the use of UDP CS=0 in connection with FRAG+LITE

Joe Touch <touch@strayalpha.com> Mon, 01 July 2019 20:19 UTC

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From: Joe Touch <touch@strayalpha.com>
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Date: Mon, 01 Jul 2019 13:18:37 -0700
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To: "C. M. Heard" <heard@pobox.com>
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Subject: Re: [tsvwg] UDP Options: on forcing the use of UDP CS=0 in connection with FRAG+LITE
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> On Jul 1, 2019, at 12:49 PM, C. M. Heard <heard@pobox.com> wrote:
> 
>> You haven’t addressed the data copying issue.
> 
> Yes, I have, in
> https://mailarchive.ietf.org/arch/msg/tsvwg/RJBWi_tiW6M_phfc22zKuVn_vh4
> 
> Can you please respond to that message and explain exactly why you think
> that the proposal in the thread "DP Options: how to do FRAG without LITE
> and forced UDP CS=0" imposes data movement requirements for packet
> reassembly beyond those required by FRAG+LITE (or FRAG without LITE) in
> in draft-ietf-tsvwg-udp-options-07? I sure don't see it.

When I’m done moving a small, fixed number of bytes, the existing FRAG+LITE option leaves the fragment at the head of the packet.

When you’re done, the frag is after a variable length string of options.

Yes, both need to be gathered together. No, they’re not the same - some UDP hardware and software implementations treat the offset where they expect the data to start as “special”; yours could be anywhere.

Joe

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