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Re: [tsvwg] A review of draft-ietf-tsvwg-udp-options-12 - How many fragments?

Gorry Fairhurst <gorry@erg.abdn.ac.uk> Mon, 14 June 2021 11:00 UTC

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To: Joseph Touch <touch@strayalpha.com>, "C. M. Heard" <heard@pobox.com>
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From: Gorry Fairhurst <gorry@erg.abdn.ac.uk>
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Date: Mon, 14 Jun 2021 12:00:05 +0100
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Subject: Re: [tsvwg] A review of draft-ietf-tsvwg-udp-options-12 - How many fragments?
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<snip>
On 14/06/2021 03:12, Joseph Touch wrote:
>> On Jun 10, 2021, at 9:07 PM, Joseph Touch<touch@strayalpha.com>  wrote:
>>
>> - regarding fragment/reassembly as being required
> Mike and I (at least) appear to agree that FRAG is required and at least single-frag messages MUST be supported.
>
> I hope we can at least require reassembly of at least 2, if not 4 fragments.
>
<snip>

I can believe that 2 fragment reassembly could be a useful general 
compromise to think more on:

* Two fragments can often be significantly more helpful than no 
fragments: where the PMTU is reduced by a small size (e.g., to include a 
tunnel header) and datagrams need to be fragmented.

* Endpoints concerned about resources, can examine the second received 
fragment and immedaitely determine whether the oiriginal datagram can be 
reassembled. There are fewer opportunities for overlapping/small 
fragments to cause mischief. It might even be possible to set a receiver 
"reordering window" outside of which unreassembled Fragments are 
silently dropped.

Gorry

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