Re: [Int-area] Discussion about Section 6.1 in draft-ietf-intarea-frag-fragile

Fernando Gont <fgont@si6networks.com> Sat, 07 September 2019 02:54 UTC

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To: Ole Troan <otroan@employees.org>, Joe Touch <touch@strayalpha.com>
Cc: Bob Hinden <bob.hinden@gmail.com>, "int-area@ietf.org" <int-area@ietf.org>, Ron Bonica <rbonica=40juniper.net@dmarc.ietf.org>, IESG <iesg@ietf.org>, Joel Halpern <joel.halpern@ericsson.com>, "draft-ietf-intarea-frag-fragile@ietf.org" <draft-ietf-intarea-frag-fragile@ietf.org>, Suresh Krishnan <suresh@kaloom.com>, "intarea-chairs@ietf.org" <intarea-chairs@ietf.org>
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From: Fernando Gont <fgont@si6networks.com>
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Subject: Re: [Int-area] Discussion about Section 6.1 in draft-ietf-intarea-frag-fragile
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On 6/9/19 19:03, Ole Troan wrote:
> Joe,
> 
> edited to focus on the two added "recommendation sentences".
> 
>>>>> 1) It introduces something new and undescribed in paragraph 2.
>>>>> "unless they also include mechanisms to detect that IP fragmentation isn't working
>>>>> reliably."
>>>>> That seems like hand-waving to me. Suggest deleting.
>>>>
>>>> Fragmentation success or failure is directly testable. Any feedback mechanism will work and specific ones are mentioned elsewhere (PLPMTUD).
>>>>
>>>> This differs from ICMP black-holing in path MTU detection.
>>>
>>> Can you please point me to where in the PLPMTUD document testing for IP fragmentation is described?
>>
>> Any feedback mechanism will detect when fragmentation - or anything else - prevents delivery.
> 
> Any pointer to such a mechanism in any IETF protocol?
> Would be interesting to get transport/application perspective on this.
> But unless there is a reference I would claim this is hand-waving.

FWIW, I don't remember seeing anything like this at the network layer.
(One might guess that in theory you *could* get feedback from upper
layers, but...)

This kind of thing is easier at *higher* layers -- such as trying to do
the 3WHS with the ECN bits set, and if you don't hear from the other
end, try with those bits cleared.

But IMO for IP it is easier said than done...


-- 
Fernando Gont
SI6 Networks
e-mail: fgont@si6networks.com
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