Re: [Int-area] WG Adoption Call: IP Fragmentation Considered Fragile

Fernando Gont <fernando@gont.com.ar> Fri, 27 July 2018 16:32 UTC

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To: Tom Herbert <tom@herbertland.com>
Cc: Joe Touch <touch@strayalpha.com>, Wassim Haddad <wassim.haddad@ericsson.com>, "internet-area@ietf.org" <int-area@ietf.org>, "intarea-chairs@ietf.org" <intarea-chairs@ietf.org>
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From: Fernando Gont <fernando@gont.com.ar>
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Date: Fri, 27 Jul 2018 18:25:09 +0200
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Subject: Re: [Int-area] WG Adoption Call: IP Fragmentation Considered Fragile
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On 07/27/2018 05:15 PM, Tom Herbert wrote:
> On Fri, Jul 27, 2018 at 5:38 AM, Fernando Gont <fernando@gont.com.ar> wrote:
>> Hi, Joe,
>>
>> On 07/26/2018 04:14 AM, Joe Touch wrote:
>>> Hi, all,
[....]
>>
>> Side coments:
>>
>> It would all seem that there are two operating environments:
>> * Controlled environments, where you can somehow make all this work
>> * Public internet, which is more of a "fingers crossed" thing (if anything).
>>
>> I'm not saying that I'm happy with the outcome, but rather that I think
>> that from an engenering point of view, it all looks like this ship has
>> sailed, and we should probably figure out how to deal with those cases
>> where fragmentation is actually needed.
>>
> Fernado,
> 
> Couldn't that same line of thinking be applied to several other
> protocol features?

Yes, indeed.


> So has the ship sailed for out ability to ever use
> extension headers or any protocol other than TCP (and sometimes UDP)?

It would seem that that's the case, yes.


> Maybe documents that recommend operational workarounds should
> distinguish problems that inherent in the protocol from those that
> have arisen because of non-conformant implementation. It's true that
> calling implementations that probably won't help to fix what is out
> there, but maybe this could help prevent new instances of
> non-conformance.

I kind of agree with you. That path from spec to implementation is what
you'd call engineering (or what others might call "taking shortcuts", etc.).

For example, what happens with EHs has a lot to do with engineering:
they could be made to work (e.g., remove performance impact), but
devices would probably be more expensive. Folks buying gear wouldn't pay
for something that its not used in practice, and vendors wouldn't just
"improve" the boxes for free. -- yeah, you could argue that "hey, there
shouldn't be penalties for EHs, since they are part of the core IPv6
spec" -- but, while probably correct, that will not change reality.

Not that I like the situation, but... I think the least we can do is to
do a reality check wrt how things are supposed to work vs. how they
actually work.

For this particular case, this I-D makes that point for fragmentation: I
I think we all agree that fragmentation is fragile -- making that point
clear at least raises awareness of the problem, and might trigger some
action on the topic (whether to correct the issue, or to circumvent it).

Thanks,
-- 
Fernando Gont
e-mail: fernando@gont.com.ar || fgont@si6networks.com
PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1