Re: [Int-area] I-D Action: draft-ietf-intarea-frag-fragile-00.txt

Mikael Abrahamsson <swmike@swm.pp.se> Thu, 16 August 2018 05:39 UTC

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Date: Thu, 16 Aug 2018 07:39:08 +0200 (CEST)
From: Mikael Abrahamsson <swmike@swm.pp.se>
To: Brian E Carpenter <brian.e.carpenter@gmail.com>
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Subject: Re: [Int-area] I-D Action: draft-ietf-intarea-frag-fragile-00.txt
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On Thu, 16 Aug 2018, Brian E Carpenter wrote:

> Whether that automatically solves the problem depends on whether
> PMTUD works, which is unpredictable. Therefore, if you want a protocol
> *design* that is universal, it can't depend on PMTUD. Disabling
> fragmentation on its own is not enough. (That isn't news.)
>
> The only universal solution therefore seems to be a fully specified
> PLPMTUD solution, either built into the protocol design, or available
> as a normative reference. I think that would be a better
> recommendation than simply saying "don't rely on fragmentation."

Summary of my views:

Networks MUST support PMTUD.
Networks MUST support IP level fragmented packets.
Protocols/applications SHOULD have PMTUD blackhole detection.
Protocols/applications SHOULD do PLPMTUD.
Protocols/applications SHOULD avoid IP level fragmentation.

> IMHO RFC4821 isn't a sufficient normative reference for this. Possibly 
> draft-ietf-tsvwg-datagram-plpmtud will do it for UDP-based protocols. 
> But IMHO we need a solution for each transport protocol, with widely 
> available libraries.

Agreed. The libraries part is extremely important. Programmers 
implementing applications should not have to worry about this, it should 
be taken care of by the libraries they use. For them it should just work.

-- 
Mikael Abrahamsson    email: swmike@swm.pp.se