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Re: [v6ops] PMTUD issue discussion

Mikael Abrahamsson <swmike@swm.pp.se> Tue, 09 September 2014 15:07 UTC

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Date: Tue, 09 Sep 2014 17:07:43 +0200
From: Mikael Abrahamsson <swmike@swm.pp.se>
To: "Templin, Fred L" <Fred.L.Templin@boeing.com>
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Cc: "v6ops@ietf.org" <v6ops@ietf.org>, Tom Perrine <tperrine@scea.com>
Subject: Re: [v6ops] PMTUD issue discussion
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On Tue, 9 Sep 2014, Templin, Fred L wrote:

> This could be problematic when PMTUD is not functioning correctly. As a 
> result, IMHO any end system that wants to try for packet sizes larger 
> than 1500 really should be using RFC4821 (maybe even MUST?).

Well, even that might not solve it as there might be devices along the 
path that re-assemble the packets (if they're fragmented) and then 
fragment them again, which will break things anyway.

But yes, supporting 4821 or PMTUD blackhole detection should definitely be 
a requirement.

One problem is that a lot of people don't even know that sending a 16k UDP 
packet fragmented into a bunch of smaller fragments, is a perfectly valid 
use of IP. They're so used to TCP and its MSS that this is all they've 
seen.

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

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