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

Mikael Abrahamsson <> Thu, 02 August 2018 15:02 UTC

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Date: Thu, 2 Aug 2018 17:02:43 +0200 (CEST)
From: Mikael Abrahamsson <>
To: Joe Touch <>
cc: Ole Troan <>, int-area <>,
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Subject: Re: [Int-area] WG Adoption Call: IP Fragmentation Considered Fragile
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On Thu, 2 Aug 2018, Joe Touch wrote:

> Just because operators/vendors “want” to do otherwise does not make it 
> possible.

I've been on hotel wifis that are behind 3 layers of NAT, PMTUD 
non-working, PMTU is like 1450, and the only thing saving the day is TCP 
MSS adjust, so the only thing that works is something over TCP or that 
happens to use small enough packets. I have been on other networks where 
basically only thing that works is 80/443 and some mail related ports. 
Complaining doesn't help, because peoples mobile phones work ok.

It's "possible", because it works well enough for what some people use it 
for. Very few complain, so there is no improvement.

So while you're technically and formally right, there is no enforcement 
and the only thing we can do is write requirements, tests, educate, but 
also educate application and protocol developers on what they might face 
in the real world. This is engineering, not physics. Real world is more 
important than map.

IP-fragmentation has always been fragile, and it's not improving. The 
Internet is growing, so this is not getting better. This is reality, even 
though we do not like it.

Mikael Abrahamsson    email: