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

Mikael Abrahamsson <swmike@swm.pp.se> Thu, 26 July 2018 07:01 UTC

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Date: Thu, 26 Jul 2018 09:01:51 +0200 (CEST)
From: Mikael Abrahamsson <swmike@swm.pp.se>
To: "Templin (US), Fred L" <Fred.L.Templin@boeing.com>
cc: 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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Subject: Re: [Int-area] WG Adoption Call: IP Fragmentation Considered Fragile
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On Tue, 24 Jul 2018, Templin (US), Fred L wrote:

> Try it - by default, iperf3 sets an 8KB UDP packet size and allows 
> packets to fragment across paths that support only smaller MTUs. I have 
> seen iperf3 exercise IP reassembly at line rates on high-speed links, 
> i.e., it shows that reassembly at high rates is feasible.
>
> We know from RFC4963 that there are dangers for reassembly at high 
> rates, but there are applications such as iperf3 that ignore the "SHOULD 
> NOT" and leverage IP fragmentation anyway. So, should the "SHOULD NOT" 
> have an asterisk?

The iperf3 usage of fragments for UDP testing seems to be platform 
specific, at least that's what I've seen. Behaviour has been different on 
MacOS compared to Linux.

Anyhow, I believe we should keep the "SHOULD NOT". This allows 
applications that feel they have a good reason to do fragmentation to do 
so, but doesn't disallow it.

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