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

Toerless Eckert <tte@cs.fau.de> Sat, 25 August 2018 03:25 UTC

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Date: Sat, 25 Aug 2018 05:24:57 +0200
From: Toerless Eckert <tte@cs.fau.de>
To: Mikael Abrahamsson <swmike@swm.pp.se>
Cc: Tom Herbert <tom@herbertland.com>, int-area <int-area@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 Fri, Aug 03, 2018 at 09:48:25AM +0200, Mikael Abrahamsson wrote:
> I've kept saying "Networks must support ip fragmentation properly.

Why ? Wheren't you also saying that you've got (like probably many
else on this thread) all the experience that only TCP MSS gets you
working connectivity in many case (like hotels) ?

IMHO, we (network layer) should accept defeat on network layer 
fragmentation and agree that we should make it easier for the
transport layer to resolve the problem.

Aka: I would lvoe to see a new ICMPv4/ICMPv6 reply and/or PTB reply option
indicating "Fragmented Packets Not Permitted". Any network device which
for whatever reason does not like Fragemnts would simply drop
fragmented packets and send this as a reply. Allows then the
transport layer to automatically use packetization  (such as TCP MSS) 
to get packets through. 

Of course. Will take a decade to get ubiquitously deployed, but
neither IPv4 nor IPv6 will go away, only the problems with fragmentation
will become worse and work if we do not have an exit strategy like this.

If we don't try an exit strategy like this, we will just get what
Joe said, the complete segmentation of the Internet with more and
more L4 or even higher layer proxies.

Btw: +1 for adopting the doc as a WG item, but primarily because everything
before section 7 is on a way to become a good read of reality. Section
7 recommendations is only a faith based exercise (praying) as long as it tries to
get the job done primarily by appealing to application developers.

Cheers
    Toerless