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

Tom Herbert <> Sun, 26 August 2018 17:08 UTC

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From: Tom Herbert <>
Date: Sun, 26 Aug 2018 10:08:07 -0700
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To: Toerless Eckert <>
Cc: Mikael Abrahamsson <>, int-area <>,
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Subject: Re: [Int-area] WG Adoption Call: IP Fragmentation Considered Fragile
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On Fri, Aug 24, 2018 at 8:24 PM, Toerless Eckert <> wrote:
> 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.

I'm curious why you think the problems with fragmentation will become
worse. The draft and much of this thread has already highlighted the
problems with fragmentation that happen because of non-conformant
implementation. While there's a lot of legacy implementation that
might hard to fix completely, I don't think we've seen a good argument
that these problems are infeasible to fix in new deployments and
products. I think this draft is an opportunity not only highlight the
problems, but to suggest some practical fixes to improve the situation
as a way forward.


> 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