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

Mikael Abrahamsson <swmike@swm.pp.se> Sat, 25 August 2018 06:32 UTC

Return-Path: <swmike@swm.pp.se>
X-Original-To: int-area@ietfa.amsl.com
Delivered-To: int-area@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 486AC129AB8; Fri, 24 Aug 2018 23:32:47 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -4.3
X-Spam-Level:
X-Spam-Status: No, score=-4.3 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (1024-bit key) header.d=swm.pp.se
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id YMfFCTQhybOY; Fri, 24 Aug 2018 23:32:45 -0700 (PDT)
Received: from uplift.swm.pp.se (swm.pp.se [212.247.200.143]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id E9F43128C65; Fri, 24 Aug 2018 23:32:44 -0700 (PDT)
Received: by uplift.swm.pp.se (Postfix, from userid 501) id 00E35AF; Sat, 25 Aug 2018 08:32:41 +0200 (CEST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=swm.pp.se; s=mail; t=1535178762; bh=wZSKogEaTgeYee/77OJsDMkpFVYosoMOQ6I1Sxxl3As=; h=Date:From:To:cc:Subject:In-Reply-To:References:From; b=fGNea9nK877EXe8/rlLwdqRh+776cmps8lx2US9eVktKS9WhuGUvTM7ruAkCB2haT q41kTkd1V4i5DfNLJBUxEoT82v6BvuDYFsr5N3Nq1HemE+a86yBEJnMPK1GFB924tH Rbmm3/0fID92R2Y5va9ftqR7Ehjwyf+zaJzklA58=
Received: from localhost (localhost [127.0.0.1]) by uplift.swm.pp.se (Postfix) with ESMTP id F291B9F; Sat, 25 Aug 2018 08:32:41 +0200 (CEST)
Date: Sat, 25 Aug 2018 08:32:41 +0200 (CEST)
From: Mikael Abrahamsson <swmike@swm.pp.se>
To: Toerless Eckert <tte@cs.fau.de>
cc: Tom Herbert <tom@herbertland.com>, int-area <int-area@ietf.org>, intarea-chairs@ietf.org
In-Reply-To: <20180825032457.ol5rlrr7h2kqi6px@faui48f.informatik.uni-erlangen.de>
Message-ID: <alpine.DEB.2.20.1808250827360.23215@uplift.swm.pp.se>
References: <CALx6S36Ef3t7Axmx9hg994DHpVM=NdW-7ygf89E==gL4XKrkQg@mail.gmail.com> <5E21B3C1-0420-404C-9824-9B7E5A850BC5@employees.org> <CALx6S34qmKngi3hK_PVrJA1DMa5kfaLww3jfqRKN=up5v0Y0Ww@mail.gmail.com> <8D23C8B1-C2DA-4A8B-A2BE-8CCF6233B3A5@strayalpha.com> <D1D5EDCE-7C43-4CD8-947C-AA43CDB18892@employees.org> <1B04E207-08FA-400F-BBED-67379FEFD64E@strayalpha.com> <137751A3-7C52-4CCF-AE9C-B99C4A85EFC1@strayalpha.com> <alpine.DEB.2.20.1808021749020.19688@uplift.swm.pp.se> <CALx6S35kw2dodgG2L3LE3A5y8RYEXy6izQWgrQTwg7-yPqpzOg@mail.gmail.com> <alpine.DEB.2.20.1808030857370.19688@uplift.swm.pp.se> <20180825032457.ol5rlrr7h2kqi6px@faui48f.informatik.uni-erlangen.de>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
Organization: People's Front Against WWW
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII; format=flowed
Archived-At: <https://mailarchive.ietf.org/arch/msg/int-area/CtS-bzMGRh3-lg2OmQtWGAlpNzg>
Subject: Re: [Int-area] WG Adoption Call: IP Fragmentation Considered Fragile
X-BeenThere: int-area@ietf.org
X-Mailman-Version: 2.1.27
Precedence: list
List-Id: IETF Internet Area Mailing List <int-area.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/int-area>, <mailto:int-area-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/int-area/>
List-Post: <mailto:int-area@ietf.org>
List-Help: <mailto:int-area-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/int-area>, <mailto:int-area-request@ietf.org?subject=subscribe>
X-List-Received-Date: Sat, 25 Aug 2018 06:32:47 -0000

On Sat, 25 Aug 2018, 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) ?

Correct. The reason for this is that whatever we design must be resilient 
to failure. Networks should work properly, but applications should 
handle it when they don't. Degraded performance is ok.

> 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.

I want to keep the fragmentation requirement for the network.

> 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.

I am not opposed to this option being created, but you still need PLPMTUD. 
This option might trigger faster PLPMTUD, but it doesn't make the problem 
go away. If the application still keeps sending packets that needs to be 
fragmented, what should the stack do, just send an error to the 
application? Yes, this will mean we will fail faster, but apart from that?

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