Re: [Gen-art] Review of draft-ietf-6man-rfc1981bis-04

Brian E Carpenter <brian.e.carpenter@gmail.com> Wed, 15 February 2017 21:26 UTC

Return-Path: <brian.e.carpenter@gmail.com>
X-Original-To: ietf@ietfa.amsl.com
Delivered-To: ietf@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id BD891129556; Wed, 15 Feb 2017 13:26:51 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2
X-Spam-Level:
X-Spam-Status: No, score=-2 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=gmail.com
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 9fXaPWLlugr5; Wed, 15 Feb 2017 13:26:50 -0800 (PST)
Received: from mail-pg0-x241.google.com (mail-pg0-x241.google.com [IPv6:2607:f8b0:400e:c05::241]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 7394A129B96; Wed, 15 Feb 2017 13:26:50 -0800 (PST)
Received: by mail-pg0-x241.google.com with SMTP id 75so12085933pgf.3; Wed, 15 Feb 2017 13:26:50 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:references:cc:from:organization:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding; bh=oubWh6KObmZKhsFrc9dZol3y1lYgRBAryBnz3gPWMOM=; b=fho/bPrw9PNcJ05R3n1nqEAxNCTWmXX7O1qZfHb+swuq+BZ4g+tI1ET6yLa1Qc+Hpt mmICk1uXHWV/bB9PXOmUj+cVeF422LIHicLtRiveJlJygWGsM9aHus+QhNFF0Uq4RdoE UxDXtqEoz3Ye8O9hS72vnoUG7NS0b2FXQasJI94SmuwT/9EGUWcmYKDlcp6HkqyfaTS+ RRAadJvvLeapUEe8B477ZYBgTcXGmHhEG304dJvoF0PIJ3nfVXV6IXGTr4GQIwf2mgzY WlMreQvyxNPzQtvx2LjnVp9Tre4QW8EIPyf1MbZpTdm0UV3A4el79cIUcla8S21czqrk rEiQ==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:cc:from:organization :message-id:date:user-agent:mime-version:in-reply-to :content-transfer-encoding; bh=oubWh6KObmZKhsFrc9dZol3y1lYgRBAryBnz3gPWMOM=; b=R6gt9/SEIRwfWRa7tWiZeGjNOA2vsskLs+HO3/EGV2Mus+fQe+hNDi4yBV5CclR9G3 idvxTZkykU2I0mxmEMOYJofeMkQsaDtlK6lBMxjT53ObV9Ek+ikZCgtIfQlY4wegcxHp PHtAmJZEEtD8X0Z0VqMuQKOGTkMvlgTUxXc6nSgyyI1e+/joZo1jastmuXJpwBM1xiNg tqhmW/fYZmvpYN9cj5HU57JN3mfPLxTwKlFQQoKBanWd78jVpj3FdM3z/8ErH8ErwVvS tkC6a4K0FqFrPdPTJZmIkeABaojlEN/YB2/72YOkjZ7vKaxVXmIi0P9PEMWilZTBlvKw rywQ==
X-Gm-Message-State: AMke39nnqJdItD3yHNKgTEArbmlEG+DGWDgwosr3GSSfACnFtKH+79463bkcfBgEoaxpwg==
X-Received: by 10.98.212.23 with SMTP id a23mr40461055pfh.18.1487194010033; Wed, 15 Feb 2017 13:26:50 -0800 (PST)
Received: from [192.168.178.21] ([118.148.112.221]) by smtp.gmail.com with ESMTPSA id n70sm9250021pfg.34.2017.02.15.13.26.46 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 15 Feb 2017 13:26:49 -0800 (PST)
Subject: Re: [Gen-art] Review of draft-ietf-6man-rfc1981bis-04
To: Joe Touch <touch@isi.edu>, Stewart Bryant <stewart.bryant@gmail.com>, Stewart Bryant <stewart@g3ysx.org.uk>, gen-art@ietf.org
References: <148665359396.20513.9749548375095869760.idtracker@ietfa.amsl.com> <2997d33f-3884-7831-50ed-1713c93b3867@gmail.com> <b9dfd941-0eba-c257-fef4-2f5e6bbd82a8@gmail.com> <9a1a0a47-d8fd-5cf9-0244-7ce624d58470@gmail.com> <aa18ed73-97e4-ac66-8667-8367d71bb03d@isi.edu>
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
Message-ID: <cdc76c31-933a-c17f-7efd-08d399768159@gmail.com>
Date: Thu, 16 Feb 2017 10:26:50 +1300
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1
MIME-Version: 1.0
In-Reply-To: <aa18ed73-97e4-ac66-8667-8367d71bb03d@isi.edu>
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Archived-At: <https://mailarchive.ietf.org/arch/msg/ietf/GPek12rmspVw13nFE6-jsw8EfWs>
Cc: ipv6@ietf.org, ietf@ietf.org, draft-ietf-6man-rfc1981bis.all@ietf.org
X-BeenThere: ietf@ietf.org
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: IETF-Discussion <ietf.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/ietf>, <mailto:ietf-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/ietf/>
List-Post: <mailto:ietf@ietf.org>
List-Help: <mailto:ietf-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/ietf>, <mailto:ietf-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 15 Feb 2017 21:26:52 -0000

On 16/02/2017 10:12, Joe Touch wrote:
> Brian (et al.),
> 
> 
> On 2/10/2017 11:45 AM, Brian E Carpenter wrote:
>>> practice the
>>> Internet breaks the mechanism. However it breaks it is a way that seems
>>> disruptive to some user traffic. The document is really guidance
>>> one how hosts might use  ICMP for optimization, and arguable need
>>> not be a standard at all.
>> I think that's a mischaracterisation of the mechanism (and the draft).
>> PMTUD is not an optimisation. Without it, you get black holes
> PMTUD is an optimization to avoid fragmentation.
> 
> Without it, you use fragmentation (which has overheads and other
> consequences, notably for IPv4).

In IPv6, you don't even know you *need* fragmentation without PMTUD,
since only the source is allowed to fragment. (That was one of the
many failure modes for 6to4, which is why the only safe approach was
to use 1280 always.) 

> However, it is only *with* PMTUD (and ICMP blocking) that you get black
> holes.

True for v4.

   Brian