Re: Last Call: <draft-ietf-6man-rfc2460bis-08.txt> (Internet Protocol, Version 6 (IPv6) Specification) to Internet Standard

"Joel M. Halpern" <> Tue, 14 February 2017 19:05 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id 379481294C2 for <>; Tue, 14 Feb 2017 11:05:14 -0800 (PST)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -2.002
X-Spam-Status: No, score=-2.002 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_NONE=-0.0001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Authentication-Results: (amavisd-new); dkim=pass (1024-bit key)
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id eTBEErNmfJf9 for <>; Tue, 14 Feb 2017 11:05:12 -0800 (PST)
Received: from ( []) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by (Postfix) with ESMTPS id DA6401296DD for <>; Tue, 14 Feb 2017 11:05:12 -0800 (PST)
Received: from localhost (localhost []) by (Postfix) with ESMTP id C12BA32E455; Tue, 14 Feb 2017 11:05:12 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=1.tigertech; t=1487099112; bh=gy9Danh/rFFMlL5NgCN/6mskrWK1bfdwQwj4RZFbmRQ=; h=Subject:To:References:Cc:From:Date:In-Reply-To:From; b=mPFs+CyBIxG3V/KznLLR7a/D7YW9lsMhciSZRFRxVqpMXfAodqpXnwnnZJnH/5ZxF dXUHoTU0V0Uen3VvjTVsxank7Orng1Iy6P/HmyTnCYWVh0K0SYEFfm3vBMWoFDLMtU 0zCnhpus0CkizdcHcUhoRUPX3qkkAoIl4h7Xot90=
X-Virus-Scanned: Debian amavisd-new at
Received: from Joels-MacBook-Pro.local ( []) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by (Postfix) with ESMTPSA id 282F932E452; Tue, 14 Feb 2017 11:05:12 -0800 (PST)
Subject: Re: Last Call: <draft-ietf-6man-rfc2460bis-08.txt> (Internet Protocol, Version 6 (IPv6) Specification) to Internet Standard
References: <> <> <> <> <> <> <> <> <> <> <> <> <> <> <> <> <> <> <>
From: "Joel M. Halpern" <>
Message-ID: <>
Date: Tue, 14 Feb 2017 14:05:11 -0500
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:45.0) Gecko/20100101 Thunderbird/45.7.1
MIME-Version: 1.0
In-Reply-To: <>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Archived-At: <>
Cc: IETF discussion list <>
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: IETF-Discussion <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Tue, 14 Feb 2017 19:05:14 -0000

Ole, it is true that we write in English, and there is always room for
"interpretation", sometimes reasoanble room, sometimes not.

But in this case we have a demonstrated difference in how people
understand the existing text.  When we have such a demonstrated
difference, we have an obligation to address it.


PS: The ability to do ECMP is why I helped with and supported the effort 
to get the flow label use for ECMP entropy documented.  That would 
ameliorate a number of problems.  I do not expect this revision of 2460 
to fix that, particularly since there seems to be little adoption.  I 
try not to get distracted looking for perfection.

On 2/14/17 1:59 PM, wrote:
> Joel,
>> There are two separate but related issues here.  One is what
>> behavior we want to require.  The other is whether we make the
>> document clear.
>> I think choosing to leave a document going to Internet Standard
>> ambiguous is a serious mistake, bordering on failure.  We know that
>> the choice of permitting insertion of extension headers has
>> interoperability implications.  There are weveral ways we can
>> clarify the text. o We could say "MUST NOT" be added.  Preferably
>> with explaantion of the problems being avoided.
> Yes.
>> o We could say "MUST NOT unless some other standards track RFC says
>> it is okay" which is technically correct but confusing.
> That's redundant. A new standards RFC can always be written that will
> override this.
>> o We can say "SHOULD NOT unless ..." as long as we can write a
>> clear description of the conditions under which it is safe.
> As the 6man chair we declared that as out of scope in the context of
> advancing 2460 to Internet standard.
>> o We can say "AMY< but note that doing so has the following risks"
>> if that is the IETF rough consensus.
> Middleboxes live in unregulated territory, there was no support (or
> even suggestion) in the working group for explicitly permitting
> header insertion.
>> But leaving it ambiguous ought to be a non-starter.
> Why? Leaving it as it was, including describing what we would imagine
> it would break was the preferred solution in the working group. Note
> that both IPv4 and IPv6 has this so-called ambiguity, that has caused
> no known interoperability issues and has existed for decades.
> This is perceived as an ambiguity only because we as a community have
> accepted layer violations for so long. This can be exemplified by
> discussions on maximum extension header length in IPv6. The only
> reason that discussion happens is because middleboxes require access
> to the transport header and beyond. In a purist 2460 view a router
> doing 5-tuple ECMP is not compliant with the specification.
> Clarifying that ambiguity would probably not make the operational
> community proud of us.
> The only purpose an outright ban would achieve, would be a
> pre-emptive strike against potential future standardisation.
> So when you think long enough about it, which choice you pick will
> unlikely have much consequence either way. It has no effect on
> implementations, it is not testable. In the context of 2460 this
> isn't a debate with many technical points.
> Which is why the working group could not reach a consensus, and we
> ended up decided it with a poll. Do you prefer your bike shed red,
> yellow or green. You have added a couple of more colours.
>> Personally, I would go with "MUST NOT", as I think that is the
>> robust and interoperable answer.  But that is MUCH less important
>> to me than our being unambiguous.
> There is an infinite set of creative (ab)uses of 2460 that hasn't
> been banned. I would claim it would be impossible to write a document
> which would MUST NOT every potential abuse.
> Best regards, Ole