Re: IID length text [was Re: Review of draft-ietf-6man-rfc4291bis-06]

Brian E Carpenter <brian.e.carpenter@gmail.com> Mon, 16 January 2017 19:57 UTC

Return-Path: <brian.e.carpenter@gmail.com>
X-Original-To: ipv6@ietfa.amsl.com
Delivered-To: ipv6@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id F22871299F6 for <ipv6@ietfa.amsl.com>; Mon, 16 Jan 2017 11:57:56 -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 lrYAqkmRuZbp for <ipv6@ietfa.amsl.com>; Mon, 16 Jan 2017 11:57:55 -0800 (PST)
Received: from mail-pg0-x235.google.com (mail-pg0-x235.google.com [IPv6:2607:f8b0:400e:c05::235]) (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 8F07012962C for <ipv6@ietf.org>; Mon, 16 Jan 2017 11:57:55 -0800 (PST)
Received: by mail-pg0-x235.google.com with SMTP id 194so17858936pgd.2 for <ipv6@ietf.org>; Mon, 16 Jan 2017 11:57:55 -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=Xg9aF18//bHp2tZYoipF8xFHtm92bAsqyWp2CNtr598=; b=WAwjwuJsJVF8+QZgQiA4n7eZlulsHR3Ppg8JxGYxtd2y5jVOeATzaBtsgqHmZPVluc x6FSTVJTvMSawySpcmcwyocdS6LLNXBRPTS56Vuy87JwgeJNxLWXWnO3BGY1oxKaV6AW H404mmCUV1EHVTvXxo0af0Ad/rxSEoHoPpoCe268nSTYF+UtGCny9SIiC4JQAKi7xezp 9AM0TecAnSFMGuXjmsDAcWYEWB3xFqpVFkx0llmhEgX3hkPVx8c7szb2AgOqAAAKbLUj Neof1WYKD5cEGmoke9Cd02wlapyUdTlnHluxFmL0o+Vl/jfYY0bXFqCFJAW/EpritPFU 9y1w==
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=Xg9aF18//bHp2tZYoipF8xFHtm92bAsqyWp2CNtr598=; b=ZB10JbekGtL3ycp1LEor+jgsnhhPJ1XSxILVToPcHP+w81/dPdrA9uhsgpfruZxhF2 v6SyulIn+qpAW0PypB+i6jDixTsyqjtjLBzyEvKM98MeJ5JW8v0KhwJkGTInUnkNPmDD Zkvlz7MKusuNIvQAZ5nGXAuw4U5WJGxAZAvOMXAHuligYtcxThy5l4q7EU/mjQboa0hJ Mzc0duamIe4MAFLc1IItwN8kgWlJ/D/HirONWAuTF3J84GqfYbLVhhklB2dZihCz+II2 FsaRyQEyWe5fguvVonTBWrJbbbNNhQkQfwYFCFKt9DaMMkSdTWifdh3XQb9i9Xee/Zxq JaPg==
X-Gm-Message-State: AIkVDXJOnLQcOzxoywAKfM3HaADtxdolZRjeZLFzpuYn+jPfgTELGvf3yDRbbFRnReJYtA==
X-Received: by 10.98.69.139 with SMTP id n11mr11091329pfi.65.1484596675069; Mon, 16 Jan 2017 11:57:55 -0800 (PST)
Received: from ?IPv6:2406:e007:4961:1:28cc:dc4c:9703:6781? ([2406:e007:4961:1:28cc:dc4c:9703:6781]) by smtp.gmail.com with ESMTPSA id i82sm1046345pfk.52.2017.01.16.11.57.52 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 16 Jan 2017 11:57:54 -0800 (PST)
Subject: Re: IID length text [was Re: Review of draft-ietf-6man-rfc4291bis-06]
To: Lorenzo Colitti <lorenzo@google.com>
References: <148406593094.22166.2894840062954191477.idtracker@ietfa.amsl.com> <m2fukqbbwv.wl-randy@psg.com> <F6953234-3F85-4E28-9861-433ADD01A490@gmail.com> <m2wpdzhncn.wl-randy@psg.com> <82245ef2-cd34-9bd6-c04e-f262e285f983@gmail.com> <m2d1frhjfn.wl-randy@psg.com> <18e6e13c-e605-48ff-4906-2d5531624d64@gmail.com> <CAKD1Yr1cvZ8Y3+bHeML=Xwqr+YgDspZGnZi=jqQj4qe2kMc4zw@mail.gmail.com> <m2lguffnco.wl-randy@psg.com> <CAKD1Yr1TrTiPRdyutobmb_77XJ7guNzLrg=H_p7qi4BfQ8V=GA@mail.gmail.com> <m2d1frfm6m.wl-randy@psg.com> <CAKD1Yr2Njjd8_Mr+6TRFF6C5pdcX4yFgpFVyEkykDuytu2B8mg@mail.gmail.com> <2A5073777007277764473D78@PSB> <4596c3d4-a337-f08e-7909-f14270b7085f@gmail.com> <CAN-Dau06R3iYRpYLADhvHox4C9qdsJCuxFsJapRhOQcWT4qk_g@mail.gmail.com> <CAO42Z2weZcoHiBzN94QAQ9WGhWR16PmMMFNg=5YLmr_dhPjjpA@mail.gmail.com> <fcf580ec-3617-ca5f-5337-37acb6e928ba@gmail.com> <CAKD1Yr25zNeQGvNJa=WzCjKMd9LaYrSwG=o4tUWn1Zc2ASZjrA@mail.gmail.com>
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
Message-ID: <93700502-5d49-86ce-11b0-ab9904423961@gmail.com>
Date: Tue, 17 Jan 2017 08:57:51 +1300
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0
MIME-Version: 1.0
In-Reply-To: <CAKD1Yr25zNeQGvNJa=WzCjKMd9LaYrSwG=o4tUWn1Zc2ASZjrA@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Archived-At: <https://mailarchive.ietf.org/arch/msg/ipv6/XldjLc8RfijSVPlWkOmycEKmDCA>
Cc: 6man <ipv6@ietf.org>
X-BeenThere: ipv6@ietf.org
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: "IPv6 Maintenance Working Group \(6man\)" <ipv6.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/ipv6>, <mailto:ipv6-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/ipv6/>
List-Post: <mailto:ipv6@ietf.org>
List-Help: <mailto:ipv6-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/ipv6>, <mailto:ipv6-request@ietf.org?subject=subscribe>
X-List-Received-Date: Mon, 16 Jan 2017 19:57:57 -0000

On 16/01/2017 22:36, Lorenzo Colitti wrote:
> Brian,
> 
> what's the specific rationale for this change? Is it a bug in 4291 which
> you're proposing that we resolve in 4291 bis? If so, what is the bug?

The bug is that in SLAAC, the IID length is a parameter, not a constant,
and that in routing protocols, the prefix length is a parameter, not
a constant. The addressing architecture needs to recognise that.

> The "interface identifiers are 64 bits" long text in RFC 4291 goes back all
> the way to 1998 and the text below would be a major change to text that has
> likely been baked into implementations for almost two decades years. I
> don't see why we would change that now.

Any SLAAC implementation that has 64 baked into it is already non-conformant.
But I very much doubt if anyone will need to change their code as a result
(except for any non-conformant routers such as you mentioned recently).

> BTW: if the reason for the text is a perceived contradiction between the
> fact that "IIDs are 64 bits" and "IPv6 addresses are aggregatable on all
> bit lengths" - I don't see a contradiction. 

I suggest discussing that with Randy Bush.

> In general, IPv6 addresses are
> aggregatable on all bit lengths. But global unicast addresses (other than
> ::/3) have a 64-bit IID, so links in that space are assigned 64-bit prefix
> lengths. These two properties can coexist even in global unicast space. For
> example, you could load-balance traffic to a given global unicast /64 by
> announcing it to the backbone as two /65s. The "addresses are aggregatable
> on all bit lengths" text means that the /65 are valid prefixes that can be
> routed by routers.

Sure. And this text doesn't aim to change anything in any current (and
non-broken) implememtations. It aims to respond to the objections that have
been discussed on the IETF list recently.

    Brian

> 
> Cheers,
> Lorenzo
> 
> On Sun, Jan 15, 2017 at 4:49 AM, Brian E Carpenter <
> brian.e.carpenter@gmail.com> wrote:
> 
>> NEW
>>    IPv6 routing is based on prefixes of any valid length up to 128
>> [BCP198].
>>    For example, [RFC6164] standardises 127 bit  prefixes on point-to-point
>>    links. However, consistent use of Stateless Address Autoconfiguration
>>    (SLAAC)[RFC4862] requires that all interfaces on a link use the same
>> length
>>    of Interface ID. In practice, this means that to guarantee
>> interoperability
>>    of SLAAC, a fixed length of Interface ID is necessary. For all currently
>>    allocated unicast addresses, except those that start with the binary
>>    value 000, that length is 64 bits. Note that this value is an arbitrary
>>    choice and might be changed for some future allocation of unicast
>> address
>>    space. Background on the 64 bit boundary in IPv6 addresses can be found
>>    in [RFC7421].
>>
>> Regards
>>    Brian
>>
>> --------------------------------------------------------------------
>> IETF IPv6 working group mailing list
>> ipv6@ietf.org
>> Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6
>> --------------------------------------------------------------------
>>
>