Re: What if? [was Re: Extension Header Insertion]

Fernando Gont <fernando@gont.com.ar> Tue, 10 December 2019 08:39 UTC

Return-Path: <fernando@gont.com.ar>
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 4ABD4120112 for <ipv6@ietfa.amsl.com>; Tue, 10 Dec 2019 00:39:45 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.899
X-Spam-Level:
X-Spam-Status: No, score=-1.899 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=unavailable autolearn_force=no
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 IMDfqE7NnOah for <ipv6@ietfa.amsl.com>; Tue, 10 Dec 2019 00:39:43 -0800 (PST)
Received: from fgont.go6lab.si (fgont.go6lab.si [91.239.96.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id C9AC712010E for <6man@ietf.org>; Tue, 10 Dec 2019 00:39:42 -0800 (PST)
Received: from [192.168.1.7] (unknown [181.113.147.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by fgont.go6lab.si (Postfix) with ESMTPSA id 12C5286133; Tue, 10 Dec 2019 09:39:39 +0100 (CET)
Subject: Re: What if? [was Re: Extension Header Insertion]
To: Brian E Carpenter <brian.e.carpenter@gmail.com>, adrian@olddog.co.uk, 'Ron Bonica' <rbonica=40juniper.net@dmarc.ietf.org>, '6man' <6man@ietf.org>
References: <BN7PR05MB5699D9BA988F96E2F41CD390AE580@BN7PR05MB5699.namprd05.prod.outlook.com> <00dc01d5ae73$c361b450$4a251cf0$@olddog.co.uk> <dbcdeb1a-0091-da2b-20df-d991e6c06091@gmail.com> <9bc47200-4fea-37ce-0ede-cbf6a5f70ea9@gmail.com>
From: Fernando Gont <fernando@gont.com.ar>
Autocrypt: addr=fernando@gont.com.ar; prefer-encrypt=mutual; keydata= mQINBE5so2gBEACzBQBLUy8nzgAzSZn6ViXT6TmZBFNYNqTpPRvTVtUqF6+tkI+IEd9N2E8p pXUXCd0W4dkxz6o7pagnK63m4QSueggvp881RVVHOF8oTSHOdnGxLfLeLNJFKE1FOutU3vod GK/wG/Fwzkv9MebdXpMlLV8nnJuAt66XGl/lU1JrNfrKO4SoYQi4TsB/waUQcygh7OR/PEO0 EttiU8kZUbZNv58WH+PAj/rdZCrgUSiGXiWUQQKShqKnJxLuAcTcg5YRwL8se/V6ciW0QR9i /sr52gSmLLbW5N3hAoO+nv1V/9SjJAUvzXu43k8sua/XlCXkqU7uLj41CRR72JeUZ4DQsYfP LfNPC98ZGTVxbWbFtLXxpzzDDT8i3uo7w1LJ2Ij/d5ezcARqw01HGljWWxnidUrjbTpxkJ9X EllcsH94mer728j/HKzC9OcTuz6WUBP3Crgl6Q47gY5ZIiF0lsmd9/wxbaq5NiJ+lGuBRZrD v0dQx9KmyI0/pH2AF8cW897/6ypvcyD/1/11CJcN+uAGIrklwJlVpRSbKbFtGC6In592lhu7 wnK8cgyP5cTU+vva9+g6P1wehi4bylXdlKc6mMphbtSA+T3WBNP557+mh3L62l4pGaEGidcZ DLYT2Ud18eAJmxU3HnM8P3iZZgeoK7oqgb53/eg96vkONXNIOwARAQABtCVGZXJuYW5kbyBH b250IDxmZ29udEBzaTZuZXR3b3Jrcy5jb20+iQJBBBMBAgArAhsjBQkSzAMABgsJCAcDAgYV CAIJCgsEFgIDAQIeAQIXgAUCTmylpQIZAQAKCRCuJQ1VHU50kv7wD/9fuNtTfxSLk3B3Hs3p ixTy8YXVjdkVwWlnJjFd7BOWmg7sI+LDhpjGfT6+ddOiwkumnvUZpObodj4ysH0i8c7P4C5t F9yu7WjklSlrB5Rth2CGChg5bKt541z2WHkFFxys9qBLmCSYDeKQkzLqhCjIUJizY2kOJ2GI MnSFDzJjhSFEh//oW830Y8fel1xnf/NVF+lBVtRMtMOfoWUqDjvP3sJ1G4zgkDCnF0CfncLx +hq2Mv26Uq9OTzvLH9aSQQ/f067BOkKAJKsfHdborX4E96ISTz57/4xECRSMr5dVsKVm4Y// uVIsb+L5z+a32FaiBZIAKDgnJO7Z8j6CV5e5yfuBTtX52Yi9HjYYqnYJGSDxYd6igD4bWu+7 xmJPHjkdqZgGV6dQIgiUfqkU+s5Cv350vK48CMaT/ZLo2BdsMhWsmaHmb+waePUMyq6E4E9x 9Js+EJb9ZiCfxS9exgieZQpet1L36IvhiwByvkQM009ywfa30JeMOltUtfLi5V06WQWsTzPL 5C+4cpkguSuAJVDTctjCA0moIeVDOpJ8WH9voQ4IeWapQnX35OIoj1jGJqqYdx65gc1ygbyx b8vw+pJ9E5GLse5TQnYifOWpXzX9053dtbwp/2OVhU4KLlzfCPCEsoTyfu9nIZxdI2PMwiL5 M85BfjX4NmwBLmPGoLkCDQRObKNoARAAqqXCkr250BchRDmi+05F5UQFgylUh10XTAJxBeaQ UNtdxZiZRm6jgomSrqeYtricM9t9K0qb4X2ZXmAMW8o8AYW3RrQHTjcBwMnAKzUIEXXWaLfG cid/ygmvWzIHgMDQKP+MUq1AGQrnvt/MRLvZLyczAV1RTXS58qNaxtaSpc3K/yrDozh/a4pu WcUsVvIkzyx43sqcwamDSBb6U8JFoZizuLXiARLLASgyHrrCedNIZdWSx0z0iHEpZIelA2ih AGLiSMtmtikVEyrJICgO81DkKNCbBbPg+7fi23V6M24+3syHk3IdQibTtBMxinIPyLFF0byJ aGm0fmjefhnmVJyCIl/FDkCHprVhTme57G2/WdoGnUvnT7mcwDRb8XY5nNRkOJsqqLPemKjz kx8mXdQbunXtX9bKyVgd1gIl+LLsxbdzRCch773UBVoortPdK3kMyLtZ4uMeDX3comjx+6VL bztUdJ1Zc9/njwVG8fgmQ+0Kj5+bzQfUY+MmX0HTXIx3B4R1I1a8QoOwi1N+iZNdewV5Zfq+ 29NlQLnVPjCRCKbaz9k6RJ2oIti55YUI6zSsL3lmlOXsRbXN5bRswFczkNSCJxJMlDiyAUIC WOay7ymzvgzPa+BY/mYn94vRaurDQ4/ljOfj6oqgfjts+dJev4Jj89vp8MQI3KJpZPEAEQEA AYkCJQQYAQIADwUCTmyjaAIbDAUJEswDAAAKCRCuJQ1VHU50km4xEACho45PZrUjY4Zl2opR DFNo5a6roTOPpgwO9PcBb3I5F8yX2Dnew+9OhgWXbBhAFq4DCx+9Gjs43Bn60qbZTDbLGJ/m 8N4PwEiq0e5MKceYcbetEdEUWhm5L6psU9ZZ82GR3UGxPXYe+oifEoJjOXQ39avf9S8p3yKP Diil0E79rn7LbJjMcgMLyjFg9SDoJ6pHLtniJoDhEAaSSgeV7Y745+gyMIdtQmrFHfqrFdjq D6G0HE+Z68ywc5KN67YxhvhBmSycs1ZSKAXv1zLDlXdmjHDHkU3xMcB+RkuiTba8yRFYwb/n j62CC4NhFTuIKOc4ta3dJsyXTGh/hO9UjWUnmAGfd0fnzTBZF8Qlnw/8ftx5lt4/O+eqY1EN RITScnPzXE/wMOlTtdkddQ+QN6xt6jyR2XtAIi7aAFHypIqA3lLI9hF9x+lj4UQ2yA9LqpoX 6URpPOd13JhAyDe47cwsP1u9Y+OBvQTVLSvw7Liu2b4KjqL4lx++VdBi7dXsjJ6kjIRjI6Lb WVpxe8LumMCuVDepTafBZ49gr7Fgc4F9ZSCo6ChgQNLn6WDzIkqFX+42KuHz90AHWhuW+KZR 1aJylERWeTcMCGUSBptd48KniWmD6kPKpzwoMkJtEXTuO2lVuborxzwuqOTNuYg9lWDl7zKt wPI9brGzquUHy4qRrA==
Message-ID: <99e4bdd0-711d-7406-d3bf-786b0238c1e7@gont.com.ar>
Date: Tue, 10 Dec 2019 03:39:16 -0500
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.1
MIME-Version: 1.0
In-Reply-To: <9bc47200-4fea-37ce-0ede-cbf6a5f70ea9@gmail.com>
Content-Type: text/plain; charset="utf-8"
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Archived-At: <https://mailarchive.ietf.org/arch/msg/ipv6/XRUl98TCAXYcKJlkXFglFJpL87E>
X-BeenThere: ipv6@ietf.org
X-Mailman-Version: 2.1.29
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: Tue, 10 Dec 2019 08:39:45 -0000

Hi, Brian,

On 9/12/19 20:21, Brian E Carpenter wrote:
> So, let's assume that two consecutive SRH headers are allowed in the same packet.

Part of the problem with all these discussions is that folks seem to
assume that there is no rationale for the existing rules, and they
insist on changing them without providing any analysis/rationale.

RFC8200 contains what should be considered a recommendation (at the very
least) against multiple routing headers.


A RH is meant to convey some sort of information about the path that a
packet can traverse. So two SRHs would mean that the same packet should
follow two different paths, at the same time. That doesn't seem to be
much sense to me.



> So the first one (an example from draft-ietf-6man-segment-routing-header-26) is:
> 
>        Segments Left=2
>        Last Entry=2
>        Flags=0
>        Tag=0
>        Segment List[0]=S3
>        Segment List[1]=S2
>        Segment List[2]=S1
> 
> and the second one is
> 
>        Segments Left=1
>        Last Entry=1
>        Flags=0
>        Tag=0
>        Segment List[0]=S4
>        Segment List[1]=S5
> 
> I made that up and it's obviously nonsense, but if this is allowed why aren't the rules for processing conflicting SRHs described in draft-ietf-6man-segment-routing-header-26? Do we need to recall it from the RFC Editor queue to be fixed?

It is clearly recommended against.

However, the very draft-voyer-6man-extension-header-insertion doesn't
even provide a rationale for EH insertion in the first place, let alone
for this specific case that you (reasonably) raise.

Unfortunately, when operating in a mode where analysis is discoraged,
and "why?" questions are dismissed, I'm not sure there is any other
possible alternative outcome than this -- documents with lots of
unspecified stuff, violating specs at will, and designs try to cover up
what seem to be sub-optimal design choices (like using 128-bit labels
for what are expected/supposed to be limited domains) by screwing up the
architecture to save bytes that were wasted elsewhere.

Thanks,
-- 
Fernando Gont
e-mail: fernando@gont.com.ar || fgont@si6networks.com
PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1