Re: [Lsr] Mirja Kühlewind's No Objection on draft-ietf-ospf-ospfv2-hbit-11: (with COMMENT)

Alvaro Retana <aretana.ietf@gmail.com> Mon, 02 December 2019 17:18 UTC

Return-Path: <aretana.ietf@gmail.com>
X-Original-To: lsr@ietfa.amsl.com
Delivered-To: lsr@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 5D1C11200B2; Mon, 2 Dec 2019 09:18:44 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.998
X-Spam-Level:
X-Spam-Status: No, score=-1.998 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_HELO_NONE=0.001, SPF_PASS=-0.001, UNPARSEABLE_RELAY=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 8yqAdOOfLEQL; Mon, 2 Dec 2019 09:18:42 -0800 (PST)
Received: from mail-wr1-x433.google.com (mail-wr1-x433.google.com [IPv6:2a00:1450:4864:20::433]) (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 70F38120091; Mon, 2 Dec 2019 09:18:42 -0800 (PST)
Received: by mail-wr1-x433.google.com with SMTP id n1so23993wra.10; Mon, 02 Dec 2019 09:18:42 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:in-reply-to:references:mime-version:date:message-id:subject:to :cc:content-transfer-encoding; bh=Rmq274e1wQF3W/gMax7kKahxN3MSCZIF6l4W237mV9w=; b=NuLZVmQavMsdVeqaWgkx+nh0pVxiv63aF+BjnbU6we0BI8m2kYVXn09t/aotceAlgx lUyWuV/L6cflTAHwvYJl6gc8IWvqI83va30jKF8GVMZYydBBnWh6r6sRyFsqDDiEJfBW iw2uAedE6f1RIl+1ae9RiaDOEtoSLJv8AKNczmZmF6YLYSyCwRF0ZFDHIxLX+2UWOUJI DY1Qt3gL7rsR+nBYwnB5slcNQ+nzidfYL2kp2mfopQ3jWadK9Hp6RERwyyv9aJI/R9Ik cQsaeAQqHCYxSOdFpnjpH2pwBo3U1P32s6BraKYkLOVpmy3/SqS5QzmqvW3/fZi/gkmo o14g==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:in-reply-to:references:mime-version:date :message-id:subject:to:cc:content-transfer-encoding; bh=Rmq274e1wQF3W/gMax7kKahxN3MSCZIF6l4W237mV9w=; b=Zughp4Egn1V38s8Lh65ZkDi1CDmdlVJX8EcH+sEuRSuvrnMczF9ydd/pi83coM3yA/ 30DR8Y8cFtj6YN2u3sJEb+gjHqgygb5El+KvQbIQyyiWu93mgX+lfDYK9CIlozxOGvCQ Y9xafcqMCv3RbolOVTTLNGI0wiuRa6aAmTHzkJoHQVCtpME8LE3XnSIqQKf3/YhekbAU PBybEVxk2OXheTZucVuGxxmq26pbJ+jOUMq31mA44kW/0RCwJhXxbxL4mVRwY9v8qmAK kGMOqInmcZ+YwdUMXeJ8pQXlPyRWqjVrqfcMndJ+m9UL0sh0dCEBMIb/gEasUSb0J7VB cK1g==
X-Gm-Message-State: APjAAAWC7pDBjjATbPwDdtCy6xL0UOWiQ1Xqhaq2g/nGgl16O9OsQ6yz BmM9TxrlW07oWGZjOu5Ni8IjsUjYlyjb6XHiAa1p3Ed7
X-Google-Smtp-Source: APXvYqyoSMbrU8qusjXkLyztiNSpYZWCXLC1Cw0aqmP7e3Z/9GGQbVdFAgcr2fYfEGzGCXBB3AaQToAYMKEM+WwAw7w=
X-Received: by 2002:adf:f78d:: with SMTP id q13mr7672949wrp.365.1575307120535; Mon, 02 Dec 2019 09:18:40 -0800 (PST)
Received: from 1058052472880 named unknown by gmailapi.google.com with HTTPREST; Mon, 2 Dec 2019 09:18:39 -0800
From: Alvaro Retana <aretana.ietf@gmail.com>
In-Reply-To: <157530120371.4287.7408962930016536241.idtracker@ietfa.amsl.com>
References: <157530120371.4287.7408962930016536241.idtracker@ietfa.amsl.com>
MIME-Version: 1.0
Date: Mon, 2 Dec 2019 09:18:39 -0800
Message-ID: <CAMMESsz_nBBLaka+2DwupxFQDPcB1RypSToHoYT32B0A8q5A7Q@mail.gmail.com>
To: =?UTF-8?Q?Mirja_K=C3=BChlewind_via_Datatracker?= <noreply@ietf.org>, =?UTF-8?Q?Mirja_K=C3=BChlewind?= <ietf@kuehlewind.net>, The IESG <iesg@ietf.org>
Cc: draft-ietf-ospf-ospfv2-hbit@ietf.org, lsr-chairs@ietf.org, lsr@ietf.org, Yingzhen Qu <yingzhen.ietf@gmail.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Archived-At: <https://mailarchive.ietf.org/arch/msg/lsr/W9CiaDHnEIRjcVbyX696CCJVsZA>
Subject: Re: [Lsr] =?utf-8?q?Mirja_K=C3=BChlewind=27s_No_Objection_on_draft-i?= =?utf-8?q?etf-ospf-ospfv2-hbit-11=3A_=28with_COMMENT=29?=
X-BeenThere: lsr@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Link State Routing Working Group <lsr.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/lsr>, <mailto:lsr-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/lsr/>
List-Post: <mailto:lsr@ietf.org>
List-Help: <mailto:lsr-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/lsr>, <mailto:lsr-request@ietf.org?subject=subscribe>
X-List-Received-Date: Mon, 02 Dec 2019 17:18:44 -0000

On December 2, 2019 at 10:40:05 AM, Mirja Kühlewind wrote:

Mirja:

Hi!

...
> 1) This sentence in section 3:
> "An OSPFv2 router advertising a router-LSA with the H-bit
> set indicates that it MUST NOT be used as a transit router (see
> Section 4) by other OSPFv2 routers in the area supporting the
> functionality."
> Isn't the MUST here too restrictive? What if the router is the part of the
> only path to a certain host? Or is the assumption that this host is some kind
> of endhost/deadend, but then it should never be on the shortest path anyway,
> or?
>
> Later on you say
> "When the H-bit is set, the OSPFv2 router is a Host (non-transit)
> router and is incapable of forwarding transit traffic."
> However, there might also be routers that don't understand the H bit and
> therefore will route traffic over this host anyway, no?

Completely avoiding transit traffic is the goal of the H-bit, which is
the reason/justification of the "MUST NOT".  Hence it being called the
Host-bit.

rfc6987 defines the "best effort" functionality that would be
equivalent to "SHOULD NOT": if no alternate path exits then the path
through the router can still be used.

§8 (in the third bullet) mentions the case where a rogue router can
partition a network by setting the H-Bit...and §5 talks about the
mitigation in mixed environments, where the recommendation (third
bullet) results in the rfc6987 behavior if not all the routers
advertise support.


> 2) Shouldn't this document update RFC2328, given section 4 and this sentence
> in section 2: "If the H-bit is set then the calculation of the shortest-
> path tree for an area, as described in section 16.1 of [RFC2328], is
> modified by including a check to verify that transit vertices DO NOT
> have the H-bit set (see Section 4)."
> (And why is DO NOT in upper letters?)

Because the H-bit is an optional feature and not intended to be
supported by all OSPFv2 routers, then the formal Update is not needed.


> 3) Is there an attack that by spoofing the H-bit an attacker could influence
> the routing such that traffic is router over a malicious node instead? I guess
> there are multiple ways to impact the routing that way and this might not be
> specific to the H bit but maybe still worth thinking about it once more...?

Yes.  By using the H-bit the traffic is directed away from the node,
which would force the traffic through another path, including a
specific node.  Similar to the last bullet in §8, this action would be
indistinguishable from the proper use of the H-bit, or from simply
shutting down an interface...

Thanks for the review!

Alvaro.