Re: [Idr] I-D Action: draft-ietf-idr-rs-bfd-02.txt

Nick Hilliard <nick@foobar.org> Mon, 13 March 2017 10:32 UTC

Return-Path: <nick@foobar.org>
X-Original-To: idr@ietfa.amsl.com
Delivered-To: idr@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 9182A1279EB for <idr@ietfa.amsl.com>; Mon, 13 Mar 2017 03:32:06 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -4.201
X-Spam-Level:
X-Spam-Status: No, score=-4.201 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, SPF_PASS=-0.001] autolearn=ham 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 OWap8IF2r70Q for <idr@ietfa.amsl.com>; Mon, 13 Mar 2017 03:32:04 -0700 (PDT)
Received: from mail.netability.ie (mail.netability.ie [IPv6:2a03:8900:0:100::5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 6A67D127078 for <idr@ietf.org>; Mon, 13 Mar 2017 03:32:03 -0700 (PDT)
X-Envelope-To: idr@ietf.org
Received: from cupcake.local (089-101-195156.ntlworld.ie [89.101.195.156] (may be forged)) (authenticated bits=0) by mail.netability.ie (8.15.2/8.15.2) with ESMTPSA id v2DAVwKn090218 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 13 Mar 2017 10:31:58 GMT (envelope-from nick@foobar.org)
X-Authentication-Warning: cheesecake.ibn.ie: Host 089-101-195156.ntlworld.ie [89.101.195.156] (may be forged) claimed to be cupcake.local
Message-ID: <58C6751D.60306@foobar.org>
Date: Mon, 13 Mar 2017 10:31:57 +0000
From: Nick Hilliard <nick@foobar.org>
User-Agent: Postbox 5.0.11 (Macintosh/20170302)
MIME-Version: 1.0
To: Robert Raszuk <robert@raszuk.net>
References: <148924277112.2960.17904473852401253352@ietfa.amsl.com> <m2k27tzs5k.wl-randy@psg.com> <CA+b+ERmmqtUkJMtfOE9ABFHN0gNdztjOGELmirNgWRnDENrjaA@mail.gmail.com>
In-Reply-To: <CA+b+ERmmqtUkJMtfOE9ABFHN0gNdztjOGELmirNgWRnDENrjaA@mail.gmail.com>
X-Enigmail-Version: 1.2.3
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Archived-At: <https://mailarchive.ietf.org/arch/msg/idr/HRU5YEBmUfJUVYeOAt7wzWKzxaU>
Cc: Interminable Discussion Room <idr@ietf.org>
Subject: Re: [Idr] I-D Action: draft-ietf-idr-rs-bfd-02.txt
X-BeenThere: idr@ietf.org
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: Inter-Domain Routing <idr.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/idr>, <mailto:idr-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/idr/>
List-Post: <mailto:idr@ietf.org>
List-Help: <mailto:idr-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/idr>, <mailto:idr-request@ietf.org?subject=subscribe>
X-List-Received-Date: Mon, 13 Mar 2017 10:32:06 -0000

Robert Raszuk wrote:
> Let's observe that the ultimate objective of this draft (and in fact
> much more) can be achieved by assuring that clients receive more then
> one path to given bgp destinations at normal operation. 

This is a fundamental misunderstanding.  The aim of this draft is to
ensure that traffic isn't blackholed if there is a layer 2 incongruity
on the IXP which causes connectivity to be non commutative.

Given the following topology, A's connectivity to RS works fine, and B's
connectivity to RS works fine, but A cannot communicate with B:

>    +-----+    +-----+
>    |     +--> |     |
>    |  A  |    |  B  |
>    |     | <--+     |
>    +-----+    +-----+
>       |           |
>       | +------+  |
>       +-+      +--+
>         |  RS  |
>         |      |
>         +------+

What's needed is some protocol running between A and B to ensure that
they can still talk to each other, i.e. BFD.

No amount of alternative paths will save you in this situation because
the control plane (RS) has connectivity to both data plane routers.

Nick