IPv6 over unidirectional links?

Gorry Fairhurst <gorry@erg.abdn.ac.uk> Thu, 16 July 2009 08:00 UTC

Return-Path: <owner-ipdvb@erg.abdn.ac.uk>
X-Original-To: ietfarch-ipdvb-archive@core3.amsl.com
Delivered-To: ietfarch-ipdvb-archive@core3.amsl.com
Received: from localhost (localhost [127.0.0.1]) by core3.amsl.com (Postfix) with ESMTP id 0A92E3A6A2C for <ietfarch-ipdvb-archive@core3.amsl.com>; Thu, 16 Jul 2009 01:00:13 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.526
X-Spam-Level:
X-Spam-Status: No, score=-2.526 tagged_above=-999 required=5 tests=[AWL=0.073, BAYES_00=-2.599]
Received: from mail.ietf.org ([64.170.98.32]) by localhost (core3.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id AKcDDhX9DYwf for <ietfarch-ipdvb-archive@core3.amsl.com>; Thu, 16 Jul 2009 01:00:11 -0700 (PDT)
Received: from erg.abdn.ac.uk (dee.erg.abdn.ac.uk [IPv6:2001:630:241:204:203:baff:fe9a:8c9b]) by core3.amsl.com (Postfix) with ESMTP id 8222A3A67EA for <ipdvb-archive@ietf.org>; Thu, 16 Jul 2009 01:00:08 -0700 (PDT)
Received: from dee.erg.abdn.ac.uk (localhost [IPv6:::1]) by erg.abdn.ac.uk (8.13.4/8.13.4) with ESMTP id n6G7XiGM001215 for <ipdvb-subscribed-users@dee.erg.abdn.ac.uk>; Thu, 16 Jul 2009 08:33:44 +0100 (BST)
Received: (from majordomo.lists@localhost) by dee.erg.abdn.ac.uk (8.13.4/8.12.2/Submit) id n6G7XiVA001214 for ipdvb-subscribed-users; Thu, 16 Jul 2009 08:33:44 +0100 (BST)
X-Authentication-Warning: dee.erg.abdn.ac.uk: majordomo.lists set sender to owner-ipdvb@erg.abdn.ac.uk using -f
Received: from Gorry-Fairhursts-Laptop-6.local (fgrpf.plus.com [212.159.18.54]) (authenticated bits=0) by erg.abdn.ac.uk (8.13.4/8.13.4) with ESMTP id n6G7XZZh001192 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES128-SHA bits=128 verify=NOT) for <ipdvb@erg.abdn.ac.uk>; Thu, 16 Jul 2009 08:33:36 +0100 (BST)
Message-ID: <4A5ED7CF.20503@erg.abdn.ac.uk>
Date: Thu, 16 Jul 2009 08:33:35 +0100
From: Gorry Fairhurst <gorry@erg.abdn.ac.uk>
Organization: The University of Aberdeen is a charity registered in Scotland, No SC013683.
User-Agent: Thunderbird 2.0.0.22 (Macintosh/20090605)
MIME-Version: 1.0
To: ipdvb@erg.abdn.ac.uk
Subject: IPv6 over unidirectional links?
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Content-Transfer-Encoding: 8bit
X-ERG-MailScanner: Found to be clean, Found to be clean
Sender: owner-ipdvb@erg.abdn.ac.uk
Precedence: bulk
Reply-To: ipdvb@erg.abdn.ac.uk
X-ERG-MailScanner-From: owner-ipdvb@erg.abdn.ac.uk

Here is an off-list thread that Bernhard introduced on the use of IPv6 
autoconfiguration with unidirectional links. More thoughts would be welcome.

Gorry


 >>> Bernhard Collini-Nocker wrote:
 >>>>
 >>>> Dear Gorry,
 >>>>
 >>>> I´d like to add a point that I have raised a few times in the
 >>>> past years without too much feedback/support: there is in my
 >>>> opinion an issue with unidirectional
 >>>>  links and IPv6 (neighbourhood discovery) addressing of
 >>>> rx-only network adapters.
 >>>>
 >>>> --Bernhard
 >>
 >> Hi Gorry,
 >>
 >> Gorry Fairhurst schrieb:
 >>>
 >>> Here is what I recall: this is to do with IPv6 autoconf when
 >>> you can't do DAD, NUD, etc. Is that right?
 >>>
 >> right, it is all kind of tricky when the link is not per se
 >> bidirectional. The impacts may in many cases be neglectible,
 >> but there may corner cases.
 >>>
 >>> I don't recall what you proposed to do in this case though,
 >>> because on a unidirectional link, I'd expect the sender ND
 >>> cache to be pre-populated with IPv6 addresses (since ND/SEND
 >>> could not be used to query this). So is it right that the remote
 >>> endpoints just rely on RA's to find their own on-net prefix
 >>> and configure their IPv6 addresses without being able to
 >>> validate their uniqueness (is this an issue though?
 >>> - in receive-only applications, the endpoints never send
 >>> with this prefix anyway). Maybe I have misunderstood?
 >>
 >> Well, my concern was/is that in an environment, where
 >> destination IP addresses of rx-only devices are non-unique,
 >> but are used as identifiers this might cause problems.
 >> Also, some mechanisms of IPv6 might fail in what case such an
 >> interface might be unavailable? Actually there are both
 >> operational and conceptual aspects in that problematic.
 >>>
 >>> If we need work in this space, we'd need to decide if this
 >>> were a 6man or ipdvb issue - but there is certainly no harm
 >>> discussing this in ipdvb.
 >>
 >> I guess so.
 >>
 >> --Bernhard
 >>