Re: [v6ops] SLAAC renum: Problem Statement & Operational workarounds

Fernando Gont <> Thu, 31 October 2019 19:44 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id A3B461208E3 for <>; Thu, 31 Oct 2019 12:44:47 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -1.899
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=ham autolearn_force=no
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id z3mdSzDyuXuK for <>; Thu, 31 Oct 2019 12:44:46 -0700 (PDT)
Received: from ( []) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by (Postfix) with ESMTPS id DD37C1208CA for <>; Thu, 31 Oct 2019 12:44:45 -0700 (PDT)
Received: from [] (unknown []) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by (Postfix) with ESMTPSA id 37D248679F; Thu, 31 Oct 2019 20:44:42 +0100 (CET)
To: Owen DeLong <>, Ted Lemon <>
References: <> <> <> <> <>
From: Fernando Gont <>
Openpgp: preference=signencrypt
Message-ID: <>
Date: Thu, 31 Oct 2019 16:43:08 -0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0
MIME-Version: 1.0
In-Reply-To: <>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Archived-At: <>
Subject: Re: [v6ops] SLAAC renum: Problem Statement & Operational workarounds
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: v6ops discussion list <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Thu, 31 Oct 2019 19:44:52 -0000

On 27/10/19 16:35, Owen DeLong wrote:
>> On Oct 27, 2019, at 10:14 , Ted Lemon <
>> <>> wrote:
>> On Oct 27, 2019, at 11:05 AM, Philip Homburg
>> < <>> wrote:
>>> If you think that this is an important thing to fix, feel free to 
>>> talk about it. But why in this discussion? SEND doesn't do anything for
>>> flash renumbering. From an operational point of view, RA-guard is much
>>> more attractive then SEND. So it is not clear to me that there is any
>>> need for SEND. But I could be wrong. In any case, if there is a need
>>> to discuss SEND we could do that separately.
>> I think you missed my point.  You can’t do flash renumbering by
>> advertising a prefix with a valid lifetime of zero, because that will
>> be ignored by hosts.   If it were not ignored by hosts, it would be a
>> very effective DoS vector.    And so if you want to be able to flash
>> deprecate a route, you need some way to validate that the deprecation
>> is coming from the same source as the route.   Hence my suggested
>> “limited SEND”.
>> Limited SEND would not be hard to implement.   Yes, it would be
>> marginally harder than just saying that hosts should accept flash
>> deprecation of prefixes.   But nobody with any sense is going to
>> implement that in their IP stack, so in practice if you want this to
>> work, you need some way to do flash deprecations that doesn’t create a
>> massive attack vector.
> It’s only a DOS vector if the attacker is already on-LAN.
> I recognize that there are environments where that is expected behavior
> (e.g. Coffee Shop Wifi, University networks, etc.),but
> it’s not the case for the average residential CPE and residential LAN
> segments.
> In the vast majority of situations where I would expect hostile hosts to
> be likely to be on LAN, I don’t think I’d be using
> SLAAC for address assignment in the first place. Most likely, I’d want
> stateful DHCP in such instances.

You can do SLAAC as long as you do FHS. At which point the issue raised
by Ted is a non-issue.

Fernando Gont
SI6 Networks
PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492