Re: OPS-DIR review of draft-6man-stable-privacy-addresses-16

Tim Chown <> Mon, 27 January 2014 19:10 UTC

Return-Path: <>
Received: from localhost ( []) by (Postfix) with ESMTP id 9FABC1A0239; Mon, 27 Jan 2014 11:10:55 -0800 (PST)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -1.756
X-Spam-Status: No, score=-1.756 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, RP_MATCHES_RCVD=-0.535, SPF_NEUTRAL=0.779] autolearn=ham
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id XTLRI7si_DtA; Mon, 27 Jan 2014 11:10:53 -0800 (PST)
Received: from ( [IPv6:2001:630:d0:f102::25e]) by (Postfix) with ESMTP id 45AE91A007C; Mon, 27 Jan 2014 11:10:53 -0800 (PST)
Received: from (localhost []) by (8.13.8/8.13.8) with ESMTP id s0RJAmll031851; Mon, 27 Jan 2014 19:10:48 GMT
X-DKIM: Sendmail DKIM Filter v2.8.2 s0RJAmll031851
DKIM-Signature: v=1; a=rsa-sha1; c=simple/simple;; s=201304; t=1390849848; bh=PfMDkB9huRVChx69l4CgwTZ6x2A=; h=Mime-Version:Subject:From:In-Reply-To:Date:Cc:References:To; b=hjSJpf/XY+nncnyqD5Mf76OiCfWhWFmILDFl4OFeXPjBqd0wd61mzqBYz9862jen9 Pzodp4qmK9KRZEZd969qE7dXS9Q50QUylrxcS75GdkGqGwsYx9f9WAvYMt+Hs7ox6k z/DYcLH0AWxU68aCFOefALUJRdG/EvPY2MskNNR4=
Received: from ( [2001:630:d0:f102::25d]) by ( [2001:630:d0:f102::25e]) envelope-from <> with ESMTP (valid=N/A) id q0QJAm0959647084q8 ret-id none; Mon, 27 Jan 2014 19:10:48 +0000
Received: from [] ( []) (authenticated bits=0) by (8.13.8/8.13.8) with ESMTP id s0RJ9R8V022277 (version=TLSv1/SSLv3 cipher=AES128-SHA bits=128 verify=NO); Mon, 27 Jan 2014 19:09:28 GMT
Content-Type: text/plain; charset="windows-1252"
Mime-Version: 1.0 (Mac OS X Mail 7.1 \(1827\))
Subject: Re: OPS-DIR review of draft-6man-stable-privacy-addresses-16
From: Tim Chown <>
In-Reply-To: <>
Date: Mon, 27 Jan 2014 19:09:31 +0000
Content-Transfer-Encoding: quoted-printable
Message-ID: <EMEW3|668ce6db736e9204f32cb53fc886e07aq0QJAm03tjc||>
References: <> <EMEW3|8f37f1d5d449ce20468ee92a0af181faq0M16n03tjc||> <> <> <EMEW3|12f5e9bae279fcfd68e300eb7c33b88aq0NHE703tjc||> <> <> <EMEW3|098bca4b1eaa1178fbc2402cb1bb79e2q0QHBi03tjc||> <> <>
To: Christian Huitema <>
X-Mailer: Apple Mail (2.1827)
X-ECS-MailScanner: Found to be clean, Found to be clean
X-smtpf-Report: sid=q0QJAm095964708400; tid=q0QJAm0959647084q8; client=relay,ipv6; mail=; rcpt=; nrcpt=6:0; fails=0
X-ECS-MailScanner-Information: Please contact the ISP for more information
X-ECS-MailScanner-ID: s0RJAmll031851
Cc: "" <>, Fernando Gont <>, "" <>, "" <>, "" <>
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: "IPv6 Maintenance Working Group \(6man\)" <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Mon, 27 Jan 2014 19:10:55 -0000


On 27 Jan 2014, at 17:49, Christian Huitema <> wrote:

>> So I think the thing here is that the IID can't be guaranteed to be stable per prefix, because there are factors that may cause it to change.  The only way to be sure it's stable per prefix is to store the IID used per prefix, or to find some stateless generation method for which there can be no change. Storing the per-prefix IIDs essentially puts a permanent list of all addresses the device has ever used into persistent storage on the device.
> In fact, the draft already has some text about remembering DAD collisions:
>                                                   In order to mitigate this potential problem,
>   nodes MAY record the DAD_Counter value employed for a specific
>   {Prefix, Net_Iface, Network_ID} tuple in non-volatile memory, such
>   that the same DAD_Counter value is employed when configuring an
>   address for the same Prefix and subnet at any other point in time.
> This can be a baby step towards "a permanent list of all addresses the device has ever used..." But then, we have to wonder whether we really need to guarantee that the address will remain constant for all locations that the device visits. In practice, it feels like the "stable address" property is mostly needed in the "home base" of the device, for example the corporate network if the device is registered in one. On the other hand, I don't think many will object if their device gets a different address each time they visit the same airport bar...

I agree with the likely use case. I suggested something to consider along those lines for Fernando’s related draft.