Re: Updated IID length text

Brian E Carpenter <brian.e.carpenter@gmail.com> Fri, 20 January 2017 01:23 UTC

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Subject: Re: Updated IID length text
To: Peter Dordal <pld@cs.luc.edu>, "Manfredi, Albert E" <albert.e.manfredi@boeing.com>, 6man <ipv6@ietf.org>
References: <148406593094.22166.2894840062954191477.idtracker@ietfa.amsl.com> <CAKD1Yr1cvZ8Y3+bHeML=Xwqr+YgDspZGnZi=jqQj4qe2kMc4zw@mail.gmail.com> <m2lguffnco.wl-randy@psg.com> <CAKD1Yr1TrTiPRdyutobmb_77XJ7guNzLrg=H_p7qi4BfQ8V=GA@mail.gmail.com> <m2d1frfm6m.wl-randy@psg.com> <CAKD1Yr2Njjd8_Mr+6TRFF6C5pdcX4yFgpFVyEkykDuytu2B8mg@mail.gmail.com> <2A5073777007277764473D78@PSB> <4596c3d4-a337-f08e-7909-f14270b7085f@gmail.com> <CAN-Dau06R3iYRpYLADhvHox4C9qdsJCuxFsJapRhOQcWT4qk_g@mail.gmail.com> <CAO42Z2weZcoHiBzN94QAQ9WGhWR16PmMMFNg=5YLmr_dhPjjpA@mail.gmail.com> <fcc7f136-b5da-527e-b495-5a2d7f7a3ce8@gmail.com> <55bb8bdbfbf4439da0aa702e5bc03e2c@XCH15-06-11.nw.nos.boeing.com> <bb79ce41f2cc465dab0a7f26466be26f@XCH15-06-11.nw.nos.boeing.com> <ed9fe2df-0dce-0ddc-bdee-561217d089bb@gmail.com> <e8b4d426-55b4-bd2e-ea4f-f8e56e831d44@gmail.com> <28102f87f8e043248da16d9273d4c7d7@XCH15-06-11.nw.nos.boeing.com> <049d1ecb-3780-9109-41c2-4e61f738adaf@cs.luc.edu>
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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Date: Fri, 20 Jan 2017 14:23:16 +1300
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On 20/01/2017 10:43, Peter Dordal wrote:
> On 01/19/2017 02:30 PM, Manfredi, Albert E wrote:
>> Brian, I'm completely on board with your text below. I think that this should satisfy even the objections, by avoiding any "speculation."
>>
>> Bert
>> NEW NEW
>>     IPv6 routing is based on prefixes of any valid length up to 128 [BCP198].
>>     For example, [RFC6164] standardises 127 bit prefixes on point-to-point
>>     links. However, correct use of Stateless Address Autoconfiguration
>>     (SLAAC)[RFC4862] requires all interfaces on a link to use the same length
>>     of Interface ID. Furthermore, to guarantee robust interoperability of SLAAC,
>>     a consistent length of Interface ID is desirable. For this reason, the
>>     Interface ID of all currently allocated unicast addresses, except those that
>>     start with the binary value 000, is required to be 64 bits long. Background
>>     on the 64 bit boundary in IPv6 addresses can be found in [RFC7421].
>>
> I intend no quarrel with this wording, and I think it is unfortunate 
> this 64 debate has come up again.
> Say whatever needs to be said, and ship it.
> 
> However, the text above states that SLAAC is *the* reason for 64-bit 
> IIDs. 

No, it says it's the reason for needing a *consistent* length of IID, that's
all. As others have pointed out, we wouldn't pick e.g. 8, for other reasons
including the ones you give.

   Brian

> This is only
> partly true: 64-bit IIDs also have security and privacy implications.
> 
> Security, because an attacker can't realistically probe a site that uses 
> randomized
> 64-bit IIDs. A site that uses /120 prefixes, on the other hand, is quite 
> exposed.
> 
> Privacy, because creating temporary IIDs becomes harder and harder as 
> the number
> of bits goes down. In the IPv4 world, privacy is one reason we have NAT.
> 
> Peter Dordal
> Loyola University Chicago CS Dept
> .
>