Re: Objection to draft-ietf-6man-rfc4291bis-07.txt

Fernando Gont <fgont@si6networks.com> Tue, 28 February 2017 20:36 UTC

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Subject: Re: Objection to draft-ietf-6man-rfc4291bis-07.txt
To: Brian E Carpenter <brian.e.carpenter@gmail.com>, Lorenzo Colitti <lorenzo@google.com>, David Farmer <farmer@umn.edu>
References: <20170223134026.GI5069@gir.theapt.org> <9277BC0B-04F3-4FC1-901E-F83A8F0E02D7@google.com> <58AF6429.70809@foobar.org> <902276E9-0521-4D4E-A42B-C45E64763896@google.com> <58AF726A.3040302@foobar.org> <F7C230DE-4759-4B78-ABF2-6799F85B3C62@google.com> <58B014F6.2040400@foobar.org> <6DA95097-8730-4353-A0C9-3EB4719EA891@google.com> <CAKD1Yr0qk_njAGnex_FZsYisCVw=eM8hXTr1v+wqvcfX_09wiQ@mail.gmail.com> <CAN-Dau0ohz3Wp55bs+eoFvSyoUjuKfjzKGSAsJS3wUt3z7TGtA@mail.gmail.com> <CAKD1Yr0wK8EiAbz39EZz-xZLtsSV2JROSzNECKtGo36Zc=RZ0Q@mail.gmail.com> <3fba77e0-d7ff-802e-019b-6fe152eaee67@gmail.com>
From: Fernando Gont <fgont@si6networks.com>
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Date: Tue, 28 Feb 2017 17:36:03 -0300
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On 02/28/2017 04:56 PM, Brian E Carpenter wrote:
> On 01/03/2017 05:29, Lorenzo Colitti wrote:
> ...
>>> We have defined this as a parameter not as a constant.
>>>
>>
>> I really don't understand this statement. How can you say that it's a
>> parameter, given that every RFC that has been published on this topic
>> starting from 1998 states that (most) IIDs are 64 bits long?
> 
> Yes, I think we have a long tradition of expressing this badly, and now
> is a chance to get it right. It's clear at the point where it's
> introduced in RFC4291 that it's a floating boundary:
> 
>   "A slightly sophisticated host (but still rather simple) may
>    additionally be aware of subnet prefix(es) for the link(s) it is
>    attached to, where different addresses may have different values for
>    n:
> 
>    |          n bits               |           128-n bits            |
>    +-------------------------------+---------------------------------+
>    |       subnet prefix           |           interface ID          |
>    +-------------------------------+---------------------------------+"
> 
> but later in the same document we state that (128-n) == 64. That is
> inconsistent; what we're trying to do now is fix that inconsistency
> in a way that is *also* consistent with running code, SLAAC, and the
> newly important privacy issues that require long, unpredictable IIDs.

I agree with Brian's comment. We need to get this fixed.

Regarding long IIDs:
* when it comes to privacy, either long or very short will generally do
-- with long, you can produce good unpredictable IIDs. With short IIDs,
you almost guarantee collisions of IIDs, hence the IIDs are meaningless
to track nodes (as in IPv4).

* From a network scanning et al, long IIDs are obviously desirable.
But.. /64 would do in the same way that something > 50 bits would
probably do.

Thanks,
-- 
Fernando Gont
SI6 Networks
e-mail: fgont@si6networks.com
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