Re: IID length text

Brian E Carpenter <brian.e.carpenter@gmail.com> Tue, 17 January 2017 02:33 UTC

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Subject: Re: IID length text
To: Lorenzo Colitti <lorenzo@google.com>
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> <fcf580ec-3617-ca5f-5337-37acb6e928ba@gmail.com> <32121fe2-85d5-4849-d77d-edda5825d8e7@gmail.com> <CAC8QAccN_=x9sTgTM71XFSYfUmSyaMHw_tFEw2QSr5iwi2wcGw@mail.gmail.com> <94dffda9-0a88-cfa1-6281-5d788a7ca121@gmail.com> <CAKD1Yr1QTbLsbzxwy4-MCWeAxr0rRvDe5v-6DbA9aYaK48BaZw@mail.gmail.com> <eec38f90-3751-6f74-12a0-321c3dce163a@gmail.com> <CAKD1Yr18QWOR3_jFHEQ2M0jhgkOwxhbm+SFK3jZF6XU3WtWVGQ@mail.gmail.com>
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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Date: Tue, 17 Jan 2017 15:33:06 +1300
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Cc: 6man <ipv6@ietf.org>, Alexandre Petrescu <alexandru.petrescu@gmail.com>
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On 17/01/2017 14:44, Lorenzo Colitti wrote:
> But your text does change this arbitrary choice, by removing it.

Huh? It replaces the lower case required by "that length is 64 bits"
and states that it *might* be changed in the future. And yes, if that
makes designers a bit leery about embedding the constant 64 deep in their
implementations, that is entirely intentional.

   Brian

> 
> On Tue, Jan 17, 2017 at 10:36 AM, Brian E Carpenter <
> brian.e.carpenter@gmail.com> wrote:
> 
>> Nobody is saying we should change it in the foreseeable future.
>> As for the unforeseeable future, I don't know ;-)
>>
>>     Brian
>>
>> On 17/01/2017 14:10, Lorenzo Colitti wrote:
>>> Yep. It's an arbitrary choice, just like the choice to make IPv6
>> addresses
>>> 128 bits long, or the choice to make the header 40 bytes long. That
>> doesn't
>>> mean we should change it.
>>>
>>> On Tue, Jan 17, 2017 at 7:23 AM, Brian E Carpenter <
>>> brian.e.carpenter@gmail.com> wrote:
>>>
>>>> On 17/01/2017 09:42, Behcet Sarikaya wrote:
>>>>> On Mon, Jan 16, 2017 at 2:27 PM, Alexandre Petrescu
>>>>> <alexandru.petrescu@gmail.com> wrote:
>>>>>> Le 14/01/2017 à 20:49, Brian E Carpenter a écrit :
>>>>>>>
>>>>>>> A modest suggestion:
>>>>>>>
>>>>>>> OLD
>>>>>>>    For all unicast addresses, except those that start with the binary
>>>>>>>    value 000, Interface IDs are required to be 64 bits long.
>>>> Background
>>>>>>>    on the 64 bit boundary in IPv6 addresses can be found in
>> [RFC7421].
>>>>>>>
>>>>>>> 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, consistent use of Stateless Address
>>>> Autoconfiguration
>>>>>>>    (SLAAC)[RFC4862] requires that all interfaces on a link use the
>> same
>>>>>>> length
>>>>>>>    of Interface ID. In practice, this means that to guarantee
>>>>>>> interoperability
>>>>>>>    of SLAAC, a fixed length of Interface ID is necessary. For all
>>>>>>> currently
>>>>>>>    allocated unicast addresses, except those that start with the
>> binary
>>>>>>>    value 000, that length is 64 bits. Note that this value is an
>>>> arbitrary
>>>>>>>    choice and might be changed for some future allocation of unicast
>>>>>>> address
>>>>>>>    space. Background on the 64 bit boundary in IPv6 addresses can be
>>>> found
>>>>>>>    in [RFC7421].
>>>>>>
>>>>>>
>>>>>> I agree with the change suggestion.  The new text and references are
>>>> enough
>>>>>> motivation to clarify that that 64bit limit is an arbitrary choice and
>>>> might
>>>>>> change in the future.
>>>>>>
>>>>>
>>>>> 3GPP assigns 64 bit prefixes to each UE.
>>>>> Extended Unique Identifiers defined are EUI-48 and EUI-64.
>>>>> I don't think 64 bit limit is that arbitrary?
>>>>
>>>> It's a parameter, which we happened to set initially to 48
>>>> and then changed to 64 because of FireWire. I don't know
>>>> why 3GPP chose the same value. But indeed we (the IETF) chose
>>>> it because of our now old-fashioned decision to copy Novell
>>>> Netware by embedding layer 2 addresses in layer 3. A bad
>>>> choice, as it turned out.
>>>>
>>>> The first two definitions of "arbitrary" in Merriam-Webster seem
>>>> to fit, especially the second.
>>>>
>>>> "existing or coming about seemingly at random or by chance
>>>> or as a capricious and unreasonable act of will"
>>>> "based on or determined by individual preference or convenience
>>>> rather than by necessity or the intrinsic nature of something"
>>>>
>>>> Regards
>>>>     Brian
>>>>
>>>>>
>>>>> Behcet
>>>>>
>>>>>> Alex
>>>>>>
>>>>>>>
>>>>>>> Regards
>>>>>>>    Brian
>>>>>>>
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>>>>> .
>>>>>
>>>>
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>>
>