Re: IID length text

Brian E Carpenter <brian.e.carpenter@gmail.com> Tue, 17 January 2017 01:36 UTC

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Subject: Re: IID length text
To: Lorenzo Colitti <lorenzo@google.com>
References: <148406593094.22166.2894840062954191477.idtracker@ietfa.amsl.com> <82245ef2-cd34-9bd6-c04e-f262e285f983@gmail.com> <m2d1frhjfn.wl-randy@psg.com> <18e6e13c-e605-48ff-4906-2d5531624d64@gmail.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>
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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Date: Tue, 17 Jan 2017 14:36:19 +1300
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Cc: 6man <ipv6@ietf.org>, Alexandre Petrescu <alexandru.petrescu@gmail.com>
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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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>