Re: IID length text [was Re: Review of draft-ietf-6man-rfc4291bis-06]

Brian E Carpenter <brian.e.carpenter@gmail.com> Tue, 17 January 2017 22:37 UTC

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Subject: Re: IID length text [was Re: Review of draft-ietf-6man-rfc4291bis-06]
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From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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Date: Wed, 18 Jan 2017 11:37:36 +1300
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On 18/01/2017 10:32, otroan@employees.org wrote:
> I would argue that we should not make any changes to this text (apart from the eui-64 part).

I think that the discussion on the IETF list has already shown that there is no
consensus for the current text. I don't agree with it any more, either. It hides
the tension between CIDR and the consistent length needed for SLAAC.

Hence I'm still proposing that we change it. I think the median view at the moment
is for the version that runs

  ...  For all currently
   allocated unicast addresses, except those that start with the binary
   value 000, that length should be 64 bits.

    Brian

> Cheers,
> Ole
> 
> 
> 
>> On Tue, Jan 17, 2017 at 4:00 AM, <otroan@employees.org> wrote:
>>> What breaks if all IIDs in global unicast are not 64 bits?  Especially other than SLACC?  I would hope such a REQUIREMENT has a better motivation that "we said so".  Citing the "rest of the specifications" was simply my shorthand for I don't see what else breaks.
>>
>> RFC7421, section 4.2.
>>
>> There's also a set of political considerations, where one tries to achieve balance between the provider's desire to have effective aggregation and the end-users desire to have enough address space. We specifically want to avoid provider's charging by the address.
>>
>> O.
>>  
>> Exactly, and to me RFC7421 say to me "IIDs SHOULD be 64 bits," but it does not say to me "IIDs MUST be 64 bits", this is a subtle but important difference.  Furthermore, RFC7421, section 4.3.2, also say there is operational use of IID other than 64 bits, which to me disproves the statement "IIDs MUST be 64 bits" and shifts things to "IIDs SHOULD be 64 bits."
>>
>> So lets be clear, I'm not saying that we should RECOMMEND other than 64 bit IIDs, I'm simply differentiating between section 1 and section 3 of RFC 2119.   
>>
>> So, I'm asking what breaks if we change from "IIDs MUST be 64 bits" to the in my opinion the more proper "IIDs SHOULD be 64 bits".  
>>
>> So, I would prefer:
>>
>>   ...  For all currently
>>    allocated unicast addresses, except those that start with the binary
>>    value 000, that length should be 64 bits.
>>
>> But, I'm willing to live with what Brian proposed:
>>
>>    ... For all currently
>>    allocated unicast addresses, except those that start with the binary
>>    value 000, that length is 64 bits.
>>
>> But, I can not accept what Eric proposed:
>>
>>    ...  For all currently
>>    allocated unicast addresses, except those that start with the binary
>>    value 000, that length is required to be 64 bits.
>>
>> Thanks.
>> -- 
>> ===============================================
>> David Farmer               Email:farmer@umn.edu
>> Networking & Telecommunication Services
>> Office of Information Technology
>> University of Minnesota   
>> 2218 University Ave SE        Phone: 612-626-0815
>> Minneapolis, MN 55414-3029   Cell: 612-812-9952
>> ===============================================
> 
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