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

David Farmer <farmer@umn.edu> Tue, 17 January 2017 14:30 UTC

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From: David Farmer <farmer@umn.edu>
Date: Tue, 17 Jan 2017 08:30:03 -0600
Message-ID: <CAN-Dau0Fkb-M8VM9iL9xwy89bir5PhNHJ3D1VFrnNppVXNyeOg@mail.gmail.com>
Subject: Re: IID length text [was Re: Review of draft-ietf-6man-rfc4291bis-06]
To: Ole Troan <otroan@employees.org>
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Cc: Erik Kline <ek@google.com>, 6man WG <ipv6@ietf.org>
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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.
-- 
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David Farmer               Email:farmer@umn.edu
Networking & Telecommunication Services
Office of Information Technology
University of Minnesota
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