Re: Updated IID length text

David Farmer <farmer@umn.edu> Fri, 20 January 2017 05:25 UTC

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From: David Farmer <farmer@umn.edu>
Date: Thu, 19 Jan 2017 23:25:39 -0600
Message-ID: <CAN-Dau0X2MYxOADLdaVcangeJrHo98t=buh1J2uCpEQAs93GDQ@mail.gmail.com>
Subject: Re: Updated IID length text
To: Lorenzo Colitti <lorenzo@google.com>
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On Thu, Jan 19, 2017 at 10:38 PM, Lorenzo Colitti <lorenzo@google.com>
wrote:

> On Fri, Jan 20, 2017 at 4:41 AM, Brian E Carpenter <
> brian.e.carpenter@gmail.com> wrote:
>
>> However, correct use of Stateless Address Autoconfiguration
>>    (SLAAC)[RFC4862] requires all interfaces on a link to use the same
>> length
>>    of Interface ID. Furthermore, to guarantee robust interoperability of
>> SLAAC,
>>    a consistent length of Interface ID is desirable. For this reason,
>
>
> I object to the text "for this reason", because SLAAC is not the only
> reason. There are many reasons, many of which are written in 7421, and two
> sentences in this paragraph are not sufficient to describe them. I propose
> the following alternative, which I believe to be normatively identical:
>
>    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, the Interface ID of all currently allocated unicast
> addresses,
>    except those that start with the binary value 000, is required to be 64
> bits
>    long. The rationale for the 64 bit boundary in IPv6 addresses can be
> found in
>    [RFC7421].
>
> Cheers,
> Lorenzo
>

How should that be interpreted? Do my Point-to-Point links need addresses
that begin with binary 000? How do I get an allocation of those?  Because
it says I must use a 64 bit IID with the Global Unicast Allocation that I
got from ARIN.

Here is another problem, RFC 6164 probably should have updated 4291 for
that reason.  And if there are any future exceptions should update 4291bis,
for similar reasons.

There are lots of good reasons to use 64 bit IIDs almost everywhere, but
there are exceptions.  However this text doesn't leave room for any
exceptions, even the one that it cites.

Again keeping "required" I believe is a false imperative.  If we can't fix
that by going to "should", can we at least make room for official standards
track exceptions, like the one cited and any future ones we agree on?

Thanks

-- 
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