Re: draft-bourbaki-6man-classless-ipv6-00

[David Farmer <[e-mail]>]

On Tue, Jun 6, 2017 at 8:14 PM, 神明達哉 <[e-mail]> wrote:
>
> As for the above text, my recollection is that some people (I don't
> know if that was a small group, btw - to me both groups looked equally
> vocal and equally small/large) were against one specific point in
> text like the above one:
>
> - "should be 64" instead of "must be 64" (but in my understanding they
>   were/are okay with "except when the addresses are manually
>   configured")
>
> It's also not clear to me whether the real intent of
> draft-bourbaki-6man-classless-ipv6-00 includes the subtle (but
> seemingly very important for those who were "fiercely against" it)
> change from "must" to "should".  I guess if the authors of
> 6man-classless-ipv6 are actually also happy/okay with this one:
>
>     IPv6 unicast routing is based on prefixes of any valid length up to
>     128 [BCP198].  Interface Identifiers must be 64 bit long except
>     when the addresses are manually configured, or by exceptions defined
>     in standards track documents.  For example, [RFC6164] standardises
>     127 bit prefixes on inter-router point-to-point links.  The rationale
>     for using 64 bit Interface Identifiers can be found in [RFC7421]
>
> then there will be no dispute or further time wasting (we'll still
> need to decide what to do with the magic leading bits of 000 in terms
> of the interface identifier length, but if we can agree at this level
> this will be a relatively minor point to address).
>

I think "should be 64" is the correct language, primarily because "must be
64" has been misinterpreted several times to justify hard coding 64 in IPv6
implementations, but also it seems like a false imperative.  Now that an
explicit manual configuration exception is included, I could live with
"must be 64", only if the language is further clarified as an operational
directive and not an implementation directive to hard code 64 along with
the list of exceptions.

So I'd prefer; "Interface Identifiers should be 64 bits long except..."
However, I could live with; "Operationally, Interface Identifiers must be
64 bits long except..."

I think either of these makes it clear 64 bit is the norm, but this should
not enforced by an IPv6 implementations or hard coded in some way.

Unless someone has language to clarify the purpose for the magic leading
bits of 000, I'd prefer to just level that execution out, in my experience
it only confuses the discussion.

Thanks

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