Re: Last Call: <draft-ietf-6man-rfc4291bis-07.txt> (IP Version 6 Addressing Architecture) to Internet Standard

[Alexandre Petrescu <[e-mail]>]

Le 24/02/2017 à 08:15, David Farmer a écrit :
>
>
> On Thu, Feb 23, 2017 at 9:13 PM, Fernando Gont
> <[e-mail] <mailto:[e-mail]>> wrote:
>
> I'd remove a few sentences here, as in:
>
> IPv6 unicast routing is based on prefixes of any valid length up to
> 128 [BCP198]. Subnet prefixes of /64 are RECOMMENDED for general
> purpose use, subnet prefixes of /127 are RECOMMENDED for point-
> to-point router links [RFC6164]. The rationale for the 64 bit
> boundary in IPv6 addresses can be found in [RFC7421].
>
>
> The problem is you have stripped out all the implementation guidance
> and only left operational guidance.  But maybe the the right idea is
> to separate the two, putting the operational guidance in Section 2.4
> where we are talking about prefixes and the implementation guidance
> in section 2.4.1 where we are talking about IIDs.

Well, in a sense yes.

I had an addressing architecture discussion today with a novice
practitioner and she was surprised to hear that
2001:db8:0:cd30::/60 is the same as
2001:db8:0:cd31::/60, as
2001:db8:0:cd32::/60,... yet we can't say
2001:db8:0:cd3::/60

which makes one wonder why dont we say 2001:db8:0:cd3*::/60?

An architecture document would be a good guidance on this.

But an architecture document that starts to qualify deployments as more
important than others, or cellular vs dsl, or ptp vs shared... or give
implementation guidance, it's maybe beyond archi, IMHO.

Alex

> 2nd Paragraph of 2.4;
>
> IPv6 unicast routing is based on prefixes of any valid length up to
> and including 128 [BCP198].  However, subnet prefixes of 64 bits in
> length are REQUIRED for use with Stateless Address Autoconfiguration
> (SLAAC)[RFC4862] and are RECOMMENDED for all other general purpose
> use. The rationale for the 64 bit boundary in IPv6 addresses can be
> found in [RFC7421].
>
> 4th paragraph of 2.4.1
>
> For all unicast addresses, except those that start with the binary
> value 000, support for Interface IDs that are 64 bits long is
> REQUIRED, support for other Interface IDs lengths is OPTIONAL. The
> rationale for the 64 bit boundary in IPv6 addresses can be found in
> [RFC7421].
>
> This clearly say that implementations that only support 64 bit IID
> lengths are just fine, but also says implementations that allow IID
> lengths other than 64 bits are just fine too.  I think the current
> and historic text actually implies implementations are not to allow
> other IID lengths, is that what we really intended to say?  A lot of
> implementations seem to allow other IID lengths, are they wrong?  I
> don't think so.
>
> This also gives strong operational guidance that 64 bit length
> subnet prefixes are expected in most situations.  Reinforcing the 64
> bit boundary, however without outlawing the use of other subnet
> prefix lengths when implemented and they could be useful.  This is
> done without distracting from the 64 bit boundary, by not directly
> calling attention to RFC6164 or the other longer prefix lengths.
> Since BCP198 and RFC7421 both reference RFC6164 calling it out here
> doesn't seem necessary, and would unnecessarily weaken the focus on
> the 64 bit boundary that I'm trying to maintain.
>
> I don't see how this text would require changes in any code, nor does
> it imply other IID lengths are not allowed operationally, again which
> a lot of implementations seem to allow.
>
> Thanks. -- =============================================== David
> Farmer               Email:[e-mail]
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