RE: Updated IID length text

Shoot. Grammar alert. Subject must agree with predicate.

NEW
   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, consistent 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 standard, fixed length of Interface ID is desirable. For this reason, 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. Background
   on the 64 bit boundary in IPv6 addresses can be found in [RFC7421].

Bert

> -----Original Message-----
> From: ipv6 [mailto:ipv6-bounces@ietf.org] On Behalf Of Manfredi, Albert E
> Sent: Wednesday, January 18, 2017 21:46
> To: Brian E Carpenter <brian.e.carpenter@gmail.com>; 6man <ipv6@ietf.org>
> Subject: RE: Updated IID length text
> 
> > -----Original Message-----
> > From: ipv6 [mailto:ipv6-bounces@ietf.org] On Behalf Of Brian E Carpenter
> 
> > OK, after all that discussion, here is a revised proposal. There is
> > nothing new here at all, IMHO; just clarification:
> >
> > OLD
> >    For all unicast addresses, except those that start with the binary
> >    value 000, Interface IDs are required to be 64 bits long.  Background
> >    on the 64 bit boundary in IPv6 addresses can be found in [RFC7421].
> >
> > NEW
> >    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, consistent use of Stateless Address Autoconfiguration
> >    (SLAAC)[RFC4862] requires that all interfaces on a link use the same
> > length
> >    of Interface ID. To guarantee interoperability of SLAAC, a fixed length
> of
> >    Interface ID is necessary. For all currently allocated unicast
> addresses,
> >    except those that start with the binary value 000, Interface IDs are
> >    required to be 64 bits long.  Background on the 64 bit boundary in IPv6
> >    addresses can be found in [RFC7421].
> 
> Just some minor edits, to tie together the ideas.
> 
> NEW
>    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, consistent 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 standard, fixed length of Interface ID is necessary. For this reason,
> the
>    Interface ID of all currently allocated unicast addresses, except those
> that
>    start with the binary value 000, are required to be 64 bits long.
>    Background on the 64 bit boundary in IPv6 addresses can be found in
>    [RFC7421].
> 
> I don't think that SLAAC *must* require a single standard IID length, so
> that's why I added the word "robust." Now that we have moved away from using
> the MAC address for SLAAC, it's not clear to me why a host cannot wait for a
> RA, and then decide on how many IID bits to use, based on the prefix
> length(s) advertised by the router.
> 
> Bert
> 
> 
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