Re: RFC4291bis

[David Farmer <[e-mail]>]

On Tue, Aug 7, 2018 at 6:39 PM, Brian E Carpenter <
[e-mail]> wrote:

> Hi,
>
> Assuming that we adopt draft-farmer-6man-exceptions-64
> for the standards track or BCP, I suggest that we should
> also update draft-ietf-6man-rfc4291bis as proposed below,
> and plan for the two documents to be published as RFCs
> simultaneously:
>
> OLD:
>    Interface Identifiers are 64 bit long except if the first three bits
>    of the address are 000, or when the addresses are manually
>    configured, or by exceptions defined in standards track documents.
>    The rationale for using 64 bit Interface Identifiers can be found in
>    [RFC7421].  An example of a standards track exception is [RFC6164]
>    that standardises 127 bit prefixes on inter-router point-to-point
>    links.
>
>       Note: In the case of manual configuration, the Prefix and
>       Interface Identifier can be any length as long as they add up to
>       128.
>
> NEW:
>    Interface Identifiers for stateless address autoconfiguration
>    are 64 bits long except if the first three bits
>    of the address are 000, or when the addresses are manually
>    configured, or by exceptions defined in standards track documents.
>    The rationale for using 64 bit Interface Identifiers can be found in
>    [RFC7421].  An example of a standards track exception is [RFC6164]
>    that standardises 127 bit prefixes on inter-router point-to-point
>    links. The relationship between prefix length and Interface Identifier
>    length is discussed in [I-D.farmer-6man-exceptions-64].
>
>       Note: In the case of manual configuration, the Prefix and
>       Interface Identifier can be any length as long as they add up to
>       128. In all cases, routing and forwarding processes must be
>       designed to process prefixes of any length up to /128 [BCP198].
>
> Comments:
>
> 1. This change makes it clear that the 64-bit IID length is for SLAAC.
> 2. It specifically send the reader to draft-farmer for details.
> 3. It underlines that routing must work for any length prefix.
>
>     Brian
>

That works for me, but I've been thinking "Standard Interface Identifiers
are 64 bit long..." and when refing to 64-bit IID later on in the documnet
use the term "Standard IIDs"

One of the sources of confusion in all of this is not distingusing between
the generic concept of IIDs used in section 2.4, and the standardised
64-bit IID, it gives the faulse impression that all IIDs are 64 bits in
length.

Something to think about, was the change from RFC1884 to RFC2373 intended
to be backward compatible? Or was there a flag day where we went from
RFC1884 (IPv6.0) and to RFC2373 (IPv6.1)?  As I see it RFC2373 was an
incremental change, adding SLAAC with a standardized IID length of 64 bits,
and the subnet assignment prefix (the PIO with the A flag) and allowing
backward compatibility with manual configuration and DHCPv6 based on
RFC1884. The Standard IIDs are required for SLAAC and recommended for
manual configuration and DHCPv6.

Thanks.

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