Re: <draft-ietf-6man-rfc4291bis-09.txt>

[神明達哉 <[e-mail]>]

At Fri, 7 Jul 2017 10:09:46 +1000,
Mark Smith <[e-mail]> wrote:

> > As long as the others that who were insisting that the statement "IIDs MUST
> > be 64" means that subnets must be 64 bits for both address generation and
> > on-link determination are satisfied that this is not the case for on-link
> > determination based on what has been added to section 2.1, then I could live
> > without this.
>
> I'm confused by this and have been on the occasions it has been
> discussed. I also don't understand why it matters and is related to
> the on-link property of a subnet prefix.
[...]
> So to me an "on-link prefix" is a subnet-prefix that hosts will
> attempt to send directly to across the link they're attached to,
> indicated to the host by RA PIOs, ICMP redirects or manual
> configuration on the host (per RFC5942). What you and others are
> describing as an "on-link prefix" sounds like something different to
> that.

I can't speak for others, but I believe David's understanding of
"on-link prefix" is consistent with yours.  My interpretation of his
comment is that the current (09) text of rfc4291bis could be
misunderstood regarding this point as follows:

A. According to Section 2.4.1. IIDs are 64 bit long (with some exceptions)
B. Based on this, and according to the format of Section 2.4, subnet
   prefixes are also 64 bit long (with some exceptions)
C. Some readers might jump to the conclusion from A and B that this
   64-bit subnet prefix is used by hosts "to send directly to across
   the link they're attached to", i.e., this prefix is used as an
   "on-link prefix".  Of course, this conclusion is wrong, not least
   as clarified in RFC5942.

Some people (probably including you) don't see the possibility of this
misunderstanding, and some others still think the misunderstanding is
possible.  Personally, I tend to agree with the latter group of people
- I still feel the current text is not crystal clear and could be
misunderstood by fresh readers.  On the other hand I also tend to
agree with Brian in that the wordsmith period of this doc is now over
(and it's more productive to complete this task as long as we can
agree on the high-level content).  So I'd rather move on at this
point.

--
JINMEI, Tatuya