Re: IPv6 Routing & ND vs. Addressing, (Was: Re: <draft-ietf-6man-rfc4291bis-09.txt>)

[David Farmer <[e-mail]>]

On Mon, Jul 10, 2017 at 1:53 PM, 神明達哉 <[e-mail]> wrote:

> At Sun, 9 Jul 2017 16:09:14 -0500,
> David Farmer <[e-mail]> wrote:
>
> > So, What should we say in RFC4291bis? Personally I'd prefer we eliminate
> > the term subnet from RFC4291bis, but assuming that won't happen how about
> > the following;
>
> I'm not sure if we still want to continue wordsmith rather than either
> accept the current text or give up advancing the address architecture,
> but otherwise I largely like your text.  A few comments:
>
> > Currently, IPv6 continues the IPv4 model in that a subnet prefix is
> > associated with one link. Multiple subnet prefixes may be assigned to the
> > same link.  The relationship between links and IPv6 subnet prefixes
> differs
> > from the IPv4 model in that the prefixes used for on-link determination
> are
> > separate and may differ from the assigned subnet prefixes. However,
> on-link
> > prefixes identical with assigned subnet prefixes are recommended. A
> prefix
> > length associated with a manually configured address determines the
> on-link
> > prefix associated with the manually configured address. See [RFC5942]
> "The
> > IPv6 Subnet Model: The Relationship between Links and Subnet Prefixes"
> for
> > more details.
>
> I'd interpret the last two sentences as RFC5942 indicating:
>
>   A prefix length associated with a manually configured address
>   determines the on-link prefix associated with the manually
>   configured address. (*)
>
> If I'm correct, while I agree on (*) it's not obvious to me that
> RFC5942 directly suggests this observation.  Some more explanation
> would help here.
>

I intended the reference to RFC5942 to cover the whole paragraph, not just
the next to the last sentence.

As for manual configuration, RFC5942 says;

       A host considers a prefix to be on-link only
       through explicit means, such as those specified in the on-link
       definition in the Terminology section of [RFC4861] (as modified
       by this document) or via manual configuration.  Note that the
       requirement for manually configured addresses is not explicitly
       mentioned in [RFC4861].

While that doesn't explicitly say "A prefix length associated with a
manually configured address determines the on-link prefix associated with
the manually configured address." in my opinion it strongly implies it.
How else would you provide an on-link prefix for a manually configures
address otherwise? Also, I think this need to be said explicitly some
place. But if you have suggestion to clarify, I'd be interested to here
them.


> > Note: Any on-link prefixes longer than a covering assigned subnet prefix
> > must be associated with the same link as the assigned subnet prefix.
> Also,
> > any assigned subnet prefixes longer than a covering on-link prefix must
> be
> > associated with the same link as the on-link prefix.
>
> I'm afraid the meaning of "associated with" is not very clear here.
>

I'm open to other words, suggestions.


> > When forming or assigning unicast addresses, except those that start with
> > the binary value 000, Interface IDs are required to be 64 bits long.  The
> > rationale for using 64 bit Interface Identifiers can be found in
> [RFC7421].
>
> Personally I prefer this text over the one in rfc4291bis-09:
>
>    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.
>
> since IMO "a compromise between excessive rigidity and excessive
> flexibility" is actually already provided in the existing spec and all
> we need is a clarification rather than tweaking the definition and
> listing awkward exceptions.  But I'm not sure if your version of text
> is acceptable for "draft-bourbaki-6man-classless-ipv6" authors.
> Hopefully this note clears any doubt from them:
>
> > Note: the previous paragraph implies nothing about on-link determination
> > which as discussed in section 2.1 is separate from subnet assignment in
> > IPv6.
>
> but we may need to explain it in more detail at the risk of sounding
> too verbose.
>

More detail here? Or, in 2.1?  Which is the paragraph above with the
reference to RFC5942.


> --
> JINMEI, Tatuya
>

Thanks

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