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

[David Farmer <[e-mail]>]

On Mon, Jul 3, 2017 at 12:36 PM, Bob Hinden <[e-mail]> wrote:

> Hi,
>
> I published a new 6man w.g. version (-09) of the RFC4291bis draft.  See
> links below.
>
> The summary of the changes are:
>
>        o   Added text to the last paragraph in Section 2.1 to clarify
>            the differences on how subnets are hangled in IPv4 and IPv6,
>            includes a reference to RFC5942 "The IPv6 Subnet Model: The
>            Relationship between Links and Subnet Prefixes".
>

I was thinking about suggesting a reference to RFC5942 "The IPv6 Subnet
Model", but I wasn't sure where to put it, I really like were you put it.

However, I still think the following paragraph is still too easily
misunderstood to imply subnets must be /64 or 64 bits for both address
generation and on-link determination.

   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.


How about a note clarifying the intent of the this paragraph, something
like this;

      Note: While the previous paragraph does imply 64 bit subnet prefixes
      are typically assigned to most links. It does not imply anything
      about what portion, if any, of a subnet is considered to be on-link,
      see Section 2.1 for more discussion. However, Router Advertisements
      [RFC4861] specifying 64 bit on-link prefixes are typically
      configured on most links.

Thanks

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