Re: Last Call: <draft-ietf-6man-rfc4291bis-07.txt> (IP Version 6 Addressing Architecture) to Internet Standard

David Farmer <farmer@umn.edu> Wed, 15 February 2017 06:55 UTC

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From: David Farmer <farmer@umn.edu>
Date: Wed, 15 Feb 2017 00:55:28 -0600
Message-ID: <CAN-Dau1Z+_nYJMi_pNSRzpXRO8H8qV5rZApTK6m0_Eg5yCReFA@mail.gmail.com>
Subject: Re: Last Call: <draft-ietf-6man-rfc4291bis-07.txt> (IP Version 6 Addressing Architecture) to Internet Standard
To: Lorenzo Colitti <lorenzo@google.com>
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Cc: 6man WG <ipv6@ietf.org>, draft-ietf-6man-rfc4291bis@ietf.org, IETF-Discussion Discussion <ietf@ietf.org>, 6man-chairs@ietf.org
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On Tue, Feb 14, 2017 at 7:31 PM, Lorenzo Colitti <lorenzo@google.com>; wrote:

> On Tue, Feb 14, 2017 at 11:18 AM, David Farmer <farmer@umn.edu>; wrote:
>
>> However, the Interface ID of all unicast addresses is required to be 64
>> bit with the exception of the following; addresses for point-to-point links
>> [RFC6164], Network-Specific Prefixes used for IPv4/IPv6 Translators
>> [RFC6052], and addresses that start with the binary value 000.
>>
>
> I don't think it makes sense to cite RFC6052 here, since in RFC 6052
> addresses it's not really possible to define the IID in way that makes
> sense. See https://mailarchive.ietf.org/arch/msg/ipv6/
> lyZl3I4rXhnmXYFCAQTRWyohfyI .
>

I conceded that is probably true for most of the IPv4-Embedded IPv6 Address
Formats in section 2.2 of RFC6052, but the /96 format seems
indistinguishable from other IPv6 addresses with embedded IPv4 addresses
described in Section 2.4.5 of this draft.

And the following text from from section 2.4.4 of this draft seems to
strongly imply that IPv6 address with embedded IPv4 addresses have an IID
length other than 64.

   As noted in Section 2.4, all Global Unicast addresses other than
   those that start with binary 000 have a 64-bit interface ID field
   (i.e., n + m = 64), formatted as described in Section 2.4.1.  Global
   Unicast addresses that start with binary 000 have no such constraint
   on the size or structure of the interface ID field.

   Examples of Global Unicast addresses that start with binary 000 are
   the IPv6 address with embedded IPv4 addresses described in
   Section 2.4.5.....

Further, the fact that RFC6052 describes it as a /96 prefix, also seems to
strongly imply a 32 bit IID length.  Now I can imagine counter arguments
along the line that IPv6 addresses with embedded IPv4 addresses don't have
IIDs either, but pulling on that string puts me at a loss to explain the
rationale of the exclusion for addresses that start with binary 000 at all.


So, I suppose we limit the statement to the /96 Network-Specific Prefixes.

Also, as I've read through RFC6052 several times, I wonder if there should
be a reference to RFC6052 added in section 2.4.5. of this draft.  Maybe
something like the follow added to the end of the paragraph for section 2.4.5
.

Additional IPv6 address that carry an IPv4 address are defined in IPv6
Addressing of IPv4/IPv6 Translators [RFC6052].

Thanks.

-- 
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