Re: [Gen-art] Gen-ART Last Call review of draft-ietf-trill-ia-appsubtlv

Donald Eastlake <> Mon, 04 July 2016 21:27 UTC

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From: Donald Eastlake <>
Date: Mon, 4 Jul 2016 17:26:49 -0400
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To: Paul Kyzivat <>
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Subject: Re: [Gen-art] Gen-ART Last Call review of draft-ietf-trill-ia-appsubtlv
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Hi Paul,

Thanks for your comments. Sorry for the delay in response.
Please see below.

On Mon, Jun 27, 2016 at 6:46 PM, Paul Kyzivat <>
> I am the assigned Gen-ART reviewer for this draft. The General Area
> Review Team (Gen-ART) reviews all IETF documents being processed by
> the IESG for the IETF Chair. Please treat these comments just like
> any other last call comments. For more information, please see the
> FAQ at <>.
> Document: draft-ietf-trill-ia-appsubtlv
> Reviewer: Paul Kyzivat
> Review Date: 2016-06-27
> IETF LC End Date: 2016-06-28
> IESG Telechat date: 2016-07-07
> Summary:
> This draft is on the right track but has open issues, described in
> the review.
> This is a well written document. I was generally able to follow it
> even though I know nothing about the subject.
> Issues:
> Major: 0
> Minor: 7
> Nits:  2
> (1) MINOR: (Section 2)
> "Addr Sets End" is described as follows:
>    o  Addr Sets End: The unsigned integer offset of the byte, within
>       the IA APPsub-TLV value part, of the last byte of the last
>       Address Set. This will be the byte just before the first
>       sub-sub-TLV if any sub-sub-TLVs are present ...
> But the remaining text of this section, and the examples, imply that
> this is really the length of the leading portion of this TLV ending
> with the last Address Set. The programmer in me says these differ by
> one, and that the implied definition is the reasonable one, while
> the action definition, and the name used to identify it, are wrong.
> I expect it would be difficult at this point to rename this field,
> but at least the definition can be rewritten to be consistent with
> the intended usage.

Right. How about

   Addr Sets End: The unsigned integer byte number, within the IA
   APPsub-TLV value part, of the last byte of the last Address Set,
   where the first byte is numbered 1. This will be the number of the
   byte just before ...

> (2) MINOR: (Section 5.1)
> Normally I would expect this section to request IANA to assign new
> values from the AFN table for OUI...RBridge Port ID. However it is
> worded as "IANA has allocated". Perhaps this is because they have
> already been (pre)allocated. I have no problem with that if IANA is
> OK with it.

Yup, it say "IANA has allocated" because they are already allocated. See

> But IMO the references to IPv4...64-bit MAC are gratuitous and
> inappropriate in an IANA Considerations section. If it is desired to
> include a list of "useful" AFN values then that belongs in some
> other portion of the document.

I disagree. It's "IANA Considerations", not "IANA Allocation Actions".
Someone looking for code points is likely look in the IANA
Considerations section.  All the values shown are from the same IANA
registry.  I can see no advantage to splitting this table between two
different parts of the draft.

> (3) MINOR: (Section 5.1)
> The "new" values here (OUI, MAC/24, MAC/40, IPv6/64) give "This
> document" as their reference. But anyone consulting the IANA
> registry and following it to this document would have difficulty
> finding any *definition* of these things.
> Section 6 discusses some operational issues with them, but at best
> implies a definition. (RFC7042 might be considered a definition of
> OUI, though it doesn't seem to say how big it would be.)
> I think what is needed are explicit definitions of all of these,
> including their widths. (In order to provide enough bits to complete
> a MAC/24 it must be at least 24 bits wide, but that would be bigger
> than needed for a MAC/40.  So I guess it must be at least 24 bits,
> and when used to expand a MAC/24 or MAC/40 an appropriate number of
> its high order bits are used.)
> It would be good for there to be a section, appearing in the TOC,
> for each of these so that someone coming here from the IANA registry
> will easily be able to find the definition.

This is a good point. Better definitions of these AFN types and better
references, either to within this document by explicit pointers to a
section within another document or both, are good points. Probably
Section 6 should be expanded and sub-sections added to it...

> (4) MINOR: (Section 5.2)
> This section defines a new registry with Expert Review as the
> procedure for approving new entries. What I don't see is any
> guidance to the expert on appropriate criteria to use to judge
> suitability of new entries. Without any guidance, relying on the
> whim of the expert can lead to variable, and perhaps biased,
> results.
> It would be good to give guidance on: what sorts of document
> reference are acceptable, what information needs to be included in
> the reference document, whether "special" values may be requested
> (versus just assignment in order requests are received), and the
> sorts of properties that are appropriate.

OK. Some guidance can be added.

> (5) MINOR: (Section 6)
> This section talks about the handling of OUI and IPv6/64 when they
> appear in a Fixed Address sub-sub-TLV. It says nothing about their
> meaning if these appear elsewhere, such as in a Template. I presume
> this kind of usage is nonsense, but it would be better to explicitly
> state it.

OK, the draft should explain their processing wherever they occur.

> (6) MINOR: (Section 6)
> The description of IPv6/64 says:
>    For this purpose, an 48-bit MAC address is expanded to 64
>    bits as described in [RFC7042].
> It wasn't entirely apparent to me what part of 7042 covers that. It
> would be helpful to provide the section where this aspect is
> specified. (After some study I guess that it is section 2.2.1.)


> (7) MINOR: (Section A.2)
> I believe that the values of both 'Length' and 'Address Sets End'
> are too small by 7 - presumably because they forgot to count the
> fixed fields. This also applies to the "alternative" using explict
> AFN encoding.

Thanks for catching that there is an error here.

Length should be the size everything after the 2-byte length
field. That's
  7  fixed fields
 36  three address sets, each 12 bytes
  7  sub-sub-tlv one
 14  sub-sub-tlv two
for a total of 64 so the value is off by 10.

Address Sets End should be the above less the sub-sub-tlvs, so that
would be 43 and the value shown is also off by 10.

> (8) NIT: (Section A.2)
> Based on a very quick reading, ISTM that section 2.2.1 of 7042
> suggests that the IPv6 addresses being constructed this way should
> start with 0x02 rather than 0x20. But I'm far from sure I understand
> this correctly.

Ahhh, there is indeed an error here but it is in the bottom 64 bits,
which should be a Modified EUI-64 identifier, as described in Section
2.2.1 of RFC 7042. Thus the top byte of the bottom 64 bits of the
resulting IPv6 addresses should be 0x02. The top byte of the entire
IPv6 128-bit address should be 0x20 as shown.

> (9) NIT: (Section A.2)
> There seems to be a typo in the following:
>    The OUI would them be supplied
>    by a second Fixed Address sub-sub-TLV proving the OUI.
> I think "proving" should be "providing".


 Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
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