[Gen-art] Gen-ART LC review of draft-ietf-ccamp-inter-domain-rsvp-te-06.txt

Authors,

I have been selected as the General Area Review Team (Gen-ART)
reviewer for this draft (for background on Gen-ART, please see
http://www.alvestrand.no/ietf/gen/art/gen-art-FAQ.html).

Please resolve these comments along with any other Last Call comments
you may receive.

Document: Inter domain Multiprotocol Label Switching (MPLS) and
Generalized MPLS (GMPLS) Traffic Engineering - RSVP-TE extensions
(draft-ietf-ccamp-inter-domain-rsvp-te-06.txt)

Reviewer: Eric Gray

Review Date:  August 16, 2007

IETF LC End Date: August 16, 2007

IESG Telechat date: (if known) Unknown.

Summary:
=======

This document is not ready for publishing as a Proposed Standard.
Some points require clarifications.

Comments:
========

The following paragraph (section 2) seems inconsistent with the
text in subsequent sections: it seems that it is saying that any
combination of the three methods (contiguous, nested, stitched)
could be used in a _single_ LSP - yet at least on of these is 
defined as "end-to-end" in subsequent text (contiguous).  That
would seem to imply that any combination except contigous and
either of the other two.

The paragraph reads:

"In fact, as pointed out in [RFC4726], any combination of these three
options may be used in the course of an end-to-end inter-domain LSP."

Yet the subsequent text describing "Contiguous" says "a single
end-to-end TE LSP ..."

Possibly a careful read should be made to remove innappropriate 
uses of the words "end-to-end" in connection with each method?

For example, in the cited case above, simply removing "single
end-to-end" in the description of contiguous should remove the
ambiguity in that case.

Alternatively, assuming that it is actually the case that - for
a contiguous LSP - the intent is that it be truly end-to-end,
then the original statement above needs to be modified.

Finally, if it is fact the intent that the selection method is
supposed to apply to any given LSP - on an end-to-end basis -
then the quoted statement above should be removed entirely.
--------------------------------------------------------------------
Still related to the above, but as a side note, the fact that it 
is not immediately clear which of these is the intention in this 
document is an indication of a potential for some very serious 
interoperability issues.  Some of the subsequent text mentions 
the potential for a "policy failure" that SHOULD fail the setup.  

In addition to not being absolutely clear (when would it be okay
not to fail, is there a way to indicate that an alternative is
allowed, etc?), this implies that it is possible for a domain to
have a policy (for example, against contiguous LSP setup) that is
going to result in complete non-interoperation with a domain (or
implementation) asking for contiguous LSP setup.

This sort of policy conflict may easily arise if one implementer,
or operator, interprets the specification one way and another (or
others) interprets it another in terms of expected "end to end" 
behavior and combinations of the types of "spanning" LSPs. 
---------------------------------------------------------------------
The last two paragraphs in section 2 (preceding the heading for
section 2.1) are confusing and (potentially) contradictory: one
appears to say that signaling extensions (for control/selection
of methods) are in scope while specific details are not, but the 
other seems to say otherwise.

I suspect that the word "control" is where I am getting hung-up.
If it is intended that the specifics of each method are out of
scope in this document - once a method is selected - then it is 
hard to see how "control [...] of the three signaling mechanisms"
is in scope but "specific protocol extensions required to signal 
each LSP type" is not.

Perhaps "control and" should be removed?
----------------------------------------------------------------------
In section 3, under bullet 4a - on page 6 - you use "SHOULD" in
saying whether or not a PathErr message is to be generated.  Why
- or under what circumstances - would it be appropriate not to do
so?
----------------------------------------------------------------------
Similarly, on page 7, you use the word SHOULD with respect to ERO
processing in a Path message.  When (or under what circumstances)
would it make sense not to do as specified?  What alternatives are
there?

This same observation then applies to several (all?) of the actual
procedures - although several of them do provide some degree of
amplification as to when (or why) a specific step might not apply.

Perhaps it would be best to clarify in the steps themselves and -
rather than say "SHOULD" in the introductory statement, it might
be enough to simply say that the following procedures apply (thus
avoiding the issue of using either SHOULD or MUST).
----------------------------------------------------------------------
After "However:" in section 3.2, I would suggest some form of 
modification or qualification of the first bullet similar to:

- A domain border node MUST NOT passively suppress propagation 
  of a PathErr message.

Clearly, if the device applies a successful crankback approach, 
it does not make sense for it to propagate the PathErr anyway.
----------------------------------------------------------------------
In the third bullet of section 7, page 15, "do not need to be 
considered" does not follow from "are likely to be upgraded".

True - if they are upgraded - then they are unlikely to need
to be considered in backward compatibility discussion.  But
"likely to be" is NOT the same as "are".

The point I think you are trying to make is that upgrading a
border LSR to include this capability is an essential enabling
requirement for useful operation of this capability - and that 
makes it unnecessary to consider such upgraded border LSRs in
backward compatibility.

======================================================================
NITs:

In section 1.2, page 3, the definition for ASBR should start with
an expansion of the acronym.
----------------------------------------------------------------------
In section 3.1, as currently formatted, the "factors including:"
seems to be "Farrel, Ayyangar and Vasseur" - an artifact of the 
way that your document only has a single empty text-line between
the last line of content-text and the page footer.  This is only
a problem when reading the electronic version and - most likely -
a (humorous) temporary problem that will fall out in subsequent 
versions.  If not, it might be a good idea to force the line with
a colon ending it to not orphan the next line of content-text.

In the version I read, this occurs at the bottom of page 6.
-----------------------------------------------------------------------
On page 14, second paragraph, I suggest changing "ingress LSP" to
"LSP ingress".  An LSP - however qualified - cannot "exert control".
-----------------------------------------------------------------------
First line in section 7, existing rather than esiting.
-----------------------------------------------------------------------
Last line of the first bullet in section 7 (page 15, roughly mid
page) - inter-domain rather than inte-domain.
-----------------------------------------------------------------------
Third line of third bullet (in section 7), controls verses conrols.
-----------------------------------------------------------------------
Third line of second paragraph (in section 8, page 15), suitable
instead of suiable.

--
Eric Gray
Principal Engineer
Ericsson 

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