Deborah
-----Original Message-----
From: Elwyn Davies [mailto:elwynd(_at_)dial(_dot_)pipex(_dot_)com]
Sent: Friday, August 17, 2007 12:33 PM
To: General Area Review Team
Cc: Mary Barnes; ccamp-chairs(_at_)tools(_dot_)ietf(_dot_)org; ccamp-
ads(_at_)tools(_dot_)ietf(_dot_)org;
IETF Discussion; JP Vasseur; arthi(_at_)nuovasystems(_dot_)com;
raymond_zhang(_at_)bt(_dot_)infonet(_dot_)com
Subject: Gen-art review of
draft-ietf-ccamp-inter-domain-pd-path-comp-05.txt
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: draft-ietf-ccamp-inter-domain-pd-path-comp-05.txt
Reviewer: Elwyn Davies
Review Date: 16 Aug 2007
IETF LC End Date: 16 Aug 2007
IESG Telechat date: (if known) 23 Aug 2007
Summary:
I think this document needs significant work on the core
description of
the algorithm. I found s4 to be difficult to read and it appears to
contain a number of ambiguities and inconsistencies that should be
fixed
before it goes to the IESG. The various sub-cases and routes through
the algorithm are not very clearly expressed IMO. That being said, I
think this is essentially a descriptive problem rather than any
issue of
principle. There are also a number of editorial issues (mostly need
for
acronym expansion) that need fixing in due course.
Comments:
s3.1: To avoid the sense of surprise when a Path message appears in
the
last bullet, I would suggest s/The path (ERO)/The path (specified
by an
ERO in an RSVP-TE Path message)/
s4, para 2/3: Presumably para 3 is talking about the 'next hop' being
loose or abstract as is implied by items 1) and 2). It would be
good to
make this clear. It would also be worth inserting a sentence
making it
clear that if the next hop is strict there isn't anything to do, since
otherwise one has to scan the entire section to verify that this is
the
case. It is just possible that I have misunderstood what is going on
and some of the stuff *does* apply to strict hops - in which case the
section needs a whole lot more clarity. There also needs to be some
words about the 'simple abstract node' case.
s4: Sending of PathErr. This section states that PathErr messages
'SHOULD be sent' in several places. Whilst this is consistent with
RFC
3209, both of these documents appear to be (or may be) inconsistent
with
RFC 2205 which does not appear to provide any alternative to sending a
PathErr when there is a problem processing a Path message. If it is
deemed correct to allow not sending the PathErr, reasoning should be
given as to why this might be desirable, and what is the alternative
(presumably silently ignoring the message?) and its consequences.
s4, item 1): I think the first sentence ('If the next hop is not
present in the TED.') is probably redundant and is certainly
confusing.
Part of the confusion is that the rest of the item appears to only
concern loose next hops but there is no pointer to what happens
with the
other case of abstract nodes. I think the description would be more
logical with the paragraph on abstract nodes, from later in the
section,
moved to before item 1). In that way the case splitting
(strict/loose/abstract) would be much clearer. BTW doesn't the simple
abstract case have to do some of the non-simple work?
s4, item 1, bullet 2: Which domain has to be PSC? The current one or
the one containing the next hop?
s4, item 1: Worth making even clearer that *both* conditions have
to be
satisfied.
s4, item 1: 'If the next-hop is reachable, then it SHOULD find a
domain
boundary LSR...': What does 'it' represent here? The path necessarily
crosses the boundary (unless we have some very weird topology
here ;-) )
so there is *something* on the domain boundary. What else could it
find
on the boundary? I think this is probably a badly expressed story
about
some other point. Reflecting on this, it strikes me that this is the
key point where the routing information is pulled into the TE and this
is very poorly expressed IMO.
s4, item 1: 'the ABR in the case of inter-area TE or the ASBR in the
next-hop AS in the case of inter-AS TE should be the signaled loose
next-hop in the ERO': Does this mean in the expanded ERO or the
original one? If it is the original one, how is the implementor
supposed to check it is an ABR/ASBR?
s4, item 2): The term 'ERO expansion' is not defined in any of the
standards - it is referred to as an alternative shorthand in RFC 4736
(requirements doc). It needs to be defined.
s4, item 2), bullet 1: This section contains 3 instances of
'SHOULD'. I
am happy with the first one (policy applies). The third one is
covered
by the discussion on PathErr above. The second 'SHOULD' strikes me
as a
'should' or even 'is'. What else would be done if it isn't treated
this
way? Bullet 2, sub-bullet 1 has a similar construction.
s4, item 2), bullet 2, sub 1: The condition at the beginning of this
bullet could probably be written down more clearly.
s4, item 2), bullet 2/sub 1: 'If the boundary LSR is a candidate
LSR for
intra-area H-LSP/S-LSP setup (the LSR has local policy for nesting or
stitching),...': Which LSR has the policy? The boundary LSR or the
one
asking? There is an equivalent question for sub bullet 2.
s4, para after item 2): 'Note that in both cases, path computation and
signaling process may be stopped due to policy violation.': Does this
mean some other policy violation than is already documented? If not I
think this para should be removed as it it just raises doubts as to
whether there is some other cause.
s4, 'optimization technique': I am confused about what protocol
instance would accept the proposed flooded information if the IGP
is not
running on the inter-AS link concerned. Does this require some
special
functionality in the IGP?
ss4.1/4.2: I believe that each of the examples references one or other
of the Figure 1/2 configurations - this should be made clear
explicitly.
s4.1.1, para 4: Although it is not strictly normative, harder advice
should be given on back-off times to avoid DoS/congestion.
s5: The 'tapping' problem may be well-known but not to me. It needs
either a brief explanation or a reference.
Editorial:
Abstract: Expand IGP acronym (and add to terminology?).
s2, para 4: The term Head-end is not defined.
s3.1, bullet 3: Expand ERO acronym.
s3.1: To avoid the sense of surprise when a Path message appears in
the
last bullet, I would suggest s/The path (ERO)/The path (specified
by an
ERO in an RSVP-TE Path message)/
s3.2: Expand ABR
s3.2: Expand ASBR
s3.2, Figure 2: s/(CE to ASBR =>/(CE to ASBR) =>/
s3.2, last bullet: This contains no verb! The bullet could (usefully)
say: 'The scenario supports an inter-AS TE LSP...'. This bullet might
logically appear as the 2nd on the list.
s5, para 3: A reference to s2 would help.
s6.1: A reference to how/where the Make-before-Break procedure is
defined would be good (RFC3209?).
s8: Expand FRR, MP and PLR acronyms.
s9, para 2: s/verison/version/