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/
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