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: Guidelines for IP Flow Information eXport (IPFIX) Testing
Reviewer: Joel M. Halpern
Review Date: 15-Feb-2008
IETF LC End Date: 26-Feb-2008
IESG Telechat date: N/A
Summary: This document needs some additional work before publication as
an informational RFC.
I would particularly recommend considering addressing at least the first
comment below prior to RFC publication.
I would also suggest that the test descriptions need some clarification
as described in the technical section below, particularly items 5 and 6.
Comments:
Conceptual:
1) While the document is being published as an information RFC, the
wording of the abstract and introduction make it seem that this document
is actually defining conformance to the IPFIX RFCs. The IETF has
generally carefully steered clear of defining such conformance.
So, while publishing a useful test suite is probably a good idea, I
strongly recommend fixing the wording of at least the abstract and
introduction to make it quite clear that these are not mandatory tests,
and that these tests do not define conformance.
Related to this, please do not assert (in section 3) that passing this
test suite constitutes conformance to the IPFIX architecture and
protocol. (Among other things,test suite passage proves nothing about
architectural conformance.)
Technical:
2) In the terminology section, an Observation Point is defined simply as
a place where packets can be observed. An Observation Domain is a
collection of Observation points. Then, in the middle of the definition
of an Observation domain it say "In the IPFIX MEssage it generates..."
but up till now none of the things that have been defined generate IPFIX
messages. It is possible that the "it" in the quote is supposed to be
the "Metering Process" mentioned in passing earlier in the definition.
But the English grammar does not lead the reader to such a conclusion.
Later in that same definition, it beings to appear that an Observation
Domain (which is a collection of points, not a process or entity) is
supposed to generate IPFIX messages, since it is supposed to include a
Domain ID in the messages it generates. This definition for an
Observation Domain needs to be reworked, to avoid confusing the Domain
with the Measurement Process which is running in / for / on the Domain.
3) The use of capital "MUST" in section 3.1 is almost certainly wrong.
Firstly, what I think that section is saying is that being able to
correctly perform the basic tests is a precondition for being able to
perform further test successfully. Thats a precondition, not a "MUST".
Of lesser significance, this document does not provide any description
of what it means by "MUST". We are usually careful about how such
language is used in informational RFCs. I think the meaning would be
clearer if the real intent were stated. I suspect that some readers of
this review may find my concern here pedantic. But the continual use of
MUST in the document really, really bothers me. (I hope the next comment
helps explain why it bothers me so much.)
4) Then, the test descriptions go on to keep using this language. This
is a test suite description document. Simply state how to run the test.
There is no need for "MUST". Section 3 should indicate that the test
descriptions describe the preconditions and steps that the tester goes
through. So section 3.1 would begin "The tester creates one Exporting
Process and one collection process, configures the Exporting Process to ..."
5) It is not clear what test steps like ~The tester ensures that an SCTP
association is established.~ (Or worse, the actual text which reads "the
test MUST ensure that an SCTP association is established." are supposed
to do. Is this an instruction to the tester to use network management
tools or CLI to verify a connection on both devices? Is it an
instruction to perform additional configuration? How does the tester
"ensure". A test suite should tell a tester what steps to undertake,
and what observations to perform. "Ensure" is not either one of those.
5a) To elaborate on this issue, in the middle of the test step about
ensuring that Data Records are actually exported, we finally get a
testable instruction, to whit, use a packet sniffer and check that the
packets are coming by.
6) I believe I understand how a tester would create templates, for the
template test. But how is the tester to create data sets. Particularly
data sets with specific properties, such as the padding in section 3.2.3
and 3.2.4? The best conclusion I can come to is that this is a
collector test, and that it assumes a packet generator which can
generate IPFIX packets. Having such a device in a test setup makes
sense. But the test description does not say "configure a packet
generator to generate an IPFIX packet with ..." (There are other ways
to say this, but there needs to be some description of how testers are
expected to create data sets.)
6a) Related to this, I find reading this document rather odd. I have
read many test suites for protocols and implementations of protocols.
They generally focus on a Device (or implementation, or entity) Under
Test, and the framing around that Device. This suite appears to be
trying to test two interacting devices simultaneously. That is
extremely difficult, and extremely confusing. It is particularly hard
because then the tester doesn't have enough points of control to perform
the tests and observe the results meaningfully. It is possible that
this combined suite is right for this problem. But if so, a lot of
explanation of why it is done that way and how the tester is to
accomplish his goals is needed.
Minor:
7) The abstract is worded as if one could not perform interoperability
testing without first running the tests in this document. While having
run the tests in this document will presumably increase the chances of a
successful interoperability test, they are not an inherent requirement
for such testing.
8) I would probably be inclined to lighten up the Motivation section a
bit. Or even remove it. I don't think we need to explain why test
suites are useful. If we really need a motivation section, then it
should explain something about why it is particularly complex to test
IPFIX implementations (if it is) and thus why the IETF feels it is
particularly useful to publish a test suite ourselves in this case.
9) The definition of Transport Session is actually the definition of
various kinds of transport sessions, and how they are identified. Could
the definition start with an actual definition please. (I.e. the
communication over time used to carry X between Y and Z? Or something.)
10) As an editorial matter, most testers I have worked with strongly
prefer if every step in a test is explicitly separate and named /
numbered. That way, they can check off each step as it goes. So the
beginning of 3.1.1 would be
i) Create One Exporting Process
ii) Create One Collection Process
iii) Configure the Exporting Process ...
11) It is particularly odd to see a set of Stress/Load tests that
simultaneously claim to be measuring conformance and to not specify the
level of Stress / Load. Having a description of how to perform load
tests is useful. But its relationship to the other tests is confusing.
(This obviously is helped once we no longer claim that this is a
conformance test.)
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