Thanks for your detailed review.
Sorry about the delay, we've been a little bit busy with IETF deadlines
I have been selected as the General Area Review Team (Gen-ART)
reviewer for this draft (for background on Gen-ART, please see
Please wait for direction from your document shepherd
or AD before posting a new version of the draft.
Reviewer: Ben Campbell
Review Date: 1 March 2010
IESG Telechat date: 4 March 2010
Summary: This document is almost ready for publication as a proposed standard,
but there is an open issue that should be considered first.
-- section 4.5, general:
I am confused as to how the collector determines the exporter supports this
extension. If I understand correctly (and it's probable that I do not, since
this is my first real exposure to IPFix), the collector basically has to infer
exporter support from the behavior of the exporter. But then the second
paragraph after the numbered list (i.e. 2 paragraphs after item 4) says:
"In the case where the Exporting Process does not support the
per-SCTP-stream extension, then the first Data Record received
by the Collecting Process will disable the extension for the
specific Exporter on the Collecting side."
This seems to conflict. Why would the collector need to worry about items 1-4
if it can categorically determine exporter support from the first data record?
In general, though, I think that having the collector infer support is not the
right way to do this. It would be far better to explicitly signal support, if
that is at all possible in IPFix. Otherwise, it seems like the collector has to
watch every record for violations of 1-4, and make fairly complex decisions on
a per-record basis.
We clarified the text in section 4.5 as follows
- the paragraphs 1, 2, 3, 7, 8, 9, 10, and 11 are unchanged, but
copied for completeness
- we mainly rearranged the order so that it provides a more logical
Collecting Processes must operate slightly contrary to [RFC5101] in
order to realize the full benefits of per-stream export. However, the
specification in this section contains a mechanism which allows
per-stream-capable Collecting Processes to selectively enable per-stream
export, in order to ensure interoperability of per-stream-capable
Collecting Processes with Exporting Processes which do not implement
As specified in [RFC5101], the Collecting Process SHOULD listen for a
new association request from the Exporting Process. The Exporting
Process will request a number of SCTP streams to use for export.
A Collecting Process SHOULD support the procedure for the addition of an
SCTP stream [SCTP-RESET].
In IPFIX, there is no explicit notification of the Exporting Process's
capabilities. There is also no return channel for the Collecting
Process to communicate its capabilities.
The dataRecordsReliability Options Template is expected, but cannot be
guaranteed, to only originate from a per-SCTP-stream compliant Exporting
Process. In the case where the Exporting Process uses the
per-SCTP-stream extension, the first Data Record received by the
Collecting Process is associated with the Data Records Reliability
Options Template. If the first Data Record is associated with any other
(Options) Template, the Collecting Process MUST disable the extension
for the specific Exporter on the Collecting side.
The Collecting Process MUST check that the Exporter is compliant with
the specifications in this document. For example, nothing prevents an
implementation that does not meet the specification of the
per-SCTP-stream extension from sending a Template that looks like a
dataRecordsReliability Options Template. Therefore, a Collecting Process
MUST detect if the Exporter fails to meet the specification fully. If
any of the conditions below is met, the Exporting Process does not
properly use the per-SCTP-stream extension. In this case, the
Collecting Process MUST disable the per-SCTP-stream extension for the
given Exporter and report an error message:
1. A Data Record is received before the appropriate Data Record
associated with the Data Records Reliability Options Template has been
received on the same SCTP stream (see section 4.1).
2. A Data Record associated with a Data Record Reliability
Options Template is received on an SCTP stream for a (non-Options)
Template that was defined on a different SCTP stream.
3. Loss of Data Records is detected within a stream where there has not
been received a Data Record associated with the Data Record Reliability
Options Template indicating unreliable transmission for any template.
4. A message is received with the SCTP U(nordered) flag set to 1, (i.e.,
the message was sent unordered) even if it is processed in order.
Note that it is not an error to receive a Data Record reliably if that
Data Record is associated with a Template whose Data Records are
expected to be sent unreliably.
Continuing below the paragraphs are unchanged
The Collecting Process MUST accept other non-scope Information
Elements in the Data Record Reliability Options Template.
Actually, there is nothing in RFC5101 that mandates that (Options)
Template and associated Data Records must be sent in the same SCTP stream.
-- section 4.2, 3rd paragraph from end, starting with "When an Options
I'm confused by this paragraph. Would exporters using this extension ever send
the options template and associated data records in different streams?
-- section 4.1, description of dataRecordsReliability:
I find the first sentence hard to parse.
The reliability of the export of Data Records, within
this SCTP stream, for the element(s) in the Options
Template scope, usually a templateID. A value of 'true'
means that the Exporting Process MUST send any Data
Records associated with the element(s) reliably within
this SCTP stream. A value of 'false' means that the
Exporting Process MAY send any Data Records associated
with the element(s) unreliably within this SCTP stream.
The export reliability of Data Records, within this SCTP stream, for the
element(s) in the Options Template scope. A typical example of element
for which the export reliability must be reported is the templateID, as
a specified in the Data Record Reliability Options Template. A value of
'true' means that the Exporting Process MUST send any Data Records
associated with the element(s) reliably within this SCTP stream. A
value of 'false' means that the Exporting Process MAY send any Data
Records associated with the element(s) unreliably within this SCTP stream.
-- section 4.2, first paragraph" "...exporting processes should follow..."
(Note that an identical comment applies to the first paragraph of several of
the specification sections.)
It would be best to avoid the word "should" in this context. Even though we all
know a lower case should is not normative, it's still enough to confuse a reader into
interpreting as a normative SHOULD, which is actually weaker than the real requirement.
That is, I don't think you mean to say that, in order to take advantage of this extension
and implementation SHOULD follow this specification.
Actually, this should be a "MUST"
To take advantage of per-stream export, Exporting Processes should
follow the specification in this section in addition to Section 8,
Template Management, of [RFC5101].
To take advantage of per-stream export, Exporting Processes MUST follow
the specification in this section in addition to Section 8, Template
Management, of [RFC5101].
We have corrected the other first paragraph of several of the
-- section 4.3, paragraph 3:
pedantic nit - I think you mean all IPFIX messages in a single stream MUST be
sent in order--not that all messages have to be in a single stream, right? The
current wording is (slightly) ambiguous on that point.
Not pedantic, you're actually right.
All IPFIX Messages MUST be sent in order within an SCTP stream.
All IPFIX Messages in an SCTP stream MUST be sent in order.
-- section 4.3, last paragraph:
Why mention the alternative if it is not feasible in production?
An alternative, which is not practical in
operational networks, is to restart the SCTP association with an
increased number of SCTP streams.
An alternative, which may result in the loss of Flow Records (for
example, due to lack of buffering on the Exporter), is to restart the
SCTP association with an increased number of SCTP streams
--Examples, figure 3:
Is Data 257 a typo?
-- idnits has some warnings. Please check before publication.
The warnings are about: License, copyright year, and outdated references.
I'll correct these. Not sure whether I should publish a new draft
version. Anyway, I have all those changes above in my private copy of
Please let us know if this clarifies the situation.
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