Differentiated Service Code Point and Explicit Congestion Notification Monitoring in the Two-Way Active Measurement Protocol (TWAMP)
draft-ietf-ippm-type-p-monitor-03

[Ballot comment]
My apologies for thinking slowly ... but it doesn't look like these questions will be difficult to resolve.

I talked with David Black about this draft, and he had questions that I translated into AD-speak as:

Reflecting an unknown DSCP value is a MAY. Can reflecting packets using a DSCP value you don't understand be a bad idea? How important is that the DSCP value is NOT 0 (CS0, default forwarding)?

If you are reflecting a DSCP value, are you also reflecting the ECN(0) bit unchanged?

TWAMP doesn't look congestion-controlled to me (certainly not in the reflected direction - https://tools.ietf.org/html/rfc5357 says the packet is reflected as quickly/immediately as possible in at least three places I can see. What is a typical sending rate for the Session-Sender, and is that likely to cause problems in the reflected direction?

His note to me follows:

This bullet at the end of 2.2.2 bothers me:

  o  if the negotiated/provisioned DSCP value is not known (e.g.  TWAMP
      Light), the choice of the DSCP is implementation specific.  For
      instance, Session-Reflector MAY copy the DSCP value from the
      received test packet and set it as DSCP in a reflected packet

This is implicitly recommending reflection of the DSCP value, and by
omitted implication, reflection of the ECN value.  Both of those seem
like bad ideas, it would be better to say that in this case the DSCP
should be set to 0 (CS0, Default forwarding).  I would also say that
the ECN field MUST be set to 0 (not-ECT) in the reflected packet, always.

I’m a bit concerned about setting ECT(0) or ECT(1) on the forward
measurement path, as TWAMP is not congestion-responsive.  Is the
transmission rate of TWAMP low enough to not cause a problem if CE
signals are received and ignored in the ECN field at the Reflector?

[Ballot comment]
Since rfc5357 has more discussion on the differences between unauthenticated, authenticated, and encrypted modes, it would be helpful to have a pointer to that specific point in the Security Considerations section.

[Ballot comment]
Just a few mostly editorial comments:

- Abstract: Did you mean OPTIONAL to be capitalized in the abstract? I'm not sure what the purpose of a 2119 keyword would be there.

- 1, first paragraph:
There are lots of missing articles ("the") in the first paragraph.

-1, 2nd paragraph:
There's no need to say it's OPTIONAL more than once.

- 2.1, 1st paragraph:
"DSCP and ECN monitoring flag" and "Mode" each need a leading "the".

- 2.2.1:
The MUST in the first paragraph is not really needed. The Session-Reflector either supports the extension and does these things, or does not support the extension and does not do these things.

- First bullet in list at end of 2.2.1:
s/extracts/extract

[Ballot comment]
Just a couple of nits:

In Section 2.2.1., please put a reference to rfc5357 (?) to show where the test packet formats came from and to indicate where the fields are described.

Figure 4 doesn't show the S-DSCP-ECN field in it.

[Ballot comment]
As mentioned by Al Morton, part of his OPS DIR review:

Summary: Almost ready, comments and editorial suggestions follow.

The draft header should indicate that this draft updates RFC 5357.

Section 2.2.1

Figure 1 has a number of canonical references that should
be cited to ensure IPv4 and IPv6 applicability, including
RFC 2474, RFC 3168, and other relevant updates (of which
there are many).


  o  if the negotiated/provisioned DSCP value is not known (e.g.  TWAMP
      Light), the choice of the DSCP is implementation specific.  For
      instance, Session-Reflector MAY copy the DSCP value from the
      received test packet and set it as DSCP in a reflected packet.
Question:
What about the ECN value?  From 3168:
      +-----+-----+
      | ECN FIELD |
      +-----+-----+
        ECT  CE        [Obsolete] RFC 2481 names for the ECN bits.
        0    0        Not-ECT
        0    1        ECT(1)
        1    0        ECT(0)
        1    1        CE
It makes little sense to copy a "11" == CE into the reflected packet,
and it may affect the measured performance if "11" were copied.
The draft needs more guidance here (there is a general problem
when the negotiated values are "not known"; this does not apply
to the Standards Track TWAMP protocol or its extensions).

-=-=-=-=-=-=-=-=-=-=-=-=-

Editorial comments/suggestions:

OLD
2.2.  TWAMP-Test Extension

  Monitoring of DSCP and ECN requires support by the Session-Reflector
  and changes the format of its test packet format both in
  unauthenticated, authenticated and encrypted modes.
Suggest:
  Monitoring of DSCP and ECN requires support by the Session-Reflector
  and changes the test packet format in all the original
  (unauthenticated, authenticated and encrypted) modes.

2.2.1

OLD
  o  the first six bits of the Differentiated Service field MUST be
      copied from received Session-Sender test packet into Sender DSCP
      (S-DSCP) field;

  o  the following two bits of the ECN field MUST be copied from
      received Session-Sender test packet into Sender ECN (S-ECN) field.
Suggest:
  o  the six (least-significant) bits of the Differentiated Service field MUST be
      copied from received Session-Sender test packet into Sender DSCP
      (S-DSCP) field;

  o  the two bits of the ECN field MUST be copied from
      received Session-Sender test packet into Sender ECN (S-ECN) field.

because RFC 3168 defines:
        0    1    2    3    4    5    6    7
      +-----+-----+-----+-----+-----+-----+-----+-----+
      |          DS FIELD, DSCP          | ECN FIELD |
      +-----+-----+-----+-----+-----+-----+-----+-----+

        DSCP: differentiated services codepoint
        ECN:  Explicit Congestion Notification

      Figure 2: The Differentiated Services and ECN Fields in IP.
-=-=-=-=-=-=-=-

OLD
    0    1    2    3    4    5    6    7    8
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              S-DSCP              |  S-ECN  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 1: Sender DSCP and ECN field format

Suggest:
The extra "+" within bit positions are distracting,
and don't conform to the conventions of these diagrams.
Also, there's no "8" when numbering from 0.

Some attempt should be made to put Figure 3 on a single page in the
final version. There's one line taken up by "+" that is unnecessary
in the modified field:

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Sender TTL  |  S-DSCP-ECN  |                              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                              +
    |                                                            |
>> +                                                            + <<
    |                      MBZ (14 octets)                      |
    |                                                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

(Via drafts-lastcall@iana.org): IESG/Authors/WG Chairs:

IANA has completed its review of draft-ietf-ippm-type-p-monitor-02. If any part of this review is inaccurate, please let us know.

We understand that this document requires a single IANA action.

Upon approval of this document, IANA will add the following to the TWAMP-Modes registry at http://www.iana.org/assignments/twamp-parameters:

Bit: TBD
Description: DSCP and ECN Monitoring Capability
Semantics Definition: Section 2
Reference: This document

Note:  The actions requested in this document will not be completed until the document has been approved for publication as an RFC. This message is only to confirm what actions will be performed.

The following Last Call announcement was sent out:

From: The IESG
To: IETF-Announce
CC:
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (Differentiated Service Code Point and Explicit Congestion Notification Monitoring in Two-Way Active Measurement Protocol (TWAMP)) to Proposed Standard


The IESG has received a request from the IP Performance Metrics WG (ippm)
to consider the following document:
- 'Differentiated Service Code Point and Explicit Congestion Notification
  Monitoring in Two-Way Active Measurement Protocol (TWAMP)'
  as Proposed Standard

The IESG plans to make a decision in the next few weeks, and solicits
final comments on this action. Please send substantive comments to the
ietf@ietf.org mailing lists by 2015-10-21. Exceptionally, comments may be
sent to iesg@ietf.org instead. In either case, please retain the
beginning of the Subject line to allow automated sorting.

Abstract


  This document describes an OPTIONAL extension for Two-Way Active
  Measurement Protocol (TWAMP) allowing the monitoring of the
  Differentiated Service Code Point and Explicit Congestion
  Notification fields with the TWAMP-Test protocol.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-ippm-type-p-monitor/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-ippm-type-p-monitor/ballot/


No IPR declarations have been submitted directly on this I-D.

As required by RFC 4858, this is the current template for the Document
Shepherd Write-Up.

Changes are expected over time. This version is dated 24 February 2012.

(1) What type of RFC is being requested (BCP, Proposed Standard,
Internet Standard, Informational, Experimental, or Historic)?  Why
is this the proper type of RFC?  Is this type of RFC indicated in the
title page header?

The RFC is intended as a Proposed Standard; the current notation of this in
the header is Standards Track.

(2) The IESG approval announcement includes a Document Announcement
Write-Up. Please provide such a Document Announcement Write-Up. Recent
examples can be found in the "Action" announcements for approved
documents. The approval announcement contains the following sections:

Technical Summary

The document describes an OPTIONAL extension for Two-Way Active
Measurement Protocol (TWAMP) allowing the monitoring of the
Differentiated Service Code Point and Explicit Congestion
Notification fields with the TWAMP-Test protocol.
 
Working Group Summary

The document is uncontroversial, and has clear working group consensus to move
forward, controlling for the fact that the group of participants within the WG
actively contributing on OWAMP/TWAMP is small relative to the group of all
contributors.

Document Quality

The document has been discussed and reviewed by the WG and the shepherd, and
modulo a single issue (below) is ready to go. Implementations of the protocol
option described are planned by the authors.

Personnel

The document shepherd is Brian Trammell. The responsible AD is Spencer Dawkins.

(3) Briefly describe the review of this document that was performed by
the Document Shepherd.  If this version of the document is not ready
for publication, please explain why the document is being forwarded to
the IESG.

The shepherd re-read the document in its entirety for this review. Modulo the
issue with the mode bits above, the shepherd has no concerns.

(4) Does the document Shepherd have any concerns about the depth or
breadth of the reviews that have been performed?

No. The document was well-reviewed even before being accepted as a WG item.

(5) Do portions of the document need review from a particular or from
broader perspective, e.g., security, operational complexity, AAA, DNS,
DHCP, XML, or internationalization? If so, describe the review that
took place.

No.

(6) Describe any specific concerns or issues that the Document Shepherd
has with this document that the Responsible Area Director and/or the
IESG should be aware of? For example, perhaps he or she is uncomfortable
with certain parts of the document, or has concerns whether there really
is a need for it. In any event, if the WG has discussed those issues and
has indicated that it still wishes to advance the document, detail those
concerns here.

No issues.

(7) Has each author confirmed that any and all appropriate IPR
disclosures required for full conformance with the provisions of BCP 78
and BCP 79 have already been filed. If not, explain why.

All authors have confirmed they know of no related IPR; no IPR disclosures have been filed.

(8) Has an IPR disclosure been filed that references this document?
If so, summarize any WG discussion and conclusion regarding the IPR
disclosures.

No IPR disclosures.

(9) How solid is the WG consensus behind this document? Does it
represent the strong concurrence of a few individuals, with others
being silent, or does the WG as a whole understand and agree with it?

WG consensus represents consensus of those who actively contribute on
OWAMP/TWAMP-related issues, which is a small subset of the active contributors
as a whole.

(10) Has anyone threatened an appeal or otherwise indicated extreme
discontent? If so, please summarise the areas of conflict in separate
email messages to the Responsible Area Director. (It should be in a
separate email because this questionnaire is publicly available.)

No.

(11) Identify any ID nits the Document Shepherd has found in this
document. (See http://www.ietf.org/tools/idnits/ and the Internet-Drafts
Checklist). Boilerplate checks are not enough; this check needs to be
thorough.

[minor warning] There seems to be a formatting problem: idnits complains that there are no
formfeeds at page breaks. We presume this can be corrected in editorial.

(12) Describe how the document meets any required formal review
criteria, such as the MIB Doctor, media type, and URI type reviews.

No reviews necessary.

(13) Have all references within this document been identified as
either normative or informative?

Yes.

(14) Are there normative references to documents that are not ready for
advancement or are otherwise in an unclear state? If such normative
references exist, what is the plan for their completion?

All normative references are proper, and to complete documents.

(15) Are there downward normative references references (see RFC 3967)?
If so, list these downward references to support the Area Director in
the Last Call procedure.

No.

(16) Will publication of this document change the status of any
existing RFCs? Are those RFCs listed on the title page header, listed
in the abstract, and discussed in the introduction? If the RFCs are not
listed in the Abstract and Introduction, explain why, and point to the
part of the document where the relationship of this document to the
other RFCs is discussed. If this information is not in the document,
explain why the WG considers it unnecessary.

No.

(17) Describe the Document Shepherd's review of the IANA considerations
section, especially with regard to its consistency with the body of the
document. Confirm that all protocol extensions that the document makes
are associated with the appropriate reservations in IANA registries.
Confirm that any referenced IANA registries have been clearly
identified. Confirm that newly created IANA registries include a
detailed specification of the initial contents for the registry, that
allocations procedures for future registrations are defined, and a
reasonable name for the new registry has been suggested (see RFC 5226).

The IANA considerations section requests the addition of a codepoint in the TWAMP modes registry.
Issues in the TWAMP modes registry were identified during the review of this document which have
since been corrected. This document will need to wait on the publication of draft-ietf-ippm-owamp-registry.

(18) List any new IANA registries that require Expert Review for future
allocations. Provide any public guidance that the IESG would find
useful in selecting the IANA Experts for these new registries.

No new registries.

(19) Describe reviews and automated checks performed by the Document
Shepherd to validate sections of the document written in a formal
language, such as XML code, BNF rules, MIB definitions, etc.

No automated checks necessary.