MPLS Forwarding Compliance and Performance Requirements
draft-ietf-mpls-forwarding-09

[Ballot comment]

Excellent document, thanks.

2.4.5.2, last para: "This document makes the following
recommendations." Is some text here a cut'n'paste error?

2.6.1, I don't get "Only where hardware can identify a
signature and the portion of packet covered by the signature
is cryptographic authentication highly beneficial in
protecting against DoS attacks." What is that meant to mean?
I'm guessing signature there does not mean digital signature.

2.6.1, To be honest this section reads like there's not that
much known about DoS mitigation at this layer, (or that
someone's not saying:-) Either would be surprising. Is there
not more to be said? (Honest question, I don't know how
DoS-mitigation is done down here;-)

[Ballot comment]
This is a well written document.

However I do have some comments that I would ask the authors to consider:

In 2.1.7.  MPLS Fast Reroute (FRR), there should be some discussion of RFC5286, and possibly RFC5714 and draft-ietf-rtgwg-remote-lfa since they are all deployed in MPLS networks.

=====

1.  Introduction and Document Scope

  The initial purpose of this document was to address concerns raised
  on the MPLS WG mailing list about shortcomings in implementations of
  MPLS forwarding. 

SB> "The initial purpose" implies a later purpose, but that is not clear.

=====

SB> It would be useful to warn the reader of the issues with non-IETF definitions of
MPLS. For example the  G8110 the definition of MPLS led to incorrect
assumptions which were noted in RFC5704

====
2.1.3.  Time Synchronization
  "PTP and NTP timestamp formats differ slightly.  "

SB> The difference is surely fundamental!

====
  PW services which are not timing critical bit streams in nature are
  cell oriented or frame oriented. 

SB> Actually some ATM cell streams are also timing critical

====

2.3.  Packet Rates

  Internet service providers and content providers at one time
  specified full rate forwarding with 40 byte payload packets as a
  requirement.  Today, this requirement often can be waived if the
  provider can be convinced that when long sequence of short packets
  occur no packets will be dropped.

SB> Doesn't this then feed the buffer bloat problem?

====
Appendix A.  Organization of References Section

This would be more useful as section 8.0

====

You might want to give a heads up to the work on SPRING which
will further inflate the label stack.

====

It might be useful to add some text on IPFIX in particular IEs
46,47, 70..79, 90, 91, 140, 194

[Ballot comment]
This is a well written document.

However I do have some comments that I would ask the authors to consider:

In 2.1.7.  MPLS Fast Reroute (FRR), there should be some discussion of RFC5286, and possibly RFC5714 and draft-ietf-rtgwg-remote-lfa since they are all deployed in MPLS networks.

=====

1.  Introduction and Document Scope

  The initial purpose of this document was to address concerns raised
  on the MPLS WG mailing list about shortcomings in implementations of
  MPLS forwarding. 

SB> "The initial purpose" implies a later purpose, but that is not clear.

=====

SB> It would be useful to warn the reader of the issues with non-IETF definitions of
MPLS. For example the  G8110 the definition of MPLS led to incorrect
assumptions which were noted in RFC5704

====
2.1.3.  Time Synchronization
  "PTP and NTP timestamp formats differ slightly.  "

SB> The difference is surely fundamental!

====
  PW services which are not timing critical bit streams in nature are
  cell oriented or frame oriented. 

SB> Actually some ATM cell streams are also timing critical

====

2.3.  Packet Rates

  Internet service providers and content providers at one time
  specified full rate forwarding with 40 byte payload packets as a
  requirement.  Today, this requirement often can be waived if the
  provider can be convinced that when long sequence of short packets
  occur no packets will be dropped.

SB> Doesn't this then feed the buffer bloat problem?

====
Appendix A.  Organization of References Section

This would be more useful as section 8.0

====

You might want to give a heads up to the work on SPRING which
will further inflate the label stack.

[Ballot comment]
-- Section 1.2 --

  This document is informational.  The upper case [RFC2119] key words
  are not used in this document, except in the following cases.

In fact, there's quite a lot of 2119 language in here, and this makes it sound like there isn't.  I suggest re-wording this:

NEW
  This document is informational.  The upper case [RFC2119] key words
  "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" are used in
  this document in the following cases.
END

IESG/Authors/WG Chairs:

IANA has reviewed draft-ietf-mpls-forwarding-06, which is currently in Last Call, and has the following comments:

We understand that, upon approval of this document, there are no IANA Actions that need completion. IANA requests that the IANA Considerations section of the document remain in place upon publication.

If this assessment is not accurate, please respond as soon as possible.

The following Last Call announcement was sent out:

From: The IESG
To: IETF-Announce
CC:
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (MPLS Forwarding Compliance and Performance Requirements) to Informational RFC


The IESG has received a request from the Multiprotocol Label Switching WG
(mpls) to consider the following document:
- 'MPLS Forwarding Compliance and Performance Requirements'
  as Informational RFC

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 2014-02-12. 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 provides guidelines for implementers regarding MPLS
  forwarding and a basis for evaluations of forwarding implementations.
  Guidelines cover many aspects of MPLS forwarding.  Topics are
  highlighted where implementers might otherwise overlook practical
  requirements which are unstated or under emphasized or are optional
  for conformance to RFCs but are often considered mandatory by
  providers.

The file can be obtained via
http://datatracker.ietf.org/doc/draft-ietf-mpls-forwarding/

IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-ietf-mpls-forwarding/ballot/

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

AD review
========

Hi,

Thank you for a really thorough and clear document.

I have done my usual AD review upon receiving the publication request
for this document. The purpose of the review is to catch any issues that
might otherwise show up in IETF last call and IESG evaluation. In this
case it is also an extra pair of eyes on what is a very detailed
document.

I have a number of comments below. A few are editorial nits (sorry) and
some are questions for clarification of the text. There is very little
where I come even remotely close to saying "wrong" or missing".

It looks to me that a new revision would be useful just to mop up these
comments, so I have put the document into "Revised I-D Needed" state and
will wait to see the next revision before starting the IETF last call.
Please debate any issues where you disagree with me or think that no
document change is needed.

Thanks for the work,
Adrian

===

idnits notes that...

  == Outdated reference: draft-ietf-pwe3-vccv-impl-survey-results has been
    published as RFC 7079

---

Andy may want to update his coordinates.

---

Your acronym list is commendably thorough, but a little enthusiastic.

AC is only used once and then only at the point of expansion.
CE doesn't appear to be used at all
FEC only seems to be used in this document in the context of
  Forwarding Equivalence Classes (LDP)

The following are all well-known acronyms according to
  http://www.rfc-editor.org/rfc-style-guide/abbrev.expansion.txt
  so they don't need to be included
BGP
CPU
DDoS
DoS
GMPLS
IANA
IP
IPv4
IPv6
LDP
MPLS
NTP
QoS
RTP
TCP
UDP
WG


I think Curtis may have heard this before :-)
The "preferred" (by the RFC editor) expansion of ECMP is
"Equal-Cost Multipath"

Several acronyms are qualified with (LDP) (CE, FEC, P, PE). I haven't
checked the usage in this document, but it seems to me that the terms
might have wider applicability. Indeed, a quick search revealed
"RSVP-TE PE".

The third expansion of PSC could have a reference to RFC 6378. I think
that to avoid confusion, you need to expand this in the text when you
use it. You do this well everywhere except in Section 4.7 T#32, and in
this acronym list itself at E-LSP and L-LSP.

---

Section 1.3 bullet 5

  5.  The implementer and system designer MUST support pseudowire
      control word (CW) if MPLS-TP is supported or if ACH [RFC5586] is
      being used on a pseudowire.

The wording is a bit odd. "The implementation and system design..."?

Ditto bullets 6 and 7

---

Section 1.3

While there is not wrong with the statements made in the bullets, some
of the later ones refer to recent additions to the MPLS suite. Yet the
list is presented as "there were some misconceptions." Clearly the
early silicon did not have misconceptions about the inclusion of entropy
labels.

Just tweak the words at the top of the list?

---

Section 2.1

  Tunneling encapsulations which may carry MPLS, such as MPLS in GRE,
  L2TP, or LDP, are out of scope.

I think s/LDP/UDP/

---

2.1.1

Maybe the first paragraph should clarify "special purpose labels at
the top of the label stack"

---

2.1.1

I think that this section should note that labels 0-15 were commonly
referred to as "reserved labels" and are only renamed to "special
purpose labels" by [I-D.ietf-mpls-special-purpose-labels].

---

2.1.4

  MPLS hierarchy as described in [RFC4206] can in principle add up to
  four additional labels.  MPLS hierarchy is discussed in
  Section 2.1.6.

Similar text in 2.1.6

I wonder whether the choice of "four" here is because RFC 4203 defines
      1    Packet-Switch Capable-1 (PSC-1)
      2    Packet-Switch Capable-2 (PSC-2)
      3    Packet-Switch Capable-3 (PSC-3)
      4    Packet-Switch Capable-4 (PSC-4)
If that is the case, we should note that RFC 7074 deprecates PSC-2
through 4 recognising that different switching levels within the PSC
world were not applied and that LSP nesting was arbitrary and not
limited to four levels.

On the other hand, if "four" comes from somewhere else, perhaps you
could give a clue in the text.

---

While per platform label space is mentioned in 2.1.7 I wonder whether
more information on per platform and per interface label spaces is
needed. I recall early implementations that got very confused when
parallel interfaces used the same label for different purposes.

I guess the point there is that you cannot assume that your neighbor
is or is not using the per platform label space.

Upstream label allocation may also come into this.

---

2.1.8.1

  1.  The most common case is where reordering occurs is rare,

One too many instances of "is"

---

2.1.8.1

  3.  If the edge is not using pseudowire control word (CW) and the
      core is using multipath, reordering will be far more common.  If
      this is occurring, the best solution is to use CW on the edge,
      rather than try to fix the reordering using resequencing.

Completely agree, but isn't the sequence number contained in a control
word meaning that the resequencing could, in any case, not be done
without using a control word?

---

2.1.8.1

  4.  Another avoidable case is where some core equipment has multipath
      and for some reason insists on periodically installing a new
      random number as the multipath hash seed.  If supporting MPLS-TP,
      equipment MUST provide a means to disable periodic hash reseeding
      and deployments MUST disable periodic hash reseeding.  Even if
      not supporting MPLS-TP, equipment should provide a means to
      disable periodic hash reseeding and deployments should disable
      periodic hash reseeding.

Are those two "should" really "SHOULD"?

---

Should 2.2 distinguish the order of magnitude of replication at branch
nodes? This impacts the replication method used (some devices make a
copy and cycle around, some devices can do multiple copies at once). On
the whole is no different from IP multicast processing except (as you
note) that each outgoing packet may be different by its label value.

---

2.4

So obvious you didn't say it?

  In order to support an adequately balanced load distribution across
  multiple links, IP header information must be used.  Common practice
  today is to reinspect the IP headers at each LSR and use the label
  stack and IP header information in a hash performed at each LSR.
  Further details are provided in Section 2.4.5.

Missing is the statement that a single "flow" must not be distributed
across multiple paths because of the implication for potentially
significant packet misordering. And feeding that is a common requirement
that such packet misordering must not occur because applications and
transport protocol implementations cannot survive such misordering.

---

2.4.2 uses "composite link" and "component link". I suggest picking just
one term.

---

2.4.5.1 notes that special purpose and extended special purpose labels
need to be excluded from the hash. Good.
But it seems that some special purpose labels will indicate that the
next label stack entry contains a label with special meaning. (ELI is
an example that we specifically don't have to worry about.)
How do we handle that?
Should we be dividing up the extended special purpose label space to
have one set of code points meaning "just this label is special" and
another set meaning "this label is special and the next label stack
entry is magic"?

---

An issue that arises from the multipath support (2.4.5.1) is that
hardware assumes that after a label stack entry with the S-bit set,
there are only three possible next bytes...
- a control word (indicated by b0000 or b0001)
- an IPv4 header
- an IPv6 header
This is the case regardless of how the LSP was set up, and the next
bytes cannot ever be further MPLS stack entries.

While this comes up 2.4.5.1 it may merit further discussion in an
earlier section of the document.

I note that discussion of support of PWs without the CW drives you
to say that hashing beyond the S-bit should be a configurable option
which would (of course) support any payload including MPLS in MPLS
with repeated bottom of stack. However, you might want to specifically
preclude that.

---

Q#7 introduces the terms "short-pipe" and "uniform model". It provides
a pointer to 2.1.6, but that section does not mention these terms (and
doesn't refer to RFC 3270).

---

Section 7 could usefully point back at Section 2.6.1

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.

  The MPLS Working Group request that
        MPLS Forwarding Compliance and Performance Requirements
                    draft-ietf-mpls-forwarding-03

  Is published as an Informational RFC with IETF consensus.


(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?

      We request that the document is published as an Informational. Informational
      is correct since it discusses MPLS forwarding requirements and issues, it
      gives guidelines for implementors based on operational experience, but it
      does not specify any protocol.

      Informational is the right type of RFC for this document.

(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

  Relevant content can frequently be found in the abstract
  and/or introduction of the document. If not, this may be
  an indication that there are deficiencies in the abstract
  or introduction.

      This document provides guidelines for implementers regarding MPLS
      forwarding and a basis for evaluations of forwarding implementations.
      Guidelines cover many aspects of MPLS forwarding.  Topics are
      highlighted where implementers might otherwise overlook practical
      requirements which are unstated or under emphasized or are optional
      for conformance to RFCs but are often considered mandatory by
      providers.


Working Group Summary

  Was there anything in WG process that is worth noting? For
  example, was there controversy about particular points or
  were there decisions where the consensus was particularly
  rough?

      This document has been discussed by the working group both on the
      mailing list and at a long slot at the working meeting in Vancouver.

      The working group is behind this document, there has been no mayor
      controversies and very good discussions.

Document Quality

  Are there existing implementations of the protocol? Have a
  significant number of vendors indicated their plan to
  implement the specification? Are there any reviewers that
  merit special mention as having done a thorough review,
  e.g., one that resulted in important changes or a
  conclusion that the document had no substantive issues? If
  there was a MIB Doctor, Media Type or other expert review,
  what was its course (briefly)? In the case of a Media Type
  review, on what date was the request posted?

      The question about implementations is a bit tricky - there are no
      implementations based on the document, as there were existing
      implementations when the document was started up. Instead it is the
      other  way around, the document discusses implementation and
      deployment experiences. All the scenarios discussed in the document
      have been implemented and/or deployed.

      The document is Informational and no MIB Doctor, Media type or other
      other types of expert reviews have been necessary.
     

Personnel

  Who is the Document Shepherd? Who is the Responsible Area
  Director?

      Loa Andersson, is the document Shepherd.
      Adrian Farrel is the Responsible AD

(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 has reviewed this document several times, twice - prior
      to the poll to make it a wg document and before the wglc, but the Shepherd
      has also closely followed and contributed to the discussions on the document
      on the mailing list.

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

      No such concerns, all the expertise we need to review this document are
      available in the working group, and the document have attracted a lot of
      of interest.

(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 such reviews has been necessary.

(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 such concerns.

(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.

      The document was polled for IPRs prior to starting the poll for adopting
      it as a working group document; at that time all the authors confirmed
      that they were not aware of any IPR relating to this document. The list of
      authors is the same now as it was when the IPR poll was issued.

      As part of the preparation of the publication request a new IPR poll has
      issued and if any changes as compared to the previous IPR is reported
      the Shepherd write-up will be updted.

(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 disclousers as been filed against this document.

(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?

      The working group consensus is very solid, the document has been met
      with strong interest but there are no outstanding issues.   

(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 such threats.

(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.

      There is one outdated reference, draft-ietf-pwe3-vccv-impl-survey-results
      has been published as RFC 7079.

    This will be updated if a new ID is needed or taken care of by an
      RFC Editors note.

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

      No formal reviews needed.

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

      The references are correctly split in to Normative and Informative,
      further there is an Appendix A explaining how this is done for an
      document intended to be published as in Informational RFC.

      The Appendix says:
      "The References section is split into Normative and Informative
      subsections.  References that directly specify forwarding
      encapsulations or behaviors are listed as normative.  References
      which describe signaling only, though normative with respect to
      signaling, are listed as informative.  They are informative with
      respect to MPLS forwarding."

 
(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?

      No such references to documents that are not ready to be advanced.
      All the normative references are to RFCs.

(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 downward references.

(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.

    The publication of this document will not change the status of any
    existing RFC


(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).

      There are no requests for IANA actions in this document.

(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 IANA registries that will require expert review.

(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 reviews (other than nits tool) necessary.