Applicability of the Path Computation Element (PCE) to Point-to-Multipoint (P2MP) MPLS and GMPLS Traffic Engineering (TE)
draft-ietf-pce-p2mp-app-02

[Ballot comment]
From Brian Weis' secdir review (posted 6/15)

The "Note" in the Security Considerations section points out that P2MP
computation is CPU-intensive, and posits that an attacker injecting
spurious P2MP path computation requests may be more successful than if
the attacker injected P2P computation requests. Since you brought up
the attack, it would be worth noting that the use of a message
integrity mechanism by a PCE protocol should be used to mitigate
attacks from devices that are not authorized to send requests to the
PCE device. I hesitate to be more specific because the document does
not describe a particular PCE protocol.

[Ballot comment]
The OPS-DIR review by Tina Tsou raised a couple of issues. Taking into account that the intended status of this document is Informational I do not believe that these are blocking, however it would be good if they were clarified:

1. In section 2.2.2, which mechanism is used for the PCE congestion? The congestion notification mechanism is mentioned in the document. When there are not sufficient resources for lager number of PCEs, what to do exactly? The document should specify the detailed mechanisms or some references from other documents.

2. When the PCEs are not capable of the complex P2MP reoptimization functionality, which other methods may be used?


I like the Manageability Considerations section. I have a few clarification questions and editorial comments.

3. in the intorduction to section 8

> The use of PCE to compute P2MP paths has many of the same
  manageability considerations as when it is used for P2P LSPs.

A reference for these manageability considerations would be useful

4. section 8.2 - it is not clear what is meant by

> This will result in much larger data sets to be
  controlled and modeled and will impact the utility of any management
  data models, such as MIB modules.

If you mean that the data model becomes that complex that the efficiency of configuring by SNMP and MIB modules is in doubt - maybe it's better to say it explicitly. Other protocols and data modelling structures lile NETCONF / NETMOD could be considered

5. In section 8.3 the word 'this' after the period should be capitalized 'This'

6. Maybe we can find a less colourful term than 'nervous LSRs'

[Ballot comment]
I like the Manageability Considerations section. I have a few clarification questions and editorial comments.

1. in the intorduction to section 8

> The use of PCE to compute P2MP paths has many of the same
  manageability considerations as when it is used for P2P LSPs.

A reference for these manageability considerations would be useful

2. section 8.2 - it is not clear what is meant by

> This will result in much larger data sets to be
  controlled and modeled and will impact the utility of any management
  data models, such as MIB modules.

If you mean that the data model becomes that complex that the efficiency of configuring by SNMP and MIB modules is in doubt - maybe it's better to say it explicitly. Other protocols and data modelling structures lile NETCONF / NETMOD could be considered

3. In section 8.3 the word 'this' after the period should be capitalized 'This'

4. Maybe we can find a less colourful term than 'nervous LSRs'

[Ballot comment]
Section 2.2.2., paragraph 0:
> 2.2.2. PCE Congestion

  Similar to other PCE documents that we've published, I'd suggest to
  replace "congestion" by "overload" here. In the Internet, congestion
  implicitly means "data-plane congestion", whereas what is meant here
  is "control-plane processing overload".

[Ballot comment]
This is an applicability statement for a piece of protocol that has not
  yet been written.  It is not a re-use of the defined PCE Protocol; the
  document says that "some extensions are needed."  This document is
  distinct from the p2mp PCE requirements document.

Proto-write-up for draft-ietf-pce-p2mp-app-01

Intended status : Informational Track

> (1.a)  Who is the Document Shepherd for this document?  Has the
>      Document Shepherd personally reviewed this version of the
>      document and, in particular, does he or she believe this
>      version is ready for forwarding to the IESG for publication?

JP Vasseur is the document shepherd.
He has personally reviewed the I-D and believes it is ready for
forwarding to the IESG for publication.

> (1.b)  Has the document had adequate review both from key WG members
>      and from key non-WG members?  Does the Document Shepherd have
>      any concerns about the depth or breadth of the reviews that
>      have been performed?

The I-D has had some level of discussions and review in the PCE
working group. It has not had review in any wider forums, but none was
deemed necessary or appropriate.

> (1.c)  Does the Document Shepherd have concerns that the document
>      needs more review from a particular or broader perspective,
>      e.g., security, operational complexity, someone familiar with
>      AAA, internationalization or XML?

No concerns.

> (1.d)  Does the Document Shepherd have any specific concerns or
>      issues 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.  Has an IPR disclosure related to this document
>      been filed?  If so, please include a reference to the
>      disclosure and summarize the WG discussion and conclusion on
>      this issue.

The document is sound.

No IPR discloser for this document.

> (1.e)  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?

Consensus is good.

> (1.f)  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
>      entered into the ID Tracker.)

No threats. No discontent.

> (1.g)  Has the Document Shepherd personally verified that the
>      document satisfies all ID nits?  (See
>      http://www.ietf.org/ID-Checklist.html and
>      http://tools.ietf.org/tools/idnits/).  Boilerplate checks are
>      not enough; this check needs to be thorough.  Has the document
>      met all formal review criteria it needs to, such as the MIB
>      Doctor, media type and URI type reviews?

All checks made.

> (1.h)  Has the document split its references into normative and
>      informative?  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
>      strategy for their completion?  Are there normative references
>      that are downward references, as described in [RFC3967]?  If
>      so, list these downward references to support the Area
>      Director in the Last Call procedure for them [RFC3967].

References split.
No downrefs.

> (1.i)  Has the Document Shepherd verified that the document IANA
>      consideration section exists and is consistent with the body
>      of the document?  If the document specifies protocol
>      extensions, are reservations requested in appropriate IANA
>      registries?  Are the IANA registries clearly identified?  If
>      the document creates a new registry, does it define the
>      proposed initial contents of the registry and an allocation
>      procedure for future registrations?  Does it suggest a
>      reasonable name for the new registry?  See [RFC2434].  If the
>      document describes an Expert Review process has Shepherd
>      conferred with the Responsible Area Director so that the IESG
>      can appoint the needed Expert during the IESG Evaluation?

No IANA Action.

> (1.j)  Has the Document Shepherd verified that sections of the
>      document that are written in a formal language, such as XML
>      code, BNF rules, MIB definitions, etc., validate correctly in
>      an automated checker?

No such formal language is used.

> (1.k)  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.


    The Path Computation Element (PCE) defined in [RFC4655] is an entity
    that is capable of computing a network path or route based on a
    network graph, and applying computational constraints. The intention
    is that the PCE is used to compute the path of Traffic Engineered
    Label Switched Paths (TE LSPs) within Multiprotocol Label Switching
    (MPLS) and Generalized MPLS (GMPLS) networks.

    [RFC4655] defines various deployment models that place PCEs
    differently within the network. The PCEs may be collocated with the
    Label Switching Routers (LSRs), may be part of the management system
    that requests the LSPs to be established, or may be positioned as 
one
    or more computation servers within the network.

    Requirements for point-to-multipoint (P2MP) MPLS TE LSPs are
    documented in [RFC4461] and signaling protocol extensions for
    setting up P2MP MPLS TE LSPs are defined in [RFC4875]. P2MP MPLS TE
    networks are considered in support of various features including
    layer 3 multicast VPNs [RFC4834], video distribution, etc.

    Fundamental to the determination of the paths for P2MP LSPs within a
    network is the selection of branch points. Not only is this 
selection
    constrained by the network topology and available network resources,
    but it is determined by the objective functions that may be applied
    to path computation. For example, one standard objective is to
    minimize the total cost of the tree (that is, to minimize the sum of
    the costs of each link traversed by the tree) to produce what is
    known as a Steiner Tree. Another common objective function requires
    that the cost to reach each leaf of the P2MP tree is minimized.

    The selection of branch points within the network is further
    complicated by the fact that not all LSRs in the network are
    necessarily capable of performing branching functions. This
    information may be recorded in the Traffic Engineering Database 
(TED)
    that the PCE uses to perform its computations, and may have been
    distributed using extensions to the Interior Gateway Protocol (IGP)
    operating within the network [RFC5073].

    Additionally, network policies may dictate specific branching
    behavior. For example, it may be decided that for certain types of
    LSP in certain types of network, it is important that no branch LSR
    is responsible for handling more than a certain number of downstream
    branches for any one LSP. This might arise because the replication
    mechanism used at the LSRs is a round-robin copying process that
    delays the data transmission on each downstream branch by the time
    taken to replicate the data onto each previous downstream branch.
    Alternatively, administrative policies may dictate that replication
    should be concentrated on specific key replication nodes behaving
    like IP multicast rendezvous points (perhaps to ensure appropriate
    policing of receivers in the P2MP tree, or perhaps to make 
protection
    and resiliency easier to implement).

    Path computation for P2MP TE LSPs presents a significant challenge
    because of the complexity of the computations described above.
    Determining disjoint protection paths for P2MP TE LSPs can add
    considerably to this complexity, while small modifications to a P2MP
    tree (such as adding or removing just one leaf) can completely 
change
    the optimal path. Reoptimization of a network containing multiple
    P2MP TE LSPs requires considerable computational resources. All of
    this means that an ingress LSR might not have sufficient processing
    power to perform the necessary computations, and even if it does, 
the
    act of path computation might interfere with the control and
    management plane operation necessary to maintain existing LSPs. The
    PCE architecture offers a way to offload such path computations from
    LSRs.


>      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?

No controversy.

>      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 I-D is informational and provides applicability statements.