Network Working Group                                       Fatai Zhang
Internet-Draft                                                   Huawei
Intended status: Standards Track                              A. Farrel
                                                     Old Dog Consulting
                                                           G. Bernstein
                                                      Grotto Networking
Expires: June 2, 2012                                  December 2, 2011

            Conveying Vendor-Specific Constraints in the Path
                      Computation Element Protocol


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with
   the provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on June 2, 2012.


   The Path Computation Element Protocol (PCEP) is used to convey path
   computation requests and responses between Path Computation Clients
   (PCCs) and Path Computation Elements (PCEs), and also between

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   cooperating PCEs. In PCEP the path computation requests carry
   details of the constraints and objective functions that the PCC
   wishes the PCE to apply in its computation.

   The mechanisms defined for indicating objective functions include
   the capability to convey vendor-specific objective functions. This
   document defines a facility to carry vendor-specific constraints in

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119 [RFC2119].

Table of Contents

   1. Introduction ................................................ .2
   2. Procedures .................................................. .4
   3. Protocol Elements ........................................... .6
   4. IANA Considerations ......................................... .7
   5. Management Considerations  .................................. .7
      5.1. Control of Function and Policy ......................... .8
      5.2. Information and Data Models............................. .8
      5.3. Liveness Detection and Monitoring ...................... .8
      5.4. Verifying Correct Operation.............................. 8
      5.5. Requirements on Other Protocols and Functional Components 8
      5.6. Impact on Network Operation.............................. 9
   6. Security Considerations ...................................... 9
   7. References ................................................... 9
      7.1. Normative References .................................... 9
      7.2. Informative References  ................................. 10
   8. Acknowledgements ............................................. 11
   9. Authors' Addresses ........................................... 11

1. Introduction

   A Path Computation Element (PCE) is an entity (component,
   application or network node) that is capable of computing a network
   path or route based on a network graph and applying computational
   constraints. An architecture for the use of PCEs is defined in

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   The Path Computation Element Protocol (PCEP) is defined in [RFC5440]
   to exchange path computation requests and responses between Path
   Computation Clients (PCCs) and PCEs. It is also used between
   cooperating PCEs.

   Path computations performed by a PCE depend on a set of constraints
   indicated by the PCC. These constraints include the end points of
   the path to compute (source and destination), and may include other
   simple constraints such as bandwidth requirements and metric maxima
   (for example, a maximum threshold for the hop count or the TE metric
   of the computed path).

   The PCE also needs to use some objective function to qualify the
   path it selects as meeting the requirements of the PCC. The PCE may
   have a default objective function, but the PCC can also indicate
   which objective function it wants applied by placing an Objective
   Function object in the path computation request message [RFC5541]. A
   core set of objective functions to be supported in PCEP messages is
   defined in the base PCEP requirements [RFC4657], and [RFC5541]
   defines each of these functions as an abstract formula.

   The registry of codepoints used to indicate objective functions is
   managed by IANA and can be extended in future documents. PCE
   implementations may choose to offer proprietary, vendor-specific
   objective functions, and there is scope for this within the
   codepoint registry created by [RFC5541]. That is, in the "PCE
   Objective Function" code point registry managed by IANA, the rules
   for the assignment of objective function code point values are as
   follows (using terms defined in [RFC5226])

   o Function code values 1 through 1023 are assigned by IANA using the
   "IETF Review" policy.

   o Function code values 1024 through 32767 are assigned by IANA,
   using the "First Come First Served" policy.

   o Function code values in the range 32768-65535 are for "Private

   Proprietary objective functions may operate on non-standard
   constraints or metrics. The PCEP Metric Object defined in [RFC5440]
   has scope for the definition of new, standardized metrics, but no
   facility for the definition of vendor-specific metrics. At the same
   time, there is no mechanism in PCEP for carrying other, more complex,
   vendor-specific constraints.

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   This document defines a new PCEP object, the Vendor Constraints
   object that can be used to carry arbitrary constraint information.

   This document also defines a new PCEP TLV, the VENDOR-CONSTRAINT-TLV
   that can be used to carry arbitrary constraint information within an
   existing PCEP object.

2. Procedures

   A PCC that wants to convey proprietary or vendor-specific
   constraints or metrics to a PCE does so by including a Vendor
   Constraints object in the PCReq message. The contents and format of
   the object are described in Section 3, but it is important to note
   that the object includes an Enterprise Number that is a unique
   identifier of an organization responsible for the definition of the
   content and meaning of the object.

   A PCC that wants to convey endpoints-specific vendor specific
   constraints to a PCE may do so by including a Vendor Constraints TLV
   in the endpoint-restriction-list of the END-POINTS with object type
   Generalized Endpoint.

   This Vendor Constraints TLV MAY also present in PCEP Objects
   supporting TLVs and using the registry for the PCEP TLVs, to
   indicate a vendor-specific constraint that applies to the PCEP

   A PCE that receives a PCReq message containing a Vendor Constraints
   object MUST act according to the P-bit in the object header. That is,
   if the P-bit is set, the object MUST be treated as mandatory and the
   request must either be processed using the contents of the object or
   rejected as defined in [RFC5440]. If the P-bit is clear, the object
   MAY be used by the PCE or MAY be ignored. The PCC sets the P-bit
   according to how it wishes the request to be processed.

   The PCE determines how to interpret the Vendor Constraints object or
   TLV by examining the Enterprise Number it contains.

   The Vendor Constraints object is optional in a PCReq message.
   Multiple instances of the object MAY be used on a single PCReq
   message and each MUST be treated according to its P-bit setting. The
   object can be present in two places within the PCReq message to
   enable it to apply to a single path computation request or to a set
   of synchronized requests. This usage mirrors the usage of the
   Objective Function object [RFC5541]. Thus, the PCReq message based

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   on [RFC6006] is encoded as follows using the syntax described in

        <PCReq Message> ::= <Common Header>


            <svec-list> ::= <SVEC>

            <metric-list> ::= <METRIC>

            <vendor-constraint-list> ::= <VENDOR-CONSTRAINT>

            <request-list>::= <request>

            <request>::= <RP>

            <end-point-rro-pair-list> ::=


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   The Vendor Constraints object is included in a PCRep message in
   exactly the same way as any other object as defined in [RFC5440].

   The Vendor Constraints TLV is optional in the END-POINTS with object
   type Generalized Endpoint. The vendor restriction TLV MAY be
   inserted at any place in the endpoint-restriction-list.

   The VENDOR-CONSTRAINT-TLV MUST be taken into account. If the P flag
   of the containing object is set, but the PCE does not understand the
   TLV and its enterprise number, the entire PCEP message MUST be
   rejected and the PCE MUST send a PCErr message with Error-
   Type="Reception of an invalid object" and Error-Value="Unsupported
   VENDOR-CONSTRAINT-TLV" along with the corresponding object.

   When present in the END-POINTS with object type Generalized Endpoint
   the endpoint-restriction-list is encoded as follow:

   <endpoint-restriction> ::=
3. Protocol Elements

   The Vendor Constraints object and TLV conform to the format for PCEP
   objects and TLVs defined in [RFC5440].

   VENDOR-CONSTRAINT Object-Class is to be assigned by IANA
   (recommended value=23).

    VENDOR-CONSTRAINT Object-Type is to be assigned by IANA
   (recommended value=1)

   VENDOR-CONSTRAINT-TLV Type is to be assigned by IANA (recommended

   body is as follows:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |                       Enterprise Number                       |
     ~                 Enterprise-Specific Information               ~

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   Enterprise Number

   A unique identifier of an organization encoded as a 32-bit integer.
   Enterprise Numbers are assigned by IANA and managed through an IANA
   registry [RFC2578].

   Enterprise-Specific Information

   The detailed enterprise-specific constraint information carried by
   the object. The format and interpretation of this information is a
   matter for the enterprise identified by the Enterprise Number. Such
   formats and interpretation MAY be published by the enterprise
   (possibly through an informational RFC or through commercial
   documentation) so that PCCs or PCEs that are not part of the
   organization can use the information.

4. IANA Considerations

   IANA maintains a registry of PCEP parameters. This includes sub-
   registry for PCEP Objects and PCEP TLV Type Indicators.

   IANA is requested to make an allocation from the sub-registry PCEP
   Objects as follows. The values here are suggested for use by IANA.

   Object        Name                                  Reference Class
   23       VENDOR-CONSTRAINT                              [This.I-D]
                1: Vendor-Specific Constraints             [This.I-D]

   IANA is requested to do the following allocations in the "PCEP TLV
   Type Indicators" as follow. The Values are suggested for use by IANA.

   Value     Meaning                                       Reference
    16       Vendor Constraint TLV                         [This.I-D]

   IANA is requested to make an allocation from the sub registry "PCEP-
   ERROR Object Error Types and Values" as follow. The Values are
   suggested for use by IANA.

   Error Name                                              Reference
   10    Reception of an invalid object
         Error-Value=8  Unsupported VENDOR-CONSTRAINT-TLV [This.I-D]

5. Management Considerations

   This section follows the guidance of [MANAGE].

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5.1. Control of Function and Policy

   A PCEP implementation SHUOLD allow configuring of various parameters
   as described in [RFC5440]. A PCC implementation that uses vendor-
   specific constraints MAY make the use of these constraints
   configurable either across the whole PCC, per PCE that the PCC uses,
   or per path computation request. A PCE that supports vendor-specific
   constraints MAY make the support of these constraints configurable,
   and MAY allow configuration of policies for the use of the

5.2. Information and Data Models

   A PCEP MIB module is defined in [PCE-MIB] that describes managed
   objects for modeling of PCEP communications.

   It is NOT RECOMMENDED that standard MIB modules are extended to
   include detailed information about the content of the Vendor
   Constaints object. However, the standard MIB module MAY be extended
   to report the use of the Vendor Specific object and the Enterprise
   Numbers that the objects contain.

5.3. Liveness Detection and Monitoring

   This document makes no change to the basic operation of PCEP and so
   there are no changes to the requirements for liveness detection and
   monitoring set out in [RFC4657] and [RFC5440].

5.4. Verifying Correct Operation

   This document makes no change to the basic operation of PCEP and so
   there are no changes to the requirements or techniques for
   monitoring the correct operation of the protocol out in [RFC4657]
   and [RFC5440].

   Note that "correct operation" in this context referes to the
   operation of the protocol itself, and not to the operation of the
   computation algorithms which are out of scope for all PCEP work.
   Mechanisms for verifying the correct operation of computation
   algorithms might involve comparing the results returned by more than
   one PCE. Scope for this might be limited by the use of vendor
   constraints unless multiple PCEs support the same set of constraints.

5.5. Requirements on Other Protocols and Functional Components

   This document does not place any new requirements on other network
   components or protocols. However, it may be beneficial to consider

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   whether a PCE should advertise the enterprise numbers and vendor
   constraints it supports. This advertisement could be within PCE
   Discovery ([RFC5088], [RFC5089]) or through extensions to PCEP

   Extensions for discovery and advertisement are outside the scope of
   this document.

5.6. Impact on Network Operation

   The availability of vendor constraints in PCEP messages may
   facilitate more complex and detailed path computations that may
   enhance the way in which the network is operated.

   On the other hand, the presence of additional vendor-specific
   information in PCEP messages may congest the operation of the
   protocol especially if the PCE does not support the constraints
   supplied by the PCC. Thus, a PCC SHOULD monitor the capabilities of
   a PCE either by discovery mechanisms as described in Section 5.5, or
   through the receipt of negative responses. A PCC SHOULD NOT include
   vendor constraints in a PCReq message to a PCE that it believes does
   not support the constraints and that will not forward the request to
   some other PCE that does support the constraints.

6. Security Considerations

   The protocol extensions defined in this document do not
   substantially change the nature of PCEP. Therefore, the security
   considerations set out in [RFC5440] apply unchanged.

   Operators should note that an attack on PCEP may involve making PCEP
   messages as large as possible in order to consume bandwidth and
   processing power. The Vendor Constraints object may provide a
   mechanism for this type of attack. It may be protected against by
   using the authentication and integrity procedures described in

7. References

7.1. Normative References

   [RFC2119] S. Bradner, "Key words for use in RFCs to indicate
             requirements levels", RFC 2119, March 1997.

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   [RFC5440] Vasseur, J.P., Le Roux, J.L., Ayyangar, A., Oki, E.,
             Ikejiri, A., Atlas, A., Dolganow, A., "Path Computation
             Element (PCE) communication Protocol (PCEP)", RFC 5440,
             March 2009.

   [RFC5511] Farrel, A., "Reduced Backus-Naur Form (RBNF): A Syntax to
             Form Encoding Rules in Various Routing Protocol
             Specifications", RFC 5511, April 2007.

   [RFC6006] Q. Zhao, et al., "Extensions to the Path Computation
             Element Communication Protocol (PCEP) for Point-to-
             Multipoint Traffic Engineering Label Switched Paths", RFC
             6006, September 2009.

7.2. Informative References

   [RFC2578] McCloghrie, K., Perkins, D., and J. Schoenwaelder,
             "Structure of Management Information Version 2 (SMIv2)",
             STD 58, RFC 2578, April 1999.

   [RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation
             Element (PCE) Architecture", RFC 4655, August 2006.

   [RFC4657] Ash, J. and J. Le Roux, "Path Computation Element (PCE)
             Communication Protocol Generic Requirements", RFC 4657,
             September 2006.

   [RFC5088] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
             "OSPF Protocol Extensions for Path Computation Element
             (PCE) Discovery", RFC 5088, January 2008.

   [RFC5089] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
             "IS-IS Protocol Extensions for Path Computation Element
             (PCE) Discovery", RFC 5089, January 2008.

   [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
             IANA Considerations Section in RFCs", BCP 26, RFC 5226,
             May 2008.

   [RFC5541] Le Roux, JL., Vasseur, JP., and Y. Lee, "Objective
             Function Encoding in Path Computation Element
             Communication and Discovery protocols", RFC 5541, June

   [MANAGE]  Farrel, A., "Inclusion of Manageability Sections in PCE
             Working Group Drafts", draft-ietf-pce-manageability-
             requirements, work in progress.

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   [PCE-MIB] Stephan, E. and K. Koushik, "PCE Communication Protocol
             (PCEP) Management Information Base", draft-ietf-pce-pcep-
             mib, work in progress.

8. Acknowledgements

   Thanks to Meral Shirazipour, Ramon Casellas and Cyril Margaria for
   review and comments.

9. Authors' Addresses

   Adrian Farrel
   Old Dog Consulting

   Fatai Zhang
   Huawei Technologies

   Greg Bernstein
   Grotto Networking

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