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RFC 7150

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Conveying Vendor-Specific Constraints in the Path Computation Element Communication Protocol

Obsoleted by:    7470

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Internet Engineering Task Force (IETF)                          F. Zhang
Request for Comments: 7150                                        Huawei
Category: Standards Track                                      A. Farrel
ISSN: 2070-1721                                         Juniper Networks
                                                              March 2014

           Conveying Vendor-Specific Constraints in the Path
               Computation Element Communication Protocol


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

   This document defines a facility to carry vendor-specific information
   in PCEP using a dedicated object and a new Type-Length-Variable that
   can be carried in any existing PCEP object.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

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Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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

   The Path Computation Element communication 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 endpoints 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 Traffic
   Engineering (TE) metric of the computed path).

   The PCE also needs to use an 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 new assignments can be made according to "IETF
   Review" and "First Come First Served" policies [RFC5226].  PCE
   implementations may also choose to offer proprietary, vendor-specific

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   objective functions, and there is scope for this within the codepoint
   registry created by [RFC5541] using the codepoints that are flagged
   as "Reserved for Private Use".

   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 information.

   This document defines a new PCEP object, the Vendor Information
   object that can be used to carry arbitrary, proprietary information
   such as vendor-specific constraints.

   This document also defines a new PCEP TLV, the VENDOR-INFORMATION-TLV
   that can be used to carry arbitrary information within any PCEP
   object that supports TLVs.

   It should be noted that by the very definition of "vendor-specific",
   the inclusion of either a Vendor Information object or the VENDOR-
   INFORMATION-TLV implies an inability to interoperate at a functional
   level with implementations from other vendors unless there is some
   cooperation agreement between vendors.  Sections 2.1 and 3.1 discuss
   backward compatibility, which indicates how these protocol constructs
   are handled by implementations that do not support them at all, while
   text in Sections 2 and 3 describe how implementations handle the
   constructs if they understand them, but do not support the embedded
   Enterprise Number that indicates to which vendor the constructs

   When vendor-specific information is used by an implementation, the
   vendor is encouraged to document the meaning of the information to
   encourage wider use and implementation.  In particular, when there is
   more general interest in a vendor-specific extension, the vendor is
   encouraged to bring it to the IETF for standardization as a regular
   protocol construct moving it out of the vendor-specific space.

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in

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2.  Procedures for the Vendor Information Object

   A PCC that wants to convey proprietary or vendor-specific constraints
   or metrics to a PCE does so by including a Vendor Information object
   in the PCReq message.  The contents and format of the object are
   described in Section 4, 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 PCE that receives a PCReq message containing a Vendor Information
   object MUST act according to the P flag in the object header.  That
   is, if the P flag is set, the object will be treated as mandatory and
   the request will either be processed using the contents of the object
   or be rejected as defined in [RFC5440] (see also Section 2.1).  If
   the P flag is clear, then, as defined in [RFC5440], the object may be
   used by the PCE or may be ignored.  The PCC sets the P flag according
   to how it wishes the request to be processed.

   The PCE determines how to interpret the information in the Vendor
   Information object by examining the Enterprise Number it contains.
   An implementation that supports the Vendor Information object, but
   receives one carrying an Enterprise Number that it does not support
   MUST act according to the P flag in the object.  That is, if the P
   flag is set, the PCE MUST reject the PCReq as defined in [RFC5440] by
   sending an Error message with Error-Type="Not supported Object" along
   with the corresponding Vendor Information object.

   The Vendor Information 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.
   Different instances of the object can have different Enterprise

   The object can be present in 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 on [RFC6006] is
   encoded as follows using the syntax described in [RFC5511].

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   <PCReq Message> ::= <Common Header>


       <svec-list> ::= <SVEC>

       <metric-list> ::= <METRIC>

       <vendor-info-list> ::= <VENDOR-INFORMATION>

       <request-list> ::= <request>

       <request> ::= <RP>


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

       <RRO-List> ::= <RRO> [<BANDWIDTH>] [<RRO-List>]

       <metric-list> ::= <METRIC> [<metric-list>]

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

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   Thus, the PCRep is encoded as follows:

     <PCRep Message> ::= <Common Header>

     <response> ::= <RP>


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

     <path> ::= (<ERO>|<SERO>) [<path>]

     <attribute-list> ::= [<OF>]

2.1.  Backward Compatibility for the Vendor Information Object

   A legacy implementation that does not recognize the Vendor
   Information object will act according to the procedures set out in
   [RFC5440].  If the P flag is set in the object, the message will be
   rejected using a PCErr message with an Error Type of 3 ("Unknown
   Object").  If the P flag is not set, the object can safely be ignored
   by the recipient.

3.  Procedures for the Vendor Information TLV

   The Vendor Information TLV can be used to carry vendor-specific
   information that applies to a specific PCEP object by including the
   TLV in the object.

   The PCE determines how to interpret the Vendor Information TLV by
   examining the Enterprise Number it contains.  If the Enterprise
   Number is unknown to the PCE, it MUST treat the Vendor Information
   TLV as an unknown TLV and handle it as described in [RFC5440] (see
   also Section 3.1).

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   Further specifications are needed to define the position and meaning
   of the Vendor Information TLV for specific PCEP objects.

3.1.  Backward Compatibility

   A legacy implementation that does not recognize the Vendor
   Information TLV in an object will act according to the procedures set
   out in [RFC5440].  As described in Section 7.1 of [RFC5440],
   unrecognized TLVs MUST be ignored.

4.  Protocol Elements

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




   The format of the VENDOR-INFORMATION object and the format of the
   VENDOR-INFORMATION-TLV are the same and are as shown in Figure 1.

      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               ~

        Figure 1 : Format of the Vendor Information Object and TLV

   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

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      (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.

5.  IANA Considerations

   IANA maintains a registry of PCEP parameters called the "Path
   Computation Element Protocol (PCEP) Numbers".

5.1.  New PCEP Object

   IANA has made an allocation from the "PCEP Objects" subregistry as

   Object-Class Value     Name                               Reference
       32                 VENDOR-INFORMATION                 [RFC7150]
                0: Unassigned
                1: Vendor-Specific Constraints               [RFC7150]
                2-255: Unassigned

5.2.  New PCEP TLV

   IANA has made an allocation from the "PCEP TLV Type Indicators"
   subregistry as follows.

   Value       Description                                   Reference
     7         VENDOR-INFORMATION-TLV                        [RFC7150]

6.  Management Considerations

   This section follows the guidance of [RFC5706] and [RFC6123].

6.1.  Control of Function and Policy

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

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6.2.  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 be extended to
   include detailed information about the content of the Vendor
   Information object or TLV.  However, the standard MIB module MAY be
   extended to report the use of the Vendor Information object or TLV
   and the Enterprise Numbers that the objects and TLVs contain.

6.3.  Liveness Detection and Monitoring

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

6.4.  Verifying Correct Operation

   This document makes no change to the basic operation of PCEP, 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 refers 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
   information unless multiple PCEs support the same set of vendor

6.5.  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
   whether a PCE should advertise the Enterprise Numbers and vendor
   information 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.

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6.6.  Impact on Network Operation

   The availability of vendor information 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 information
   supplied by the PCC.  Thus, a PCC SHOULD monitor the capabilities of
   a PCE either by discovery mechanisms as described in Section 6.5 or
   through the receipt of negative responses.  A PCC SHOULD NOT include
   vendor information in a PCReq message to a PCE that it believes does
   not support the information and that will not forward the request to
   some other PCE that does support the information.

7.  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.  Note that further security
   considerations for the use of PCEP over TCP are presented in

   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 Information object and TLV may provide
   a vector for this type of attack.  It may be protected against by
   using the authentication and integrity procedures described in

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5440]  Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              March 2009.

   [RFC5511]  Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
              Used to Form Encoding Rules in Various Routing Protocol
              Specifications", RFC 5511, April 2009.

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   [RFC6006]  Zhao, Q., Ed., King, D., Ed., Verhaeghe, F., Takeda, T.,
              Ali, Z., and J. Meuric, "Extensions to the Path
              Computation Element Communication Protocol (PCEP) for
              Point-to-Multipoint Traffic Engineering Label Switched
              Paths", RFC 6006, September 2010.

8.2.  Informative References

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

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

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

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

   [RFC5089]  Le Roux, JL., Ed., Vasseur, JP., Ed., 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, "Encoding of
              Objective Functions in the Path Computation Element
              Communication Protocol (PCEP)", RFC 5541, June 2009.

   [RFC5706]  Harrington, D., "Guidelines for Considering Operations and
              Management of New Protocols and Protocol Extensions", RFC
              5706, November 2009.

   [RFC6123]  Farrel, A., "Inclusion of Manageability Sections in Path
              Computation Element (PCE) Working Group Drafts", RFC 6123,
              February 2011.

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   [RFC6952]  Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
              BGP, LDP, PCEP, and MSDP Issues According to the Keying
              and Authentication for Routing Protocols (KARP) Design
              Guide", RFC 6952, May 2013.

   [PCE-MIB]  Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
              Hardwick, "Path Computation Element Protocol (PCEP)
              Management Information Base", Work in Progress, February

9.  Acknowledgements

   Thanks to Meral Shirazipour, Ramon Casellas, Cyril Margaria, Dhruv
   Dhody, Julien Meuric, and Robert Sparks for review and comments.

10.  Contributors

   Greg Bernstein
   Grotto Networking

   Ina Minei
   Juniper Networks

Authors' Addresses

   Adrian Farrel
   Juniper Networks

   Fatai Zhang
   Huawei Technologies