RFC 9358

Internet Engineering Task Force (IETF)                            Y. Lee
Request for Comments: 9358                           Samsung Electronics
Category: Standards Track                                       H. Zheng
ISSN: 2070-1721                                      Huawei Technologies
                                                           D. Ceccarelli
                                                           Cisco Systems
                                                           February 2023

Path Computation Element Communication Protocol (PCEP) Extensions for
  Establishing Relationships between Sets of Label Switched Paths and
                            Virtual Networks


   This document describes how to extend the Path Computation Element
   Communication Protocol (PCEP) association mechanism introduced by RFC
   8697 to further associate sets of Label Switched Paths (LSPs) with a
   higher-level structure such as a Virtual Network (VN) requested by a
   customer or application.  This extended association mechanism can be
   used to facilitate control of a VN using the PCE architecture.

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 7841.

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

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Terminology
   3.  Operation Overview
   4.  Extensions to PCEP
   5.  Security Considerations
   6.  IANA Considerations
     6.1.  ASSOCIATION Object Type Indicator
     6.2.  PCEP TLV Type Indicator
     6.3.  PCEP Error
   7.  Manageability Considerations
     7.1.  Control of Function and Policy
     7.2.  Information and Data Models
     7.3.  Liveness Detection and Monitoring
     7.4.  Verification of Correct Operations
     7.5.  Requirements on Other Protocols
     7.6.  Impact on Network Operations
   8.  References
     8.1.  Normative References
     8.2.  Informative References

   Authors' Addresses

1.  Introduction

   The Path Computation Element Communication Protocol (PCEP) provides
   mechanisms for Path Computation Elements (PCEs) to perform path
   computations in response to requests from Path Computation Clients
   (PCCs) [RFC5440].

   [RFC8051] describes general considerations for a stateful PCE
   deployment and examines its applicability and benefits as well as its
   challenges and limitations through a number of use cases.  [RFC8231]
   describes a set of extensions to PCEP to provide stateful control.
   For its computations, a stateful PCE has access to not only the
   information carried by the network's Interior Gateway Protocol (IGP)
   but also the set of active paths and their reserved resources.  The
   additional state allows the PCE to compute constrained paths while
   considering individual Label Switched Paths (LSPs) and their

   [RFC8281] describes the setup, maintenance, and teardown of PCE-
   initiated LSPs under the stateful PCE model.

   [RFC8697] introduces a generic mechanism to create a grouping of
   LSPs.  This grouping can then be used to define associations between
   sets of LSPs or between a set of LSPs and a set of attributes.

   [RFC8453] introduces a framework for Abstraction and Control of TE
   Networks (ACTN) and describes various VN operations initiated by a
   customer or application.  A VN is a customer view of the TE network.
   Depending on the agreement between client and provider, various VN
   operations and VN views are possible.

   [RFC8637] examines the PCE and ACTN architectures and describes how
   the PCE architecture is applicable to ACTN.  [RFC6805] and [RFC8751]
   describe a hierarchy of stateful PCEs with the parent PCE
   coordinating multi-domain path computation functions between child
   PCEs, thus making it the base for PCE applicability for ACTN.  As
   [RFC8751] explains, in the context of ACTN, the child PCE is
   identified with the Provisioning Network Controller (PNC), and the
   parent PCE is identified with the Multi-Domain Service Coordinator

   In this context, there is a need to associate a set of LSPs with a VN
   "construct" to facilitate VN operations in the PCE architecture.
   This association allows a PCE to identify which LSPs belong to a
   certain VN.  The PCE could then use this association to optimize all
   LSPs belonging to the VN at once.  The PCE could further take VN-
   specific actions on the LSPs, such as relaxing constraints, taking
   policy actions, setting default behavior, etc.

   This document specifies a PCEP extension to associate a set of LSPs
   based on their VN.

2.  Terminology

   This document uses terminology from [RFC4655], [RFC5440], [RFC6805],
   [RFC8231], and [RFC8453].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Operation Overview

   As per [RFC8697], LSPs are associated with other LSPs with which they
   interact by adding them to a common association group.

   An association group based on VN is useful for various optimizations
   that should be applied by considering all the LSPs in the
   association.  This includes, but is not limited to, the following:

   Path Computation:  When computing a path for an LSP, it is useful to
      analyze the impact of this LSP on the other LSPs belonging to the
      same VN.  The aim would be to optimize all LSPs belonging to the
      VN rather than a single LSP.  Also, the optimization criteria
      (such as minimizing the load of the most loaded link (MLL)
      [RFC5541]) could be applied for all the LSPs belonging to the VN
      identified by the VN association.

   Path Reoptimization:  The PCE would like to use advanced path
      computation algorithms and optimization techniques that consider
      all the LSPs belonging to a VN and optimize them all together
      during the path reoptimization.

   In this document, we define a new association group called the "VN
   Association Group (VNAG)".  This grouping is used to define the
   association between a set of LSPs and a VN.

   The ASSOCIATION object contains a field to identify the type of
   association, and this document defines a new Association Type value
   of 7 to indicate that the association is a "VN Association".  The
   Association Identifier in the ASSOCIATION object is the VNAG
   Identifier and is handled in the same way as the generic Association
   Identifier defined in [RFC8697].

   In this document, "VNAG object" refers to an ASSOCIATION object with
   the Association Type set to "VN Association" (7).

   Local policies on the PCE define the computational and optimization
   behavior for the LSPs in the VN.  An LSP MUST NOT belong to more than
   one VNAG.  If an implementation encounters more than one VNAG object
   in a PCEP message, it MUST process the first occurrence, and it MUST
   ignore the others.

   [RFC8697] specifies the mechanism by which a PCEP speaker can
   advertise which Association Types it supports.  This is done using
   the ASSOC-Type-List TLV carried within an OPEN object.  A PCEP
   speaker MUST include the VN Association Type (7) in the ASSOC-Type-
   List TLV before using the VNAG object in a PCEP message.  As per
   [RFC8697], if the implementation does not support the VN Association
   Type, it will return a PCErr message with Error-Type=26 (Association
   Error) and Error-value=1 (Association Type is not supported).

   The Association Identifiers (VNAG IDs) for this Association Type are
   dynamic in nature and created by the parent PCE (MDSC) based on the
   VN operations for the LSPs belonging to the same VN.  Operator
   configuration of VNAG IDs is not supported, so there is no need for
   an Operator-configured Association Range to be set.  Thus, the VN
   Association Type (7) MUST NOT be present in the Operator-configured
   Association Range TLV if that TLV is present in the OPEN object.  If
   an implementation encounters the VN Association Type (7) in an
   Operator-configured Association Range TLV, it MUST ignore the
   associated Start-Assoc-ID and Range values.

   This association is useful in a PCEP session between a parent PCE
   (MDSC) and a child PCE (PNC).  When computing the path, the child PCE
   (PNC) refers to the VN association in the request from the parent PCE
   (MDSC) and maps the VN to the associated LSPs and network resources.
   From the perspective of the parent PCE, it receives a VN creation
   request from its customer, with the VN uniquely identified by the
   association parameters (Section 6.1.4 of [RFC8697]) in the VNAG or
   the Virtual Network Identifier encoded in the VIRTUAL-NETWORK-TLV.
   This VN may comprise multiple LSPs in the network in a single domain
   or across multiple domains.  The parent PCE sends a PCInitiate
   message with this association information in the VNAG object.  This
   in effect binds an LSP that is to be instantiated at the child PCE
   with the VN.  The VN association information MUST be included as a
   part of the first PCRpt message.  Figure 1 shows an example of a
   typical VN operation using PCEP.  It is worth noting that in a multi-
   domain scenario, the different domains are controlled by different
   child PCEs.  In order to set up the cross-domain tunnel, multiple
   segments need to be stitched by the border nodes in each domain that
   receive the instruction from their child PCE (PNC).

                .            ****** ..                   MPI    .
             .                .        .                        .
          .                   .          .   PCInitiate LSPx    .
        .                    .             .   with VNAG        .
       .                    .                .                  .
      .                    .                  .                 .
     .                    .                    .                .
     v                    v                    v                .
   ******               ******               ******             .
   *PNC1*               *PNC2*               *PNC4*             .
   ******               ******               ******             .
   +---------------+    +---------------+    +---------------+  .
   |               |----|               |----|              C|  .
   |               |    |               |    |               |  .
   |DOMAIN 1       |----|DOMAIN 2       |----|DOMAIN 4       |  .
   +---------------+    +---------------+    +---------------+  .
                                            /                   .
                       ******              /                    .
                       ******            /
                       |               |
                       |               |
                       |DOMAIN 3       |

   MDSC -> parent PCE
   PNC  -> child  PCE
   MPI  -> PCEP

       Figure 1: Example of VN Operations in H-PCE (Hierarchical PCE)

   Whenever changes occur with the instantiated LSP in a domain network,
   the domain child PCE reports the changes using a PCRpt message in
   which the VNAG object indicates the relationship between the LSP and
   the VN.

   Whenever an update occurs with VNs in the parent PCE (due to the
   customer's request), the parent PCE sends a PCUpd message to inform
   each affected child PCE of this change.

4.  Extensions to PCEP

   The VNAG uses the generic ASSOCIATION object [RFC8697].

   This document defines one new mandatory TLV called the "VIRTUAL-
   NETWORK-TLV".  Optionally, the new TLV can be jointly used with the
   existing VENDOR-INFORMATION-TLV specified in [RFC7470] as described

   VIRTUAL-NETWORK-TLV:  Used to communicate the Virtual Network

   VENDOR-INFORMATION-TLV:  Used to communicate arbitrary vendor-
      specific behavioral information, as described in [RFC7470].

   The format of the VIRTUAL-NETWORK-TLV 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
   |           Type=65             |            Length             |
   |                                                               |
   //                   Virtual Network Identifier                //
   |                                                               |

                Figure 2: Format of the VIRTUAL-NETWORK-TLV

   Type (16 bits):  65

   Length (16 bits):  Indicates the length of the value portion of the
      TLV in octets and MUST be greater than 0.  The TLV MUST be zero-
      padded so that the TLV is 4-octet aligned.

   Virtual Network Identifier (variable):  A symbolic name for the VN
      that uniquely identifies the VN.  It SHOULD be a string of
      printable ASCII [RFC0020] characters (i.e., 0x20 to 0x7E), without
      a NULL terminator.  The Virtual Network Identifier is a human-
      readable string that identifies a VN.  It can be specified with
      the association information, which may be conveyed in a VENDOR-
      INFORMATION-TLV.  An implementation uses the Virtual Network
      Identifier to maintain a mapping to the VNAG and the LSPs
      associated with the VN.  The Virtual Network Identifier MAY be
      specified by the customer, set via an operator policy, or auto-
      generated by the PCEP speaker.

   The VIRTUAL-NETWORK-TLV MUST be included in VNAG object.  If a PCEP
   speaker receives the VNAG object without the VIRTUAL-NETWORK-TLV, it
   MUST send a PCErr message with Error-Type=6 (Mandatory Object
   missing) and Error-value=18 (VIRTUAL-NETWORK-TLV missing) and close
   the session.

   The format of VENDOR-INFORMATION-TLV is defined in [RFC7470].

   If a PCEP speaker receives a VNAG object with a TLV that violates the
   rules specified in this document, the PCEP speaker MUST send a PCErr
   message with Error-Type=10 (Reception of an invalid object) and
   Error-value=11 (Malformed object) and MUST close the PCEP session.

5.  Security Considerations

   The security considerations described in [RFC5440], [RFC8231], and
   [RFC8281] apply to the extensions defined in this document as well.

   This document introduces the VN Association Type (7) for the
   ASSOCIATION object.  Additional security considerations related to
   LSP associations due to a malicious PCEP speaker are described in
   [RFC8697] and apply to the VN Association Type.  Hence, securing the
   PCEP session using Transport Layer Security (TLS) [RFC8253] is

6.  IANA Considerations

6.1.  ASSOCIATION Object Type Indicator

   IANA has assigned the following new value in the "ASSOCIATION Type
   Field" subregistry within the "Path Computation Element Protocol
   (PCEP) Numbers" registry:

   | Value | Name           | Reference |
   | 7     | VN Association | RFC 9358  |

                  Table 1

6.2.  PCEP TLV Type Indicator

   IANA has assigned the following new value in the "PCEP TLV Type
   Indicators" subregistry within the "Path Computation Element Protocol
   (PCEP) Numbers" registry:

   | Value | Name                | Reference |
   | 65    | VIRTUAL-NETWORK-TLV | RFC 9358  |

                     Table 2

6.3.  PCEP Error

   IANA has allocated the following new error value in the "PCEP-ERROR
   Object Error Types and Values" subregistry within the "Path
   Computation Element Protocol (PCEP) Numbers" registry:

   | Error-Type | Meaning        | Error-value         | Reference |
   | 6          | Mandatory      | 18: VIRTUAL-        | RFC 9358  |
   |            | Object missing | NETWORK-TLV missing |           |

                                Table 3

7.  Manageability Considerations

7.1.  Control of Function and Policy

   An operator MUST be allowed to mark LSPs that belong to the same VN.
   This could also be done automatically based on the VN configuration.

7.2.  Information and Data Models

   The PCEP YANG module [PCE-PCEP-YANG] should support the association
   between LSPs including VN association.

7.3.  Liveness Detection and Monitoring

   Mechanisms defined in this document do not imply any new liveness
   detection and monitoring requirements in addition to those already
   listed in [RFC5440].

7.4.  Verification of Correct Operations

   Mechanisms defined in this document do not imply any new operation
   verification requirements in addition to those already listed in

7.5.  Requirements on Other Protocols

   Mechanisms defined in this document do not imply any new requirements
   on other protocols.

7.6.  Impact on Network Operations

   [RFC8637] describes the network operations when PCE is used for VN
   operations.  Section 3 further specifies the operations when VN
   associations are used.

8.  References

8.1.  Normative References

   [RFC0020]  Cerf, V., "ASCII format for network interchange", STD 80,
              RFC 20, DOI 10.17487/RFC0020, October 1969,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8231]  Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for Stateful PCE", RFC 8231,
              DOI 10.17487/RFC8231, September 2017,

   [RFC8253]  Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
              "PCEPS: Usage of TLS to Provide a Secure Transport for the
              Path Computation Element Communication Protocol (PCEP)",
              RFC 8253, DOI 10.17487/RFC8253, October 2017,

   [RFC8281]  Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for PCE-Initiated LSP Setup in a Stateful PCE
              Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,

   [RFC8697]  Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H.,
              Dhody, D., and Y. Tanaka, "Path Computation Element
              Communication Protocol (PCEP) Extensions for Establishing
              Relationships between Sets of Label Switched Paths
              (LSPs)", RFC 8697, DOI 10.17487/RFC8697, January 2020,

8.2.  Informative References

              Dhody, D., Ed., Beeram, V., Hardwick, J., and J. Tantsura,
              "A YANG Data Model for Path Computation Element
              Communications Protocol (PCEP)", Work in Progress,
              Internet-Draft, draft-ietf-pce-pcep-yang-20, 23 October
              2022, <https://datatracker.ietf.org/doc/html/draft-ietf-

   [RFC4655]  Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
              Computation Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,

   [RFC5541]  Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding of
              Objective Functions in the Path Computation Element
              Communication Protocol (PCEP)", RFC 5541,
              DOI 10.17487/RFC5541, June 2009,

   [RFC6805]  King, D., Ed. and A. Farrel, Ed., "The Application of the
              Path Computation Element Architecture to the Determination
              of a Sequence of Domains in MPLS and GMPLS", RFC 6805,
              DOI 10.17487/RFC6805, November 2012,

   [RFC7470]  Zhang, F. and A. Farrel, "Conveying Vendor-Specific
              Constraints in the Path Computation Element Communication
              Protocol", RFC 7470, DOI 10.17487/RFC7470, March 2015,

   [RFC8051]  Zhang, X., Ed. and I. Minei, Ed., "Applicability of a
              Stateful Path Computation Element (PCE)", RFC 8051,
              DOI 10.17487/RFC8051, January 2017,

   [RFC8453]  Ceccarelli, D., Ed. and Y. Lee, Ed., "Framework for
              Abstraction and Control of TE Networks (ACTN)", RFC 8453,
              DOI 10.17487/RFC8453, August 2018,

   [RFC8637]  Dhody, D., Lee, Y., and D. Ceccarelli, "Applicability of
              the Path Computation Element (PCE) to the Abstraction and
              Control of TE Networks (ACTN)", RFC 8637,
              DOI 10.17487/RFC8637, July 2019,

   [RFC8751]  Dhody, D., Lee, Y., Ceccarelli, D., Shin, J., and D. King,
              "Hierarchical Stateful Path Computation Element (PCE)",
              RFC 8751, DOI 10.17487/RFC8751, March 2020,


   Dhruv Dhody
   Huawei Technologies
   Divyashree Technopark, Whitefield
   Bangalore 560066
   Email: dhruv.ietf@gmail.com

   Qin Wu
   Huawei Technologies
   Email: bill.wu@huawei.com

   Xian Zhang
   Huawei Technologies
   Email: zhang.xian@huawei.com

   Adrian Farrel
   Old Dog Consulting
   Email: adrian@olddog.co.uk

Authors' Addresses

   Young Lee
   Samsung Electronics
   Republic of Korea
   Email: younglee.tx@gmail.com

   Haomian Zheng
   Huawei Technologies
   H1, Huawei Xiliu Beipo Village Songshan Lake
   Guangdong, 523808
   Email: zhenghaomian@huawei.com

   Daniele Ceccarelli
   Cisco Systems
   Email: daniele.ietf@gmail.com