



Internet Engineering Task Force (IETF)                      S. Litkowski
Request for Comments: 9005                           Cisco Systems, Inc.
Category: Standards Track                                   S. Sivabalan
ISSN: 2070-1721                                                    Ciena
                                                             J. Tantsura
                                                        Juniper Networks
                                                             J. Hardwick
                                                     Metaswitch Networks
                                                            李呈 (C. Li)
                                  华为技术有限公司 (Huawei Technologies)
                                                              March 2021


  Path Computation Element Communication Protocol (PCEP) Extension for
          Associating Policies and Label Switched Paths (LSPs)

Abstract

   This document introduces a simple mechanism to associate policies
   with a group of Label Switched Paths (LSPs) via an extension to the
   Path Computation Element Communication Protocol (PCEP).  The
   extension allows a PCEP speaker to advertise to a PCEP peer that a
   particular LSP belongs to a particular Policy Association Group
   (PAG).

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
   https://www.rfc-editor.org/info/rfc9005.

Copyright Notice

   Copyright (c) 2021 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
   (https://trustee.ietf.org/license-info) 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.

Table of Contents

   1.  Introduction
     1.1.  Requirements Language
   2.  Terminology
   3.  Motivation
     3.1.  Policy-Based Constraints
   4.  Overview
   5.  Policy Association Group
     5.1.  POLICY-PARAMETERS-TLV
   6.  Security Considerations
   7.  IANA Considerations
     7.1.  ASSOCIATION Object Type Indicators
     7.2.  PCEP TLV Type Indicators
     7.3.  PCEP Errors
   8.  Manageability Considerations
     8.1.  Control of Function and Policy
     8.2.  Information and Data Models
     8.3.  Liveness Detection and Monitoring
     8.4.  Verifying Correct Operations
     8.5.  Requirements on Other Protocols
     8.6.  Impact on Network Operations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Appendix A.  Example of Policy Parameters
   Acknowledgments
   Contributors
   Authors' Addresses

1.  Introduction

   [RFC5440] describes the Path Computation Element Communication
   Protocol (PCEP), which enables the communication between a Path
   Computation Client (PCC) and a Path Control Element (PCE) or between
   two PCEs based on the PCE architecture [RFC4655].  [RFC5394] provides
   additional details on policy within the PCE architecture and also
   provides context for the support of PCE policy.

   "Path Computation Element Communication Protocol (PCEP) Extensions
   for Stateful PCE" ([RFC8231]) describes a set of extensions to PCEP
   to enable active control of Multiprotocol Label Switching Traffic
   Engineering (MPLS-TE) and Generalized MPLS (GMPLS) tunnels.
   [RFC8281] describes the setup and teardown of PCE-initiated LSPs
   under the active stateful PCE model without the need for local
   configuration on the PCC, thus allowing for a dynamic network.
   Currently, the LSPs can either be signaled via Resource Reservation
   Protocol Traffic Engineering (RSVP-TE) or segment routed as specified
   in [RFC8664].

   [RFC8697] introduces a generic mechanism to create a grouping of LSPs
   that can then be used to define associations between a set of LSPs
   and a set of attributes (such as configuration parameters or
   behaviors) and is equally applicable to stateful PCE (active and
   passive modes) and stateless PCE.

   This document specifies a PCEP extension to associate one or more
   LSPs with policies using the generic association mechanism.

   A PCEP speaker may want to influence the PCEP peer with respect to
   path selection and other policies.  This document describes a PCEP
   extension to associate policies by creating a Policy Association
   Group (PAG) and encoding this association in PCEP messages.  The
   specification is applicable to both stateful and stateless PCEP
   sessions.

   Note that the actual policy definition and the associated parameters
   are out of scope of this document.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "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.

2.  Terminology

   The following terminology is used in this document.

   Association parameters:  As described in [RFC8697], the combination
      of the mandatory fields Association Type, Association ID, and
      Association Source in the ASSOCIATION object uniquely identifies
      the association group.  If the optional TLVs -- Global Association
      Source or Extended Association ID -- are included, then they are
      included in combination with mandatory fields to uniquely identify
      the association group.

   Association information:  As described in [RFC8697], the ASSOCIATION
      object could include other optional TLVs based on the Association
      Types that provide "information" related to the association.

   LSR:  Label Switching Router

   MPLS:  Multiprotocol Label Switching

   PAG:  Policy Association Group

   PAT:  Policy Association Type

   PCC:  Path Computation Client; any client application requesting a
      path computation to be performed by a Path Computation Element.

   PCE:  Path Computation Element; 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.

   PCEP:  Path Computation Element Communication Protocol

3.  Motivation

   Paths computed using PCE can be subjected to various policies at both
   the PCE and the PCC.  For example, in a centralized TE scenario,
   network operators may instantiate LSPs and specify policies for
   traffic accounting, path monitoring, telemetry, etc., for some LSPs
   via the stateful PCE.  Similarly, a PCC could request a user-specific
   or service-specific policy to be applied at the PCE, such as a
   constraints relaxation policy, to meet optimal QoS and resiliency
   levels.

   PCEP speakers can use the generic mechanism of [RFC8697] to associate
   a set of LSPs with a policy, without the need to know the details of
   such a policy.  This simplifies network operations, avoids frequent
   software upgrades, and provides the ability to introduce new policies
   more quickly.

                                                            PAG Y
                                             {Service-Specific Policy
                                                       for constraint
               Monitor LSP                                relaxation}
                    |                                          |
                    | PAG X                    PCReq/PCRpt     |
                    V {Monitor LSP}            {PAG Y}         V
                 +-----+                   ----------------> +-----+
      _ _ _ _ _ _| PCE |                  |                  | PCE |
     |           +-----+                  |      ----------> +-----+
     | PCInitiate/PCUpd                   |     |    PCReq/PCRpt
     |{PAG X}                             |     |    {PAG Y}
     |                                    |     |
     |              .-----.               |     |         .-----.
     |             (       )              |  +----+      (       )
     |         .--(         )--.          |  |PCC1|--.--(         )--.
     V        (                 )         |  +----+ (                 )
   +---+     (                   )        |        (                   )
   |PCC|----(   (G)MPLS network    )   +----+     ( (G)MPLS network   )
   +---+     (                   )     |PCC2|------(                   )
   PAG X      (                 )      +----+       (                 )
   {Monitor    '--(         )--'                     '--(         )--'
   LSP}            (       )                             (       )
                    '-----'                               '-----'

   Case 1: Policy requested by PCE        Case 2: Policy requested by
           and enforced by PCC                    PCC and enforced by
                                                  PCE

         Figure 1: Sample Use Cases for Carrying Policies over PCEP

3.1.  Policy-Based Constraints

   In the context of a policy-enabled path computation framework
   [RFC5394], path computation policies may be applied at a PCC, a PCE,
   or both.  A Label Switching Router (LSR) with a policy-enabled PCC
   can receive:

   *  A service request via signaling, including over a Network-Network
      Interface (NNI) or User-Network Interface (UNI) reference point.

   *  A configuration request over a management interface to establish a
      service.

   The PCC may apply user-specific or service-specific policies to
   decide how the path selection process should be constrained -- that
   is, which constraints, diversities, optimization criteria, and
   constraint-relaxation strategies should be applied to increase the
   likelihood that the service LSP(s) will be successfully established
   and will provide the necessary QoS and resilience against network
   failures.  The user-specific or service-specific policies are applied
   to the PCC and are then passed to the PCE along with the path
   computation request in the form of constraints [RFC5394].

   The PCEP speaker can use the generic mechanism as per [RFC8697] to
   associate a set of LSPs with user-specific or service-specific
   policies.  This would simplify the path computation message exchanges
   in PCEP.

4.  Overview

   As per [RFC8697], LSPs are associated with other LSPs with which they
   interact by adding them to a common association group.  Grouping can
   also be used to define the association between LSPs and the policies
   associated with them.  As described in [RFC8697], the association
   group is uniquely identified by the combination of the following
   fields in the ASSOCIATION object: Association Type, Association ID,
   Association Source, and (if present) Global Association Source or
   Extended Association ID.  This document defines a new Association
   Type called "Policy Association" with value 3 based on the generic
   ASSOCIATION object.  This new Association Type is called "Policy
   Association Type" (PAT).

   [RFC8697] specifies the mechanism for the capability advertisement of
   the Association Types supported by a PCEP speaker by defining an
   ASSOC-Type-List TLV to be carried within an OPEN object.  This
   capability exchange for the PAT MUST be done before using the Policy
   Association.  Thus, the PCEP speaker MUST include the PAT in the
   ASSOC-Type-List TLV and MUST receive the same from the PCEP peer
   before using the PAG in PCEP messages.

   The Policy Association Type (3) is operator configured (as specified
   in [RFC8697]), i.e., the association is created by the operator
   manually on the PCEP peers, and an LSP belonging to this association
   is conveyed via PCEP messages to the PCEP peer.  There is no need to
   convey an explicit Operator-configured Association Range, which could
   only serve to artificially limit the available Association IDs.
   Thus, for the Policy Association Type, the Operator-configured
   Association Range MUST NOT be set and MUST be ignored if received.

   A PAG can have one or more LSPs.  The association parameters
   including Association Identifier, Policy Association Type (PAT), as
   well as the Association Source IP address are manually configured by
   the operator and are used to identify the PAG as described in
   [RFC8697].  The Global Association Source and Extended Association ID
   MAY also be included.

   As per the processing rules specified in Section 6.4 of [RFC8697], if
   a PCEP speaker does not support this Policy Association Type, it
   would return a PCEP error (PCErr) message with Error-Type 26
   "Association Error" and Error-value 1 "Association type is not
   supported".  The PAG and the policy MUST be configured on the PCEP
   peers as per the operator-configured association procedures.  All
   further processing is as per Section 6.4 of [RFC8697].  If a PCE
   speaker receives a PAG in a PCEP message and the Policy Association
   information is not configured, it MUST return a PCErr message with
   Error-Type 26 "Association Error" and Error-value 4 "Association
   unknown".

   Associating a particular LSP with multiple policy groups is allowed
   from a protocol perspective; however, there is no assurance that the
   PCEP speaker will be able to apply multiple policies.  If a PCEP
   speaker does not support handling of multiple policies for an LSP, it
   MUST NOT add the LSP into the association group and MUST return a
   PCErr with Error-Type 26 "Association Error" and Error-value 7
   "Cannot join the association group".

5.  Policy Association Group

   Association groups and their memberships are defined using the
   ASSOCIATION object defined in [RFC8697].  Two object types for IPv4
   and IPv6 are defined.  The ASSOCIATION object includes "Association
   type" indicating the type of the association group.  This document
   adds a new Association Type, Policy Association Type (PAT).

   PAG may carry optional TLVs including but not limited to:

   POLICY-PARAMETERS-TLV:
      Used to communicate opaque information useful to applying the
      policy, described in Section 5.1.

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

5.1.  POLICY-PARAMETERS-TLV

   The ASSOCIATION object (for PAT) can carry an optional POLICY-
   PARAMETERS-TLV with opaque information that is needed to apply the
   policy at the PCEP peer.  In some cases, to apply a PCE policy
   successfully, it is required to also associate some policy parameters
   that need to be evaluated.  This TLV is used to carry those policy
   parameters.  The TLV could include one or more policy-related
   parameters.  The encoding format and the order MUST be known to the
   PCEP peers; this could be done during the configuration of the policy
   (and its association parameters) for the PAG.  The TLV format is as
   per the format of the PCEP TLVs, as defined in [RFC5440] and shown in
   Figure 2.  Only one POLICY-PARAMETERS-TLV can be carried, and only
   the first occurrence is processed.  Any others MUST be ignored.

       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=48               |          Length               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      //                     Policy Parameters                       //
      |                                                               |
      +---------------------------------------------------------------+

                 Figure 2: The POLICY-PARAMETERS-TLV Format

   The POLICY-PARAMETERS-TLV type is 48, and it has a variable length.
   The Value field is variable and padded to a 4-byte alignment; padding
   is not included in the Length field.  The PCEP peer implementation
   needs to be aware of the encoding format, order, and meaning of the
   policy parameters well in advance based on the policy.  Note that
   from the protocol point of view, this data is opaque and can be used
   to carry parameters in any format understood by the PCEP peers and
   associated with the policy.  The exact use of this TLV is beyond the
   scope of this document.  Examples are included for illustration
   purposes in Appendix A.

   If the PCEP peer is unaware of the policy parameters associated with
   the policy and it receives the POLICY-PARAMETERS-TLV, it MUST reject
   the PCEP message and send a PCErr message with Error-Type 26
   "Association Error" and Error-value 12 "Not expecting policy
   parameters".  Further, if at least one parameter in the POLICY-
   PARAMETERS-TLV received by the PCEP speaker is considered
   unacceptable in the context of the associated policy (e.g., out of
   range value, badly encoded value, etc.), the PCEP speaker MUST reject
   the PCEP message and send a PCErr message with Error-Type 26
   "Association Error" and Error-value 13 "Unacceptable policy
   parameters".

   Note that the vendor-specific behavioral information is encoded in
   the VENDOR-INFORMATION-TLV, which can be used along with this TLV.

6.  Security Considerations

   The security considerations described in [RFC8697], [RFC8231],
   [RFC5394], and [RFC5440] apply to the extensions described in this
   document as well.  In particular, a malicious PCEP speaker could be
   spoofed and used as an attack vector by creating spurious Policy
   Associations as described in [RFC8697].  Further, as described in
   [RFC8697], a spurious LSP can have policies that are inconsistent
   with those of the legitimate LSPs of the group and, thus, cause
   problems in the handling of the policy for the legitimate LSPs.  It
   should be noted that Policy Association could provide an adversary
   with the opportunity to eavesdrop on the relationship between the
   LSPs.  [RFC8697] suggests that the implementations and operators use
   indirect values as a way to hide any sensitive business
   relationships.  Thus, securing the PCEP session using Transport Layer
   Security (TLS) [RFC8253], as per the recommendations and best current
   practices in BCP 195 [RFC7525], is RECOMMENDED.

   Further, extra care needs to be taken by the implementation with
   respect to the POLICY-PARAMETERS-TLV while decoding, verifying, and
   applying these policy variables.  This TLV parsing could be exploited
   by an attacker; thus, extra care must be taken while configuring a
   Policy Association that uses the POLICY-PARAMETERS-TLV and making
   sure that the data is easy to parse and verify before use.  Ensuring
   agreement among all relevant PCEP peers as to the format and layout
   of the policy parameters information is key for correct operations.
   Note that the parser for POLICY-PARAMETERS-TLV is particularly
   sensitive since it is opaque to PCEP and can be used to convey data
   with many different internal structures/formats.  The choice of
   decoder is dependent on the additional metadata associated with the
   policy; thus, additional risk of using a wrong decoder and getting
   garbage results is incurred.  Using standard and well-known policy
   formats could help alleviate those risks.


7.  IANA Considerations

7.1.  ASSOCIATION Object Type Indicators

   This document defines a new Association Type in the subregistry
   "ASSOCIATION Type Field" of the "Path Computation Element Protocol
   (PCEP) Numbers" registry that was originally defined in [RFC8697].

                +=======+====================+===========+
                | Value | Name               | Reference |
                +=======+====================+===========+
                | 3     | Policy Association | RFC 9005  |
                +-------+--------------------+-----------+

                                 Table 1

7.2.  PCEP TLV Type Indicators

   The following TLV Type Indicator value has been registered within the
   "PCEP TLV Type Indicators" subregistry of the "Path Computation
   Element Protocol (PCEP) Numbers" registry.

               +=======+=======================+===========+
               | Value | Description           | Reference |
               +=======+=======================+===========+
               | 48    | POLICY-PARAMETERS-TLV | RFC 9005  |
               +-------+-----------------------+-----------+

                                  Table 2

7.3.  PCEP Errors

   This document defines new Error-values for Error-Type 26 "Association
   Error" defined in [RFC8697].  IANA has allocated new error values
   within the "PCEP-ERROR Object Error Types and Values" subregistry of
   the "Path Computation Element Protocol (PCEP) Numbers" registry as
   follows:

    +============+===================+===================+===========+
    | Error-Type | Meaning           | Error-value       | Reference |
    +============+===================+===================+===========+
    | 26         | Association Error |                   | [RFC8697] |
    +------------+-------------------+-------------------+-----------+
    |            |                   | 12: Not expecting | RFC 9005  |
    |            |                   | policy parameters |           |
    +------------+-------------------+-------------------+-----------+
    |            |                   | 13: Unacceptable  | RFC 9005  |
    |            |                   | policy parameters |           |
    +------------+-------------------+-------------------+-----------+

                                 Table 3

8.  Manageability Considerations

8.1.  Control of Function and Policy

   An operator MUST be allowed to configure the Policy Associations at
   PCEP peers and associate them with the LSPs.  They MAY also allow
   configuration to related policy parameters and provide information on
   the encoding format and order to parse the associated POLICY-
   PARAMETERS-TLV.

8.2.  Information and Data Models

   [RFC7420] describes the PCEP MIB; there are no new MIB objects for
   this document.

   The PCEP YANG module is defined in [PCE-PCEP-YANG].  That module
   supports associations as defined in [RFC8697]; thus, it supports the
   Policy Association Groups.

   An implementation SHOULD allow the operator to view the PAG
   configured.  Further implementation SHOULD allow one to view
   associations reported by each peer and the current set of LSPs in the
   PAG.

8.3.  Liveness Detection and Monitoring

   The mechanisms defined in this document do not imply any new liveness
   detection and monitoring requirements in addition to those already
   listed in [RFC5440] and [RFC8231].

8.4.  Verifying Correct Operations

   Verifying the correct operation of a policy can be performed by
   monitoring various parameters as described in [RFC5440] and
   [RFC8231].  A PCEP implementation SHOULD provide information on
   failed path computation due to applying policy and log error events,
   e.g., parsing failure for a POLICY-PARAMETERS-TLV.

8.5.  Requirements on Other Protocols

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

8.6.  Impact on Network Operations

   The mechanisms defined in this document do not have any impact on
   network operations in addition to those already listed in [RFC5440],
   [RFC8231], and [RFC8281].

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

   [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,
              <https://www.rfc-editor.org/info/rfc8231>.

   [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,
              <https://www.rfc-editor.org/info/rfc8253>.

   [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,
              <https://www.rfc-editor.org/info/rfc8697>.

9.2.  Informative References

   [PCE-PCEP-YANG]
              Dhody, D., Ed., Hardwick, J., Beeram, V., and J. Tantsura,
              "A YANG Data Model for Path Computation Element
              Communications Protocol (PCEP)", Work in Progress,
              Internet-Draft, draft-ietf-pce-pcep-yang-16, 22 February
              2021,
              <https://tools.ietf.org/html/draft-ietf-pce-pcep-yang-16>.

   [RFC4655]  Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
              Computation Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

   [RFC5394]  Bryskin, I., Papadimitriou, D., Berger, L., and J. Ash,
              "Policy-Enabled Path Computation Framework", RFC 5394,
              DOI 10.17487/RFC5394, December 2008,
              <https://www.rfc-editor.org/info/rfc5394>.

   [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
              "Network Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
              <https://www.rfc-editor.org/info/rfc5905>.

   [RFC7420]  Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
              Hardwick, "Path Computation Element Communication Protocol
              (PCEP) Management Information Base (MIB) Module",
              RFC 7420, DOI 10.17487/RFC7420, December 2014,
              <https://www.rfc-editor.org/info/rfc7420>.

   [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,
              <https://www.rfc-editor.org/info/rfc7470>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <https://www.rfc-editor.org/info/rfc7525>.

   [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,
              <https://www.rfc-editor.org/info/rfc8281>.

   [RFC8664]  Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "Path Computation Element Communication
              Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
              DOI 10.17487/RFC8664, December 2019,
              <https://www.rfc-editor.org/info/rfc8664>.

Appendix A.  Example of Policy Parameters

   An example could be a monitoring and telemetry policy, P1, that is
   dependent on a profile (GOLD/SILVER/BRONZE) as set by the operator.
   The PCEP peers need to be aware of policy P1 (and its associated
   characteristics) in advance as well the fact that the policy
   parameter will encode the profile of a type string in the POLICY-
   PARAMETERS-TLV.  As an example, LSP1 could encode the PAG with the
   POLICY-PARAMETERS-TLV using the string "GOLD".

   The following is another example where the path computation at the
   PCE could be dependent on when the LSP was configured at the PCC.
   For such a policy, P2, the timestamp can be encoded in the POLICY-
   PARAMETERS-TLV, and the exact encoding could be the 64-bit timestamp
   format as defined in [RFC5905].

   While the above example has a single field in the POLICY-PARAMETERS-
   TLV, it is possible to include multiple fields, but the exact order,
   encoding format, and meanings need to be known in advance at the PCEP
   peers.

Acknowledgments

   We would like to acknowledge and thank Santiago Alvarez, Zafar Ali,
   Luis Tomotaki, Victor Lopez, Rob Shakir, and Clarence Filsfils for
   working on earlier draft versions with similar motivation.

   Special thanks to the authors of [RFC8697].  This document borrowed
   some of its text.  The authors would like to thank Aijun Wang, Peng
   Shuping, and Gyan Mishra for their useful comments.

   Thanks to Hariharan Ananthakrishnan for shepherding this document.
   Thanks to Deborah Brungard for providing comments and being the
   responsible AD for this document.

   Thanks to Nic Leymann for the RTGDIR review.

   Thanks to Benjamin Kaduk and Murray Kucherawy for their comments
   during the IESG review.

Contributors

   The following individuals have contributed extensively:

   Mahendra Singh Negi
   RtBrick Inc
   N-17L, 18th Cross Rd, HSR Layout
   Bangalore 560102
   Karnataka
   India

   Email: mahend.ietf@gmail.com


   Dhruv Dhody
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore 560066
   Karnataka
   India

   Email: dhruv.ietf@gmail.com


   The following individuals have contributed text that was
   incorporated:

   Qin Wu
   Huawei Technologies
   101 Software Avenue, Yuhua District
   Nanjing
   Jiangsu, 210012
   China

   Email: sunseawq@huawei.com


   Xian Zhang
   Huawei Technologies
   Bantian, Longgang District
   Shenzhen
   518129
   China

   Email: zhang.xian@huawei.com


   Udayasree Palle

   Email: udayasreereddy@gmail.com


   Mike Koldychev
   Cisco Systems, Inc.
   Canada

   Email: mkoldych@cisco.com


Authors' Addresses

   Stephane Litkowski
   Cisco Systems, Inc.
   11 Rue Camille Desmoulins
   92130 Issy-les-Moulineaux
   France

   Email: slitkows@cisco.com


   Siva Sivabalan
   Ciena
   385 Terry Fox Drive
   Kanata Ontario K2K 0L1
   Canada

   Email: msiva282@gmail.com


   Jeff Tantsura
   Juniper Networks

   Email: jefftant.ietf@gmail.com


   Jonathan Hardwick
   Metaswitch Networks
   33 Genotin Road
   Enfield
   United Kingdom

   Email: Jonathan.Hardwick@metaswitch.com


   Cheng Li
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing
   100095
   China

   Email: c.l@huawei.com

   Additional contact information:

      李呈
      中国
      100095
      北京
      华为北研所
      华为技术有限公司
