



PCE Working Group                                                  C. Li
Internet-Draft                                                   M. Chen
Intended status: Standards Track                     Huawei Technologies
Expires: 8 August 2026                                          W. Cheng
                                                            China Mobile
                                                               R. Gandhi
                                                     Cisco Systems, Inc.
                                                                Q. Xiong
                                                         ZTE Corporation
                                                         4 February 2026


 Path Computation Element Communication Protocol (PCEP) Extensions for
           Associated Bidirectional Segment Routing (SR) LSPs
                    draft-ietf-pce-sr-bidir-path-21

Abstract

   The Path Computation Element Communication Protocol (PCEP) provides
   mechanisms for Path Computation Elements (PCEs) to perform path
   computations in response to Path Computation Clients (PCCs) requests.
   Segment Routing (SR) can be used to steer packets through a network
   employing the source routing paradigm.  SR can be applied to both
   MPLS (SR-MPLS) and IPv6 (SRv6) data planes.  Stateful PCEP extensions
   for SR allow a PCE to maintain state and to control and initiate SR
   Traffic Engineering (TE) LSPs.

   PCEP supports grouping of two unidirectional MPLS-TE Label Switched
   Paths (LSPs), signaled via RSVP-TE, using association.  This document
   defines PCEP extensions for grouping two unidirectional SR LSPs (one
   in each direction in the network) into a single associated
   bidirectional SR LSP.  The mechanisms defined in this document are
   applicable to both stateless and stateful PCEs for PCE-initiated and
   PCC-initiated LSPs.


Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.






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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 8 August 2026.

Copyright Notice

   Copyright (c) 2026 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/
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  PCE-Initiated Associated Bidirectional SR LSPs  . . . . .   4
     3.2.  PCC-Initiated Associated Bidirectional SR LSPs  . . . . .   6
   4.  PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Bidirectional SR LSP Association Group  . . . . . . . . .   9
     4.2.  Bidirectional LSP Association Group TLV . . . . . . . . .   9
     4.3.  PATH-ATTRIB Object  . . . . . . . . . . . . . . . . . . .   9
     4.4.  MULTIPATH-OPPDIR-PATH TLV . . . . . . . . . . . . . . . .   9
   5.  Additional PCEP Considerations  . . . . . . . . . . . . . . .  10
     5.1.  PLSP-ID Usage . . . . . . . . . . . . . . . . . . . . . .  10
     5.2.  Error Handling  . . . . . . . . . . . . . . . . . . . . .  10
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Huawei's Commercial Delivery  . . . . . . . . . . . . . .  11
     6.2.  ZTE's Commercial Delivery . . . . . . . . . . . . . . . .  11
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   8.  Manageability Considerations  . . . . . . . . . . . . . . . .  12
     8.1.  Control of Function and Policy  . . . . . . . . . . . . .  12
     8.2.  Information and Data Models . . . . . . . . . . . . . . .  12
     8.3.  Liveness Detection and Monitoring . . . . . . . . . . . .  12
     8.4.  Verify Correct Operations . . . . . . . . . . . . . . . .  12
     8.5.  Requirements On Other Protocols . . . . . . . . . . . . .  12
     8.6.  Impact On Network Operations  . . . . . . . . . . . . . .  13



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   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     9.1.  Association Type  . . . . . . . . . . . . . . . . . . . .  13
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     10.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  16
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   Segment Routing (SR) [RFC8402] can be used to steer packets through a
   network employing the source routing paradigm.  SR can be applied to
   both MPLS (SR-MPLS) and IPv6 (SRv6) data planes.

   [RFC5440] describes the Path Computation Element (PCE) Communication
   Protocol (PCEP).  [RFC8231] specifies a set of extensions to PCEP to
   enable stateful control of Traffic Engineering (TE) Label Switched
   Paths (LSPs) within and across PCEP sessions.  [RFC8664] specifies
   extensions to the PCEP for SR networks that allow a stateful PCE to
   compute and initiate SR TE paths, as well as a PCC to request, report
   or delegate them.

   There are some applications that require bidirectional paths in SR
   networks, for example, such as in mobile backhaul transport networks.
   There are features such as directed BFD [RFC9612] and Performance
   Measurement [RFC9503] that require the ingress node (PCC) to be aware
   of the reverse direction SR path.  For such features, the reverse SR
   paths need to be communicated to the ingress nodes (PCCs) using PCEP
   mechanisms.  This allows both endpoint nodes to be aware of the
   forward and reverse SR paths.

   An SR Policy [RFC9256] contains one or more Candidate Paths (CPs),
   which may be computed by a PCE.  A Candidate Path of an SR Policy can
   contain one or more Segment Lists (SLs).  In PCEP messages, an SL is
   encoded as an Explicit Route Object (ERO) as described in Section 4.3
   of [RFC8664].  [I-D.ietf-pce-multipath] defines PCEP extensions for
   carrying multiple SLs in the PCEP messages along with their opposite
   direction SLs, as described in Section 7.4 (Opposite Direction
   Tunnels) in [I-D.ietf-pce-multipath].

   As per [RFC8697], TE LSPs can be associated by adding them to a
   common association group by a PCEP peer.  [RFC9059] uses the
   association group object to group two unidirectional RSVP-TE LSPs
   into an associated bidirectional LSP.  This document extends this
   procedure and allows to group two unidirectional SR LSPs into an
   associated bidirectional SR LSP.  This extension also utilizes the
   procedure defined in [I-D.ietf-pce-multipath] to carry the multiple



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   EROs and the associated reverse path EROs for an SR LSP.  Note that
   the association group and the procedure introduced in this document
   are specific to SR-TE and SRv6 Path Setup Types.

2.  Terminology

   The reader is assumed to be familiar with the terminology defined in
   [RFC8231], [RFC8281], [RFC8697], [RFC8408], [RFC9059], and
   [I-D.ietf-pce-multipath].

   This document uses the following terms defined in [RFC5440]:

   Explicit Route Object (ERO), Path Computation Client (PCC), Path
   Computation Element (PCE), Path Computation Element Communication
   Protocol (PCEP), PCEP Peer, PCEP speaker.

   This document uses the following term defined in [RFC3031]:

   Label Switched Path (LSP).

   Note that the base PCEP specification [RFC4655] originally defined
   the use of the PCE architecture for MPLS and GMPLS networks with LSPs
   instantiated using the RSVP-TE signaling protocol.  Over time,
   support for additional path setup types, such as SR-TE Path Setup
   Type [RFC8664] and SRv6 Path Setup Type [RFC9603], have been
   introduced.  As specified in [RFC9603], the term "LSP" used in the
   PCEP specifications would be equivalent to an SRv6 path (represented
   as a list of SRv6 segments) in the context of supporting SRv6 in PCEP
   using SRv6 Path Setup Type.

2.1.  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.

3.  Overview

   Associated bidirectional SR LSPs can be created and updated by a
   Stateful PCE or by a PCC as described in the sub-sections below.

3.1.  PCE-Initiated Associated Bidirectional SR LSPs

   High-level steps for creating associated bidirectional SR LSPs by a
   Stateful PCE are shown in Figure 1.




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   Step 1 - Stateful PCE Behaviour:


   *  Stateful PCE creates and updates the SR LSP and the associated
      reverse SR LSP EROs, for the 'Bidirectional SR LSP Association' on
      a PCC via PCInitiate and PCUpd messages, respectively.

   Step 2 - PCC Behaviour:


   *  The PCC upon receiving the PCInitiate for the SR LSP and the
      associated reverse SR LSP EROs, locally assigns a PLSP-ID and
      reports it to the PCE via a PCRpt message.






































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                               +-----+
                               | PCE |
                               +-----+
     PCInitiate:               /     \       PCInitiate:
     Tunnel 1 (0)             /       \      Tunnel 2 (0)
     LSP1 (F1, R2)           /         \     LSP2 (F2, R1)
     Association #1         /           \    Association #1
     (Single LSP)          /             \   (Single LSP)
                          v               v
                     +-----+    LSP1     +-----+
                     |  S  |------------>|  D  |
                     |     |<------------|     |
                     +-----+    LSP2     +-----+
                           <no signaling>

    Legends: F=Forward LSP EROs, R=Reverse LSP EROs, (0)=PLSP-ID

    Figure 1a: Step 1: PCE-Initiated Associated Bidirectional SR LSP
                  with Forward Direction LSPs and Reverse Direction EROs

   ---------------------------------------------------------------------

                               +-----+
                               | PCE |
                               +-----+
     PCRpt:                    ^     ^       PCRpt:
     Tunnel 1 (100)           /       \      Tunnel 2 (200)
     LSP1 (F1, R2==F2)       /         \     LSP2 (F2, R1==F1)
     Association #1         /           \    Association #1
     (Single LSP)          /             \   (Single LSP)
                          /               \
                     +-----+    LSP1     +-----+
                     |  S  |------------>|  D  |
                     |     |<------------|     |
                     +-----+    LSP2     +-----+
                           <no signaling>

    Legends: F=Forward LSP EROs, R=Reverse LSP EROs, (100,200)=PLSP-IDs

    Figure 1b: Step 2: PCC-Reported Bidirectional SR LSP
                 with Forward Direction LSPs and Reverse Direction EROs

3.2.  PCC-Initiated Associated Bidirectional SR LSPs

   High-level steps for creating associated bidirectional SR LSPs by a
   PCC are shown in Figure 2.

   Step 1 - PCC Behaviour:



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   *  PCC creates and updates an SR LSP for the 'Bidirectional SR LSP
      Association' and reports the change in the association group of an
      SR LSP to PCE(s) via a PCRpt message.

   Step 2 - Stateful PCE Behaviour:


   *  Stateful PCE updates the SR LSP and the associated reverse SR LSP
      EROs, for the 'Bidirectional SR LSP Association' on a PCC via a
      PCUpd message.









































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                              +-----+
                              | PCE |
                              +-----+
     Report/Delegate:         ^     ^        Report/Delegate:
     Tunnel 1 (100)          /       \       Tunnel 2 (200)
     LSP1 (F1)              /         \      LSP2 (F2)
     Association #2        /           \     Association #2
                          /             \
                         /               \
                    +-----+    LSP1     +-----+
                    |  S  |------------>|  D  |
                    |     |<------------|     |
                    +-----+    LSP2     +-----+
                          <no signaling>

    Legends: F=Forward LSP EROs, (100,200)=PLSP-IDs

    Figure 2a: Step 1: PCC-Initiated Associated Bidirectional SR LSP
                       with Forward Direction LSPs

   ---------------------------------------------------------------------

                              +-----+
                              | PCE |
                              +-----+
     PCUpd:                   /     \        PCUpd:
     Tunnel 1 (100)          /       \       Tunnel 2 (200)
     LSP1 (F1, R2==F2)      /         \      LSP2 (F2, R1==F1)
     Association #2        /           \     Association #2
     (Single LSP)         /             \    (Single LSP)
                         v               v
                    +-----+    LSP1     +-----+
                    |  S  |------------>|  D  |
                    |     |<------------|     |
                    +-----+    LSP2     +-----+
                          <no signaling>

    Legends: F=Forward LSP EROs, R=Reverse LSP EROs, (100,200)=PLSP-IDs

    Figure 2b: Step 2: PCE-Updated Associated Bidirectional SR LSP
                 with Forward Direction LSPs and Reverse Direction EROs

4.  PCEP Extensions

   Two unidirectional SR LSPs (one in each direction between two nodes
   in a network) can be associated together by using the association
   group defined in this document for the PCEP messages and employing
   the the procedures defined in [RFC9059] and [I-D.ietf-pce-multipath].



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4.1.  Bidirectional SR LSP Association Group

   For associating two unidirectional SR LSPs, this document defines a
   new Association Type called 'Bidirectional SR LSP Association' for
   the Association Group object (Class-Value 40) as follows:

   *  Association Type (value 8) = Bidirectional SR LSP Association

   The handling of the Association ID, Association Source, optional
   Global Association Source and optional Extended Association ID in
   this association are set as defined in [RFC8697].

   [RFC8697] specifies the mechanism for the capability advertisement of
   the Association Types supported by a PCEP speaker by defining an
   ASSOC-Type-List TLV (value 35) to be carried within an OPEN object.
   The PCEP speaker MUST include the 'Bidirectional SR LSP Association'
   type in the ASSOC-Type-List TLV and MUST receive the same from the
   PCEP peer before using them in the PCEP messages.

   An SR LSP MUST NOT be part of more than one 'Bidirectional SR LSP
   Association' on a PCE.  A PCE, upon detecting this condition, MUST
   NOT send the associated reverse EROs to the ingress node PCC.  This
   error condition MUST be logged and an alarm MUST be generated.

4.2.  Bidirectional LSP Association Group TLV

   A PCEP message for an associated bidirectional SR LSP MAY include the
   'Bidirectional LSP Association Group TLV' to indicate the co-routed
   path using the C flag defined in Section 4.2 of [RFC9059].

   As there is no reverse SR LSP instantiated, the Reverse LSP (R flag)
   MUST NOT be set for an associated bidirectional SR LSP and MUST be
   ignored.  This error condition MUST be logged and generate an alarm.

4.3.  PATH-ATTRIB Object

   When a PCE informs an ingress node PCC about the associated reverse
   SR LSP EROs computed for an SR LSP with the 'Bidirectional SR LSP
   Association', it MUST include the 'PATH-ATTRIB' object with R
   (reverse) flag set to 1 to indicate that the ERO is for the reverse
   direction [I-D.ietf-pce-multipath].

4.4.  MULTIPATH-OPPDIR-PATH TLV

   The PCE MAY include the 'MULTIPATH-OPPDIR-PATH TLV' to indicate the
   co-routed path properties (in N and L flags) for the reverse ERO
   [I-D.ietf-pce-multipath] for an SR LSP.




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   The PCC MUST detect the mismatch of the co-routed path properties in
   the 'MULTIPATH-OPPDIR-PATH TLV' for the reverse ERO and the co-routed
   path (C) flag in the 'Bidirectional LSP Association Group TLV' for
   the (forward) SR LSP and log as an error condition and generate an
   alarm.

5.  Additional PCEP Considerations

   Additional considerations for associating bidirectional SR LSPs are
   summarized in the sub-sections below.

5.1.  PLSP-ID Usage

   As per [RFC8231], an ingress node PCC reports a unique PLSP-ID for
   each LSP of an SR Policy.  For an associated bidirectional SR LSP,
   the PCE will maintain two PLSP-IDs, one from the ingress node PCC and
   one from the egress node PCC.  In the examples shown in Figure 1 and
   Figure 2, the ingress node PCC S reports the Tunnel 1, LSP1 to the
   PCE with PLSP-ID 100 whereas the egress node PCC D reports the Tunnel
   2, LSP2 to the PCE with PLSP-ID 200.

5.2.  Error Handling

   The error handling as described in Section 5.7 of [RFC9059] continues
   to apply for the 'Bidirectional SR LSP Association'.

   The PST for SR LSP uses either value "1: Traffic-engineering path is
   set up using Segment Routing" [RFC8664] or "3: Traffic engineering
   path is set up using SRv6" [RFC9603].  If a PCEP speaker receives a
   non-SR LSP PST value for the 'Bidirectional SR LSP Association', the
   PCE speaker MUST return a PCErr message with Error-Type = 26
   (Association Error) and Error-value = "16: Path Setup Type not
   supported" [RFC9059].

6.  Implementation Status

   [Note to the RFC Editor - remove this section before publication, as
   well as remove the reference to [RFC7942].

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC7942].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not



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   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to [RFC7942], "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".


6.1.  Huawei's Commercial Delivery

   The feature is developing based on Huawei VRP8.

   *  Organization: Huawei

   *  Implementation: Huawei's Commercial Delivery implementation based
      on VRP8.

   *  Description: The implementation is under development.

   *  Maturity Level: Product

   *  Contact: tanren@huawei.com


6.2.  ZTE's Commercial Delivery

   *  Organization: ZTE

   *  Implementation: ZTE's Commercial Delivery implementation based on
      Rosng v8.

   *  Description: The implementation is under development.

   *  Maturity Level: Product

   *  Contact: zhan.shuangping@zte.com.cn

7.  Security Considerations

   The security considerations described in [RFC5440], [RFC8231],
   [RFC8281], [RFC8408], [RFC9059], and [I-D.ietf-pce-multipath] apply
   to the extensions defined in this document as well.





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   A new Association Type for the Association object, 'Bidirectional SR
   LSP Association' is introduced in this document.  Additional security
   considerations related to LSP associations due to a malicious PCEP
   speaker are described in [RFC8697] and apply to this Association
   Type.  Hence, securing the PCEP session using Transport Layer
   Security (TLS) [RFC8253] as per the recommendations and best current
   practices in [RFC9325].

8.  Manageability Considerations

   The manageability requirements and considerations listed in
   [RFC5440], [RFC8231], [RFC8281], [RFC8697], and
   [I-D.ietf-pce-multipath] apply to the PCEP protocol extensions
   defined in this document.  In addition, the requirements and
   considerations listed in this section apply.

8.1.  Control of Function and Policy

   The mechanisms defined in this document do not imply any new control
   or policy requirements.

8.2.  Information and Data Models

   [RFC7420] describes the PCEP MIB; there are no new MIB Objects
   defined for LSP associations.

   The PCEP YANG module [RFC9826] defines a data model for LSP
   associations.  However, it does not include information for
   associated bidirectional SR LSPs.

8.3.  Liveness Detection and Monitoring

   Mechanisms defined in this document do not imply any new liveness
   detection and monitoring requirements.

8.4.  Verify Correct Operations

   Mechanisms defined in this document do not imply any new operation
   verification requirements.

8.5.  Requirements On Other Protocols

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







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8.6.  Impact On Network Operations

   Associating two SR LSPs to form an associated bidirectional SR LSP
   requires an operator to ensure that the correct LSP associations are
   employed on both sides of the bidirectional SR LSP.  New tools such
   as directed BFD [RFC9612] and Performance Measurement [RFC9503] can
   be used to verify the correct operation of a bidirectional SR LSP.

9.  IANA Considerations


9.1.  Association Type

   This document defines a new Association Type, originally described in
   [RFC8697].  IANA is requested to update the value it has assigned
   through the early allocation process in the "ASSOCIATION Type Field"
   registry [RFC8697] within the "Path Computation Element Protocol
   (PCEP) Numbers" registry group, making it permanent:


   Type          Name                                 Reference
   ------------------------------------------------------------------
   8             Bidirectional SR LSP Association     [This document]

10.  References

10.1.  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>.




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   [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>.

   [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>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

   [RFC8408]  Sivabalan, S., Tantsura, J., Minei, I., Varga, R., and J.
              Hardwick, "Conveying Path Setup Type in PCE Communication
              Protocol (PCEP) Messages", RFC 8408, DOI 10.17487/RFC8408,
              July 2018, <https://www.rfc-editor.org/info/rfc8408>.

   [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>.

   [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>.

   [RFC9059]  Gandhi, R., Ed., Barth, C., and B. Wen, "Path Computation
              Element Communication Protocol (PCEP) Extensions for
              Associated Bidirectional Label Switched Paths (LSPs)",
              RFC 9059, DOI 10.17487/RFC9059, June 2021,
              <https://www.rfc-editor.org/info/rfc9059>.

   [RFC9256]  Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
              A., and P. Mattes, "Segment Routing Policy Architecture",
              RFC 9256, DOI 10.17487/RFC9256, July 2022,
              <https://www.rfc-editor.org/info/rfc9256>.






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   [RFC9325]  Sheffer, Y., Saint-Andre, P., and T. Fossati,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 9325, DOI 10.17487/RFC9325, November
              2022, <https://www.rfc-editor.org/info/rfc9325>.

   [I-D.ietf-pce-multipath]
              Koldychev, M., Sivabalan, S., Saad, T., Beeram, V. P.,
              Bidgoli, H., Peng, S., and S. Sidor, "Path Computation
              Element Communication Protocol (PCEP) Extensions for
              Signaling Multipath Information", Work in Progress,
              Internet-Draft, draft-ietf-pce-multipath-19, 2 February
              2026, <https://datatracker.ietf.org/doc/html/draft-ietf-
              pce-multipath-19>.

10.2.  Informative References

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,
              <https://www.rfc-editor.org/info/rfc3031>.

   [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>.

   [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>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

   [RFC9503]  Gandhi, R., Ed., Filsfils, C., Chen, M., Janssens, B., and
              R. Foote, "Simple Two-Way Active Measurement Protocol
              (STAMP) Extensions for Segment Routing Networks",
              RFC 9503, DOI 10.17487/RFC9503, October 2023,
              <https://www.rfc-editor.org/info/rfc9503>.








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   [RFC9603]  Li, C., Ed., Kaladharan, P., Sivabalan, S., Koldychev, M.,
              and Y. Zhu, "Path Computation Element Communication
              Protocol (PCEP) Extensions for IPv6 Segment Routing",
              RFC 9603, DOI 10.17487/RFC9603, July 2024,
              <https://www.rfc-editor.org/info/rfc9603>.

   [RFC9612]  Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen,
              "Bidirectional Forwarding Detection (BFD) Reverse Path for
              MPLS Label Switched Paths (LSPs)", RFC 9612,
              DOI 10.17487/RFC9612, July 2024,
              <https://www.rfc-editor.org/info/rfc9612>.

   [RFC9826]  Dhody, D., Ed., Beeram, V., Hardwick, J., and J. Tantsura,
              "A YANG Data Model for the Path Computation Element
              Communication Protocol (PCEP)", RFC 9826,
              DOI 10.17487/RFC9826, September 2025,
              <https://www.rfc-editor.org/info/rfc9826>.

Acknowledgments

   Many thanks to Marina Fizgeer, Adrian Farrel, Andrew Stone, Tarek
   Saad, Samuel Sidor, and Mike Koldychev for the detailed review of
   this document and for providing many useful comments.  Also, thank
   you, John Scudder, for the RtgDir Early review, Carlos Pignataro for
   the OpsDir review, Dhruv Dhody for the Shepherd review, Ketan
   Talaulikar for the WG AD review, which helped improve this document.

Contributors

   The following people have substantially contributed to this document:





















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

    Email: dhruv.ietf@gmail.com


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

    Email: lizhenbin@huawei.com


    Jie Dong
    Huawei Technologies
    Huawei Campus, No. 156 Beiqing Rd.
    Beijing  100095
    China

    Email: jie.dong@huawei.com

Authors' Addresses

   Cheng Li
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing
   100095
   China
   Email: c.l@huawei.com


   Mach(Guoyi) Chen
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing
   100095
   China
   Email: Mach.chen@huawei.com







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   Weiqiang Cheng
   China Mobile
   China
   Email: chengweiqiang@chinamobile.com


   Rakesh Gandhi
   Cisco Systems, Inc.
   Canada
   Email: rgandhi@cisco.com


   Quan Xiong
   ZTE Corporation
   China
   Email: xiong.quan@zte.com.cn



































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