



PCE Working Group                                                  C. Li
Internet-Draft                                                   M. Chen
Intended status: Standards Track                     Huawei Technologies
Expires: 29 May 2026                                            W. Cheng
                                                            China Mobile
                                                               R. Gandhi
                                                     Cisco Systems, Inc.
                                                                Q. Xiong
                                                         ZTE Corporation
                                                        25 November 2025


 Path Computation Element Communication Protocol (PCEP) Extensions for
          Associated Bidirectional Segment Routing (SR) Paths
                    draft-ietf-pce-sr-bidir-path-17

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) leverages the source routing and tunneling
   paradigms.  The Stateful PCEP extensions allow stateful control of
   Segment Routing Traffic Engineering (TE) Paths.  Furthermore, PCEP
   can be used to allow a PCE to compute SR TE paths in the network.

   This document defines PCEP extensions for grouping two unidirectional
   SR Paths (one in each direction in the network) into a single
   associated bidirectional SR Path.  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/.

   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."




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   This Internet-Draft will expire on 29 May 2026.

Copyright Notice

   Copyright (c) 2025 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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Bidirectional SR Policy Association . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   5
   3.  PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Double-Sided Bidirectional with Reverse LSP
           Association . . . . . . . . . . . . . . . . . . . . . . .   5
       3.1.1.  Bidirectional LSP Association Group TLV . . . . . . .   6
   4.  PCEP Procedure  . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  PCE-Initiated Associated Bidirectional SR Paths . . . . .   7
     4.2.  PCC-Initiated Associated Bidirectional SR Paths . . . . .   8
     4.3.  Stateless PCE . . . . . . . . . . . . . . . . . . . . . .  11
     4.4.  Bidirectional (B) Flag  . . . . . . . . . . . . . . . . .  11
     4.5.  PLSP-ID Usage . . . . . . . . . . . . . . . . . . . . . .  11
     4.6.  Error Handling  . . . . . . . . . . . . . . . . . . . . .  11
   5.  Implementation Status . . . . . . . . . . . . . . . . . . . .  12
     5.1.  Huawei's Commercial Delivery  . . . . . . . . . . . . . .  12
     5.2.  ZTE's Commercial Delivery . . . . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   7.  Manageability Considerations  . . . . . . . . . . . . . . . .  13
     7.1.  Control of Function and Policy  . . . . . . . . . . . . .  13
     7.2.  Information and Data Models . . . . . . . . . . . . . . .  13
     7.3.  Liveness Detection and Monitoring . . . . . . . . . . . .  14
     7.4.  Verify Correct Operations . . . . . . . . . . . . . . . .  14
     7.5.  Requirements On Other Protocols . . . . . . . . . . . . .  14
     7.6.  Impact On Network Operations  . . . . . . . . . . . . . .  14
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
     8.1.  Association Type  . . . . . . . . . . . . . . . . . . . .  14
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  15



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     9.2.  Informative References  . . . . . . . . . . . . . . . . .  15
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  18
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   Segment routing (SR) [RFC8402] leverages the source routing and
   tunneling paradigms.  SR supports steering packets onto an explicit
   forwarding path at the ingress node.  SR is specified for
   unidirectional paths.  However, some applications require
   bidirectional paths in SR networks, for example, in mobile backhaul
   transport networks.  The requirement for bidirectional SR Paths is
   specified in [RFC9545] and [I-D.ietf-spring-srv6-path-segment].

   [RFC5440] describes the Path Computation Element (PCE) Communication
   Protocol (PCEP).  PCEP enables the communication between a Path
   Computation Client (PCC) and a PCE, or between PCE and PCE, for the
   purpose of computation of Traffic Engineering (TE) Label Switched
   Paths (LSP).  [RFC8231] specifies a set of extensions to PCEP to
   enable stateful control of TE LSPs within and across PCEP sessions.
   The mode of operation where LSPs are initiated from the PCE is
   described in [RFC8281].

   [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.  As specified in
   [RFC8664], an SR path corresponds to an MPLS Label Switching Path
   (LSP) in PCEP when using the SR-TE path setup type.  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.

   [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, and it
   is equally applicable to the stateful PCE (active and passive modes)
   [RFC8231] and the stateless PCE [RFC5440].

   For bidirectional SR paths, there are use-cases such as directed BFD
   [RFC9612] and Performance Measurement (PM) [RFC9503] which require
   the ingress node (PCC) to be aware of the reverse direction SR Path.
   For such use-cases, the reverse SR Paths need to be communicated to
   the ingress node (PCCs) using PCEP mechanisms.  This allows both
   endpoint ingress nodes to be aware of the SR Paths in both
   directions, including their status and all other path related
   information.




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   [RFC9059] defines PCEP extensions for grouping two unidirectional
   Resource Reservation Protocol - Traffic Engineering (RSVP-TE) LSPs
   into an associated bidirectional LSP when using a stateful PCE for
   both PCE-initiated and PCC-initiated LSPs as well as when using a
   stateless PCE.  Specifically, it defines the procedure for 'Double-
   Sided Bidirectional LSP Association', where the PCE creates the
   association and provisions the forward LSPs at their ingress nodes.
   The RSVP-TE signals the forward LSPs to the egress nodes.  Thus, both
   endpoints learn the reverse LSPs forming the bidirectional LSP
   association.

   This document extends the bidirectional LSP association to SR paths
   by specifying PCEP extensions for grouping two unidirectional SR
   Paths into an associated bidirectional SR Path.  Note that the
   procedure for using the association group defined in this document is
   specific to the associated bidirectional SR Paths.  Associating an
   unidirectional SR Path with a reverse direction unidirectional RSVP-
   TE LSP to form a bidirectional LSP and vice versa, are outside the
   scope of this document.

1.1.  Bidirectional SR Policy Association

   An SR Policy contains one or more SR Policy Candidate Paths (CPs)
   [RFC9256] where one or more Candidate Paths can be computed via PCE.
   Each CP maps to a unique PLSP-ID in PCEP and each LSP in a CP is
   identified using a unique LSP-ID.  The two unidirectional Candidate
   Paths can be associated to form a bidirectional Candidate Path using
   the procedure defined in this document.

   Each Candidate Path of an SR Policy can contain one or more Segment
   Lists (SLs) [RFC9256].  When a Candidate Path is computed by the PCE,
   it means that the PCE computed all SLs of that Candidate Path.
   [I-D.ietf-pce-multipath] defines a procedure for carrying multiple
   SLs in a Candidate Path.  That procedure works at the SL level to
   identify the forward and the reverse direction SLs in a Candidate
   Path as shown in an Example in Section 7.4 (Opposite Direction
   Tunnels) in [I-D.ietf-pce-multipath].  Whereas the procedure defined
   in this document works at the Candidate Path level to identify the
   forward and the reverse direction LSPs of a Candidate Path in a
   bidirectional SR Policy.

2.  Terminology

   This document makes use of the terms defined in [RFC8408].  The
   reader is assumed to be familiar with the terminology defined in
   [RFC5440], [RFC8231], [RFC8281], [RFC8697], and [RFC9059].





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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.  PCEP Extensions

   As per [RFC8697], TE LSPs are associated by adding them to a common
   association group by a PCEP peer.  [RFC9059] uses the association
   group object and the procedures as specified in [RFC8697] to group
   two unidirectional RSVP-TE LSPs.  Similarly, two SR Paths can also be
   associated using a similar technique.  This document extends these
   association mechanisms for bidirectional SR Paths.  Two
   unidirectional SR Paths (one in each direction in the network) can be
   associated together by using the association group defined in this
   document for PCEP messages.

   [I-D.ietf-pce-sr-path-segment] defines a mechanism for communicating
   Path Segment Identifier (PSID) in PCEP for SR.  The SR-MPLS PSID is
   defined in [RFC9545] and SRv6 PSID is defined in
   [I-D.ietf-spring-srv6-path-segment].  The PSID can be used for
   identifying the SR Path of an associated bidirectional SR Path.  The
   PATH-SEGMENT TLV MAY be included for the SR Path in the LSP object to
   support the use-cases as required.  The PATH-SEGMENT TLV MUST be
   handled as defined in [I-D.ietf-pce-sr-path-segment] and is not
   modified for an associated bidirectional SR Path.

3.1.  Double-Sided Bidirectional with Reverse LSP Association

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

   *  Association Type (value 8) = Double-Sided Bidirectional with
      Reverse LSP Association

   The bidirectional association can be either dynamic or operator-
   configured.  As per [RFC8697], the association group could be
   manually created by the operator on the PCEP peers, and the LSPs
   belonging to this association are conveyed via PCEP messages to the
   PCEP peer; alternately, the association group could be created
   dynamically by the PCEP speaker, and both the association group
   information and the LSPs belonging to the association group are
   conveyed to the PCEP peer.  The Operator-configured Association Range



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   MUST be set for this Association Type to mark a range of Association
   Identifiers that are used for operator-configured associations to
   avoid any Association Identifier clash within the scope of the
   Association Source (Refer to [RFC8697]).  Specifically, for the PCE-
   initiated associated bidirectional SR Paths, the Association Type is
   dynamically created by the PCE on the PCE peers.

   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.
   This capability exchange for the Bidirectional Association MUST be
   done before using the Bidirectional Association Type.  Thus, the PCEP
   speaker MUST include the bidirectional Association Type in the ASSOC-
   Type-List TLV and MUST receive the same from the PCEP peer before
   using the Bidirectional Association in PCEP messages.

   A member of the 'Double-Sided Bidirectional with Reverse LSP
   Association' can take the role of a forward or reverse direction SR
   Path and follow the similar rules as defined in Section 4.2 of
   [RFC9059] for LSPs.

   *  An SR Path (forward or reverse) MUST NOT be part of more than one
      'Double-Sided Bidirectional with Reverse LSP Association'.  A PCE,
      upon detecting this condition, MUST NOT send the reverse SR Path
      to ingress node PCC.

   *  The endpoint nodes of the SR Paths in 'Double-Sided Bidirectional
      with Reverse LSP Association' MUST be matching in the reverse
      directions.

3.1.1.  Bidirectional LSP Association Group TLV

   When a PCE informs an ingress node PCC about the reverse SR Path
   using the 'Double-Sided Bidirectional with Reverse LSP Association',
   it MUST include the 'Bidirectional LSP Association Group TLV' to
   indicate the reverse direction and the co-routed path properties as
   defined in Section 4.2 of [RFC9059].  All fields and processing rules
   for this association group are followed as per Section 4 of
   [RFC9059].








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4.  PCEP Procedure

   The PCEP procedure defined in this document for an associated
   bidirectional SR Path is applicable to the three scenarios described
   in Section 5 of [RFC9059].  Note that the procedure in this document
   differs from the procedure defined in Section 5 of [RFC9059] where
   the ingress and egress node PCCs learn the reverse LSPs via RSVP
   signaling and report them to the PCE.

4.1.  PCE-Initiated Associated Bidirectional SR Paths

   Using the procedures defined in [RFC8697] and [RFC9059], associated
   bidirectional SR Paths can be created and updated by a Stateful PCE
   and is summarized below as Stateful PCE and PCC behaviours as a
   reminder.

   Stateful PCE Behaviours:


   *  Stateful PCE MAY create and update the forward and reverse SR
      Paths independently for the 'Double-Sided Bidirectional with
      Reverse LSP Association'.

   *  Stateful PCE MUST create and update the SR Paths and their
      association on a PCC via PCInitiate and PCUpd messages,
      respectively, using the procedures described in [RFC8697].

   *  The reverse direction SR Path SHOULD be informed by the Stateful
      PCE via PCInitiate message with the matching association group for
      the use-cases which require the PCC to be aware of the reverse
      direction SR Path.

   PCC Behaviours:


   *  The PCC upon receiving the PCInitiate for reverse SR Path, MUST
      locally assign a new PLSP-ID and issue a PCRpt to the PCE
      containing the PLSP-ID.

   *  PCC MUST NOT instantiate a reverse SR Path.

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








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                                  +-----+
                                  | PCE |
                                  +-----+
     PCInitiate:                  /     \     PCInitiate:
     Tunnel 1 (F)                /       \    Tunnel 2 (F)
     LSP1 (F,0), LSP2 (R,0)     /         \   LSP2 (F,0), LSP1 (R,0)
     Association #1            /           \  Association #1
                              /             \
                             v               v
                        +-----+    LSP1     +-----+
                        |  S  |------------>|  D  |
                        |     |<------------|     |
                        +-----+    LSP2     +-----+
                              <no signaling>

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

     Figure 1a: Step 1: PCE-Initiated Associated Bidirectional SR Path
                        with Forward and Reverse Direction SR Paths


                                  +-----+
                                  | PCE |
                                  +-----+
     PCRpt:                       ^     ^     PCRpt:
     Tunnel 1 (F)                /       \    Tunnel 2 (F)
     LSP1 (F,100), LSP2 (R,100) /         \   LSP2 (F,200), LSP1 (R,200)
     Association #1            /           \  Association #1
                              /             \
                             /               \
                        +-----+    LSP1     +-----+
                        |  S  |------------>|  D  |
                        |     |<------------|     |
                        +-----+    LSP2     +-----+
                              <no signaling>

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

     Figure 1b: Step 2: PCC-Reported Bidirectional SR Path
                        with Forward and Reverse Direction SR Paths

4.2.  PCC-Initiated Associated Bidirectional SR Paths

   Using the procedures defined in [RFC8697] and [RFC9059], associated
   bidirectional SR Paths can be created and updated by a PCC and and is
   summarized below as PCC and Stateful PCE behaviours as a reminder.

   PCC Behaviours:



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   *  PCC MAY create and update the forward SR Path and update the
      reverse SR Path independently for the 'Double-Sided Bidirectional
      with Reverse LSP Association'.

   *  PCC MUST NOT instantiate a reverse SR Path.

   *  PCC MAY establish and remove the association relationship for an
      SR Path.

   *  PCC MUST report the change in the association group of an SR Path
      to PCE(s) via PCRpt message.

   *  PCC MAY delegate the forward and reverse SR Paths independently to
      a Stateful PCE, where the PCE would control the SR Paths.

   *  The PCC upon receiving the PCInitiate for reverse SR Path, MUST
      locally assign a new PLSP-ID and issue a PCRpt to the PCE
      containing the PLSP-ID.

   Stateful PCE Behaviours:


   *  Stateful PCE updates the SR Paths in the 'Double-Sided
      Bidirectional with Reverse LSP Association' via PCUpd message,
      using the procedures described in [RFC8697].

   *  The reverse direction SR Path SHOULD be informed by the Stateful
      PCE via PCInitiate message with the matching association group for
      the use-cases which require the PCC to be aware of the reverse
      direction SR Path.

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

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



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

     Figure 2a: Step 1: PCC-Initiated Associated Bidirectional SR
                        Path with Forward Direction SR Paths


                                 +-----+
                                 | PCE |
                                 +-----+
    PCInitiate:                  /     \     PCInitiate:
    Tunnel 1 (F)                /       \    Tunnel 2 (F)
    LSP1 (F,100), LSP2 (R,0)   /         \   LSP2 (F,200), LSP1 (R,0)
    Association #2            /           \  Association #2
                             /             \
                            v               v
                       +-----+    LSP1     +-----+
                       |  S  |------------>|  D  |
                       |     |<------------|     |
                       +-----+    LSP2     +-----+
                             <no signaling>

     Legends: F = Forward LSP, R = Reverse LSP, (0,100,200) = PLSP-IDs

     Figure 2b: Step 2: PCE-Initiated Associated Bidirectional SR
                        Path with Reverse Direction SR Paths


                                 +-----+
                                 | PCE |
                                 +-----+
    PCRpt:                       ^     ^     PCRpt:
    Tunnel 1 (F)                /       \    Tunnel 2 (F)
    LSP1 (F,100), LSP2 (R,100) /         \   LSP2 (F,200), LSP1 (R,200)
    Association #2            /           \  Association #2
                             /             \
                            /               \
                       +-----+    LSP1     +-----+
                       |  S  |------------>|  D  |
                       |     |<------------|     |
                       +-----+    LSP2     +-----+
                             <no signaling>

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

     Figure 2c: Step 3: PCC-Reported Associated Bidirectional SR
                        Path with Reverse Direction SR Paths





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4.3.  Stateless PCE

   As defined in Section 5.3 of [RFC9059], for a stateless PCE, it might
   be useful to associate a path computation request to an association
   group, thus enabling it to associate a common set of configuration
   parameters or behaviors with the request [RFC8697].  A PCC can
   request co-routed or non-co-routed forward and reverse direction
   paths from a stateless PCE for a bidirectional SR Path.

4.4.  Bidirectional (B) Flag

   The Bidirectional (B) flag in the Request Parameters (RP) object
   [RFC5440] and Stateful PCE Request Parameter (SRP) object [RFC9504]
   follow the procedure defined in Section 5.4 of [RFC9059].

4.5.  PLSP-ID Usage

   For a bidirectional LSP computation when using both direction LSPs on
   a node, the LSPs on a node would need to be identified using the same
   PLSP-ID based on the PCEP session to the ingress or the egress node.
   Note that the PLSP-ID space is independent at each PCC, the PLSP-ID
   allocated by the egress PCC might not be able to be used for the LSP
   at the ingress PCC (PLSP-ID conflict may occur).  In other words, a
   given LSP will be identified by PLSP-ID A at the ingress node while
   it will be identified by PLSP-ID B at the egress node.  The PCE will
   maintain two PLSP-IDs for the bidirectional LSP.

   In the examples shown in Figure 1 and Figure 2, the ingress PCC S may
   report to the PCE an LSP1 with PLSP-ID 100.  The egress PCC D may
   report to the PCE an LSP2 with PLSP-ID 200.  Both of these LSPs are
   part of a bidirectional LSP.  When the PCE notifies PCC S of the
   reverse direction LSP2, it does so by sending a PCInitiate to PCC S
   with the PLSP-ID set to zero and the R bit set in the 'Bidirectional
   LSP Association Group TLV'.  PCC S upon reception of this assigns a
   PLSP-ID (example PLSP-ID 100) and issues a PCRpt to the PCE.  Thus,
   there would be two PLSP-IDs associated with LSP2 (100 at PCC S and
   200 at PCC D).

   For an associated bidirectional SR Path, the LSP-IDENTIFIERS TLV
   [RFC8231] MUST be included in all forward and reverse LSPs.

4.6.  Error Handling

   The error handling as described in Section 5.7 of [RFC9059] continues
   to apply for the 'Double-Sided Bidirectional with Reverse LSP
   Association'.





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   [RFC9059] in Section 5.7, defines a PCErr message for the Path Setup
   Type (PST) of '0: Path is set up using the RSVP-TE signaling
   protocol' [RFC8408].  The PST for SR Path is set to '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 an unsupported PST value for the 'Double-Sided
   Bidirectional with Reverse 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].

5.  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
   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".


5.1.  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



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   *  Contact: tanren@huawei.com


5.2.  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

6.  Security Considerations

   The security considerations described in [RFC5440], [RFC8231],
   [RFC8281], and [RFC8408] apply to the extensions defined in this
   document as well.

   A new Association Type for the Association object, 'Double-Sided
   Bidirectional with Reverse 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] is
   recommended.

7.  Manageability Considerations

   All manageability requirements and considerations listed in
   [RFC5440], [RFC8231], and [RFC8281] apply to PCEP protocol extensions
   defined in this document.  In addition, requirements and
   considerations listed in this section apply.

7.1.  Control of Function and Policy

   The mechanisms defined in this document do not imply any control or
   policy requirements in addition to those already listed in [RFC5440],
   [RFC8231], and [RFC8281].

7.2.  Information and Data Models

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




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

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], [RFC8231], and [RFC8281].

7.4.  Verify Correct Operations

   Mechanisms defined in this document do not imply any new operation
   verification requirements in addition to those already listed in
   [RFC5440], [RFC8231], and [RFC8408].

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

   Mechanisms defined in [RFC5440], [RFC8231], and [RFC8408] also apply
   to PCEP extensions defined in this document.

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

8.  IANA Considerations


8.1.  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               Double-Sided Bidirectional            [This document]
                   with Reverse LSP Association




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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>.

   [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>.

   [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>.

9.2.  Informative References







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   [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>.

   [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>.

   [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>.

   [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>.

   [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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   [RFC9504]  Lee, Y., Zheng, H., Gonzalez de Dios, O., Lopez, V., and
              Z. Ali, "Path Computation Element Communication Protocol
              (PCEP) Extensions for Stateful PCE Usage in GMPLS-
              Controlled Networks", RFC 9504, DOI 10.17487/RFC9504,
              December 2023, <https://www.rfc-editor.org/info/rfc9504>.

   [RFC9545]  Cheng, W., Ed., Li, H., Li, C., Ed., Gandhi, R., and R.
              Zigler, "Path Segment Identifier in MPLS-Based Segment
              Routing Networks", RFC 9545, DOI 10.17487/RFC9545,
              February 2024, <https://www.rfc-editor.org/info/rfc9545>.

   [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>.

   [I-D.ietf-pce-sr-path-segment]
              Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong,
              "Path Computation Element Communication Protocol (PCEP)
              Extension for Path Segment in Segment Routing (SR)", Work
              in Progress, Internet-Draft, draft-ietf-pce-sr-path-
              segment-14, 13 October 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-pce-sr-
              path-segment-14>.

   [I-D.ietf-spring-srv6-path-segment]
              Li, C., Cheng, W., Chen, M., Dhody, D., and Y. Zhu, "Path
              Segment Identifier (PSID) in SRv6 (Segment Routing in
              IPv6)", Work in Progress, Internet-Draft, draft-ietf-
              spring-srv6-path-segment-13, 13 October 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-spring-
              srv6-path-segment-13>.






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   [I-D.ietf-pce-multipath]
              Koldychev, M., Sivabalan, S., Saad, T., Beeram, V. P.,
              Bidgoli, H., Yadav, B., Peng, S., Mishra, G. S., and S.
              Sidor, "Path Computation Element Communication Protocol
              (PCEP) Extensions for Signaling Multipath Information",
              Work in Progress, Internet-Draft, draft-ietf-pce-
              multipath-16, 17 October 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-pce-
              multipath-16>.

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 providing many useful comments.  Also, thank you,
   John Scudder for RtgDir Early review, and Carlos Pignataro for OpsDir
   review, which helped improve this document.

Contributors

   The following people have substantially contributed to this document:

    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




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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


   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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