Path Computation Element Communication Protocol (PCEP) Extensions for Associated Bidirectional Segment Routing (SR) Paths
draft-ietf-pce-sr-bidir-path-19

PCE Working Group C. Li
Internet-Draft M. Chen
Intended status: Standards Track Huawei Technologies
Expires: 4 June 2026 W. Cheng
 China Mobile
 R. Gandhi
 Cisco Systems, Inc.
 Q. Xiong
 ZTE Corporation
 1 December 2025
 Path Computation Element Communication Protocol (PCEP) Extensions for
 Associated Bidirectional Segment Routing (SR) Paths
 draft-ietf-pce-sr-bidir-path-19
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."
Li, et al. Expires 4 June 2026 [Page 1]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
 This Internet-Draft will expire on 4 June 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
 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5
 3.1. PCE-Initiated Associated Bidirectional SR Paths . . . . . 5
 3.2. PCC-Initiated Associated Bidirectional SR Paths . . . . . 7
 4. PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . . 9
 4.1. Double-Sided Bidirectional with Reverse LSP
 Association . . . . . . . . . . . . . . . . . . . . . . . 9
 4.2. Bidirectional LSP Association Group TLV . . . . . . . . . 10
 4.3. PATH-ATTRIB Object . . . . . . . . . . . . . . . . . . . 10
 5. Additional PCEP Considerations . . . . . . . . . . . . . . . 10
 5.1. Stateless PCE . . . . . . . . . . . . . . . . . . . . . . 11
 5.2. Bidirectional (B) Flag . . . . . . . . . . . . . . . . . 11
 5.3. PLSP-ID Usage . . . . . . . . . . . . . . . . . . . . . . 11
 5.4. Path Segment Identifier Applicability . . . . . . . . . . 11
 5.5. Error Handling . . . . . . . . . . . . . . . . . . . . . 12
 6. Implementation Status . . . . . . . . . . . . . . . . . . . . 12
 6.1. Huawei's Commercial Delivery . . . . . . . . . . . . . . 12
 6.2. ZTE's Commercial Delivery . . . . . . . . . . . . . . . . 13
 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
 8. Manageability Considerations . . . . . . . . . . . . . . . . 13
 8.1. Control of Function and Policy . . . . . . . . . . . . . 14
 8.2. Information and Data Models . . . . . . . . . . . . . . . 14
 8.3. Liveness Detection and Monitoring . . . . . . . . . . . . 14
 8.4. Verify Correct Operations . . . . . . . . . . . . . . . . 14
 8.5. Requirements On Other Protocols . . . . . . . . . . . . . 14
 8.6. Impact On Network Operations . . . . . . . . . . . . . . 14
 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
 9.1. Association Type . . . . . . . . . . . . . . . . . . . . 15
Li, et al. Expires 4 June 2026 [Page 2]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
 10.1. Normative References . . . . . . . . . . . . . . . . . . 15
 10.2. Informative References . . . . . . . . . . . . . . . . . 16
 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 (LSPs). [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].
Li, et al. Expires 4 June 2026 [Page 3]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
 For bidirectional SR paths, there are use-cases such as directed BFD
 [RFC9612] and Performance Measurement (PM) [RFC9503] that 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 nodes (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.
 [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 via RSVP signaling.
 An SR Policy contains one or more Candidate Paths (CPs) [RFC9256]
 from which one or more Candidate Paths can be computed via PCE. A
 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 PCEP extensions for carrying
 multiple SLs in a Candidate Path. In PCEP messages, an SR path SL is
 encoded as an Explicit Route Object (ERO) as described in Section 4.3
 of [RFC8664]. In case of multiple SLs of a CP, multiple EROs are
 encoded in a PCEP message along with their path properties as
 specified in [I-D.ietf-pce-multipath].
 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.
 [I-D.ietf-pce-multipath] defines PCEP extensions for carrying
 multiple SLs along with their opposite direction SLs for each CP of
 an SR Policy, as shown in an example in Section 6.4 (Opposite
 Direction Tunnels) in [I-D.ietf-pce-multipath]. The procedure
 defined in this document for associating the forward and reverse SR
 paths, works in conjunction with the procedure defined in
 [I-D.ietf-pce-multipath] which carries multiple EROs and the
 associated reverse path EROs for an LSP.
Li, et al. Expires 4 June 2026 [Page 4]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
 Note that the procedure for using the association group defined in
 this document is specific to the associated bidirectional SR paths.
 Associating a unidirectional SR path with a reverse direction
 unidirectional RSVP-TE LSP to form a bidirectional LSP is outside the
 scope of this document.
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], [RFC9059], and
 [I-D.ietf-pce-multipath].
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 paths can be created and updated by a
 Stateful PCE or by a PCC using the procedures defined in [RFC8697],
 [RFC9059], and [I-D.ietf-pce-multipath] as described in the sub-
 sections below.
3.1. PCE-Initiated Associated Bidirectional SR Paths
 High-level steps for creating associated bidirectional SR paths by a
 Stateful PCE are shown in Figure 1.
 Step 1 - Stateful PCE Behaviour:
 * Stateful PCE MAY create and update both, the SR path EROs and the
 associated reverse SR path EROs, for the 'Double-Sided
 Bidirectional with Reverse LSP Association'. Stateful PCE MUST
 create and update both, the SR path EROs and the associated
 reverse SR path EROs, on a PCC via PCInitiate and PCUpd messages,
 respectively.
 Step 2 - PCC Behaviour:
Li, et al. Expires 4 June 2026 [Page 5]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
 * The PCC upon receiving the PCInitiate for the SR path and the
 associated reverse SR path EROs, MUST locally assign a PLSP-ID and
 report them to the PCE via a PCRpt message.
 +-----+
 | PCE |
 +-----+
 PCInitiate: / \ PCInitiate:
 Tunnel 1 (0) / \ Tunnel 2 (0)
 LSP1 (F1, R2) / \ LSP2 (F2, R1)
 Association #1 / \ Association #1
 / \
 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 Path
 with Forward and Reverse Direction SR Paths
 ---------------------------------------------------------------------
 +-----+
 | PCE |
 +-----+
 PCRpt: ^ ^ PCRpt:
 Tunnel 1 (100) / \ Tunnel 2 (200)
 LSP1 (F1, R2) / \ LSP2 (F2, R1)
 Association #1 / \ Association #1
 / \
 / \
 +-----+ 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 Path
 with Forward and Reverse Direction SR Paths
Li, et al. Expires 4 June 2026 [Page 6]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
3.2. PCC-Initiated Associated Bidirectional SR Paths
 High-level steps for creating associated bidirectional SR paths by a
 PCC are shown in Figure 2.
 Step 1 - PCC Behaviour:
 * PCC MAY create and update an SR path for the 'Double-Sided
 Bidirectional with Reverse LSP Association'. PCC MUST report the
 change in the association group of an SR path to PCE(s) via a
 PCRpt message.
 Step 2 - Stateful PCE Behaviour:
 * Stateful PCE MUST update both, the SR path EROs and the associated
 reverse SR path EROs, for the 'Double-Sided Bidirectional with
 Reverse LSP Association' on a PCC via a PCUpd message.
Li, et al. Expires 4 June 2026 [Page 7]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
 +-----+
 | 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
 Path with Forward Direction SR Paths
 ---------------------------------------------------------------------
 +-----+
 | PCE |
 +-----+
 PCUpd: / \ PCUpd:
 Tunnel 1 (100) / \ Tunnel 2 (200)
 LSP1 (F1, R2) / \ LSP2 (F2, R1)
 Association #2 / \ Association #2
 / \
 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
 Path with Reverse Direction SR Paths
Li, et al. Expires 4 June 2026 [Page 8]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
4. 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 between two nodes in a
 network) can be associated together by using the association group
 defined in this document for PCEP messages.
4.1. 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 LSP
 belonging to this association is conveyed to the PCEP peer;
 alternatively, the association group could be created dynamically by
 the PCEP speaker, and both the association group information and the
 LSP belonging to the association group is conveyed to the PCEP peer.
 The Operator-configured Association Range 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].
Li, et al. Expires 4 June 2026 [Page 9]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
 [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.
 * An SR path (forward or reverse direction) MUST NOT be part of more
 than one 'Double-Sided Bidirectional with Reverse LSP Association'
 on a PCE. A PCE, upon detecting this condition, MUST NOT send the
 associated reverse SR path EROs to the ingress node PCC.
 * The endpoint nodes of the SR paths (forward and reverse direction)
 in 'Double-Sided Bidirectional with Reverse LSP Association' MUST
 be matching in the reverse directions.
4.2. Bidirectional LSP Association Group TLV
 The 'Bidirectional LSP Association Group TLV' defined in Section 4.2
 of [RFC9059] is also applicable to the 'Double-Sided Bidirectional
 with Reverse LSP Association' defined in this document. A PCEP
 message for an associated bidirectional SR path MAY include the
 'Bidirectional LSP Association Group TLV' to indicate the co-routed
 path property using the C flag defined in Section 4.2 of [RFC9059].
 Note that the Reverse LSP (R flag) is not applicable to the
 associated bidirectional SR paths. The processing rules for this
 association group TLV are followed as described in Section 4.2 of
 [RFC9059].
4.3. PATH-ATTRIB Object
 When a PCE informs an ingress node PCC about the associated reverse
 SR path EROs computed for an SR path with the 'Double-Sided
 Bidirectional with Reverse LSP Association', it MUST include the
 'PATH-ATTRIB' object to indicate the reverse direction for each ERO,
 and it MAY optionally include the 'MULTIPATH-OPPDIR-PATH TLV' to
 indicate the co-routed path properties for the ERO using the
 procedure defined in Section 3 of [I-D.ietf-pce-multipath].
5. Additional PCEP Considerations
 The PCEP extensions defined in this document for an associated
 bidirectional SR path are applicable to the three scenarios described
 in Section 5 of [RFC9059].
Li, et al. Expires 4 June 2026 [Page 10]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
 Additional considerations for associating bidirectional SR paths are
 summarized in the sub-sections below.
5.1. 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 SR
 paths from a stateless PCE for an associated bidirectional SR path
 using the 'Bidirectional Association Group TLV' as described in
 Section 4.2 of [RFC9059].
5.2. Bidirectional (B) Flag
 The Bidirectional (B) flag in the Request Parameters (RP) object
 [RFC5440] and Stateful PCE Request Parameter (SRP) object [RFC9504]
 follows the procedure defined in Section 5.4 of [RFC9059].
5.3. PLSP-ID Usage
 For an SR Policy, the ingress PCC node reports a unique PLSP-ID
 [RFC8231] for each CP of the SR Policy.
 For an associated bidirectional SR path, 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.
5.4. Path Segment Identifier Applicability
 [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, such as PM, 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.
Li, et al. Expires 4 June 2026 [Page 11]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
5.5. 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'.
 [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].
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
 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
Li, et al. Expires 4 June 2026 [Page 12]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
 * 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], and [I-D.ietf-pce-multipath] 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.
8. Manageability Considerations
 All manageability requirements and considerations listed in
 [RFC5440], [RFC8231], [RFC8281], and [I-D.ietf-pce-multipath] apply
 to PCEP protocol extensions defined in this document. In addition,
 requirements and considerations listed in this section apply.
Li, et al. Expires 4 June 2026 [Page 13]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
8.1. 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], [RFC8281], and [I-D.ietf-pce-multipath].
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 associated bidirectional
 SR path information.
8.3. 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], [RFC8281], and
 [I-D.ietf-pce-multipath].
8.4. 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], [RFC8408], and [I-D.ietf-pce-multipath].
8.5. Requirements On Other Protocols
 Mechanisms defined in this document do not imply any new requirements
 on other protocols.
8.6. Impact On Network Operations
 Mechanisms defined in [RFC5440], [RFC8231], [RFC8408], and
 [I-D.ietf-pce-multipath] 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.
9. IANA Considerations
Li, et al. Expires 4 June 2026 [Page 14]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
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 Double-Sided Bidirectional [This document]
 with Reverse LSP Association
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>.
 [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>.
Li, et al. Expires 4 June 2026 [Page 15]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
 [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>.
 [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>.
10.2. Informative References
 [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>.
Li, et al. Expires 4 June 2026 [Page 16]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
 [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>.
 [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>.
Li, et al. Expires 4 June 2026 [Page 17]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
 [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>.
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, and Carlos Pignataro
 for the OpsDir review, which helped improve this document.
Contributors
 The following people have substantially contributed to this document:
Li, et al. Expires 4 June 2026 [Page 18]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
 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
Li, et al. Expires 4 June 2026 [Page 19]
Internet-Draft PCEP for Associated Bidirectional SR December 2025
 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
Li, et al. Expires 4 June 2026 [Page 20]