PCE Working Group S. Sidor Internet-Draft Z. Ali Intended status: Standards Track Cisco Systems, Inc. Expires: 13 April 2026 C. Li Huawei Technologies M. Koldychev Ciena Corporation 10 October 2025 Binding Label/Segment Identifier (SID) Extensions in Path Computation Element Communication Protocol (PCEP) draft-sidor-pce-binding-label-sid-extensions-01 Abstract The Path Computation Element Communication Protocol (PCEP) provides mechanisms for Path Computation Elements (PCEs) to instantiate and manage Label Switched Paths (LSPs) on a Path Computation Client (PCC). This includes the ability for a PCE to specify a Binding Segment Identifier (SID) for an LSP as described in RFC9604. A binding value specified by a PCE may not be available for use on the PCC. This can lead to LSP instantiation failures or entire PCEP message being rejected. This document proposes extensions to PCEP to allow a PCC to fall back to allocating a Binding SID from its own dynamic range if the value specified by the PCE is unavailable. It also defines a mechanism for the PCC to report both the requested and the allocated binding values back to the PCE. 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." This Internet-Draft will expire on 13 April 2026. Sidor, et al. Expires 13 April 2026 [Page 1] Internet-Draft PCEP Binding SID Extensions October 2025 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . . 4 4.1. STATEFUL-PCE-CAPABILITY TLV . . . . . . . . . . . . . . . 4 4.2. TE-PATH-BINDING TLV . . . . . . . . . . . . . . . . . . . 4 5. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 4 6. Manageability Considerations . . . . . . . . . . . . . . . . 5 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 8.1. STATEFUL-PCE-CAPABILITY TLV Flag . . . . . . . . . . . . 6 8.2. TE-PATH-BINDING TLV Flags . . . . . . . . . . . . . . . . 6 8.3. PCEP Errors . . . . . . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 9.1. Normative References . . . . . . . . . . . . . . . . . . 7 9.2. Informative References . . . . . . . . . . . . . . . . . 8 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction This document proposes extensions to the Path Computation Element Communication Protocol (PCEP) to enhance the management of Binding Segment Identifiers (SIDs) for Label Switched Paths (LSPs). Specifically, it defines mechanisms for a Path Computation Client (PCC) to handle situations where a Binding SID (BSID) requested by a Path Computation Element (PCE) is unavailable, allowing for fallback allocation and subsequent reporting of the allocated values back to the PCE. These extensions aim to improve the robustness and flexibility of LSP instantiation and management in PCEP-controlled networks. Sidor, et al. Expires 13 April 2026 [Page 2] Internet-Draft PCEP Binding SID Extensions October 2025 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 2. Terminology This document uses the following terms defined in [RFC5440]: PCC, PCE, PCEP Peer, and PCEP speaker. The base PCEP specification [RFC4655] originally defined the use of the PCE architecture for Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) networks with Label Switched Paths (LSPs) instantiated using the Resource Reservation Protocol - Traffic Engineering (RSVP-TE) signaling protocol. Over time, support for additional path setup types, such as SRv6, has been introduced [RFC9603]. The term "LSP" is used extensively in PCEP specifications and, in the context of this document, refers to a Candidate Path within an SR Policy, which may be an Segment Routing over IPv6 (SRv6) path (still represented using the LSP Object as specified in [RFC8231]. It also uses the term Binding Segment Identifier (BSID), as defined in [RFC9604], which refers to a local label or SID that represents an SR Policy or an SR-TE LSP. 3. Motivation The PCEP provides mechanisms for PCEs to instantiate and manage LSPs on a PCC. A Stateful PCE [RFC8231] can instantiate LSPs on a PCC. When instantiating a SR-TE LSP [RFC8664], the PCE may request a specific BSID to be associated with the LSP using the TE-PATH-BINDING TLV [RFC9604]. A significant operational challenge arises when the BSID requested by the PCE is already in use, falls outside the valid range, or is otherwise unavailable on the PCC. In the current PCEP specification, such a conflict or unavailability typically results in an LSP instantiation failure. This "hard failure" approach can be disruptive, requiring manual steps from an operator or complex retry logic at the PCE, and can have negative impact on automated provisioning capabilities that PCEP aims to provide. It can also lead to entire PCEP messages being rejected, forcing the PCE to re- evaluate and re-initiate the entire LSP setup process. Sidor, et al. Expires 13 April 2026 [Page 3] Internet-Draft PCEP Binding SID Extensions October 2025 To improve network resilience and operational efficiency, it is desirable to have more flexible mechanisms for handling BSID unavailability scenarios. Instead of failure, a PCC should ideally be able to gracefully handle such situations, for instance, by allocating a Binding SID from its local dynamic range. Furthermore, the PCE needs to be aware of the actual BSID allocated by the PCC to maintain an accurate view of the network state. This document defines extensions to PCEP to address these operational needs. 4. PCEP Extensions 4.1. STATEFUL-PCE-CAPABILITY TLV A new flag is proposed for the STATEFUL-PCE-CAPABILITY TLV, originally defined in Section 5.4 of [RFC8231]. * F (BSID-FALLBACK-CAPABILITY): If set, indicates that the PCEP peer supports LSP creation and fall back to dynamic binding value allocation if the specific binding value is unavailable, as detailed in Section 5. 4.2. TE-PATH-BINDING TLV New flags are proposed in the TE-PATH-BINDING TLV, which was originally defined in Section 4 of [RFC9604]. * A (Allocated): If set, indicates that the binding value encoded in the TLV represents an allocated binding value. * D (Down on BSID Unavailability): If set, indicates that LSP can be created even if specified binding value is unavailable, but LSP will be in down state. * F (Fallback): If set, indicates that binding value allocation from the dynamic range will be performed if the specified binding value is unavailable. 5. Operation The PCEP protocol extensions defined in this document MUST NOT be used if one or both PCEP speakers have not indicated support for the extensions by setting the F flag (BSID-FALLBACK-CAPABILITY) in the STATEFUL-PCE-CAPABILITY TLV in their respective OPEN messages. When a PCE wants to instantiate or update an LSP and suggest a binding value, it includes the TE-PATH-BINDING TLV in the PCInitiate or PCUpd message. The PCE can set the F flag or the D flag in this TLV to control the PCC's behavior in case the requested binding value is unavailable. The F and D flags are mutually exclusive. If a PCEP speaker receives a TE-PATH-BINDING TLV where both the F flag and the Sidor, et al. Expires 13 April 2026 [Page 4] Internet-Draft PCEP Binding SID Extensions October 2025 D flag are set, the PCEP speaker MUST send a PCErr message with Error-Type 10 (Reception of an invalid object) and Error-Value TBD5 (Mutually exclusive F and D flags are both set). The LSP instantiation or update request associated with this malformed TLV MUST be rejected. If the PCC receives a TE-PATH-BINDING TLV with the F flag set and the requested binding value is unavailable, the PCC MUST attempt to allocate a new binding value from its dynamic pool. If successful, the LSP is brought up with the new binding value. If the PCC receives a TE-PATH-BINDING TLV with the D flag set and the requested binding value is unavailable, the PCC MUST instantiate the LSP but keep it in a down state. In its PCRpt message, the PCC reports the status of the binding value allocation. If the originally requested binding value and the allocated binding value differ, two instances of the TE-PATH-BINDING TLV MUST be included in the PCRpt message: * A TLV instance with the originally requested binding value with the A flag cleared. * A TLV instance with the actually allocated binding value with the A flag set. If the requested binding value was successfully allocated, only a single instance of the TE-PATH-BINDING TLV with the A flag set SHOULD be included in the PCEP message. The A, D and F flags in the TE-PATH-BINDING TLV MUST NOT be used if one or both PCEP speakers have not set the BSID-FALLBACK-CAPABILITY in the STATEFUL-PCE-CAPABILITY TLV in their respective OPEN messages. If a PCEP speaker receives a PCEP message containing the A, D, or F flags in the TE-PATH-BINDING TLV, or any other element specific to these extensions, from a peer that has not advertised the BSID- FALLBACK-CAPABILITY in its OPEN message, the receiving PCEP speaker MUST send a PCErr message with Error-Type 10 (Reception of an invalid object) and Error-Value TBD6 (Unsupported Binding SID Extension Flags). 6. Manageability Considerations All manageability requirements and considerations listed in [RFC5440], [RFC8231], and [RFC9604] apply to the PCEP extensions defined in this document. Sidor, et al. Expires 13 April 2026 [Page 5] Internet-Draft PCEP Binding SID Extensions October 2025 A PCE or PCC implementation MAY allow the capability of supporting PCEP extensions introduced in this document to be enabled/disabled as part of the global configuration. An implementation SHOULD allow the operator to view the advertised and received capabilities. 7. Security Considerations The security considerations described in [RFC5440], [RFC8231], and [RFC9604] are applicable to this document. No additional security measures are required. As per [RFC8231], it is RECOMMENDED that these PCEP extensions can only be activated on authenticated and encrypted sessions across PCEs and PCCs belonging to the same administrative authority, using Transport Layer Security (TLS) [RFC8253] as per the recommendations and best current practices in [RFC9325]. 8. IANA Considerations 8.1. STATEFUL-PCE-CAPABILITY TLV Flag IANA maintains a registry, named "STATEFUL-PCE-CAPABILITY TLV Flag Field", within the "Path Computation Element Protocol (PCEP) Numbers" registry group. IANA is requested to make the following assignment: +======+==============================+===============+ | Bit | Description | Reference | +======+==============================+===============+ | TBA1 | F (BSID-FALLBACK-CAPABILITY) | This document | +------+------------------------------+---------------+ Table 1 8.2. TE-PATH-BINDING TLV Flags IANA maintains a registry, named "TE-PATH-BINDING TLV Flag Field", within the "Path Computation Element Protocol (PCEP) Numbers" registry group. IANA is requested to make the following assignments: Sidor, et al. Expires 13 April 2026 [Page 6] Internet-Draft PCEP Binding SID Extensions October 2025 +======+=================================+===============+ | Bit | Description | Reference | +======+=================================+===============+ | TBA2 | A (Allocated) | This document | +------+---------------------------------+---------------+ | TBA3 | D (Down on BSID Unavailability) | This document | +------+---------------------------------+---------------+ | TBA4 | F (Fallback) | This document | +------+---------------------------------+---------------+ Table 2 8.3. PCEP Errors IANA maintains a registry, named "PCEP-ERROR Object Error Types and Values", within the "Path Computation Element Protocol (PCEP) Numbers" registry group. IANA is requested to make the following assignments: +============+=================+====================+===========+ | Error-Type | Meaning | Error-value | Reference | +============+=================+====================+===========+ | 10 | Reception of an | TBD5: Mutually | This | | | invalid object | exclusive F and D | document | | | | flags are both set | | +------------+-----------------+--------------------+-----------+ | | | TBD6: Unsupported | This | | | | Binding SID | document | | | | Extension Flags | | +------------+-----------------+--------------------+-----------+ Table 3 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, . [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, DOI 10.17487/RFC5440, March 2009, . Sidor, et al. Expires 13 April 2026 [Page 7] Internet-Draft PCEP Binding SID Extensions October 2025 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path Computation Element Communication Protocol (PCEP) Extensions for Stateful PCE", RFC 8231, DOI 10.17487/RFC8231, September 2017, . [RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody, "PCEPS: Usage of TLS to Provide a Secure Transport for the Path Computation Element Communication Protocol (PCEP)", RFC 8253, DOI 10.17487/RFC8253, October 2017, . [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, . [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, . [RFC9604] Sivabalan, S., Filsfils, C., Tantsura, J., Previdi, S., and C. Li, Ed., "Carrying Binding Label/SID in PCE-Based Networks", RFC 9604, DOI 10.17487/RFC9604, August 2024, . 9.2. Informative References [RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, DOI 10.17487/RFC4655, August 2006, . [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, . Sidor, et al. Expires 13 April 2026 [Page 8] Internet-Draft PCEP Binding SID Extensions October 2025 Appendix A. Acknowledgements The authors would like to thank Rajesh Melarcode Venkateswaran for their contributions to this document. Authors' Addresses Samuel Sidor Cisco Systems, Inc. Eurovea Central 3 Pribinova 10 811 09 Bratislava Slovakia Email: ssidor@cisco.com Zafar Ali Cisco Systems, Inc. Email: zali@cisco.com Cheng Li Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China Email: c.l@huawei.com Mike Koldychev Ciena Corporation 385 Terry Fox Dr. Kanata Ontario K2K 0L1 Canada Email: mkoldych@proton.me Sidor, et al. Expires 13 April 2026 [Page 9]