PCE Working Group S. Sidor Internet-Draft Z. Ali Intended status: Standards Track Cisco Systems, Inc. Expires: 4 September 2025 C. Li Huawei Technologies M. Koldychev Ciena Corporation 3 March 2025 LSP State Reporting Extensions in Path Computation Element Communication Protocol (PCEP) draft-sidor-pce-lsp-state-reporting-extensions-02 Abstract The Path Computation Element Communication Protocol (PCEP) is defined in multiple RFCs for enabling communication between Path Computation Elements (PCEs) and Path Computation Clients (PCCs). Although PCEP defines various LSP identifiers, attributes, and constraints, there are operational attributes available on the PCC that can enhance path computation and improve the debugging experience, which are not currently supported in PCEP. This document proposes extensions to PCEP to include: * Support for explicit or dynamic path types * Mechanisms to mark LSPs as eligible for use as transit LSPs * Allowing instantiation of LSP and optionally do fallback to Binding label/Segment Identifier (SID) allocation by the PCC when the binding value specified by the PCE is unavailable These extensions aim to address the existing gaps, enhancing the overall functionality and operational efficiency of PCEP. 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. Sidor, et al. Expires 4 September 2025 [Page 1] Internet-Draft STATE-REPORTING-EXTENSIONS March 2025 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 4 September 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 . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Overview of Extensions to PCEP . . . . . . . . . . . . . . . 4 3.1. STATEFUL-PCE-CAPABILITY TLV Flag . . . . . . . . . . . . 4 3.2. LSP-EXTENDED-FLAG TLV Flags . . . . . . . . . . . . . . . 5 3.3. TE-PATH-BINDING TLV Flag . . . . . . . . . . . . . . . . 5 4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Binding Label/SID Flags . . . . . . . . . . . . . . . . . 5 4.2. Explicit or Dynamic Path . . . . . . . . . . . . . . . . 6 4.3. Transit Eligible . . . . . . . . . . . . . . . . . . . . 7 5. Manageability Considerations . . . . . . . . . . . . . . . . 7 5.1. Control of Function and Policy . . . . . . . . . . . . . 7 5.2. Information and Data Models . . . . . . . . . . . . . . . 7 5.3. Verify Correct Operations . . . . . . . . . . . . . . . . 7 5.4. Impact On Network Operations . . . . . . . . . . . . . . 8 Sidor, et al. Expires 4 September 2025 [Page 2] Internet-Draft STATE-REPORTING-EXTENSIONS March 2025 6. Implementation Status . . . . . . . . . . . . . . . . . . . . 8 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 8.1. STATEFUL-PCE-CAPABILITY TLV Flag . . . . . . . . . . . . 8 8.2. TE-PATH-BINDING TLV Flag . . . . . . . . . . . . . . . . 9 8.3. LSP-EXTENDED-FLAG TLV Flags . . . . . . . . . . . . . . . 9 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 9.1. Normative References . . . . . . . . . . . . . . . . . . 10 9.2. Informative References . . . . . . . . . . . . . . . . . 11 Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 1. Introduction A Stateful Path Computation Element (PCE) maintains comprehensive information on the current network state, including computed Label Switched Paths (LSPs), reserved network resources, and the pending path computation requests. This information is critical for computing paths for traffic-engineering LSPs and any associated or dependent LSPs. [RFC9604] outlines the usage of Binding labels/ Segment Identifiers (SID) usage for an RSVP-TE-signaled Label Switched Paths (LSPs) and Segment-routing Traffic Engineering paths. It specifies the possibility of a PCE explicitly requesting the allocation of a specific binding value by a PCC. However, [RFC9604] only considers the option of rejecting entire request if the specified binding value is unavailable, but section 6.2 of [RFC9256] allows also fallback to a dynamically allocated binding value. This document introduces the possibility for a PCC to accept such request and include originally specified binding value for which allocation failed, as well as a binding value allocated from the dynamic range as a fallback. This document specifies a set of extensions to Path Computation Element Communication Protocol(PCEP) to enhance the accuracy of path computations by considering whether the Binding label/SID of an LSP can be utilized in the path computation for another LSP, based on LSP transit eligibility, for example as described in case of LSP stitching in [I-D.ietf-pce-stateful-interdomain]. Additionally, this document introduces the ability to encode information regarding whether a path included in an Explicit Route Object (ERO) was specified explicitly or it is the result of dynamic path computation executed by a PCE or PCC. Such information can help in debuggability and can be used by other PCEs in the network to avoid triggering unnecessary path computations for LSPs where it is not intended (e.g., PCE-initiated LSPs with explicit path). Sidor, et al. Expires 4 September 2025 [Page 3] Internet-Draft STATE-REPORTING-EXTENSIONS March 2025 The mechanisms described in this document are applicable to all path setup types. 2. Terminology The following terminologies are used in this document: BSID: Binding Segment Identifier. ERO: Explicit Route Object. IGP: Interior Gateway Protocol. NAI: Node or Adjacency Identifier. P2P: Point-to-Point. PCE: Path Computation Element. PCEP: Path Computation Element Protocol. SID: Segment Identifier. SR: Segment Routing. SR-TE: Segment Routing Traffic Engineering. LSP: Label Switched Path. LSPA: Label Switched Path Attributes. 3. Overview of Extensions to PCEP 3.1. STATEFUL-PCE-CAPABILITY TLV Flag New flags are 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 fallback to dynamic binding value allocation if the specific binding value is unavailable, as detailed in Section 4.1 of this document. * T (TRANSIT-ELIGIBLE-CAPABILITY): If set, indicates that the PCEP peer supports the advertisement of the Transit Eligible flag in the LSP-EXTENDED-FLAG as described in Section 4.3 of this document. Sidor, et al. Expires 4 September 2025 [Page 4] Internet-Draft STATE-REPORTING-EXTENSIONS March 2025 3.2. LSP-EXTENDED-FLAG TLV Flags New flags are introduced in the LSP-EXTENDED-FLAG TLV, which was initially defined in Section 3.1 of [RFC9357]. * E (Explicit): If set, indicates that the path encoded in the Explicit Route Object (ERO) is explicitly specified and not dynamically computed by the PCEP peer. * T (Transit Eligible): If set, indicates that the binding value of the LSP can be used in paths computed for other LSPs. 3.3. TE-PATH-BINDING TLV Flag New flags 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. 4. Operation The PCEP protocol extensions defined in Section 3.3 of this draft MUST NOT be used if one or both PCEP speakers have not indicated support for the extensions using the F flag in the STATEFUL-PCE- CAPABILITY TLV in their respective OPEN messages. 4.1. Binding Label/SID Flags [RFC9604] specifies the possibility for a PCE to explicitly request the allocation of a specific binding value by a PCC. If the specified binding value is unavailable, the entire request MUST be rejected. However, if either the D or F flag in the TE-PATH-BINDING TLV is set and the specified binding value in the PCInitiate or PCUpd message is unavailable, the PCC MUST NOT reject the request and MUST proceed with the LSP operation as specified in the message. If the D flag is set, LSP instantiation is allowed, but the LSP SHOULD remain in an operational down state. If the F flag is set, the PCC MUST do a fallback to binding value allocation from the dynamic range, as described in Section 6.2 of [RFC9256]. Sidor, et al. Expires 4 September 2025 [Page 5] Internet-Draft STATE-REPORTING-EXTENSIONS March 2025 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 requested binding value with the A flag cleared * A TLV instance with allocated binding value with the A flag set The A flag MUST NOT be set if TE-PATH-BINDING TLV is included in PCInitiate and PCUpd messages as encoded value represents requested Binding Label/SID. The A, D and F flags 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. 4.2. Explicit or Dynamic Path [RFC9256] describes various types of Segment Routing (SR) Policy Candidate Paths and methods to identify them. Specifically, Sections 5.1 and 5.2 are describing explicit and dynamic candidate paths, but there is currently no way to encode this information in PCEP. A similar limitation applies to LSPs of other path setup types. For instance, if an operator requests the creation of a PCE-Initiated Candidate Path with an Explicit Path, then such path will be encoded in the ERO object of the PCInitiate message sent to the PCC. If the delegation of such LSP is transferred to another PCE, the new PCE will not know whether the path of the LSP was computed dynamically or explicitly specified by the operator. Even if similar problem does not exist for LSPs originated on the PCC, information about the type of path may be valuable for other purposes, such as debuggability. For LSPs initiated by PCC, the E flag value is initially set by the PCC in the PCRpt message and the PCE MUST set the flag value in PCUpd messages for such LSP based on the last reported state. For PCE-initiated LSPs, the E flag value is initially set by the PCE in PCInitiate message but MAY be modified in the PCUpd messages. The PCC MUST set the flag value in PCRpt messages for such LSP based on the value received from the last PCInitiate or PCUpd message. Sidor, et al. Expires 4 September 2025 [Page 6] Internet-Draft STATE-REPORTING-EXTENSIONS March 2025 4.3. Transit Eligible The T flag in the LSP-EXTENDED-FLAG TLV MUST NOT be set unless the TRANSIT-ELIGIBLE-CAPABILITY is supported by both PCEP peers. If the TRANSIT-ELIGIBLE-CAPABILITY is not advertised, the PCE implementation MAY use a local policy to determine the value of the Transit Eligible flag. For PCC-initiated LSPs, the T flag value is initially set by the PCC in the PCRpt message. The PCE MUST set the flag value in PCUpd messages for these LSPs based on the last reported state. For PCE-initiated LSPs, the T flag value is initially set by the PCE in the PCInitiate message but MAY be modified in subsequent PCUpd messages. The PCC MUST set the flag value in PCRpt messages for these LSPs based on the value received from the latest PCInitiate or PCUpd message. 5. 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. 5.1. Control of Function and Policy 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. 5.2. Information and Data Models An implementation SHOULD allow the operator to view the capability defined in this document. Sections 4.1 and 4.1.1 of [I-D.ietf-pce-pcep-yang] should be extended to include the capability introduced in Section 3.1 for the PCEP peer. 5.3. Verify Correct Operations Operation verification requirements already listed in [RFC5440], [RFC8231], [RFC8281] and [RFC8664] are applicable to mechanisms defined in this document. Sidor, et al. Expires 4 September 2025 [Page 7] Internet-Draft STATE-REPORTING-EXTENSIONS March 2025 5.4. Impact On Network Operations The mechanisms defined in [RFC5440], [RFC8231], and [RFC8281] also apply to the PCEP extensions defined in this document. 6. Implementation Status [Note to the RFC Editor - remove this section before publication, as well as remove the reference to RFC 7942.] 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". 7. Security Considerations The security considerations described in [RFC5440], [RFC8231], [RFC8253], [RFC8281], [RFC8664]. 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 to manage the Flags field of the STATEFUL-PCE- CAPABILITY TLV. IANA is requested to make the following assignments: Sidor, et al. Expires 4 September 2025 [Page 8] Internet-Draft STATE-REPORTING-EXTENSIONS March 2025 +======+=================================+===============+ | Bit | Description | Reference | +======+=================================+===============+ +------+---------------------------------+---------------+ | TBA1 | F (BSID-FALLBACK-CAPABILITY) | This document | +------+---------------------------------+---------------+ | TBA2 | T (TRANSIT-ELIGIBLE-CAPABILITY) | This document | +------+---------------------------------+---------------+ Table 1 8.2. TE-PATH-BINDING TLV Flag IANA maintains a registry, named "TE-PATH-BINDING TLV Flag Field", within the "Path Computation Element Protocol (PCEP) Numbers" registry group to manage the Flags field of the TE-PATH-BINDING TLV. IANA is requested to make the following assignments: +======+=================================+===============+ | Bit | Description | Reference | +======+=================================+===============+ +------+---------------------------------+---------------+ | TBA3 | A (Allocated) | This document | +------+---------------------------------+---------------+ | TBA4 | D (Down on BSID Unavailability) | This document | +------+---------------------------------+---------------+ | TBA5 | F (Fallback) | This document | +------+---------------------------------+---------------+ Table 2 8.3. LSP-EXTENDED-FLAG TLV Flags IANA maintains a registry, named "LSP-EXTENDED-FLAG TLV Flag Field", within the "Path Computation Element Protocol (PCEP) Numbers" registry group to manage the Flags field of the LSP-EXTENDED-FLAG TLV. IANA is requested to make the following assignments: +======+======================+===============+ | Bit | Description | Reference | +======+======================+===============+ +------+----------------------+---------------+ | TBA6 | E (Explicit) | This document | +------+----------------------+---------------+ | TBA7 | T (Transit Eligible) | This document | +------+----------------------+---------------+ Table 3 Sidor, et al. Expires 4 September 2025 [Page 9] Internet-Draft STATE-REPORTING-EXTENSIONS March 2025 9. References 9.1. Normative References [I-D.ietf-pce-pcep-yang] Dhody, D., Beeram, V. P., Hardwick, J., and J. Tantsura, "A YANG Data Model for Path Computation Element Communications Protocol (PCEP)", Work in Progress, Internet-Draft, draft-ietf-pce-pcep-yang-30, 26 January 2025, . [I-D.ietf-pce-stateful-interdomain] Dugeon, O., Meuric, J., Lee, Y., and D. Ceccarelli, "PCEP Extension for Stateful Inter-Domain Tunnels", Work in Progress, Internet-Draft, draft-ietf-pce-stateful- interdomain-06, 6 January 2025, . [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, . [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, . Sidor, et al. Expires 4 September 2025 [Page 10] Internet-Draft STATE-REPORTING-EXTENSIONS March 2025 [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, . [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, . [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, . [RFC9357] Xiong, Q., "Label Switched Path (LSP) Object Flag Extension for Stateful PCE", RFC 9357, DOI 10.17487/RFC9357, February 2023, . [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 [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, . Appendix A. Contributors Rajesh Melarcode Venkateswaran Cisco Systems, Inc. Email: rmelarco@cisco.com Andrew Stone Nokia Email: andrew.stone@nokia.com Authors' Addresses Sidor, et al. Expires 4 September 2025 [Page 11] Internet-Draft STATE-REPORTING-EXTENSIONS March 2025 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 4 September 2025 [Page 12]