Binding Label/Segment Identifier (SID) Extensions in Path Computation Element Communication Protocol (PCEP)
draft-sidor-pce-binding-label-sid-extensions-01

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,
              <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>.

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, <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>.

   [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>.

   [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>.

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

   [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,
              <https://www.rfc-editor.org/info/rfc9604>.

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,
              <https://www.rfc-editor.org/info/rfc4655>.

   [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>.

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]