Internet-Draft STATE-REPORTING-EXTENSIONS July 2025
Sidor, et al. Expires 5 January 2026 [Page]
Workgroup:
PCE Working Group
Internet-Draft:
draft-sidor-pce-lsp-state-reporting-extensions-03
Published:
Intended Status:
Standards Track
Expires:
Authors:
S. Sidor
Cisco Systems, Inc.
Z. Ali
Cisco Systems, Inc.
C. Li
Huawei Technologies
M. Koldychev
Ciena Corporation
A. Stone
Nokia

LSP State Reporting Extensions in Path Computation Element Communication Protocol (PCEP)

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 Label Switched Path (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:

These extensions aim to address the existing gaps, enhancing the overall functionality and operational efficiency of PCEP.

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 5 January 2026.

Table of Contents

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.

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).

Additionally, this document specifies a set of extensions to PCEP to enhance the accuracy of path computations by considering LSP transit eligibility, for example as described in case of LSP stitching in [I-D.ietf-pce-stateful-interdomain].

The mechanisms described in this document are applicable to all path setup types.

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

The following terminologies are used in this document:

3. Object Formats

3.1. STATEFUL-PCE-CAPABILITY TLV

A new flag is proposed for the STATEFUL-PCE-CAPABILITY TLV, originally defined in Section 5.4 of [RFC8231].

  • 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 4.2.

3.2. LSP-EXTENDED-FLAG TLV

New flags are introduced in the LSP-EXTENDED-FLAG TLV, which was initially defined in Section 3.1 of [RFC9357].

4. Operation

4.1. Explicit or Dynamic Path

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 a 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.

4.2. LSP Transit Eligibility

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] and [RFC8231] 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 or 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] and [RFC8231] are applicable to mechanisms defined in this document.

5.4. Impact On Network Operations

The mechanisms defined in [RFC5440] and [RFC8231] 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 [RFC8231] and [RFC5440] are applicable to this document. No additional security measures are required.

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:

Table 1
Bit Description Reference
TBA1 T (TRANSIT-ELIGIBLE-CAPABILITY) This document

8.2. 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:

Table 2
Bit Description Reference
TBA2 E (Explicit) This document
TBA3 T (Transit Eligible) This document

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, , <https://datatracker.ietf.org/doc/html/draft-ietf-pce-pcep-yang-30>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <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, , <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, , <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, , <https://www.rfc-editor.org/info/rfc8231>.
[RFC9357]
Xiong, Q., "Label Switched Path (LSP) Object Flag Extension for Stateful PCE", RFC 9357, DOI 10.17487/RFC9357, , <https://www.rfc-editor.org/info/rfc9357>.

9.2. Informative References

[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-07, , <https://datatracker.ietf.org/doc/html/draft-ietf-pce-stateful-interdomain-07>.
[RFC7942]
Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", BCP 205, RFC 7942, DOI 10.17487/RFC7942, , <https://www.rfc-editor.org/info/rfc7942>.

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
Zafar Ali
Cisco Systems, Inc.
Cheng Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing
100095
China
Mike Koldychev
Ciena Corporation
385 Terry Fox Dr.
Kanata Ontario K2K 0L1
Canada
Andrew Stone
Nokia