PCEP Extensions to support BFD parameters
draft-ietf-pce-pcep-bfd-parameters-01

PCE Working Group                                             M. Fizgeer
Internet-Draft                                                 O. Bachar
Intended status: Standards Track                   Ribbon Communications
Expires: 19 February 2026                                 18 August 2025

               PCEP Extensions to support BFD parameters
                 draft-ietf-pce-pcep-bfd-parameters-01

Abstract

   This document proposes extension to PCEP to configure LSP parameters.
   Some of LSP parameters are needed to configure S-BFD for candidate
   paths.  Each candidate path is identified in PCEP by its uniquely
   assigned PLSP-ID.  The mechanism proposed in this document is
   applicable to to all path setup types.  This extension can work with
   ifferent PCEP Path Setup Types but especially suitable for Segment
   Routing (SR-MPLS, SRv6)..

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.

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
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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on 19 February 2026.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Overview of Protocol Extensions . . . . . . . . . . . . . . .   4
     4.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Processing  . . . . . . . . . . . . . . . . . . . . . . .   4
     4.3.  Objects and TLVs  . . . . . . . . . . . . . . . . . . . .   5
       4.3.1.  LSP S-BFD Capability  . . . . . . . . . . . . . . . .   5
       4.3.2.  S-BFD parameters  . . . . . . . . . . . . . . . . . .   6
   5.  Error Handling  . . . . . . . . . . . . . . . . . . . . . . .   8
   6.  Implementation Note . . . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  PCEP TLV Type Indicators  . . . . . . . . . . . . . . . .   8
     7.2.  PCEP Errors . . . . . . . . . . . . . . . . . . . . . . .   9
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   9.  Implementation Status [Note to the RFC Editor - remove this
           section before publication, as well as remove the reference
           to RFC 7942.] . . . . . . . . . . . . . . . . . . . . . .  10
   10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .  10
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     11.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Appendix A.  Contributors . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   Path Computation Element (PCE) Communication Protocol (PCEP)
   [RFC5440] enables the communication between a Path Computation Client
   (PCC) and a Path Computation Element (PCE), or between two PCEs based
   on the PCE architecture [RFC4655].

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   PCEP Extensions for the Stateful PCE Model [RFC8231] describes a set
   of extensions to PCEP to enable active control of Multiprotocol Label
   Switching Traffic Engineering (MPLS-TE) and Generalized MPLS (GMPLS)
   tunnels.  [RFC8281] describes the setup and teardown of PCE-initiated
   LSPs under the active stateful PCE model, without the need for local
   configuration on the PCC, thus allowing for dynamic centralized
   control of a network.

   PCEP Extensions for Segment Routing [RFC8664] specifies extensions to
   the Path Computation Element Protocol (PCEP) that allow a stateful
   PCE to compute and initiate Traffic Engineering (TE) paths, as well
   as a PCC to request a path subject to certain constraint(s) and
   optimization criteria in SR networks.

   PCEP Extensions for Establishing Relationships Between Sets of LSPs
   [RFC8697] introduces a generic mechanism to create a grouping of LSPs
   which can then be used to define associations between a set of LSPs
   and a set of attributes (such as configuration parameters or
   behaviors) and is equally applicable to stateful PCE (active and
   passive modes) and stateless PCE.

   This document specifies PCEP extensions to signal additional
   information to configure LSP attributes.  This is accomplished via
   the use of the existing LSPA object, by defining a new capability and
   new TLVs.  This is applicable and need for stateful PCE.

2.  Terminology

   The following terminologies are used in this document:

   *  PCC: Path Computation Client.  Any client application requesting a
      path computation to be performed by a Path Computation Element.

   *  PCE: Path Computation Element.  An entity (component, application,
      or network node) that is capable of computing a network path or
      route based on a network graph and applying computational
      constraints.

   *  PCEP: Path Computation Element Protocol.

   *  PCEP Tunnel: The entity.  identified by the PLSP-ID, as per [I-
      D.koldychev-pce-operational].

   *  LSP: Label Switched Path.

   *  LSPA: LSP Attributes.

   *  PCT: Path Setup Type.

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3.  Motivation

   S-BFD [RFC7880] protocol is used for detecting failures in different
   tunnels path setup types.  There are several protocol parameters that
   need to be configured and exchanged between PCEP speakers.  As the
   parameters are associated to LSPs or tunnels, they are exchanged via
   PCEP.  The LSPS-BFD-Capability TLV, the LSP-S-BFD TLV and its sub-
   TLVs, defined in this document, allow PCEP speakers to exchange
   additional information about S-BFD.

4.  Overview of Protocol Extensions

4.1.  Overview

   A new option to define S-BFD parameters is defined in this document.

   A PCEP speaker indicates its ability to support S-BFD parameters
   during the PCEP initialization phase, as follows.  When the PCEP
   session is created, it sends an Open message with an OPEN object that
   contains the LSP-S-BFD-Capability TLV (see Section 4.3.1).

   If a PCEP speaker receives the PCEP LSP-S-BFD-Capability TLV with B
   flag = 1 in the Open object, then it means its peer is capable to
   receive and to send S-BFD TLVs towards that peer.

   If a PCEP speaker has not received this TLV in the Open object, or if
   it receives it with B flag set to 0, then it MUST NOT send any S-BFD
   TLVs in LSPA object towards that peer.

   Defining S-BFD parameters via PCEP MAY be also used together with a
   PCE as a Central Controller (PCECC) architecture and procedures
   [RFC9050].

4.2.  Processing

   If a PCEP speaker is capable of S-BFD and its peer is capable of
   S-BFD, then the PCEP speaker MAY send LSP-S-BFD TLV towards that
   peer, to report the S-BFD state (Enabled/Disabled) for the configured
   LSP.  The LSP-S-BFD TLV SHALL be sent as an optional TLV in the LSPA
   object.  A PCC SHALL send it in the PCRpt message.

   A PCE SHALL send it in the PCInit or in the PCUpd message.  If the
   LSP-S-BFD TLV is received from a PCEP peer with the B flag set to 1,
   then S-BFD SHALL be applied for specified LSP.  If PCC received this
   TLV via PCUpd with B=0 and there is no S-BFD applied for the LSP,
   then the PCC SHALL ignore the TLV.

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   If PCE received this TLV with B=0 and there is no S-BFD applied for
   the LSP (editing a PCC-initiated LSP) then it MAY ignore it.  If B=0
   and LSP-BFD-Parameters sub-TLV is received, then the PCEP speaker MAY
   ignore the sub-TLV.  Ignoring or saving the S-BFD configuration is
   implementation decision.

   Editor note: Alternatively, it can be defined implicitly as follows:
   If the LSP-S-BFD TLV is not received from PCEP peer but there is
   S-BFD for that LSP then S-BFD SHALL be removed for specified LSP.

4.3.  Objects and TLVs

4.3.1.  LSP S-BFD Capability

   The LSP-S-BFD-Capability TLV is an optional TLV.  It MAY be carried
   within an OPEN object sent by PCEP speaker in an Open message to a
   PCEP peer to indicate it supports S-BFD capability.  A legacy PCEP
   speaker (that does not recognize the LSP-S-BFD-Capability TLV) MUST
   ignore the TLV in accordance with [ RFC5440].

    The LSP-S-BFD-Capability TLV has the following format:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Type              |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Reserved          |B|  Num of PSTs  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     PST#1     |      ...      |     PST#N     |    Padding    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type: TBD1

   Length: 4

   B flag: A PCEP speaker sets this bit to 1 to indicate that it is
   capable of S-BFD, and it supports configuring the S-BFD via PCEP

   Num of PSTs: The number of PSTs in the following list, excluding
   padding.

   List of PSTs: A list of the PSTs that the PCEP speaker supports.
   Each PST is a single byte in length.  Duplicate entries in this list
   MUST be ignored.  The PCEP speaker MUST pad the list with zeros so
   that it is a multiple of four bytes in length.

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   This document defines the following PST value: * PST = 0: Path is set
   up using the RSVP-TE signaling protocol * PST = 1: Path is set up
   using the SR-TE

   Any PST defined in this capability MUST be defined in PCEP session
   supported PST capabilitiy list.  If some PST value in this list is
   not defined PCEP session supported PST capabilitiy list, PCEP speker
   MUST send a PCErr message with Error-Type = 21 (Invalid traffic
   engineering path setup type) and Error-value = 2 (Mismatched path
   setup type) and close the PCEP session.

   If the PCEP speaker and its peer have no S-BFD PSTs in common, then
   PCEP speaker cannot define S-BFD in any created LSP using PCEP.
   Creation locally LSP with S-BFD in PCC may be decision as local
   ploicy, but S-BFD parameters SHALL NOT be sent to PCE via PCEP.

4.3.2.  S-BFD parameters

4.3.2.1.  LSP S-BFD TLV

   The PCEP LSP-S-BFD TLV is an optional TLV.  It MAY be carried within
   the LSPA object.

   The PCEP LSP-S-BFD TLV has the following format:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             Type              |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Reserved                          |B|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      //                     Optional sub-TLVs                       //
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type: TBD2

   Length: The total length in bytes of the remainder of the TLV, that
   is, excluding the Type and Length fields.

   B flag: Enable/Disable S-BFD for this LSP.  If B=1 then S-BFD will be
   enabled.  If B=0 then S-BFD will be disabled for that LSP.  If the
   PCEP speaker received LSP-S-BFD TLV from PCEP peer with B flag is set
   to 0, then S-BFD SHALL be removed (in case of PCE update) or SHALL
   NOT be applied (in case of PCE initiated message) for specified LSP

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4.3.2.2.  LSP-S-BFD Parameters sub-TLV

   The PCEP LSP-S-BFD-Parameters sub-TLV is optional.  It MAY be carried
   within the LSP-S-BFD TLV.  The PCEP LSP-S-BFD-Parameters sub-TLV has
   the following format:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             Type              |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Min Tx Interval                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Reserved                 |   Multiplier |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Type: TBD3
  Length: 8
  Min Tx Interval: 32 bits - Specify the Minimal Transmit Interval
  (microseconds).

  Multiplier: 1..255

   If B=0 and LSP-S-BFD-Parameters sub-TLV is received, then the PCEP
   speaker SHALL ignore the sub-TLV.

4.3.2.3.  LSP-S-BFD-Discriminator sub-TLV

   The PCEP LSP-S-BFD-Discriminator sub-TLV and is optional.  It MAY be
   carried within the LSP-S-BFD TLV.  The PCEP LSP-S-BFD-Discriminator
   sub-TLV has the following format:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             Type              |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                      Remote Discriminator                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type: TBD4
   Length: 4
   Remote Discriminator: 32 bits

   If speaker sends S-BFD TLV with B flag 1, then LSP-S-BFD-
   Discriminator sub TLV is MUST.

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   In this case if this sub TLV is missed, PCEP speaker SHALL Error-
   Type=6 "Mandatory Object missing" with Error-value TBD9 "LSP-S-BFD-
   Discriminator".

   If B flag is 0 and LSP-S-BFD-Discriminator sub-TLV is received, then
   the PCEP speaker SHALL ignore the LSP-S-BFD-Discriminator sub-TLV.

5.  Error Handling

   If a PCEP speaker has not received S-BFD-Capability TLV from a peer
   in the Open object, and it received an LSP S-BFD TLV (see
   Section 4.3.2.1) from that peer, then it MUST ignore the content of
   the LSP S-BFD TLV, and it MUST return a PCErr message with Error-
   Type=19 "Invalid Operation" with Error-value = TBD5 "S-BFD capability
   is not negotiated".

   If Multiplier value in the LSP-S-BFD-Parameters sub-TLV is not in the
   legal range (1..255), then the PCEP Speaker MUST return a PCErr
   message with Error-Type=23 "Bad parameter value" and Error-value =
   TBD6 "Multiplier is out of range".

6.  Implementation Note

   In some implementations there is limitation that LSPs in the same
   association group must have same S-BFD parameter values.  If either
   the Min Tx Interval, the Multiplier or the Remote Discriminator
   values received in the LSP-BFD Parameters sub-TLVs for LSPs that are
   members in the same Association Group are not identical, then the
   PCEP Speaker SHOULD return a PCErr message with Error-Type=26
   "Association Error" with Error-value TBD7 "Invalid S-BFD parameter
   value"

7.  IANA Considerations

7.1.  PCEP TLV Type Indicators

   This document defines new TLVs and sub-TLVs for carrying additional
   information about S-BFD.  IANA is requested to make the assignment of
   new values for the existing "PCEP TLV Type Indicators" registry as
   follows:

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        +=======+================================+===============+
        | Value | Description                    | Reference     |
        +=======+================================+===============+
        | TBD1  | LSP-S-BFD-Capability TLV       | This document |
        +-------+--------------------------------+---------------+
        | TBD2  | LSP-S-BFD TLV                  | This document |
        +-------+--------------------------------+---------------+
        | TBD3  | LSP-BFD-Parameters sub-TLV     | This document |
        +-------+--------------------------------+---------------+
        | TBD4  | LSP-S-BFD-DISCRIMINATOR sub-TLV| This document |
        +-------+--------------------------------+---------------+

                                  Figure 1

7.2.  PCEP Errors

   This document defines new Error-Values within the different Error-
   Types.  IANA is requested to allocate new types:

   +============+=============+=========================+===========+
   | Error Type | Error Value | Meaning                 | Reference |
   +============+=============+=========================+===========+
   | 19         | TBD5        | S-BFD capability is     | This      |
   |            |             | not negotiated          | document  |
   +------------+-------------+-------------------------+-----------+
   | 23         | TBD6        | Multiplier is out of    | This      |
   |            |             | range                   | document  |
   +------------+-------------+-------------------------+-----------+
   | 26         | TBD7        | Invalid S-BFD           | This      |
   |            |             | parameter value         | document  |
   +------------+-------------+-------------------------+-----------+
   | 23         | TBD8        | Remote Discriminator    | This      |
   |            |             | is out of range         | document  |
   +------------+-------------+-------------------------+-----------+
   | 6          | TBD9        | LSP-S-BFD-Discriminator | This      |
   |            |             | missing                 | document  |
   +------------+-------------+-------------------------+-----------+

8.  Security Considerations

   This document defines new LSP parameters, which do not add any new
   security concerns beyond those discussed in [RFC5440], [RFC8231],
   [RFC8664], [RFC5880] and [RFC8697] in itself.

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9.  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.

   In some implementations there is limitation that LSPs in the same
   association group must have same S-BFD parameter values.

   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".

 9.1. Ribbon Implementation
        Organization: Ribbon Communications
        Implementation: Head-end (PCC) and controller (PCE).
        Description: All features supported with limitation that LSPs in
    the same association group must have same S-BFD parameter values
        Maturity Level: Production.
        Coverage: Full.
        Contact: marina.fizgeer@rbbn.com

10.  Acknowledgement

   Would like to thank Avantika Sushil, Alexander Ferdman, Itay Katz,
   Galina Mintz and Boris Khasanov for review and suggestions.

11.  References

11.1.  Normative References

   [RFC7880]  Pignataro, C., "Key words for use in RFCs to Indicate
              Requirement Levels", RFC 7880, DOI DOI 10.17487/RFC7880,
              July 2016, <http://www.rfc-editor.org/info/rfc7880>.

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   [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>.

   [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>.

   [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>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <https://www.rfc-editor.org/info/rfc5880>.

   [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>.

   [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>.

11.2.  Informative References

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   [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>.

Appendix A.  Contributors

   Dhruv Dhody
     Huawei Technologies Divyashree Techno Park, Whitefield Bangalore,
     Karnataka 560066 India

     Email: dhruv.ietf@gmail.com

Authors' Addresses

   Marina Fizgeer
   Ribbon Communications
   Hasivim 30,
   Petah-Tikva
   Israel
   Email: marina.fizgeer@rbbn.com

   Orly Bachar
   Ribbon Communications
   Hasivim 30,
   Petah-Tikva
   Israel
   Email: orly.bachar@rbbn.com

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