Update to Automatic Bandwidth Adjustment Procedure of Stateful PCE for MPLS-TE and SR-TE LSPs
draft-ietf-pce-stateful-pce-autobw-update-03

PCE Working Group                                                S. Peng
Internet-Draft                                       Huawei Technologies
Updates: 8733 (if approved)                                     D. Dhody
Intended status: Standards Track                                  Huawei
Expires: 9 May 2026                                            R. Gandhi
                                                     Cisco Systems, Inc.
                                                         5 November 2025

 Update to Automatic Bandwidth Adjustment Procedure of Stateful PCE for
                         MPLS-TE and SR-TE LSPs
              draft-ietf-pce-stateful-pce-autobw-update-03

Abstract

   The Stateful PCE extensions allow Stateful control of Traffic
   Engineering (TE) LSPs using PCEP for RSVP-TE and Segment Routing (SR)
   (for both MPLS and IPv6 Data planes) for both PCE-Initiated and PCC-
   Initiated LSPs.

   Extensions to the Path Computation Element Communication Protocol
   (PCEP) for MPLS-TE Label Switched Path (LSP) Automatic Bandwidth
   Adjustments with Stateful PCE are defined in RFC 8733.  It defines
   the AUTO-BANDWIDTH-ATTRIBUTES TLV and a set of sub-TLVs for each of
   the attributes.  The sub-TLVs are included if there is a change since
   the last information sent in the PCEP message.  However, it lacks a
   mechanism to remove an attribute identified by the sub-TLV
   explicitly.

   This document updates RFC 8733 by defining the behaviour to remove an
   attribute explicitly.

   In addition, this document updates RFC 8733 by applying the PCEP
   extensions to SR-TE LSPs (for both MPLS and IPv6 Data planes), in
   addition to MPLS-TE LSPs.

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/.

Peng, et al.               Expires 9 May 2026                   [Page 1]
Internet-Draft             LSP Auto-BW Update              November 2025

   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 9 May 2026.

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.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Updated Procedures  . . . . . . . . . . . . . . . . . . . . .   5
   4.  PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Example 1 . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  Example 2 . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.3.  Example 3 . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Auto-Bandwidth for Segment Routing LSPs . . . . . . . . . . .   7
   7.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  AUTO-BANDWIDTH-CAPABILITY TLV Flag Field  . . . . . . . .   8
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

Peng, et al.               Expires 9 May 2026                   [Page 2]
Internet-Draft             LSP Auto-BW Update              November 2025

1.  Introduction

   [RFC5440] describes the Path Computation Element Communication
   Protocol (PCEP).  PCEP defines the communication between a Path
   Computation Client (PCC) and a Path Computation Element (PCE), or
   between PCEs, enabling computation of Multiprotocol Label Switching
   (MPLS) for Traffic Engineering Label Switched Path (TE LSP)
   characteristics.

   [RFC8231] specifies extensions to PCEP to enable stateful control of
   MPLS TE LSPs.  It describes two modes of operation - Passive stateful
   PCE and Active stateful PCE.  Further, [RFC8281] describes the setup,
   maintenance and teardown of PCE-Initiated LSPs for the stateful PCE
   model.

   PCEP Extensions for Segment Routing (SR) [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 for Segment Routing.
   [RFC9603] extends PCEP for Segment Routing for IPv6 data plane.  As
   specified in [RFC8664], an LSP can be MPLS-TE LSP or SR-TE LSP based
   on the path setup type.  As specified in [RFC9603], the term "LSP"
   used in the PCEP specifications would be equivalent to an SRv6 path
   (represented as a list of SRv6 segments) in the context of supporting
   SRv6 in PCEP using SRv6 path setup type.

   [RFC8733] describes the auto-bandwidth feature that allows automatic
   and dynamic adjustment of the TE LSP bandwidth reservation based on
   the volume of traffic flowing through the LSP.  It describes PCEP
   extensions for auto-bandwidth adjustment when employing an active
   stateful PCE for both PCE-initiated [RFC8281] and PCC-initiated LSPs.
   It defines the AUTO-BANDWIDTH-ATTRIBUTES TLV that provides the
   'configurable knobs' of the feature, and it can be included as an
   optional TLV in the LSPA object.  The TLV is encoded in all PCEP
   messages for the LSP while the auto-bandwidth adjustment feature is
   enabled.  The absence of the TLV indicates the PCEP speaker wishes to
   disable the feature.  The TLV includes multiple AUTO-BANDWIDTH-
   ATTRIBUTES sub-TLVs defined in [RFC8733].  The AUTO-BANDWIDTH-
   ATTRIBUTES sub-TLVs are included if there is a change since the last
   information was sent in the PCEP message.  It also states that in the
   case of a missing sub-TLV, as per the local policy, either the
   default value or some other operator-configured value is used.

   Since the missing sub-TLV in a subsequent PCEP message is considered
   to indicate as no change, there is no mechanism to remove a
   particular attribute encoded in the sub-TLV.  This document updates
   [RFC8733] to define such a procedure.

Peng, et al.               Expires 9 May 2026                   [Page 3]
Internet-Draft             LSP Auto-BW Update              November 2025

   Note that for the attributes that have an associated default value,
   they could simply encode the default value in the sub-TLV, but this
   cannot be used for the attributes that do not have a default value.

   This document proposes to use a special value of all zeros to
   indicate "restore to default", which could mean going back to the
   default values or removal of the attribute itself.

   The following table includes the sub-TLVs and the default values as
   per [RFC8733].

     +======+=====+==========================+======================+
     | Type | Len |                     Name |              Default |
     +======+=====+==========================+======================+
     | 1    |  4  |          Sample-Interval |          300 seconds |
     +------+-----+--------------------------+----------------------+
     | 2    |  4  |      Adjustment-Interval |        86400 seconds |
     +------+-----+--------------------------+----------------------+
     | 3    |  4  | Down-Adjustment-Interval |  Adjustment-Interval |
     +------+-----+--------------------------+----------------------+
     | 4    |  4  |     Adjustment-Threshold |                 none |
     +------+-----+--------------------------+----------------------+
     | 5    |  8  |    Adjustment-Threshold- |                5%, 0 |
     |      |     |               Percentage |                      |
     +------+-----+--------------------------+----------------------+
     | 6    |  4  |         Down-Adjustment- | Adjustment-Threshold |
     |      |     |                Threshold |                      |
     +------+-----+--------------------------+----------------------+
     | 7    |  8  |         Down-Adjustment- |          Adjustment- |
     |      |     |     Threshold-Percentage | Threshold-Percentage |
     +------+-----+--------------------------+----------------------+
     | 8    |  4  |        Minimum-Bandwidth |                    0 |
     +------+-----+--------------------------+----------------------+
     | 9    |  4  |        Maximum-Bandwidth |                 none |
     +------+-----+--------------------------+----------------------+
     | 10   |  8  |       Overflow-Threshold |                 none |
     +------+-----+--------------------------+----------------------+
     | 11   |  8  |      Overflow-Threshold- |                 none |
     |      |     |               Percentage |                      |
     +------+-----+--------------------------+----------------------+
     | 12   |  8  |      Underflow-Threshold |                 none |
     +------+-----+--------------------------+----------------------+
     | 13   |  8  |     Underflow-Threshold- |                 none |
     |      |     |               Percentage |                      |
     +------+-----+--------------------------+----------------------+

                                 Table 1

Peng, et al.               Expires 9 May 2026                   [Page 4]
Internet-Draft             LSP Auto-BW Update              November 2025

   Thus, the use of the special value of all zeros in the value portion
   of the sub-TLV can be used to indicate "restore to default", which
   could mean :

   *  if an explicit default value is set for the sub-TLV:

      -  Restore to the default values

   *  if the default value is set to another sub-TLV value:

      -  Remove the associated attribute

   *  if there is no default value for the sub-TLV:

      -  Remove the associated attribute

   The value portion of the sub-TLV consists of encoded data (of the
   specified length and type), which is set to zero.  In cases where the
   value portion of the sub-TLV contains multiple fields, all fields are
   set to zero.

2.  Conventions

   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.

3.  Updated Procedures

   Section 5.2 of [RFC8733] defines the AUTO-BANDWIDTH-ATTRIBUTES TLV
   and its associated sub-TLVs.

   This document updates [RFC8733] by adding this text at the end of
   paragraph 3 in section 5.2:

Peng, et al.               Expires 9 May 2026                   [Page 5]
Internet-Draft             LSP Auto-BW Update              November 2025

   A special value of all zeros in the value portion of the sub-TLV
   indicates that the attribute identified by the sub-TLV is restored
   to the default value. The value of all zeros is not considered an
   invalid value and MUST be checked before individual fields.

   For the attributes that have an associated default value, on
   receiving such a sub-TLV, the PCEP speaker MUST consider it as
   an instruction to restore to the default values. Note that, the
   PCEP speaker could also set the default value in the sub-TLV
   itself.

   For the attributes that do not have an associated default value,
   on receiving such a sub-TLV, the PCEP speaker MUST consider it
   as a removal of the specific auto-bandwidth attribute.

4.  PCEP Extensions

   Section 5.1.1 of [RFC8733] defines the AUTO-BANDWIDTH-CAPABILITY TLV
   as an optional TLV for use in the OPEN Object for auto-bandwidth
   adjustment.  This document adds a new flag -

   Z (TBD): The flag indicates that a PCEP speaker supports the use of
   the special value of all zeros in the value field as specified in
   this document.

   The presence of the Z flag can give a clear indication to the PCEP
   peer whether they can use the updated procedures defined in this
   document.

5.  Examples

5.1.  Example 1

   Consider an LSP with the following information in the AUTO-BANDWIDTH-
   ATTRIBUTES TLV in the PCInitiate message:

   *  Sample-Interval: 600 (in sec)

   *  Adjustment-Interval: 172800 (2 days in sec)

   *  Adjustment-Threshold: 0x49989680 (10 Mbps in bps)

   Now, if the PCE would like to not use the Adjustment-Thresholds
   feature for the LSP and set the Adjustment-Interval to 1 day, it
   could send the AUTO-BANDWIDTH-ATTRIBUTES TLV in the PCUpd message
   with the following sub-TLVs:

   *  Adjustment-Interval: 86400 (1 day in seconds, the default value)

Peng, et al.               Expires 9 May 2026                   [Page 6]
Internet-Draft             LSP Auto-BW Update              November 2025

   *  Adjustment-Threshold: 0x0

   On receiving the special value of all zeros in the value portion of
   the Adjustment-Threshold sub-TLV, the PCEP speaker would consider
   that to be the removal of the Adjustment-Threshold feature.

   Note that, the PCE could also set the Adjustment-Interval: 0x0
   instead of the default value to trigger the restore to default.  The
   Sample-Interval remains unchanged.

5.2.  Example 2

   Consider an LSP with the following information in the AUTO-BANDWIDTH-
   ATTRIBUTES TLV in the PCInitiate message:

   *  Sample-Interval = 1000

   Now, if the PCC receives an update with Sample-Interval with the
   special value of all zeros, this will lead to Sample-Interval being
   set to the default value of 300.

5.3.  Example 3

   Consider an LSP with the following information in the AUTO-BANDWIDTH-
   ATTRIBUTES TLV in the PCInitiate message:

   *  Adjustment-Threshold: 0x49989680 (10 Mbps in bps)

   *  Down-Adjustment-Threshold: 0x93312D00 (20 Mbps in bps)

   Now, if the PCC receives an update with Down-Adjustment-Threshold
   with the special value of all zeros, this will lead to the removal of
   the Down-Adjustment-Threshold attribute and only Adjustment-Threshold
   remains.

   If the PCC receives an update with Adjustment-Threshold with the
   special value of all zeros, this will lead to the removal of the
   Adjustment-Threshold attribute as well.

6.  Auto-Bandwidth for Segment Routing LSPs

   The PCEP extensions defined in [RFC8733] for the MPLS-TE LSP path
   setup type, apply equally to the SR-TE LSP path setup types, for both
   SR-MPLS [RFC8664] and SRv6 [RFC9603] data planes.

Peng, et al.               Expires 9 May 2026                   [Page 7]
Internet-Draft             LSP Auto-BW Update              November 2025

7.  Backward Compatibility

   Note that to achieve the same objective, an [RFC8733] compliant
   implementation could send a PCEP message without the AUTO-BANDWIDTH-
   ATTRIBUTES TLV first and then include the AUTO-BANDWIDTH-ATTRIBUTES
   TLV with the updated sub-TLV.  This is the same as "turning it off
   and on again", but would cause unnecessary path computation churn
   (compared to targeted removal of the attribute).

   An existing implementation of [RFC8733] that does not support this
   update (where the Z flag is not set) will not recognize or use the
   special value of all zeros in the sub-TLV.  If such a sub-TLV is
   received, as per [RFC8733], implementations may treat the sub-TLV as
   malformed and ignore it.

8.  Security Considerations

   This document does not add any substantial new security concerns
   beyond those already discussed in [RFC8733].

9.  IANA Considerations

9.1.  AUTO-BANDWIDTH-CAPABILITY TLV Flag Field

   [RFC8733] defines the AUTO-BANDWIDTH-CAPABILITY TLV.  IANA created a
   registry to manage the Flag field of the AUTO-BANDWIDTH-CAPABILITY
   TLV within the "Path Computation Element Protocol (PCEP) Numbers"
   registry group.  This document requests IANA to allocate a new bit in
   the AUTO-BANDWIDTH-CAPABILITY TLV Flag Field registry, as follows.
   IANA is requested to make allocations starting from the least
   significant bit (31).

        +=====+=====================================+============+
        | Bit | Description                         | Reference  |
        +=====+=====================================+============+
        | TBD | Z flag (special value of all zeros) | [This.I-D] |
        +-----+-------------------------------------+------------+

                                 Table 2

10.  References

10.1.  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>.

Peng, et al.               Expires 9 May 2026                   [Page 8]
Internet-Draft             LSP Auto-BW Update              November 2025

   [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>.

   [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>.

   [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>.

   [RFC8733]  Dhody, D., Ed., Gandhi, R., Ed., Palle, U., Singh, R., and
              L. Fang, "Path Computation Element Communication Protocol
              (PCEP) Extensions for MPLS-TE Label Switched Path (LSP)
              Auto-Bandwidth Adjustment with Stateful PCE", RFC 8733,
              DOI 10.17487/RFC8733, February 2020,
              <https://www.rfc-editor.org/info/rfc8733>.

10.2.  Informative References

   [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>.

   [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>.

Appendix A.  Acknowledgments

   Thanks to Aijun Wang, Andrew Stone, and Luis Miguel Contreras Murillo
   for their review comments.

Peng, et al.               Expires 9 May 2026                   [Page 9]
Internet-Draft             LSP Auto-BW Update              November 2025

Authors' Addresses

   Shuping Peng
   Huawei Technologies
   Huawei Bld., No.156 Beiqing Rd.
   Beijing
   100095
   China
   Email: pengshuping@huawei.com

   Dhruv Dhody
   Huawei
   India
   Email: dhruv.ietf@gmail.com

   Rakesh Gandhi
   Cisco Systems, Inc.
   Canada
   Email: rgandhi@cisco.com

Peng, et al.               Expires 9 May 2026                  [Page 10]