Update to Automatic Bandwidth Adjustment procedure of Stateful PCE
draft-peng-pce-stateful-pce-autobw-update-01

PCE Working Group                                                S. Peng
Internet-Draft                                       Huawei Technologies
Updates: 8733 (if approved)                                     D. Dhody
Intended status: Standards Track                                  Huawei
Expires: 27 June 2024                                          R. Gandhi
                                                     Cisco Systems, Inc.
                                                        25 December 2023

   Update to Automatic Bandwidth Adjustment procedure of Stateful PCE
              draft-peng-pce-stateful-pce-autobw-update-01

Abstract

   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.  But it lacks a
   mechanism to explicitly remove an attribute identified by the sub-
   TLV.

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

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 27 June 2024.

Copyright Notice

   Copyright (c) 2023 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.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Updated Procedures  . . . . . . . . . . . . . . . . . . . . .   5
   4.  Extensions  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .   6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  AUTO-BANDWIDTH-CAPABILITY TLV Flag Field  . . . . . . . .   7
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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 operations - Passive
   stateful PCE and Active stateful PCE.  Further, [RFC8281] describes
   the setup, maintenance and teardown of PCE-Initiated LSPs for the
   stateful PCE model.

   [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

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   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 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
   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.

   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].

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     +======+=====+==========================+======================+
     | 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

   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 the default value is set for the sub-TLV:

      -  Restore to the default values

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

      -  Remove the associated attribute

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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:

   A special value of all zeros in the value portion of the sub-TLV
   indicates 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.  Extensions

   The 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 if they can use the updated procedures defined in this document.

5.  Example

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

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   *  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 sec, the default value)

   *  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 as 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.

6.  Backward Compatibility

   Note that to achieve the same objective, an [RFC8733] compliant
   implementation could send a PCEP message without AUTO-BANDWIDTH-
   ATTRIBUTES TLV first and then include the AUTO-BANDWIDTH-ATTRIBUTES
   TLV with the updated sub-TLV.

   An existing implementation of [RFC8733] that does not support this
   update (Z flag is not set) could consider a special value of all
   zeros in the sub-TLV to be a malformed sub-TLV thus ignoring it and
   keeping the previous value.  A PCEP speaker SHOULD use other
   techniques in this case.

7.  Security Considerations

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

8.  IANA Considerations

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8.1.  AUTO-BANDWIDTH-CAPABILITY TLV Flag Field

   [RFC8733] defines the AUTO-BANDWIDTH-CAPABILITY TLV.  IANA created a
   subregistry to manage the Flag field of the AUTO-BANDWIDTH-CAPABILITY
   TLV within the "Path Computation Element Protocol (PCEP) Numbers"
   registry.  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

9.  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/rfc/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/rfc/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/rfc/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/rfc/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/rfc/rfc8281>.

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   [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/rfc/rfc8733>.

Appendix A.  Acknowledgments

   TBD

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

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