PCE Working Group S. Peng Internet-Draft Huawei Technologies Updates: 8733 (if approved) D. Dhody Intended status: Standards Track Huawei Expires: 8 June 2025 R. Gandhi Cisco Systems, Inc. 5 December 2024 Update to Automatic Bandwidth Adjustment procedure of Stateful PCE draft-ietf-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. However, 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 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 8 June 2025. Copyright Notice Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved. Peng, et al. Expires 8 June 2025 [Page 1] Internet-Draft Auto-BW-Update December 2024 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 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Updated Procedures . . . . . . . . . . . . . . . . . . . . . 5 4. Extensions . . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . . . 6 5.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . . . 6 5.3. Example 3 . . . . . . . . . . . . . . . . . . . . . . . . 7 6. Backward Compatibility . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 8.1. AUTO-BANDWIDTH-CAPABILITY TLV Flag Field . . . . . . . . 7 9. Normative References . . . . . . . . . . . . . . . . . . . . 8 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 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 Peng, et al. Expires 8 June 2025 [Page 2] Internet-Draft Auto-BW-Update December 2024 '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 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]. Peng, et al. Expires 8 June 2025 [Page 3] Internet-Draft Auto-BW-Update December 2024 +======+=====+==========================+======================+ | 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 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 Peng, et al. Expires 8 June 2025 [Page 4] Internet-Draft Auto-BW-Update December 2024 * 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: 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 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 - Peng, et al. Expires 8 June 2025 [Page 5] Internet-Draft Auto-BW-Update December 2024 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. 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 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. 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. Peng, et al. Expires 8 June 2025 [Page 6] Internet-Draft Auto-BW-Update December 2024 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. 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. 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. 7. Security Considerations This document does not add any substantial new security concerns beyond those already discussed in [RFC8733]. 8. IANA Considerations 8.1. 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 Peng, et al. Expires 8 June 2025 [Page 7] Internet-Draft Auto-BW-Update December 2024 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, . [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, DOI 10.17487/RFC5440, March 2009, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [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, . [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, . [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, . Peng, et al. Expires 8 June 2025 [Page 8] Internet-Draft Auto-BW-Update December 2024 Appendix A. Acknowledgments Thanks to Aijun Wang, Andrew Stone, and Luis Miguel Contreras Murillo for their review comments. 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 8 June 2025 [Page 9]