PCE Working Group Y. Liu Internet Draft China Mobile Intended status: Standards Track C. Lin Expires: April 14, 2024 New H3C Technologies Y. Qiu New H3C Technologies October 11, 2023 PCEP Extension to Support Signaling Candidate Path Threshold Constraints of SR Policy draft-liu-pce-sr-policy-cp-threshold-00 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), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on April 14 2024. Copyright Notice Copyright (c) 2023 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 (http://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 liu, et al. Expires April, 2024 [Page 1] Internet-Draft PCEP for CP Threshold Constraints October 2023 respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Abstract This document defines the extension of PCEP to signal the threshold and metric constraint parameters of candidate paths for SR Policy to support flexible path selection. Table of Contents 1. Introduction...................................................2 2. Terminology....................................................3 3. PCEP Extensions................................................3 3.1. SR Bandwidth Constraint TLV...............................3 3.2. SR Metric Constraint TLV..................................4 3.3. SR Segment List Bandwidth Constraint TLV..................5 4. IANA Considerations............................................6 5. Security Considerations........................................6 6. References.....................................................7 6.1. Normative References......................................7 6.2. Informative References....................................8 7. Acknowledgments................................................8 Authors' Addresses................................................9 1. Introduction Segment routing (SR) [RFC8402] is a source routing paradigm that explicitly indicates the forwarding path for packets at the ingress node. The ingress node steers packets into a specific path according to the Segment Routing Policy (SR Policy) as defined in [RFC9256]. An SR Policy may have multiple candidate paths that are provisioned or signaled [I-D.ietf-idr-segment-routing-te-policy] [RFC8664] from one of more sources. [I-D.liu-spring-sr-policy-flexible-path-selection] proposes a flexible SR policy candidate path selection method. Based on the real-time resource usage and forwarding quality of candidate paths, the head node can perform dynamic path switching among multiple candidate paths in the SR policy. Multiple threshold parameters for SR Policy candidate path selection are listed in Section 4.1 of [I- D.liu-spring-sr-policy-flexible-path-selection]. PCEP Extensions for Segment Routing [RFC8664] specifies extensions that allow PCEP to work with basic SR-TE paths. liu, et al. Expires April, 2024 [Page 2] Internet-Draft PCEP for CP Threshold Constraints October 2023 PCEP extension to support Segment Routing Policy Candidate Paths [I- D.ietf-pce-segment-routing-policy-cp] specifies extensions that allow PCEP to signal additional attributes of an SR Policy, which are not covered by [RFC8664]. SR Policy is modeled in PCEP as an Association and the SR Candidate Paths are the members of that Association. Thus, the PCE can take computation and control decisions about the Candidate Paths, with the additional knowledge that these Candidate Paths belong to the same SR Policy. This document defines PCEP extensions to signal threshold and metric constraint parameters of candidate path (CP) for an SR Policy. 2. Terminology The definitions of the basic terms are identical to those found in Segment Routing Policy Architecture [RFC9256]. 3. PCEP Extensions As defined in [RFC8697], TE LSPs are associated by adding them to a common association group by a PCEP peer. [I-D.ietf-pce-segment- routing-policy-cp] defines SR Policy Association (SRPA), and the SR Candidate Paths are the members of this Association. This document defines the following three TLVs to signal threshold and metric constraint parameters for candidate paths. * SR Bandwidth Constraint TLV * SR Metric Constraint TLV * SR Segment List Bandwidth Constraint TLV 3.1. SR Bandwidth Constraint TLV The SR Bandwidth Constraint TLV is used to carry the bandwidth threshold constraint parameter of a candidate path. The SR Bandwidth Constraint TLV is an optional TLV for the SRPA object. The format of the SR Bandwidth Constraint TLV is defined as follows: liu, et al. Expires April, 2024 [Page 3] Internet-Draft PCEP for CP Threshold Constraints October 2023 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Bandwidth | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: * Type: to be assigned by IANA * Length: 4 octets * Flags: 1 octet of flags. None are defined at this stage. Flags SHOULD be set to zero on transmission and MUST be ignored on receipt. * Bandwidth: 4 octets which specify the bandwidth threshold in unit of bytes per second in IEEE floating point format. 3.2. SR Metric Constraint TLV The SR Metric Constraint TLV is used to carry the metric Constraint of a candidate path. The SR Metric Constraint TLV is an optional TLV for the SRPA object. The format of the SR Metric Constraint Sub-TLV is defined as follows: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Metric Type | Flags | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Metric Margin | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Metric Bound | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: * Type: to be assigned by IANA * Length: 12 octets liu, et al. Expires April, 2024 [Page 4] Internet-Draft PCEP for CP Threshold Constraints October 2023 * Metric Type: 1-octet field which identifies the type of the metric being used. The metric type code points are listed in Section 8.6 of [I-D.ietf-idr-bgp-ls-sr-policy]. * Flags: 1-octet field that indicates the validity of the metric fields and their semantics. The following bit positions are defined and the other bits MUST be cleared by the originator and MUST be ignored by a receiver. 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |M|A|B| | +-+-+-+-+-+-+-+-+ where: - M-Flag: Indicates that the metric margin allowed is specified when set. - A-Flag: Indicates that the metric margin is specified as an absolute value when set and is expressed as a percentage of the minimum metric when clear. - B-Flag: Indicates that the metric bound allowed for the path is specified when set. * Metric Margin: 4-octet value which indicates the metric margin when the M-flag is set. The metric margin is specified as either an absolute value or as a percentage of the minimum computed path metric based on the A-flag. The metric margin loosens the criteria for minimum metric path calculation up to the specified metric to accommodate for other factors such as bandwidth availability, minimal SID stack depth, and maximizing of ECMP for the SR path computed. * Metric Bound: 4-octet value which indicates the maximum metric that is allowed when the B-flag is set. If the computed path metric crosses the specified bound value, then the path is considered invalid. * RESERVED: 1 octet of reserved bits. SHOULD be set to zero on transmission and MUST be ignored on receipt. 3.3. SR Segment List Bandwidth Constraint TLV The SR Segment List Bandwidth Constraint TLV is an optional TLV for use in the LSP Object for signaling the bandwidth allocated to the specific SID-List. The SR Segment List Bandwidth Constraint TLV has the following format: liu, et al. Expires April, 2024 [Page 5] Internet-Draft PCEP for CP Threshold Constraints October 2023 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Bandwidth | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: * Type: to be assigned by IANA * Length: 4 octets * Bandwidth: 4 octets which specify the bandwidth threshold in unit of bytes per second in IEEE floating point format. 4. IANA Considerations This document defines the new TLVs for carrying additional information about SR Policy and SR Candidate Paths. IANA is requested to make the assignment of new allocations in the existing "PCEP TLV Type Indicators" sub-registry as follows: +=======+==================================+=================+ | Value | Description | Reference | +=======+==================================+=================+ | TBA1 | SR Bandwidth Constraint TLV | This document | +-------+----------------------------------+-----------------+ | TBA2 | SR Metric Constraint TLV | This document | +-------+----------------------------------+-----------------+ | TBA3 | SR Segment List Bandwidth | This document | | | Constraint TLV | | +-------+----------------------------------+-----------------+ 5. Security Considerations [I-D.ietf-pce-segment-routing-policy-cp] has discussed the security considerations for distributing SR Policy through PCEP. This document does not introduce any new security issues. liu, et al. Expires April, 2024 [Page 6] Internet-Draft PCEP for CP Threshold Constraints October 2023 6. References 6.1. Normative References [I-D.ietf-idr-segment-routing-te-policy] Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., Jain, D., and S. Lin, "Advertising Segment Routing Policies in BGP", draft-ietf- idr-segment-routing-te-policy-25 (work in progress), September 2023. [I-D.liu-spring-sr-policy-flexible-path-selection] Liu, Y., Lin, C., Peng, S., and Qiu, Y., "Flexible Candidate Path Selection of SR Policy", draft-liu-spring-sr-policy-flexible-path- selection-02 (work in progress), September 2023. [I-D.ietf-idr-bgp-ls-sr-policy] Previdi, S., Talaulikar, K., Dong, J., Gredler, H., Tantsura, J., "Advertisement of Segment Routing Policies using BGP Link-State", draft-ietf-idr- bgp-ls-sr-policy-01 (work in progress), July 2023. [I-D.ietf-pce-segment-routing-policy-cp] Koldychev, M., Sivabalan, S., Barth, C., Peng, S., Bidgoli, H., "PCEP extension to support Segment Routing Policy Candidate Paths", draft- ietf-pce-segment-routing-policy-cp-12 (work in progress), July 2023. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, July 2018, . [RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., Hardwick, J., "Path Computation Element Communication Protocol (PCEP) Extensions for Segment Routing", RFC8664, DOI 10.17487/RFC8664, December 2019, . liu, et al. Expires April, 2024 [Page 7] Internet-Draft PCEP for CP Threshold Constraints October 2023 [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, . [RFC9256] Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and P. Mattes, "Segment Routing Policy Architecture", RFC 9256, DOI 10.17487/RFC9256, July 2022, . 6.2. Informative References TBD 7. Acknowledgments The authors would like to thank the following for their valuable contributions of this document: TBD liu, et al. Expires April, 2024 [Page 8] Internet-Draft PCEP for CP Threshold Constraints October 2023 Authors' Addresses Yisong Liu China Mobile Beijing China Email: liuyisong@chinamobile.com Changwang Lin New H3C Technologies Beijing China Email: linchangwang.04414@h3c.com Yuanxiang Qiu New H3C Technologies Beijing China Email: qiuyuanxiang@h3c.com liu, et al. Expires April, 2024 [Page 9]