IDR Working Group Y. Liu Internet Draft China Mobile Intended status: Standards Track C. Lin Expires: February 26, 2025 New H3C Technologies Y. Qiu New H3C Technologies August 29, 2024 Advertisement of SR Policy Flexible Candidate Path Selection Result using BGP Link-State draft-liu-idr-bgp-ls-srp-flexible-path-selection-01 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." 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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 BGP Link-State to advertise the result of SR Policy flexible candidate path selection. Such information can be used by external components for path computation, re-optimization, service placement, network visualization, etc. Table of Contents 1. Introduction...................................................2 2. Terminology....................................................3 3. Carry the result of SR Policy Flexible Path Selection..........3 4. SR Segment List State Change Reason sub-TLV....................4 5. SR Candidate Path Used Bandwidth TLV...........................5 6. SR Segment List Delay Sub-TLV..................................5 7. SR Segment List Loss Ratio Sub-TLV.............................6 8. Operations.....................................................6 9. IANA Considerations............................................6 10. Security Considerations.......................................7 11. References....................................................7 11.1. Normative References.....................................7 11.2. Informative References...................................8 12. 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-sr-policy-safi] [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. Compared to the method where the controller first collects forwarding quality data and then performs path optimization, the head node automatically switches candidate Liu, et al. Expires February, 2025 [Page 2] Internet-Draft BGP-LS for Flexible Path Selection August 2024 paths based on network quality, resulting in higher real-time performance. 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]. This document defines extensions to BGP-LS to advertise the result of SR Policy flexible candidate path selection. After path switching at the head node, the controller can perceive the specific changes in network quality in real time to determine whether further optimization is needed. 2. Terminology The definitions of the basic terms are identical to those found in Segment Routing Policy Architecture [RFC9256]. 3. Carry the result of SR Policy Flexible Path Selection As defined in [I-D.ietf-idr-bgp-ls-sr-policy], an "NLRI Type" known as SR Policy Candidate Path NLRI (value 5) is defined for the advertisement of SR Policy Information. Through this SR Policy Candidate Path NLRI, the state details of individual SR Policy Candidate paths along with their underlying segment lists can be reported to the controller. After flexible path selection, the head node of SR policy needs to report the result of path selection to the controller, which includes the following information: * State of the candidate path * State of the Segment List within the candidate path * Reason for the change in the state of the Segment List * Used bandwidth of the candidate path * Transmission delay of SR Policy * Packet loss rate of SR Policy [I-D.ietf-idr-bgp-ls-sr-policy] defines SR Candidate Path State TLV for reporting candidate path state. When the active candidate path is not selected due to transmission quality not meeting the requirements, set E-Flag to 1 and V-Flag to 0 in the SR Candidate Path State TLV. If the forwarding quality of the active candidate path meets the requirements, set E-Flag to 1 and V-Flag to 1. Liu, et al. Expires February, 2025 [Page 3] Internet-Draft BGP-LS for Flexible Path Selection August 2024 [I-D.ietf-idr-bgp-ls-sr-policy] also defines SR Segment List TLV for reporting segment list state. When a valid Segment List does not meet the quality requirements, set V-Flag to 0 and M-Flag to 1 in the reported SR Segment List TLV. This document defines the extensions of BGP-LS to advertise the reason for the change in the state of the Segment List and the current actual forwarding quality of the path. 4. SR Segment List State Change Reason sub-TLV SR Segment List State Change Reason Sub-TLV is used to report the reasons for the change in segment list state. This Sub-TLV is optional and should be carried when the segment list is not available. If SL is available, MUST not carry this TLV. The sub-TLV has the following format: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Where: * Type: TBA1 * Length: The value is 4. * Flags: 2-octet field that indicates the reason of the segment list. The following bit positions are defined. Other bits MUST be cleared by the originator and MUST be ignored by a receiver. 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |B|D|L|F| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Where: - B-Flag: Indicates insufficient bandwidth - D-Flag: Indicates that the delay exceeds the quality requirements. - L-Flag: Indicates that the packet loss rate has exceeded the threshold. Liu, et al. Expires February, 2025 [Page 4] Internet-Draft BGP-LS for Flexible Path Selection August 2024 - F-Flag: Indicates that the forwarding path fails. * RESERVED: 2 octets. MUST be set to 0 by the originator and MUST be ignored by a receiver. 5. SR Candidate Path Used Bandwidth TLV Define SR Candidate Path Used Bandwidth TLV to report the current bandwidth used by the candidate path. The TLV has the following format: 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: TBA2 * Length: The value is 4. * Bandwidth: The current bandwidth used by the candidate path, in kbps. 6. SR Segment List Delay Sub-TLV Define SR Segment List Delay sub-TLV to report the current delay of segment list path. The sub-TLV has the following format: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Delay | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Where: * Type: TBA3 * Length: The value is 4. * Delay: The delay of segment list path, in milliseconds. When the path fails, the delay is set to 0xFFFFFFFF. Liu, et al. Expires February, 2025 [Page 5] Internet-Draft BGP-LS for Flexible Path Selection August 2024 7. SR Segment List Loss Ratio Sub-TLV Define SR Segment List Loss Ratio sub-TLV to report the current packet loss ratio of segment list path. The sub-TLV has the following format: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Loss Ratio | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Where: * Type: TBA4 * Length: The value is 4. * Loss Ratio: The packet loss ratio of segment list path. The value range is 0~100. 8. Operations The document does not bring new operation beyond the description of operations defined in Section 6 of [I-D.ietf-idr-bgp-ls-sr-policy]. The existing operations defined in [I-D.ietf-idr-bgp-ls-sr-policy] can apply to this document directly. The Segment List State Change Reason Sub-TLV is optional and SHOULD be carried when the segment list is not available. If SL is available, MUST not carry this TLV. 9. IANA Considerations IANA maintains a registry called "BGP-LS NLRI and Attribute TLVs" in the "Border Gateway Protocol - Link State (BGP-LS) Parameters" registry group. The following TLV code points are suggested (for early allocation by IANA): Liu, et al. Expires February, 2025 [Page 6] Internet-Draft BGP-LS for Flexible Path Selection August 2024 +=======+==================================+=================+ | Value | Description | Reference | +=======+==================================+=================+ | TBA1 | SR SL State Change Reason sub-TLV| This document | +-------+----------------------------------+-----------------+ | TBA2 | SR CP Used Bandwidth TLV | This document | +-------+----------------------------------+-----------------+ | TBA3 | SR SL Delay sub-TLV | This document | +-------+----------------------------------+-----------------+ | TBA4 | SR SL Loss Ratio sub-TLV | This document | +-------+----------------------------------+-----------------+ 10. Security Considerations Procedures and protocol extensions defined in this document do not affect the BGP security model. 11. References 11.1. Normative References [I-D.ietf-idr-bgp-ls-sr-policy] Previdi, S., Talaulikar, K., Dong, J., Gredler, H., and Tantsura, J., "Advertisement of Segment Routing Policies using BGP Link-State", draft- ietf-idr-bgp-ls-sr-policy-03 (work in progress), November 2023. [I-D.ietf-idr-sr-policy-safi] Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., and Jain, D., "Advertising Segment Routing Policies in BGP", draft-ietf-idr-sr-policy-safi-00 (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-04 (work in progress), October 2023. [I-D.ietf-idr-sr-policy-metric] Zhang, K., Dong, J., and Talaulikar, K., "BGP SR Policy Extensions for metric", draft-ietf-idr- sr-policy-metric-00 (work in progress), December 2023. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Liu, et al. Expires February, 2025 [Page 7] Internet-Draft BGP-LS for Flexible Path Selection August 2024 [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, . [RFC9256] Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and P. Mattes, "Segment Routing Policy Architecture", RFC 9256, DOI 10.17487/RFC9256, July 2022, . 11.2. Informative References TBD 12. Acknowledgments The authors would like to thank the following for their valuable contributions of this document: TBD Liu, et al. Expires February, 2025 [Page 8] Internet-Draft BGP-LS for Flexible Path Selection August 2024 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 February, 2025 [Page 9]