Internet DRAFT - draft-liu-idr-bgp-ls-srp-flexible-path-selection

draft-liu-idr-bgp-ls-srp-flexible-path-selection



IDR Working Group                                                Y. Liu
Internet Draft                                             China Mobile
Intended status: Standards Track                                 C. Lin
Expires: August 26, 2024                           New H3C Technologies
                                                                 Y. Qiu
                                                   New H3C Technologies
                                                      February 26, 2024



    Advertisement of SR Policy Flexible Candidate Path Selection Result
                           using BGP Link-State
           draft-liu-idr-bgp-ls-srp-flexible-path-selection-00


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   respect to this document. Code Components extracted from this
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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

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   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.


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   [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.

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      - 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.

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  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):







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   +=======+==================================+=================+
   | 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, <https://www.rfc-
             editor.org/info/rfc2119>.



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   [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>.

   [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, <https://www.rfc-editor.org/info/rfc8402>.

   [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, <https://www.rfc-
             editor.org/info/rfc8664>.

   [RFC9256] Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
             P. Mattes, "Segment Routing Policy Architecture", RFC
             9256, DOI 10.17487/RFC9256, July 2022, <https://www.rfc-
             editor.org/info/rfc9256>.

  11.2. Informative References

   TBD

  12. Acknowledgments

   The authors would like to thank the following for their valuable
   contributions of this document:

   TBD


















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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


























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