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PCEP Extension to Support Signaling Candidate Path Threshold Constraints of SR Policy
draft-liu-pce-sr-policy-cp-threshold-01

Document Type Active Internet-Draft (individual)
Authors Yisong Liu , Changwang Lin , Yuanxiang Qiu
Last updated 2024-04-29
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draft-liu-pce-sr-policy-cp-threshold-01
PCE Working Group                                                Y. Liu
Internet Draft                                             China Mobile
Intended status: Standards Track                                 C. Lin
Expires: October 30, 2024                          New H3C Technologies
                                                                 Y. Qiu
                                                   New H3C Technologies
                                                         April 29, 2024

        PCEP Extension to Support Signaling Candidate Path Threshold
                         Constraints of SR Policy
                  draft-liu-pce-sr-policy-cp-threshold-01

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   This Internet-Draft will expire on October 30, 2024.

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   respect to this document. Code Components extracted from this
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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
   4. IANA Considerations ......................................... 5
   5. Security Considerations ..................................... 6
   6. References .................................................. 6
      6.1. Normative References ................................... 6
      6.2. Informative References ................................. 7
   7. Acknowledgments ............................................. 7
   Authors' Addresses ............................................. 8

  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. 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.

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   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

  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:

    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                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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   where:

   - Type: to be assigned by IANA

   - Length: Specifies the length of the value field. The value MUST be
      4.

   - 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: Specifies the length of the value field. The value MUST be
      12.

   - Metric Type: 1-octet field which identifies the type of the metric
      being used. The metric type code points are as follows:

           *  0: Bandwidth threshold in bytes per second.
           *  1: Weight threshold.
           *  2: Real-time bandwidth threshold in bytes per second.
           *  3: Round trip delay threshold in microseconds.
           *  4: Round trip loss threshold. The unit is 0.000003%.

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   - 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|F|       |
               +-+-+-+-+-+-+-+-+
         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 metric when clear.
           *  B-Flag: Indicates that the metric bound allowed for the
              path is specified when set.
           *  F-Flag: Indicates that the Metric Margin and Metric Bound
              are floating-point numbers when set to 1. When set to 0,
              it indicates they are integer numbers.
   - Metric Margin: 4-octet value which indicates the minimum threshold
      when the M-flag is set. The metric margin is specified as either
      an absolute value or as a percentage of the path metric based on
      the A-Flag.

   - Metric Bound: 4-octet value which indicates the maximum threshold
      that is allowed when the B-flag is set. If the 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.

  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:

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   +=======+==================================+=================+
   | Value | Description                      |  Reference      |
   +=======+==================================+=================+
   |  TBA1 | SR Bandwidth Constraint TLV      |  This document  |
   +-------+----------------------------------+-----------------+
   |  TBA2 | SR Metric Constraint TLV         |  This document  |
   +-------+----------------------------------+-----------------+

  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.

6. References

  6.1. Normative References

   [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-02 (work
             in progress), March 2024.

   [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-05 (work in progress), February 2024.

   [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-04 (work in progress), March 2024.

   [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-15 (work in progress),
             March 2024.

   [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>.

   [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>.

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   [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>.

   [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,
             <https://www.rfc-editor.org/info/rfc8697>.

   [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>.

  6.2. Informative References

   TBD

  7. 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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