Validity of SR Policy Candidate Path
draft-chen-spring-sr-policy-cp-validity-01

SPRING Working Group                                             R. Chen
Internet-Draft                                                   D. Zhao
Intended status: Standards Track                         ZTE Corporation
Expires: 22 April 2024                                      L. Changwang
                                                    New H3C Technologies
                                                         20 October 2023

                  Validity of SR Policy Candidate Path
               draft-chen-spring-sr-policy-cp-validity-01

Abstract

   An SR Policy comprises one or more candidate paths (CP) of which at a
   given time one and only one may be active (i.e., installed in
   forwarding and usable for steering of traffic).  Each CP in turn may
   have one or more SID-List of which one or more may be active; when
   multiple SID-List are active then traffic is load balanced over them.
   However, a candidate path is valid when at least one SID-List is
   active.  This candidate path validity criterion cannot meet the needs
   of some scenarios.

   This document defines the new candidate path validity criterion.

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   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Validity of a Candidate Path  . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   SR Policy architecture are specified in [RFC9256].  An SR Policy
   comprises one or more candidate paths (CP) of which at a given time
   one and only one may be active (i.e., installed in forwarding and
   usable for steering of traffic).  Each CP in turn may have one or
   more SID-List of which one or more may be active; when multiple SID-
   List are active then traffic is load balanced over them.  However, a
   candidate path is valid when at least one SID-List is active.  This
   candidate path validity criterion cannot meet the needs of some
   scenarios.

   This document defines the new candidate path validity criterion, and
   it does not change the segment list invalidation rules defined in SR
   Policy architecture are specified in [RFC9256].

1.1.  Requirements Language

   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.

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2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  Motivation

   The candidate path validity criterion defined in [RFC9256] can't meet
   the needs of the following scenarios:

                                      +----------------------+
                            +---------| SL1(Weight 1, 100MB) |
    +----------------+      |         +----------------------+
    |  CP1 (200MB)   |------+
    +----------------+      |         +----------------------+
                            +---------| SL2(Weight 1, 100MB) |
                                      +----------------------+

                                  Figure 1

   The SR Policy POL1 has two candidate paths: CP1 and CP2, and CP1 is
   the active candidate path (it is valid and has the highest
   Preference).  The two segment lists (SL1 and SL2) of CP1 are
   installed as the forwarding instantiation of SR Policy POL1.

   The CP1 carries a total of 200MB of traffic.  Within the POL1, the
   flow-based hashing over its each SL with a ratio 50%, that is each SL
   carry 100MB of traffic.  At this time, Use the segment list
   invalidity rule defined in RFC9256, if it is determined that one of
   the segment list is invalid, the remaining Segment List cannot carry
   200MB of traffic.  However, the CP1 is still active.

4.  Validity of a Candidate Path

   A headend MAY be informed about the validity control parameters of a
   candidate path for an SR Policy <Color, Endpoint> by various means
   including: via configuration, PCEP, or BGP.  The detailed protocol
   extension will be described in a separate document.

   This document defines the following validity control parameters under
   candidate Path to control the validity judgment of candidate Path:

   *  valid SL quantity: 8-bit value, The value is 1-0xff.

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      Indicates the minimum number of valid segment Lists under the
      active candidate path.  When the number of valid segment Lists
      under candidate path is greater than or equal to this field, the
      candidate path is considered valid.

      0xff indicates that the candidate path is considered valid only if
      all the segment Lists are valid.

   *  valid SL weight: 32-bit value, The value is 0-0xffffffff.

      Indicates the minimum value of the sum of the weights of the valid
      segment List under the active candidate Path.

      When the sum of the weights of the valid segment Lists under the
      candidate path is greater than or equal to this field, the
      candidate Path is considered valid.

      0 indicates no requirement for weight.

      0xffffffff indicates that the candidate path is considered valid
      only if all the segment Lists are valid.

   *  valid SL weight ratio: 8-bit value, The value is 0-100.

      WTV: The sum weights of the valid segment list under the active
      CP.

      WTA: The sum weights of all the segment lists under the active CP.

      Indicates the minimum proportion WTV/WTA.

      When WTV/WTA is greater than or equal to this field, the candidate
      Path is considered valid.

      0 indicates no requirement on weight proportion.

      100 indicates that the candidate path is considered valid only if
      all the segment lists are valid.

   Candidate path is considered valid only when all three validity
   control parameters are satisfied.

5.  IANA Considerations

   This document makes no request of IANA.

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6.  Security Considerations

   The security considerations of segment routing in [RFC9256] are
   applicable to this document.

7.  Acknowledgements

   TBD.

8.  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,
              <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>.

   [RFC9256]  Filsfils, C., Talaulikar, K., Ed., 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>.

Authors' Addresses

   Ran Chen
   ZTE Corporation
   Nanjing
   China
   Email: chen.ran@zte.com.cn

   Detao Zhao
   ZTE Corporation
   Nanjing
   China
   Email: zhao.detao@zte.com.cn

   Changwang Lin
   New H3C Technologies
   Beijing
   China
   Email: linchangwang.04414@h3c.com

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