SPRING Working Group                                             R. Chen
Internet-Draft                                           ZTE Corporation
Intended status: Standards Track                                  Y. Liu
Expires: 30 July 2025                                       China Mobile
                                                           K. Talaulikar
                                                     Cisco Systems, Inc.
                                                                 D. Zhao
                                                         ZTE Corporation
                                                                  Z. Ali
                                                     Cisco Systems, Inc.
                                                         26 January 2025
Validity of SR Policy Candidate Path draft-chen-spring-sr-policy-cp-validity-04

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.

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). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on 30 July 2025.
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Copyright Notice

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This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://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 respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Validity of a Candidate Path . . . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
7.1. Normative References . . . . . . . . . . . . . . . . . . 4
7.2. Informative 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 criterions based on [RFC9256]. For the segment list invalidation rules, refer to [RFC9256] and [I-D.liu-spring-sr-policy-flexible-path-selection]. This document does not change the segment list invalidation rules.
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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.
2.  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.
3.  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 count: 8-bit value, The value is 1-0xff. 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.
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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.

Candidate path is considered valid only if both validity control parameters are satisfied.
4.  IANA Considerations
This document makes no request of IANA.
5.  Security Considerations
The security considerations of segment routing in [RFC9256] are applicable to this document.
6.  Acknowledgements
The authors would like to thank Joel Halpern, Samuel Sidor and Changwang Lin for their review and discussion of this document.
7.  References

7.1.  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>.
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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>.

[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>.
7.2.  Informative References
[I-D.liu-spring-sr-policy-flexible-path-selection]
Liu, Y., Lin, C., Peng, S., Chen, R., Mishra, G. S., and Y. Qiu, "Flexible Candidate Path Selection of SR Policy", Work in Progress, Internet-Draft, draft-liu-spring-sr- policy-flexible-path-selection-08, 18 December 2024, <https://datatracker.ietf.org/doc/html/draft-liu-spring- sr-policy-flexible-path-selection-08>.

Authors' Addresses

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


Yisong Liu China Mobile Beijing China Email: liuyisong@chinamobile.com


Ketan Talaulikar Cisco Systems, Inc. Email: ketant.ietf@gmail.com


Detao Zhao ZTE Corporation Nanjing China Email: zhao.detao@zte.com.cn Zafar Ali Cisco Systems, Inc. Email: zali@cisco.com
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