PCE Working Group Y. Liu
Internet Draft China Mobile
Intended status: Standards Track C. Lin
Expires: August 15, 2025 New H3C Technologies
S. Peng
Huawei Technologies
Y. Qiu
New H3C Technologies
February 15, 2025
PCEP Extensions to Support Signaling Candidate Path Threshold Constraints of SR Policy draft-liu-pce-sr-policy-cp-threshold-03Status of this Memo
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AbstractThis document defines the extensions 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...................................................3
2. Terminology....................................................3
3. PCEP Extensions................................................3
3.1. SR Bandwidth Constraint TLV...............................4
3.2. SR Metric Constraint TLV..................................4
4. IANA Considerations............................................6
5. Security Considerations........................................6
6. References.....................................................6
6.1. Normative References......................................6
6.2. Informative References....................................8
7. Acknowledgments................................................8
Authors' Addresses................................................9
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1. IntroductionSegment 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.
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 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 two TLVs for PCE to signal threshold and metric constraint parameters for candidate paths to PCC.
* SR Bandwidth Constraint TLV * SR Metric Constraint TLV
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3.1. SR Bandwidth Constraint TLVThe 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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:
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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%.
- 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
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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:
+=======+==================================+=================+ | 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.
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[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>.
[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>.
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6.2. Informative ReferencesTBD
7. Acknowledgments
The authors would like to thank the following for their valuable contributions of this document:
TBD
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Authors' AddressesYisong Liu China Mobile Beijing China
Email: liuyisong@chinamobile.com
Changwang Lin New H3C Technologies Beijing China
Email: linchangwang.04414@h3c.com
Shuping Peng Huawei Technologies Beijing China Email: pengshuping@huawei.com
Yuanxiang Qiu New H3C Technologies Beijing China
Email: qiuyuanxiang@h3c.com
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