IDR Working Group Y. Liu
Internet Draft China Mobile
Intended status: Standards Track C. Lin
Expires: May 24, 2025 New H3C Technologies
Y. Qiu
New H3C Technologies
November 8, 2024
BGP Extension for Distributing CP Threshold Constraints of SR Policy draft-liu-idr-bgp-sr-policy-cp-threshold-02Status of this Memo
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AbstractThis document defines the extension of BGP to distribute threshold and metric constraint parameters of candidate paths for SR Policy to achieve flexible path selection.
Table of Contents
1. Introduction ................................................ 2
2. Terminology ................................................. 3
3. Carrying Constraint Parameters of CP in BGP ................. 3
4. SR Bandwidth Constraint Sub-TLV ............................. 4
5. SR Metric Constraint Sub-TLV ................................ 5
6. Operations .................................................. 6
7. IANA Considerations ......................................... 6
8. Security Considerations ..................................... 7
9. References .................................................. 7
9.1. Normative References ................................... 7
9.2. Informative References ................................. 8
10. 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.
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 to distribute threshold and metric constraint parameters of candidate path (CP) for an SR Policy.
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2. TerminologyThe definitions of the basic terms are identical to those found in Segment Routing Policy Architecture [RFC9256].
3. Carrying Constraint Parameters of CP in BGP
As defined in [I-D.ietf-idr-sr-policy-safi], a new SAFI is defined (the SR Policy SAFI with codepoint 73) as well as a new NLRI. The NLRI contains the SR Policy candidate path and, according to [I- D.ietf-idr-sr-policy-safi], the content of the SR Policy Candidate Path is encoded in the Tunnel Encapsulation Attribute defined in [RFC9012] using a new Tunnel-Type called SR Policy Type with codepoint 15.
This document defines the following three Sub-TLVs to carry threshold and metric constraint parameters for candidate paths.
* SR Bandwidth Constraint Sub-TLV
* SR Metric Constraint Sub-TLV
* SR Segment List Bandwidth Constraint Sub-TLV
The new SR Policy encoding structure with Sub-TLVs of CP constraint parameters is expressed as below:
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy (15)
Binding SID
SRv6 Binding SID
Preference
Priority
Policy Name
Policy Candidate Path Name
Explicit NULL Label Policy (ENLP) SR Bandwidth Constraint Sub-TLV
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SR Metric Constraint Sub-TLVSegment List
Weight
Segment
Segment
SR Segment List Bandwidth Constraint Sub-TLV
...
...
4. SR Bandwidth Constraint Sub-TLV
The SR Bandwidth Constraint sub-TLV is used to carry the bandwidth threshold constraint parameter of a candidate path.
The SR Bandwidth Constraint sub-TLV is optional and it MUST NOT appear more than once in the SR Policy encoding.
The format of the SR Bandwidth 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 | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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.
- RESERVED: 2 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
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5. SR Metric Constraint Sub-TLVThe SR Metric Constraint sub-TLV is used to carry the metric Constraint of a candidate path.
The SR Metric Constraint sub-TLV is optional. Multiple instances of this sub-TLV may be used to carry different metric type uses.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric Margin |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric Bound |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
- Type: to be assigned by IANA.- Length: Specifies the length of the value field. The value MUST be
4.
- Flags: 1-octet field that indicates the semantics of Metric Value.
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.* 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.
* Flag: Indicates that the metric bound allowed for the path
is specified when set.
* F-Flag: Indicates that the Metric Margin and Metric Bound
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are floating-point numbers when set to 1. When set to 0, it indicates they are integer numbers.- 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%.
- 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.
6. Operations
The document does not bring new operation beyond the description of operations defined in Section 4 of [I-D.ietf-idr-sr-policy-safi]. The existing operations defined in [I-D.ietf-idr-sr-policy-safi] can apply to this document directly.
Typically, but not limit to, the SR policies carrying the constraint parameters of CP are configured by a controller.
After configuration, the SR policies carrying the constraint parameters of CP will be advertised by BGP update messages. The operation of advertisement is the same as defined in [I-D.ietf-idr- sr-policy-safi], as well as the reception.
7. IANA Considerations
This document defines a new sub-TLV in the registry "BGP Tunnel Encapsulation Attribute sub-TLVs" to be assigned by IANA:
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+=======+==================================+=================+
| Value | Description | Reference |
+=======+==================================+=================+
| TBA1 | SR Bandwidth Constraint sub-TLV | This document |
+-------+----------------------------------+-----------------+
| TBA2 | SR Metric Constraint sub-TLV | This document |
+-------+----------------------------------+-----------------+
8. Security Considerations[I-D.ietf-idr-sr-policy-safi] has discussed the security considerations for distributing SR Policy through BGP. This document does not introduce any new security issues.
9. References
9.1. 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., Mishra, G., and Qiu, Y., "Flexible Candidate Path Selection of SR Policy", draft-liu-spring-sr-policy- flexible-path-selection-05 (work in progress), February 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>.
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[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>.
9.2. Informative References
TBD
10. 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
Yuanxiang Qiu New H3C Technologies Beijing China
Email: qiuyuanxiang@h3c.com
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