BGP Extension for Distributing CP Threshold Constraints of SR Policy
draft-liu-idr-bgp-sr-policy-cp-threshold-01
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Yisong Liu , Changwang Lin , Yuanxiang Qiu | ||
| Last updated | 2024-04-23 | ||
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draft-liu-idr-bgp-sr-policy-cp-threshold-01
IDR Working Group Y. Liu
Internet Draft China Mobile
Intended status: Standards Track C. Lin
Expires: October 24, 2024 New H3C Technologies
Y. Qiu
New H3C Technologies
April 24, 2024
BGP Extension for Distributing CP Threshold Constraints of SR Policy
draft-liu-idr-bgp-sr-policy-cp-threshold-01
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Abstract
This 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. Terminology
The 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)
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SR Bandwidth Constraint Sub-TLV
SR Metric Constraint Sub-TLV
Segment 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-TLV
The 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' 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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