Internet DRAFT - draft-liu-idr-bgp-ls-srp-flexible-path-selection
draft-liu-idr-bgp-ls-srp-flexible-path-selection
IDR Working Group Y. Liu
Internet Draft China Mobile
Intended status: Standards Track C. Lin
Expires: August 26, 2024 New H3C Technologies
Y. Qiu
New H3C Technologies
February 26, 2024
Advertisement of SR Policy Flexible Candidate Path Selection Result
using BGP Link-State
draft-liu-idr-bgp-ls-srp-flexible-path-selection-00
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Abstract
This document defines the extension of BGP Link-State to advertise
the result of SR Policy flexible candidate path selection. Such
information can be used by external components for path computation,
re-optimization, service placement, network visualization, etc.
Table of Contents
1. Introduction...................................................2
2. Terminology....................................................3
3. Carry the result of SR Policy Flexible Path Selection..........3
4. SR Segment List State Change Reason sub-TLV....................4
5. SR Candidate Path Used Bandwidth TLV...........................5
6. SR Segment List Delay Sub-TLV..................................5
7. SR Segment List Loss Ratio Sub-TLV.............................6
8. Operations.....................................................6
9. IANA Considerations............................................6
10. Security Considerations.......................................7
11. References....................................................7
11.1. Normative References.....................................7
11.2. Informative References...................................8
12. 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. Compared to the method where the
controller first collects forwarding quality data and then performs
path optimization, the head node automatically switches candidate
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paths based on network quality, resulting in higher real-time
performance.
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-LS to
advertise the result of SR Policy flexible candidate path selection.
After path switching at the head node, the controller can perceive
the specific changes in network quality in real time to determine
whether further optimization is needed.
2. Terminology
The definitions of the basic terms are identical to those found in
Segment Routing Policy Architecture [RFC9256].
3. Carry the result of SR Policy Flexible Path Selection
As defined in [I-D.ietf-idr-bgp-ls-sr-policy], an "NLRI Type" known
as SR Policy Candidate Path NLRI (value 5) is defined for the
advertisement of SR Policy Information. Through this SR Policy
Candidate Path NLRI, the state details of individual SR Policy
Candidate paths along with their underlying segment lists can be
reported to the controller.
After flexible path selection, the head node of SR policy needs to
report the result of path selection to the controller, which
includes the following information:
* State of the candidate path
* State of the Segment List within the candidate path
* Reason for the change in the state of the Segment List
* Used bandwidth of the candidate path
* Transmission delay of SR Policy
* Packet loss rate of SR Policy
[I-D.ietf-idr-bgp-ls-sr-policy] defines SR Candidate Path State TLV
for reporting candidate path state. When the active candidate path
is not selected due to transmission quality not meeting the
requirements, set E-Flag to 1 and V-Flag to 0 in the SR Candidate
Path State TLV. If the forwarding quality of the active candidate
path meets the requirements, set E-Flag to 1 and V-Flag to 1.
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[I-D.ietf-idr-bgp-ls-sr-policy] also defines SR Segment List TLV for
reporting segment list state. When a valid Segment List does not
meet the quality requirements, set V-Flag to 0 and M-Flag to 1 in
the reported SR Segment List TLV.
This document defines the extensions of BGP-LS to advertise the
reason for the change in the state of the Segment List and the
current actual forwarding quality of the path.
4. SR Segment List State Change Reason sub-TLV
SR Segment List State Change Reason Sub-TLV is used to report the
reasons for the change in segment list state.
This Sub-TLV is optional and should be carried when the segment list
is not available. If SL is available, MUST not carry this TLV.
The sub-TLV has the following format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
* Type: TBA1
* Length: The value is 4.
* Flags: 2-octet field that indicates the reason of the segment
list. The following bit positions are defined. Other bits MUST be
cleared by the originator and MUST be ignored by a receiver.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|B|D|L|F| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
- B-Flag: Indicates insufficient bandwidth
- D-Flag: Indicates that the delay exceeds the quality
requirements.
- L-Flag: Indicates that the packet loss rate has exceeded the
threshold.
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- F-Flag: Indicates that the forwarding path fails.
* RESERVED: 2 octets. MUST be set to 0 by the originator and MUST be
ignored by a receiver.
5. SR Candidate Path Used Bandwidth TLV
Define SR Candidate Path Used Bandwidth TLV to report the current
bandwidth used by the candidate path.
The TLV has the following format:
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: TBA2
* Length: The value is 4.
* Bandwidth: The current bandwidth used by the candidate path, in
kbps.
6. SR Segment List Delay Sub-TLV
Define SR Segment List Delay sub-TLV to report the current delay of
segment list path.
The sub-TLV has the following format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Delay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
* Type: TBA3
* Length: The value is 4.
* Delay: The delay of segment list path, in milliseconds. When the
path fails, the delay is set to 0xFFFFFFFF.
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7. SR Segment List Loss Ratio Sub-TLV
Define SR Segment List Loss Ratio sub-TLV to report the current
packet loss ratio of segment list path.
The sub-TLV has the following format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Loss Ratio |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
* Type: TBA4
* Length: The value is 4.
* Loss Ratio: The packet loss ratio of segment list path. The value
range is 0~100.
8. Operations
The document does not bring new operation beyond the description of
operations defined in Section 6 of [I-D.ietf-idr-bgp-ls-sr-policy].
The existing operations defined in [I-D.ietf-idr-bgp-ls-sr-policy]
can apply to this document directly.
The Segment List State Change Reason Sub-TLV is optional and SHOULD
be carried when the segment list is not available. If SL is
available, MUST not carry this TLV.
9. IANA Considerations
IANA maintains a registry called "BGP-LS NLRI and Attribute TLVs" in
the "Border Gateway Protocol - Link State (BGP-LS) Parameters"
registry group.
The following TLV code points are suggested (for early allocation by
IANA):
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+=======+==================================+=================+
| Value | Description | Reference |
+=======+==================================+=================+
| TBA1 | SR SL State Change Reason sub-TLV| This document |
+-------+----------------------------------+-----------------+
| TBA2 | SR CP Used Bandwidth TLV | This document |
+-------+----------------------------------+-----------------+
| TBA3 | SR SL Delay sub-TLV | This document |
+-------+----------------------------------+-----------------+
| TBA4 | SR SL Loss Ratio sub-TLV | This document |
+-------+----------------------------------+-----------------+
10. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the BGP security model.
11. References
11.1. Normative References
[I-D.ietf-idr-bgp-ls-sr-policy] Previdi, S., Talaulikar, K., Dong,
J., Gredler, H., and Tantsura, J., "Advertisement of
Segment Routing Policies using BGP Link-State", draft-
ietf-idr-bgp-ls-sr-policy-03 (work in progress), November
2023.
[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-00 (work
in progress), September 2023.
[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-04 (work in progress), October 2023.
[I-D.ietf-idr-sr-policy-metric] Zhang, K., Dong, J., and Talaulikar,
K., "BGP SR Policy Extensions for metric", draft-ietf-idr-
sr-policy-metric-00 (work in progress), December 2023.
[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>.
[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>.
[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>.
11.2. Informative References
TBD
12. 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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