Internet DRAFT - draft-liu-pce-sr-policy-cp-threshold
draft-liu-pce-sr-policy-cp-threshold
PCE Working Group Y. Liu
Internet Draft China Mobile
Intended status: Standards Track C. Lin
Expires: April 14, 2024 New H3C Technologies
Y. Qiu
New H3C Technologies
October 11, 2023
PCEP Extension to Support Signaling Candidate Path Threshold
Constraints of SR Policy
draft-liu-pce-sr-policy-cp-threshold-00
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Abstract
This document defines the extension 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...................................................2
2. Terminology....................................................3
3. PCEP Extensions................................................3
3.1. SR Bandwidth Constraint TLV...............................3
3.2. SR Metric Constraint TLV..................................4
3.3. SR Segment List Bandwidth Constraint TLV..................5
4. IANA Considerations............................................6
5. Security Considerations........................................6
6. References.....................................................7
6.1. Normative References......................................7
6.2. Informative References....................................8
7. 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-segment-routing-te-policy] [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.
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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 a 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 three TLVs to signal threshold and metric
constraint parameters for candidate paths.
* SR Bandwidth Constraint TLV
* SR Metric Constraint TLV
* SR Segment List Bandwidth Constraint TLV
3.1. SR Bandwidth Constraint TLV
The 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:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type: to be assigned by IANA
* Length: 4 octets
* Flags: 1 octet of flags. None are defined at this stage. Flags
SHOULD be set to zero on transmission and MUST be ignored on
receipt.
* 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:
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: 12 octets
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* Metric Type: 1-octet field which identifies the type of the metric
being used. The metric type code points are listed in Section 8.6
of [I-D.ietf-idr-bgp-ls-sr-policy].
* 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| |
+-+-+-+-+-+-+-+-+
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 minimum metric when clear.
- B-Flag: Indicates that the metric bound allowed for the path
is specified when set.
* Metric Margin: 4-octet value which indicates the metric margin
when the M-flag is set. The metric margin is specified as either
an absolute value or as a percentage of the minimum computed path
metric based on the A-flag. The metric margin loosens the
criteria for minimum metric path calculation up to the specified
metric to accommodate for other factors such as bandwidth
availability, minimal SID stack depth, and maximizing of ECMP for
the SR path computed.
* Metric Bound: 4-octet value which indicates the maximum metric
that is allowed when the B-flag is set. If the computed 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.
3.3. SR Segment List Bandwidth Constraint TLV
The SR Segment List Bandwidth Constraint TLV is an optional TLV for
use in the LSP Object for signaling the bandwidth allocated to the
specific SID-List.
The SR Segment List Bandwidth Constraint TLV has the following
format:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type: to be assigned by IANA
* Length: 4 octets
* Bandwidth: 4 octets which specify the bandwidth threshold in unit
of bytes per second in IEEE floating point format.
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 |
+-------+----------------------------------+-----------------+
| TBA3 | SR Segment List Bandwidth | This document |
| | Constraint TLV | |
+-------+----------------------------------+-----------------+
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.
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6. References
6.1. Normative References
[I-D.ietf-idr-segment-routing-te-policy] Previdi, S., Filsfils, C.,
Talaulikar, K., Mattes, P., Jain, D., and S. Lin,
"Advertising Segment Routing Policies in BGP", draft-ietf-
idr-segment-routing-te-policy-25 (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-02 (work in progress), September 2023.
[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-01 (work in progress), July 2023.
[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-12 (work in progress),
July 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>.
[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>.
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[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>.
6.2. Informative References
TBD
7. 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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