Inter-Domain Routing R. Chen
Internet-Draft D. Zhao
Intended status: Standards Track ZTE Corporation
Expires: 2 September 2024 S. Sidor
M. Koldychev
Z. Ali
Cisco Systems, Inc.
1 March 2024
PCEP extension to support Candidate Paths validity
draft-chen-pce-sr-policy-cp-validity-01
Abstract
This document defines PCEP extensions for signaling the validity
control parameters of a candidate path for an SR Policy.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
3. PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. CP Validity TLV . . . . . . . . . . . . . . . . . . . . . 3
3.2. Stateful PCEP Messages . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
SR Policy architecture are specified in [RFC9256]. An SR Policy
comprises one or more candidate paths (CP) of which at a given time
one and only one may be active (i.e., installed in forwarding and
usable for steering of traffic). Each CP in turn may have one or
more SID-List of which one or more may be active; when multiple SID-
List are active then traffic is load balanced over them.
[I-D.chen-spring-sr-policy-cp-validity]supplemented candidate path
validity criterion in [RFC9256]. It defines three validity control
parameters under candidate Path to control the validity judgment of
candidate Path.
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 for signaling the validity
control parameters of a candidate path for an SR Policy.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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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. We define the CP validity TLV in the SR Policy
Association (SRPA) object to signal the validity control parameters
of a candidate path.
3.1. CP Validity TLV
The format of the CP Validity 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| valid SL count | Reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| valid SL weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
where:
Type: to be assigned by IANA.
Length: the total length of the value field not including Type and
Length fields.
valid SL count：1-octet field which indicates the minimum number of
valid segment Lists under the active candidate path. When the number
of valid segment Lists under candidate path is greater than or equal
to this field, the candidate path is considered valid. 0 indicates no
requirement for SL count. 0xff indicates that the candidate path is
considered valid only if all the segment Lists are valid.
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valid SL weight: 4-octet field which indicates the minimum value of
the sum of the weights of the valid segment List under the active
candidate Path. When the sum of the weights of the valid segment
Lists under the candidate path is greater than or equal to this
field, the candidate Path is considered valid. 0 indicates no
requirement for weight.0xffffffff indicates that the candidate path
is considered valid only if all the segment Lists are valid.
Unless specifically stated otherwise, the CP Validity TLV is assumed
to be single instance. Meaning, only one instance of the TLV SHOULD
be present in the object and only the first instance of the TLV
SHOULD be interpreted and subsequent instances SHOULD be ignored.
3.2. Stateful PCEP Messages
As per [RFC8697], the ASSOCIATION object MAY be carried in the PCUpd,
PCRpt, and Path Computation Initiate (PCInitiate) messages. The CP
Validity TLV is carried in a SR Policy Association (SRPA) object and
MAY also be carried in the PCUpd, PCRpt, and Path Computation
Initiate (PCInitiate) messages.
When carried in a PCRpt message, this object is used to report the
validity control parameters of a candidate path for a SR Policy.
When an LSP is delegated to a stateful PCE, the stateful PCE can
create the validity control parameters of a candidate path for a SR
Policy. This is done by including the CP Validity TLV in a PCUpd
message.
A PCE initiating a new SR policy can also include the validity
control parameters of a candidate path for this policy. This is done
by including the CP Validity TLV in a PCInitiate message.
4. IANA Considerations
This document defines the new TLV for carrying additional information
about SR Policy and SR Candidate Paths. IANA is requested to make
the assignment of a new value for the existing "PCEP TLV Type
Indicators" registry as follows:
Value Description Reference
------- ------------------------- --------------
TBD CP Validity TLV This document
Figure 2
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5. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the security considerations discussed in
[I-D.ietf-pce-segment-routing-policy-cp].
6. Acknowledgements
TBD.
7. Normative References
[I-D.chen-spring-sr-policy-cp-validity]
Chen, R., Zhao, D., and C. Lin, "Validity of SR Policy
Candidate Path", Work in Progress, Internet-Draft, draft-
chen-spring-sr-policy-cp-validity-01, 19 October 2023,
<https://datatracker.ietf.org/doc/html/draft-chen-spring-
sr-policy-cp-validity-01>.
[I-D.ietf-pce-segment-routing-policy-cp]
Koldychev, M., Sivabalan, S., Barth, C., Peng, S., and H.
Bidgoli, "PCEP Extensions for SR Policy Candidate Paths",
Work in Progress, Internet-Draft, draft-ietf-pce-segment-
routing-policy-cp-14, 9 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
segment-routing-policy-cp-14>.
[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>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
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>.
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[RFC9256] Filsfils, C., Talaulikar, K., Ed., 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>.
Authors' Addresses
Ran Chen
ZTE Corporation
Nanjing
China
Email: chen.ran@zte.com.cn
Detao Zhao
ZTE Corporation
Nanjing
China
Email: zhao.detao@zte.com.cn
Samuel Sidor
Cisco Systems, Inc.
Bratislava
Slovakia
Email: ssidor@cisco.com
Mike Koldychev
Cisco Systems, Inc.
Email: mkoldych@cisco.com
Zafar Ali
Cisco Systems, Inc.
Email: zali@cisco.com
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