Inter-Domain Routing R. Chen
Internet-Draft D. Zhao
Intended status: Standards Track ZTE Corporation
Expires: 12 April 2025 K. Talaulikar
Cisco Systems, Inc.
Y. Liu
China Mobile
L. Changwang
New H3C Technologies
9 October 2024
Validity of SR Policy Candidate Path
draft-chen-idr-bgp-sr-policy-cp-validity-03
Abstract
This document defines extensions to BGP to distribute the validity
control parameters of a candidate path for an SR Policy.
Status of This Memo
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This Internet-Draft will expire on 12 April 2025.
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Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. Carrying CP Validity Sub-TLV in BGP . . . . . . . . . . . . . 3
3. CP Validity Sub-TLV . . . . . . . . . . . . . . . . . . . . . 3
4. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
8. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
SR Policy architecture is 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.
This document defines extensions to BGP to distribute the validity
control parameters of a candidate path for an SR Policy.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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2. Carrying CP Validity Sub-TLV 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 CP Validity Sub-TLV to carry the
validity control parameters of a candidate path.
The new SR Policy encoding structure with CP Validity Sub-TLV 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)
CP Validity
Segment List
Weight
Segment
Segment
...
...
Figure 1
3. CP Validity Sub-TLV
The format of the CP Validity 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 | valid SL count| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| valid SL weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 2
where:
Type: to be assigned by IANA.
Length: the total length of the value field not including Type and
Length fields. The total length must be 6.
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.
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.
4. Operations
The document does not bring new operation beyond the description of
operations defined in [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 validity
control parameters of the candidate path are configured by a
controller.
After configuration, the SR policies carrying the validity control
parameters of the candidate path 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.
5. 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
------- ------------------------- --------------
TBD CP Validity Sub-TLV This document
Figure 3
6. Security Considerations
The security considerations of BGP [RFC4271] and BGP SR policy
[I-D.ietf-idr-sr-policy-safi] apply to the extensions described in
this document as well. It does not introduce additional security
issues compared to existing SR policy extensions. The CP Validity
information is critical to determining the validity of the CP, and a
wrong CP Validity information may cause unexpected forwarding actions
and results.
Implementations need to make sure that the CP Validity information is
correct to avoid unexpected forwarding actions and results.
Additionally, the distribution of CP validity information from the
controller to the ingress router needs to be protected. The security
considereations in [I-D.ietf-idr-sr-policy-safi] apply to this
distribution procedure.
7. Acknowledgements
TBD.
8. Normative References
[I-D.chen-spring-sr-policy-cp-validity]
Chen, R., Liu, Y., Talaulikar, K., Sidor, S., Zhao, D.,
Lin, C., and Z. Ali, "Validity of SR Policy Candidate
Path", Work in Progress, Internet-Draft, draft-chen-
spring-sr-policy-cp-validity-03, 21 July 2024,
<https://datatracker.ietf.org/doc/html/draft-chen-spring-
sr-policy-cp-validity-03>.
[I-D.ietf-idr-sr-policy-safi]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., and
D. Jain, "Advertising Segment Routing Policies in BGP",
Work in Progress, Internet-Draft, draft-ietf-idr-sr-
policy-safi-09, 3 October 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-sr-
policy-safi-09>.
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[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>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[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>.
[RFC9012] Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
"The BGP Tunnel Encapsulation Attribute", RFC 9012,
DOI 10.17487/RFC9012, April 2021,
<https://www.rfc-editor.org/info/rfc9012>.
[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
Ketan Talaulikar
Cisco Systems, Inc.
Email: ketant.ietf@gmail.com
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Yisong Liu
China Mobile
Beijing
China
Email: liuyisong@chinamobile.com
Changwang Lin
New H3C Technologies
Beijing
China
Email: linchangwang.04414@h3c.com
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