Supplement of BGP-LS Distribution for SR Policies and State
draft-lp-idr-bgp-ls-sr-policy-supplement-01
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Yao Liu , Shaofu Peng , Zhenqiang Li | ||
| Last updated | 2025-02-20 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
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draft-lp-idr-bgp-ls-sr-policy-supplement-01
IDR Working Group Y. Liu
Internet-Draft S. Peng
Intended status: Standards Track ZTE
Expires: 24 August 2025 Z. Li
China Mobile
20 February 2025
Supplement of BGP-LS Distribution for SR Policies and State
draft-lp-idr-bgp-ls-sr-policy-supplement-01
Abstract
This document supplements additional information of the segment list
in the BGP-LS advertisement for SR Policy state information. Two new
flags are introduced in SR Segment List TLV of BGP-LS SR Policy
Candidate Path NLRI.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 24 August 2025.
Copyright Notice
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This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. BGP-LS Extensions for Distributing Segment List States . . . 3
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 3
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Normative References . . . . . . . . . . . . . . . . . . 4
5.2. Informative References . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction
SR Policy architecture details 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. Each CP in turn may have one or
more SID-List of which one or more may be active; when multiple are
active then traffic is load balanced over them.
[I-D.ietf-idr-bgp-ls-sr-policy] describes a mechanism to collect the
SR policy information that is locally available in a node and
advertise it into BGP Link State (BGP-LS) updates. Various TLVs are
defined to enable the headend to report the state at the candidate
path level and the segment list level.
Currently, a few segment-list-related information is not yet included
in [I-D.ietf-idr-bgp-ls-sr-policy]:
* Whether the segment list is a backup path.[I-D.ietf-pce-multipath]
proposes extensions to PCEP to specify the protection relationship
among segment lists within the candidate path. There would be
segment lists in the CP acting as backup for one or more primary
segment lists, the backup lists only carry rerouted traffic after
the protected path fails.
* Whether the segment list is in administrative shut state.For the
candidate path. There's already a B Flag in the SR Candidate Path
State TLV in [I-D.ietf-idr-bgp-ls-sr-policy] indicating the CP is
in an administrative shut state. In some usecases, the segment
list may also be shut by an administrator for traffic engineering
or power saving purpose, e.g, the network administrator may shut
certain segment list when the load on the SR Policy is light.
This information may also be needed and reported via BGP-LS.
This document supplements some additional information of the segment
list state as mentioned above in the BGP-LS advertisement for SR
Policy state information .
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1.1. 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 [RFC2119] [RFC8174]
when, and only when, they appear in all capitals, as shown here.
2. BGP-LS Extensions for Distributing Segment List States
SR Segment List TLV is defined in [I-D.ietf-idr-bgp-ls-sr-policy] to
report the SID-List(s) of a candidate path.As show in Figure 1,this
document introduces two new flags in the flag field of SR Segment
List TLV, where,
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | | | | | | | |S|B| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: New Flags in the Flag Field of SR Segment List TLV
* S-Flag: Indicates the segment list is in administrative shut state
when set. The segment list may be shut by the administrator via
CLI or other methods, and it is out of the scope of this document.
* B-Flag: Indicates that the segment list is a pure backup path as
specified in [I-D.ietf-pce-multipath] section 4.4 when set. When
B-Flag is clear, it indicates it is the primary path that carries
normal traffic.
3. IANA Considerations
This document requests bit 9 and bit 10 in the flag field of "SR
Segment List TLV" [I-D.ietf-idr-bgp-ls-sr-policy] under the "BGP-LS
Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute
TLVs" registry.
Bit Description Reference
------------------------------------------------------------------
9 Administrative Shut State Flag(S-Flag) This document
10 Backup Path State Flag(B-Flag) This document
4. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the security considerations discussed in
[I-D.ietf-idr-bgp-ls-sr-policy].
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5. References
5.1. Normative References
[I-D.ietf-idr-bgp-ls-sr-policy]
Previdi, S., Talaulikar, K., Dong, J., Gredler, H., and J.
Tantsura, "Advertisement of Segment Routing Policies using
BGP Link-State", Work in Progress, Internet-Draft, draft-
ietf-idr-bgp-ls-sr-policy-14, 17 February 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
ls-sr-policy-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>.
[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>.
5.2. Informative References
[I-D.ietf-pce-multipath]
Koldychev, M., Sivabalan, S., Saad, T., Beeram, V. P.,
Bidgoli, H., Yadav, B., Peng, S., and G. S. Mishra, "PCEP
Extensions for Signaling Multipath Information", Work in
Progress, Internet-Draft, draft-ietf-pce-multipath-12, 8
October 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-pce-multipath-12>.
[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>.
[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
Yao Liu
ZTE
Nanjing
China
Email: liu.yao71@zte.com.cn
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Shaofu Peng
ZTE
Nanjing
China
Email: peng.shaofu@zte.com.cn
Zhenqiang Li
China Mobile
Email: lizhenqiang@chinamobile.com
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