Supplement of BGP-LS Distribution for SR Policies and State
draft-lp-idr-bgp-ls-sr-policy-supplement-05
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Yao Liu , Shaofu Peng , Zhenqiang Li | ||
| Last updated | 2026-02-05 | ||
| 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-05
IDR Working Group Y. Liu
Internet-Draft S. Peng
Intended status: Standards Track ZTE
Expires: 9 August 2026 Z. Li
China Mobile
5 February 2026
Supplement of BGP-LS Distribution for SR Policies and State
draft-lp-idr-bgp-ls-sr-policy-supplement-05
Abstract
This document supplements additional information of the segment list
in the BGP-LS advertisement for SR Policy state information. A new
flag and a new sub-TLV are introduced in the SR Segment List TLV of
BGP-LS SR Policy Candidate Path NLRI.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 9 August 2026.
Copyright Notice
Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved.
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
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. BGP-LS Extensions for Distributing Segment List States . . . 3
3.1. New Flag in SR Segment List TLV . . . . . . . . . . . . . 3
3.2. MPLS LSE Sub-TLV . . . . . . . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.1. Normative References . . . . . . . . . . . . . . . . . . 4
6.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
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.
[RFC9857] 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, the following segment-list-related information is not yet
included in [RFC9857]:
* Whether the segment list is in administrative shut state. For the
candidate path, there's already an S-Flag in the SR Candidate Path
State TLV in [RFC9857] 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.
* The 32-bit MPLS LSE information. [I-D.ietf-mpls-mna-hdr] defines
the MPLS Network Actions (MNA) sub-stack solution for carrying
Network Actions and Ancillary Data in the MPLS label stack,
different Label Stack Entry(LSE) formats are defined for different
purpose. Unlike traditional MPLS LSE, which consists of 20-bit
MPLS label, 3-bit TC, 1-bit S(bottom of stack indication) and
8-bit TTL, some LSEs defined for MNA repurposed the TC and TTL
field to carry additional information. MNA such as Network
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Resource Partition (NRP) [I-D.ietf-mpls-mna-nrp-selector], IOAM
[I-D.ietf-mpls-mna-ioam] may be inserted in the SID list in the
format of LSEs. The contents of the LSEs inserted in the SID-
lists may be required by the controller when the headend reports
the state of SR Policies via BGP-LS. However, SR Segment List TLV
[RFC9857] only supports carrying MPLS labels with the TC, S and
TTL fields set to 0 in SR Segment Sub-TLV, which is not sufficient
under the MNA architecture.
This document supplements some additional information of the segment
list state as mentioned above in the BGP-LS advertisement for SR
Policy state information.
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 [RFC2119] [RFC8174]
when, and only when, they appear in all capitals, as shown here.
3. BGP-LS Extensions for Distributing Segment List States
3.1. New Flag in SR Segment List TLV
SR Segment List TLV is defined in [RFC9857] to report the SID-List(s)
of a candidate path. As show in Figure 1,this document introduces a
new flag 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| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.
3.2. MPLS LSE Sub-TLV
The MPLS LSE sub-TLV is defined in this section to carry the generic
MPLS LSE information. The MPLS LSE sub-TLV is an optional sub-TLV of
SR Segment List TLV, and it may be used as the sub-TLV of other TLVs,
for the latter case, the detailed usage is out of the scope of this
document.
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ MPLS LSEs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: MPLS LSE Sub-TLV
Type: TBA
Length: Variable, the total length (in octets) of MPLS LSE portion in
octets, MUST be the multiple of 4. The value indicates the number of
the LSEs in this sub-TLV.
MPLS LSEs: one or more 4-octet-field carrying the MPLS LSEs.
4. IANA Considerations
This document requests bit 9 in the flag field of "SR Segment List
TLV" [RFC9857] 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
This document requests a new type sub-TLV of "SR Segment List TLV"
[RFC9857] under the "BGP-LS Node Descriptor, Link Descriptor, Prefix
Descriptor, and Attribute TLVs" registry.
Type Description Reference
------------------------------------------------------------------
TBA MPLS LSE Sub-TLV This document
5. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the security considerations discussed in [RFC9857].
6. References
6.1. Normative References
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[I-D.ietf-pce-multipath]
Koldychev, M., Sivabalan, S., Saad, T., Beeram, V. P.,
Bidgoli, H., Peng, S., and S. Sidor, "Path Computation
Element Communication Protocol (PCEP) Extensions for
Signaling Multipath Information", Work in Progress,
Internet-Draft, draft-ietf-pce-multipath-19, 2 February
2026, <https://datatracker.ietf.org/doc/html/draft-ietf-
pce-multipath-19>.
[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>.
[RFC9857] Previdi, S., Talaulikar, K., Ed., Dong, J., Gredler, H.,
and J. Tantsura, "Advertisement of Segment Routing
Policies Using BGP - Link State", RFC 9857,
DOI 10.17487/RFC9857, October 2025,
<https://www.rfc-editor.org/info/rfc9857>.
6.2. Informative References
[I-D.ietf-mpls-mna-hdr]
Rajamanickam, J., Gandhi, R., Zigler, R., Song, H., and K.
Kompella, "MPLS Network Action (MNA) Sub-Stack
Specification including In-Stack Network Actions and
Data", Work in Progress, Internet-Draft, draft-ietf-mpls-
mna-hdr-19, 3 February 2026,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
mna-hdr-19>.
[I-D.ietf-mpls-mna-ioam]
Gandhi, R., Mirsky, G., Li, T., Song, H., and B. Wen,
"Supporting In Situ Operations, Administration and
Maintenance Using MPLS Network Actions", Work in Progress,
Internet-Draft, draft-ietf-mpls-mna-ioam-04, 20 November
2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
mpls-mna-ioam-04>.
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[I-D.ietf-mpls-mna-nrp-selector]
Li, T., Beeram, V. P., Drake, J., Saad, T., and I. Meilik,
"MPLS Network Actions for Network Resource Partition
Selector", Work in Progress, Internet-Draft, draft-ietf-
mpls-mna-nrp-selector-03, 23 December 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
mna-nrp-selector-03>.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/info/rfc6790>.
[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>.
[RFC8662] Kini, S., Kompella, K., Sivabalan, S., Litkowski, S.,
Shakir, R., and J. Tantsura, "Entropy Label for Source
Packet Routing in Networking (SPRING) Tunnels", RFC 8662,
DOI 10.17487/RFC8662, December 2019,
<https://www.rfc-editor.org/info/rfc8662>.
[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: [email protected]
Shaofu Peng
ZTE
Nanjing
China
Email: [email protected]
Zhenqiang Li
China Mobile
Email: [email protected]
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