Supplement of BGP-LS Distribution for SR Policies and State
draft-lp-idr-bgp-ls-sr-policy-supplement-04
This document is an Internet-Draft (I-D).
Anyone may submit an I-D to the IETF.
This I-D is not endorsed by the IETF and has no formal standing in the
IETF standards process.
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Yao Liu , Shaofu Peng , Zhenqiang Li | ||
| Last updated | 2025-11-02 | ||
| 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 | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-lp-idr-bgp-ls-sr-policy-supplement-04
IDR Working Group Y. Liu
Internet-Draft S. Peng
Intended status: Standards Track ZTE
Expires: 6 May 2026 Z. Li
China Mobile
2 November 2025
Supplement of BGP-LS Distribution for SR Policies and State
draft-lp-idr-bgp-ls-sr-policy-supplement-04
Abstract
This document supplements additional information of the segment list
in the BGP-LS advertisement for SR Policy state information. Two new
flags 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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 6 May 2026.
Copyright Notice
Copyright (c) 2025 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
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Liu, et al. Expires 6 May 2026 [Page 1]
Internet-Draft BGP-LS SR Policy November 2025
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. BGP-LS Extensions for Distributing Segment List States . . . 3
3.1. New Flags in SR Segment List TLV . . . . . . . . . . . . 3
3.2. MPLS LSE Sub-TLV . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . . 5
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, a few segment-list-related information is not yet included
in [RFC9857]:
* 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 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.
Liu, et al. Expires 6 May 2026 [Page 2]
Internet-Draft BGP-LS SR Policy November 2025
Besides, [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 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 carry 20-bit MPLS labels, which are encoded in SR
Segment Sub-TLV, carrying 32-bit MPLS LSEs in BGP-LS is not yet
supported.
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 Flags 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
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.
Liu, et al. Expires 6 May 2026 [Page 3]
Internet-Draft BGP-LS SR Policy November 2025
* 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.
3.2. 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.
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 and bit 10 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.
Liu, et al. Expires 6 May 2026 [Page 4]
Internet-Draft BGP-LS SR Policy November 2025
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
[I-D.ietf-pce-multipath]
Koldychev, M., Sivabalan, S., Saad, T., Beeram, V. P.,
Bidgoli, H., Yadav, B., Peng, S., Mishra, G. S., and S.
Sidor, "Path Computation Element Communication Protocol
(PCEP) Extensions for Signaling Multipath Information",
Work in Progress, Internet-Draft, draft-ietf-pce-
multipath-16, 17 October 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
multipath-16>.
[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 Solution",
Work in Progress, Internet-Draft, draft-ietf-mpls-mna-hdr-
16, 3 October 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
mna-hdr-16>.
Liu, et al. Expires 6 May 2026 [Page 5]
Internet-Draft BGP-LS SR Policy November 2025
[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-03, 30 May 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
mna-ioam-03>.
[I-D.ietf-mpls-mna-nrp-selector]
Li, T., Drake, J., Beeram, V. P., Saad, T., and I. Meilik,
"MPLS Network Actions for Network Resource Partition
Selector", Work in Progress, Internet-Draft, draft-ietf-
mpls-mna-nrp-selector-00, 13 May 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
mna-nrp-selector-00>.
[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: liu.yao71@zte.com.cn
Liu, et al. Expires 6 May 2026 [Page 6]
Internet-Draft BGP-LS SR Policy November 2025
Shaofu Peng
ZTE
Nanjing
China
Email: peng.shaofu@zte.com.cn
Zhenqiang Li
China Mobile
Email: lizhenqiang@chinamobile.com
Liu, et al. Expires 6 May 2026 [Page 7]