BGP SR Policy Extensions for Segment List Identifier
draft-ietf-idr-sr-policy-seglist-id-06
| Document | Type | Active Internet-Draft (idr WG) | |
|---|---|---|---|
| Authors | Changwang Lin , Weiqiang Cheng , Yao Liu , Ketan Talaulikar , Mengxiao Chen | ||
| Last updated | 2025-09-24 | ||
| Replaces | draft-lin-idr-sr-policy-seglist-id | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | Susan Hares | ||
| Shepherd write-up | Show Last changed 2024-06-07 | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | shares@ndzh.com |
draft-ietf-idr-sr-policy-seglist-id-06
IDR C. Lin
Internet-Draft New H3C Technologies
Intended status: Standards Track W. Cheng
Expires: 28 March 2026 China Mobile
Y. Liu
ZTE
K. Talaulikar
Cisco Systems
M. Chen
New H3C Technologies
24 September 2025
BGP SR Policy Extensions for Segment List Identifier
draft-ietf-idr-sr-policy-seglist-id-06
Abstract
Segment Routing is a source routing paradigm that explicitly
indicates the forwarding path for packets at the ingress node. An SR
Policy is a set of candidate paths, each consisting of one or more
segment lists. This document defines extensions to BGP SR Policy to
specify the identifier of segment list.
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 28 March 2026.
Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
Lin, et al. Expires 28 March 2026 [Page 1]
Internet-Draft BGP SR Policy Segment List Identifier September 2025
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Segment List Identifier in SR Policy . . . . . . . . . . . . 3
2.1. Segment List ID Sub-TLV . . . . . . . . . . . . . . . . . 5
3. Security Considerations . . . . . . . . . . . . . . . . . . . 6
4. Implementation Status . . . . . . . . . . . . . . . . . . . . 6
4.1. New H3C Technologies . . . . . . . . . . . . . . . . . . 7
4.2. ZTE Corp . . . . . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Segment routing (SR) [RFC8402] is a source routing paradigm that
explicitly indicates the forwarding path for packets at the ingress
node. The ingress node steers packets into a specific path according
to the Segment Routing Policy (SR Policy) as defined in [RFC9256].
In order to distribute SR policies to the headend, [RFC9830]
specifies a mechanism by using BGP.
However, there is no identifier for segment list in BGP SR Policy,
which may cause inconvenience for other mechanisms to designate
segment lists distributed by BGP.
Lin, et al. Expires 28 March 2026 [Page 2]
Internet-Draft BGP SR Policy Segment List Identifier September 2025
Consider the case of a network controller distributing SR policies to
the headend nodes where the headend nodes need to collect traffic
forwarding statistics per segment list. When a headend node reports
each statistic to the controller, it needs to specify the segment
list which the statistic belongs to. Due to the lack of identifier,
the headend node usually reports all SIDs in the associated segment
list along with the statistic, and then the controller needs to
compare the SIDs one by one to recognize which segment list it is.
The advertisement of all SIDs in the segment list consumes a lot of
octets, and the comparison of SIDs can be complicated.
Consider a second example where a network controller distributes SR
policies using BGP, and then it uses NETCONF to set some
configurations of the segment lists which are not suitable to be
carried in BGP. The controller needs to specify which segment list
these configurations belong to when it issues them. In this case, a
simple identifier of segment list can also be helpful.
An identifier of segment list may also serve as a user-friendly
attribute for debugging and troubleshooting purposes, such as
displaying an invalid segment list when its associated BFD session is
down.
This document defines extensions to BGP SR Policy to specify the
identifier of segment list.
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.
2. Segment List Identifier in SR Policy
As defined in [RFC9830], the SR policy encoding structure is as
follows:
Lin, et al. Expires 28 March 2026 [Page 3]
Internet-Draft BGP SR Policy Segment List Identifier September 2025
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encapsulation 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)
Segment List
Weight
Segment
Segment
...
...
Figure 1: SR Policy Encoding
SR policy with segment list identifier is expressed as below:
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encapsulation 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)
Segment List
Weight
Segment List Identifier
Segment
Segment
...
...
Figure 2: SR policy with segment list identifier Encoding
The segment list identifier can be advertised using the Segment List
ID sub-TLV, as defined in Section 2.1.
Lin, et al. Expires 28 March 2026 [Page 4]
Internet-Draft BGP SR Policy Segment List Identifier September 2025
When signaling SR Policy by PCEP [I-D.ietf-pce-multipath] (see
section 5.2), a segment list is identified by "Path ID", which is a
4-octet identifier. In this document, the segment list identifier is
also represented using a 4-octet ID.
2.1. Segment List ID Sub-TLV
The Segment List ID sub-TLV is defined in the BGP Tunnel
Encapsulation Attribute [RFC9012]. The Segment List ID sub-TLV can
be carried in the BGP Tunnel Encapsulation Attribute with the tunnel
type set to SR Policy.
The Segment List ID sub-TLV specifies the identifier of the segment
list by a 4-octet number. The Segment List ID is unique within the
context of a Candidate Path.
The Segment List ID sub-TLV is optional and it MUST NOT appear more
than once inside the Segment List sub-TLV. If multiple instances are
present, then the first one is considered valid and the other
instances MUST be ignored and MUST NOT considered to be malformed.
The Segment List ID sub-TLV has the following format:
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 | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Segment List ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Segment List ID sub-TLV
where:
* Type: TBD(19).
* Length: 6.
* Flags: 1 octet of flags. None are defined at this stage. Flags
SHOULD be set to zero on transmission and MUST be ignored on
receipt.
* RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
Lin, et al. Expires 28 March 2026 [Page 5]
Internet-Draft BGP SR Policy Segment List Identifier September 2025
* Segment List ID: 4 octets which carry a 32-bit unsigned non-zero
number that serves as the identifier associated with the segment
list. A value of 0 indicates that there is no identifier
associated with the Segment List. The scope of this identifier is
the SR Policy Candidate path.
The validation of an SR Policy NLRI with the Segment List ID sub-TLV
in the BGP tunnel encapsulation attribute [RFC9012] follows the
procedures in section 4.2 of [RFC9830].
The Segment List ID sub-TLV is considered malformed if its format
does not match the above description. If its format is considered
malformed, the associated BGP SR Policy NLRI is considered malformed
and the "treat-as-withdraw" strategy of [RFC7606] MUST be applied.
3. Security Considerations
The protocol extensions defined in this document do not affect the
base BGP security model. The security requirements and mechanisms
described in [RFC9830] also apply to this document. SR operates
within a trusted SR domain [RFC8402] and its security considerations
also apply to BGP sessions when carrying SR Policy information.
The Segment List ID sub-TLV is an optional sub-TLV that specifies an
identifier associated with a segment list. The scope of this
identifier is the SR Policy Candidate Path. The Segment List ID
uniquely identifies a segment list within an SR Policy Candidate
Path.
The Segment List ID is assigned by a controller, distributed via BGP,
and used as an identifier for the segment list. Since this
identifier may expose mission-critical or commercially sensitive
network information, it introduces a confidentiality risk.
Network operators MUST ensure that only trusted nodes (including both
routers and controller applications) within the SR domain are
permitted to receive this information.
4. Implementation Status
[Note to the RFC Editor - remove this section before publication, as
well as remove the reference to [RFC7942].
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
Lin, et al. Expires 28 March 2026 [Page 6]
Internet-Draft BGP SR Policy Segment List Identifier September 2025
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
4.1. New H3C Technologies
* Organization: New H3C Technologies.
* Implementation: H3C CR16000, CR19000 series routers
implementation.
* Description: All sections including all the "MUST" and "SHOULD"
clauses have been implemented in above-mentioned New H3C
Products(running Version 7.1.099 and above).
* Maturity Level: Product
* Coverage: All sections.
* Version: Draft-03
* Licensing: N/A
* Implementation experience: Nothing specific.
* Contact: linchangwang.04414@h3c.com
* Last updated: February 10, 2025
4.2. ZTE Corp
* Organization: ZTE Corporation
* Implementation: ZTE's ZXR10 core router
* Description: The implementation in lab has been completed. The
commercial implementation is under development.
Lin, et al. Expires 28 March 2026 [Page 7]
Internet-Draft BGP SR Policy Segment List Identifier September 2025
* Maturity Level: Product
* Coverage: All
* Version: Draft-03
* Licensing: N/A
* Implementation experience: Nothing specific.
* Contact: feng.jun99@zte.com.cn
* Last updated: February 6, 2025
5. IANA Considerations
This document defines a new Sub-TLV in the registry "SR Policy
Segment List Sub-TLVs" [RFC9830]:
Value Description Reference
-------------------------------------------------------
TBA (19) Segment List ID sub-TLV This document
6. Acknowledgments
The authors would like to thank Susan Hares, Hao Li, Haiyang Zhang,
Yisong Liu, Ran Chen, Libin Liu, Lancheng Qin and Xinxin Yi for their
review and discussion of this document.
7. References
7.1. Normative References
[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>.
[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015,
<https://www.rfc-editor.org/info/rfc7606>.
[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>.
Lin, et al. Expires 28 March 2026 [Page 8]
Internet-Draft BGP SR Policy Segment List Identifier September 2025
[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>.
[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>.
[RFC9830] Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., and
D. Jain, "Advertising Segment Routing Policies in BGP",
RFC 9830, DOI 10.17487/RFC9830, 12 September 2025,
<https://www.rfc-editor.org/info/rfc9830>.
7.2. Informative 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-14, 5 September 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
multipath-14>.
Authors' Addresses
Changwang Lin
New H3C Technologies
8 Yongjia North Road
Beijing
Haidian District, 100094
China
Email: linchangwang.04414@h3c.com
Lin, et al. Expires 28 March 2026 [Page 9]
Internet-Draft BGP SR Policy Segment List Identifier September 2025
Weiqiang Cheng
China Mobile
32 Xuanwumen West Street
Beijing
Xicheng District, 100053
China
Email: chengweiqiang@chinamobile.com
Yao Liu
ZTE
China
Email: liu.yao71@zte.com.cn
Ketan Talaulikar
Cisco Systems
India
Email: ketant.ietf@gmail.com
Mengxiao Chen
New H3C Technologies
China
Email: chen.mengxiao@h3c.com
Lin, et al. Expires 28 March 2026 [Page 10]