BGP SR Policy Extensions for BFD Configuration
draft-li-bgp-sr-policy-bfd-extension-00
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Zhenqiang Li , liusong | ||
| Last updated | 2026-02-13 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
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draft-li-bgp-sr-policy-bfd-extension-00
Inter-Domain Routing Z. Li, Ed.
Internet-Draft S. Liu, Ed.
Intended status: Standards Track China Mobile
Expires: 17 August 2026 13 February 2026
BGP SR Policy Extensions for BFD Configuration
draft-li-bgp-sr-policy-bfd-extension-00
Abstract
Segment Routing (SR) Policies require fast failure detection for
Candidate Paths (CPs) to enable rapid rerouting and high
availability. Currently, the provisioning of SR Policies and the
configuration of associated Bidirectional Forwarding Detection (BFD)
or Seamless BFD (S-BFD) sessions are performed independently. This
often necessitates separate mechanisms (e.g., manual configuration,
NETCONF, or additional signaling) to associate BFD/S-BFD sessions
with the SR Policies, resulting in complex and error-prone operations
This document defines extensions to BGP SR Policy for the
simultaneous provisioning of SR Policy CPs and their BFD/S-BFD
configuration parameters during policy advertisement. The extensions
include optional sub-TLVs within the Tunnel Encapsulation Attribute
to carry BFD/S-BFD configuration parameters (e.g., discriminators,
intervals, multipliers).
These extensions simplify deployment in distributed or controller-
based environments, reduce configuration overhead, and enhance
operational efficiency for SR-based traffic engineering.
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 17 August 2026.
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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
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. BGP SR Policy Extensions for BFD/S-BFD Configuration . . . . 3
2.1. BFD Parameters Sub-TLV . . . . . . . . . . . . . . . . . 4
2.2. S-BFD Parameters Sub-TLV . . . . . . . . . . . . . . . . 5
3. BGP SR Policy Speaker Behavior . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Normative References . . . . . . . . . . . . . . . . . . 8
6.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Segment Routing (SR) [RFC8402] enables source routing by allowing a
headend node to steer packet flows along specific paths using an
ordered list of segments, eliminating intermediate per-path states.
An SR Policy [RFC9256] defines such paths as one or more Candidate
Paths (CPs), each comprising one or more segment lists.
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To ensure high availability and fast failure detection in SR
networks, Bidirectional Forwarding Detection (BFD) [RFC5880] or
Seamless BFD (S-BFD) [RFC7880] is commonly used to monitor SR Policy
path liveliness. However, current deployments configure SR Policies
and BFD/S-BFD sessions independently. Typically, an SR Policy
Controller [RFC9256] defines the set of policies and advertises them
to SR Policy headend routers (typically ingress routers) via BGP SR
Policy [RFC9830], or PCEP [RFC8664][RFC9603]. After SR Policies are
advertised and installed, separate mechanisms (e.g., manual
configuration, NETCONF/YANG, or additional signaling) are required to
associate BFD/S-BFD parameters with the paths. This leads to
increased operational complexity, longer provisioning times, and
potential inconsistencies.
[I-D.ietf-pce-pcep-bfd-parameters] extends PCEP [RFC5440] to carry
S-BFD parameters, which can be used together with [RFC8664] or
[RFC9603] to complete S-BFD configuration while distributing SR
Policies.
This document extends BGP SR Policy [RFC9830] to carry BFD/S-BFD
parameters. These extensions enable simultaneous provisioning of SR
Policies and their monitoring sessions, reducing separate
configuration steps.
BGP itself does not install SR Policy CPs or BFD/S-BFD sessions into
the data plane; these actions remain the responsibility of the SR
Policy Module (SRPM) on the headend node.
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. BGP SR Policy Extensions for BFD/S-BFD Configuration
This section defines extensions to BGP SR Policy that allow an SR
Policy Candidate Path (CP) to be advertised together with the
configuration parameters required to establish BFD [RFC5880] or S-BFD
[RFC7880] sessions for monitoring the liveness of the path. The
extensions are designed to be carried within the existing BGP SR
Policy SAFI (73) and the Tunnel Encapsulation Attribute as specified
in [RFC9830].
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The BFD and S-BFD configuration parameters are carried in new
optional sub-TLVs of the Tunnel Encapsulation Attribute [RFC9012].
These sub-TLVs are applicable only for the SR Policy SAFI (AFI/SAFI
1/73 or 2/73). They MAY appear at most once in a given Tunnel
Encapsulation Attribute; if multiple instances of the same sub-TLV
are present, only the first instance is processed and subsequent
instances MUST be ignored. The Extended BGP SR Policy Encoding
structure is as follows.
SR Policy SAFI NLRl: <Distinguisher, Color, Endpoint>
Attributes:
Tunnel Encapsulation Attribute (23)
Tunnel Type: SR Policy (15)
Binding SID
Preference
Priority
BFD Parameters (This Document)
S-BFD Parameters (This Document)
SR Policy Name
SR Policy Candidate Path Name
Explicit NULL Label Policy (ENLP)
Segment List
Weight
Segment
Segment
...
...
Figure 1: Extended BGP SR Policy Encoding
The introduced sub-TLVs in this document are not used by the BGP path
selection process. They are passed unchanged to the SRPM on the
headend node, which is responsible for validating the parameters and
instantiating the corresponding BFD/S-BFD sessions.
2.1. BFD Parameters Sub-TLV
The BFD Parameters sub-TLV carries the configuration parameters
needed to establish a BFD session for monitoring the SR Policy CP.
The format of this BFD Parameters Sub-TLV is as follows.
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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 (TBD1) | Length | Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Vers | Diag |Sta|P|F|C|A|D|M| Detect Mult | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| My Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Your Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Desired Min TX Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Required Min RX Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Required Min Echo RX Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: BFD Parameters Sub-TLV Format
Type: To be assigned by IANA from the "BGP Tunnel Encapsulation
Attribute Sub-TLVs" registry (suggested value 21).
Length: Length of the value field in octets. MUST be 24.
Flags: 1 octet. Bits 0-7 are reserved and MUST be set to zero on
transmission and ignored on receipt.
Reserved: 1 octet. MUST be set to zero on transmission and ignored
on receipt.
Other parameters have the same meaning as defined in [RFC5880].
2.2. S-BFD Parameters Sub-TLV
The S-BFD Parameters sub-TLV carries the configuration parameters
needed to establish a S-BFD session for monitoring the SR Policy CP.
The format of this S-BFD Parameters Sub-TLV is as follows.
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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 (TBD2) | Length | Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Vers | Diag |Sta|P|F|C|A|D|M| Detect Mult | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| My Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Your Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Desired Min TX Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Required Min RX Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Required Min Echo RX Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: S-BFD Parameters Sub-TLV Format
Type: To be assigned by IANA from the "BGP Tunnel Encapsulation
Attribute Sub-TLVs" registry (suggested value 22).
Length: Length of the value field in octets. MUST be 24.
Flags: 1 octet. Bits 0-7 are reserved and MUST be set to zero on
transmission and ignored on receipt.
Reserved: 1 octet. MUST be set to zero on transmission and ignored
on receipt.
Other parameters have the same meaning as defined in [RFC7880].
When establishing an S-BFD session, the headend typically acts as an
initiator and the endpoint as a reflector, as described in Section 3
of [RFC7880]. My Discriminator field contains the discriminator that
will be used by the initiator, while Your Discriminator field
specifies the reflector's discriminator.
3. BGP SR Policy Speaker Behavior
A BGP SR Policy speaker that receives an SR Policy UPDATE containing
BFD/S-BFD sub-TLVs MUST perform the following steps:
1. If the BFD/S-BFD sub-TLVs are malformed (e.g., length
inconsistent, reserved fields non-zero), the UPDATE MUST be
handled according to the "treat-as-withdraw" strategy [RFC7606].
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2. If multiple BFD-related sub-TLVs (BFD Parameters, S-BFD
Parameters) are present in the same UPDATE, only the first one is
processed and subsequent ones MUST be ignored.
3. If the sub-TLVs are syntactically valid, the speaker MUST pass
them unchanged to the SRPM together with the rest of the SR
Policy CP information.
The SRPM on the headend node is responsible for interpreting the BFD/
S-BFD parameters and instantiating the corresponding monitoring
sessions in the data plane. If the SRPM cannot support a requested
parameter (e.g., an interval value below its hardware capability), it
SHOULD log an error and MAY fall back to locally configured defaults
or disable BFD/S-BFD for that CP.
4. IANA Considerations
This document defines new Sub-TLVs for the BGP Tunnel Encapsulation
Attribute that enable BFD/S-BFD configuration to be advertised along
with SR Policy Candidate Paths.
IANA is requested to allocate two new code points in the "BGP Tunnel
Encapsulation Attribute Sub-TLVs" registry:
+============+==========================+===============+
| Code Point | Description | Reference |
+============+==========================+===============+
| TBD1 | BFD Parameters Sub-TLV | This document |
+------------+--------------------------+---------------+
| TBD2 | S-BFD Parameters Sub-TLV | This document |
+------------+--------------------------+---------------+
Table 1: BGP Tunnel Encapsulation Attribute Sub-TLV
Values
The suggested values are 21 for BFD Parameters Sub-TLV, 22 for S-BFD
Parameters Sub-TLV.
5. Security Considerations
The security considerations of BGP [RFC4271], BGP SR Policy
[RFC9830], BFD [RFC5880], and S-BFD [RFC7880] apply to this document.
Advertisements of BFD/S-BFD parameters via BGP SR Policy may expose
sensitive network information, such as failure detection
capabilities, session intervals, and discriminator values. These
advertisements should be confined within trusted administrative
domains to prevent information disclosure.
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Malicious modification of BFD/S-BFD parameters in BGP SR Policy
advertisements could lead to denial of service or reduced monitoring
effectiveness. For example, setting extremely short intervals might
overwhelm network resources, while setting inappropriate
discriminators could prevent session establishment. Implementations
should validate received parameters against acceptable ranges before
applying them.
Unauthorized configuration of BFD/S-BFD sessions could be used to
create false failure indications or hide actual failures. Network
operators should ensure that BGP SR Policy sessions carrying BFD/
S-BFD configuration parameters are properly authenticated and
authorized.
For BFD/S-BFD sessions established based on the parameters advertised
via BGP SR Policy, the security mechanisms defined in [RFC5880] and
[RFC7880] should be used to protect against session spoofing and
unauthorized access. This includes using authentication where
appropriate.
6. References
6.1. 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>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[RFC7880] Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.
Pallagatti, "Seamless Bidirectional Forwarding Detection
(S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016,
<https://www.rfc-editor.org/info/rfc7880>.
[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>.
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[RFC9830] Previdi, S., Filsfils, C., Talaulikar, K., Ed., Mattes,
P., and D. Jain, "Advertising Segment Routing Policies in
BGP", RFC 9830, DOI 10.17487/RFC9830, September 2025,
<https://www.rfc-editor.org/info/rfc9830>.
6.2. Informative References
[I-D.ietf-pce-pcep-bfd-parameters]
Fizgeer, M. and O. Bachar, "PCEP Extensions to support BFD
parameters", Work in Progress, Internet-Draft, draft-ietf-
pce-pcep-bfd-parameters-01, 20 August 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
pcep-bfd-parameters-01>.
[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>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[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>.
[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>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/info/rfc8664>.
[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>.
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[RFC9603] Li, C., Ed., Kaladharan, P., Sivabalan, S., Koldychev, M.,
and Y. Zhu, "Path Computation Element Communication
Protocol (PCEP) Extensions for IPv6 Segment Routing",
RFC 9603, DOI 10.17487/RFC9603, July 2024,
<https://www.rfc-editor.org/info/rfc9603>.
Authors' Addresses
Zhenqiang Li (editor)
China Mobile
29 Finance Avenue, Xicheng District
Beijing
China
Email: lizhenqiang@chinamobile.com
Song Liu (editor)
China Mobile
10 Manbai Road, Changping District
Beijing
China
Email: liusongwl@chinamobile.com
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