



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.




Li & Liu                 Expires 17 August 2026                 [Page 1]

Internet-Draft      SR Policy for  BFD Configuration       February 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
   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.















Li & Liu                 Expires 17 August 2026                 [Page 2]

Internet-Draft      SR Policy for  BFD Configuration       February 2026


   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].






Li & Liu                 Expires 17 August 2026                 [Page 3]

Internet-Draft      SR Policy for  BFD Configuration       February 2026


   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.










Li & Liu                 Expires 17 August 2026                 [Page 4]

Internet-Draft      SR Policy for  BFD Configuration       February 2026


      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.













Li & Liu                 Expires 17 August 2026                 [Page 5]

Internet-Draft      SR Policy for  BFD Configuration       February 2026


       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].




Li & Liu                 Expires 17 August 2026                 [Page 6]

Internet-Draft      SR Policy for  BFD Configuration       February 2026


   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.



Li & Liu                 Expires 17 August 2026                 [Page 7]

Internet-Draft      SR Policy for  BFD Configuration       February 2026


   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>.





Li & Liu                 Expires 17 August 2026                 [Page 8]

Internet-Draft      SR Policy for  BFD Configuration       February 2026


   [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>.







Li & Liu                 Expires 17 August 2026                 [Page 9]

Internet-Draft      SR Policy for  BFD Configuration       February 2026


   [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





























Li & Liu                 Expires 17 August 2026                [Page 10]
