



Network Working Group                                          A. Mishra
Internet-Draft                                      Aalyria Technologies
Intended status: Experimental                            M. Jethanandani
Expires: 7 May 2026                                         Arrcus, Inc.
                                                               A. Saxena
                                                       Ciena Corporation
                                                           S. Pallagatti
                                                                 Zscaler
                                                                 M. Chen
                                                                  Huawei
                                                         3 November 2025


                             BFD Stability
                      draft-ietf-bfd-stability-21

Abstract

   This document describes extensions to the Bidirectional Forwarding
   Detection (BFD) protocol to measure BFD stability.  Specifically, it
   describes a mechanism for the detection of BFD packet loss.

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 7 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



Mishra, et al.             Expires 7 May 2026                   [Page 1]

Internet-Draft                BFD Stability                November 2025


   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.  Note to the RFC Editor  . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Functionality . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  NULL Auth Type  . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Theory of Operation . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Loss Measurement  . . . . . . . . . . . . . . . . . . . .   6
     6.2.  Out of Order Packets  . . . . . . . . . . . . . . . . . .   7
   7.  Stability YANG Module . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .   7
     7.2.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
     8.1.  Auth Type . . . . . . . . . . . . . . . . . . . . . . . .  14
     8.2.  IETF XML Registry . . . . . . . . . . . . . . . . . . . .  14
     8.3.  The "YANG Module Names" Registry  . . . . . . . . . . . .  15
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
     9.1.  BFD NULL Auth Security Considerations . . . . . . . . . .  15
     9.2.  YANG Security Considerations  . . . . . . . . . . . . . .  16
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  16
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  16
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  17
     12.2.  Informative References . . . . . . . . . . . . . . . . .  18
   Appendix A.  Experimental Status  . . . . . . . . . . . . . . . .  19
   Appendix B.  Examples . . . . . . . . . . . . . . . . . . . . . .  19
     B.1.  Single Hop BFD Configuration  . . . . . . . . . . . . . .  19
     B.2.  Use of NULL Auth  . . . . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   The Bidirectional Forwarding Detection (BFD) [RFC5880] protocol
   operates by transmitting and receiving BFD control packets, generally
   at high frequency, over the datapath being monitored.  In order to
   prevent significant data loss due to a datapath failure, BFD session
   detection time as defined in BFD [RFC5880] is set to the smallest
   feasible value.






Mishra, et al.             Expires 7 May 2026                   [Page 2]

Internet-Draft                BFD Stability                November 2025


   A BFD [RFC5880] session will remain in the Up state as long as it
   receives at least one BFD packet within the Detection Time interval.
   However, additional packet loss within that time interval is not
   noted by the BFD state machinery.  Noting the other missed packets
   provides a valuable indicator of systemic issues or a deteriorating
   network that may warrant preventive action.

   This document proposes an experimental mechanism to detect lost
   packets in a BFD session in addition to the datapath fault detection
   mechanisms of BFD.  Such a mechanism, combined with 'received-packet-
   count' defined in the YANG Data Model for Bidrectional Forward
   Detection (BFD) [RFC9314] permits operators to measure the stability
   of BFD sessions.  The details of the motivation for experimental
   status can be found in Appendix A.  Implementations may also do
   additional analysis of the packet loss over a time interval.  Such an
   analysis is outside the scope of this document.

   This document does not propose any BFD extension to measure data
   traffic loss or delay on a link or tunnel, and the scope is limited
   to BFD packets.

1.1.  Note to the RFC Editor

   This document uses several placeholder values throughout the
   document.  Please replace them as follows and remove this section
   before publication.

   RFC XXXX, where XXXX is the number assigned to this document at the
   time of publication.

   2025-10-30, with the actual date of the publication of this document.

2.  Terminology

   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 RFC
   2119 [RFC2119] and RFC 8174 [RFC8174].

   The reader is expected to be familiar with the BFD [RFC5880].  In
   particular, the term 'meticulous' specified in Meticulous Keyed ISAAC
   for BFD Optimized Authentication
   [I-D.ietf-bfd-secure-sequence-numbers] means that the Sequence number
   is incremented on every new packet that is sent.







Mishra, et al.             Expires 7 May 2026                   [Page 3]

Internet-Draft                BFD Stability                November 2025


3.  Use Cases

   Bidirectional Forwarding Detection, as defined in BFD [RFC5880]
   cannot detect any BFD packet loss if the loss does not last for the
   Detection Time.  This document proposes a method to detect dropped
   packets on the receiver.  For example, if the receiver receives BFD
   control packet k at time t but receives packet k+3 at time t+10ms,
   and never receives packet k+1 and/or k+2, then it has experienced a
   packet loss.

   This proposal enables BFD implementations to generate diagnostic
   information on the health of each BFD session that could be used to
   preempt probability of a failure on a datapath that BFD was
   monitoring by allowing time for a corrective action to be taken.

   In a faulty datapath scenario, an operator can use BFD health
   information to trigger the delay and loss measurement OAM protocol
   Connectivity Fault Management (CFM) [Y-1731] or Packet Loss and Delay
   Measurement for MPLS Networks [RFC6374] to further isolate the issue.

4.  Functionality

   BFD stability measurement requires that a BFD Meticulous
   Authentication type is configured.

   The ietf-bfd-stability YANG model, defined in this document, provides
   the ability to configure BFD stability measurement for BFD sessions
   by configuring the 'stability' flag.  The 'lost-packet-count' leaf
   permits monitoring of stability issues as defined in this document
   for BFD sessions that have the stability flag enabled.

   The configuration of BFD stability measurement and monitoring using
   other methods than the attached YANG model is out of scope from this
   document.

5.  NULL Auth Type

   The NULL Authentication Type, defined in this document, can be used
   to provide a meticulously increasing sequence number BFD [RFC5880]
   for stability measurement.  It provides none of the protections
   desired for authentication and is used only to provide BFD stability
   services to BFD sessions that otherwise have no authentication in
   use.

   If the Authentication Present (A) bit is set in the header as defined
   in Section 4 of BFD [RFC5880], and the Authentication Type field
   contains TBD, the Authentication section has the following format:




Mishra, et al.             Expires 7 May 2026                   [Page 4]

Internet-Draft                BFD Stability                November 2025


        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Auth Type   |   Auth Len    |  Auth Key ID  |   Reserved    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        Sequence Number                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 1: NULL Auth Type

   where:

   Auth Type (8 bits): The Authentication Type, which in this case is
   TBD (NULL, to be assigned by IANA, with a suggested value of 6).

   Auth Len (8 bits): The length of the NULL Auth Type, in bytes; i.e.,
   8 bytes

   Auth Key ID (8 bits): The authentication key ID in use for this
   packet.  MUST be set to zero and MUST be ignored on receipt.

   Reserved (8 bits): This byte MUST be set to zero on transmit and MUST
   be ignored on receipt.

   Sequence Number (32 bits): The sequence number for this packet.  This
   value is incremented for each successive packet transmitted for a
   session.  Implementations will use sequence numbers (bfd.XmitAuthSeq)
   as defined in BFD [RFC5880].

   If bfd.AuthSeqKnown is 1, and the received Sequence Number field is
   not equal to bfd.RcvAuthSeq + 1 (in a circular number space), then
   the loss count is incremented by the difference between the received
   Sequence Number and bfd.RcvAuthSeq and bfd.RcvAuthSeq is set to the
   received Sequence Number.

   Otherwise (bfd.AuthSeqKnown is 0), bfd.AuthSeqKnown MUST be set to 1,
   and bfd.RcvAuthSeq MUST be set to the value of the received Sequence
   Number field as defined in BFD [RFC5880], Section 6.8.1, and the
   packet MUST be accepted.

   According to BFD [RFC5880], Section 6.7.3 a receiver MUST discard a
   received packet that lies outside the range of bfd.RcvAuthSeq and
   bfd.RcvAuthSeq + (3 * Detect Multi).  If it is within that range, but
   is missing a packet, it can be used to detect a loss.  In case of
   NULL authentication where packets containing sequence numbers are
   accepted on receipt, an attacker with unauthenticated sequence number
   could move the Sequence Number forward.  Meanwhile, the actual BFD
   neighbor that continues to send packets will find them discarded and



Mishra, et al.             Expires 7 May 2026                   [Page 5]

Internet-Draft                BFD Stability                November 2025


   the session would drop.  To prevent such an attack, the received
   Sequence Number MUST NOT be compared with bfd.RcvAuthSeq for purposes
   of discarding the BFD packets.

6.  Theory of Operation

   This mechanism allows operators to measure the loss of BFD control
   packets.  A BFD authentication type carrying a meticulously
   increasing sequence number is required to support this loss
   measurement.  Authentication types that provide for meticulously
   increasing sequence numbers include:

   *  Meticulously Keyed MD5 and SHA1, defined in [RFC5880].

   *  Meticulously Keyed ISAAC, defined in
      [I-D.ietf-bfd-secure-sequence-numbers].

   *  The NULL authentication mechanism, which does not provide for
      authentication but carries a meticulously increasing sequence
      number, defined in this document.

   Other authentication types that provide for meticulously increasing
   sequence numbers appropriate for this mechanism may be defined in
   future specifications.

6.1.  Loss Measurement

   Loss measurement counts the number of BFD control packets missed at
   the receiver during any Detection Time BFD [RFC5880], Section 6.8.4
   period.  The loss is detected by comparing the Sequence Number field
   in successive BFD control packets.  The Sequence Number in each
   successive control packet generated on a BFD session by the
   transmitter is incremented by one.  This loss count can then be
   exposed using the YANG module defined in the subsequent section.  See
   discussion on Out of Order Packets (Section 6.2) later in the
   document.

   The first BFD authentication section with a non-zero sequence number,
   in a valid BFD control packet, processed by the receiver, is used for
   bootstrapping the logic.











Mishra, et al.             Expires 7 May 2026                   [Page 6]

Internet-Draft                BFD Stability                November 2025


6.2.  Out of Order Packets

   Some transmission mechanisms - for example, Link Aggregate Groups
   (LAG), or Equal Cost Multipath (ECMP) - can result in out of order
   packet delivery.  In circumstances where BFD packets are not lost,
   but are delivered out of order, strict comparison of increasing
   sequence numbers may result in classifying the out of order packets
   as packet loss.

   Implementations MAY provide mechanisms wherein all expected packets
   received across an expected interval, but delivered out of order are
   not considered lost packets.

7.  Stability YANG Module

7.1.  Data Model Overview

   This YANG module augments the base BFD YANG module to add attributes
   such as the flag 'stability' related to the experiment of BFD
   Stability.  The feature statement 'stability' needs to be enabled to
   indicate that BFD Stability is supported by the implementation.  In
   addition, a loss count per-session or lsp for BFD packets that are
   lost has also been added in this model.




























Mishra, et al.             Expires 7 May 2026                   [Page 7]

Internet-Draft                BFD Stability                November 2025


   module: ietf-bfd-stability

     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh
               /bfd-ip-sh:sessions/bfd-ip-sh:session:
       +--rw stability?   boolean {stability}?
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/bfd:bfd/bfd-ip-mh:ip-mh
               /bfd-ip-mh:session-groups/bfd-ip-mh:session-group:
       +--rw stability?   boolean {stability}?
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/bfd:bfd/bfd-lag:lag
               /bfd-lag:sessions/bfd-lag:session:
       +--rw stability?   boolean {stability}?
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/bfd:bfd/bfd-mpls:mpls
               /bfd-mpls:session-groups/bfd-mpls:session-group:
       +--rw stability?   boolean {stability}?
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh
               /bfd-ip-sh:sessions/bfd-ip-sh:session
               /bfd-ip-sh:session-statistics:
       +--ro lost-packet-count?   yang:counter64 {stability}?
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/bfd:bfd/bfd-ip-mh:ip-mh
               /bfd-ip-mh:session-groups/bfd-ip-mh:session-group
               /bfd-ip-mh:sessions/bfd-ip-mh:session-statistics:
       +--ro lost-packet-count?   yang:counter64 {stability}?
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/bfd:bfd/bfd-lag:lag
               /bfd-lag:sessions/bfd-lag:session/bfd-lag:member-links
               /bfd-lag:micro-bfd-ipv4/bfd-lag:session-statistics:
       +--ro lost-packet-count?   yang:counter64 {stability}?
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/bfd:bfd/bfd-lag:lag
               /bfd-lag:sessions/bfd-lag:session/bfd-lag:member-links
               /bfd-lag:micro-bfd-ipv6/bfd-lag:session-statistics:
       +--ro lost-packet-count?   yang:counter64 {stability}?
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/bfd:bfd/bfd-mpls:mpls
               /bfd-mpls:session-groups/bfd-mpls:session-group
               /bfd-mpls:sessions/bfd-mpls:session-statistics:
       +--ro lost-packet-count?   yang:counter64 {stability}?








Mishra, et al.             Expires 7 May 2026                   [Page 8]

Internet-Draft                BFD Stability                November 2025


7.2.  YANG Module

   This YANG module imports modules defined in Common YANG Types
   [RFC6991], A YANG Data Model for Routing [RFC8349], and YANG Data
   Model for Bidirectional Forwading Detection (BFD) [RFC9314].

   <CODE BEGINS> file "ietf-bfd-stability@2025-10-30.yang"
   module ietf-bfd-stability {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-stability";
     prefix "bfd-s";

     import ietf-yang-types {
       prefix "yang";
       reference
         "RFC 6991: Common YANG Data Types";
     }

     import ietf-routing {
       prefix "rt";
       reference
         "RFC 8349: A YANG Data Model for Routing Management
          (NMDA version)";
     }

     import ietf-bfd {
       prefix bfd;
       reference
         "RFC 9314: YANG Data Model for Bidirectional
          Forwarding Detection.";
     }

     import ietf-bfd-ip-sh {
       prefix bfd-ip-sh;
       reference
         "RFC 9314: YANG Data Model for Bidirectional
          Forwarding Detection.";
     }

     import ietf-bfd-ip-mh {
       prefix bfd-ip-mh;
       reference
         "RFC 9314: YANG Data Model for Bidirectional
          Forwarding Detection.";
     }

     import ietf-bfd-lag {
       prefix bfd-lag;



Mishra, et al.             Expires 7 May 2026                   [Page 9]

Internet-Draft                BFD Stability                November 2025


       reference
         "RFC 9314: YANG Data Model for Bidirectional
          Forwarding Detection.";
     }

     import ietf-bfd-mpls {
       prefix bfd-mpls;
       reference
         "RFC 9314: YANG Data Model for Bidirectional
          Forwarding Detection.";
     }

     import ietf-key-chain {
       prefix key-chain;
       reference
         "RFC 8177: YANG Key Chain.";
     }

     organization
       "IETF BFD Working Group";

     contact
       "WG Web:   <http://tools.ietf.org/wg/bfd>
        WG List:  <rtg-bfd@ietf.org>

        Authors: Mahesh Jethanandani (mjethanandani@gmail.com)
                 Ashesh Mishra (mishra.ashesh@gmail.com)
                 Ankur Saxena (ankurpsaxena@gmail.com)
                 Santosh Pallagatti (santosh.pallagati@gmail.com)
                 Mach Chen (mach.chen@huawei.com).";


     description
       "This YANG module augments the base BFD YANG model to add
        experimental attributes related to BFD Stability.
        In particular, it adds a per-session count for BFD packets
        that are lost.

        Copyright (c) 2025 IETF Trust and the persons identified as
        authors of the code.  All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject to
        the license terms contained in the Revised BSD License set
        forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (https://trustee.ietf.org/license-info).




Mishra, et al.             Expires 7 May 2026                  [Page 10]

Internet-Draft                BFD Stability                November 2025


        This version of this YANG module is part of RFC XXXX
        (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
        for full legal notices.

        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 (RFC 2119) (RFC 8174) when, and only when,
        they appear in all capitals, as shown here.";

     revision "2025-10-30" {
       description
         "Initial Version.";
       reference
         "RFC XXXX: BFD Stability.";
     }

     feature stability {
       description
         "This feature enables BFD sessions to be monitored for lost
          packets.";
     }

     identity null-auth {
       base key-chain:crypto-algorithm;
       description
         "BFD Null Auth type defined in this draft.";
       reference
         "RFC XXXX: BFD Stability.";
     }

     grouping lost-packet-count {
       leaf lost-packet-count {
         if-feature "stability";
         type yang:counter64;
         description
           "Number of BFD packets that were lost, where loss is
            determined by the fact that the sequence number is
            not consecutive. This counter should be present only if
            stability is configured.";
       }
       description
         "Grouping of statistics related to BFD stability.";
     }

     augment "/rt:routing/rt:control-plane-protocols/" +
             "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh/" +
             "bfd-ip-sh:sessions/bfd-ip-sh:session" {



Mishra, et al.             Expires 7 May 2026                  [Page 11]

Internet-Draft                BFD Stability                November 2025


       leaf stability {
         if-feature "stability";
         type boolean;
         must "../bfd-ip-sh:authentication/bfd-ip-sh:meticulous = " +
              "'true'";
         default false;
         description
           "If set to true, this enables the BFD session to monitor
            for stability, i.e., to watch how many packets are getting
            dropped.";
       }
       description
         "Augment the 'bfd' container to add attributes related to BFD
          stability for IP Single Hop Sessions.";
     }

     augment "/rt:routing/rt:control-plane-protocols/" +
             "rt:control-plane-protocol/bfd:bfd/bfd-ip-mh:ip-mh/" +
             "bfd-ip-mh:session-groups/bfd-ip-mh:session-group" {
       leaf stability {
         if-feature "stability";
         type boolean;
         must "../bfd-ip-mh:authentication/bfd-ip-mh:meticulous = " +
              "'true'";
         default false;
         description
           "If set to true, this enables the BFD session to monitor
            for stability, i.e., to watch how many packets are getting
            dropped.";
       }
       description
         "Augment the 'bfd' container to add attributes related to BFD
          stability for Multi Hop Sessions.";
     }

     augment "/rt:routing/rt:control-plane-protocols/" +
             "rt:control-plane-protocol/bfd:bfd/bfd-lag:lag/" +
             "bfd-lag:sessions/bfd-lag:session" {
       leaf stability {
         if-feature "stability";
         type boolean;
         must "../bfd-lag:authentication/bfd-lag:meticulous = " +
              "'true'";
         default false;
         description
           "If set to true, this enables the BFD session to monitor
            for stability, i.e., to watch how many packets are getting
            dropped.";



Mishra, et al.             Expires 7 May 2026                  [Page 12]

Internet-Draft                BFD Stability                November 2025


       }
       description
         "Augment the 'bfd' container to add attributes related to BFD
          stability for LAG session.";
     }

     augment "/rt:routing/rt:control-plane-protocols/" +
             "rt:control-plane-protocol/bfd:bfd/bfd-mpls:mpls/" +
       "bfd-mpls:session-groups/bfd-mpls:session-group" {
       leaf stability {
         if-feature "stability";
         type boolean;
         must "../bfd-mpls:authentication/bfd-mpls:meticulous = " +
              "'true'";
         default false;
         description
           "If set to true, this enables the BFD session to monitor
            for stability, i.e., to watch how many packets are getting
            dropped.";
       }
       description
         "Augment the 'bfd' container to add attributes related to BFD
          stability for MPLS.";
     }

     augment "/rt:routing/rt:control-plane-protocols/" +
             "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh/" +
             "bfd-ip-sh:sessions/bfd-ip-sh:session/" +
             "bfd-ip-sh:session-statistics" {
       uses lost-packet-count;
       description
         "Augment the 'bfd' container to add statistics related to BFD
          stability for IP Single Hop Sessions.";
     }

     augment "/rt:routing/rt:control-plane-protocols/" +
             "rt:control-plane-protocol/bfd:bfd/bfd-ip-mh:ip-mh/" +
             "bfd-ip-mh:session-groups/bfd-ip-mh:session-group/" +
             "bfd-ip-mh:sessions/bfd-ip-mh:session-statistics" {
       uses lost-packet-count;
       description
         "Augment the 'bfd' container to add statistics related to BFD
          stability for IP Multi Hop Sessions.";
     }

     augment "/rt:routing/rt:control-plane-protocols/" +
             "rt:control-plane-protocol/bfd:bfd/bfd-lag:lag/" +
             "bfd-lag:sessions/bfd-lag:session/bfd-lag:member-links/" +



Mishra, et al.             Expires 7 May 2026                  [Page 13]

Internet-Draft                BFD Stability                November 2025


             "bfd-lag:micro-bfd-ipv4/bfd-lag:session-statistics" {
       uses lost-packet-count;
       description
         "Augment the 'bfd' container to add statistics related to BFD
          stability for Micro BFD sessions for IPv4.";
     }

     augment "/rt:routing/rt:control-plane-protocols/" +
             "rt:control-plane-protocol/bfd:bfd/bfd-lag:lag/" +
             "bfd-lag:sessions/bfd-lag:session/bfd-lag:member-links/" +
             "bfd-lag:micro-bfd-ipv6/bfd-lag:session-statistics" {
       uses lost-packet-count;
       description
         "Augment the 'bfd' container to add statistics related to BFD
          stability for Micro BFD sessions for IPv6.";
     }

     augment "/rt:routing/rt:control-plane-protocols/" +
             "rt:control-plane-protocol/bfd:bfd/bfd-mpls:mpls/" +
             "bfd-mpls:session-groups/bfd-mpls:session-group/" +
             "bfd-mpls:sessions/bfd-mpls:session-statistics" {
       uses lost-packet-count;
       description
         "Augment the 'bfd' container to add statistics related to BFD
          stability for MPLS sessions.";
     }
   }
   <CODE ENDS>

8.  IANA Considerations

   This document requests one new authentication type and registers one
   URIs in the "ns" subregistry of the "IETF XML" registry [RFC3688].

8.1.  Auth Type

   This document requests an update to the registry titled "BFD
   Authentication Types".  IANA is requested to assign a new BFD
   AuthType:

   *  NULL Auth Type, with a suggested value of 6.

8.2.  IETF XML Registry

   Following the format in [RFC3688], the following registrations are
   requested:





Mishra, et al.             Expires 7 May 2026                  [Page 14]

Internet-Draft                BFD Stability                November 2025


   URI: urn:ietf:params:xml:ns:yang:ietf-bfd-stability
   Registrant Contact: The IESG
   XML: N/A, the requested URI is an XML namespace.


8.3.  The "YANG Module Names" Registry

   This document registers one YANG module in the "YANG Module Names"
   registry [RFC6020].  Following the format in [RFC6020], the following
   registrations are requested:

   name:         ietf-bfd-stability
   namespace:    urn:ietf:params:xml:ns:yang:ietf-bfd-stability
   prefix:       bfd-s
   reference:    RFC XXXX

9.  Security Considerations

9.1.  BFD NULL Auth Security Considerations

   The use of a BFD authentication mechanism that protects the BFD
   packets is RECOMMENDED.

   The Security Considerations of [RFC5880] for unauthenticated BFD all
   apply to the new NULL authentication type.  The NULL Authentication
   type, defined in this document, provides none of the properties
   desired for authenticating BFD packets.  It is intended to provide
   BFD sessions that otherwise would not use authentication, a sequence
   number that can be used for purposes of detecting lost packets.

   The lack of a computed AuthKey/Digest over the BFD packet, but the
   presence of a Sequence Number makes this authentication type
   susceptible to injection attacks.  BFD without authentication is
   vulnerable to session resets; the NULL Auth type does not change
   this.

   When the NULL Authentication type is used for BFD Stability purposes,
   maliciously injected packets that do not reset the BFD session can
   resemble high packet loss.  Sessions such as multi-hop routed paths,
   tunnels without authentication, or MPLS LSP, therefore, have security
   guarantees that are identical to situations where BFD is run without
   authentication.









Mishra, et al.             Expires 7 May 2026                  [Page 15]

Internet-Draft                BFD Stability                November 2025


9.2.  YANG Security Considerations

   The YANG module specified in this document defines a schema for data
   that is designed to be accessed via network management protocols such
   as NETCONF [RFC6241] or RESTCONF [RFC8040].  These YANG-based
   management protocols have to use a secure transport layer (e.g., SSH
   [RFC4252], TLS [RFC8446], and QUIC [RFC9000]) and have to use mutual
   authentication.

   The NETCONF Access Control Model (NACM) [RFC8341] provides the means
   to restrict access for particular NETCONF or RESTCONF users to a
   preconfigured subset of all available NETCONF or RESTCONF protocol
   operations and content.

   The YANG module does not define any writeable/creatable/deletable
   data nodes that can have an adverse impact on a BFD session.

   The only readable data nodes in YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control read access (e.g., via get, get-config, or
   notification) to these data nodes.

   The model defines a read-only node to indicate the number of packets
   that were lost.  Access to this information may allow a malicious
   user information on which links are experiencing issues.  In
   addition, and as stated in Out of Order Packets (Section 6.2), on
   links such as LAG or ECMP, there is a possibility of packets being
   delivered out-of-order.  A strict comparison of increasing sequence
   numbers may result in classifying those out of order packets as
   packet loss.

   The YANG module does not define any RPC operations.

10.  Contributors

   The authors of this document would like to acknowledge Jeff Haas as a
   contributor to this document.  His contribution lead to a significant
   improvement of the document.  In addition, Manav Bhatia contributed
   to this document.

11.  Acknowledgements

   Authors would like to thank Nobo Akiya, Dileep Singh, Basil Saji,
   Sagar Soni, Albert Fu, Peng Fang, and Mallik Mudigonda who
   contributed to this document.  Thanks to Christian Huitema for the
   SECDIR and Ebben Aries for the YANG Doctors review.

   Thanks to Reshad Rehman for being the shepherd of the document.



Mishra, et al.             Expires 7 May 2026                  [Page 16]

Internet-Draft                BFD Stability                November 2025


12.  References

12.1.  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>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC4252]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
              January 2006, <https://www.rfc-editor.org/info/rfc4252>.

   [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>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
              RFC 6991, DOI 10.17487/RFC6991, July 2013,
              <https://www.rfc-editor.org/info/rfc6991>.

   [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>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [RFC8349]  Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for
              Routing Management (NMDA Version)", RFC 8349,
              DOI 10.17487/RFC8349, March 2018,
              <https://www.rfc-editor.org/info/rfc8349>.








Mishra, et al.             Expires 7 May 2026                  [Page 17]

Internet-Draft                BFD Stability                November 2025


   [RFC9314]  Jethanandani, M., Ed., Rahman, R., Ed., Zheng, L., Ed.,
              Pallagatti, S., and G. Mirsky, "YANG Data Model for
              Bidirectional Forwarding Detection (BFD)", RFC 9314,
              DOI 10.17487/RFC9314, September 2022,
              <https://www.rfc-editor.org/info/rfc9314>.

12.2.  Informative References

   [I-D.ietf-bfd-secure-sequence-numbers]
              DeKok, A., Jethanandani, M., Agarwal, S., Mishra, A., and
              J. Haas, "Meticulous Keyed ISAAC for BFD Optimized
              Authentication", Work in Progress, Internet-Draft, draft-
              ietf-bfd-secure-sequence-numbers-27, 16 October 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-bfd-
              secure-sequence-numbers-27>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC6374]  Frost, D. and S. Bryant, "Packet Loss and Delay
              Measurement for MPLS Networks", RFC 6374,
              DOI 10.17487/RFC6374, September 2011,
              <https://www.rfc-editor.org/info/rfc6374>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC9000]  Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,
              <https://www.rfc-editor.org/info/rfc9000>.

   [Y-1731]   ITU-T, "OAM Functions and Mechanisms for Ethernet-based
              Networks", Recommendation G.8013/Y.1731, November 2013.










Mishra, et al.             Expires 7 May 2026                  [Page 18]

Internet-Draft                BFD Stability                November 2025


Appendix A.  Experimental Status

   This document describes an experiment that will present a candidate
   solution to predict whether a given BFD [RFC5880] session will
   continue to be stable.  The experiment will use the packet lost count
   and the 'received-packet-count' defined in the YANG Data Model for
   Bidirectional Forward Detection (BFD) [RFC9314] to determine how
   stable is the session.  The reason why this document is on an
   Experimental track is because there are no known implementations or
   proof-of-concept.  As a result, the authors are not clear whether a
   simple lost count is enough to predict the stability or there will be
   a need to have a more granular count.

   This document is classified as Experimental and is not part of the
   IETF Standards Track.

Appendix B.  Examples

   This section tries to show some examples in how the model can be
   configured for stability.

B.1.  Single Hop BFD Configuration

   This example demonstrates how a Single Hop BFD session can be
   configured to enable monitoring of a session for stability.

   =============== NOTE: '\' line wrapping per RFC 8792 ===============

   <?xml version="1.0" encoding="UTF-8"?>
   <key-chains
       xmlns="urn:ietf:params:xml:ns:yang:ietf-key-chain"
       xmlns:kc="urn:ietf:params:xml:ns:yang:ietf-key-chain">
     <key-chain>
       <name>bfd-stability-config</name>
       <description>"An example for BFD Stabalized configuration."</de\
   scription>
       <key>
         <key-id>55</key-id>
         <lifetime>
           <send-lifetime>
             <start-date-time>2025-01-01T00:00:00Z</start-date-time>
             <end-date-time>2025-02-01T00:00:00Z</end-date-time>
           </send-lifetime>
           <accept-lifetime>
             <start-date-time>2024-12-31T23:59:55Z</start-date-time>
             <end-date-time>2025-02-01T00:00:05Z</end-date-time>
           </accept-lifetime>
         </lifetime>



Mishra, et al.             Expires 7 May 2026                  [Page 19]

Internet-Draft                BFD Stability                November 2025


         <crypto-algorithm>kc:sha-1</crypto-algorithm>
       </key>
     </key-chain>
   </key-chains>
   <interfaces
       xmlns="urn:ietf:params:xml:ns:yang:ietf-interfaces"
       xmlns:if-type="urn:ietf:params:xml:ns:yang:iana-if-type">
     <interface>
       <name>eth0</name>
       <type>if-type:ethernetCsmacd</type>
     </interface>
   </interfaces>
   <routing
       xmlns="urn:ietf:params:xml:ns:yang:ietf-routing"
       xmlns:bfd-types="urn:ietf:params:xml:ns:yang:ietf-bfd-types"
       xmlns:stability="urn:ietf:params:xml:ns:yang:ietf-bfd-stability\
   ">
     <control-plane-protocols>
       <control-plane-protocol>
         <type>bfd-types:bfdv1</type>
         <name>name:BFD</name>
         <bfd xmlns="urn:ietf:params:xml:ns:yang:ietf-bfd">
           <ip-sh xmlns="urn:ietf:params:xml:ns:yang:ietf-bfd-ip-sh">
             <sessions>
               <session>
                 <interface>eth0</interface>
                 <dest-addr>2001:db8:0:113::101</dest-addr>
                 <desired-min-tx-interval>10000</desired-min-tx-interv\
   al>
                 <required-min-rx-interval>
                   10000
                 </required-min-rx-interval>
                 <stability:stability>true</stability:stability>
                 <authentication>
                   <key-chain>bfd-stability-config</key-chain>
                   <meticulous>true</meticulous>
                 </authentication>
               </session>
             </sessions>
           </ip-sh>
         </bfd>
       </control-plane-protocol>
     </control-plane-protocols>
   </routing>







Mishra, et al.             Expires 7 May 2026                  [Page 20]

Internet-Draft                BFD Stability                November 2025


B.2.  Use of NULL Auth

   This example demonstrates how to configure NULL Auth to enable
   monitoring of a session for stability.

   =============== NOTE: '\' line wrapping per RFC 8792 ===============

   <?xml version="1.0" encoding="UTF-8"?>
   <key-chains
       xmlns="urn:ietf:params:xml:ns:yang:ietf-key-chain"
       xmlns:stability="urn:ietf:params:xml:ns:yang:ietf-bfd-stability\
   ">
     <key-chain>
       <name>bfd-stability-config</name>
       <description>"An example for BFD Stability configuration."</des\
   cription>
       <key>
         <key-id>55</key-id>
         <lifetime>
           <send-lifetime>
             <start-date-time>2025-01-01T00:00:00Z</start-date-time>
             <end-date-time>2025-02-01T00:00:00Z</end-date-time>
           </send-lifetime>
           <accept-lifetime>
             <start-date-time>2024-12-31T23:59:55Z</start-date-time>
             <end-date-time>2025-02-01T00:00:05Z</end-date-time>
           </accept-lifetime>
         </lifetime>
         <crypto-algorithm>stability:null-auth</crypto-algorithm>
       </key>
     </key-chain>
   </key-chains>
   <interfaces
       xmlns="urn:ietf:params:xml:ns:yang:ietf-interfaces"
       xmlns:if-type="urn:ietf:params:xml:ns:yang:iana-if-type">
     <interface>
       <name>eth0</name>
       <type>if-type:ethernetCsmacd</type>
     </interface>
   </interfaces>
   <routing
       xmlns="urn:ietf:params:xml:ns:yang:ietf-routing"
       xmlns:bfd-types="urn:ietf:params:xml:ns:yang:ietf-bfd-types"
       xmlns:stability="urn:ietf:params:xml:ns:yang:ietf-bfd-stability\
   ">
     <control-plane-protocols>
       <control-plane-protocol>
         <type>bfd-types:bfdv1</type>



Mishra, et al.             Expires 7 May 2026                  [Page 21]

Internet-Draft                BFD Stability                November 2025


         <name>name:BFD</name>
         <bfd xmlns="urn:ietf:params:xml:ns:yang:ietf-bfd">
           <ip-sh xmlns="urn:ietf:params:xml:ns:yang:ietf-bfd-ip-sh">
             <sessions>
               <session>
                 <interface>eth0</interface>
                 <dest-addr>2001:db8:0:113::101</dest-addr>
                 <desired-min-tx-interval>10000</desired-min-tx-interv\
   al>
                 <required-min-rx-interval>
                   10000
                 </required-min-rx-interval>
                 <stability:stability>true</stability:stability>
                 <authentication>
                   <key-chain>bfd-stability-config</key-chain>
                   <meticulous>true</meticulous>
                 </authentication>
               </session>
             </sessions>
           </ip-sh>
         </bfd>
       </control-plane-protocol>
     </control-plane-protocols>
   </routing>


Authors' Addresses

   Ashesh Mishra
   Aalyria Technologies
   Email: ashesh@aalyria.com


   Mahesh Jethanandani
   Arrcus, Inc.
   United States of America
   Email: mjethanandani@gmail.com


   Ankur Saxena
   Ciena Corporation
   3939 North 1st Street
   San Jose, CA 95134
   United States of America
   Email: ankurpsaxena@gmail.com
   URI:   www.ciena.com





Mishra, et al.             Expires 7 May 2026                  [Page 22]

Internet-Draft                BFD Stability                November 2025


   Santosh Pallagatti
   Zscaler
   Bangalore 560103
   Karnataka
   India
   Email: santosh.pallagatti@gmail.com


   Mach Chen
   Huawei
   Email: mach.chen@huawei.com








































Mishra, et al.             Expires 7 May 2026                  [Page 23]
