Optimizing BFD Authentication
draft-ietf-bfd-optimizing-authentication-36

Network Working Group                                    M. Jethanandani
Internet-Draft                                                    Arrcus
Intended status: Experimental                                  A. Mishra
Expires: 15 May 2026                                Aalyria Technologies
                                                                 J. Haas
                                                                     HPE
                                                               A. Saxena
                                                       Ciena Corporation
                                                               M. Bhatia
                                                                  Google
                                                        11 November 2025

                     Optimizing BFD Authentication
              draft-ietf-bfd-optimizing-authentication-36

Abstract

   This document describes an experimental optimization to BFD
   Authentication.  This optimization enables BFD to scale better when
   there is a desire to use authentication where applying the same
   authentication mechanism to every BFD Control Packet may adversely
   impact performance.  This optimization partitions BFD Authentication
   into a more computationally intensive mechanism that is applied to
   BFD significant changes, and a less computationally intensive
   mechanism applied to the majority of BFD Control Packets.

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
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   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 15 May 2026.

Copyright Notice

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

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   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     1.2.  Note to RFC Editor  . . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  BFD Control Packets That Require More Computationally Intensive
           Authentication  . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Protecting BFD Significant Changes with More
           Computationally Intensive Authentication  . . . . . . . .   6
   4.  Using Less Computationally Intensive Auth Types . . . . . . .   6
   5.  Periodic More Computationally Intensive Reauthentication  . .   6
   6.  Optimized Authentication Modes  . . . . . . . . . . . . . . .   7
   7.  Signaling Optimized Authentication  . . . . . . . . . . . . .   8
     7.1.  Transmitting and Receiving Using Optimized
           Authentication  . . . . . . . . . . . . . . . . . . . . .   9
     7.2.  Optimized Authentication Operations . . . . . . . . . . .  10
   8.  Optimizing Authentication YANG Data Model . . . . . . . . . .  11
     8.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .  11
     8.2.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .  11
     8.3.  The YANG Data Model . . . . . . . . . . . . . . . . . . .  11
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
     9.1.  IETF XML Registry . . . . . . . . . . . . . . . . . . . .  15
     9.2.  The YANG Module Names Registry  . . . . . . . . . . . . .  16
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  16
     10.1.  Protocol Security Considerations . . . . . . . . . . . .  16
     10.2.  YANG Security Considerations . . . . . . . . . . . . . .  18
   11. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  18
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  18
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     13.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  21
     A.1.  Single Hop BFD Configuration  . . . . . . . . . . . . . .  21
   Appendix B.  Experimental Status  . . . . . . . . . . . . . . . .  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

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1.  Introduction

   BFD [RFC5880] authentication procedures, when enabled, authenticate
   each control packet using the same authentication mechanism.  Devices
   implementing BFD are often resource constrained and authentication
   may adversely impact the performance of BFD, thus discouraging the
   deployment of authentication.

   When implemented in software, BFD authentication mechanisms compete
   with other necessary work done by the systems implementing the
   protocol.  When implemented using hardware acceleration, these
   mechanisms may scale better situationally, but still impose a cost on
   the implementation.  BFD's value is tied to its ability to scale in
   terms of numbers of sessions, and a detection time that relies on
   sending its control packets at a high rate.  Implementers and
   operators are forced to evaluate tradeoffs of the benefits of
   authentication vs. its impact on BFD performance.

   The authentication mechanisms documented in [RFC5880], MD5
   Message-Digest Algorithm [RFC1321] and Secure Hash Algorithm (SHA-1)
   [RFC3174], are not particularly strong in a cryptographic sense.
   However, they may still not appropriately scale situationally in a
   given implementation.  In the future, there may be a desire to use
   stronger authentication mechanisms than those already specified, and
   those mechanisms are likely to use even more resources.

   The BFD prototocol can broadly be described as the set of procedures
   that handle its state machine changes to reach the Up state, and once
   BFD is in the Up state sending those Up packets at the negotiated
   high rate.  The number of BFD Control Packets needed to signal state
   changes (called significant changes) is very small, while the
   majority of the Control Packets validate that the session remains in
   the Up state.

   This document describes an experimental optimization to BFD
   Authentication.  This optimization partitions BFD Authentication into
   a more computationally intensive (MCI) mechanism used to authenticate
   significant changes, and a less computationally intensive (LCI)
   mechanism applied to the majority of the BFD Control Packets that
   don't signal such significant changes.

   The details of the motivation for experimental status are given in
   Appendix B.

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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.

1.2.  Note to RFC Editor

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

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

   RFC YYYY, where YYYY is the number assigned to
   [I-D.ietf-bfd-secure-sequence-numbers]

   2025-11-12 with the actual date of the publication of this document.

2.  Terminology

   The following terms used in this document have been defined in BFD
   [RFC5880].

   *  Auth Type

   *  Detect Multiplier

   *  Detection Time

   The following terms are introduced in this document.

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      +==================+=========================================+
      | Term             | Meaning                                 |
      +==================+=========================================+
      | significant      | State change, a demand mode change (to  |
      | change           | D bit) or a poll sequence change (P or  |
      |                  | F bit).  Changes to BFD control packets |
      |                  | that do not require a poll sequence,    |
      |                  | such as bfd.DetectMult are also         |
      |                  | considered as a significant change.     |
      +------------------+-----------------------------------------+
      | More             | The authentication mechanism applied to |
      | Computationally  | BFD Control Packets that are            |
      | Intensive (MCI)  | significant changes.                    |
      | authentication   |                                         |
      +------------------+-----------------------------------------+
      | Less             | The authentication mechanism applied to |
      | Computationally  | BFD Control Packets that are NOT        |
      | Intensive (LCI)  | significant changes.                    |
      | authentication   |                                         |
      +------------------+-----------------------------------------+
      | configured MCI   | Interval at which BFD control packets   |
      | reauthentication | are retried using more computationally  |
      | interval         | intensive authentication.               |
      +------------------+-----------------------------------------+

                                 Table 1

   The authentication mechanisms described in this optimization are
   paired as more and less computationally intensive.  While it will be
   generally the case that the relationship between these mechanisms
   will be "stronger" and "less strong", this document doesn't use the
   term "strong" to avoid conflation with either mechanism's relative
   cryptographic strength.  The relative criteria for each mechanism is
   the impact on the implementation.

3.  BFD Control Packets That Require More Computationally Intensive
    Authentication

   The intention of these optimized procedures is to permit more
   computationally intensive authentication for BFD state changes and
   utilize the less computationally intensive authentication mechanisms
   to provide protection for the session in the Up state while
   performing less overall work.  Such procedures are intended to aid
   BFD session scaling without compromising BFD session security.

   All BFD Control Packets with the state AdminDown, Down, and Init MUST
   use MCI authentication.

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   Once the BFD state machine has reached the Up state, it will continue
   to send BFD Control Packets with MCI authentication in the Up state
   for a period as discussed in Section 7.2.  If optimized
   authentication mechanisms are in use, as defined in Section 6, the
   session MAY switch to the LCI mode.

   The contents of an Up packet must not change aside from the
   Authentication Section unless MCI authentication is in use.

3.1.  Protecting BFD Significant Changes with More Computationally
      Intensive Authentication

   This document proposes that BFD control packets that signal a state
   change, a change in demand mode (D bit), or a poll sequence (P or F
   bit change) be categorized as a "significant change".  Control
   packets that do not require a poll sequence, such as bfd.DetectMult
   are also considered as a significant change.

   Such significant changes are intended to be protected by more
   computationally intensive authentication.

4.  Using Less Computationally Intensive Auth Types

   The majority of packets exchanged in a BFD session in the Up state
   are not significant changes.  This document proposes a new optimized
   authentication mode where packets that are not significant changes
   may use a less computationally intensive authentication mechanism.

   Once the session has reached the Up state, the session can use a less
   computationally intensive Auth Type derived from the format in
   Section 7.  Currently, this includes:

   *  Meticulous Keyed ISAAC authentication as described in
      [I-D.ietf-bfd-secure-sequence-numbers].  This authentication type
      protects the BFD session when BFD Up packets do not change,
      because only the paired devices know the shared secret, key, and
      sequence number to select the ISAAC result.

   Other mechanisms may be defined in the future.

5.  Periodic More Computationally Intensive Reauthentication

   When using the less computationally intensive authentication
   mechanism, BFD should periodically test the session using the MCI
   authentication mechanism.  MCI authentication is tested using a Poll
   sequence.  To test MCI authentication, a Poll sequence SHOULD be
   initiated by the sender using the MCI authentication mode rather than
   the LCI mechanism.  If a control packet with the Final (F) bit is not

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   received using MCI authentication within twice the Detect Interval as
   would be calculated by the receiving system, the session has been
   compromised, and MUST be brought down.

   The value "twice the Detect interval as would be calculated by the
   receiving system" is, roughly, twice the number of packets the local
   system would transmit to the receiving system within its own Detect
   Interval.  This accommodates for possible packet loss from the
   sending system during the Poll sequence to the receiving system, plus
   time for the receiving system to transmit control packet with the
   Final (F) bit set to the local system.

   This "more computationally intensive reauthentication interval" for
   performing such periodic tests using the more computationally
   intensive authentication mechanism can be configured depending on the
   capability of the system.

   Most packets transmitted in a BFD session are BFD Up packets.  MCI
   authenticating a limited subset of these packets with a Poll sequence
   as described above, for example every one minute, significantly
   reduces the computational demand for the system while maintaining
   security of the session across the configured MCI reauthentication
   interval.

6.  Optimized Authentication Modes

   The cryptographic authentication mechanisms specified in Section 6.7
   of BFD [RFC5880] describe enabling and disabling of authentication as
   a one time operation.  "... implementations using this mechanism
   SHOULD only allow the authentication state to be changed at most once
   without some form of intervention (so that authentication cannot be
   turned on and off repeatedly simply based on the receipt of BFD
   Control packets from remote systems)."  (Section 6.7.1 of [RFC5880])
   Once enabled, every packet must have Authentication Bit set and the
   associated Authentication Type appended (Section 4.1 of [RFC5880]).
   In addition, it states that an implementation SHOULD NOT allow the
   authentication state to be changed based on the receipt of a BFD
   control packet.

   This document proposes that an "optimized" authentication mode that
   permits both a more computationally intensive authentication mode and
   a less computationally intensive mode to be used within the same BFD
   session.  This pairing of a MCI and a LCI mode of authentication is
   carried in new BFD authentication types representing a given
   optimized authentication type pairing.

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   This document defines in Section 3.1 which BFD control packets
   require MCI authentication.  A BFD control packet that fails
   authentication is discarded, or a BFD control packet that was
   supposed to be MCI authenticated, but was not; e.g. a significant
   change packet, is discarded.  However, there is no change to the
   state machine for BFD, as the decision of a significant change is
   still decided by how many valid consecutive packets were received.

   In this specification, the contents of an Up packet MUST NOT change
   aside from the Authentication Section without MCI authentication.
   The full procedure is documented in the following sections.

7.  Signaling Optimized Authentication

   When the Authentication Present (A) bit is set and the Auth Type
   ([RFC5880], Section 4.1) is a type supporting Optimized BFD
   Authentication, the Auth Type signals a pairing of a more
   computationally intensive authentication type and a less
   computationally intensive authentication type.  This pairing is
   advertised in a single Auth Type value in order to permit
   implementations to be aware that:

   *  Optimized BFD procedures will be in use.

   *  The pairing of the MCI and LCI authentication mechanisms will be
      used for that session.

   *  The requirement to carry a Sequence Number.

   *  The current MCI or LCI mode will be carried as described below:

        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  |   Opt. Mode   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        Sequence Number                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                   Authentication Specific Data                ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 1: Common Optimized BFD Authentication Section

   The values of Auth Type and Auth Len are defined in their respective
   optimized BFD authentication procedural documents.

   The values of the Optimized Authentication Mode field are:

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   1.  When using the more computationally intensive authentication type
       for optimized BFD Auth Types.

   2.  When using the less computationally intensive authentication type
       for optimized BFD Auth Types.

   Authentication Specific Data: When using the more computationally
   intensive authentication type, the remainder of the Authentication
   Section carries that type's data.

7.1.  Transmitting and Receiving Using Optimized Authentication

   The procedures for authenticating BFD Control packets using Optimized
   Authentication is similar to the existing procedures covered in
   Section 6.7 of [RFC5880].  Optimized Authentication modes have common
   procedural requirements for authentication regardless of which more
   or less computationally intensive authentication modes are used.

   The required value of the Auth Len field for a given Optimized
   Authentication mode is defined in the respective specifications for
   their respective more and less computationally intensive modes.

   The following common procedures apply to authenticating BFD Control
   packets utilizing Optimized Authentication:

   If the received BFD Control packet does not contain an Authentication
   Section ([RFC5880], Section 4.1), or the Auth Type is not a supported
   Optimized Authentication Auth Type, then the received packet MUST be
   discarded.

   If the received BFD Control packet contains an optimized
   authentication type using these procedures and the Optimized
   Authentication Mode field is not 1 or 2, then the received packet
   MUST be discarded.

   If bfd.SessionState is AdminDown, Down, or Init and the Optimized
   Authentication Mode field is not 1, then the received packet MUST be
   discarded.

   If bfd.SessionState is Up and there is a significant change as
   defined Section 3.1, and the Optimized Authentication Mode field is
   not 1, then the received packet MUST be discarded.

   If the Auth Len field is not equal to a value appropriate for the
   Optimized Authentication Mode field, the packet MUST be discarded.

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   If bfd.AuthSeqKnown is 1, examine the Sequence Number field.  If the
   sequence number lies outside of the range of bfd.RcvAuthSeq+1 to
   bfd.RcvAuthSeq+(3*Detect Mult) inclusive (when treated as an unsigned
   32-bit circular number space) the received packet MUST be discarded.

   Otherwise (bfd.AuthSeqKnown is 0), bfd.AuthSeqKnown MUST be set to 1,
   bfd.RcvAuthSeq MUST be set to the value of the received Sequence
   Number field, and the received packet MUST be accepted.

   For the specified Auth Type and Optimized Authentication Mode,
   perform the appropriate authentication procedures.  If authentication
   succeeds, the received packet MUST be accepted.  Otherwise, the
   received packet MUST be discarded.

7.2.  Optimized Authentication Operations

   As noted in Section 3.1, when using optimized BFD procedures, more
   computationally intensive authentication is used in the BFD state
   machine to bring a BFD session to the Up state or to make any change
   of the BFD parameters as carried in the BFD Control packet when in
   the Up state.

   Once the BFD session has reached the Up state, the BFD Up state MUST
   be signaled to the remote BFD system using the MCI authentication
   mode for an interval that is at least the Detection Time before
   switching to the LCI authentication mode.  This is to permit
   mechanisms such as Meticulous Keyed ISAAC for BFD Authentication
   [I-D.ietf-bfd-secure-sequence-numbers], or other approved less
   intensive authentication mechanisms, to be bootstrapped before
   switching to the LCI mode.

   It is RECOMMENDED that when using optimized authentication that
   implementations switch from MCI authentication to LCI authentication
   mode after an interval that is at least the Detection Time.  In the
   circumstances where a BFD session successfully reaches the Up state
   with MCI authentication, but there are problems with the LCI
   authentication, this will permit the remote system to tear down the
   session as quickly as possible.

   BFD sessions using optimized authentication that succeed in reaching
   the Up state using MCI authentication and fail using LCI
   authentication SHOULD bring the issue to the attention of the
   operator.  Further, implementations MAY wish to throttle session
   restarts.

   It is further RECOMMENDED that BFD implementations using optimized
   authentication defer notifying their client that the session has
   reached the Up state until it has transitioned to using the LCI

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   authentication mode.  In the event where LCI authentication is
   failing in the protocol, this avoids propagating the failed
   transitions to the LCI mode to their clients.

8.  Optimizing Authentication YANG Data Model

8.1.  Data Model Overview

   The YANG 1.1 [RFC7950] model defined in this document augments the
   "ietf-bfd" module to add data nodes relevant to the management of the
   feature defined in this document.  It adds an interval value that
   specifies how often the BFD session should be re-authenticated using
   more computationally intensive authentication once it is in the Up
   state.

8.2.  Tree Diagram

   The tree diagram for the YANG modules defined in this document use
   annotations defined in YANG Tree Diagrams.  [RFC8340].

   module: ietf-bfd-opt-auth

     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:authentication:
       +--rw reauth-interval?   uint32
     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:authentication:
       +--rw reauth-interval?   uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/bfd:bfd/bfd-lag:lag
               /bfd-lag:sessions/bfd-lag:session/bfd-lag:authentication:
       +--rw reauth-interval?   uint32
     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:authentication:
       +--rw reauth-interval?   uint32

8.3.  The YANG Data Model

   This YANG module imports modules defined in YANG Key Chain [RFC8177],
   A YANG Data Model for Routing Management (NMDA version) [RFC8349],
   and YANG Data Model for Bidirectional Forwarding Detection (BFD)
   [RFC9314].

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   Implementations supporting the optimization procedures defined in
   this document enable optimization by using one of the newly defined
   key-chain crypto-algorithms defined in this YANG module.

   <CODE BEGINS> file "ietf-bfd-opt-auth@2025-11-12.yang"
   module ietf-bfd-opt-auth {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-opt-auth";
     prefix "bfd-oa";

     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 (BFD).";
     }

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

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

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

     import ietf-bfd-mpls {
       prefix bfd-mpls;
       reference

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         "RFC 9314: YANG Data Model for Bidirectional
         Forwarding Detection (BFD).";
     }

     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 (ashesh@aalyria.com)
                 Ankur Saxena (ankurpsaxena@gmail.com)
                 Manav Bhatia (mnvbhatia@google.com)
                 Jeffrey Haas (jhaas@juniper.net).";

     description
       "This YANG module augments the base BFD YANG model to add
        attributes related to the experimental BFD Optimized
        Authentication.

        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).

        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 "2025-11-12" {
       description
         "Initial Version.";
       reference
         "RFC XXXX: Optimizing BFD Authentication.";

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     }

     feature optimized-auth {
       description
         "Indicates that the implementation supports optimized
          authentication.";
       reference
         "RFC XXXX: Optimizing BFD Authentication.";
     }

     grouping bfd-opt-auth-config {
       description
         "Grouping for BFD Optimized Authentication Parameters.";
       leaf reauth-interval {
         type uint32;
         units "seconds";
         default "60";
         description
           "Interval of time after which more computationally intensive
            authentication should be utilized to prevent an
            on-path-attacker attack.

            A value of zero means that we do not do periodic
            reauthentication using the more computationally intensive
            authentication method.

            This value SHOULD have jitter applied to it to avoid
            self-synchronization during expensive authentication
            operations.";
       }
     }

     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:authentication" {
       uses bfd-opt-auth-config;

       description
         "Augment the 'authentication' container for single hop BFD
          module to add attributes related to BFD optimized
          authentication.";
     }

     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:authentication" {

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       uses bfd-opt-auth-config;

       description
         "Augment the 'authentication' container for multi-hop BFD
          module to add attributes related to BFD optimized
          authentication.";
     }

     augment "/rt:routing/rt:control-plane-protocols/" +
             "rt:control-plane-protocol/bfd:bfd/bfd-lag:lag/" +
             "bfd-lag:sessions/bfd-lag:session/" +
             "bfd-lag:authentication" {
       uses bfd-opt-auth-config;

       description
         "Augment the 'authentication' container for BFD over LAG
          module to add attributes related to BFD optimized
          authentication.";
     }

     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:authentication" {
       uses bfd-opt-auth-config;

       description
         "Augment the 'authentication' container for BFD over MPLS
          module to add attributes related to BFD optimized
          authentication.";
     }
   }
   <CODE ENDS>

9.  IANA Considerations

   This documents requests the assignment of one URI and one YANG model.

9.1.  IETF XML Registry

   This document registers one URIs in the "ns" subregistry of the "IETF
   XML" registry [RFC3688].  Following the format in [RFC3688], the
   following registration is requested:

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

9.2.  The YANG Module Names Registry

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

   name:         ietf-bfd-opt-auth
   namespace:    urn:ietf:params:xml:ns:yang:ietf-bfd-opt-auth
   prefix:       bfd-oa
   maintained by IANA: No
   reference:    RFC XXXX

10.  Security Considerations

10.1.  Protocol Security Considerations

   Devices implementing BFD are often resource constrained, whether in a
   single session, or a multidimensional set of scaled sessions.
   Desired detection intervals for the BFD sessions, and their number,
   are common scaling considerations for BFD implementations.  Security
   mechanisms also impact the performance of implementations, whether in
   software or hardware, due to the use of additional computational
   resources these mechanisms use.

   The optimized procedures in this document provide a different level
   of resistance to attack than methods using a single authentication
   mechanism:

   *  The more computationally intensive authentication mechanisms used
      for optimized authentication are expected to have similar
      cryptographic strength acceptable for BFD for authenticating the
      entire session, as described in [RFC5880].

   *  When the BFD state machine is attempting to move from the Down
      state to the Up state, the more computationally intensive
      authentication mechanism is intended to protect vs. attempts to
      inappropriately start BFD sessions.

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   *  When the BFD state machine is in the Up state, the more
      computationally intensive authentication mechanism is intended to
      protect vs. attempts to change BFD session parameters or to reset
      the BFD session.

   *  When the BFD state machine is in the Up state, the less
      computationally intensive authentication mechanism is intended to
      provide resistance to keeping a BFD session in the Up state
      inappropriately.  Since the procedures for changing BFD state
      require the more computationally intensive mechanism and the less
      computationally intensive mechanism requires that the contents of
      the Control Packet in the Up state not change its contents, the
      only thing that successfully spoofing such packets can do is keep
      the session Up.

   *  The periodic more computationally intensive re-authentication
      procedure provides protection against long-term successful
      spoofing of the less computationally intensive authentication
      mechanism.

   In other words, the intention of optimized BFD procedures is to make
   it difficult to reset or inappropriately start BFD sessions.
   However, protecting against keeping the session Up is seen as a less
   interesting attack and can receive less protection.

   The recent escalating series of attacks on MD5 and SHA-1 described in
   Finding Collisions in the Full SHA-1 [SHA-1-attack1] and New
   Collision Search for SHA-1 [SHA-1-attack2] raise concerns about their
   remaining useful lifetime as outlined in Updated Security
   Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithm
   [RFC6151] and Security Considerations for the SHA-0 and SHA-1
   Message-Digest Algorithm [RFC6194].  If replaced by stronger
   algorithms the computational overhead will make the task of
   authenticating every packet even more difficult to achieve.

   The procedures described in this document provide a mechanism which
   could enable implementations to leverage stronger security to address
   the concerns above when strong authentication is required.  However,
   this requires operators to evaluate the tradeoffs of the less
   computationally intensive mechanisms adequately address their desired
   security stance.

   Keys generated and distributed out of band for the purposes described
   in this specification are generally limited in the security they can
   provide.  It is essential that these keys are selected well, and
   protected when stored.

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10.2.  YANG Security Considerations

   This section is modeled after the template described in Section 3.7
   of [I-D.ietf-netmod-rfc8407bis].

   The "ietf-bfd-opt-auth" YANG module defines a data model that is
   designed to be accessed via YANG-based management protocols, such as
   NETCONF [RFC6241] or RESTCONF [RFC8040].  These YANG-based management
   protocols (1) have to use a secure transport layer (e.g., SSH
   [RFC4252] TLS [RFC8446], and QUIC [RFC9000]) and (2) have to use
   mutual authentication.

   The Network Configuration 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.

   There are a number of data nodes defined in this YANG module that are
   writable/creatable/deletable (i.e., "config true", which is the
   default).  All writable data nodes are likely to be sensitive or
   vulnerable in some network environments.  Write operations (e.g.,
   edit-config) and delete operations to these data nodes without proper
   protection or authentication can have a negative effect on network
   operations.  The following subtrees and data nodes have particular
   sensitivities/vulnerabilities:

   *  'reauth-interval' specifies the interval in Up state, after which
      more computationally intensive authentication SHOULD be performed
      to prevent a Person-In-The-Middle (PITM) attack.  If this interval
      is set very low, the utility of these optimization procedures is
      lessened.  If this interval is set very high, attacks detected by
      the more computationally intensive authentication mechanisms may
      happen overly late.

   There are no particularly sensitive readable data nodes.

   There are no RPC operations defined in this model.

11.  Contributors

   The authors of this document would like to acknowledge Reshad Rahman
   as a contributor to this document.

12.  Acknowledgments

   The authors would like to thank Qiufang Ma, Stephen Farrell, and Acee
   Lindem for providing directorate review of this document.

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13.  References

13.1.  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>.

   [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>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [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>.

   [RFC8177]  Lindem, A., Ed., Qu, Y., Yeung, D., Chen, I., and J.
              Zhang, "YANG Data Model for Key Chains", RFC 8177,
              DOI 10.17487/RFC8177, June 2017,
              <https://www.rfc-editor.org/info/rfc8177>.

   [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>.

   [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>.

13.2.  Informative References

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   [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>.

   [I-D.ietf-netmod-rfc8407bis]
              Bierman, A., Boucadair, M., and Q. Wu, "Guidelines for
              Authors and Reviewers of Documents Containing YANG Data
              Models", Work in Progress, Internet-Draft, draft-ietf-
              netmod-rfc8407bis-28, 5 June 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
              rfc8407bis-28>.

   [RFC1321]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
              DOI 10.17487/RFC1321, April 1992,
              <https://www.rfc-editor.org/info/rfc1321>.

   [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, DOI 10.17487/RFC2026, October 1996,
              <https://www.rfc-editor.org/info/rfc2026>.

   [RFC3174]  Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1
              (SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001,
              <https://www.rfc-editor.org/info/rfc3174>.

   [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>.

   [RFC6151]  Turner, S. and L. Chen, "Updated Security Considerations
              for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
              RFC 6151, DOI 10.17487/RFC6151, March 2011,
              <https://www.rfc-editor.org/info/rfc6151>.

   [RFC6194]  Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security
              Considerations for the SHA-0 and SHA-1 Message-Digest
              Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011,
              <https://www.rfc-editor.org/info/rfc6194>.

   [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>.

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   [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>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [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>.

   [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>.

   [SHA-1-attack1]
              Wang, X., Yin, Y., and H. Yu, "Finding Collisions in the
              Full SHA-1", 2005.

   [SHA-1-attack2]
              Wang, X., Yao, A., and F. Yao, "New Collision Search for
              SHA-1", 2005.

Appendix A.  Examples

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

A.1.  Single Hop BFD Configuration

   This example demonstrates how a Single Hop BFD session can be
   configured for optimized authentication.

   =============== 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:opt-auth="urn:ietf:params:xml:ns:yang:ietf-bfd-opt-auth"
       xmlns:bfd-mki="urn:ietf:params:xml:ns:yang:ietf-bfd-met-keyed-i\
   saac">

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     <key-chain>
       <name>bfd-auth-config</name>
       <description>"An example for BFD Optimized Auth configuration."\
   </description>
       <key>
         <key-id>55</key-id>
         <lifetime>
           <send-lifetime>
             <start-date-time>2017-01-01T00:00:00Z</start-date-time>
             <end-date-time>2017-02-01T00:00:00Z</end-date-time>
           </send-lifetime>
           <accept-lifetime>
             <start-date-time>2016-12-31T23:59:55Z</start-date-time>
             <end-date-time>2017-02-01T00:00:05Z</end-date-time>
           </accept-lifetime>
         </lifetime>
         <crypto-algorithm>bfd-mki:optimized-sha1-meticulous-keyed-isa\
   ac</crypto-algorithm>
         <key-string>
           <keystring>testvector</keystring>
         </key-string>
       </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:iana-bfd-types="urn:ietf:params:xml:ns:yang:iana-bfd-type\
   s"
       xmlns:opt-auth="urn:ietf:params:xml:ns:yang:ietf-bfd-opt-auth"
       xmlns:bfd-mki="urn:ietf:params:xml:ns:yang:ietf-bfd-met-keyed-i\
   saac">
     <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>

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                 <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>
                 <authentication>
                   <key-chain>bfd-auth-config</key-chain>
                   <opt-auth:reauth-interval>30</opt-auth:reauth-inter\
   val>
                 </authentication>
               </session>
             </sessions>
           </ip-sh>
         </bfd>
       </control-plane-protocol>
     </control-plane-protocols>
   </routing>

Appendix B.  Experimental Status

   This document describes an experiment that presents a candidate
   solution to update BFD Authentication that is currently specified in
   [RFC5880].  This experiment is intended to provide additional
   insights into what happens when the optimized authentication
   mechanism defined in this document is used.  Here are the reasons why
   this document is on the Experimental track:

   *  In the initial stages of the document, there were significant
      participation and reviews from the working group.  Since then,
      there has been considerable changes to the document, e.g. the use
      of ISAAC, allowing for ISAAC bootstrapping when a BFD session
      comes up and use of a single Auth Type to indicate use of
      optimized authentication etc.  These changes did not get
      significant review from the working group and therefore does not
      meet the bar set in Section 4.1.1 of [RFC2026]

   *  There are no known implementations at this time.

   *  The work in this document could become very valuable in the
      future, especially if the need for deploying BFD authentication at
      scale becomes a reality.

   This document is classified as Experimental and is not part of the
   IETF Standards Track.  Implementations based on this document should
   not be considered as compliant with BFD [RFC5880].

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Authors' Addresses

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

   Ashesh Mishra
   Aalyria Technologies
   Email: ashesh@aalyria.com

   Jeffrey Haas
   HPE
   Email: jhaas@juniper.net

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

   Manav Bhatia
   Google
   Doddanekkundi
   Bangalore 560048
   India
   Email: mnvbhatia@google.com

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