Optimizing BFD Authentication
draft-ietf-bfd-optimizing-authentication-25

Network Working Group                                    M. Jethanandani
Internet-Draft                                                    Arrcus
Intended status: Experimental                                  A. Mishra
Expires: 6 December 2025                            Aalyria Technologies
                                                               A. Saxena
                                                       Ciena Corporation
                                                               M. Bhatia
                                                                  Google
                                                                 J. Haas
                                                        Juniper Networks
                                                             4 June 2025

                     Optimizing BFD Authentication
              draft-ietf-bfd-optimizing-authentication-25

Abstract

   This document describes an experimental optimization to BFD
   Authentication.  It provides procedure where only important BFD state
   transitions require strong authentication and permits the majority of
   BFD Control Packets to use a less computationally intensive
   authentication mechanism.  This enables BFD to scale better when
   there is a desire to use strong authentication.

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 6 December 2025.

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 . . . . . . . . . . . . . . . . . .   3
     1.2.  Note to RFC Editor  . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  BFD Control Packets That Require Strong Authentication  . . .   4
     3.1.  Protecting BFD Significant Changes with Strong
           Authentication  . . . . . . . . . . . . . . . . . . . . .   5
   4.  Using Less Computationally Intensive Auth Types . . . . . . .   5
   5.  Periodic Strong Reauthentication  . . . . . . . . . . . . . .   5
   6.  Optimized Authentication Modes  . . . . . . . . . . . . . . .   6
   7.  Signaling Optimized Authentication  . . . . . . . . . . . . .   6
     7.1.  Transmitting and Receiving Using Optimized
           Authentication  . . . . . . . . . . . . . . . . . . . . .   8
     7.2.  Optimized Authentication Operations . . . . . . . . . . .   9
   8.  Optimizing Authentication YANG Model  . . . . . . . . . . . .  10
     8.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .  10
     8.2.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .  10
     8.3.  The YANG Model  . . . . . . . . . . . . . . . . . . . . .  10
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
     9.1.  IETF XML Registry . . . . . . . . . . . . . . . . . . . .  15
     9.2.  The YANG Module Names Registry  . . . . . . . . . . . . .  15
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  15
     10.1.  Protocol Security Considerations . . . . . . . . . . . .  15
     10.2.  YANG Security Considerations . . . . . . . . . . . . . .  16
   11. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  17
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  17
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  17
     13.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  19
     A.1.  Single Hop BFD Configuration  . . . . . . . . . . . . . .  20
   Appendix B.  Experimental Status  . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

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1.  Introduction

   Authenticating every BFD [RFC5880] control packet with MD5
   Message-Digest Algorithm [RFC1321], or Secure Hash Algorithm (SHA-1)
   is a computationally intensive process.  This makes it difficult, if
   not impossible, to authenticate BFD every packet at high session
   scale and at faster rates.

   This document describes an experimental procedure whereby only
   important BFD state transitions require strong authentication.  The
   majority of BFD Control Packets use a less computationally intensive
   authentication mechanism.  The details of the motivation for
   experimental status are given in Appendix B.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD 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.

   2025-06-04 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 D     |
    | change           | 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.RequiredMinRxInterval,                   |
    |                  | bfd.RequiredMinTxInterval, or bfd.DetectMult |
    |                  | are also considered as a significant change. |
    +------------------+----------------------------------------------+
    | configured       | Interval at which BFD control packets are    |
    | strong           | retried with strong authentication.          |
    | reauthentication |                                              |
    | interval         |                                              |
    +------------------+----------------------------------------------+

                                  Table 1

3.  BFD Control Packets That Require Strong Authentication

   For purposes of this document, "strong authentication" refers to BFD
   authentication mechanisms such as those already defined for use with
   BFD.  For example, MD5 and SHA1.  (Section 6.7 of [RFC5880]) The use
   of stronger cryptographic mechanisms such as SHA2 while using
   optimized BFD authentication is left for future study.

   The intention of these optimized procedures is to permit strong
   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 will aid BFD session scaling without
   compromising BFD session security.

   All BFD Control Packets with the states AdminDown, Down, and Init
   require strong authentication.

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

   The contents of an Up packet MUST NOT change aside from the
   Authentication Section without strong authentication.

   In addition to these requirements, BFD "significant changes" require
   strong authentication:

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3.1.  Protecting BFD Significant Changes with Strong 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 a change in
   bfd.RequiredMinRxInterval or bfd.RequiredMinTxInterval, are also
   considered as a significant change.

   Such significant changes are intended to be protected by strong
   authentication.

4.  Using Less Computationally Intensive Auth Types

   The majority of packets exchanged on 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.  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.

5.  Periodic Strong Reauthentication

   When using the less computationally intensive authentication
   mechanism, BFD should periodically test the session using the strong
   authentication mechanism.  Strong authentication is tested using a
   Poll sequence.  To test strong authentication, a Poll sequence SHOULD
   be initiated by the sender using the strong authentication mode
   rather than the less computationally intensive mechanism.  If a
   control packet with the Final (F) bit is not received within the
   Detect Interval, the session has been compromised, and MUST be
   brought down.

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

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   Most packets transmitted on a BFD session are BFD Up packets.
   Strongly authenticating a small 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 strong
   reauthentication interval.

6.  Optimized Authentication Modes

   The cryptographic authentication mechanisms specified in Section 6.7
   of BFD [RFC5880] describes enabling and disabling of authentication
   as a one time operation.  As a security precaution, it mentions that
   authentication state be allowed to change at most once.  Once
   enabled, every packet must have Authentication Bit set and the
   associated Authentication Type appended.  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 strong authentication mode and a less computationally
   intensive mode to be used within the same BFD session.  This pairing
   of a strong and an less computationally intensive mode of
   authentication is carried in new BFD authentication types
   representing a given optimized authentication type pairing.

   This document defines in Section 3.1 which BFD control packets are
   required to be strongly authenticated.  A BFD control packet that
   fails authentication is discarded, or a BFD control packet that was
   supposed to be strongly 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 strong 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 is a
   type supporting Optimized BFD Authentication, the Auth Type signals a
   pairing of a strong 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.

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   *  The pairing of the strong and less computationally intensive
      authentication mechanisms will be used for that session.

   *  The requirement to carry a Sequence Number.

   *  The current strong or less computationally intensive 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 BFD Authentication Section

   The Meticulous Keyed MD5 (Section 6.7.3 of [RFC5880]), Meticulous
   Keyed SHA-1 (Section 6.7.4 of [RFC5880]), and Meticulous Keyed ISAAC
   Authentication (Section 5 of [I-D.ietf-bfd-secure-sequence-numbers])
   Sections define the fourth octet as "Reserved".  This document
   repurposes the "Reserved" field as the "Optimized Authentication
   Mode" field when used for authentication types for optimized BFD
   procedures.

   The values of the Optimized Authentication Mode field are:

   1.  When using the strong 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 strong authentication
   type, the remainder of the Authentication Section carries that type's
   data.

   For example, for Auth Type "Optimized MD5 Meticulous Keyed ISAAC
   Authentication" (type TBD):

   When Optimized Authentication Mode is 1, the format of the
   authentication section is the same as Section 4.3 of [RFC5880],
   excepting that Auth Type is still TBD and that Reserved is set to 1.

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   When Optimized Authentication Mode is 2, the format of the
   authentication section is the same as Section 5 of
   [I-D.ietf-bfd-secure-sequence-numbers], excepting that Auth Type is
   still TBD and that Reserved is set to 2.

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 strong
   and 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
   the strong mode and less computationally intensive mode.

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

   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.

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   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, strong
   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 strong authentication
   mode for an interval that is at least the Detection Time before
   switching to the less computationally intensive authentication mode.
   This is to permit mechanisms such as Meticulous Keyed ISAAC for BFD
   Authentication [I-D.ietf-bfd-secure-sequence-numbers] to be
   bootstrapped before switching to the less computationally intensive
   mode.

   It is RECOMMENDED that when using optimized authentication that
   implementations switch from strong authentication to the less
   computationally intensive 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 strong authentication,
   but there are problems with the optimized 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 strong authentication and fail using the optimized
   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 optimized
   authentication mode.  In the event where optimized authentication is
   failing in the protocol, this avoids propagating the failed
   transitions to the optimized mode to their clients.

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8.  Optimizing Authentication YANG Model

8.1.  Data Model Overview

   The YANG 1.1 [RFC7950] model defined in this document augments the
   "ietf-bfd" module to add configuration relevant to the management of
   the feature defined in this document.  In particular, it adds crypto
   algorithms that are described in this model, and in Meticulous Keyed
   ISAAC for BFD Authentication [I-D.ietf-bfd-secure-sequence-numbers].
   It adds a feature statement to enable optimized authentication.
   Finally, it adds an interval value that specifies how often the BFD
   session should be re-authenticated 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 Model

   This YANG module imports 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@2025-06-04.yang"
   module ietf-bfd-opt-auth {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-opt-auth";
     prefix "bfdoa";

     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).";
     }

     import ietf-key-chain {
       prefix key-chain;
       reference
         "RFC 8177: YANG Data Model for Key Chains.";
     }

     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 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.";

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     revision "2025-06-04" {
       description
         "Initial Version.";
       reference
         "RFC XXXX: Optimizing BFD Authentication.";
     }

     feature optimized-auth {
       description
         "When enabled, this implementation supports optimized
          authentication as described in this document.";
     }

     identity optimized-md5-meticulous-keyed-isaac {
       base key-chain:crypto-algorithm;
       description
         "BFD Optimized Authentication using Meticulous Keyed MD5 as the
          strong authentication and Meticulous Keyed ISAAC Keyed as the
          less computationally intensive authentication.";
       reference
         "RFC XXXX: Meticulous Keyed ISAAC for BFD Authentication.";
     }

     identity optimized-sha1-meticulous-keyed-isaac {
       base key-chain:crypto-algorithm;
       description
         "BFD Optimized Authentication using Meticulous Keyed SHA-1 as
         the strong authentication and Meticulous Keyed ISAAC Keyed as
         the less computationally intensive authentication.";
       reference
         "RFC XXXX: Meticulous Keyed ISAAC for 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 strong authentication
            should be utilized to prevent an on-path-attacker attack.
            Default is 1 minute.

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

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            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" {
       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;

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       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:

   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:       bfdoa
   reference:    RFC XXXX

10.  Security Considerations

10.1.  Protocol Security Considerations

   The approach described in this document enhances the ability to
   authenticate a BFD session by taking away the onerous requirement
   that every BFD control packet be strongly authenticated.  By strongly
   authenticating packets that affect the state of the session, the
   security of the BFD session is maintained.  In this mode, packets
   that are a significant change but are not strongly authenticated, are
   dropped by the system.  Therefore, a malicious user that tries to

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   inject a non-authenticated packet; e.g. with a Down state to take a
   session down will fail.  That combined with the proposal of using
   sequence number defined in Meticulous Keyed ISAAC for BFD
   Authentication [I-D.ietf-bfd-secure-sequence-numbers] further
   enhances the security of BFD sessions.

   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.

10.2.  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].  The lowest NETCONF layer
   is the secure transport layer, and the mandatory-to-implement secure
   transport is Secure Shell (SSH) [RFC6242].  The lowest RESTCONF layer
   is HTTPS, and the mandatory-to-implement secure transport is TLS
   [RFC8446].  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.

   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).  These data nodes may be considered sensitive or vulnerable
   in some network environments.  Write operations (e.g., edit-config)
   to these data nodes without proper protection can have a negative
   effect on network operations.  Some of the subtrees and data nodes
   and their sensitivity/vulnerability are described here.

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   *  'reauth-interval' specifies the interval in Up state, after which
      a strong 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 strong
      authentication mechanisms may happen overly late.

   Some of the readable data nodes in this 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.

   There are no read-only data nodes defined in this model.

   Some of the RPC operations in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control access to these operations.

   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 and Stephen Farrell for
   providing directorate review of this document.

13.  References

13.1.  Normative References

   [I-D.ietf-bfd-secure-sequence-numbers]
              DeKok, A., Jethanandani, M., Agarwal, S., Mishra, A., and
              A. Saxena, "Meticulous Keyed ISAAC for BFD Optimized
              Authentication", Work in Progress, Internet-Draft, draft-
              ietf-bfd-secure-sequence-numbers-20, 5 May 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-bfd-
              secure-sequence-numbers-20>.

   [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>.

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   [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>.

   [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>.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

   [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>.

   [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>.

   [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>.

   [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>.

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   [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>.

   [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

   [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>.

   [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>.

   [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>.

   [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.

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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">
     <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 xmlns:opt-auth=
         "urn:ietf:params:xml:ns:yang:ietf-bfd-opt-auth">opt-auth:opti\
   mized-sha1-meticulous-keyed-isaac</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"

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       xmlns:opt-auth="urn:ietf:params:xml:ns:yang:ietf-bfd-opt-auth">
     <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>
                 <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 method
   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]

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   *  There are no known implementations (even proof-of-concept) or
      implementation plans.  As a result, we do not currently know if
      there will be interop issues with legacy implementations or what
      exactly are the performance benefits of the optimization method.

   *  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].

Authors' Addresses

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

   Ashesh Mishra
   Aalyria Technologies
   Email: ashesh@aalyria.com

   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

   Jeffrey Haas
   Juniper Networks
   Email: jhaas@pfrc.org

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