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BFD Stability
draft-ietf-bfd-stability-15

Document Type Active Internet-Draft (bfd WG)
Authors Ashesh Mishra , Mahesh Jethanandani , Ankur Saxena , Santosh Pallagatti , Mach Chen
Last updated 2024-07-04
Replaces draft-ashesh-bfd-stability
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
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Stream WG state In WG Last Call
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Document shepherd Reshad Rahman
Shepherd write-up Show Last changed 2020-07-23
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Send notices to Reshad Rahman <reshad@yahoo.com>
draft-ietf-bfd-stability-15
Network Working Group                                          A. Mishra
Internet-Draft                                      Aalyria Technologies
Intended status: Standards Track                         M. Jethanandani
Expires: 5 January 2025                                   Kloud Services
                                                               A. Saxena
                                                       Ciena Corporation
                                                           S. Pallagatti
                                                                  VMware
                                                                 M. Chen
                                                                  Huawei
                                                             4 July 2024

                             BFD Stability
                      draft-ietf-bfd-stability-15

Abstract

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

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 5 January 2025.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights

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   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Functionality . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  NULL Auth Type  . . . . . . . . . . . . . . . . . . . . . . .   3
   6.  Theory of Operation . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Loss Measurement  . . . . . . . . . . . . . . . . . . . .   5
     6.2.  Out of Order Packets  . . . . . . . . . . . . . . . . . .   5
   7.  Stability YANG Module . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .   6
     7.2.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     8.1.  Auth Type . . . . . . . . . . . . . . . . . . . . . . . .  13
     8.2.  IETF XML Registry . . . . . . . . . . . . . . . . . . . .  13
     8.3.  The "YANG Module Names" Registry  . . . . . . . . . . . .  14
   9.  Security Consideration  . . . . . . . . . . . . . . . . . . .  14
     9.1.  YANG Security Considerations  . . . . . . . . . . . . . .  14
     9.2.  BFD NULL Auth Security Considerations . . . . . . . . . .  15
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  15
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
   12. Normative References  . . . . . . . . . . . . . . . . . . . .  15
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  17
     A.1.  Single Hop BFD Configuration  . . . . . . . . . . . . . .  17
     A.2.  Use of NULL Auth  . . . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction

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

   This document proposes a mechanism to detect lost packets in a BFD
   session in addition to the datapath fault detection mechanisms of
   BFD.  Such a mechanism presents significant value to measure the
   stability of BFD sessions and provides data to the operators for the
   cause of a BFD failure.

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

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in RFC
   2119 [RFC2119] and RFC 8174 [RFC8174].

   The reader is expected to be familiar with the BFD [RFC5880],
   Optimizing BFD Authentication
   [I-D.ietf-bfd-optimizing-authentication] and Meticulous Keyed ISAAC
   for BFD Authentication [I-D.ietf-bfd-secure-sequence-numbers].

3.  Use Cases

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

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

   In a faulty datapath scenario, an operator can use BFD health
   information to trigger delay and loss measurement OAM protocol
   (Connectivity Fault Management (CFM) or Loss Measurement (LM)-Delay
   Measurement (DM)) to further isolate the issue.

4.  Functionality

   The functionality proposed for BFD stability measurement is achieved
   by configuring the 'stability' flag in the attached YANG model in
   conjunction with any BFD Meticulous Authentication.

5.  NULL Auth Type

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

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   If the Authentication Present (A) bit is set in the header, and the
   Authentication Type field contains TBD, the Authentication section
   has the following format:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Auth Type   |   Auth Len    |  Auth Key ID  |   Reserved    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        Sequence Number                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 1: NULL Auth Type

   where:

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

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

   Auth Key ID: The authentication key ID in use for this packet.  Must
   be set to zero and ignored on receipt.

   Reserved: This byte MUST be set to zero on transmit and ignored on
   receipt.

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

   If bfd.AuthSeqKnown is 0, bfd.AuthSeqKnown is set to 1, and
   bfd.RcvAuthSeq is set to the value of the received Sequence Number
   field.

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

   Unlike other authentication mechanisms defined for BFD that provide
   an Auth Key/Digest field, when bfd.AuthSeqKnown is 1, the received
   Sequence Number MUST NOT be compared vs. bfd.RcvAuthSeq for purposes
   of discarding the BFD packets.

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6.  Theory of Operation

   This mechanism allows operators to measure the loss of BFD control
   packets.

   When using MD5 or SHA authentication, BFD MUST use an authentication
   type (bfd.AuthType) that is of type meticulous.  Other authentication
   types that provide for meticulously increasing sequence numbers can
   also be used.  This includes the NULL authentication mechanism
   defined in this document or Meticulous Keyed ISAAC for BFD
   Authentication [I-D.ietf-bfd-secure-sequence-numbers].

6.1.  Loss Measurement

   Loss measurement counts the number of BFD control packets missed at
   the receiver during any Detection Time period.  The loss is detected
   by comparing the Sequence Number field in successive BFD control
   packets.  The Sequence Number in each successive control packet
   generated on a BFD session by the transmitter is incremented by one.
   This loss count can then be exposed using the YANG module defined in
   the subsequent section.

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

6.2.  Out of Order Packets

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

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

7.  Stability YANG Module

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7.1.  Data Model Overview

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

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   module: ietf-bfd-stability

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

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7.2.  YANG Module

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

   <CODE BEGINS> file "ietf-bfd-stability@2024-07-05.yang"
   module ietf-bfd-stability {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-stability";
     prefix "bfds";

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

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

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

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

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

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

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

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

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

     organization
       "IETF BFD Working Group";

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

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

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

        Copyright (c) 2024 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

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        (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 "2024-07-05" {
       description
         "Initial Version.";
       reference
         "RFC XXXX: BFD Stability.";
     }

     feature stability {
       description
         "If supported, the feature allows for BFD sessions to be
          monitored for frames lost.";
     }

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

     grouping lost-packet-count {
       leaf lost-packet-count {
         if-feature "stability";
         type yang:counter64;
         description
           "Number of BFD packets that were lost without bringing the
            session down. This counter should be present only if
            stability is configured.";
       }
       description
         "Grouping of statistics related to BFD stability.";
     }

     augment "/rt:routing/rt:control-plane-protocols/" +
             "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh/" +
             "bfd-ip-sh:sessions/bfd-ip-sh:session" {
       leaf stability {
         if-feature "stability";

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

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

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

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

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

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

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

     augment "/rt:routing/rt:control-plane-protocols/" +
             "rt:control-plane-protocol/bfd:bfd/bfd-lag:lag/" +
             "bfd-lag:sessions/bfd-lag:session/bfd-lag:member-links/" +
             "bfd-lag:micro-bfd-ipv4/bfd-lag:session-statistics" {
       uses lost-packet-count;

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       description
         "Augment the 'bfd' container to add statistics related to BFD
          stability for Micro BFD sessions for IPv4.";
     }

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

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

8.  IANA Considerations

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

8.1.  Auth Type

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

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

8.2.  IETF XML Registry

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

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

8.3.  The "YANG Module Names" Registry

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

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

9.  Security Consideration

9.1.  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.

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

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

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

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   The YANG module does not define any RPC operations.

9.2.  BFD NULL Auth Security Considerations

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

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

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

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

10.  Contributors

   The authors of this document would like to acknowledge Jeff Haas as a
   contributor to this document.  Jeff played a role not only as a
   shepherd but also actively contributed to the improvement of the
   document.  In addition, Manav Bhatia and Peng Fang contributed to
   this document.

11.  Acknowledgements

   Authors would like to thank Nobo Akiya, Dileep Singh, Basil Saji,
   Sagar Soni, Albert Fu and Mallik Mudigonda who also contributed to
   this document.

12.  Normative References

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   [I-D.ietf-bfd-optimizing-authentication]
              Jethanandani, M., Mishra, A., Saxena, A., Bhatia, M., and
              J. Haas, "Optimizing BFD Authentication", Work in
              Progress, Internet-Draft, draft-ietf-bfd-optimizing-
              authentication-17, 1 July 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-bfd-
              optimizing-authentication-17>.

   [I-D.ietf-bfd-secure-sequence-numbers]
              DeKok, A., Jethanandani, M., Agarwal, S., Mishra, A., and
              A. Saxena, "Meticulous Keyed ISAAC for BFD
              Authentication", Work in Progress, Internet-Draft, draft-
              ietf-bfd-secure-sequence-numbers-15, 20 May 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-bfd-
              secure-sequence-numbers-15>.

   [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>.

   [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>.

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

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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>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

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

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

   [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>.

Appendix A.  Examples

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

A.1.  Single Hop BFD Configuration

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

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

   <?xml version="1.0" encoding="UTF-8"?>
   <key-chains
       xmlns="urn:ietf:params:xml:ns:yang:ietf-key-chain"
       xmlns:kc="urn:ietf:params:xml:ns:yang:ietf-key-chain">
     <key-chain>
       <name>bfd-stability-config</name>
       <description>"An example for BFD Stabalized configuration."</de\
   scription>

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

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                 </authentication>
               </session>
             </sessions>
           </ip-sh>
         </bfd>
       </control-plane-protocol>
     </control-plane-protocols>
   </routing>

A.2.  Use of NULL Auth

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

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

   <?xml version="1.0" encoding="UTF-8"?>
   <key-chains
       xmlns="urn:ietf:params:xml:ns:yang:ietf-key-chain"
       xmlns:stability="urn:ietf:params:xml:ns:yang:ietf-bfd-stability\
   ">
     <key-chain>
       <name>bfd-stability-config</name>
       <description>"An example for BFD Stability configuration."</des\
   cription>
       <key>
         <key-id>55</key-id>
         <lifetime>
           <send-lifetime>
             <start-date-time>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>stability:null-auth</crypto-algorithm>
       </key>
     </key-chain>
   </key-chains>
   <interfaces
       xmlns="urn:ietf:params:xml:ns:yang:ietf-interfaces"
       xmlns:if-type="urn:ietf:params:xml:ns:yang:iana-if-type">
     <interface>
       <name>eth0</name>
       <type>if-type:ethernetCsmacd</type>

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

Authors' Addresses

   Ashesh Mishra
   Aalyria Technologies
   Email: ashesh@aalyria.com

   Mahesh Jethanandani
   Kloud Services
   CA
   United States of America
   Email: mjethanandani@gmail.com

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

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

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

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