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Versions: (draft-zheng-bfd-yang) 00 01 02 03 04 05 06 07 08 09 10

Network Working Group                                     R. Rahman, Ed.
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                           L. Zheng, Ed.
Expires: September 3, 2018                           Huawei Technologies
                                                    M. Jethanandani, Ed.

                                                           S. Pallagatti

                                                               G. Mirsky
                                                         ZTE Corporation
                                                           March 2, 2018


      YANG Data Model for Bidirectional Forwarding Detection (BFD)
                       draft-ietf-bfd-yang-10.txt

Abstract

   This document defines a YANG data model that can be used to configure
   and manage Bidirectional Forwarding Detection (BFD).

   The YANG modules in this document conform to the Network Management
   Datastore Architecture (NMDA).

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 September 3, 2018.

Copyright Notice

   Copyright (c) 2018 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



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   (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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Design of the Data Model  . . . . . . . . . . . . . . . . . .   4
     2.1.  Design of Configuration Model . . . . . . . . . . . . . .   5
       2.1.1.  Common BFD configuration parameters . . . . . . . . .   6
       2.1.2.  Single-hop IP . . . . . . . . . . . . . . . . . . . .   7
       2.1.3.  Multihop IP . . . . . . . . . . . . . . . . . . . . .   7
       2.1.4.  MPLS Traffic Engineering Tunnels  . . . . . . . . . .   8
       2.1.5.  MPLS Label Switched Paths . . . . . . . . . . . . . .   8
       2.1.6.  Link Aggregation Groups . . . . . . . . . . . . . . .   9
     2.2.  Design of Operational State Model . . . . . . . . . . . .   9
     2.3.  Notifications . . . . . . . . . . . . . . . . . . . . . .  10
     2.4.  RPC Operations  . . . . . . . . . . . . . . . . . . . . .  10
     2.5.  BFD top level hierarchy . . . . . . . . . . . . . . . . .  10
     2.6.  BFD IP single-hop hierarchy . . . . . . . . . . . . . . .  10
     2.7.  BFD IP multihop hierarchy . . . . . . . . . . . . . . . .  12
     2.8.  BFD over LAG hierarchy  . . . . . . . . . . . . . . . . .  14
     2.9.  BFD over MPLS LSPs hierarchy  . . . . . . . . . . . . . .  17
     2.10. BFD over MPLS-TE hierarchy  . . . . . . . . . . . . . . .  19
     2.11. Interaction with other YANG modules . . . . . . . . . . .  21
       2.11.1.  Module ietf-interfaces . . . . . . . . . . . . . . .  21
       2.11.2.  Module ietf-ip . . . . . . . . . . . . . . . . . . .  21
       2.11.3.  Module ietf-mpls . . . . . . . . . . . . . . . . . .  22
       2.11.4.  Module ietf-te . . . . . . . . . . . . . . . . . . .  22
     2.12. IANA BFD YANG Module  . . . . . . . . . . . . . . . . . .  22
     2.13. BFD types YANG Module . . . . . . . . . . . . . . . . . .  25
     2.14. BFD top-level YANG Module . . . . . . . . . . . . . . . .  37
     2.15. BFD IP single-hop YANG Module . . . . . . . . . . . . . .  39
     2.16. BFD IP multihop YANG Module . . . . . . . . . . . . . . .  42
     2.17. BFD over LAG YANG Module  . . . . . . . . . . . . . . . .  45
     2.18. BFD over MPLS YANG Module . . . . . . . . . . . . . . . .  49
     2.19. BFD over MPLS-TE YANG Module  . . . . . . . . . . . . . .  53
   3.  Data Model examples . . . . . . . . . . . . . . . . . . . . .  56
     3.1.  IP single-hop . . . . . . . . . . . . . . . . . . . . . .  56
     3.2.  IP multihop . . . . . . . . . . . . . . . . . . . . . . .  56
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  57
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  60
     5.1.  IANA-Maintained iana-bfd-types module . . . . . . . . . .  61



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   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  61
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  61
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  61
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  64
   Appendix A.  Echo function configuration example  . . . . . . . .  64
     A.1.  Example YANG module for BFD echo function configuration .  65
   Appendix B.  Change log . . . . . . . . . . . . . . . . . . . . .  67
     B.1.  Changes between versions -09 and -10  . . . . . . . . . .  67
     B.2.  Changes between versions -08 and -09  . . . . . . . . . .  67
     B.3.  Changes between versions -07 and -08  . . . . . . . . . .  67
     B.4.  Changes between versions -06 and -07  . . . . . . . . . .  67
     B.5.  Changes between versions -05 and -06  . . . . . . . . . .  68
     B.6.  Changes between versions -04 and -05  . . . . . . . . . .  68
     B.7.  Changes between versions -03 and -04  . . . . . . . . . .  68
     B.8.  Changes between versions -02 and -03  . . . . . . . . . .  68
     B.9.  Changes between versions -01 and -02  . . . . . . . . . .  68
     B.10. Changes between versions -00 and -01  . . . . . . . . . .  68
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  69

1.  Introduction

   This document defines a YANG data model that can be used to configure
   and manage Bidirectional Forwarding Detection (BFD) [RFC5880].  BFD
   is a network protocol which is used for liveness detection of
   arbitrary paths between systems.  Some examples of different types of
   paths over which we have BFD:

   1) Two systems directly connected via IP.  This is known as BFD over
   single-hop IP, a.k.a.  BFD for IPv4 and IPv6 [RFC5881]

   2) Two systems connected via multiple hops as described in BFD for
   Multiple Hops.  [RFC5883]

   3) Two systems connected via MPLS Label Switched Paths (LSPs) as
   described in BFD for MPLS LSP [RFC5884]

   4) Two systems connected via a Link Aggregation Group (LAG) interface
   as described in BFD on LAG Interfaces [RFC7130]

   5) Two systems connected via pseudowires (PWs), this is known as
   Virtual Circuit Connectivity Verification (VCCV) as described in BFD
   for PW VCCV [RFC5885].  This is not addressed in this document.

   BFD typically does not operate on its own.  Various control
   protocols, also known as BFD clients, use the services provided by
   BFD for their own operation as described in Generic Application of
   BFD [RFC5882].  The obvious candidates which use BFD are those which
   do not have "hellos" to detect failures, e.g. static routes, and



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   routing protocols whose "hellos" do not support sub-second failure
   detection, e.g.  OSPF and IS-IS.

   The YANG modules in this document conform to the Network Management
   Datastore Architecture (NMDA) Network Management Datastore
   Architecture [I-D.ietf-netmod-revised-datastores].  This means that
   the data models do not have separate top-level or sibling containers
   for configuration and operational state data.

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.

2.  Design of the Data Model

   Since BFD is used for liveliness detection of various forwarding
   paths, there is no uniform key to identify a BFD session.  So the BFD
   data model is split in multiple YANG modules where each module
   corresponds to one type of forwarding path.  For example, BFD for IP
   single-hop is in one YANG module and BFD for MPLS-TE is in another
   YANG module.  The main difference between these modules is how a BFD
   session is uniquely identified, i.e the key for the list containing
   the BFD sessions for that forwarding path.  To avoid duplication of
   BFD definitions, we have common types and groupings which are used by
   all the modules.

   A new control-plane protocol "bfdv1" is defined and a "bfd" container
   is created under control-plane-protocol as specified in "A YANG Data
   Model for Routing Management (NMDA Version)"
   [I-D.ietf-netmod-rfc8022bis].  This new "bfd" container is augmented
   by all the YANG modules for their respective specific information:

   1.  ietf-bfd-ip-sh.yang augments "/routing/control-plane-protocols/
       control-plane-protocol/bfd/" with the "ip-sh" container for BFD
       sessions over IP single-hop.

   2.  ietf-bfd-ip-mh.yang augments "/routing/control-plane-protocols/
       control-plane-protocol/bfd/" with the "ip-mh" container for BFD
       sessions over IP multi-hop.

   3.  ietf-bfd-lag.yang augments "/routing/control-plane-protocols/
       control-plane-protocol/bfd/" with the "lag" container for BFD
       sessions over LAG.




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   4.  ietf-bfd-mpls.yang augments "/routing/control-plane-protocols/
       control-plane-protocol/bfd/" with the "mpls" container for BFD
       over MPLS LSPs.

   5.  ietf-bfd-mpls-te.yang augments "/routing/control-plane-protocols/
       control-plane-protocol/bfd/" with the "mpls-te" container for BFD
       over MPLS-TE.

   BFD can operate in the following contexts:

   1.  At the network device level

   2.  In Logical Network Elements as described in YANG Logical Network
       Element [I-D.ietf-rtgwg-lne-model]

   3.  In Network Instances as described in YANG Logical Network Element
       [I-D.ietf-rtgwg-ni-model]

   When used at the network device level, the BFD YANG model is used
   "as-is".  When the BFD model is to be used in a Logical Network
   Element or in a Network Instance, the approach taken is to do a
   schema-mount (see Schema Mount [I-D.ietf-netmod-schema-mount]) of the
   BFD model in the appropriate location.  For example, if an
   implementation supports BFD IP multihop in network instances, the
   implementation would do schema-mount of the BFD IP multihop model in
   a mount-point which resides in a network instance.

2.1.  Design of Configuration Model

   The configuration model consists mainly of the parameters specified
   in BFD [RFC5880].  Some examples are desired minimum transmit
   interval, required minimum receive interval, detection multiplier,
   etc

   BFD clients are applications that use BFD for fast detection of
   failures.  Some implementations have BFD session configuration under
   the BFD clients.  For example, BFD session configuration under
   routing applications such as OSPF, IS-IS, BGP etc.  Other
   implementations have BFD session configuration centralized under BFD,
   i.e. outside the multiple BFD clients.

   The BFD parameters of interest to a BFD client are mainly the
   multiplier and interval(s) since those parameters impact the
   convergence time of the BFD clients when a failure occurs.  Other
   parameters such as BFD authentication are not specific to the
   requirements of the BFD client.  Ideally all configuration should be
   centralized under BFD.  However, this is a problem for clients of BFD
   which auto-discover their peers.  For example, IGPs do not have the



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   peer address configured, instead the IGP is enabled on an interface
   and the IGP peers are auto-discovered.  So for an operator to
   configure BFD to an IGP peer, the operator would first have to
   determine the peer addresses.  And when a new peer is discovered, BFD
   configuration would need to be added.  To avoid this issue, we define
   grouping client-cfg-parms in Section 2.13 for BFD clients to
   configure BFD: this allows BFD clients such as the IGPs to have
   configuration (multiplier and intervals) for the BFD sessions they
   need.  For example, when a new IGP peer is discovered, the IGP would
   create a BFD session to the newly discovered peer and similarly when
   an IGP peer goes away, the IGP would remove the BFD session to that
   peer.  The mechanism how the BFD sessions are created and removed by
   the BFD clients is outside the scope of this document, but typically
   this would be done by use of an API implemented by the BFD module on
   the system.  For BFD clients which create BFD sessions via their own
   configuration, authentication parameters (if required) are still
   specified in BFD.

2.1.1.  Common BFD configuration parameters

   The basic BFD configuration parameters are:

   local-multiplier
           This is the detection time multiplier as defined in BFD
           [RFC5880].

   desired-min-tx-interval
           This is the Desired Min TX Interval as defined in BFD
           [RFC5880].

   required-min-rx-interval
           This is the Required Min RX Interval as defined in BFD
           [RFC5880].

   Although BFD [RFC5880] allows for different values for transmit and
   receive intervals, some implementations allow users to specify just
   one interval which is used for both transmit and receive intervals or
   separate values for transmit and receive intervals.  The BFD YANG
   model supports this: there is a choice between "min-interval", used
   for both transmit and receive intervals, and "desired-min-tx-
   interval" and "required-min-rx-interval".  This is supported via a
   grouping which is used by the YANG modules for the various forwarding
   paths.

   For BFD authentication we have:

   key-chain




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           This is a reference to key-chain defined in YANG Data Model
           for Key Chains [RFC8177].  The keys, cryptographic
           algorithms, key lifetime etc are all defined in the key-chain
           model.

   meticulous
           This enables meticulous mode as per BFD [RFC5880].

2.1.2.  Single-hop IP

   For single-hop IP, there is an augment of the "bfd" data node in
   Section 2.  The "ip-sh" node contains a list of IP single-hop
   sessions where each session is uniquely identified by the interface
   and destination address pair.  For the configuration parameters we
   use what is defined in Section 2.1.1.  The "ip-sh" node also contains
   a list of interfaces, this is used to specify authentication
   parameters for BFD sessions which are created by BFD clients, see
   Section 2.1.

   [RFC5880] and [RFC5881] do not specify whether echo function is
   continuous or on demand.  Therefore the mechanism used to start and
   stop echo function is implementation specific and should be done by
   augmentation:

      1) Configuration.  This is suitable for continuous echo function.
      An example is provided in Appendix A.

      2) RPC.  This is suitable for on-demand echo function.

2.1.3.  Multihop IP

   For multihop IP, there is an augment of the "bfd" data node in
   Section 2.

   Because of multiple paths, there could be multiple multihop IP
   sessions between a source and a destination address.  We identify
   this as a "session-group".  The key for each "session-group" consists
   of:

   source address
           Address belonging to the local system as per BFD for Multiple
           Hops [RFC5883]

   destination address
           Address belonging to the remote system as per BFD for
           Multiple Hops [RFC5883]





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   For the configuration parameters we use what is defined in
   Section 2.1.1

   Here are some extra parameters:

   tx-ttl
           TTL of outgoing BFD control packets.

   rx-ttl
           Minimum TTL of incoming BFD control packets.

2.1.4.  MPLS Traffic Engineering Tunnels

   For MPLS-TE tunnels, BFD is configured under the MPLS-TE tunnel since
   the desired failure detection parameters is a property of the MPLS-TE
   tunnel.  This is achieved by augmenting the MPLS-TE data model in
   YANG Data Model for TE Topologies [I-D.ietf-teas-yang-te].  For BFD
   parameters which are specific to the TE application, e.g. whether to
   tear down the tunnel in the event of a BFD session failure, these
   parameters will be defined in the YANG model of the MPLS-TE
   application.

   On top of the usual BFD parameters, we have the following per MPLS-TE
   tunnel:

   encap
           Encapsulation for the BFD packets: choice between IP, G-ACh
           and IP with G-ACh as per MPLS Generic Associated Channel
           [RFC5586]

   For general MPLS-TE data, "mpls-te" data node is added under the
   "bfd" node in Section 2.  Since some MPLS-TE tunnels are uni-
   directional there is no MPLS-TE configuration for these tunnels on
   the egress node (note that this does not apply to bi-directional
   MPLS-TP tunnels).  The BFD parameters for the egress node are added
   under "mpls-te".

2.1.5.  MPLS Label Switched Paths

   Here we address MPLS LSPs whose FEC is an IP address.  The "bfd" node
   in Section 2 is augmented with "mpls" which contains a list of
   sessions uniquely identified by an IP prefix.  Because of multiple
   paths, there could be multiple MPLS sessions to an MPLS FEC.  We
   identify this as a "session-group".

   Since these LSPs are uni-directional there is no LSP configuration on
   the egress node.




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   The BFD parameters for the egress node are added under "mpls".

2.1.6.  Link Aggregation Groups

   Per BFD on LAG Interfaces [RFC7130], configuring BFD on LAG consists
   of having micro-BFD sessions on each LAG member link.  Since the BFD
   parameters are an attribute of the LAG, they should be under the LAG.
   However there is no LAG YANG model which we can augment.  So a "lag"
   data node is added to the "bfd" node in Section 2, the configuration
   is per-LAG: we have a list of LAGs.  The destination IP address of
   the micro-BFD sessions is configured per-LAG and per address-family
   (IPv4 and IPv6)

2.2.  Design of Operational State Model

   The operational state model contains both the overall statistics of
   BFD sessions running on the device and the per session operational
   information.

   The overall statistics of BFD sessions consist of number of BFD
   sessions, number of BFD sessions up etc.  This information is
   available globally (i.e. for all BFD sessions) under the "bfd" node
   in Section 2 and also per type of forwarding path.

   For each BFD session, mainly three categories of operational state
   data are shown.  The fundamental information of a BFD session such as
   the local discriminator, remote discriminator and the capability of
   supporting demand detect mode are shown in the first category.  The
   second category includes a BFD session running information, e.g. the
   remote BFD state and the diagnostic code received.  Another example
   is the actual transmit interval between the control packets, which
   may be different from the desired minimum transmit interval
   configured, is shown in this category.  Similar examples are actual
   received interval between the control packets and the actual transmit
   interval between the echo packets.  The third category contains the
   detailed statistics of the session, e.g. when the session
   transitioned up/down and how long it has been in that state.

   For some path types, there may be more than 1 session on the virtual
   path to the destination.  For example, with IP multihop and MPLS
   LSPs, there could be multiple BFD sessions from the source to the
   same destination to test the various paths (ECMP) to the destination.
   This is represented by having multiple "sessions" under each
   "session-group".







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2.3.  Notifications

   This YANG model defines notifications to inform end-users of
   important events detected during the protocol operation.  Pair of
   local and remote discriminator identifies a BFD session on local
   system.  Notifications also give more important details about BFD
   sessions; e.g. new state, time in previous state, network-instance
   and the reason that the BFD session state changed.  The notifications
   are defined for each type of forwarding path but use groupings for
   common information.

2.4.  RPC Operations

   None.

2.5.  BFD top level hierarchy

   At the "bfd" node under control-plane-protocol, there is no
   configuration data, only operational state data.  The operational
   state data consist of overall BFD session statistics, i.e. for BFD on
   all types of forwarding paths.  The "bfd" node under control-plane-
   protocol can be used in a network device (top-level), or mounted in
   an LNE or in a network instance.

 module: ietf-bfd
   augment /rt:routing/rt:control-plane-protocols/rt:control-plane-proto
 col:
     +--rw bfd
        +--ro summary
           +--ro number-of-sessions?              yang:gauge32
           +--ro number-of-sessions-up?           yang:gauge32
           +--ro number-of-sessions-down?         yang:gauge32
           +--ro number-of-sessions-admin-down?   yang:gauge32

2.6.  BFD IP single-hop hierarchy

   An "ip-sh" node is added under "bfd" node in control-plane-protocol.
   The configuration and operational state data for each BFD IP single-
   hop session is under this "ip-sh" node.  The "ip-sh" node can be used
   in a network device (top-level), or mounted in an LNE or in a network
   instance.

 module: ietf-bfd-ip-sh
   augment /rt:routing/rt:control-plane-protocols/rt:control-plane-proto
 col/bfd:bfd:
     +--rw ip-sh
        +--ro summary
        |  +--ro number-of-sessions?              yang:gauge32



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        |  +--ro number-of-sessions-up?           yang:gauge32
        |  +--ro number-of-sessions-down?         yang:gauge32
        |  +--ro number-of-sessions-admin-down?   yang:gauge32
        +--rw sessions* [interface dest-addr]
        |  +--rw interface                   if:interface-ref
        |  +--rw dest-addr                   inet:ip-address
        |  +--rw source-addr?                inet:ip-address
        |  +--rw local-multiplier?           multiplier
        |  +--rw (interval-config-type)?
        |  |  +--:(tx-rx-intervals)
        |  |  |  +--rw desired-min-tx-interval?    uint32
        |  |  |  +--rw required-min-rx-interval?   uint32
        |  |  +--:(single-interval) {single-minimum-interval}?
        |  |     +--rw min-interval?               uint32
        |  +--rw demand-enabled?             boolean {demand-mode}?
        |  +--rw admin-down?                 boolean
        |  +--rw authentication! {authentication}?
        |  |  +--rw key-chain?    kc:key-chain-ref
        |  |  +--rw meticulous?   boolean
        |  +--ro path-type?                  identityref
        |  +--ro ip-encapsulation?           boolean
        |  +--ro local-discriminator?        discriminator
        |  +--ro remote-discriminator?       discriminator
        |  +--ro remote-multiplier?          multiplier
        |  +--ro demand-capability?          boolean {demand-mode}?
        |  +--ro source-port?                inet:port-number
        |  +--ro dest-port?                  inet:port-number
        |  +--ro session-running
        |  |  +--ro session-index?                uint32
        |  |  +--ro local-state?                  state
        |  |  +--ro remote-state?                 state
        |  |  +--ro local-diagnostic?
        |  |  |       iana-bfd-types:diagnostic
        |  |  +--ro remote-diagnostic?
        |  |  |       iana-bfd-types:diagnostic
        |  |  +--ro remote-authenticated?         boolean
        |  |  +--ro remote-authentication-type?   iana-bfd-types:auth-ty
 pe
        |  |  |       {authentication}?
        |  |  +--ro detection-mode?               enumeration
        |  |  +--ro negotiated-tx-interval?       uint32
        |  |  +--ro negotiated-rx-interval?       uint32
        |  |  +--ro detection-time?               uint32
        |  |  +--ro echo-tx-interval-in-use?      uint32 {echo-mode}?
        |  +--ro session-statistics
        |     +--ro create-time?                    yang:date-and-time
        |     +--ro last-down-time?                 yang:date-and-time
        |     +--ro last-up-time?                   yang:date-and-time



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        |     +--ro down-count?                     yang:counter32
        |     +--ro admin-down-count?               yang:counter32
        |     +--ro receive-packet-count?           yang:counter64
        |     +--ro send-packet-count?              yang:counter64
        |     +--ro receive-invalid-packet-count?   yang:counter64
        |     +--ro send-failed-packet-count?       yang:counter64
        +--rw interfaces* [interface]
           +--rw interface         if:interface-ref
           +--rw authentication! {authentication}?
              +--rw key-chain?    kc:key-chain-ref
              +--rw meticulous?   boolean

   notifications:
     +---n singlehop-notification
        +--ro local-discr?                 discriminator
        +--ro remote-discr?                discriminator
        +--ro new-state?                   state
        +--ro state-change-reason?         iana-bfd-types:diagnostic
        +--ro time-of-last-state-change?   yang:date-and-time
        +--ro dest-addr?                   inet:ip-address
        +--ro source-addr?                 inet:ip-address
        +--ro session-index?               uint32
        +--ro path-type?                   identityref
        +--ro interface?                   if:interface-ref
        +--ro echo-enabled?                boolean


2.7.  BFD IP multihop hierarchy

   An "ip-mh" node is added under the "bfd" node in cntrol-plane-
   protocol.  The configuration and operational state data for each BFD
   IP multihop session is under this "ip-mh" node.  In the operational
   state model we support multiple BFD multihop sessions per remote
   address (ECMP), the local discriminator is used as key.  The "ip-mh"
   node can be used in a network device (top-level), or mounted in an
   LNE or in a network instance.

 module: ietf-bfd-ip-mh
   augment /rt:routing/rt:control-plane-protocols/rt:control-plane-proto
 col/bfd:bfd:
     +--rw ip-mh
        +--ro summary
        |  +--ro number-of-sessions?              yang:gauge32
        |  +--ro number-of-sessions-up?           yang:gauge32
        |  +--ro number-of-sessions-down?         yang:gauge32
        |  +--ro number-of-sessions-admin-down?   yang:gauge32
        +--rw session-group* [source-addr dest-addr]
           +--rw source-addr                 inet:ip-address



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           +--rw dest-addr                   inet:ip-address
           +--rw local-multiplier?           multiplier
           +--rw (interval-config-type)?
           |  +--:(tx-rx-intervals)
           |  |  +--rw desired-min-tx-interval?    uint32
           |  |  +--rw required-min-rx-interval?   uint32
           |  +--:(single-interval) {single-minimum-interval}?
           |     +--rw min-interval?               uint32
           +--rw demand-enabled?             boolean {demand-mode}?
           +--rw admin-down?                 boolean
           +--rw authentication! {authentication}?
           |  +--rw key-chain?    kc:key-chain-ref
           |  +--rw meticulous?   boolean
           +--rw tx-ttl?                     bfd-types:hops
           +--rw rx-ttl                      bfd-types:hops
           +--ro sessions*
              +--ro path-type?              identityref
              +--ro ip-encapsulation?       boolean
              +--ro local-discriminator?    discriminator
              +--ro remote-discriminator?   discriminator
              +--ro remote-multiplier?      multiplier
              +--ro demand-capability?      boolean {demand-mode}?
              +--ro source-port?            inet:port-number
              +--ro dest-port?              inet:port-number
              +--ro session-running
              |  +--ro session-index?                uint32
              |  +--ro local-state?                  state
              |  +--ro remote-state?                 state
              |  +--ro local-diagnostic?
              |  |       iana-bfd-types:diagnostic
              |  +--ro remote-diagnostic?
              |  |       iana-bfd-types:diagnostic
              |  +--ro remote-authenticated?         boolean
              |  +--ro remote-authentication-type?
              |  |       iana-bfd-types:auth-type {authentication}?
              |  +--ro detection-mode?               enumeration
              |  +--ro negotiated-tx-interval?       uint32
              |  +--ro negotiated-rx-interval?       uint32
              |  +--ro detection-time?               uint32
              |  +--ro echo-tx-interval-in-use?      uint32
              |          {echo-mode}?
              +--ro session-statistics
                 +--ro create-time?                    yang:date-and-tim
 e
                 +--ro last-down-time?                 yang:date-and-tim
 e
                 +--ro last-up-time?                   yang:date-and-tim
 e



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                 +--ro down-count?                     yang:counter32
                 +--ro admin-down-count?               yang:counter32
                 +--ro receive-packet-count?           yang:counter64
                 +--ro send-packet-count?              yang:counter64
                 +--ro receive-invalid-packet-count?   yang:counter64
                 +--ro send-failed-packet-count?       yang:counter64

   notifications:
     +---n multihop-notification
        +--ro local-discr?                 discriminator
        +--ro remote-discr?                discriminator
        +--ro new-state?                   state
        +--ro state-change-reason?         iana-bfd-types:diagnostic
        +--ro time-of-last-state-change?   yang:date-and-time
        +--ro dest-addr?                   inet:ip-address
        +--ro source-addr?                 inet:ip-address
        +--ro session-index?               uint32
        +--ro path-type?                   identityref

2.8.  BFD over LAG hierarchy

   A "lag" node is added under the "bfd" node in control-plane-protocol.
   The configuration and operational state data for each BFD LAG session
   is under this "lag" node.  The "lag" node can be used in a network
   device (top-level), or mounted in an LNE or in a network instance.

 module: ietf-bfd-lag
   augment /rt:routing/rt:control-plane-protocols/rt:control-plane-proto
 col/bfd:bfd:
     +--rw lag
        +--rw micro-bfd-ipv4-session-statistics
        |  +--ro summary
        |     +--ro number-of-sessions?              yang:gauge32
        |     +--ro number-of-sessions-up?           yang:gauge32
        |     +--ro number-of-sessions-down?         yang:gauge32
        |     +--ro number-of-sessions-admin-down?   yang:gauge32
        +--rw micro-bfd-ipv6-session-statistics
        |  +--ro summary
        |     +--ro number-of-sessions?              yang:gauge32
        |     +--ro number-of-sessions-up?           yang:gauge32
        |     +--ro number-of-sessions-down?         yang:gauge32
        |     +--ro number-of-sessions-admin-down?   yang:gauge32
        +--rw sessions* [lag-name]
           +--rw lag-name                    if:interface-ref
           +--rw ipv4-dest-addr?             inet:ipv4-address
           +--rw ipv6-dest-addr?             inet:ipv6-address
           +--rw local-multiplier?           multiplier
           +--rw (interval-config-type)?



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           |  +--:(tx-rx-intervals)
           |  |  +--rw desired-min-tx-interval?    uint32
           |  |  +--rw required-min-rx-interval?   uint32
           |  +--:(single-interval) {single-minimum-interval}?
           |     +--rw min-interval?               uint32
           +--rw demand-enabled?             boolean {demand-mode}?
           +--rw admin-down?                 boolean
           +--rw authentication! {authentication}?
           |  +--rw key-chain?    kc:key-chain-ref
           |  +--rw meticulous?   boolean
           +--rw use-ipv4?                   boolean
           +--rw use-ipv6?                   boolean
           +--ro member-links* [member-link]
              +--ro member-link       if:interface-ref
              +--ro micro-bfd-ipv4
              |  +--ro path-type?              identityref
              |  +--ro ip-encapsulation?       boolean
              |  +--ro local-discriminator?    discriminator
              |  +--ro remote-discriminator?   discriminator
              |  +--ro remote-multiplier?      multiplier
              |  +--ro demand-capability?      boolean {demand-mode}?
              |  +--ro source-port?            inet:port-number
              |  +--ro dest-port?              inet:port-number
              |  +--ro session-running
              |  |  +--ro session-index?                uint32
              |  |  +--ro local-state?                  state
              |  |  +--ro remote-state?                 state
              |  |  +--ro local-diagnostic?
              |  |  |       iana-bfd-types:diagnostic
              |  |  +--ro remote-diagnostic?
              |  |  |       iana-bfd-types:diagnostic
              |  |  +--ro remote-authenticated?         boolean
              |  |  +--ro remote-authentication-type?
              |  |  |       iana-bfd-types:auth-type {authentication}?
              |  |  +--ro detection-mode?               enumeration
              |  |  +--ro negotiated-tx-interval?       uint32
              |  |  +--ro negotiated-rx-interval?       uint32
              |  |  +--ro detection-time?               uint32
              |  |  +--ro echo-tx-interval-in-use?      uint32
              |  |          {echo-mode}?
              |  +--ro session-statistics
              |     +--ro create-time?
              |     |       yang:date-and-time
              |     +--ro last-down-time?
              |     |       yang:date-and-time
              |     +--ro last-up-time?
              |     |       yang:date-and-time
              |     +--ro down-count?                     yang:counter32



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              |     +--ro admin-down-count?               yang:counter32
              |     +--ro receive-packet-count?           yang:counter64
              |     +--ro send-packet-count?              yang:counter64
              |     +--ro receive-invalid-packet-count?   yang:counter64
              |     +--ro send-failed-packet-count?       yang:counter64
              +--ro micro-bfd-ipv6
                 +--ro path-type?              identityref
                 +--ro ip-encapsulation?       boolean
                 +--ro local-discriminator?    discriminator
                 +--ro remote-discriminator?   discriminator
                 +--ro remote-multiplier?      multiplier
                 +--ro demand-capability?      boolean {demand-mode}?
                 +--ro source-port?            inet:port-number
                 +--ro dest-port?              inet:port-number
                 +--ro session-running
                 |  +--ro session-index?                uint32
                 |  +--ro local-state?                  state
                 |  +--ro remote-state?                 state
                 |  +--ro local-diagnostic?
                 |  |       iana-bfd-types:diagnostic
                 |  +--ro remote-diagnostic?
                 |  |       iana-bfd-types:diagnostic
                 |  +--ro remote-authenticated?         boolean
                 |  +--ro remote-authentication-type?
                 |  |       iana-bfd-types:auth-type {authentication}?
                 |  +--ro detection-mode?               enumeration
                 |  +--ro negotiated-tx-interval?       uint32
                 |  +--ro negotiated-rx-interval?       uint32
                 |  +--ro detection-time?               uint32
                 |  +--ro echo-tx-interval-in-use?      uint32
                 |          {echo-mode}?
                 +--ro session-statistics
                    +--ro create-time?
                    |       yang:date-and-time
                    +--ro last-down-time?
                    |       yang:date-and-time
                    +--ro last-up-time?
                    |       yang:date-and-time
                    +--ro down-count?                     yang:counter32
                    +--ro admin-down-count?               yang:counter32
                    +--ro receive-packet-count?           yang:counter64
                    +--ro send-packet-count?              yang:counter64
                    +--ro receive-invalid-packet-count?   yang:counter64
                    +--ro send-failed-packet-count?       yang:counter64

   notifications:
     +---n lag-notification
        +--ro local-discr?                 discriminator



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        +--ro remote-discr?                discriminator
        +--ro new-state?                   state
        +--ro state-change-reason?         iana-bfd-types:diagnostic
        +--ro time-of-last-state-change?   yang:date-and-time
        +--ro dest-addr?                   inet:ip-address
        +--ro source-addr?                 inet:ip-address
        +--ro session-index?               uint32
        +--ro path-type?                   identityref
        +--ro lag-name?                    if:interface-ref
        +--ro member-link?                 if:interface-ref

2.9.  BFD over MPLS LSPs hierarchy

   An "mpls" node is added under the "bfd" node in control-plane-
   protocol.  The configuration is per MPLS FEC under this "mpls" node.
   In the operational state model we support multiple BFD sessions per
   MPLS FEC (ECMP), the local discriminator is used as key.  The "mpls"
   node can be used in a network device (top-level), or mounted in an
   LNE or in a network instance.

 module: ietf-bfd-mpls
   augment /rt:routing/rt:control-plane-protocols/rt:control-plane-proto
 col/bfd:bfd:
     +--rw mpls
        +--ro summary
        |  +--ro number-of-sessions?              yang:gauge32
        |  +--ro number-of-sessions-up?           yang:gauge32
        |  +--ro number-of-sessions-down?         yang:gauge32
        |  +--ro number-of-sessions-admin-down?   yang:gauge32
        +--rw egress
        |  +--rw enable?                     boolean
        |  +--rw local-multiplier?           multiplier
        |  +--rw (interval-config-type)?
        |  |  +--:(tx-rx-intervals)
        |  |  |  +--rw desired-min-tx-interval?    uint32
        |  |  |  +--rw required-min-rx-interval?   uint32
        |  |  +--:(single-interval) {single-minimum-interval}?
        |  |     +--rw min-interval?               uint32
        |  +--rw authentication! {authentication}?
        |     +--rw key-chain?    kc:key-chain-ref
        |     +--rw meticulous?   boolean
        +--rw session-group* [mpls-fec]
           +--rw mpls-fec                    inet:ip-prefix
           +--rw local-multiplier?           multiplier
           +--rw (interval-config-type)?
           |  +--:(tx-rx-intervals)
           |  |  +--rw desired-min-tx-interval?    uint32
           |  |  +--rw required-min-rx-interval?   uint32



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           |  +--:(single-interval) {single-minimum-interval}?
           |     +--rw min-interval?               uint32
           +--rw demand-enabled?             boolean {demand-mode}?
           +--rw admin-down?                 boolean
           +--rw authentication! {authentication}?
           |  +--rw key-chain?    kc:key-chain-ref
           |  +--rw meticulous?   boolean
           +--ro sessions*
              +--ro path-type?              identityref
              +--ro ip-encapsulation?       boolean
              +--ro local-discriminator?    discriminator
              +--ro remote-discriminator?   discriminator
              +--ro remote-multiplier?      multiplier
              +--ro demand-capability?      boolean {demand-mode}?
              +--ro source-port?            inet:port-number
              +--ro dest-port?              inet:port-number
              +--ro session-running
              |  +--ro session-index?                uint32
              |  +--ro local-state?                  state
              |  +--ro remote-state?                 state
              |  +--ro local-diagnostic?
              |  |       iana-bfd-types:diagnostic
              |  +--ro remote-diagnostic?
              |  |       iana-bfd-types:diagnostic
              |  +--ro remote-authenticated?         boolean
              |  +--ro remote-authentication-type?
              |  |       iana-bfd-types:auth-type {authentication}?
              |  +--ro detection-mode?               enumeration
              |  +--ro negotiated-tx-interval?       uint32
              |  +--ro negotiated-rx-interval?       uint32
              |  +--ro detection-time?               uint32
              |  +--ro echo-tx-interval-in-use?      uint32
              |          {echo-mode}?
              +--ro session-statistics
              |  +--ro create-time?                    yang:date-and-tim
 e
              |  +--ro last-down-time?                 yang:date-and-tim
 e
              |  +--ro last-up-time?                   yang:date-and-tim
 e
              |  +--ro down-count?                     yang:counter32
              |  +--ro admin-down-count?               yang:counter32
              |  +--ro receive-packet-count?           yang:counter64
              |  +--ro send-packet-count?              yang:counter64
              |  +--ro receive-invalid-packet-count?   yang:counter64
              |  +--ro send-failed-packet-count?       yang:counter64
              +--ro mpls-dest-address?      inet:ip-address




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   notifications:
     +---n mpls-notification
        +--ro local-discr?                 discriminator
        +--ro remote-discr?                discriminator
        +--ro new-state?                   state
        +--ro state-change-reason?         iana-bfd-types:diagnostic
        +--ro time-of-last-state-change?   yang:date-and-time
        +--ro dest-addr?                   inet:ip-address
        +--ro source-addr?                 inet:ip-address
        +--ro session-index?               uint32
        +--ro path-type?                   identityref
        +--ro mpls-dest-address?           inet:ip-address

2.10.  BFD over MPLS-TE hierarchy

   YANG Data Model for TE Topologies [I-D.ietf-teas-yang-te] is
   augmented.  BFD is configured per MPLS-TE tunnel, and BFD session
   operational state data is provided per MPLS-TE LSP.

 module: ietf-bfd-mpls-te
   augment /rt:routing/rt:control-plane-protocols/rt:control-plane-proto
 col/bfd:bfd:
     +--rw mpls-te
        +--rw egress
        |  +--rw enable?                     boolean
        |  +--rw local-multiplier?           multiplier
        |  +--rw (interval-config-type)?
        |  |  +--:(tx-rx-intervals)
        |  |  |  +--rw desired-min-tx-interval?    uint32
        |  |  |  +--rw required-min-rx-interval?   uint32
        |  |  +--:(single-interval) {single-minimum-interval}?
        |  |     +--rw min-interval?               uint32
        |  +--rw authentication! {authentication}?
        |     +--rw key-chain?    kc:key-chain-ref
        |     +--rw meticulous?   boolean
        +--ro summary
           +--ro number-of-sessions?              yang:gauge32
           +--ro number-of-sessions-up?           yang:gauge32
           +--ro number-of-sessions-down?         yang:gauge32
           +--ro number-of-sessions-admin-down?   yang:gauge32
   augment /te:te/te:tunnels/te:tunnel:
     +--rw local-multiplier?           multiplier
     +--rw (interval-config-type)?
     |  +--:(tx-rx-intervals)
     |  |  +--rw desired-min-tx-interval?    uint32
     |  |  +--rw required-min-rx-interval?   uint32
     |  +--:(single-interval) {single-minimum-interval}?
     |     +--rw min-interval?               uint32



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     +--rw demand-enabled?             boolean {demand-mode}?
     +--rw admin-down?                 boolean
     +--rw authentication! {authentication}?
     |  +--rw key-chain?    kc:key-chain-ref
     |  +--rw meticulous?   boolean
     +--rw encap?                      identityref
   augment /te:te/te:lsps-state/te:lsp:
     +--ro path-type?              identityref
     +--ro ip-encapsulation?       boolean
     +--ro local-discriminator?    discriminator
     +--ro remote-discriminator?   discriminator
     +--ro remote-multiplier?      multiplier
     +--ro demand-capability?      boolean {demand-mode}?
     +--ro source-port?            inet:port-number
     +--ro dest-port?              inet:port-number
     +--ro session-running
     |  +--ro session-index?                uint32
     |  +--ro local-state?                  state
     |  +--ro remote-state?                 state
     |  +--ro local-diagnostic?             iana-bfd-types:diagnostic
     |  +--ro remote-diagnostic?            iana-bfd-types:diagnostic
     |  +--ro remote-authenticated?         boolean
     |  +--ro remote-authentication-type?   iana-bfd-types:auth-type
     |  |       {authentication}?
     |  +--ro detection-mode?               enumeration
     |  +--ro negotiated-tx-interval?       uint32
     |  +--ro negotiated-rx-interval?       uint32
     |  +--ro detection-time?               uint32
     |  +--ro echo-tx-interval-in-use?      uint32 {echo-mode}?
     +--ro session-statistics
     |  +--ro create-time?                    yang:date-and-time
     |  +--ro last-down-time?                 yang:date-and-time
     |  +--ro last-up-time?                   yang:date-and-time
     |  +--ro down-count?                     yang:counter32
     |  +--ro admin-down-count?               yang:counter32
     |  +--ro receive-packet-count?           yang:counter64
     |  +--ro send-packet-count?              yang:counter64
     |  +--ro receive-invalid-packet-count?   yang:counter64
     |  +--ro send-failed-packet-count?       yang:counter64
     +--ro mpls-dest-address?      inet:ip-address

   notifications:
     +---n mpls-te-notification
        +--ro local-discr?                 discriminator
        +--ro remote-discr?                discriminator
        +--ro new-state?                   state
        +--ro state-change-reason?         iana-bfd-types:diagnostic
        +--ro time-of-last-state-change?   yang:date-and-time



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        +--ro dest-addr?                   inet:ip-address
        +--ro source-addr?                 inet:ip-address
        +--ro session-index?               uint32
        +--ro path-type?                   identityref
        +--ro mpls-dest-address?           inet:ip-address
        +--ro tunnel-name?                 string

2.11.  Interaction with other YANG modules

   Generic YANG Data Model for Connectionless OAM protocols
   [I-D.ietf-lime-yang-connectionless-oam] describes how the LIME
   connectionless OAM model could be extended to support BFD.

   Also, the operation of the BFD data model depends on configuration
   parameters that are defined in other YANG modules.

2.11.1.  Module ietf-interfaces

   The following boolean configuration is defined in A YANG Data Model
   for Interface Management [I-D.ietf-netmod-rfc7223bis]:

   /if:interfaces/if:interface/if:enabled
           If this configuration is set to "false", no BFD packets can
           be transmitted or received on that interface.

2.11.2.  Module ietf-ip

   The following boolean configuration is defined in A YANG Data Model
   for IP Management [I-D.ietf-netmod-rfc7277bis]:

   /if:interfaces/if:interface/ip:ipv4/ip:enabled
           If this configuration is set to "false", no BFD IPv4 packets
           can be transmitted or received on that interface.

   /if:interfaces/if:interface/ip:ipv4/ip:forwarding
           If this configuration is set to "false", no BFD IPv4 packets
           can be transmitted or received on that interface.

   /if:interfaces/if:interface/ip:ipv6/ip:enabled
           If this configuration is set to "false", no BFD IPv6 packets
           can be transmitted or received on that interface.

   /if:interfaces/if:interface/ip:ipv6/ip:forwarding
           If this configuration is set to "false", no BFD IPv6 packets
           can be transmitted or received on that interface.






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2.11.3.  Module ietf-mpls

   The following boolean configuration is defined in A YANG Data Model
   for MPLS Base [I-D.ietf-mpls-base-yang]:

   /rt:routing/mpls:mpls/mpls:interface/mpls:config/mpls:enabled
           If this configuration is set to "false", no BFD MPLS packets
           can be transmitted or received on that interface.

2.11.4.  Module ietf-te

   The following configuration is defined in the "ietf-te" YANG module
   YANG Data Model for TE Topology [I-D.ietf-teas-yang-te]:

   /ietf-te:te/ietf-te:tunnels/ietf-te:tunnel/ietf-te:config/ietf-
   te:admin-status
           If this configuration is not set to "state-up", no BFD MPLS
           packets can be transmitted or received on that tunnel.

2.12.  IANA BFD YANG Module

  <CODE BEGINS> file "iana-bfd-types@2018-03-01.yang"

  module iana-bfd-types {

    yang-version 1.1;

    namespace "urn:ietf:params:xml:ns:yang:iana-bfd-types";

    prefix "iana-bfd-types";

    organization "IANA";

    contact
      "        Internet Assigned Numbers Authority

      Postal: ICANN
              4676 Admiralty Way, Suite 330
              Marina del Rey, CA 90292

      Tel:    +1 310 823 9358
      <mailto:iana@iana.org>";

    description
      "This module defines YANG data types for IANA-registered
       BFD parameters.

       This YANG module is maintained by IANA and reflects the



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       'BFD Diagnostic Codes' and 'BFD Authentication Types' registries.

       Copyright (c) 2018 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 Simplified BSD License
       set forth in Section 4.c of the IETF Trust's Legal Provisions
       Relating to IETF Documents
       (http://trustee.ietf.org/license-info).

       This version of this YANG module is part of RFC XXXX; see
       the RFC itself for full legal notices.";

    // RFC Ed.: replace XXXX with actual RFC number and remove
    // this note

    reference "RFC XXXX";

    revision 2018-03-01 {
      description "Initial revision.";
      reference "RFC XXXX: IANA BFD YANG Data Types.";
    }

    /*
     * Type Definitions
     */
    typedef diagnostic {
      type enumeration {
        enum none {
          value 0;
          description "None";
        }
        enum control-expiry {
          value 1;
          description "Control timer expiry";
        }
        enum echo-failed {
          value 2;
          description "Echo failure";
        }
        enum neighbor-down {
          value 3;
          description "Neighbor down";
        }
        enum forwarding-reset {
          value 4;



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          description "Forwarding reset";
        }
        enum path-down {
          value 5;
          description "Path down";
        }
        enum concatenated-path-down {
          value 6;
          description "Concatenated path down";
        }
        enum admin-down {
          value 7;
          description "Admin down";
        }
        enum reverse-concatenated-path-down {
          value 8;
          description "Reverse concatenated path down";
        }
        enum mis-connectivity-defect {
          value 9;
          description "Mis-connectivity defect as specified in RFC6428";
        }
      }
      description
        "BFD diagnostic as defined in RFC 5880, values are maintained in
        the 'BFD Diagnostic Codes' IANA registry. Range is 0 to 31.";
    }

    typedef auth-type {
      type enumeration {
        enum reserved {
          value 0;
          description "Reserved";
        }
        enum simple-password {
          value 1;
          description "Simple password";
        }
        enum keyed-md5 {
          value 2;
          description "Keyed MD5";
        }
        enum meticulous-keyed-md5 {
          value 3;
          description "Meticulous keyed MD5";
        }
        enum keyed-sha1 {
          value 4;



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          description "Keyed SHA1";
        }
        enum meticulous-keyed-sha1 {
          value 5;
          description "Meticulous keyed SHA1";
        }
      }
      description
        "BFD authentication type as defined in RFC 5880, values are
         maintained in the 'BFD Authentication Types' IANA registry.
         Range is 0 to 255.";
    }
  }

  <CODE ENDS>

2.13.  BFD types YANG Module

   This YANG module imports typedefs from [RFC6991] and the "control-
   plane-protocol" identity from [I-D.ietf-netmod-rfc8022bis].

<CODE BEGINS> file "ietf-bfd-types@2018-03-01.yang"

module ietf-bfd-types {

  yang-version 1.1;

  namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-types";

  prefix "bfd-types";

  import iana-bfd-types {
    prefix "iana-bfd-types";
  }

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

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

  import ietf-routing {
    prefix "rt";
    // RFC Ed.: replace XXXX with actual RFC number of



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    // draft-ietf-netmod-rfc8022bis and remove this note.
    reference
      "RFC XXXX: A YANG Data Model for Routing Management";
  }

  import ietf-key-chain {
    prefix "kc";
    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>

     Editors:  Reshad Rahman (rrahman@cisco.com),
               Lianshu Zheng (vero.zheng@huawei.com),
               Mahesh Jethanandani (mjethanandani@gmail.com)";

  description
    "This module contains a collection of BFD specific YANG data type
     definitions, as per RFC 5880, and also groupings which are common
     to other BFD YANG modules.

     Copyright (c) 2018 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 Simplified BSD License
     set forth in Section 4.c of the IETF Trust's Legal Provisions
     Relating to IETF Documents
     (http://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC XXXX; see
     the RFC itself for full legal notices.";

  // RFC Ed.: replace XXXX with actual RFC number and remove this
  // note

  reference "RFC XXXX";

  revision 2018-03-01 {
    description "Initial revision.";
    reference "RFC XXXX: YANG Data Model for BFD";
  }




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  /*
   * Feature definitions
   */
  feature single-minimum-interval {
    description
      "This feature indicates that the server supports configuration
       of one minimum interval value which is used for both transmit and
       receive minimum intervals.";
  }

  feature authentication {
    description
      "This feature indicates that the server supports BFD
       authentication as defined in RFC 5880.";
  }

  feature demand-mode {
    description
      "This feature indicates that the server supports BFD demand mode
       as defined in RFC 5880.";
  }

  feature echo-mode {
    description
      "This feature indicates that the server supports BFD echo mode
       as defined in RFC 5880.";
  }

  /*
   * Identity definitions
   */
  identity bfdv1 {
    base "rt:control-plane-protocol";
    description "BFD protocol version 1 as per RFC 5880.";
  }

  identity path-type {
    description
      "Base identity for BFD path type. The path type indicates
       the type of path on which BFD is running.";
  }
  identity path-ip-sh {
    base path-type;
    description "BFD on IP single hop as described in RFC 5881.";
  }
  identity path-ip-mh {
    base path-type;
    description "BFD on IP multihop paths as described in RFC 5883.";



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  }
  identity path-mpls-te {
    base path-type;
    description
      "BFD on MPLS Traffic Engineering as described in RFC 5884.";
  }
  identity path-mpls-lsp {
    base path-type;
    description
      "BFD on MPLS Label Switched Path as described in RFC 5884.";
  }
  identity path-lag {
    base path-type;
    description
      "Micro-BFD on LAG member links as described in RFC 7130.";
  }

  identity encap-type {
    description
      "Base identity for BFD encapsulation type.";
  }
  identity encap-ip {
    base encap-type;
    description "BFD with IP encapsulation.";
  }

  /*
   * Type Definitions
   */
  typedef discriminator {
    type uint32;
    description "BFD discriminator as described in RFC 5880.";
  }

  typedef state {
    type enumeration {
      enum adminDown {
        value 0;
        description "admindown";
      }
      enum down {
        value 1;
        description "down";
      }
      enum init {
        value 2;
        description "init";
      }



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      enum up {
        value 3;
        description "up";
      }
    }
    description "BFD state as defined in RFC 5880.";
  }

  typedef multiplier {
    type uint8 {
      range 1..255;
    }
    description "BFD multiplier as described in RFC 5880.";
  }

  typedef hops {
    type uint8 {
      range 1..255;
    }
    description
      "This corresponds to Time To Live for IPv4 and corresponds to hop
       limit for IPv6.";
  }

  /*
   * Groupings
   */
  grouping auth-parms {
    description
      "Grouping for BFD authentication parameters
       (see section 6.7 of RFC 5880).";
    container authentication {
      if-feature authentication;
      presence
        "Enables BFD authentication (see section 6.7 of RFC 5880).";
      description "Parameters for BFD authentication.";

      leaf key-chain {
        type kc:key-chain-ref;
        description "Name of the key-chain as per RFC 8177.";
      }

      leaf meticulous {
        type boolean;
        description
          "Enables meticulous mode as described in section 6.7 " +
          "of RFC 5880.";
      }



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    }
  }

  grouping base-cfg-parms {
    description "BFD grouping for base config parameters.";
    leaf local-multiplier {
      type multiplier;
      default 3;
      description "Multiplier transmitted by local system.";
    }

    choice interval-config-type {
      description
        "Two interval values or one value used for both transmit and
         receive.";
      case tx-rx-intervals {
        leaf desired-min-tx-interval {
          type uint32;
          units microseconds;
          default 1000000;
          description
            "Desired minimum transmit interval of control packets.";
        }

        leaf required-min-rx-interval {
          type uint32;
          units microseconds;
          default 1000000;
          description
            "Required minimum receive interval of control packets.";
        }
      }
      case single-interval {
        if-feature single-minimum-interval;

        leaf min-interval {
          type uint32;
          units microseconds;
          default 1000000;
          description
            "Desired minimum transmit interval and required " +
            "minimum receive interval of control packets.";
        }
      }
    }
  }

  grouping client-cfg-parms {



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    description
      "BFD grouping for configuration parameters
       used by clients of BFD, e.g. IGP or MPLS.";

    leaf enable {
      type boolean;
      default false;
      description
        "Indicates whether the BFD is enabled.";
    }
    uses base-cfg-parms;
  }

  grouping common-cfg-parms {
    description
      "BFD grouping for common configuration parameters.";

    uses base-cfg-parms;

    leaf demand-enabled {
      if-feature demand-mode;
      type boolean;
      default false;
      description
        "To enable demand mode.";
    }

    leaf admin-down {
      type boolean;
      default false;
      description
        "Is the BFD session administratively down.";
    }
    uses auth-parms;
  }

  grouping all-session {
    description "BFD session operational information";
    leaf path-type {
      type identityref {
        base path-type;
      }
      config "false";
      description
        "BFD path type, this indicates the path type that BFD is
        running on.";
    }
    leaf ip-encapsulation {



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      type boolean;
      config "false";
      description "Whether BFD encapsulation uses IP.";
    }
    leaf local-discriminator {
      type discriminator;
      config "false";
      description "Local discriminator.";
    }
    leaf remote-discriminator {
      type discriminator;
      config "false";
      description "Remote discriminator.";
    }
    leaf remote-multiplier {
      type multiplier;
      config "false";
      description "Remote multiplier.";
    }
    leaf demand-capability {
      if-feature demand-mode;
      type boolean;
      config "false";
      description "Local demand mode capability.";
    }
    leaf source-port {
      when "../ip-encapsulation = 'true'" {
        description
          "Source port valid only when IP encapsulation is used.";
      }
      type inet:port-number;
      config "false";
      description "Source UDP port";
    }
    leaf dest-port {
      when "../ip-encapsulation = 'true'" {
        description
          "Destination port valid only when IP encapsulation is used.";
      }
      type inet:port-number;
      config "false";
      description "Destination UDP port.";
    }

    container session-running {
      config "false";
      description "BFD session running information.";
      leaf session-index {



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        type uint32;
        description
          "An index used to uniquely identify BFD sessions.";
      }
      leaf local-state {
        type state;
        description "Local state.";
      }
      leaf remote-state {
        type state;
        description "Remote state.";
      }
      leaf local-diagnostic {
        type iana-bfd-types:diagnostic;
        description "Local diagnostic.";
      }
      leaf remote-diagnostic {
        type iana-bfd-types:diagnostic;
        description "Remote diagnostic.";
      }
      leaf remote-authenticated {
        type boolean;
        description
          "Indicates whether incoming BFD control packets are
          authenticated.";
      }
      leaf remote-authentication-type {
        when "../remote-authenticated = 'true'" {
          description
            "Only valid when incoming BFD control packets are
             authenticated.";
        }
        if-feature authentication;
        type iana-bfd-types:auth-type;
        description
          "Authentication type of incoming BFD control packets.";
      }
      leaf detection-mode {
        type enumeration {
          enum async-with-echo {
            value "1";
            description "Async with echo.";
          }
          enum async-without-echo {
            value "2";
            description "Async without echo.";
          }
          enum demand-with-echo {



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            value "3";
            description "Demand with echo.";
          }
          enum demand-without-echo {
            value "4";
            description "Demand without echo.";
          }
        }
        description "Detection mode.";
      }
      leaf negotiated-tx-interval {
        type uint32;
        units microseconds;
        description "Negotiated transmit interval.";
      }
      leaf negotiated-rx-interval {
        type uint32;
        units microseconds;
        description "Negotiated receive interval.";
      }
      leaf detection-time {
        type uint32;
        units microseconds;
        description "Detection time.";
      }
      leaf echo-tx-interval-in-use {
        when "../../path-type = 'bfd-types:path-ip-sh'" {
          description
            "Echo is supported for IP single-hop only.";
        }
        if-feature echo-mode;
        type uint32;
        units microseconds;
        description "Echo transmit interval in use.";
      }
    }

    container session-statistics {
      config "false";
      description "BFD per-session statistics.";

      leaf create-time {
        type yang:date-and-time;
        description
          "Time and date when this session was created.";
      }
      leaf last-down-time {
        type yang:date-and-time;



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        description
          "Time and date of last time this session went down.";
      }
      leaf last-up-time {
        type yang:date-and-time;
        description
          "Time and date of last time this session went up.";
      }
      leaf down-count {
        type yang:counter32;
        description
          "The number of times this session has transitioned in the
           down state.";
      }
      leaf admin-down-count {
        type yang:counter32;
        description
          "The number of times this session has transitioned in the
           admin-down state.";
      }
      leaf receive-packet-count {
        type yang:counter64;
        description
          "Count of received packets in this session. This includes
           valid and invalid received packets.";
      }
      leaf send-packet-count {
        type yang:counter64;
        description "Count of sent packets in this session.";
      }
      leaf receive-invalid-packet-count {
        type yang:counter64;
        description
          "Count of invalid received packets in this session.";
      }
      leaf send-failed-packet-count {
        type yang:counter64;
        description
          "Count of packets which failed to be sent in this session.";
      }
    }
  }

  grouping session-statistics-summary {
    description "Grouping for session statistics summary.";
    container summary {
      config false;
      description "BFD session statistics summary.";



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      leaf number-of-sessions {
        type yang:gauge32;
        description "Number of BFD sessions.";
      }
      leaf number-of-sessions-up {
        type yang:gauge32;
        description "Number of BFD sessions currently in up state.";
      }
      leaf number-of-sessions-down {
        type yang:gauge32;
        description "Number of BFD sessions currently in down state.";
      }
      leaf number-of-sessions-admin-down {
        type yang:gauge32;
        description
          "Number of BFD sessions currently in admin-down state.";
      }
    }
  }

  grouping notification-parms {
    description
      "This group describes common parameters that will be sent " +
      "as part of BFD notification.";

    leaf local-discr {
      type discriminator;
      description "BFD local discriminator.";
    }

    leaf remote-discr {
      type discriminator;
      description "BFD remote discriminator.";
    }

    leaf new-state {
      type state;
      description "Current BFD state.";
    }

    leaf state-change-reason {
      type iana-bfd-types:diagnostic;
      description "BFD state change reason.";
    }

    leaf time-of-last-state-change {
      type yang:date-and-time;
      description



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        "Calendar time of previous state change.";
    }

    leaf dest-addr {
      type inet:ip-address;
      description "BFD peer address.";
    }

    leaf source-addr {
      type inet:ip-address;
      description "BFD local address.";
    }

    leaf session-index {
      type uint32;
      description "An index used to uniquely identify BFD sessions.";
    }

    leaf path-type {
      type identityref {
        base path-type;
      }
      description "BFD path type.";
    }
  }
}

<CODE ENDS>

2.14.  BFD top-level YANG Module

   This YANG module imports and augments "/routing/control-plane-
   protocols/control-plane-protocol" from [I-D.ietf-netmod-rfc8022bis].

   <CODE BEGINS> file "ietf-bfd@2018-03-01.yang"

   module ietf-bfd {

     yang-version 1.1;

     namespace "urn:ietf:params:xml:ns:yang:ietf-bfd";

     prefix "bfd";

     import ietf-bfd-types {
       prefix "bfd-types";
       // RFC Ed.: replace XXXX with actual RFC number and remove this
       // note



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       reference "RFC XXXX: YANG Data Model for BFD";
     }

     import ietf-routing {
       prefix "rt";
       // RFC Ed.: replace XXXX with actual RFC number of
       // draft-ietf-netmod-rfc8022bis and remove this note.
       reference
         "RFC XXXX: A YANG Data Model for Routing Management";
     }

     organization "IETF BFD Working Group";

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

        Editors:  Reshad Rahman (rrahman@cisco.com),
                  Lianshu Zheng (vero.zheng@huawei.com),
                  Mahesh Jethanandani (mjethanandani@gmail.com)";

     description
       "This module contains the YANG definition for BFD parameters as
        per RFC 5880.

        Copyright (c) 2018 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 Simplified BSD License
        set forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (http://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC XXXX; see
        the RFC itself for full legal notices.";

     // RFC Ed.: replace XXXX with actual RFC number and remove this
     // note

     reference "RFC XXXX";

     revision 2018-03-01 {
       description "Initial revision.";
       reference "RFC XXXX: YANG Data Model for BFD";
     }




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     augment "/rt:routing/rt:control-plane-protocols/"
           + "rt:control-plane-protocol" {
        when "derived-from-or-self(rt:type, 'bfd-types:bfdv1')" {
         description
           "This augmentation is only valid for a control-plane protocol
            instance of BFD (type 'bfdv1').";
       }
       description "BFD augmentation.";

       container bfd {
         description "BFD top level container.";

         uses bfd-types:session-statistics-summary;
       }
     }
   }

   <CODE ENDS>

2.15.  BFD IP single-hop YANG Module

   This YANG module imports "interface-ref" from
   [I-D.ietf-netmod-rfc7223bis].

   <CODE BEGINS> file "ietf-bfd-ip-sh@2018-03-01.yang"

   module ietf-bfd-ip-sh {

     yang-version 1.1;

     namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-ip-sh";

     prefix "bfd-ip-sh";

     import ietf-bfd-types {
       prefix "bfd-types";
     }

     import ietf-bfd {
       prefix "bfd";
     }

     import ietf-interfaces {
       prefix "if";
       // RFC Ed.: replace XXXX with actual RFC number of
       // draft-ietf-netmod-rfc7223bis and remove this note.
       reference
         "RFC XXXX: A YANG Data Model for Interface Management";



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     }

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

     import ietf-routing {
       prefix "rt";
       // RFC Ed.: replace XXXX with actual RFC number of
       // draft-ietf-netmod-rfc8022bis and remove this note.
       reference
         "RFC XXXX: A YANG Data Model for Routing Management";
     }

     organization "IETF BFD Working Group";

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

        Editors:  Reshad Rahman (rrahman@cisco.com),
                  Lianshu Zheng (vero.zheng@huawei.com),
                  Mahesh Jethanandani (mjethanandani@gmail.com)";

     description
       "This module contains the YANG definition for BFD IP single-hop
        as per RFC 5881.

        Copyright (c) 2018 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 Simplified BSD License
        set forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (http://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC XXXX; see
        the RFC itself for full legal notices.";

     // RFC Ed.: replace XXXX with actual RFC number and remove this
     // note

     reference "RFC XXXX";

     revision 2018-03-01 {



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       description "Initial revision.";
       reference "RFC XXXX: A YANG data model for BFD IP single-hop";
     }

     /*
      * Augments
      */
     augment "/rt:routing/rt:control-plane-protocols/"
           + "rt:control-plane-protocol/bfd:bfd" {
       description "BFD augmentation for IP single-hop";
       container ip-sh {
         description "BFD IP single-hop top level container";

         uses bfd-types:session-statistics-summary;

         list sessions {
           key "interface dest-addr";
           description "List of IP single-hop sessions";
           leaf interface {
             type if:interface-ref;
             description
               "Interface on which the BFD session is running.";
           }
           leaf dest-addr {
             type inet:ip-address;
             description "IP address of the peer.";
           }
           leaf source-addr {
             type inet:ip-address;
             description "Local IP address.";
           }

           uses bfd-types:common-cfg-parms;

           uses bfd-types:all-session;
         }
         list interfaces {
           key "interface";
           description "List of interfaces.";
           leaf interface {
             type if:interface-ref;
             description
               "BFD information for this interface.";
           }

           uses bfd-types:auth-parms;
         }
       }



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     }

     /*
      * Notifications
      */
     notification singlehop-notification {
       description
         "Notification for BFD single-hop session state change. An " +
         "implementation may rate-limit notifications, e.g. when a" +
         "session is continuously changing state.";

       uses bfd-types:notification-parms;

       leaf interface {
         type if:interface-ref;
         description "Interface to which this BFD session belongs to.";
       }

       leaf echo-enabled {
         type boolean;
         description "Was echo enabled for BFD.";
       }
     }

   }

   <CODE ENDS>

2.16.  BFD IP multihop YANG Module

   This YANG module imports typedefs from [RFC6991].

<CODE BEGINS> file "ietf-bfd-ip-mh@2018-03-01.yang"

module ietf-bfd-ip-mh {

  yang-version 1.1;

  namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-ip-mh";

  prefix "bfd-ip-mh";

  import ietf-bfd-types {
    prefix "bfd-types";
  }

  import ietf-bfd {
    prefix "bfd";



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  }

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

  import ietf-routing {
    prefix "rt";
    // RFC Ed.: replace XXXX with actual RFC number of
    // draft-ietf-netmod-rfc8022bis and remove this note.
    reference
      "RFC XXXX: A YANG Data Model for Routing Management";
  }

  organization "IETF BFD Working Group";

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

     Editors:  Reshad Rahman (rrahman@cisco.com),
               Lianshu Zheng (vero.zheng@huawei.com),
               Mahesh Jethanandani (mjethanandani@gmail.com)";

  description
    "This module contains the YANG definition for BFD IP multi-hop
     as per RFC 5883.

     Copyright (c) 2018 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 Simplified BSD License
     set forth in Section 4.c of the IETF Trust's Legal Provisions
     Relating to IETF Documents
     (http://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC XXXX; see
     the RFC itself for full legal notices.";

  // RFC Ed.: replace XXXX with actual RFC number and remove this
  // note

  reference "RFC XXXX";

  revision 2018-03-01 {



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    description "Initial revision.";
    reference "RFC XXXX: A YANG data model for BFD IP multihop.";
  }

  /*
   * Augments
   */
  augment "/rt:routing/rt:control-plane-protocols/"
        + "rt:control-plane-protocol/bfd:bfd" {
    description "BFD augmentation for IP multihop.";
    container ip-mh {
      description "BFD IP multihop top level container.";

      uses bfd-types:session-statistics-summary;

      list session-group {
        key "source-addr dest-addr";
        description
          "Group of BFD IP multi-hop sessions (for ECMP). A " +
          "group of sessions is between 1 source and 1  " +
          "destination, each session has a different field " +
          "in UDP/IP hdr for ECMP.";

        leaf source-addr {
          type inet:ip-address;
          description
            "Local IP address.";
        }
        leaf dest-addr {
          type inet:ip-address;
          description
            "IP address of the peer.";
        }
        uses bfd-types:common-cfg-parms;

        leaf tx-ttl {
          type bfd-types:hops;
          default 255;
          description "Hop count of outgoing BFD control packets.";
        }
        leaf rx-ttl {
          type bfd-types:hops;
          mandatory true;
          description
            "Minimum allowed hop count value for incoming BFD control
             packets. Control packets whose hop count is lower than this
             value are dropped.";
        }



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        list sessions {
          config false;
          description
            "The multiple BFD sessions between a source and a " +
            "destination.";
          uses bfd-types:all-session;
        }
      }
    }
  }

  /*
   * Notifications
   */
  notification multihop-notification {
    description
      "Notification for BFD multi-hop session state change. An " +
      "implementation may rate-limit notifications, e.g. when a" +
      "session is continuously changing state.";

    uses bfd-types:notification-parms;
  }
}

<CODE ENDS>

2.17.  BFD over LAG YANG Module

   This YANG module imports "interface-ref" from
   [I-D.ietf-netmod-rfc7223bis].

   <CODE BEGINS> file "ietf-bfd-lag@2018-03-01.yang"

   module ietf-bfd-lag {

     yang-version 1.1;

     namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-lag";

     prefix "bfd-lag";

     import ietf-bfd-types {
       prefix "bfd-types";
     }

     import ietf-bfd {
       prefix "bfd";
     }



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     import ietf-interfaces {
       prefix "if";
       // RFC Ed.: replace XXXX with actual RFC number of
       // draft-ietf-netmod-rfc7223bis and remove this note.
       reference
         "RFC XXXX: A YANG Data Model for Interface Management";
     }

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

     import ietf-routing {
       prefix "rt";
       // RFC Ed.: replace XXXX with actual RFC number of
       // draft-ietf-netmod-rfc8022bis and remove this note.
       reference
         "RFC XXXX: A YANG Data Model for Routing Management";
     }

     organization "IETF BFD Working Group";

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

        Editors:  Reshad Rahman (rrahman@cisco.com),
                  Lianshu Zheng vero.zheng@huawei.com),
                  Mahesh Jethanandani (mjethanandani@gmail.com)";

     description
       "This module contains the YANG definition for BFD over LAG
        interfaces as per RFC7130.

        Copyright (c) 2018 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 Simplified BSD License
        set forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (http://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC XXXX; see
        the RFC itself for full legal notices.";




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     // RFC Ed.: replace XXXX with actual RFC number and remove this
     // note

     reference "RFC XXXX";

     revision 2018-03-01 {
       description "Initial revision.";
       reference "RFC XXXX: A YANG data model for BFD over LAG";
     }

     /*
      * Augments
      */
     augment "/rt:routing/rt:control-plane-protocols/"
           + "rt:control-plane-protocol/bfd:bfd" {
       description "BFD augmentation for LAG";
       container lag {
         description "BFD over LAG top level container";

         container micro-bfd-ipv4-session-statistics {
           description "Micro-BFD IPv4 session counters.";
           uses bfd-types:session-statistics-summary;
         }
         container micro-bfd-ipv6-session-statistics {
           description "Micro-BFD IPv6 session counters.";
           uses bfd-types:session-statistics-summary;
         }

         list sessions {
           key "lag-name";
           description "A LAG interface on which BFD is running.";
           leaf lag-name {
             type if:interface-ref ;
             description "Name of the LAG";
           }
           leaf ipv4-dest-addr {
             type inet:ipv4-address;
             description
               "IPv4 address of the peer, for IPv4 micro-BFD.";
           }
           leaf ipv6-dest-addr {
             type inet:ipv6-address;
             description
               "IPv6 address of the peer, for IPv6 micro-BFD.";
           }
           uses bfd-types:common-cfg-parms;

           leaf use-ipv4 {



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             type boolean;
             description "Using IPv4 micro-BFD.";
           }
           leaf use-ipv6 {
             type boolean;
             description "Using IPv6 micro-BFD.";
           }

           list member-links {
             key "member-link";
             config false;
             description
               "Micro-BFD over LAG. This represents one member link.";

             leaf member-link {
               type if:interface-ref;
               description
                 "Member link on which micro-BFD is running.";
             }
             container micro-bfd-ipv4 {
               when "../../use-ipv4 = 'true'" {
                 description "Needed only if IPv4 is used.";
               }
               description
                 "Micro-BFD IPv4 session state on member link.";
               uses bfd-types:all-session;
             }
             container micro-bfd-ipv6 {
               when "../../use-ipv6 = 'true'" {
                 description "Needed only if IPv6 is used.";
               }
               description
                 "Micro-BFD IPv6 session state on member link.";
               uses bfd-types:all-session;
             }
           }
         }
       }
     }

     /*
      * Notifications
      */
     notification lag-notification {
       description
         "Notification for BFD over LAG session state change. " +
         "An implementation may rate-limit notifications, e.g. when a" +
         "session is continuously changing state.";



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       uses bfd-types:notification-parms;

       leaf lag-name {
         type if:interface-ref;
         description "LAG interface name.";
       }

       leaf member-link {
         type if:interface-ref;
         description "Member link on which BFD is running.";
       }
     }
   }

   <CODE ENDS>

2.18.  BFD over MPLS YANG Module

   This YANG module imports typedefs from [RFC6991].

   <CODE BEGINS> file "ietf-bfd-mpls@2018-03-01.yang"

   module ietf-bfd-mpls {

     yang-version 1.1;

     namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-mpls";

     prefix "bfd-mpls";

     import ietf-bfd-types {
       prefix "bfd-types";
     }

     import ietf-bfd {
       prefix "bfd";
     }

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

     import ietf-routing {
       prefix "rt";
       // RFC Ed.: replace XXXX with actual RFC number of
       // draft-ietf-netmod-rfc8022bis and remove this note.
       reference



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         "RFC XXXX: A YANG Data Model for Routing Management";
     }

     organization "IETF BFD Working Group";

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

        Editors:   Reshad Rahman (rrahman@cisco.com),
                   Lianshu Zheng (vero.zheng@huawei.com),
                   Mahesh Jethanandani (mjethanandani@gmail.com)";

     description
       "This module contains the YANG definition for BFD parameters for
        MPLS LSPs as per RFC 5884.

        Copyright (c) 2018 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 Simplified BSD License
        set forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (http://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC XXXX; see
        the RFC itself for full legal notices.";

     // RFC Ed.: replace XXXX with actual RFC number and remove this
     // note

     reference "RFC XXXX";

     revision 2018-03-01 {
       description "Initial revision.";
       reference "RFC XXXX: A YANG data model for BFD over MPLS LSPs";
     }

     /*
      * Identity definitions
      */
     identity encap-gach {
       base bfd-types:encap-type;
       description
         "BFD with G-ACh encapsulation as per RFC 5586.";
     }



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     identity encap-ip-gach {
       base bfd-types:encap-type;
       description
         "BFD with IP and G-ACh encapsulation as per RFC 5586.";
     }

     /*
      * Groupings
      */
     grouping encap-cfg {
       description "Configuration for BFD encapsulation";

       leaf encap {
         type identityref {
           base bfd-types:encap-type;
         }
         default bfd-types:encap-ip;
         description "BFD encapsulation";
       }
     }

     grouping mpls-dest-address {
       description "Destination address as per RFC 5884.";

       leaf mpls-dest-address {
         type inet:ip-address;
         config "false";
         description
           "Destination address as per RFC 5884.
            Needed if IP encapsulation is used.";
       }
     }

     /*
      * Augments
      */
     augment "/rt:routing/rt:control-plane-protocols/"
           + "rt:control-plane-protocol/bfd:bfd" {
       description "BFD augmentation for MPLS.";
       container mpls {
         description "BFD MPLS top level container.";

         uses bfd-types:session-statistics-summary;

         container egress {
           description "Egress configuration.";

           uses bfd-types:client-cfg-parms;



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           uses bfd-types:auth-parms;
         }

         list session-group {
           key "mpls-fec";
           description
             "Group of BFD MPLS sessions (for ECMP). A group of " +
             "sessions is for 1 FEC, each session has a different " +
             "field in UDP/IP hdr for ECMP.";
           leaf mpls-fec {
             type inet:ip-prefix;
             description "MPLS FEC.";
           }

           uses bfd-types:common-cfg-parms;

           list sessions {
             config false;
             description
               "The BFD sessions for an MPLS FEC. Local " +
               "discriminator is unique for each session in the " +
               "group.";
             uses bfd-types:all-session;

             uses bfd-mpls:mpls-dest-address;
           }
         }
       }
     }

     /*
      * Notifications
      */
     notification mpls-notification {
       description
         "Notification for BFD over MPLS FEC session state change. " +
         "An implementation may rate-limit notifications, e.g. when a" +
         "session is continuously changing state.";

       uses bfd-types:notification-parms;

       leaf mpls-dest-address {
         type inet:ip-address;
         description
           "Destination address as per RFC 5884.
            Needed if IP encapsulation is used.";
       }
     }



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   }

   <CODE ENDS>

2.19.  BFD over MPLS-TE YANG Module

   This YANG module imports and augments "/te/tunnels/tunnel" from
   [I-D.ietf-teas-yang-te].

   <CODE BEGINS> file "ietf-bfd-mpls-te@2018-03-01.yang"

   module ietf-bfd-mpls-te {

     yang-version 1.1;

     namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-mpls-te";

     prefix "bfd-mpls-te";

     import ietf-bfd-types {
       prefix "bfd-types";
     }

     import ietf-bfd {
       prefix "bfd";
     }

     import ietf-bfd-mpls {
       prefix "bfd-mpls";
     }

     import ietf-te {
       prefix "te";
     }

     import ietf-routing {
       prefix "rt";
       // RFC Ed.: replace XXXX with actual RFC number of
       // draft-ietf-netmod-rfc8022bis and remove this note.
       reference
         "RFC XXXX: A YANG Data Model for Routing Management";
     }

     organization "IETF BFD Working Group";

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



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        Editors:  Reshad Rahman (rrahman@cisco.com),
                  Lianshu Zheng (vero.zheng@huawei.com),
                  Mahesh Jethanandani (mjethanandani@gmail.com)";

     description
       "This module contains the YANG definition for BFD parameters for
        MPLS Traffic Engineering as per RFC 5884.

        Copyright (c) 2018 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 Simplified BSD License
        set forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (http://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC XXXX; see
        the RFC itself for full legal notices.";

     // RFC Ed.: replace XXXX with actual RFC number and remove this
     // note

     reference "RFC XXXX";

     revision 2018-03-01 {
       description "Initial revision.";
       reference "RFC XXXX: A YANG data model for BFD over MPLS-TE";
     }

     /*
      * Augments
      */
     augment "/rt:routing/rt:control-plane-protocols/"
           + "rt:control-plane-protocol/bfd:bfd" {
       description "BFD augmentation for MPLS-TE.";
       container mpls-te {
         description "BFD MPLS-TE top level container.";

         container egress {
           description "Egress configuration.";

           uses bfd-types:client-cfg-parms;

           uses bfd-types:auth-parms;
         }




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         uses bfd-types:session-statistics-summary;
       }
     }

     augment "/te:te/te:tunnels/te:tunnel" {
       description "BFD configuration on MPLS-TE tunnel.";

       uses bfd-types:common-cfg-parms;

       uses bfd-mpls:encap-cfg;
     }

     augment "/te:te/te:lsps-state/te:lsp" {
       when "/te:te/te:lsps-state/te:lsp/te:origin-type != 'transit'" {
         description "BFD information not needed at transit points.";
       }
       description "BFD state information on MPLS-TE LSP.";

       uses bfd-types:all-session;

       uses bfd-mpls:mpls-dest-address;
     }

     /*
      * Notifications
      */
     notification mpls-te-notification {
       description
         "Notification for BFD over MPLS-TE session state change. " +
         "An implementation may rate-limit notifications, e.g. when a" +
         "session is continuously changing state.";

       uses bfd-types:notification-parms;

       uses bfd-mpls:mpls-dest-address;

       leaf tunnel-name {
         type string;
         description "MPLS-TE tunnel on which BFD was running.";
       }
     }
   }

   <CODE ENDS>







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3.  Data Model examples

   This section presents some simple and illustrative examples on how to
   configure BFD.

3.1.  IP single-hop

   The following is an example configuration for a BFD IP single-hop
   session.  The desired transmit interval and the required receive
   interval are both set to 10ms.

<?xml version="1.0" encoding="UTF-8"?>
<config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <interfaces xmlns="urn:ietf:params:xml:ns:yang:ietf-interfaces">
    <interface>
      <name>eth0</name>
      <type xmlns:ianaift="urn:ietf:params:xml:ns:yang:iana-if-type">ianaift:ethernetCsmacd</type>
    </interface>
  </interfaces>
  <routing xmlns="urn:ietf:params:xml:ns:yang:ietf-routing">
    <control-plane-protocols>
      <control-plane-protocol>
        <type xmlns:bfd-types="urn:ietf:params:xml:ns:yang:ietf-bfd-types">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>
              <interface>eth0</interface>
              <dest-addr>2001:db8:0:113::101</dest-addr>
              <desired-min-tx-interval>10000</desired-min-tx-interval>
              <required-min-rx-interval>10000</required-min-rx-interval>
            </sessions>
          </ip-sh>
        </bfd>
      </control-plane-protocol>
    </control-plane-protocols>
  </routing>
</config>


3.2.  IP multihop

   The following is an example configuration for a BFD IP multihop
   session group.  The desired transmit interval and the required
   receive interval are both set to 150ms.






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<?xml version="1.0" encoding="UTF-8"?>
<config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <routing xmlns="urn:ietf:params:xml:ns:yang:ietf-routing">
    <control-plane-protocols>
      <control-plane-protocol>
        <type xmlns:bfd-types="urn:ietf:params:xml:ns:yang:ietf-bfd-types">bfd-types:bfdv1</type>
        <name>name:BFD</name>
        <bfd xmlns="urn:ietf:params:xml:ns:yang:ietf-bfd">
          <ip-mh xmlns="urn:ietf:params:xml:ns:yang:ietf-bfd-ip-mh">
            <session-group>
              <source-addr>2001:db8:0:113::103</source-addr>
              <dest-addr>2001:db8:0:114::100</dest-addr>
              <desired-min-tx-interval>150000</desired-min-tx-interval>
              <required-min-rx-interval>150000</required-min-rx-interval>
              <rx-ttl>240</rx-ttl>
            </session-group>
          </ip-mh>
        </bfd>
      </control-plane-protocol>
    </control-plane-protocols>
  </routing>
</config>

4.  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
   [RFC5246].

   The NETCONF access control model [RFC6536] 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.  These are the subtrees and data nodes
   and their sensitivity/vulnerability:

   /routing/control-plane-protocols/control-plane-protocol/bfd/ip-sh/
   sessions: the list specifies the IP single-hop BFD sessions.



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   /routing/control-plane-protocols/control-plane-protocol/bfd/ip-sh/
   sessions: data nodes local-multiplier, desired-min-tx-interval,
   required-min-rx-interval, min-interval and authentication all impact
   the BFD IP single-hop session.

   /routing/control-plane-protocols/control-plane-protocol/bfd/ip-mh/
   session-group: the list specifies the IP multi-hop BFD session
   groups.

   /routing/control-plane-protocols/control-plane-protocol/bfd/ip-mh/
   session-group: data nodes local-multiplier, desired-min-tx-interval,
   required-min-rx-interval, min-interval and authentication all impact
   the BFD IP multi-hop session.

   /routing/control-plane-protocols/control-plane-protocol/bfd/lag/
   sessions: the list specifies the BFD sessions over LAG.

   /routing/control-plane-protocols/control-plane-protocol/bfd/lag/
   sessions: data nodes local-multiplier, desired-min-tx-interval,
   required-min-rx-interval, min-interval and authentication all impact
   the BFD over LAG session.

   /routing/control-plane-protocols/control-plane-protocol/bfd/mpls/
   session-group: the list specifies the session groups for BFD over
   MPLS.

   /routing/control-plane-protocols/control-plane-protocol/bfd/mpls/
   session-group: data nodes local-multiplier, desired-min-tx-interval,
   required-min-rx-interval, min-interval and authentication all impact
   the BFD over MPLS LSPs session.

   /routing/control-plane-protocols/control-plane-protocol/bfd/mpls/
   egress: data nodes local-multiplier, desired-min-tx-interval,
   required-min-rx-interval, min-interval and authentication all impact
   the BFD over MPLS LSPs sessions for which this device is an MPLS LSP
   egress node.

   /te/tunnels/tunnel: data nodes local-multiplier, desired-min-tx-
   interval, required-min-rx-interval, min-interval and authentication
   all impact the BFD session over the MPLS-TE tunnel.

   /routing/control-plane-protocols/control-plane-protocol/bfd/mpls-te/
   egress: data nodes local-multiplier, desired-min-tx-interval,
   required-min-rx-interval, min-interval and authentication all impact
   the BFD over MPLS-TE sessions for which this device is an MPLS-TE
   egress node.





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   The YANG module has writeable data nodes which can be used for
   creation of BFD sessions and modification of BFD session parameters.
   The system should "police" creation of BFD sessions to prevent new
   sessions from causing existing BFD sessions to fail.  For BFD session
   modification, the BFD protocol has mechanisms in place which allow
   for in service modification.

   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.  These are the subtrees and data
   nodes and their sensitivity/vulnerability:

   /routing/control-plane-protocols/control-plane-protocol/bfd/ip-sh/
   summary: access to this information discloses the number of BFD IP
   single-hop sessions which are up, down and admin-down.  The counters
   include BFD sessions for which the user does not have read-access.

   /routing/control-plane-protocols/control-plane-protocol/bfd/ip-mh/
   summary: access to this information discloses the number of BFD IP
   multi-hop sessions which are up, down and admin-down.  The counters
   include BFD sessions for which the user does not have read-access.

   /routing/control-plane-protocols/control-plane-protocol/bfd/lag/
   micro-bfd-ipv4-session-statistics/summary: access to this information
   discloses the number of micro BFD IPv4 LAG sessions which are up,
   down and admin-down.  The counters include BFD sessions for which the
   user does not have read-access.

   /routing/control-plane-protocols/control-plane-protocol/bfd/lag/
   micro-bfd-ipv6-session-statistics/summary: access to this information
   discloses the number of micro BFD IPv6 LAG sessions which are up,
   down and admin-down.  The counters include BFD sessions for which the
   user does not have read-access.

   /routing/control-plane-protocols/control-plane-protocol/bfd/mpls/
   summary: access to this information discloses the number of BFD
   sessions over MPLS LSPs which are up, down and admin-down.  The
   counters include BFD sessions for which the user does not have read-
   access.

   /routing/control-plane-protocols/control-plane-protocol/bfd/mpls-te/
   summary: access to this information discloses the number of BFD
   sessions over MPLS-TE which are up, down and admin-down.  The
   counters include BFD sessions for which the user does not have read-
   access.





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5.  IANA Considerations

   The IANA is requested to as assign a new namespace URI from the IETF
   XML registry.

   This document registers the following namesace URIs in the IETF XML
   registry [RFC3688]:

   --------------------------------------------------------------------

   URI: urn:ietf:params:xml:ns:yang:ietf-bfd

   Registrant Contact: The IESG.

   XML: N/A, the requested URI is an XML namespace.

   --------------------------------------------------------------------

   --------------------------------------------------------------------

   URI: urn:ietf:params:xml:ns:yang:ietf-bfd-ip-sh

   Registrant Contact: The IESG.

   XML: N/A, the requested URI is an XML namespace.

   --------------------------------------------------------------------

   --------------------------------------------------------------------

   URI: urn:ietf:params:xml:ns:yang:ietf-bfd-mh

   Registrant Contact: The IESG.

   XML: N/A, the requested URI is an XML namespace.

   --------------------------------------------------------------------

   --------------------------------------------------------------------

   URI: urn:ietf:params:xml:ns:yang:ietf-bfd-lag

   Registrant Contact: The IESG.

   XML: N/A, the requested URI is an XML namespace.

   --------------------------------------------------------------------




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   --------------------------------------------------------------------

   URI: urn:ietf:params:xml:ns:yang:ietf-bfd-mpls

   Registrant Contact: The IESG.

   XML: N/A, the requested URI is an XML namespace.

   --------------------------------------------------------------------

   --------------------------------------------------------------------

   URI: urn:ietf:params:xml:ns:yang:ietf-bfd-mpls-te

   Registrant Contact: The IESG.

   XML: N/A, the requested URI is an XML namespace.

   --------------------------------------------------------------------

5.1.  IANA-Maintained iana-bfd-types module

   This document defines the initial version of the IANA-maintained
   iana-bfd-types YANG module.

   The iana-bfd-types YANG module is intended to reflect the "BFD
   Diagnostic Codes" registry and "BFD Authentication Types" registry at
   https://www.iana.org/assignments/bfd-parameters/bfd-parameters.xhtml

6.  Acknowledgements

   We would also like to thank Nobo Akiya and Jeff Haas for their
   encouragement on this work.  We would also like to thank Rakesh
   Gandhi and Tarek Saad for their help on the MPLS-TE model.  We would
   also like to thank Acee Lindem for his guidance.

7.  References

7.1.  Normative References

   [I-D.ietf-mpls-base-yang]
              Saad, T., Raza, K., Gandhi, R., Liu, X., and V. Beeram, "A
              YANG Data Model for MPLS Base", draft-ietf-mpls-base-
              yang-06 (work in progress), February 2018.







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   [I-D.ietf-netmod-rfc7223bis]
              Bjorklund, M., "A YANG Data Model for Interface
              Management", draft-ietf-netmod-rfc7223bis-03 (work in
              progress), January 2018.

   [I-D.ietf-netmod-rfc7277bis]
              Bjorklund, M., "A YANG Data Model for IP Management",
              draft-ietf-netmod-rfc7277bis-03 (work in progress),
              January 2018.

   [I-D.ietf-netmod-rfc8022bis]
              Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for
              Routing Management (NMDA Version)", draft-ietf-netmod-
              rfc8022bis-11 (work in progress), January 2018.

   [I-D.ietf-teas-yang-te]
              Saad, T., Gandhi, R., Liu, X., Beeram, V., Shah, H., and
              I. Bryskin, "A YANG Data Model for Traffic Engineering
              Tunnels and Interfaces", draft-ietf-teas-yang-te-12 (work
              in progress), February 2018.

   [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>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
              "MPLS Generic Associated Channel", RFC 5586,
              DOI 10.17487/RFC5586, June 2009,
              <https://www.rfc-editor.org/info/rfc5586>.

   [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>.

   [RFC5881]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
              DOI 10.17487/RFC5881, June 2010,
              <https://www.rfc-editor.org/info/rfc5881>.



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   [RFC5882]  Katz, D. and D. Ward, "Generic Application of
              Bidirectional Forwarding Detection (BFD)", RFC 5882,
              DOI 10.17487/RFC5882, June 2010,
              <https://www.rfc-editor.org/info/rfc5882>.

   [RFC5883]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883,
              June 2010, <https://www.rfc-editor.org/info/rfc5883>.

   [RFC5884]  Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
              "Bidirectional Forwarding Detection (BFD) for MPLS Label
              Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884,
              June 2010, <https://www.rfc-editor.org/info/rfc5884>.

   [RFC5885]  Nadeau, T., Ed. and C. Pignataro, Ed., "Bidirectional
              Forwarding Detection (BFD) for the Pseudowire Virtual
              Circuit Connectivity Verification (VCCV)", RFC 5885,
              DOI 10.17487/RFC5885, June 2010,
              <https://www.rfc-editor.org/info/rfc5885>.

   [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>.

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536,
              DOI 10.17487/RFC6536, March 2012,
              <https://www.rfc-editor.org/info/rfc6536>.

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

   [RFC7130]  Bhatia, M., Ed., Chen, M., Ed., Boutros, S., Ed.,
              Binderberger, M., Ed., and J. Haas, Ed., "Bidirectional
              Forwarding Detection (BFD) on Link Aggregation Group (LAG)
              Interfaces", RFC 7130, DOI 10.17487/RFC7130, February
              2014, <https://www.rfc-editor.org/info/rfc7130>.

   [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>.




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   [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>.

7.2.  Informative References

   [I-D.ietf-lime-yang-connectionless-oam]
              Kumar, D., Wang, Z., Wu, Q., Rahman, R., and S. Raghavan,
              "Generic YANG Data Model for the Management of Operations,
              Administration, and Maintenance (OAM) Protocols that use
              Connectionless Communications", draft-ietf-lime-yang-
              connectionless-oam-18 (work in progress), November 2017.

   [I-D.ietf-netmod-revised-datastores]
              Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore
              Architecture", draft-ietf-netmod-revised-datastores-10
              (work in progress), January 2018.

   [I-D.ietf-netmod-schema-mount]
              Bjorklund, M. and L. Lhotka, "YANG Schema Mount", draft-
              ietf-netmod-schema-mount-08 (work in progress), October
              2017.

   [I-D.ietf-rtgwg-lne-model]
              Berger, L., Hopps, C., Lindem, A., Bogdanovic, D., and X.
              Liu, "YANG Model for Logical Network Elements", draft-
              ietf-rtgwg-lne-model-07 (work in progress), February 2018.

   [I-D.ietf-rtgwg-ni-model]
              Berger, L., Hopps, C., Lindem, A., Bogdanovic, D., and X.
              Liu, "YANG Model for Network Instances", draft-ietf-rtgwg-
              ni-model-10 (work in progress), February 2018.

Appendix A.  Echo function configuration example

   As mentioned in Section 2.1.2, the mechanism to start and stop the
   echo function, as defined in [RFC5880] and [RFC5881], is
   implementation specific.  In this section we provide an example of
   how the echo function can be implemented via configuration.






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 module: example-bfd-echo
   augment /rt:routing/rt:control-plane-protocols/rt:control-plane-proto
 col/bfd:bfd/bfd-ip-sh:ip-sh/bfd-ip-sh:sessions:
     +--rw echo {bfd-types:echo-mode}?
        +--rw desired-min-echo-tx-interval?    uint32
        +--rw required-min-echo-rx-interval?   uint32

A.1.  Example YANG module for BFD echo function configuration


module example-bfd-echo {
  namespace "tag:example.com,2018:example-bfd-echo";

  prefix "example-bfd-echo";

  import ietf-bfd-types {
    prefix "bfd-types";
  }

  import ietf-bfd {
    prefix "bfd";
  }

  import ietf-bfd-ip-sh {
    prefix "bfd-ip-sh";
  }

  import ietf-routing {
    prefix "rt";
  }

  organization "IETF BFD Working Group";

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

     Editors:  Reshad Rahman (rrahman@cisco.com),
               Lianshu Zheng (vero.zheng@huawei.com),
               Mahesh Jethanandani (mjethanandani@gmail.com)";

  description
    "This module contains an example YANG augmentation for configuration
     of BFD echo function.

     Copyright (c) 2018 IETF Trust and the persons
     identified as authors of the code.  All rights reserved.




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     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 Simplified BSD License
     set forth in Section 4.c of the IETF Trust's Legal Provisions
     Relating to IETF Documents
     (http://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC XXXX; see
     the RFC itself for full legal notices.";

  revision 2018-03-01 {
    description "Initial revision.";
    reference
      "RFC XXXX: A YANG data model example augmentation for BFD echo
       function";
  }

  // RFC Ed.: replace XXXX with actual RFC number and remove this
  // note

  /*
   * Groupings
   */
  grouping echo-cfg-parms {
    description "BFD grouping for echo config parameters";
    leaf desired-min-echo-tx-interval {
      type uint32;
      units microseconds;
      default 0;
      description
        "This is the minimum interval that the local system would like
         to use when transmitting BFD echo packets.  If 0, the echo
         function as defined in BFD [RFC5880] is disabled.";
    }

    leaf required-min-echo-rx-interval {
      type uint32;
      units microseconds;
      default 0;
      description
        "This is the Required Min Echo RX Interval as defined in BFD
        [RFC5880].";
    }
  }

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



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    description "Augmentation for BFD echo function.";

    container echo {
      if-feature bfd-types:echo-mode;

      description "BFD echo function container";

      uses echo-cfg-parms;
    }
  }
}

Appendix B.  Change log

   RFC Editor: Remove this section upon publication as an RFC.

B.1.  Changes between versions -09 and -10

   o  Addressed comments from YANG DOctor review.

   o  Addressed comments from WGLC.

B.2.  Changes between versions -08 and -09

   o  Mostly cosmetic changes to abide by draft-ietf-netmod-rfc6087bis.

   o  Specified yang-version 1.1.

   o  Added data model examples.

   o  Some minor changes.

B.3.  Changes between versions -07 and -08

   o  Timer intervals in client-cfg-parms are not mandatory anymore.

   o  Added list of interfaces under "ip-sh" node for authentication
      parameters.

   o  Renamed replay-protection to meticulous.

B.4.  Changes between versions -06 and -07

   o  New ietf-bfd-types module.

   o  Grouping for BFD clients to have BFD multiplier and interval
      values.




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   o  Change in ietf-bfd-mpls-te since MPLS-TE model changed.

   o  Removed bfd- prefix from many names.

B.5.  Changes between versions -05 and -06

   o  Adhere to NMDA-guidelines.

   o  Echo function config moved to appendix as example.

   o  Added IANA YANG modules.

   o  Addressed various comments.

B.6.  Changes between versions -04 and -05

   o  "bfd" node in augment of control-plane-protocol.

   o  Removed augment of network-instance.  Replaced by schema-mount.

   o  Added information on interaction with other YANG modules.

B.7.  Changes between versions -03 and -04

   o  Updated author information.

   o  Fixed YANG compile error in ietf-bfd-lag.yang which was due to
      incorrect when statement.

B.8.  Changes between versions -02 and -03

   o  Fixed YANG compilation warning due to incorrect revision date in
      ietf-bfd-ip-sh module.

B.9.  Changes between versions -01 and -02

   o  Replace routing-instance with network-instance from YANG Network
      Instances [I-D.ietf-rtgwg-ni-model]

B.10.  Changes between versions -00 and -01

   o  Remove BFD configuration parameters from BFD clients, all BFD
      configuration parameters in BFD

   o  YANG module split in multiple YANG modules (one per type of
      forwarding path)

   o  For BFD over MPLS-TE we augment MPLS-TE model



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   o  For BFD authentication we now use YANG Data Model for Key Chains
      [RFC8177]

Authors' Addresses

   Reshad Rahman (editor)
   Cisco Systems
   Canada

   Email: rrahman@cisco.com


   Lianshu Zheng (editor)
   Huawei Technologies
   China

   Email: vero.zheng@huawei.com


   Mahesh Jethanandani (editor)

   Email: mjethanandani@gmail.com


   Santosh Pallagatti
   India

   Email: santosh.pallagatti@gmail.com


   Greg Mirsky
   ZTE Corporation

   Email: gregimirsky@gmail.com

















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