Network Working Group                                     R. Rahman, Ed.
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                           L. Zheng, Ed.
Expires: September 11, 2017 January 1, 2018                             Huawei Technologies
                                                           S. Pallagatti
                                                    M. Jethanandani Jethanandani, Ed.
                                                           Cisco Systems
                                                           S. Pallagatti

                                                               G. Mirsky
                                                         ZTE Corporation
                                                          March 10,
                                                           June 30, 2017

      Yang

      YANG Data Model for Bidirectional Forwarding Detection (BFD)
                       draft-ietf-bfd-yang-05.txt
                       draft-ietf-bfd-yang-06.txt

Abstract

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

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 RFC 2119 [RFC2119].

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   This Internet-Draft will expire on September 11, 2017. January 1, 2018.

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Contributors  . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Design of the Data Model  . . . . . . . . . . . . . . . . . .   4
     2.1.  Design of Configuration Model . . . . . . . . . . . . . .   4   5
       2.1.1.  Common BFD configuration parameters . . . . . . . . .   5
       2.1.2.  Single-hop IP . . . . . . . . . . . . . . . . . . . .   6
       2.1.3.  Multi-hop IP  . . . . . . . . . . . . . . . . . . . .   6
       2.1.4.  MPLS Traffic Engineering Tunnels  . . . . . . . . . .   7
       2.1.5.  MPLS Label Switched Paths . . . . . . . . . . . . . .   7
       2.1.6.  Link Aggregation Groups . . . . . . . . . . . . . . .   7   8
     2.2.  Design of Operational Model . . . . . . . . . . . . . . .   8
     2.3.  Notifications . . . . . . . . . . . . . . . . . . . . . .   8   9
     2.4.  RPC Operations  . . . . . . . . . . . . . . . . . . . . .   9
     2.5.  BFD top level hierarchy . . . . . . . . . . . . . . . . .   9
     2.6.  BFD IP single-hop hierarchy . . . . . . . . . . . . . . .   9
     2.7.  BFD IP multi-hop hierarchy  . . . . . . . . . . . . . . .  11
     2.8.  BFD over LAG hierarchy  . . . . . . . . . . . . . . . . .  13
     2.9.  BFD over MPLS LSPs hierarchy  . . . . . . . . . . . . . .  15  16
     2.10. BFD over MPLS-TE hierarchy  . . . . . . . . . . . . . . .  17  18
     2.11. Examples  . . . . . Interaction with other YANG modules . . . . . . . . . . .  19
       2.11.1.  Module ietf-interfaces . . . . . . . .  19
     2.12. Interaction with other YANG modules . . . . . . .  20
       2.11.2.  Module ietf-ip . . . .  19
       2.12.1.  Module ietf-interfaces . . . . . . . . . . . . . . .  19
       2.12.2.  20
       2.11.3.  Module ietf-ip . ietf-mpls . . . . . . . . . . . . . . . . . .  19
       2.12.3.  20
       2.11.4.  Module ietf-mpls ietf-te . . . . . . . . . . . . . . . . . . .  20
       2.12.4.
     2.12. IANA BFD YANG Module ietf-te .  . . . . . . . . . . . . . . . . . .  20  21
     2.13. BFD top-level Yang YANG Module . . . . . . . . . . . . . . . .  20  23
     2.14. BFD IP single-hop Yang YANG Module . . . . . . . . . . . . . .  32  36
     2.15. BFD IP multi-hop Yang YANG Module  . . . . . . . . . . . . . .  35  38
     2.16. BFD over LAG Yang YANG Module  . . . . . . . . . . . . . . . .  38  41
     2.17. BFD over MPLS Yang YANG Module . . . . . . . . . . . . . . . .  42  44
     2.18. BFD over MPLS-TE Yang YANG Module  . . . . . . . . . . . . . .  45  47
     2.19. Security Considerations . . . . . . . . . . . . . . . . .  48  50
     2.20. IANA Considerations . . . . . . . . . . . . . . . . . . .  48  50
       2.20.1.  IANA-Maintained iana-bfd-types module  . . . . . . .  51
     2.21. Acknowledgements  . . . . . . . . . . . . . . . . . . . .  48  52
   3.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  49  52
     3.1.  Normative References  . . . . . . . . . . . . . . . . . .  49  52
     3.2.  Informative References  . . . . . . . . . . . . . . . . .  50  53
   Appendix A.  Echo function configuration example  . . . . . . . .  54
     A.1.  Example YANG module for BFD echo function . . . . . . . .  55
   Appendix B.  Change log . . . . . . . . . . . . . . . . . . . . .  51
     A.1.  57
     B.1.  Changes between versions -05 and -06  . . . . . . . . . .  57
     B.2.  Changes between versions -04 and -05  . . . . . . . . . .  51
     A.2.  57
     B.3.  Changes between versions -03 and -04  . . . . . . . . . .  52
     A.3.  57
     B.4.  Changes between versions -02 and -03  . . . . . . . . . .  52
     A.4.  57
     B.5.  Changes between versions -01 and -02  . . . . . . . . . .  52
     A.5.  58
     B.6.  Changes between versions -00 and -01  . . . . . . . . . .  52  58
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  52  58

1.  Introduction

   YANG [RFC6020] is a data definition language that was introduced to
   define the contents of a conceptual data store that allows networked
   devices to be managed using NETCONF [RFC6241].  YANG is proving
   relevant beyond its initial confines, as bindings to other interfaces
   (e.g RESTCONF [I-D.ietf-netconf-restconf]) and encodings other than
   XML (e.g JSON) are being defined.  Furthermore, YANG data models can
   be used as the basis of implementation for other interfaces, such as
   CLI and programmatic APIs.

   This document defines a YANG data model that can be used to configure
   and manage Bidirectional Forwarding Detection (BFD)[RFC5880]. (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 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) [RFC5885]

   5) Two systems connected via a Link Aggregation Group (LAG) interface
   [RFC7130] 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 "hellos" to detect failures, e.g. static routes, and
   routing protocols whose Hellos "hellos" do not support sub-
   second sub-second failure
   detection, e.g.  OSPF and IS-IS.

1.1.  Contributors

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 [RFC8022].  This new "bfd" node is
   augmented by all the YANG modules for their respective specific
   information.  Each BFD YANG module which augments
   the "bfd" node contains a "config" node and an "oper" node.

   BFD can operate in the following contexts:

   1.  Network devices as described in Network Device YANG
       Organizational Models [I-D.ietf-rtgwg-device-model]

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

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

   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
   locations.  For example, if an implementation supports BFD IP multi-
   hop in network instances, the implementation would do schema-mount of
   the BFD IP multi-hop model in a mount-point which resides in a
   network instance.

   The data models in this document strive to follow the "Network
   Management Datastore Architecture" (NMDA) guidelines described in
   [I-D.dsdt-nmda-guidelines].  This means that the data models do NOT
   have separate top-level or sibling containers for configuration and
   operational data.  One exception at the moment is the model for MPLS-
   TE in Section 2.1.4

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 is 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.  To avoid splitting the BFD
   configuration between BFD clients and this centralized model of BFD,
   all the configuration is kept under this centralized model of BFD.
   The only BFD configuration under BFD clients should be an "enable"
   knob which makes those clients react to BFD liveliness detection
   events.

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.  There are also intervals for the echo function (if
   supported):

   desired-min-echo-tx-interval
           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 [RFC5880] is disabled.

   required-min-echo-rx-interval
           This is the Required Min Echo RX Interval as defined in
           [RFC5880].  For BFD authentication we have:

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

   replay-protection
           This specifies meticulous v/s non-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.  We have  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

   [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.  Multi-hop IP

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

   Because of multiple paths, there could be multiple multi-hop IP
   sessions between a source and a destination address.  We have identify
   this as a list for BFD sessions over multi-hop IP. "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]

   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
   [I-D.ietf-teas-yang-te].  For BFD parameters
   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 address. 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.

   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 Model

   The operational 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 items
   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 session types, there may be more than 1 session on the
   virtual path to the destination.  For example, with IP multi-hop 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.
   Each of the BFD sessions on the same virtual path  This is uniquely
   identified represented by the local discriminator. having multiple "sessions" under
   each "session-group".

2.3.  Notifications

   This YANG model defines notifications to inform clients of BFD 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

   TBD

   None.

2.5.  BFD top level hierarchy

   At the "bfd" node under control-plane-protocol, there is no
   configuration data, only operational data.  The operational 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 mounted 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-protocol:
    +--rw bfd
         +--rw config
         +--ro oper
       +--ro bfd-session-statistics
          +--ro session-count?              uint32
          +--ro session-up-count?           uint32
          +--ro session-down-count?         uint32
          +--ro session-admin-down-count?   uint32

2.6.  BFD IP single-hop hierarchy

   An "ip-sh" node is added under "bfd" node in control-plane-protocol.
   The configuration and operational data for each BFD IP single-hop
   session is under this "ip-sh" node.  The "ip-sh" node can be mounted 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-protocol/bfd:bfd: /rt:routing/rt:control-plane-protocols/rt:control-plane-protoco
 l/bfd:bfd:
    +--rw ip-sh
         +--rw config
       +--ro bfd-session-statistics
       |  +--rw session-cfg  +--ro session-count?              uint32
       |  +--ro session-up-count?           uint32
       |  +--ro session-down-count?         uint32
       |  +--ro session-admin-down-count?   uint32
       +--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?                bfd-multiplier
         |
          +--rw (interval-config-type)?
          |        |  +--:(tx-rx-intervals)
          |  |  |  +--rw desired-min-tx-interval          uint32
          |  |  |  +--rw required-min-rx-interval         uint32
          |        |  +--:(single-interval)
          |        |     +--rw min-interval                     uint32
         |
          +--rw demand-enabled?                  boolean
         |
                                                 {bfd-demand-mode}?
          +--rw admin-down?                      boolean
         |
          +--rw authentication-parms! {bfd-authentication}?
          |        |  +--rw key-chain?           kc:key-chain-ref
          |        |  +--rw replay-protection?   identityref
         |
          +--rw desired-min-echo-tx-interval?    uint32
         |
          +--rw required-min-echo-rx-interval?   uint32
          +--ro oper
            +--ro bfd-session-statistics
            |  +--ro session-count?              uint32
            |  +--ro session-up-count?           uint32
            |  +--ro session-down-count?         uint32
            |  +--ro session-admin-down-count?   uint32
            +--ro sessions* [interface dest-addr]
               +--ro interface               if:interface-ref
               +--ro dest-addr               inet:ip-address
               +--ro source-addr?            inet:ip-address
               +--ro path-type?                       identityref
          +--ro ip-encapsulation?                boolean
          +--ro local-discriminator?             bfd-discriminator
          +--ro remote-discriminator?            bfd-discriminator
          +--ro remote-multiplier?               bfd-multiplier
          +--ro out-interface?          if:interface-ref
               +--ro demand-capability?               boolean
                                                 {bfd-demand-mode}?
          +--ro source-port?                     inet:port-number
          +--ro dest-port?                       inet:port-number
          +--ro session-running
          |  +--ro session-index?                uint32
          |  +--ro local-state?                  bfd-state
          |  +--ro remote-state?                 bfd-state
          |  +--ro local-diagnostic?             iana-bfd-types:
                                                 bfd-diagnostic
          |  +--ro remote-diagnostic?            iana-bfd-types:
                                                 bfd-diagnostic
          |  +--ro remote-authenticated?         boolean
          |  +--ro remote-authentication-type?   iana-bfd-types:
                                                 bfd-auth-type
          |  +--ro detection-mode?               enumeration
          |  +--ro negotiated-tx-interval?       uint32
          |  +--ro negotiated-rx-interval?       uint32
          |  +--ro echo-tx-interval-in-use? detection-time?               uint32
          |  +--ro detection-time? echo-tx-interval-in-use?      uint32 {bfd-echo-mode}?
          +--ro sesssion-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?             uint32
             +--ro admin-down-count?       uint32
             +--ro receive-packet-count?   uint64
             +--ro send-packet-count?      uint64
             +--ro receive-bad-packet?     uint64
             +--ro send-failed-packet?     uint64
 notifications:
    +---n bfd-singlehop-notification
       +--ro local-discr?                 bfd-discriminator
       +--ro remote-discr?                bfd-discriminator
       +--ro new-state?                   bfd-state
       +--ro state-change-reason?      string         iana-bfd-types:bfd-diagnostic
       +--ro time-in-previous-state?   string 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 multi-hop hierarchy

   An "ip-mh" node is added under the "bfd" node in cntrol-plane-
   protocol.  The configuration and operational data for each BFD IP
   multi-hop session is under this "ip-mh" node.  In the operational
   model we support multiple BFD multi-hop sessions per remote address
   (ECMP), the local discriminator is used as key.  The "ip-mh" node can
   be mounted 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-protocol/bfd:bfd:
    +--rw ip-mh
         +--rw config
       +--ro bfd-session-statistics
       |  +--rw session-cfg  +--ro session-count?              uint32
       |  +--ro session-up-count?           uint32
       |  +--ro session-down-count?         uint32
       |  +--ro session-admin-down-count?   uint32
       +--rw sessions* session-group* [source-addr dest-addr]
         |
          +--rw source-addr                 inet:ip-address
         |
          +--rw dest-addr                   inet:ip-address
         |
          +--rw local-multiplier?           bfd-multiplier
         |
          +--rw (interval-config-type)?
          |        |  +--:(tx-rx-intervals)
          |  |  |  +--rw desired-min-tx-interval     uint32
          |  |  |  +--rw required-min-rx-interval    uint32
          |        |  +--:(single-interval)
          |        |     +--rw min-interval                uint32
         |
          +--rw demand-enabled?             boolean
         | {bfd-demand-mode}?
          +--rw admin-down?                 boolean
         |
          +--rw authentication-parms! {bfd-authentication}?
          |        |  +--rw key-chain?           kc:key-chain-ref
          |        |  +--rw replay-protection?   identityref
         |
          +--rw tx-ttl?                     bfd:ttl
         |                     bfd:hops
          +--rw rx-ttl                      bfd:ttl
         +--ro oper
            +--ro bfd-session-statistics
            |  +--ro session-count?              uint32
            |  +--ro session-up-count?           uint32
            |  +--ro session-down-count?         uint32
            |  +--ro session-admin-down-count?   uint32
            +--ro session-group* [source-addr dest-addr]
               +--ro source-addr    inet:ip-address
               +--ro dest-addr      inet:ip-address                      bfd:hops
          +--ro sessions* [local-discriminator]
                  +--ro ttl?                    bfd:ttl
             +--ro path-type?              identityref
             +--ro local-discriminator ip-encapsulation?       boolean
             +--ro local-discriminator?    bfd-discriminator
             +--ro remote-discriminator?   bfd-discriminator
             +--ro remote-multiplier?      bfd-multiplier
             +--ro out-interface?          if:interface-ref
                  +--ro demand-capability?      boolean {bfd-demand-mode}?
             +--ro source-port?            inet:port-number
             +--ro dest-port?              inet:port-number
             +--ro session-running
             |  +--ro session-index?                uint32
             |  +--ro local-state?                  bfd-state
             |  +--ro remote-state?                 bfd-state
             |  +--ro local-diagnostic?             iana-bfd-types:
                                                    bfd-diagnostic
             |  +--ro remote-diagnostic?            iana-bfd-types:
                                                    bfd-diagnostic
             |  +--ro remote-authenticated?         boolean
             |  +--ro remote-authentication-type?   iana-bfd-types:
                                                    bfd-auth-type
             |  +--ro detection-mode?               enumeration
             |  +--ro negotiated-tx-interval?       uint32
             |  +--ro negotiated-rx-interval?       uint32
             |  +--ro echo-tx-interval-in-use? detection-time?               uint32
             |  +--ro detection-time? echo-tx-interval-in-use?      uint32
                                                    {bfd-echo-mode}?
             +--ro sesssion-statistics 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?             uint32
                +--ro admin-down-count?       uint32
                +--ro receive-packet-count?   uint64
                +--ro send-packet-count?      uint64
                +--ro receive-bad-packet?     uint64
                +--ro send-failed-packet?     uint64

 notifications:
    +---n bfd-multihop-notification
       +--ro local-discr?                 bfd-discriminator
       +--ro remote-discr?                bfd-discriminator
       +--ro new-state?                   bfd-state
       +--ro state-change-reason?      string         iana-bfd-types:bfd-diagnostic
       +--ro time-in-previous-state?   string 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 data for each BFD LAG session is
   under this "lag" node.  The "lag" node can be mounted 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-protocol/bfd:bfd:
    +--rw lag
       +--rw config micro-bfd-ipv4-session-statistics
       |  +--rw session-cfg  +--ro bfd-session-statistics
       |     +--rw sessions* [lag-name]     +--ro session-count?              uint32
       |     +--ro session-up-count?           uint32
       |     +--ro session-down-count?         uint32
       |     +--ro session-admin-down-count?   uint32
       +--rw micro-bfd-ipv6-session-statistics
       |  +--ro bfd-session-statistics
       |     +--ro session-count?              uint32
       |     +--ro session-up-count?           uint32
       |     +--ro session-down-count?         uint32
       |     +--ro session-admin-down-count?   uint32
       +--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?           bfd-multiplier
         |
          +--rw (interval-config-type)?
          |        |  +--:(tx-rx-intervals)
          |  |  |  +--rw desired-min-tx-interval     uint32
          |  |  |  +--rw required-min-rx-interval    uint32
          |        |  +--:(single-interval)
          |        |     +--rw min-interval                uint32
         |
          +--rw demand-enabled?             boolean
         | {bfd-demand-mode}?
          +--rw admin-down?                 boolean
         |
          +--rw authentication-parms! {bfd-authentication}?
          |  +--rw key-chain?           kc:key-chain-ref
          |  +--rw replay-protection?   identityref
         +--ro oper
            +--ro micro-bfd-ipv4-session-statistics
            |  +--ro bfd-session-statistics
            |     +--ro session-count?              uint32
            |     +--ro session-up-count?           uint32
            |     +--ro session-down-count?         uint32
            |     +--ro session-admin-down-count?   uint32
            +--ro micro-bfd-ipv6-session-statistics
            |  +--ro bfd-session-statistics
            |     +--ro session-count?              uint32
            |     +--ro session-up-count?           uint32
            |     +--ro session-down-count?         uint32
            |     +--ro session-admin-down-count?   uint32
            +--ro session-lag* [lag-name]
               +--ro lag-name        if:interface-ref
               +--ro
          +--rw use-ipv4?                   boolean
               +--ro
          +--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?    bfd-discriminator
             |  +--ro remote-discriminator?   bfd-discriminator
             |  +--ro remote-multiplier?      bfd-multiplier
             |  +--ro out-interface?          if:interface-ref
                  |  +--ro demand-capability?      boolean {bfd-demand-mode}?
             |  +--ro source-port?            inet:port-number
             |  +--ro dest-port?              inet:port-number
             |  +--ro session-running
             |  |  +--ro session-index?                uint32
             |  |  +--ro local-state?                  bfd-state
             |  |  +--ro remote-state?                 bfd-state
             |  |  +--ro local-diagnostic?             iana-bfd-types:
                                                       bfd-diagnostic
             |  |  +--ro remote-diagnostic?            iana-bfd-types:
                                                       bfd-diagnostic
             |  |  +--ro remote-authenticated?         boolean
             |  |  +--ro remote-authentication-type?   iana-bfd-types:
                                                       bfd-auth-type
             |  |  +--ro detection-mode?               enumeration
             |  |  +--ro negotiated-tx-interval?       uint32
             |  |  +--ro negotiated-rx-interval?       uint32
             |  |  +--ro echo-tx-interval-in-use? detection-time?               uint32
             |  |  +--ro detection-time? echo-tx-interval-in-use?      uint32
                                                       {bfd-echo-mode}?
             |  +--ro sesssion-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?             uint32
             |     +--ro admin-down-count?       uint32
             |     +--ro receive-packet-count?   uint64
             |     +--ro send-packet-count?      uint64
             |     +--ro receive-bad-packet?     uint64
             |     +--ro send-failed-packet?     uint64
             +--ro micro-bfd-ipv6
                +--ro path-type?              identityref
                +--ro ip-encapsulation?       boolean
                +--ro local-discriminator?    bfd-discriminator
                +--ro remote-discriminator?   bfd-discriminator
                +--ro remote-multiplier?      bfd-multiplier
                +--ro out-interface?          if:interface-ref
                     +--ro demand-capability?      boolean {bfd-demand-mode}?
                +--ro source-port?            inet:port-number
                +--ro dest-port?              inet:port-number
                +--ro session-running
                |  +--ro session-index?                uint32
                |  +--ro local-state?                  bfd-state
                |  +--ro remote-state?                 bfd-state
                |  +--ro local-diagnostic?             iana-bfd-types:
                                                       bfd-diagnostic
                |  +--ro remote-diagnostic?            iana-bfd-types:
                                                       bfd-diagnostic
                |  +--ro remote-authenticated?         boolean
                |  +--ro remote-authentication-type?   iana-bfd-types:
                                                       bfd-auth-type
                |  +--ro detection-mode?               enumeration
                |  +--ro negotiated-tx-interval?       uint32
                |  +--ro negotiated-rx-interval?       uint32
                |  +--ro echo-tx-interval-in-use? detection-time?               uint32
                |  +--ro detection-time? echo-tx-interval-in-use?      uint32
                                                       {bfd-echo-mode}?
                +--ro sesssion-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?             uint32
                   +--ro admin-down-count?       uint32
                   +--ro receive-packet-count?   uint64
                   +--ro send-packet-count?      uint64
                   +--ro receive-bad-packet?     uint64
                   +--ro send-failed-packet?     uint64
 notifications:
    +---n bfd-lag-notification
       +--ro local-discr?                 bfd-discriminator
       +--ro remote-discr?                bfd-discriminator
       +--ro new-state?                   bfd-state
       +--ro state-change-reason?      string         iana-bfd-types:bfd-diagnostic
       +--ro time-in-previous-state?   string 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 model we support multiple BFD sessions per MPLS
   FEC (ECMP), the local discriminator is used as key.  The "mpls" node
   can be mounted 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-protocol/bfd:bfd:
    +--rw mpls
         +--rw config
       +--ro bfd-session-statistics
       |  +--ro session-count?              uint32
       |  +--ro session-up-count?           uint32
       |  +--ro session-down-count?         uint32
       |  +--ro session-admin-down-count?   uint32
       +--rw egress
       |  |  +--rw local-multiplier?           bfd-multiplier
       |  |  +--rw (interval-config-type)?
       |  |  |  +--:(tx-rx-intervals)
       |  |  |  |  +--rw desired-min-tx-interval     uint32
       |  |  |  |  +--rw required-min-rx-interval    uint32
       |  |  |  +--:(single-interval)
       |  |  |     +--rw min-interval                uint32
       |  |  +--rw authentication-parms! {bfd-authentication}?
       |  |     +--rw key-chain?           kc:key-chain-ref
       |  |     +--rw replay-protection?   identityref
         |  +--rw session-cfg
         |
       +--rw sessions* session-group* [mpls-fec]
         |
          +--rw mpls-fec                    inet:ip-address
         |                    inet:ip-prefix
          +--rw local-multiplier?           bfd-multiplier
         |
          +--rw (interval-config-type)?
          |        |  +--:(tx-rx-intervals)
          |  |  |  +--rw desired-min-tx-interval     uint32
          |  |  |  +--rw required-min-rx-interval    uint32
          |        |  +--:(single-interval)
          |        |     +--rw min-interval                uint32
         |
          +--rw demand-enabled?             boolean
         | {bfd-demand-mode}?
          +--rw admin-down?                 boolean
         |
          +--rw authentication-parms! {bfd-authentication}?
          |  +--rw key-chain?           kc:key-chain-ref
          |  +--rw replay-protection?   identityref
          +--ro oper
            +--ro bfd-session-statistics
            |  +--ro session-count?              uint32
            |  +--ro session-up-count?           uint32
            |  +--ro session-down-count?         uint32
            |  +--ro session-admin-down-count?   uint32
            +--ro session-group* [mpls-fec]
               +--ro mpls-fec    inet:ip-address
               +--ro sessions* [local-discriminator]
             +--ro path-type?              identityref
             +--ro local-discriminator ip-encapsulation?       boolean
             +--ro local-discriminator?    bfd-discriminator
             +--ro remote-discriminator?   bfd-discriminator
             +--ro remote-multiplier?      bfd-multiplier
             +--ro out-interface?          if:interface-ref
                  +--ro demand-capability?      boolean {bfd-demand-mode}?
             +--ro source-port?            inet:port-number
             +--ro dest-port?              inet:port-number
             +--ro session-running
             |  +--ro session-index?                uint32
             |  +--ro local-state?                  bfd-state
             |  +--ro remote-state?                 bfd-state
             |  +--ro local-diagnostic?             iana-bfd-types:
                                                    bfd-diagnostic
             |  +--ro remote-diagnostic?            iana-bfd-types:
                                                    bfd-diagnostic
             |  +--ro remote-authenticated?         boolean
             |  +--ro remote-authentication-type?   iana-bfd-types:
                                                    bfd-auth-type
             |  +--ro detection-mode?               enumeration
             |  +--ro negotiated-tx-interval?       uint32
             |  +--ro negotiated-rx-interval?       uint32
             |  +--ro echo-tx-interval-in-use? detection-time?               uint32
             |  +--ro detection-time? echo-tx-interval-in-use?      uint32
                                                    {bfd-echo-mode}?
             +--ro sesssion-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?             uint32
             |  +--ro admin-down-count?       uint32
             |  +--ro receive-packet-count?   uint64
             |  +--ro send-packet-count?      uint64
             |  +--ro receive-bad-packet?     uint64
             |  +--ro send-failed-packet?     uint64
             +--ro mpls-dest-address?      inet:ip-address
 notifications:
    +---n bfd-mpls-notification
       +--ro local-discr?                 bfd-discriminator
       +--ro remote-discr?                bfd-discriminator
       +--ro new-state?                   bfd-state
       +--ro state-change-reason?      string         iana-bfd-types:bfd-diagnostic
       +--ro time-in-previous-state?   string 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

   The MPLS-TE

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

 module: ietf-bfd-mpls-te
 augment /rt:routing/rt:control-plane-protocols
         /rt:control-plane-protocol/bfd:bfd:
    +--rw mpls-te
       +--rw config
       |  +--rw egress
       |     +--rw local-multiplier?           bfd-multiplier
       |     +--rw (interval-config-type)?
       |     |  +--:(tx-rx-intervals)
       |     |  |  +--rw desired-min-tx-interval     uint32
       |     |  |  +--rw required-min-rx-interval    uint32
       |     |  +--:(single-interval)
       |     |     +--rw min-interval                uint32
       |     +--rw authentication-parms! {bfd-authentication}?
       |        +--rw key-chain?           kc:key-chain-ref
       |        +--rw replay-protection?   identityref
       +--ro oper
          +--ro bfd-session-statistics
             +--ro session-count?              uint32
             +--ro session-up-count?           uint32
             +--ro session-down-count?         uint32
             +--ro session-admin-down-count?   uint32
 augment /te:te/te:tunnels/te:tunnel/te:config:
    +--rw local-multiplier?           bfd-multiplier
    +--rw (interval-config-type)?
    |  +--:(tx-rx-intervals)
    |  |  +--rw desired-min-tx-interval     uint32
    |  |  +--rw required-min-rx-interval    uint32
    |  +--:(single-interval)
    |     +--rw min-interval                uint32
    +--rw demand-enabled?             boolean {bfd-demand-mode}?
    +--rw admin-down?                 boolean
    +--rw authentication-parms! {bfd-authentication}?
    |  +--rw key-chain?           kc:key-chain-ref
    |  +--rw replay-protection?   identityref
    +--rw encap?                      identityref
 augment /te:te/te:lsps-state/te:lsp:
    +--ro path-type?              identityref
    +--ro ip-encapsulation?       boolean
    +--ro local-discriminator?    bfd-discriminator
    +--ro remote-discriminator?   bfd-discriminator
    +--ro remote-multiplier?      bfd-multiplier
    +--ro out-interface?          if:interface-ref
      +--ro demand-capability?      boolean {bfd-demand-mode}?
    +--ro source-port?            inet:port-number
    +--ro dest-port?              inet:port-number
    +--ro session-running
    |  +--ro session-index?                uint32
    |  +--ro local-state?                  bfd-state
    |  +--ro remote-state?                 bfd-state
    |  +--ro local-diagnostic?          bfd-diagnostic             iana-bfd-types:bfd-diagnostic
    |  +--ro remote-diagnostic?         bfd-diagnostic            iana-bfd-types:bfd-diagnostic
    |  +--ro remote-authenticated?         boolean
    |  +--ro remote-authentication-type?   iana-bfd-types:bfd-auth-type
                                           {bfd-authentication}?
    |  +--ro detection-mode?               enumeration
    |  +--ro negotiated-tx-interval?       uint32
    |  +--ro negotiated-rx-interval?       uint32
    |  +--ro echo-tx-interval-in-use? detection-time?               uint32
    |  +--ro detection-time? echo-tx-interval-in-use?      uint32 {bfd-echo-mode}?
    +--ro sesssion-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?             uint32
    |  +--ro admin-down-count?       uint32
    |  +--ro receive-packet-count?   uint64
    |  +--ro send-packet-count?      uint64
    |  +--ro receive-bad-packet?     uint64
    |  +--ro send-failed-packet?     uint64
    +--ro mpls-dest-address?      inet:ip-address
 notifications:
    +---n bfd-mpls-te-notification
       +--ro local-discr?                 bfd-discriminator
       +--ro remote-discr?                bfd-discriminator
       +--ro new-state?                   bfd-state
       +--ro state-change-reason?      string         iana-bfd-types:bfd-diagnostic
       +--ro time-in-previous-state?   string 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
       +--ro tunnel-name?                 string

2.11.  Examples

2.12.  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.

2.12.1.

2.11.1.  Module ietf-interfaces

   The following boolean configuration is defined in the "ietf-
   interfaces" A YANG module Data Model
   for Interface Management [RFC7223]:

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

2.12.2.

2.11.2.  Module ietf-ip

   The following boolean configuration is defined in the "ietf-ip" A YANG
   module Data Model
   for IP Management [RFC7277]:

   /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.

2.12.3.

2.11.3.  Module ietf-mpls

   The following boolean configuration is defined in the "ietf-mpls" A YANG module 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.

2.12.4.

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.

2.13.

2.12.  IANA BFD top-level Yang YANG Module

  <CODE BEGINS> file "ietf-bfd@2017-03-07.yang" "iana-bfd-types@2017-06-30.yang"

  module ietf-bfd iana-bfd-types {
    namespace "urn:ietf:params:xml:ns:yang:ietf-bfd";
     // replace with IANA namespace when assigned
     prefix "bfd";

     import ietf-interfaces {
       prefix "if";
     }

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

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

     import ietf-routing { "urn:ietf:params:xml:ns:yang:iana-bfd-types";

    prefix "rt";

     }

     import ietf-key-chain {
       prefix "kc";
     } "iana-bfd-types";

    organization "IETF BFD Working Group"; "IANA";

    contact
       "WG Web:   <http://tools.ietf.org/wg/bfd>
        WG List:  <rtg-bfd@ietf.org>
        WG Chair: Jeff Haas
        WG Chair: Reshad Rahman
        Editor:   Lianshu Zheng and Reshad Rahman";
      "        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 contains the a collection of YANG definition data types
       considered defined by IANA and used for BFD parameters as
        per RFC5880. BFD.

       Copyright (c) 2017 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.";

    revision 2017-03-07 2017-06-30 {
      description "Initial revision.";
      reference "RFC XXXX: A IANA BFD YANG data model for BFD"; Data Types.";
    }
    // RFC Ed.: replace XXXX with actual RFC number and remove this
    // note

     identity bfdv1 {
       base "rt:control-plane-protocol";
       description "BFD protocol version 1 as per RFC5880.";
     }

     typedef bfd-discriminator {
       type uint32 {
         range 1..4294967295;

       }
       description "BFD discriminator";
     }

    typedef bfd-diagnostic {
      type enumeration {
        enum none {
          value 0;
          description "None";
        }
        enum controlExpiry control-expiry {
          value 1;
          description "Control timer expiry";
        }
        enum echoFailed echo-failed {
          value 2;
          description "Echo failure";
        }
        enum nborDown neighbor-down {
          value 3;
          description "Neighbor down";
        }
        enum fwdingReset forwarding-reset {
          value 4;
          description "Forwarding reset";
        }
        enum pathDown path-down {
          value 5;
          description "Path down";
        }
        enum concPathDown concatenated-path-down {
          value 6;
          description "Concatenated path down";
        }
        enum adminDown admin-down {
          value 7;
          description "Admin down";
        }
        enum reverseConcPathDown 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"; diagnostic as defined in RFC5880. Range is 0 to 31.";
    }

    typedef bfd-state bfd-auth-type {
      type enumeration {
        enum adminDown reserved {
          value 0;
          description "admindown"; "Reserved";
        }
        enum down simple-password {
          value 1;
          description "down"; "Simple password";
        }
        enum init keyed-md5 {
          value 2;
          description "init"; "Keyed MD5";
        }
        enum up meticulous-keyed-md5 {
          value 3;
          description "up";
         }
       }
       description "BFD state"; "Meticulous keyed MD5";
        }

     typedef bfd-multiplier {
       type uint8
        enum keyed-sha1 {
         range 1..255;
       }
          value 4;
          description "Multiplier"; "Keyed SHA1";
        }

     typedef ttl {
       type uint8
        enum meticulous-keyed-sha1 {
         range 1..255;
       }
          value 5;
          description "Time To Live"; "Meticulous keyed SHA1";
        }
      }

     identity bfd-path-type {
      description
         "Base identity for BFD path type. The session type indicates
          the
        "BFD authentication type of path on which BFD as defined in RFC5880. Range is running"; 0 to
         255.";
    }
     identity bfd-path-ip-sh {
       base bfd-path-type;
       description "BFD on IP single hop";

  }
     identity bfd-path-ip-mh {
       base

  <CODE ENDS>

2.13.  BFD top-level YANG Module

 <CODE BEGINS> file "ietf-bfd@2017-06-30.yang"

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

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

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

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

   import ietf-routing {
     prefix "rt";
   }

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

   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 RFC5880.

      Copyright (c) 2017 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.";

   revision 2017-06-30 {
     description "Initial revision.";
     reference "RFC XXXX: A YANG data model for BFD";
   }

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

   identity bfdv1 {
     base "rt:control-plane-protocol";
     description "BFD protocol version 1 as per RFC5880.";
   }

   typedef bfd-discriminator {
     type uint32 {
       range 1..4294967295;
     }
     description "BFD discriminator";
   }

   typedef bfd-state {
     type enumeration {
       enum adminDown {
         value 0;
         description "admindown";
       }
       enum down {
         value 1;
         description "down";
       }
       enum init {
         value 2;
         description "init";
       }
       enum up {
         value 3;
         description "up";
       }
     }
     description "BFD state as defined in RFC5880";
   }

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

   /*
    * Identity definitions
    */
   identity bfd-path-type {
     description
       "Base identity for BFD path type. The session type indicates
        the type of path on which BFD is running";
   }
   identity bfd-path-ip-sh {
     base bfd-path-type;
     description "BFD on IP single hop";
   }
   identity bfd-path-ip-mh {
     base bfd-path-type;
     description "BFD on IP multi hop";
   }
   identity bfd-path-mpls-te {
     base bfd-path-type;
     description "BFD on MPLS Traffic Engineering";
   }
   identity bfd-path-mpls-lsp {
     base bfd-path-type;
     description "BFD on MPLS Label Switched Path";
   }
   identity bfd-path-lag {
     base bfd-path-type;
     description "Micro-BFD on LAG member links";
   }

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

     feature bfd-authentication {
       description "BFD authentication supported";
     }

   identity bfd-auth-replay-protection {
     description
       "Base identity for BFD authentication replay protection"; protection. " +
       "See section 6.7 of RFC5880.";
   }
   identity bfd-auth-replay-protection-non-meticulous {
     base bfd-auth-replay-protection;
     description "Non-meticulous (see section 6.7.3 of RFC5880)";
   }
   identity bfd-auth-replay-protection-meticulous {
     base bfd-auth-replay-protection;
     description "Meticulous (see section 6.7.3 of RFC5880)";
   }

   /*
    * Feature definitions.
    */
   feature bfd-authentication {
           description "BFD authentication supported";
         }

   feature bfd-demand-mode {
     description "BFD demand mode supported";
   }

   feature bfd-echo-mode {
     description "BFD echo mode supported";
   }

   /*
    * Groupings
    */
   grouping bfd-auth-parms {
     description
       "Grouping for BFD authentication parameters
        (see section 6.7 of RFC5880).";
     container authentication-parms {
       if-feature bfd-authentication;
       presence
         "Enables BFD authentication (see section 6.7 of RFC5880).";
       description "Parameters for BFD authentication";

       leaf key-chain {
         type kc:key-chain-ref;
         description "Name of key-chain";
       }

       leaf replay-protection {
         type identityref {
           base bfd-auth-replay-protection;
         }
         description
           "Protection against replays";
       }
     }
   }

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

     choice interval-config-type {
       description
         "Two interval values or 1 value used for both tx and rx";
       case tx-rx-intervals {
         leaf desired-min-tx-interval {
           type uint32;
           units microseconds;
           mandatory true;
           description
             "Desired minimum transmit interval of control packets";
         }

         leaf required-min-rx-interval {
           type uint32;
           units microseconds;
           mandatory true;
           description
             "Required minimum receive interval of control packets";
         }
       }
       case single-interval {
         leaf min-interval {
           type uint32;
           units microseconds;
           mandatory true;
           description
             "Desired minimum transmit interval and required " +
             "minimum receive interval of control packets";
         }
       }
     }
   }
   grouping bfd-grouping-common-cfg-parms {
     description "BFD grouping for common config parameters";

     uses bfd-grouping-base-cfg-parms;

     leaf demand-enabled {
       if-feature bfd-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 bfd-auth-parms;
   }

   grouping bfd-grouping-echo-cfg-parms {
     description "BFD grouping for echo config parameters";
     leaf desired-min-echo-tx-interval {
       type uint32;
       units microseconds;
       default 0;
       description "Desired minumum transmit interval for echo";
     }

     leaf required-min-echo-rx-interval {
       type uint32;
       units microseconds;
       default 0;
       description "Required minimum receive interval for echo";
     }
   }

   grouping bfd-client-base-cfg-parms {
     description
       "BFD grouping which could be used by a protocol which
        is a client of BFD to enable its use of BFD";

     container bfd-cfg {
       description "BFD configuration";
       leaf enabled {
         type boolean;
         default false;
         description "True if BFD is enabled";
       }
     }
   }

   grouping bfd-all-session {
     description "BFD session operational information";
     leaf path-type {
       type identityref {
         base bfd-path-type;
       }
       config "false";
       description
         "BFD session type, this indicates the path type that BFD is
         running on";
     }
     leaf ip-encapsulation {
       type boolean;
       config "false";
       description "Whether BFD encapsulation uses IP";
     }
     leaf local-discriminator {
       type bfd-discriminator;
       config "false";
       description "Local discriminator";
     }
     leaf remote-discriminator {
       type bfd-discriminator;
       config "false";
       description "Remote discriminator";
     }
     leaf remote-multiplier {
       type bfd-multiplier;
       config "false";
       description "Remote multiplier";
     }
     leaf out-interface {
         type if:interface-ref;
         description "Outgoing physical interface name";
       }
       leaf demand-capability {
       if-feature bfd-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 {
         type uint32;
         description
           "An index used to uniquely identify BFD sessions";
       }
       leaf local-state {
         type bfd-state;
         description "Local state";
       }
       leaf remote-state {
         type bfd-state;
         description "Remote state";
       }
       leaf local-diagnostic {
         type bfd-diagnostic; iana-bfd-types:bfd-diagnostic;
         description "Local diagnostic";
       }
       leaf remote-diagnostic {
         type bfd-diagnostic; iana-bfd-types:bfd-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 bfd-authentication;
         type iana-bfd-types:bfd-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 {
             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-path-ip-sh'" {
           description
             "Echo is supported for IP single-hop only.";
         }
         if-feature bfd-echo-mode;
         type uint32;
         units microseconds;
         description "Echo transmit interval in use";
       }
         leaf detection-time {
           type uint32;
           units microseconds;
           description "Detection time";
         }
     }

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

       leaf create-time {
         type yang:date-and-time;
         description
           "Time and date when session was created";
       }
       leaf last-down-time {
         type yang:date-and-time;
         description
           "Time and date of last time the session went down";
       }
       leaf last-up-time {
         type yang:date-and-time;
         description
           "Time and date of last time the session went up";
       }
       leaf down-count {
         type uint32;
         description "Session Down Count";
       }
       leaf admin-down-count {
         type uint32;
         description "Session Admin-Down Count";
       }
       leaf receive-packet-count {
         type uint64;
         description "Received Packet Count";
       }
       leaf send-packet-count {
         type uint64;
         description "Sent Packet Count";
       }
       leaf receive-bad-packet {
         type uint64;
         description "Received bad packet count";
       }
       leaf send-failed-packet {
         type uint64;
         description "Packet Failed to Send Count";

       }
     }
   }

   grouping bfd-session-statistics {
     description "Grouping for session counters";
     container bfd-session-statistics {
       config false;
       description "BFD session counters";
       leaf session-count {
         type uint32;
         description "Number of sessions";
       }
       leaf session-up-count {
         type uint32;
         description "Count of sessions which are up";
       }
       leaf session-down-count {
         type uint32;
         description "Count of sessions which are down";
       }
       leaf session-admin-down-count {
         type uint32;
         description "Count of sessions which are admin-down";
       }
     }
   }

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

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

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

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

     leaf time-in-previous-state time-of-last-state-change {
       type string; yang:date-and-time;
       description
           "How long the BFD session was in the
         "Calendar time of previous state"; 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 bfd-path-type;
       }
       description "BFD path type";
     }
   }

   augment "/rt:routing/rt:control-plane-protocols/"
         + "rt:control-plane-protocol" {
      when "rt:type = 'bfd: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";
         container config {
           description "BFD configuration container";
         }

         container oper {
           config "false";
           description "BFD operational container.";

       uses bfd-session-statistics;
     }

   }
 }
   }

 <CODE ENDS>

2.14.  BFD IP single-hop Yang YANG Module

   <CODE BEGINS> file "ietf-bfd-ip-sh@2017-03-07.yang" "ietf-bfd-ip-sh@2017-06-30.yang"

   module ietf-bfd-ip-sh {
     namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-ip-sh";
     // replace with IANA namespace when assigned

     prefix "bfd-ip-sh";

     import ietf-bfd {
       prefix "bfd";
     }

     import ietf-interfaces {
       prefix "if";
     }

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

     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>
        WG Chair: Jeff Haas
        WG Chair:

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

     description
       "This module contains the YANG definition for BFD IP single-hop
        as per RFC5881.

        Copyright (c) 2017 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.";

     revision 2017-03-07 2017-06-30 {
       description "Initial revision.";
       reference "RFC XXXX: A YANG data model for BFD IP single-hop";
     }

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

     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";

         container config {
           description "BFD IP single-hop configuration container";
           container session-cfg {
             description "BFD IP single-hop session configuration";
             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"; for BFD IP single-hop";
     }
               leaf source-addr

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

     augment "/rt:routing/rt:control-plane-protocols/"
           + "rt:control-plane-protocol/bfd:bfd" {
                 type inet:ip-address;
       description "Local address";
               }

               uses bfd:bfd-grouping-common-cfg-parms;

               uses bfd:bfd-grouping-echo-cfg-parms;
             }
           }
         } "BFD augmentation for IP single-hop";
       container oper ip-sh {
           config "false";
         description "BFD IP single-hop operational top level container";

         uses bfd:bfd-session-statistics;

         list sessions {
           key "interface dest-addr";
           description "BFD "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 "BFD peer address"; "IP address of the peer";
           }
           leaf source-addr {
             type inet:ip-address;
             description "BFD source "Local address";
           }

           uses bfd:bfd-grouping-common-cfg-parms;

           uses bfd:bfd-grouping-echo-cfg-parms;

           uses bfd:bfd-all-session;
         }

       }
     }
     }

     notification bfd-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:bfd-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>

2.15.  BFD IP multi-hop Yang YANG Module

<CODE BEGINS> file "ietf-bfd-ip-mh@2017-03-07.yang" "ietf-bfd-ip-mh@2017-06-30.yang"

module ietf-bfd-ip-mh {
  namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-ip-mh";
  // replace with IANA namespace when assigned
  prefix "bfd-ip-mh";

  import ietf-bfd {
    prefix "bfd";
  }

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

  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>
        WG Chair: Jeff Haas
        WG Chair:

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

  description
    "This module contains the YANG definition for BFD IP multi-hop
     as per RFC5883.

     Copyright (c) 2017 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.";

  revision 2017-03-07 2017-06-30 {
    description "Initial revision.";
    reference "RFC XXXX: A YANG data model for BFD IP multi-hop";
  }

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

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

         container config {
           description "BFD IP multi-hop configuration container";
           container session-cfg {
             description "BFD IP multi-hop session configuration";

      uses bfd:bfd-session-statistics;

      list sessions session-group {
        key "source-addr dest-addr";
              description "List
                "Group of BFD IP multi-hop sessions"; 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:bfd-grouping-common-cfg-parms;

        leaf tx-ttl {
          type bfd:ttl; bfd:hops;
          default 255;
          description "TTL "Hop count of outgoing BFD control packets";
        }
        leaf rx-ttl {
          type bfd:ttl; bfd:hops;
          mandatory true;
          description
            "Minimum allowed TTL hop count value for incoming BFD control
                    packets";
               }
             }
           }
         }
         container oper {
           config "false";

           description "BFD IP multi-hop operational container";

           uses bfd:bfd-session-statistics;

           list session-group {
             key "source-addr dest-addr";
             description
               "BFD IP multi-hop group of sessions. A group of " +
               "sessions
             packets. Control packets whose hop count 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 "BFD source address";
             }
             leaf dest-addr {
               type inet:ip-address;
               description "BFD peer address"; lower than this
                   value are dropped.";
        }
        list sessions {
               key "local-discriminator";
                config false;
          description
            "The multiple BFD sessions between a source and a. " +
                 "destination. Local discriminator is unique for a " +
                 "each session in the group.";
               leaf ttl {
                 type bfd:ttl;
                 description "TTL of outgoing packets";
               }
            "destination.";
          uses bfd:bfd-all-session;
        }
      }
    }
  }
     }

  notification bfd-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:bfd-notification-parms;
  }
}

<CODE ENDS>
2.16.  BFD over LAG Yang YANG Module

   <CODE BEGINS> file "ietf-bfd-lag@2017-03-07.yang" "ietf-bfd-lag@2017-06-30.yang"

   module ietf-bfd-lag {
     namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-lag";
     // replace with IANA namespace when assigned
     prefix "bfd-lag";

     import ietf-bfd {
       prefix "bfd";
     }

     import ietf-interfaces {
       prefix "if";
     }

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

     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>
        WG Chair: Jeff Haas
        WG Chair:

        Editors:  Reshad Rahman
        Editor: (rrahman@cisco.com),
                  Lianshu Zheng and Reshad Rahman"; 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) 2017 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.";

     revision 2017-03-07 2017-06-30 {
       description "Initial revision.";
       reference "RFC XXXX: A YANG data model for BFD over LAG";
     }

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

     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 config {
           description "BFD over LAG configuration container"; micro-bfd-ipv4-session-statistics {
           description "Micro-BFD IPv4 session counters";
           uses bfd:bfd-session-statistics;
         }
         container session-cfg micro-bfd-ipv6-session-statistics {
           description "BFD over LAG "Micro-BFD IPv6 session configuration"; counters";
           uses bfd:bfd-session-statistics;
         }

         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:bfd-grouping-common-cfg-parms;
             }
           }
         }

         container oper {
           config "false";
           description "BFD over LAG operational container.";

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

           list session-lag {
             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 use-ipv4 {
             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:bfd-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:bfd-all-session;
             }
           }
         }
       }
     }
     }

     notification bfd-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.";

       uses bfd:bfd-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>

2.17.  BFD over MPLS Yang YANG Module

   <CODE BEGINS> file "ietf-bfd-mpls@2017-03-07.yang" "ietf-bfd-mpls@2017-06-30.yang"

   module ietf-bfd-mpls {
     namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-mpls";
     // replace with IANA namespace when assigned
     prefix "bfd-mpls";

     import ietf-bfd {
       prefix "bfd";
     }

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

     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>
        WG Chair: Jeff Haas
        WG Chair:

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

     description
       "This module contains the YANG definition for BFD parameters for
        MPLS LSPs as per RFC5884.

        Copyright (c) 2017 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.";

     revision 2017-03-07 2017-06-30 {
       description "Initial revision.";
       reference "RFC XXXX: A YANG data model for BFD over MPLS LSPs";
     }

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

     identity bfd-encap-gach {
       base bfd:bfd-encap-type;
       description
         "BFD with G-ACh encapsulation as per RFC5586.";
     }

     identity bfd-encap-ip-gach {
       base bfd:bfd-encap-type;
       description
         "BFD with IP and G-ACh encapsulation as per RFC5586.";
     }

     grouping bfd-encap-cfg {
       description "Configuration for BFD encapsulation";

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

     grouping bfd-mpls-dest-address {
       description "Destination address as per RFC5884";

       leaf mpls-dest-address {
         type inet:ip-address;
         config "false";
         description
           "Destination address as per RFC5884.
            Needed if IP encapsulation is used";
       }
     }

     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";

         container config {
           description "BFD MPLS configuration container";

         uses bfd:bfd-session-statistics;

         container egress {
           description "Egress configuration";

           uses bfd:bfd-grouping-base-cfg-parms;

           uses bfd:bfd-auth-parms;
         }

           container session-cfg {
             description "BFD MPLS session configuration";

         list sessions session-group {
           key "mpls-fec";
           description "List
             "Group of BFD MPLS sessions";
               leaf mpls-fec {
                 type inet:ip-address;
                 description "MPLS FEC";
               }

               uses bfd:bfd-grouping-common-cfg-parms;
             }
           }
         }

         container oper {
           config "false";

           description "BFD MPLS operational container";

           uses bfd:bfd-session-statistics;

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

           uses bfd:bfd-grouping-common-cfg-parms;

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

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

         }
       }
     }
     }

     notification bfd-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:bfd-notification-parms;

       leaf mpls-dest-address {
         type inet:ip-address;
         description
           "Destination address as per RFC5884.
            Needed if IP encapsulation is used";
       }
     }
   }

   <CODE ENDS>

2.18.  BFD over MPLS-TE Yang YANG Module

   <CODE BEGINS> file "ietf-bfd-mpls-te@2017-03-07.yang" "ietf-bfd-mpls-te@2017-06-30.yang"

   module ietf-bfd-mpls-te {
     namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-mpls-te";
     // replace with IANA namespace when assigned
     prefix "bfd-mpls-te";

     import ietf-bfd {
       prefix "bfd";
     }

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

     import ietf-te {
       prefix "te";
     }

     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>
        WG Chair: Jeff Haas
        WG Chair:

        Editors:  Reshad Rahman
        Editor: (rrahman@cisco.com),
                  Lianshu Zheng and Reshad Rahman"; (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 RFC5884.

        Copyright (c) 2017 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.";

     revision 2017-03-07 2017-06-30 {
       description "Initial revision.";
       reference "RFC XXXX: A YANG data model for BFD over MPLS-TE";
     }

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

     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 config {
           description "BFD MPLS-TE configuration container";

           container egress {
             description "Egress configuration";

             uses bfd:bfd-grouping-base-cfg-parms;
             uses bfd:bfd-auth-parms;
           }
         }

         container oper {
           config "false";
           description "BFD operational container";
           uses bfd:bfd-session-statistics;
         }
       }
     }

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

       uses bfd:bfd-grouping-common-cfg-parms;

       uses bfd-mpls:bfd-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:bfd-all-session;

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

     notification bfd-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:bfd-notification-parms;

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

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

2.19.  Security Considerations

   The YANG module defined in this memo is designed to be accessed via
   the NETCONF protocol [RFC6241].  The lowest NETCONF layer is the
   secure transport layer and the mandatory to implement secure
   transport is SSH [RFC6242].  The NETCONF access control model
   [RFC6536] provides the means to restrict access for particular
   NETCONF users to a pre-configured subset of all available NETCONF
   protocol operations and content.

   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.

2.20.  IANA Considerations

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

   URI:TBD

   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.

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

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

   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.

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

2.20.1.  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

2.21.  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.

3.  References

3.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>. 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

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

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

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <http://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,
              <http://www.rfc-editor.org/info/rfc5881>.

   [RFC5882]  Katz, D. and D. Ward, "Generic Application of
              Bidirectional Forwarding Detection (BFD)", RFC 5882,
              DOI 10.17487/RFC5882, June 2010,
              <http://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, <http://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, <http://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,
              <http://www.rfc-editor.org/info/rfc5885>.

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

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

   [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, <http://www.rfc-editor.org/info/rfc7130>.

   [RFC7223]  Bjorklund, M., "A YANG Data Model for Interface
              Management", RFC 7223, DOI 10.17487/RFC7223, May 2014,
              <http://www.rfc-editor.org/info/rfc7223>.

   [RFC7277]  Bjorklund, M., "A YANG Data Model for IP Management",
              RFC 7277, DOI 10.17487/RFC7277, June 2014,
              <http://www.rfc-editor.org/info/rfc7277>.

   [RFC8022]  Lhotka, L. and A. Lindem, "A YANG Data Model for Routing
              Management", RFC 8022, DOI 10.17487/RFC8022, November
              2016, <http://www.rfc-editor.org/info/rfc8022>.

3.2.  Informative References

   [I-D.dsdt-nmda-guidelines]
              Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Guidelines for YANG Module Authors
              (NMDA)", draft-dsdt-nmda-guidelines-01 (work in progress),
              May 2017.

   [I-D.ietf-lime-yang-connectionless-oam]
              Kumar, D., Wang, Z., Wu, Q., Rahman, R., and S. Raghavan,
              "Generic YANG Data Model for Connectionless Operations,
              Administration, and Maintenance(OAM) protocols", draft-
              ietf-lime-yang-connectionless-oam-04
              ietf-lime-yang-connectionless-oam-07 (work in progress),
              February
              June 2017.

   [I-D.ietf-mpls-base-yang]
              Raza, K., Gandhi, R., Liu, X., Beeram, V., Saad, T.,
              Bryskin, I., Chen, X., Jones, R., and B. Wen, "A YANG Data
              Model for MPLS Base", draft-ietf-mpls-base-yang-02 draft-ietf-mpls-base-yang-04 (work
              in progress), March 2017.

   [I-D.ietf-netconf-restconf]
              Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", draft-ietf-netconf-restconf-18 (work in
              progress), October 2016.

   [I-D.ietf-netmod-routing-cfg]
              Lhotka, L. and A. Lindem, "A YANG Data Model for Routing
              Management", draft-ietf-netmod-routing-cfg-25 (work in
              progress), November 2016.

   [I-D.ietf-netmod-schema-mount]
              Bjorklund, M. and L. Lhotka, "YANG Schema Mount", draft-
              ietf-netmod-schema-mount-04
              ietf-netmod-schema-mount-05 (work in progress), March May 2017.

   [I-D.ietf-rtgwg-device-model]
              Lindem, A., Berger, L., Bogdanovic, D., and C. Hopps,
              "Network Device YANG Organizational Models", Logical Organization", draft-ietf-
              rtgwg-device-model-01
              rtgwg-device-model-02 (work in progress), October 2016. March 2017.

   [I-D.ietf-rtgwg-lne-model]
              Berger, L., Hopps, C., Lindem, A., and D. Bogdanovic,
              "YANG Logical Network Elements", draft-ietf-rtgwg-lne-
              model-01
              model-02 (work in progress), October 2016. March 2017.

   [I-D.ietf-rtgwg-ni-model]
              Berger, L., Hopps, C., Lindem, A., and D. Bogdanovic,
              "YANG Network Instances", draft-ietf-rtgwg-ni-model-01 draft-ietf-rtgwg-ni-model-02
              (work in progress), October 2016.

   [I-D.ietf-rtgwg-yang-key-chain] March 2017.

   [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-06 (work
              in progress), March 2017.

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

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

Appendix A.  Echo function configuration example

   The following intervals are added for the echo function (if
   supported):

   desired-min-echo-tx-interval
           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.

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

 module: example-bfd-echo
 augment /rt:routing/rt:control-plane-protocols/rt:control-plane-protoco
 l/bfd:bfd/bfd-ip-sh:ip-sh/bfd-ip-sh:sessions:
    +--rw echo {bfd-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

module example-bfd-echo {
  namespace "tag:example.com,2017:example-bfd-echo";

  prefix "example-bfd-echo";

  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) 2017 IETF Trust and the persons
     identified as authors of the code.  All rights reserved.

     Redistribution and Y.
              Yang, "Routing Key Chain YANG Data Model", draft-ietf-
              rtgwg-yang-key-chain-15 (work use in progress), February 2017.

   [I-D.ietf-teas-yang-te]
              Saad, T., Gandhi, R., Liu, X., Beeram, V., Shah, H.,
              Bryskin, I., Chen, X., Jones, R., source and B. Wen, "A 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 Data
              Model module is part of RFC XXXX; see
     the RFC itself for Traffic Engineering Tunnels full legal notices.";

  revision 2017-06-30 {
    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 Interfaces",
              draft-ietf-teas-yang-te-05 (work in progress), October
              2016. remove this
  // note

  /*
   * Groupings
   */
  grouping bfd-grouping-echo-cfg-parms {
    description "BFD grouping for echo config parameters";
    leaf desired-min-echo-tx-interval {
      type uint32;
      units microseconds;
      default 0;
      description "Desired minumum transmit interval for echo";
    }

    leaf required-min-echo-rx-interval {
      type uint32;
      units microseconds;
      default 0;
      description "Required minimum receive interval for echo";
    }
  }

  augment "/rt:routing/rt:control-plane-protocols/"
        + "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh/"
        + "bfd-ip-sh:sessions" {
    description "Augmentation for BFD echo fucntion.";
    container echo {
      if-feature bfd-echo-mode;

      description "BFD echo function container";

      uses bfd-grouping-echo-cfg-parms;
    }
  }
}

Appendix A. B.  Change log

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

A.1.

B.1.  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.2.  Changes between versions -04 and -05

   o  "bfd" node in augment of control-plane-protocol as per A YANG Data
      Model for Routing Management [RFC8022].

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

   o  Added information on interaction with other YANG modules.

A.2.

B.3.  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.

A.3.

B.4.  Changes between versions -02 and -03

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

A.4.

B.5.  Changes between versions -01 and -02

   o  Replace routing-instance, which has been removed from
      [I-D.ietf-netmod-routing-cfg], A YANG Data
      Model for Routing Management [RFC8022], with network-instance from
      YANG Network Instances [I-D.ietf-rtgwg-ni-model]

A.5.

B.6.  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

   o  For BFD authentication we now use key-chain in
      [I-D.ietf-rtgwg-yang-key-chain] 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
   Santosh Pallagatti
   India

   Email: santosh.pallagatti@gmail.com

   Mahesh Jethanandani (editor)
   Cisco Systems

   Email: mjethanandani@gmail.com

   Santosh Pallagatti
   India

   Email: santosh.pallagatti@gmail.com
   Greg Mirsky
   ZTE Corporation

   Email: gregimirsky@gmail.com