Network Working Group                                      L. Zheng, Ed.
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                          R. Rahman, Ed.
Expires: February August 20, 2016                                   Cisco Systems
                                                           S. Pallagatti
                                                        Juniper Networks

                                                         M. Jethanandani
                                                           Cisco Systems
                                                               G. Mirsky
                                                                Ericsson
                                                         August 19, 2015
                                                       February 17, 2016

      Yang Data Model for Bidirectional Forwarding Detection (BFD)
                       draft-ietf-bfd-yang-00.txt
                       draft-ietf-bfd-yang-01.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 February August 20, 2016.

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Contributors  . . . . . . . . . . . . . . . . . . . . . .   3   4
   2.  Design of the Data Model  . . . . . . . . . . . . . . . . . .   3   4
     2.1.  Design of Configuration Model . . . . . . . . . . . . . .   4
       2.1.1.  Common BFD configuration parameters . . . . . . . . .   5
       2.1.2.  Single-hop IP . . . . . . . . . . . . . . . . . . . .   4
       2.1.2.   6
       2.1.3.  Multi-hop IP  . . . . . . . . . . . . . . . . . . . .   5
       2.1.3.   6
       2.1.4.  MPLS Traffic Engineering Tunnels  . . . . . . . . . . . . .   6
       2.1.4.  LDP
       2.1.5.  MPLS Label Switched Paths . . . . . . . . . . . . . .   6
       2.1.5.   7
       2.1.6.  Link Aggregation Groups . . . . . . . . . . . . . . .   6
       2.1.6.  Per-interface Configuration . . . . . . . . . . . . .   7
     2.2.  Design of Operational Model . . . . . . . . . . . . . . .   7
     2.3.  Notifications . . . . . . . . . . . . . . . . . . . . . .   8
     2.4.  RPC Operations  . . . . . . . . . . . . . . . . . . . . .   8
     2.5.  BFD Configuration Data Hierarchy top level hierarchy . . . . . . . . . . . . . . . . .   8
       2.5.1.  Centralized
     2.6.  BFD Configuration IP single-hop hierarchy . . . . . . . . . . . .   8
       2.5.2.  Configuration in . . .   9
     2.7.  BFD clients IP multi-hop hierarchy  . . . . . . . . . . . .   9
     2.6.  Operational Data Hierarchy . . .  11
     2.8.  BFD over LAG hierarchy  . . . . . . . . . . . .  11
     2.7.  Notifications . . . . .  13
     2.9.  BFD over MPLS LSPs hierarchy  . . . . . . . . . . . . . .  15
     2.10. BFD over MPLS-TE hierarchy  . . .  14
     2.8. . . . . . . . . . . . .  17
     2.11. Examples  . . . . . . . . . . . . . . . . . . . . . . . .  16
     2.9.  19
     2.12. Interaction with other YANG modules . . . . . . . . . . .  16
     2.10.  19
     2.13. BFD top-level Yang Module . . . . . . . . . . . . . . . .  19
     2.14. BFD IP single-hop Yang Module . . . . . . .  16
     2.11. . . . . . . .  32
     2.15. BFD Client Example Configuration IP multi-hop Yang Module  . . . . . .  31
     2.12. Security Considerations . . . . . . . .  35
     2.16. BFD over LAG Yang Module  . . . . . . . . . . . . . . .  33
     2.13. IANA Considerations .  38
     2.17. BFD over MPLS Yang Module . . . . . . . . . . . . . . . .  41
     2.18. BFD over MPLS-TEYang Module . .  33
     2.14. Acknowledgements . . . . . . . . . . . . .  45
     2.19. Security Considerations . . . . . . .  33
   3.  References . . . . . . . . . .  47
     2.20. IANA Considerations . . . . . . . . . . . . . . .  33
     3.1.  Normative References . . . .  47
     2.21. Acknowledgements  . . . . . . . . . . . . . .  33
     3.2.  Informative . . . . . .  47
   3.  References  . . . . . . . . . . . . . . . . .  34
   Appendix A.  Change log . . . . . . . .  47
     3.1.  Normative References  . . . . . . . . . . . . .  35
     A.1.  Changes between versions -03 and -04 . . . . .  47
     3.2.  Informative References  . . . . .  35
     A.2.  Changes between versions -02 and -03 . . . . . . . . . .  35
     A.3.  Changes between versions -01 and -02 . .  49
   Appendix A.  Change log . . . . . . . .  35
     A.4. . . . . . . . . . . . . .  49
     A.1.  Changes between versions -00 and -01  . . . . . . . . . .  35  49
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  35  50

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 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 [RFC5881]

   2) Two systems connected via multiple hops [RFC5883]

   3) Two systems connected via MPLS Label Switched Paths (LSPs)
   [RFC5884]

   4) 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]

   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 [RFC5882].  The obvious candidates which
   use BFD are those which do not have Hellos to detect failures, e.g.
   static routes, and routing protocols whose Hellos do not suport support 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.

   The new top-level container "bfd" is augmented by all the YANG
   modules for their respective specific information.

   The "routing-protocol" data model follows node in [I-D.ietf-netmod-routing-cfg] has
   been augmented with the "bfd" data node.  Where appropriate for
   specific types of forwarding path, the respective BFD YANG modules
   follow a VRF-centric model by augmenting the
   "routing-protocol" data that new "bfd" node under
   "routing-protocol".

   Each node in [I-D.ietf-netmod-routing-cfg]. every "bfd" sub-tree has a "config" node and an "oper"
   node.

2.1.  Design of Configuration Model

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

   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.  So the
   configuration model has groupings, containing multiplier and
   interval(s), which  Other
   parameters such as BFD authentication are not specific to be used by the
   requirements of the BFD clients.  Other parameters
   which remain under client.  To avoid splitting the BFD control, e.g. demand mode
   configuration between BFD clients and authentication,
   are configured BFD, all the configuration is
   under BFD.

   We provide groupings, which contain the basic  The only BFD session parameters,
   for applications configuration under BFD clients should be an
   "enable" knob which makes those clients react to use.  This ensures consistency of BFD liveliness
   detection events.

2.1.1.  Common BFD configuration parameters
   across applications.

   The basic BFD configuration parameters are:

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

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

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

   Although [RFC5880] allows for different values for transmit and
   receive intervals, many 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.  Our  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" "desired-min-tx-
   interval" and "required-min-rx-interval".

2.1.1.  Single-hop IP

   For single-hop IP, the BFD multiplier and interval(s) are configured
   in BFD clients.  It  This is highly desirable to have the BFD configuration
   consistent between those clients.  Therefore, we have supported via a
   grouping for
   BFD configuration that applications can import in their YANG module:

   - This provides consistency since the same grouping which is being used in
   all applications making use of BFD.

   - Not all implementations of those BFD clients have support for BFD,
   we must use if-feature in by the respective YANG modules.

   An application importing modules for the BFD configuration grouping could do so
   in a hierarchical manner if it has multiple levels at which BFD
   configuration can be applied.  In a subsequent section, we provide an
   example of how a BFD client would use various forwarding
   paths.  There are also intervals for the grouping in such a way.

   The configuration items are:

   enabled
           Set to true to enable BFD.

   local-multiplier echo function (if
   supported):

   desired-min-echo-tx-interval
           This is the detection time multiplier minimum interval that the local system would like
           to use when transmitting BFD echo packets.  If 0, the echo
           function as defined in
           [RFC5880].

   min-interval [RFC5880] is disabled.

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

           OR

   desired-min-tx-interval

   For BFD authentication we have:

   key-chain
           This is the Desired Min TX Interval as a reference to key-chain defined in [RFC5880].

   required-min-rx-interval
           [I-D.ietf-rtgwg-yang-key-chain].  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
           [RFC5880].

2.1.2.  Single-hop IP

   For single-hop IP, there is an augment of the "bfd" data node under
   "routing-protocol" in Section 2.  We have a list of IP single-hop
   sessions where each session is uniquely identified by the Required Min RX Interval as interface
   and destination address pair.  For the configuration parameters we
   use what is defined in [RFC5880].

2.1.2. Section 2.1.1

2.1.3.  Multi-hop IP

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

   We have a list for BFD sessions over multi-hop IP.  The key consists
   of:

   source address
           Address belonging to the local system as per [RFC5883]

   destination address
           Address belonging to the remote system as per [RFC5883]

   Since we are following a VRF-centric model we do not need a VRF field
   in the key.

   Here is the list of parameters:

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

   desired-min-tx-interval
           This is

   For the Desired Min TX Interval as defined in [RFC5880].

   required-min-rx-interval
           This configuration parameters we use what is the Required Min RX Interval as defined in [RFC5880].

   demand-enabled
           Set to true to enable demand mode as defined in [RFC5880].

   enable-authentication
           Set to true to enable BFD authentication.

   authentication-algorithm
           Authentication algorithm to use, if enabled.

   key-chain-name
           Key-chain to be used for authentication, if enabled.
   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.

2.1.3.

2.1.4.  MPLS Traffic Engineering Tunnels

   For Traffic Engineering (TE) MPLS-TE tunnels, BFD is configured under the TE MPLS-TE tunnel since it is the Traffic Enginnering application which knows
   the desired failure detection parameters.  The grouping for BFD
   clients in Section 2.1.1 can be used by parameters is a property of the TE application for MPLS-TE
   tunnel.  This is achieved by augmenting the
   basic BFD parameters. MPLS-TE data model in
   [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 TE MPLS-TE application.

2.1.4.  LDP Label Switched Paths

   For LDP LSPs,

   On top of the usual BFD is configured under parameters, we have the LDP FEC.  The grouping following per MPLS-TE
   tunnel:

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

   For general MPLS-TE data, "mpls-te" data node is added under the top-
   level "bfd" node in Section 2.1.1 can be used by the LDP application 2.  Since some MPLS-TE tunnels are uni-
   directional there is no MPLS-TE configuration for these tunnels on
   the basic BFD parameters.  For 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 top-level
   "bfd" node in Section 2 is augmented with "mpls" which contains a
   list of sessions uniquely identified by an IP address.

   Since these LSPs are specific to uni-directional there is no LSP configuration on
   the LDP application, if any, these egress node.  The BFD parameters will be defined in the
   YANG model of for the LDP application.

2.1.5. egress node are added
   under "mpls".

2.1.6.  Link Aggregation Groups

   Per [RFC7130], configuring BFD on LAG consists of having micro-BFD
   sessions on each LAG member link.  The grouping for BFD clients in
   Section 2.1.1 can be used by the LAG application for  Since the basic BFD
   parameters.  This grouping can be used per-LAG or per member-link.
   For BFD parameters which are specific to the LAG application, e.g.
   the IP address an
   attribute of the peer system which can be reached by the LAG,
   the parameters will they should be defined in under the LAG.  However there is
   no LAG YANG model of the LAG
   application.

2.1.6.  Per-interface Configuration

   With multiplier and intervals configured under the BFD clients, which we
   still need a central location to configure authentication, demand
   mode, etc.  This can be done by configuring the following parameters
   per interface:

   demand-enabled
           Set to true to enable demand mode as defined in [RFC5880].

   enable-authentication
           Set to true to enable BFD authentication.

   authentication-algorithm
           Authentication algorithm to use, if enabled.

   key-chain-name
           Key-chain to be used for authentication, if enabled.

   desired-min-echo-tx-interval
           This augment.  So a "lag" data node is the minimum interval that the local system would like
   added to use when transmitting BFD echo packets.  If 0, the echo
           function as defined top-level "bfd" node in [RFC5880] is disabled.

   required-min-echo-rx-interval
           This Section 2, the configuration is
   per-LAG: we have a list of LAGs.  The destination IP address of the Required Min Echo RX Interval as defined in
           [RFC5880].
   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
   statistics.  Since BFD is used for liveness detection
   information.

   The overall statistics of arbitrary
   paths, there is no uniform key to identify a BFD session.  E.g. a sessions consist of number of BFD
   single-hop IP session is uniquely identified by the combination
   sessions, number of
   destination IP address and interface whereas a multihop IP session BFD sessions up etc.  This information is
   uniquely identified by
   available globally (i.e. for all BFD sessions) under the combination of source IP address top level
   "bfd" node in Section 2 and
   destination IP address (in the context also per type of a VRF). forwarding path.

   For this reason,
   for per-session operational statistics, we do not have a single list
   with different type BFD sessions.  Instead, we have a container where
   we have multiple lists, where each list corresponds to one specific
   path type for BFD.  For example, we have one operational list for BFD
   single-hop IP, another list for BFD multi-hop IP, etc.  In each list, 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 FSM the
   device in
   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
   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 is uniquely
   identified by the source UDP port local discriminator.

2.3.  Notifications

   This YANG model defines a list of 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, routing-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

2.5.  BFD Configuration Data Hierarchy

2.5.1.  Centralized BFD Configuration

   The following is top level hierarchy

   At the centralized top level there is no configuration data, only operational
   data.  The operational data hierarchy:

   We have a container which contains a list for each session type.
   This contains consist of overall BFD session configuration for only statistics
   globally and per routing-instance
   module: ietf-bfd
      +--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
   augment /rt:routing/rt:routing-instance
           /rt:routing-protocols/rt:routing-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 multi-hop sessions.

   We have per-interface single-hop hierarchy

   The configuration and operational data for authentication, demand-mode,
   etc.  This is used e.g. for each BFD IP single-hop sessions whose base BFD
   configuration belongs to the
   session is under "ip-sh" node under routing-instance.  Overall BFD clients. IP
   single-hop session statistics are available per routing-instance and
   globally (for all routing instances).

  module: ietf-bfd ietf-bfd-ip-sh
  augment /rt:routing/rt:routing-instance/rt:routing-protocols/
            rt:routing-protocol: /bfd:bfd:
     +--rw bfd ip-sh
        +--rw bfd-cfg
         | 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
  augment /rt:routing/rt:routing-instance/rt:routing-protocols
          /rt:routing-protocol/bfd:bfd:
     +--rw ip-sh
        +--rw bfd-session-cfg config
        |  +--rw session-cfg
        |     +--rw session-ip-mh* [source-addr sessions* [interface dest-addr]
        |  |        +--rw source-addr                 inet:ip-address
         | interface                        if:interface-ref
        |        +--rw dest-addr                        inet:ip-address
        |  |        +--rw admin-down?                 boolean
         | source-addr?                     inet:ip-address
        |        +--rw local-multiplier?           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
        |  |        +--rw enable-authentication? admin-down?                      boolean
        |  |        +--rw authentication-parms authentication-parms! {bfd-authentication}?
        |        |     |  +--rw key-chain-name?   string
         | key-chain?           kc:key-chain-ref
        |        |  +--rw algorithm?        bfd-auth-algorithm replay-protection?   identityref
        |        +--rw desired-min-echo-tx-interval?    uint32
        |        +--rw tx-ttl?                     ttl required-min-echo-rx-interval?   uint32
        +--ro oper
           +--ro bfd-session-statistics
           |  +--ro session-count?              uint32
           |     +--rw rx-ttl                      ttl  +--ro session-up-count?           uint32
           |  +--rw bfd-interface-cfg* [interface] {bfd-interface-config}?  +--ro session-down-count?         uint32
           |     +--rw  +--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 local-discriminator?    bfd-discriminator
              +--ro remote-discriminator?   bfd-discriminator
              +--ro remote-multiplier?      bfd-multiplier
              +--ro out-interface?          if:interface-ref
              +--ro demand-capability?      boolean
              +--ro source-port?            inet:port-number
              +--ro dest-port?              inet:port-number
              +--ro session-running
              |     +--rw local-multiplier?                multiplier  +--ro session-index?             uint32
              |     +--rw (interval-config-type)?  +--ro local-state?               bfd-state
              |  +--ro remote-state?              bfd-state
              |  +--:(tx-rx-intervals)  +--ro local-diagnostic?          bfd-diagnostic
              |  +--ro remote-diagnostic?         bfd-diagnostic
              |  +--ro detection-mode?            enumeration
              |  +--rw desired-min-tx-interval  +--ro negotiated-tx-interval?    uint32
              |     |  |  +--rw required-min-rx-interval  +--ro negotiated-rx-interval?    uint32
              |     |  +--:(single-interval)
         |     |     +--rw min-interval  +--ro echo-tx-interval-in-use?   uint32
              |     +--rw demand-enabled?                  boolean
         |     +--rw enable-authentication?           boolean
         |     +--rw authentication-parms {bfd-authentication}?
         |     |  +--rw key-chain-name?   string
         |     |  +--rw algorithm?        bfd-auth-algorithm
         |     +--rw desired-min-echo-tx-interval?  +--ro detection-time?            uint32
         |     +--rw required-min-echo-rx-interval?
              +--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

2.5.2.  Configuration in
                 +--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
        +--ro time-in-previous-state?   string
        +--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 clients

   The following is the configuration data IP multi-hop hierarchy for a hypothetical
   BFD client called example-bfd-routing-app.

   The BFD configuration is
   supported conditionally via use of if-feature.

   We have a list of areas and in operational data for each area we have a list of
   interfaces.  The BFD configuration grouping is used in a hierarchical
   fashion, it can be applied in "area" and "interface":

   - If BFD configuration IP multi-hop
   session is applied under an interface, that
   configuration takes precedence over any BFD configuration, if any, at
   the area level

   - If BFD configuration is applied "ip-mh" node under an "area" and none of the
   interfaces in that area has BFD configuration, then all interfaces
   belong to the "area" in question inherit the BFD configuration for
   the area in question.

   - If routing-instance.  In the
   operational model we support multiple BFD client implementation supports "interface all", then all
   the interfaces belonging to that area will inherit multi-hop sessions per
   remote address (ECMP), the BFD
   configuration under "interface all".  Additionally, if there local discriminator is
   specific interface configuration, then the specific interface will
   override the "interface all" parameters.

   - The tx used as key.
   Overall BFD IP multi-hop session statistics are available per
   routing-instance and rx intervals can be configured separately or a single
   interval can be configured. globally (for all routing instances).

   module: example-bfd-routing-app ietf-bfd-ip-mh
   augment /bfd:bfd:
      +--rw area* [area-id] ip-mh
         +--rw area-id 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
   augment /rt:routing/rt:routing-instance/rt:routing-protocols
           /rt:routing-protocol/bfd:bfd:
      +--rw bfd-cfg ip-mh
         +--rw config
         |  +--rw enabled?                    boolean session-cfg
         |     +--rw sessions* [source-addr dest-addr]
         |        +--rw source-addr                 inet:ip-address
         |        +--rw dest-addr                   inet:ip-address
         |        +--rw local-multiplier?           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 interface* [interface]
            +--rw interface    if:interface-ref
            +--rw bfd-cfg
               +--rw enabled? demand-enabled?             boolean
         |        +--rw local-multiplier?           multiplier admin-down?                 boolean
         |        +--rw (interval-config-type)?
                  +--:(tx-rx-intervals) authentication-parms! {bfd-authentication}?
         |        |  +--rw desired-min-tx-interval     uint32 key-chain?           kc:key-chain-ref
         |        |  +--rw required-min-rx-interval    uint32
                  +--:(single-interval) replay-protection?   identityref
         |        +--rw min-interval                uint32

2.6.  Operational Data Hierarchy

   The complete data hierarchy of BFD YANG operational model is
   presented below.

   module: ietf-bfd
   augment /rt:routing/rt:routing-instance/rt:routing-protocols/
            rt:routing-protocol: tx-ttl?                     bfd:ttl
         |        +--rw bfd rx-ttl                      bfd:ttl
         +--ro bfd-oper oper
            +--ro bfd-session-statistics
            |  +--ro ip-sh-session-num?     uint32
            |  +--ro ip-mh-session-num?     uint32 bfd-session-statistics
            |     +--ro total-session-num? session-count?              uint32
            |     +--ro session-up-num? session-up-count?           uint32
            |     +--ro sess-down-num? session-down-count?         uint32
            |     +--ro sess-admin-down-num? session-admin-down-count?   uint32
            +--ro bfd-session-lists
               +--ro session-ip-sh* [interface session-group* [source-addr dest-addr]
               |
               +--ro interface               if:interface-ref
               | source-addr    inet:ip-address
               +--ro dest-addr      inet:ip-address
               |
               +--ro source-addr?            inet:ip-address
               | sessions* [local-discriminator]
                  +--ro session-type?           bfd-session-type
               | ttl?                    bfd:ttl
                  +--ro local-discriminator?    discriminator
               | path-type?              identityref
                  +--ro local-discriminator     bfd-discriminator
                  +--ro remote-discriminator?   discriminator
               |   bfd-discriminator
                  +--ro remote-multiplier?      multiplier
               |      bfd-multiplier
                  +--ro out-interface?          if:interface-ref
               |
                  +--ro demand-capability?      boolean
               |
                  +--ro source-port?            inet:port-number
               |
                  +--ro dest-port?              inet:port-number
               |
                  +--ro session-running*
               | session-running
                  |  +--ro session-index?             uint32
                  |  |  +--ro local-state?                   state
               |               bfd-state
                  |  +--ro remote-state?                  state
               |              bfd-state
                  |  +--ro local-diagnostic?              diagnostic
               |          bfd-diagnostic
                  |  +--ro remote-diagnostic?             diagnostic
               |         bfd-diagnostic
                  |  +--ro detection-mode?            enumeration
                  |  |  +--ro negotiated-tx-interval?    uint32
                  |  |  +--ro negotiated-rx-interval?    uint32
                  |  |  +--ro negotiated-echo-tx-interval? echo-tx-interval-in-use?   uint32
                  |  |  +--ro detection-time?            uint32
               |
                  +--ro sesssion-statistics*
               | 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-multihop-notification
         +--ro session-ip-mh-group* [source-addr dest-addr]
               | local-discr?              bfd-discriminator
         +--ro source-addr      inet:ip-address
               | remote-discr?             bfd-discriminator
         +--ro dest-addr new-state?                bfd-state
         +--ro state-change-reason?      string
         +--ro time-in-previous-state?   string
         +--ro dest-addr?                inet:ip-address
               |
         +--ro session-ip-mh* [source-port]
               | source-addr?              inet:ip-address
         +--ro ttl?                    ttl
               | session-index?            uint32
         +--ro session-type?           bfd-session-type
               | path-type?                identityref
         +--ro local-discriminator?    discriminator routing-instance?         rt:routing-instance-ref

2.8.  BFD over LAG hierarchy

   The configuration and operational data for each BFD LAG session is
   under "lag" node.  Overall BFD LAG session statistics are available
   globally.

   module: ietf-bfd-lag
   augment /bfd:bfd:
      +--rw lag
         +--rw config
         |     +--ro remote-discriminator?   discriminator  +--rw session-cfg
         |     +--ro remote-multiplier?      multiplier     +--rw sessions* [lag-name]
         |     +--ro out-interface?        +--rw lag-name                    if:interface-ref
         |     +--ro demand-capability?      boolean        +--rw ipv4-dest-addr?             inet:ipv4-address
         |     +--ro source-port             inet:port-number        +--rw ipv6-dest-addr?             inet:ipv6-address
         |     +--ro dest-port?              inet:port-number        +--rw local-multiplier?           bfd-multiplier
         |     +--ro session-running*        +--rw (interval-config-type)?
         |        |  +--ro session-index?  +--:(tx-rx-intervals)
         |        |  |  +--rw desired-min-tx-interval     uint32
         |        |  +--ro local-state?                   state  |  +--rw required-min-rx-interval    uint32
         |  +--ro remote-state?                  state        |  +--:(single-interval)
         |  +--ro local-diagnostic?              diagnostic        |     +--rw min-interval                uint32
         |  +--ro remote-diagnostic?             diagnostic        +--rw demand-enabled?             boolean
         |        +--rw admin-down?                 boolean
         |  +--ro detection-mode?                enumeration        +--rw authentication-parms! {bfd-authentication}?
         |           +--rw key-chain?           kc:key-chain-ref
         |           +--rw replay-protection?   identityref
         +--ro negotiated-tx-interval?        uint32 oper
            +--ro micro-bfd-ipv4-session-statistics
            |  +--ro bfd-session-statistics
            |     +--ro negotiated-rx-interval? session-count?              uint32
            |     |     +--ro negotiated-echo-tx-interval? session-up-count?           uint32
            |     |     +--ro detection-time? session-down-count?         uint32
            |     +--ro sesssion-statistics*
               | session-admin-down-count?   uint32
            +--ro create-time?            yang:date-and-time micro-bfd-ipv6-session-statistics
            |  +--ro last-down-time?         yang:date-and-time bfd-session-statistics
            |     +--ro last-up-time?           yang:date-and-time session-count?              uint32
            |     +--ro down-count? session-up-count?           uint32
            |     +--ro admin-down-count? session-down-count?         uint32
            |     +--ro receive-packet-count?   uint64
               | session-admin-down-count?   uint32
            +--ro send-packet-count?      uint64
               | session-lag* [lag-name]
               +--ro receive-bad-packet?     uint64
               | lag-name        if:interface-ref
               +--ro send-failed-packet?     uint64 use-ipv4?       boolean
               +--ro session-te-tunnel* [tunnel-name]
               | use-ipv6?       boolean
               +--ro tunnel-name             string member-links* [member-link]
                  +--ro member-link       if:interface-ref
                  +--ro micro-bfd-ipv4
                  |  +--ro session-type?           bfd-session-type path-type?              identityref
                  |  +--ro local-discriminator?    discriminator    bfd-discriminator
                  |  +--ro remote-discriminator?   discriminator   bfd-discriminator
                  |  +--ro remote-multiplier?      multiplier      bfd-multiplier
                  |  +--ro out-interface?          if:interface-ref
                  |  +--ro demand-capability?      boolean
                  |  +--ro source-port?            inet:port-number
                  |  +--ro dest-port?              inet:port-number
                  |  +--ro session-running* session-running
                  |  |  +--ro session-index?             uint32
                  |  |  +--ro local-state?                   state               bfd-state
                  |  |  +--ro remote-state?                  state              bfd-state
                  |  |  +--ro local-diagnostic?              diagnostic          bfd-diagnostic
                  |  |  +--ro remote-diagnostic?             diagnostic         bfd-diagnostic
                  |  |  +--ro detection-mode?            enumeration
                  |  |  +--ro negotiated-tx-interval?    uint32
                  |  |  +--ro negotiated-rx-interval?    uint32
                  |  |  +--ro negotiated-echo-tx-interval? echo-tx-interval-in-use?   uint32
                  |  |  +--ro detection-time?            uint32
                  |  +--ro sesssion-statistics* 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 session-ldp-lsp-group* [ldp-fec]
               |  +--ro ldp-fec            inet:ip-prefix
               |  +--ro session-ldp-lsp* [source-port]
               |     +--ro ttl?                    ttl
               | micro-bfd-ipv6
                     +--ro session-type?           bfd-session-type
               | path-type?              identityref
                     +--ro local-discriminator?    discriminator
               |    bfd-discriminator
                     +--ro remote-discriminator?   discriminator
               |   bfd-discriminator
                     +--ro remote-multiplier?      multiplier
               |      bfd-multiplier
                     +--ro out-interface?          if:interface-ref
               |
                     +--ro demand-capability?      boolean
               |
                     +--ro source-port source-port?            inet:port-number
               |
                     +--ro dest-port?              inet:port-number
               |
                     +--ro session-running*
               | session-running
                     |  +--ro session-index?             uint32
                     |     |  +--ro local-state?                   state
               |               bfd-state
                     |  +--ro remote-state?                  state
               |              bfd-state
                     |  +--ro local-diagnostic?              diagnostic
               |          bfd-diagnostic
                     |  +--ro remote-diagnostic?             diagnostic
               |         bfd-diagnostic
                     |  +--ro detection-mode?            enumeration
                     |     |  +--ro negotiated-tx-interval?    uint32
                     |     |  +--ro negotiated-rx-interval?    uint32
                     |     |  +--ro negotiated-echo-tx-interval? echo-tx-interval-in-use?   uint32
                     |     |  +--ro detection-time?            uint32
               |
                     +--ro sesssion-statistics*
               | 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 session-lag* [lag-name] local-discr?              bfd-discriminator
         +--ro lag-name             if:interface-ref remote-discr?             bfd-discriminator
         +--ro session-lag-micro* [member-link] new-state?                bfd-state
         +--ro member-link             if:interface-ref state-change-reason?      string
         +--ro time-in-previous-state?   string
         +--ro session-type?           bfd-session-type dest-addr?                inet:ip-address
         +--ro local-discriminator? 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

   The configuration is per MPLS FEC under "mpls".  In the operational
   model we support multiple BFD sessions per MPLS FEC (ECMP), the local
   discriminator is used as key.

                        module: ietf-bfd-mpls
   augment /bfd:bfd:

      +--rw mpls
         +--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 /rt:routing/rt:routing-instance/rt:routing-protocols
           /rt:routing-protocol/bfd:bfd:
      +--rw mpls
         +--rw config
         |  +--rw session-cfg
         |     +--rw sessions* [mpls-fec]
         |        +--rw mpls-fec                    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
         |        +--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     bfd-discriminator
                  +--ro remote-discriminator?   discriminator   bfd-discriminator
                  +--ro remote-multiplier?      multiplier      bfd-multiplier
                  +--ro out-interface?          if:interface-ref
                  +--ro demand-capability?      boolean
                  +--ro source-port?            inet:port-number
                  +--ro dest-port?              inet:port-number
                  +--ro session-running* session-running
                  |  +--ro session-index?             uint32
                  |  +--ro local-state?                   state               bfd-state
                  |  +--ro remote-state?                  state              bfd-state
                  |  +--ro local-diagnostic?              diagnostic          bfd-diagnostic
                  |  +--ro remote-diagnostic?             diagnostic         bfd-diagnostic
                  |  +--ro detection-mode?            enumeration
                  |  +--ro negotiated-tx-interval?    uint32
                  |  +--ro negotiated-rx-interval?    uint32
                  |  +--ro negotiated-echo-tx-interval? echo-tx-interval-in-use?   uint32
                  |  +--ro detection-time?            uint32
                  +--ro sesssion-statistics* 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

2.7.  Notifications

   The BFD YANG data model defines notifications for BFD session state
   changes.

   module: ietf-bfd
   augment /rt:routing/rt:routing-instance/rt:routing-protocols/
            rt:routing-protocol:
                  +--ro mpls-dest-address?      inet:ip-address
   notifications:
      +---n bfd-singlehop-notification
      | bfd-mpls-notification
         +--ro local-discr?              discriminator
      |              bfd-discriminator
         +--ro remote-discr?             discriminator
      |             bfd-discriminator
         +--ro new-state?                state
      |                bfd-state
         +--ro state-change-reason?      string
      |
         +--ro time-in-previous-state?   string
      |
         +--ro dest-addr?                inet:ip-address
      |
         +--ro source-addr?              inet:ip-address
      |
         +--ro session-index?            uint32
      |
         +--ro session-type?             bfd-session-type
      | path-type?                identityref
         +--ro interface?                if:interface-ref
      | routing-instance?         rt:routing-instance-ref
         +--ro echo-enabled?             boolean
      +---n bfd-multihop-notification mpls-dest-address?        inet:ip-address

2.10.  BFD over MPLS-TE hierarchy

   The MPLS-TE YANG model [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 /bfd:bfd:
      +--rw mpls-te
         +--rw config
         |  +--ro local-discr?              discriminator  +--rw egress
         |  +--ro remote-discr?             discriminator     +--rw local-multiplier?           bfd-multiplier
         |  +--ro new-state?                state     +--rw (interval-config-type)?
         |  +--ro state-change-reason?      string     |  +--ro time-in-previous-state?   string  +--:(tx-rx-intervals)
         |  +--ro dest-addr?                inet:ip-address     |  +--ro source-addr?              inet:ip-address  |  +--ro session-index?  +--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 session-type?             bfd-session-type
      +---n bfd-te-tunnel-notification 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
      +--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 local-discr?              discriminator path-type?              identityref
      +--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
      +--ro source-port?            inet:port-number
      +--ro dest-port?              inet:port-number
      +--ro session-running
      |  +--ro remote-discr?             discriminator session-index?             uint32
      |  +--ro new-state?                state local-state?               bfd-state
      |  +--ro state-change-reason?      string remote-state?              bfd-state
      |  +--ro time-in-previous-state?   string local-diagnostic?          bfd-diagnostic
      |  +--ro dest-addr?                inet:ip-address remote-diagnostic?         bfd-diagnostic
      |  +--ro source-addr?              inet:ip-address detection-mode?            enumeration
      |  +--ro session-index? negotiated-tx-interval?    uint32
      |  +--ro session-type?             bfd-session-type negotiated-rx-interval?    uint32
      |  +--ro tunnel-name?              string
      +---n bfd-ldp-lsp-notification echo-tx-interval-in-use?   uint32
      |  +--ro local-discr?              discriminator
      | detection-time?            uint32
      +--ro remote-discr?             discriminator sesssion-statistics
      |  +--ro new-state?                state create-time?            yang:date-and-time
      |  +--ro state-change-reason?      string last-down-time?         yang:date-and-time
      |  +--ro time-in-previous-state?   string last-up-time?           yang:date-and-time
      |  +--ro dest-addr?                inet:ip-address down-count?             uint32
      |  +--ro source-addr?              inet:ip-address admin-down-count?       uint32
      |  +--ro session-index?            uint32 receive-packet-count?   uint64
      |  +--ro session-type?             bfd-session-type send-packet-count?      uint64
      |  +--ro ldp-fec?                  inet:ip-prefix receive-bad-packet?     uint64
      |  +--ro source-port?              inet:port-number send-failed-packet?     uint64
      +--ro mpls-dest-address?      inet:ip-address
   notifications:
      +---n bfd-lag-notification bfd-mpls-te-notification
         +--ro local-discr?              discriminator              bfd-discriminator
         +--ro remote-discr?             discriminator             bfd-discriminator
         +--ro new-state?                state                bfd-state
         +--ro state-change-reason?      string
         +--ro time-in-previous-state?   string
         +--ro dest-addr?                inet:ip-address
         +--ro source-addr?              inet:ip-address

2.8.
         +--ro session-index?            uint32
         +--ro path-type?                identityref
         +--ro mpls-dest-address?        inet:ip-address
         +--ro tunnel-name?              string

2.11.  Examples

2.9.

2.12.  Interaction with other YANG modules

   TBD.

2.10.

2.13.  BFD top-level Yang Module

   <CODE BEGINS> file "ietf-bfd@2015-07-01.yang" "ietf-bfd@2016-02-17.yang"
   module ietf-bfd {
     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 {
       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>
        WG Chair: Jeff Haas
        WG Chair: Nobo Akiya Reshad Rahman
        Editor:   Lianshu Zheng and Reshad Rahman";

     description
       "This module contains the YANG definition for BFD parameters as
        per RFC5880, RFC5881 RFC5880.";

     revision 2016-02-17 {
       description
         "* Split in several modules
          * This module contains common definitions and RFC5883";
            summary information.";
       reference "RFC XXXX: A YANG data model for BFD";
     }

     revision 2015-07-01 {
       description "Initial revision.";
       reference "RFC XXXX: A YANG data model for BFD";
     }

     identity bfd {
       base "rt:routing-protocol";
       description "BFD protocol";
     }
     typedef discriminator bfd-discriminator {
       type uint32 {
         range 1..4294967295;
       }
       description "BFD discriminator";
     }

     typedef diagnostic bfd-diagnostic {
       type enumeration {
         enum none {
           value 0;
           description "None";
         }
         enum controlExpiry {
           value 1;
           description "Control timer expiry";
         }
         enum echoFailed {
           value 2;
           description "Echo failure";
         }
         enum nborDown {
           value 3;
           description "Neighbor down";
         }
         enum fwdingReset {
           value 4;
           description "Forwarding reset";
         }
         enum pathDown {
           value 5;
           description "Path down";
         }
         enum concPathDown {
           value 6;
           description "Concatenated path down";
         }
         enum adminDown {
           value 7;
           description "Admin down";
         }
         enum reverseConcPathDown {
           value 8;
           description "Reverse concatenated path down";
         }
       }
       description "BFD diagnostic";
     }
     typedef state 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";
     }

     typedef multiplier bfd-multiplier {
       type uint8 {
         range 1..255;
       }
       description "Multiplier";
     }

     typedef ttl {
       type uint8 {
         range 1..255;
       }
       description "Time To Live";
     }
     typedef bfd-session-type

     identity bfd-path-type {
       description
         "Base identity for BFD path type. The session type enumeration {
         enum ip-single-hop indicates
          the type of path on which BFD is running";
     }
     identity bfd-path-ip-sh {
       base bfd-path-type;
       description "IP "BFD on IP single hop";
     }
         enum ip-multi-hop
     identity bfd-path-ip-mh {
       base bfd-path-type;
       description "IP "BFD on IP multi hop";

     }
         enum te-tunnel
     identity bfd-path-mpls-te {
       base bfd-path-type;
       description "Traffic Engineering tunnes"; "BFD on MPLS Traffic Engineering";
     }
         enum ldp-lsp
     identity bfd-path-mpls-lsp {
       base bfd-path-type;
       description "LDP "BFD on MPLS Label Switched Path";
     }
         enum lag
     identity bfd-path-lag {
       base bfd-path-type;
       description "Micro-BFD on LAG member links";
     }
       }

     identity bfd-encap-type {
       description
         "BFD session type, this indicates the path type that
         "Base identity for BFD is
          running on"; encapsulation type.";
     }
     typedef bfd-auth-algorithm {
       type enumeration {
         enum simple-password
     identity bfd-encap-ip {
       base bfd-encap-type;
       description
             "Simple password"; "BFD with IP encapsulation.";
     }

         enum keyed-md5

     feature bfd-authentication {
       description
             "Keyed message Digest 5"; "BFD authentication supported";
     }

         enum meticulous-keyed-md5

     identity bfd-auth-replay-protection {
       description
             "Meticulous keyed message Digest 5";
         "Base identity for BFD authentication replay protection";
     }

         enum keyed-sha-1
     identity bfd-auth-replay-protection-non-meticulous {
       base bfd-auth-replay-protection;
       description
             "Keyed secure hash algorithm (SHA1) "; "Non-meticulous (see RFC5880)";
     }

         enum meticulous-keyed-sha-1
     identity bfd-auth-replay-protection-meticulous {
       base bfd-auth-replay-protection;
       description "Meticulous keyed secure hash algorithm (SHA1) ";
         } (see RFC5880)";
     }

     grouping bfd-auth-parms {
       description "Authentication algorithm";
     }
     feature bfd-interface-config
         "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 "BFD per-interface config supported"; "Name of key-chain";
         }
     feature bfd-authentication

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

     grouping bfd-grouping-base-cfg-parms {
       description "BFD grouping for base config parameters";
       leaf local-multiplier {
         type multiplier; 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 {
         type boolean;
         default false;
         description "To enbale enable demand mode";
       }

       leaf enable-authentication admin-down {
         type boolean;
         default false;
         description
           "If set, the Authentication Section is present and
           "Is the BFD session is to be authenticated (see RFC5880 section 6.7
            for details).";
       }
       container authentication-parms {
         if-feature bfd-authentication;
         description "Parameters for authentication";
         leaf key-chain-name {
           type string;
           must "../algorithm" {
             error-message
               "May not be configured without algorithm";
             description "Requires algorithm";
           }
           description
             "Key chain name";
         }
         leaf algorithm {
           type bfd-auth-algorithm;
           must "../key-chain" {
             error-message
               "May not be configured without key-chain";
             description "Requires key-chain";
           }
           description "Authentication algorithm to be used";
         } 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 for base config parameters 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";
         }
         uses bfd-grouping-base-cfg-parms;
       }
     }

     grouping bfd-all-session {
       description "BFD session operational information";
       leaf session-type path-type {
         type bfd-session-type; identityref {
           base bfd-path-type;
         }
         description
           "BFD session type, this indicates the path type that BFD is
           running on";
       }
       leaf local-discriminator {
         type discriminator; bfd-discriminator;
         description "Local discriminator";
       }
       leaf remote-discriminator {
         type discriminator; bfd-discriminator;
         description "Remote discriminator";
       }
       leaf remote-multiplier {
         type multiplier; bfd-multiplier;
         description "Remote multiplier";
       }
       leaf out-interface {
         type if:interface-ref;
         description "Outgoing physical interface name";
       }
       leaf demand-capability {
         type boolean;
         description "Local demand mode capability";
       }
       leaf source-port {
         type inet:port-number;
         description "Source UDP port";

       }
       leaf dest-port {
         type inet:port-number;
         description "Destination UDP port";
       }
       list

       container session-running {
         description "BFD session running information";
         leaf session-index {
           type uint32;
           description
             "An index used to uniquely identify BFD sessions";
         }
         leaf local-state {
           type state; bfd-state;
           description "Local state";
         }
         leaf remote-state {
           type state; bfd-state;
           description "Remote state";
         }
         leaf local-diagnostic {
           type diagnostic; bfd-diagnostic;
           description "Local diagnostic";
         }
         leaf remote-diagnostic {
           type diagnostic; bfd-diagnostic;
           description "Remote diagnostic";
         }
         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 negotiated-echo-tx-interval echo-tx-interval-in-use {
           when "../../path-type = 'bfd-path-ip-sh'" {
             description
               "Echo is supported for IP single-hop only.";
           }
           type uint32;
           units microseconds;
           description "Negotiated echo "Echo transmit interval"; interval in use";
         }
         leaf detection-time {
           type uint32;
           units microseconds;
           description "Detection time";
         }
       }
       list

       container sesssion-statistics {
         description "BFD session 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 {
         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;
         description "BFD state change reason";
       }

       leaf time-in-previous-state {
         type string;
         description
           "How long the BFD session was in the previous state";
       }

       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:routing-instance/rt:routing-protocols/"
       + "rt:routing-protocol" {
       when "rt:type = 'bfd:bfd'" {
         description
           "This augment is only valid for a protocol instance
           of BFD.";
       }
       description "BFD augmentation.";

       container bfd {
         presence "BFD";
         description "BFD top-level top level container";
         container bfd-cfg config {
           description "BFD configuration container";
         }

         container oper {
           config "false";
           description
             "BFD operational container for this routing instance";
           uses bfd-session-statistics;
         }
       }
     }

     container bfd {
       presence "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 Module

   <CODE BEGINS> file "ietf-bfd-ip-sh@2016-02-17.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: Reshad Rahman
        Editor:   Lianshu Zheng and Reshad Rahman";

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

     revision 2016-02-17 {
       description "Initial revision.";
       reference "RFC XXXX: A YANG data model for BFD IP single-hop";
     }

     augment "/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 oper {
           config "false";
           description "BFD IP single-hop operational container";
           uses bfd:bfd-session-statistics;
         }
       }
     }

     augment "/rt:routing/rt:routing-instance/rt:routing-protocols/"
       + "rt:routing-protocol/bfd:bfd" {
       description "BFD augmentation for IP single-hop.";

       container ip-sh {
         description "BFD IP single-hop container";
         container config {
           description "BFD configuration";
           container bfd-session-cfg session-cfg {
             description "BFD IP single-hop session configuration";

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

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

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

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

           list sessions {
             key "interface dest-addr";
             description "BFD IP single-hop sessions";
             leaf interface {
               type if:interface-ref;
               description
                 "Interface on which the BFD session administratively down"; is running.";
             }
               uses bfd-grouping-common-cfg-parms;
             leaf tx-ttl dest-addr {
               type ttl;
                 default 255; inet:ip-address;
               description "TTL of outgoing BFD control packets"; "BFD peer address";
             }
             leaf rx-ttl source-addr {
               type ttl;
                 mandatory true; inet:ip-address;
               description
                   "Minimum allowed TTL value for incoming BFD control
                    packets"; "BFD source address";
             }

             uses bfd:bfd-all-session;
           }
         }
           list bfd-interface-cfg
       }
     }

     notification bfd-singlehop-notification {
             if-feature bfd-interface-config;
             key interface;
       description "Per-interface
         "Notification for BFD configuration"; 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"; "Interface to which this BFD session belongs to";
       }
             uses bfd-grouping-common-cfg-parms;
             uses bfd-grouping-echo-cfg-parms;

       leaf echo-enabled {
         type boolean;
         description "Was echo enabled for BFD";
       }
     }
         container bfd-oper

   }
   <CODE ENDS>

2.15.  BFD IP multi-hop Yang Module

   <CODE BEGINS> file "ietf-bfd-ip-mh@2016-02-17.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: Reshad Rahman
        Editor:   Lianshu Zheng and Reshad Rahman";

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

     revision 2016-02-17 {
       description "Initial revision.";
       reference "RFC XXXX: A YANG data model for BFD IP multi-hop";
     }

     augment "/bfd:bfd" {
           config "false";
       description "BFD operational container"; augmentation for IP multi-hop";
       container bfd-session-statistics ip-mh {
         description "BFD session counters";
             leaf ip-sh-session-num IP multi-hop top level container";

         container config {
               type uint32;
           description "IP single hop session number"; "BFD IP multi-hop configuration container";
         }
             leaf ip-mh-session-num
         container oper {
               type uint32;
           config "false";
           description "IP multi hop session Number"; "BFD IP multi-hop operational container";
           uses bfd:bfd-session-statistics;
         }
             leaf total-session-num {
               type uint32;
               description "Total session number";
       }
             leaf session-up-num
     }

     augment "/rt:routing/rt:routing-instance/rt:routing-protocols/"
       + "rt:routing-protocol/bfd:bfd" {
       when "rt:type = 'bfd:bfd'" {
               type uint32;
         description "Session up number";
           "This augment is only valid for a protocol instance
           of BFD.";
       }
             leaf sess-down-num
       description "BFD augmentation for IP multi-hop.";

       container ip-mh {
               type uint32;
         description "Session down number";
             }
             leaf sess-admin-down-num "BFD IP multi-hop container";
         container config {
               type uint32;
           description "Session admin-down number";
             }
           } "BFD configuration";
           container bfd-session-lists session-cfg {
             description
               "Contains multiple "BFD IP multi-hop session lists, one per type"; configuration";

             list session-ip-sh sessions {
               key "interface "source-addr dest-addr";
               description "BFD "List of IP single-hop multi-hop sessions";

               leaf interface source-addr {
                 type if:interface-ref; inet:ip-address;
                 description
                   "Interface on which the BFD session is running.";
                   "Local IP address";
               }
               leaf dest-addr {
                 type inet:ip-address;
                 description "BFD peer address";
                   "IP address of the peer";
               }
               uses bfd:bfd-grouping-common-cfg-parms;

               leaf source-addr tx-ttl {
                 type inet:ip-address; bfd:ttl;
                 default 255;
                 description "BFD source address"; "TTL of outgoing BFD control packets";
               }
               leaf rx-ttl {
                 type bfd:ttl;
                 mandatory true;
                 description
                   "Minimum allowed TTL value for incoming BFD control
                    packets";
               }
             }
           }
         }

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

           container bfd-session-statistics {
             description "BFD session counters";
             uses bfd-all-session; bfd:bfd-session-statistics;
           }

           list session-ip-mh-group session-group {
             key "source-addr dest-addr";
             description
               "BFD IP multi-hop group of sessions. A group of " +
               "sessions is between 1 source and 1 destination, " +
               "each session uses has a different source UDP port 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";
             }
             list session-ip-mh sessions {
               key "source-port"; "local-discriminator";
               description
                 "The BFD sessions between a source and a. " +
                 "destination. Source UDP port Local discriminator is unique for " +
                 "each session in the group.";
               leaf ttl {
                 type ttl; bfd:ttl;
                 description "TTL of outgoing packets";
               }
               uses bfd-all-session; bfd:bfd-all-session;
             }
           }
             list session-te-tunnel
         }
       }
     }

     notification bfd-multihop-notification {
               key "tunnel-name";
       description "BFD over TE tunnel";
         "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;

       leaf tunnel-name routing-instance {
         type string; rt:routing-instance-ref;
         description "Name of TE tunnel"; "Routing instance";
       }
               uses bfd-all-session;
     }
             list session-ldp-lsp-group

   }
   <CODE ENDS>

2.16.  BFD over LAG Yang Module

   <CODE BEGINS> file "ietf-bfd-lag@2016-02-17.yang"
   module ietf-bfd-lag {
               key "ldp-fec";
     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";
     }

     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: Reshad Rahman
        Editor:   Lianshu Zheng and Reshad Rahman";

     description
                 "BFD
       "This module contains the YANG definition for BFD over LDP LSP group of sessions. LAG
        interfaces as per RFC7130.";

     revision 2016-02-17 {
       description "Initial revision.";
       reference "RFC XXXX: A group of " +
                 "sessions is to one LDP FEC, each session uses a " +
                 "different source UDP port YANG data model for ECMP.";
               leaf ldp-fec BFD over LAG";
     }

     augment "/bfd:bfd" {
                 type inet:ip-prefix;
       description "LDP FEC";
               } "BFD augmentation for LAG";
       container lag {
         description "BFD over LAG top level container";

         container config {
           description "BFD over LAG configuration container";
           container session-cfg {
             description "BFD over LAG session configuration";
             list session-ldp-lsp sessions {
               key "source-port"; "lag-name";
               description
                   "The BFD sessions "A LAG interface on an LDP FEC. Source UDP " +
                   "port which BFD is unique for each session in running";
               leaf lag-name {
                 type if:interface-ref ;
                 description "Name of the group."; LAG";
               }
               leaf ttl ipv4-dest-addr {
                 type ttl; inet:ipv4-address;
                 description "TTL
                   "IPv4 address of outgoing packets"; 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-all-session; 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 session-lag-micro member-links {
               key "member-link";
               description
                 "Micro-BFD over LAG. This represents BFD " +
                   "over 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-all-session; bfd:bfd-all-session;
               }
             }
           }
         }
       }
     }

     grouping bfd-notification-parms
     notification bfd-lag-notification {
       description
         "This group describes common parameters that will be sent
         "Notification for BFD over LAG session state change. " +
         "as part of BFD notification";
         "An implementation may rate-limit notifications, e.g. when a" +
         "session is continuously changing state.";

       uses bfd:bfd-notification-parms;

       leaf local-discr lag-name {
         type discriminator; if:interface-ref;
         description "BFD local discriminator"; "LAG interface name";
       }

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

       leaf new-state {
         type state;
         description "Current
     }
   }
   <CODE ENDS>

2.17.  BFD state"; over MPLS Yang Module

   <CODE BEGINS> file "ietf-bfd-mpls@2016-02-17.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";
     }

       leaf state-change-reason

     import ietf-inet-types {
         type string;
         description "BFD state change reason";
       prefix "inet";
     }

       leaf time-in-previous-state

     import ietf-routing {
         type string;
       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: Reshad Rahman
        Editor:   Lianshu Zheng and Reshad Rahman";

     description
           "How long
       "This module contains the YANG definition for BFD session was in the previous state"; parameters for
        MPLS LSPs as per RFC5884.";

     revision 2016-02-17 {
       description "Initial revision.";
       reference "RFC XXXX: A YANG data model for BFD over MPLS LSPs";
     }

       leaf dest-addr

     identity bfd-encap-gach {
         type inet:ip-address;
       base bfd:bfd-encap-type;
       description
         "BFD peer address"; with G-ACh encapsulation as per RFC5586.";
     }
       leaf source-addr

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

     grouping bfd-encap-cfg {
         type uint32;
       description "An index used to uniquely identify "Configuration for BFD sessions";
       } encapsulation";

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

     notification bfd-singlehop-notification

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

       leaf interface mpls-dest-address {
         type if:interface-ref; inet:ip-address;
         config "false";
         description "Interface to which this BFD session belongs to";
           "Destination address as per RFC5884.
            Needed if IP encapsulation is used";
       }

       leaf echo-enabled
     }

     augment "/bfd:bfd" {
         type boolean;
       description "Was echo enabled "BFD augmentation for BFD"; MPLS";
       container mpls {
         description "BFD MPLS top level container";

         container config {
           description "BFD MPLS configuration container";

           container egress {
             description "Egress configuration";

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

             uses bfd:bfd-auth-parms;
           }
         }

     notification bfd-multihop-notification

         container oper {
           config "false";
           description
         "Notification for BFD multi-hop session state change. An " +
         "implementation may rate-limit notifications, e.g. when a" +
         "session is continuously changing state."; "BFD MPLS operational container";
           uses bfd-notification-parms; bfd:bfd-session-statistics;
         }
     notification bfd-te-tunnel-notification
       }
     }

     augment "/rt:routing/rt:routing-instance/rt:routing-protocols/"
       + "rt:routing-protocol/bfd:bfd" {
       description
         "Notification "BFD augmentation for BFD over TE tunnel MPLS.";

       container mpls {
         description "BFD MPLS container";

         container config {
           description "BFD MPLS configuration container";

           container session-cfg {
             description "BFD MPLS session state change. " +
         "An implementation may rate-limit notifications, e.g. when a" +
         "session is continuously changing state.";
       uses bfd-notification-parms; configuration";
             list sessions {
               key "mpls-fec";
               description "List of BFD MPLS sessions";
               leaf tunnel-name mpls-fec {
                 type string; inet:ip-address;
                 description "TE tunnel to which this BFD session belongs to"; "MPLS FEC";
               }

               uses bfd:bfd-grouping-common-cfg-parms;
             }
     notification bfd-ldp-lsp-notification
           }
         }
         container oper {
           config "false";
           description
         "Notification for BFD over LDP LSP "BFD MPLS operational container";
           uses bfd:bfd-session-statistics;

           list session-group {
             key "mpls-fec";
             description
               "BFD MPLS group of sessions. A group of sessions is" +
               "for 1 FEC, each session state change. has a different field in " +
         "An implementation may rate-limit notifications, e.g. when a" +
         "session is continuously changing state.";
       uses bfd-notification-parms;
               "UDP/IP hdr for ECMP.";
             leaf ldp-fec mpls-fec {
               type inet:ip-prefix; inet:ip-address;
               description "LDP FEC"; "MPLS-FEC";
             }
       leaf source-port
             list sessions {
         type inet:port-number;
               key "local-discriminator";
               description "Source UDP port";
                 "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-lag-notification bfd-mpls-notification {
       description
         "Notification for BFD over LAG MPLS FEC session state change. " +
         "An implementation may rate-limit notifications, e.g. when a" +
         "session is continuously changing state.";

       uses bfd-notification-parms; bfd:bfd-notification-parms;

       leaf lag-name routing-instance {
         type if:interface-ref; rt:routing-instance-ref;
         description "LAG interface name"; "Routing instance";
       }

       leaf member-link mpls-dest-address {
         type if:interface-ref; inet:ip-address;
         description "Member link on which BFD
           "Destination address as per RFC5884.
            Needed if IP encapsulation is running"; used";

       }
     }
   }
   <CODE ENDS>

2.11.

2.18.  BFD Client Example Configuration Yang over MPLS-TEYang Module

   <CODE BEGINS> file "ietf-bfd-mpls-te@2016-02-17.yang"
   module example-bfd-routing-app ietf-bfd-mpls-te {
     namespace "urn:ietf:params:xml:ns:yang:example-bfd-routing-app"; "urn:ietf:params:xml:ns:yang:ietf-bfd-mpls-te";
     // replace with IANA namespace when assigned
     prefix bfd-routing-app; "bfd-mpls-te";

     import ietf-bfd {
       prefix "bfd";
     }

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

     import ietf-te {
       prefix "te";
     }

     organization
        "ACME"; "IETF BFD Working Group";

     contact
        "acme@acme.com";
       "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";

     description
        "Testing
       "This module contains the YANG definition for BFD grouping (simulating a routing application)"; parameters for
        MPLS Traffic Engineering as per RFC5884.";

     revision 2015-07-01 2016-02-04 {
       description "Initial revision.";
       reference "RFC XXXX: An example A YANG data model for BFD routing application"; over MPLS-TE";
     }

      feature routing-app-bfd

     augment "/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 under routing-app";
      }

      list area container";

           container egress {
        key "area-id";
             description "Specify a routing area.";

        leaf area-id "Egress configuration";

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

             uses bfd:bfd-auth-parms;
           }
         }

         container oper {
          type uint32;
           config "false";
           description "Area"; "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:bfd-client-base-cfg-parms bfd-mpls:bfd-encap-cfg;
     }

     augment "/te:te/te:lsps-state/te:lsp" {
          if-feature routing-app-bfd;
       when "/te:te/te:lsps-state/te:lsp/te:origin-type != 'transit'" {
         description "BFD information not needed at transit points";
       }

        list interface
       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 {
          key "interface";
       description "List of interfaces";
         "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 interface tunnel-name {
         type if:interface-ref; string;
         description "Interface";
          }
          uses bfd:bfd-client-base-cfg-parms {
            if-feature routing-app-bfd;
          } "MPLS-TE tunnel on which BFD was running.";
       }
     }
   }

2.12.
   <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.

2.13.

2.20.  IANA Considerations

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

   URI:TBD

2.14.

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.

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>.

   [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>.

3.2.  Informative References

   [I-D.ietf-netconf-restconf]
              Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", draft-ietf-netconf-restconf-07 draft-ietf-netconf-restconf-09 (work in
              progress), July December 2015.

   [I-D.ietf-netmod-routing-cfg]
              Lhotka, L. and A. Lindem, "A YANG Data Model for Routing
              Management", draft-ietf-netmod-routing-cfg-19 draft-ietf-netmod-routing-cfg-20 (work in
              progress), May October 2015.

   [I-D.ietf-rtgwg-yang-key-chain]
              Lindem, A., Qu, Y., Yeung, D., Chen, H., Zhang, J., and Y.
              Yang, "Key Chain YANG Data Model", draft-ietf-rtgwg-yang-
              key-chain-01 (work in progress), February 2016.

   [I-D.ietf-teas-yang-te]
              Saad, T., Gandhi, R., Liu, X., Beeram, V., Shah, H., Chen,
              X., Jones, R., and B. Wen, "A YANG Data Model for Traffic
              Engineering Tunnels and Interfaces", draft-ietf-teas-yang-
              te-02 (work in progress), October 2015.

Appendix A.  Change log

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

A.1.  Changes between versions -03 -00 and -04

   o  Follow VRF-centric model -01

   o  IP single-hop session  Remove BFD configuration parameters from BFD clients, all BFD
      configuration parameters in BFD clients

A.2.  Changes between versions -02 and -03

   o  Fixed date mismatch

   o  Updated authors

A.3.  Changes between versions -01 and -02

   o  Fixed errors and warnings from "pyang --ietf"

   o  Added appendix for "Change log"

A.4.  Changes between versions -00 and -01

   In the  YANG module section: split in multiple YANG modules (one per type of
      forwarding path)

   o  Added missing filename  For BFD over MPLS-TE we augment MPLS-TE model

   o  Added missing CODE ENDS  For BFD authentication we now use key-chain in
      [I-D.ietf-rtgwg-yang-key-chain]

Authors' Addresses

   Lianshu Zheng (editor)
   Huawei Technologies
   China

   Email: vero.zheng@huawei.com

   Reshad Rahman (editor)
   Cisco Systems
   Canada

   Email: rrahman@cisco.com

   Santosh Pallagatti
   Juniper Networks
   India

   Email: santoshpk@juniper.net santosh.pallagatti@gmail.com

   Mahesh Jethanandani
   Cisco Systems

   Email: mjethanandani@gmail.com

   Greg Mirsky
   Ericsson

   Email: gregory.mirsky@ericsson.com