Yang Data Model for Bidirectional Forwarding Detection (BFD)
draft-ietf-bfd-yang-02

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Network Working Group                                      L. Zheng, Ed.
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                          R. Rahman, Ed.
Expires: January 8, 2017                                   Cisco Systems
                                                           S. Pallagatti

                                                         M. Jethanandani
                                                           Cisco Systems
                                                               G. Mirsky
                                                                Ericsson
                                                            July 7, 2016

      Yang Data Model for Bidirectional Forwarding Detection (BFD)
                       draft-ietf-bfd-yang-02.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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

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

   This Internet-Draft will expire on January 8, 2017.

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Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Contributors  . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Design of the Data Model  . . . . . . . . . . . . . . . . . .   4
     2.1.  Design of Configuration Model . . . . . . . . . . . . . .   4
       2.1.1.  Common BFD configuration parameters . . . . . . . . .   5
       2.1.2.  Single-hop IP . . . . . . . . . . . . . . . . . . . .   6
       2.1.3.  Multi-hop IP  . . . . . . . . . . . . . . . . . . . .   6
       2.1.4.  MPLS Traffic Engineering Tunnels  . . . . . . . . . .   6
       2.1.5.  MPLS Label Switched Paths . . . . . . . . . . . . . .   7
       2.1.6.  Link Aggregation Groups . . . . . . . . . . . . . . .   7
     2.2.  Design of Operational Model . . . . . . . . . . . . . . .   7
     2.3.  Notifications . . . . . . . . . . . . . . . . . . . . . .   8
     2.4.  RPC Operations  . . . . . . . . . . . . . . . . . . . . .   8
     2.5.  BFD top level hierarchy . . . . . . . . . . . . . . . . .   8
     2.6.  BFD IP single-hop hierarchy . . . . . . . . . . . . . . .   9
     2.7.  BFD IP multi-hop hierarchy  . . . . . . . . . . . . . . .  11
     2.8.  BFD over LAG hierarchy  . . . . . . . . . . . . . . . . .  13
     2.9.  BFD over MPLS LSPs hierarchy  . . . . . . . . . . . . . .  15
     2.10. BFD over MPLS-TE hierarchy  . . . . . . . . . . . . . . .  17
     2.11. Examples  . . . . . . . . . . . . . . . . . . . . . . . .  19
     2.12. Interaction with other YANG modules . . . . . . . . . . .  19
     2.13. BFD top-level Yang Module . . . . . . . . . . . . . . . .  19
     2.14. BFD IP single-hop Yang Module . . . . . . . . . . . . . .  31
     2.15. BFD IP multi-hop Yang Module  . . . . . . . . . . . . . .  34
     2.16. BFD over LAG Yang Module  . . . . . . . . . . . . . . . .  37
     2.17. BFD over MPLS Yang Module . . . . . . . . . . . . . . . .  41
     2.18. BFD over MPLS-TE Yang Module  . . . . . . . . . . . . . .  44
     2.19. Security Considerations . . . . . . . . . . . . . . . . .  46
     2.20. IANA Considerations . . . . . . . . . . . . . . . . . . .  47
     2.21. Acknowledgements  . . . . . . . . . . . . . . . . . . . .  47
   3.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  47

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     3.1.  Normative References  . . . . . . . . . . . . . . . . . .  47
     3.2.  Informative References  . . . . . . . . . . . . . . . . .  48
   Appendix A.  Change log . . . . . . . . . . . . . . . . . . . . .  49
     A.1.  Changes between versions -01 and -02  . . . . . . . . . .  49
     A.2.  Changes between versions -00 and -01  . . . . . . . . . .  49
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  49

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 support sub-
   second failure detection, e.g.  OSPF and IS-IS.

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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 "network-instance" data node in [I-D.ietf-rtgwg-ni-model] 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 that new "bfd" node under
   "network-instance".

   Each node in 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.  Other
   parameters such as BFD authentication are not specific to the
   requirements of the BFD client.  To avoid splitting the BFD
   configuration between BFD clients and BFD, all the configuration is
   under BFD.  The only BFD configuration under BFD clients should be an
   "enable" knob which makes those clients react to BFD liveliness
   detection events.

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2.1.1.  Common BFD configuration parameters

   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, some implementations allow users to specify just
   one interval which is used for both transmit and receive intervals or
   separate values for transmit and receive intervals.  The BFD YANG
   model supports this: there is a choice between "min-interval", used
   for both transmit and receive intervals, and "desired-min-tx-
   interval" and "required-min-rx-interval".  This is supported via a
   grouping which is used by the YANG modules for the various forwarding
   paths.  There are also intervals for the echo function (if
   supported):

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

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

   For BFD authentication we have:

   key-chain
           This is a reference to key-chain defined in
           [I-D.ietf-rtgwg-yang-key-chain].  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].

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2.1.2.  Single-hop IP

   For single-hop IP, there is an augment of the "bfd" data node under
   "network-instance" in Section 2.  We have a list of IP single-hop
   sessions where each session is uniquely identified by the interface
   and destination address pair.  For the configuration parameters we
   use what is defined in Section 2.1.1

2.1.3.  Multi-hop IP

   For multi-hop IP, there is an augment of the "bfd" data node under
   "network-instance" 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.

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

   Here are some extra parameters:

   tx-ttl
           TTL of outgoing BFD control packets.

   rx-ttl
           Minimum TTL of incoming BFD control packets.

2.1.4.  MPLS Traffic Engineering Tunnels

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

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

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   encap
           Encapsulation for the BFD 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.  Since some MPLS-TE tunnels are uni-
   directional there is no MPLS-TE configuration for these tunnels on
   the egress node (note that this does not apply to bi-directional
   MPLS-TP tunnels).  The BFD parameters for the egress node are added
   under "mpls-te".

2.1.5.  MPLS Label Switched Paths

   Here we address MPLS LSPs whose FEC is an IP address.  The 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 uni-directional there is no LSP configuration on
   the egress node.  The BFD parameters for the egress node are added
   under "mpls".

2.1.6.  Link Aggregation Groups

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

2.2.  Design of Operational Model

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

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

   For each BFD session, mainly three categories of operational items
   are shown.  The fundamental information of a BFD session such as the
   local discriminator, remote discriminator and the capability of
   supporting demand detect mode are shown in the first category.  The
   second category includes a BFD session running information, e.g. the

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   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 local discriminator.

2.3.  Notifications

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

2.4.  RPC Operations

   TBD

2.5.  BFD top level hierarchy

   At the top level there is no configuration data, only operational
   data.  The operational data consist of overall BFD session statistics
   globally and per network-instance

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   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 /ni:network-instances/ni:network-instance:
      +--rw bfd!
         +--rw config
         +--ro oper
            +--ro bfd-session-statistics
               +--ro session-count?              uint32
               +--ro session-up-count?           uint32
               +--ro session-down-count?         uint32
               +--ro session-admin-down-count?   uint32

2.6.  BFD IP single-hop hierarchy

   The configuration and operational data for each BFD IP single-hop
   session is under "ip-sh" node under network-instance.  Overall BFD IP
   single-hop session statistics are available per network-instance and
   globally (for all network instances).

  module: ietf-bfd-ip-sh
  augment /bfd:bfd:
     +--rw ip-sh
        +--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 /ni:network-instances/ni:network-instance/bfd:bfd:
     +--rw ip-sh
        +--rw config
        |  +--rw session-cfg
        |     +--rw sessions* [interface dest-addr]
        |        +--rw interface                        if:interface-ref
        |        +--rw dest-addr                        inet:ip-address
        |        +--rw source-addr?                     inet:ip-address
        |        +--rw local-multiplier?                bfd-multiplier
        |        +--rw (interval-config-type)?
        |        |  +--:(tx-rx-intervals)
        |        |  |  +--rw desired-min-tx-interval          uint32

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        |        |  |  +--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 desired-min-echo-tx-interval?    uint32
        |        +--rw required-min-echo-rx-interval?   uint32
        +--ro oper
           +--ro bfd-session-statistics
           |  +--ro session-count?              uint32
           |  +--ro session-up-count?           uint32
           |  +--ro session-down-count?         uint32
           |  +--ro session-admin-down-count?   uint32
           +--ro sessions* [interface dest-addr]
              +--ro interface               if:interface-ref
              +--ro dest-addr               inet:ip-address
              +--ro source-addr?            inet:ip-address
              +--ro path-type?              identityref
              +--ro 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 session-index?             uint32
              |  +--ro local-state?               bfd-state
              |  +--ro remote-state?              bfd-state
              |  +--ro local-diagnostic?          bfd-diagnostic
              |  +--ro remote-diagnostic?         bfd-diagnostic
              |  +--ro detection-mode?            enumeration
              |  +--ro negotiated-tx-interval?    uint32
              |  +--ro negotiated-rx-interval?    uint32
              |  +--ro echo-tx-interval-in-use?   uint32
              |  +--ro detection-time?            uint32
              +--ro sesssion-statistics
                 +--ro create-time?            yang:date-and-time
                 +--ro last-down-time?         yang:date-and-time
                 +--ro last-up-time?           yang:date-and-time
                 +--ro down-count?             uint32
                 +--ro admin-down-count?       uint32
                 +--ro receive-packet-count?   uint64
                 +--ro send-packet-count?      uint64
                 +--ro receive-bad-packet?     uint64

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                 +--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 IP multi-hop hierarchy

   The configuration and operational data for each BFD IP multi-hop
   session is under "ip-mh" node under network-instance.  In the
   operational model we support multiple BFD multi-hop sessions per
   remote address (ECMP), the local discriminator is used as key.
   Overall BFD IP multi-hop session statistics are available per
   network-instance and globally (for all network instances).

   module: ietf-bfd-ip-mh
   augment /bfd:bfd:
      +--rw ip-mh
         +--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 /ni:network-instances/ni:network-instance/bfd:bfd:
      +--rw ip-mh
         +--rw config
         |  +--rw session-cfg
         |     +--rw sessions* [source-addr dest-addr]
         |        +--rw source-addr                 inet:ip-address
         |        +--rw dest-addr                   inet:ip-address
         |        +--rw local-multiplier?           bfd-multiplier
         |        +--rw (interval-config-type)?
         |        |  +--:(tx-rx-intervals)
         |        |  |  +--rw desired-min-tx-interval     uint32
         |        |  |  +--rw required-min-rx-interval    uint32
         |        |  +--:(single-interval)
         |        |     +--rw min-interval                uint32

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         |        +--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 tx-ttl?                     bfd:ttl
         |        +--rw rx-ttl                      bfd:ttl
         +--ro oper
            +--ro bfd-session-statistics
            |  +--ro bfd-session-statistics
            |     +--ro session-count?              uint32
            |     +--ro session-up-count?           uint32
            |     +--ro session-down-count?         uint32
            |     +--ro session-admin-down-count?   uint32
            +--ro session-group* [source-addr dest-addr]
               +--ro source-addr    inet:ip-address
               +--ro dest-addr      inet:ip-address
               +--ro sessions* [local-discriminator]
                  +--ro ttl?                    bfd:ttl
                  +--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
                  |  +--ro session-index?             uint32
                  |  +--ro local-state?               bfd-state
                  |  +--ro remote-state?              bfd-state
                  |  +--ro local-diagnostic?          bfd-diagnostic
                  |  +--ro remote-diagnostic?         bfd-diagnostic
                  |  +--ro detection-mode?            enumeration
                  |  +--ro negotiated-tx-interval?    uint32
                  |  +--ro negotiated-rx-interval?    uint32
                  |  +--ro echo-tx-interval-in-use?   uint32
                  |  +--ro detection-time?            uint32
                  +--ro sesssion-statistics
                     +--ro create-time?            yang:date-and-time
                     +--ro last-down-time?         yang:date-and-time
                     +--ro last-up-time?           yang:date-and-time
                     +--ro down-count?             uint32
                     +--ro admin-down-count?       uint32
                     +--ro receive-packet-count?   uint64
                     +--ro send-packet-count?      uint64
                     +--ro receive-bad-packet?     uint64
                     +--ro send-failed-packet?     uint64

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   notifications:
      +---n bfd-multihop-notification
         +--ro local-discr?              bfd-discriminator
         +--ro remote-discr?             bfd-discriminator
         +--ro new-state?                bfd-state
         +--ro state-change-reason?      string
         +--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 network-instance?         string

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
         |  +--rw session-cfg
         |     +--rw sessions* [lag-name]
         |        +--rw lag-name                    if:interface-ref
         |        +--rw ipv4-dest-addr?             inet:ipv4-address
         |        +--rw ipv6-dest-addr?             inet:ipv6-address
         |        +--rw local-multiplier?           bfd-multiplier
         |        +--rw (interval-config-type)?
         |        |  +--:(tx-rx-intervals)
         |        |  |  +--rw desired-min-tx-interval     uint32
         |        |  |  +--rw required-min-rx-interval    uint32
         |        |  +--:(single-interval)
         |        |     +--rw min-interval                uint32
         |        +--rw demand-enabled?             boolean
         |        +--rw admin-down?                 boolean
         |        +--rw authentication-parms! {bfd-authentication}?
         |           +--rw key-chain?           kc:key-chain-ref
         |           +--rw replay-protection?   identityref
         +--ro oper
            +--ro micro-bfd-ipv4-session-statistics
            |  +--ro bfd-session-statistics
            |     +--ro session-count?              uint32
            |     +--ro session-up-count?           uint32
            |     +--ro session-down-count?         uint32
            |     +--ro session-admin-down-count?   uint32
            +--ro micro-bfd-ipv6-session-statistics

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            |  +--ro bfd-session-statistics
            |     +--ro session-count?              uint32
            |     +--ro session-up-count?           uint32
            |     +--ro session-down-count?         uint32
            |     +--ro session-admin-down-count?   uint32
            +--ro session-lag* [lag-name]
               +--ro lag-name        if:interface-ref
               +--ro use-ipv4?       boolean
               +--ro use-ipv6?       boolean
               +--ro member-links* [member-link]
                  +--ro member-link       if:interface-ref
                  +--ro micro-bfd-ipv4
                  |  +--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
                  |  |  +--ro session-index?             uint32
                  |  |  +--ro local-state?               bfd-state
                  |  |  +--ro remote-state?              bfd-state
                  |  |  +--ro local-diagnostic?          bfd-diagnostic
                  |  |  +--ro remote-diagnostic?         bfd-diagnostic
                  |  |  +--ro detection-mode?            enumeration
                  |  |  +--ro negotiated-tx-interval?    uint32
                  |  |  +--ro negotiated-rx-interval?    uint32
                  |  |  +--ro echo-tx-interval-in-use?   uint32
                  |  |  +--ro detection-time?            uint32
                  |  +--ro sesssion-statistics
                  |     +--ro create-time?            yang:date-and-time
                  |     +--ro last-down-time?         yang:date-and-time
                  |     +--ro last-up-time?           yang:date-and-time
                  |     +--ro down-count?             uint32
                  |     +--ro admin-down-count?       uint32
                  |     +--ro receive-packet-count?   uint64
                  |     +--ro send-packet-count?      uint64
                  |     +--ro receive-bad-packet?     uint64
                  |     +--ro send-failed-packet?     uint64
                  +--ro micro-bfd-ipv6
                     +--ro path-type?              identityref
                     +--ro local-discriminator?    bfd-discriminator
                     +--ro remote-discriminator?   bfd-discriminator
                     +--ro remote-multiplier?      bfd-multiplier
                     +--ro out-interface?          if:interface-ref
                     +--ro demand-capability?      boolean

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                     +--ro source-port?            inet:port-number
                     +--ro dest-port?              inet:port-number
                     +--ro session-running
                     |  +--ro session-index?             uint32
                     |  +--ro local-state?               bfd-state
                     |  +--ro remote-state?              bfd-state
                     |  +--ro local-diagnostic?          bfd-diagnostic
                     |  +--ro remote-diagnostic?         bfd-diagnostic
                     |  +--ro detection-mode?            enumeration
                     |  +--ro negotiated-tx-interval?    uint32
                     |  +--ro negotiated-rx-interval?    uint32
                     |  +--ro echo-tx-interval-in-use?   uint32
                     |  +--ro detection-time?            uint32
                     +--ro sesssion-statistics
                        +--ro create-time?            yang:date-and-time
                        +--ro last-down-time?         yang:date-and-time
                        +--ro last-up-time?           yang:date-and-time
                        +--ro down-count?             uint32
                        +--ro admin-down-count?       uint32
                        +--ro receive-packet-count?   uint64
                        +--ro send-packet-count?      uint64
                        +--ro receive-bad-packet?     uint64
                        +--ro send-failed-packet?     uint64
   notifications:
      +---n bfd-lag-notification
         +--ro local-discr?              bfd-discriminator
         +--ro remote-discr?             bfd-discriminator
         +--ro new-state?                bfd-state
         +--ro state-change-reason?      string
         +--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 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
   module: ietf-bfd-mpls
   augment /bfd:bfd:
      +--rw mpls
         +--rw config

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         |  +--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 /ni:network-instances/ni:network-instance/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?   bfd-discriminator
                  +--ro remote-multiplier?      bfd-multiplier

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                  +--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 session-index?             uint32
                  |  +--ro local-state?               bfd-state
                  |  +--ro remote-state?              bfd-state
                  |  +--ro local-diagnostic?          bfd-diagnostic
                  |  +--ro remote-diagnostic?         bfd-diagnostic
                  |  +--ro detection-mode?            enumeration
                  |  +--ro negotiated-tx-interval?    uint32
                  |  +--ro negotiated-rx-interval?    uint32
                  |  +--ro echo-tx-interval-in-use?   uint32
                  |  +--ro detection-time?            uint32
                  +--ro sesssion-statistics
                  |  +--ro create-time?            yang:date-and-time
                  |  +--ro last-down-time?         yang:date-and-time
                  |  +--ro last-up-time?           yang:date-and-time
                  |  +--ro down-count?             uint32
                  |  +--ro admin-down-count?       uint32
                  |  +--ro receive-packet-count?   uint64
                  |  +--ro send-packet-count?      uint64
                  |  +--ro receive-bad-packet?     uint64
                  |  +--ro send-failed-packet?     uint64
                  +--ro mpls-dest-address?      inet:ip-address
   notifications:
      +---n bfd-mpls-notification
         +--ro local-discr?              bfd-discriminator
         +--ro remote-discr?             bfd-discriminator
         +--ro new-state?                bfd-state
         +--ro state-change-reason?      string
         +--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 network-instance?         string
         +--ro 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:

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      +--rw mpls-te
         +--rw config
         |  +--rw egress
         |     +--rw local-multiplier?           bfd-multiplier
         |     +--rw (interval-config-type)?
         |     |  +--:(tx-rx-intervals)
         |     |  |  +--rw desired-min-tx-interval     uint32
         |     |  |  +--rw required-min-rx-interval    uint32
         |     |  +--:(single-interval)
         |     |     +--rw min-interval                uint32
         |     +--rw authentication-parms! {bfd-authentication}?
         |        +--rw key-chain?           kc:key-chain-ref
         |        +--rw replay-protection?   identityref
         +--ro oper
            +--ro bfd-session-statistics
               +--ro session-count?              uint32
               +--ro session-up-count?           uint32
               +--ro session-down-count?         uint32
               +--ro session-admin-down-count?   uint32
   augment /te:te/te:tunnels/te:tunnel/te:config:
      +--rw local-multiplier?           bfd-multiplier
      +--rw (interval-config-type)?
      |  +--:(tx-rx-intervals)
      |  |  +--rw desired-min-tx-interval     uint32
      |  |  +--rw required-min-rx-interval    uint32
      |  +--:(single-interval)
      |     +--rw min-interval                uint32
      +--rw demand-enabled?             boolean
      +--rw admin-down?                 boolean
      +--rw authentication-parms! {bfd-authentication}?
      |  +--rw key-chain?           kc:key-chain-ref
      |  +--rw replay-protection?   identityref
      +--rw encap?                      identityref
   augment /te:te/te:lsps-state/te:lsp:
      +--ro path-type?              identityref
      +--ro 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 session-index?             uint32
      |  +--ro local-state?               bfd-state
      |  +--ro remote-state?              bfd-state
      |  +--ro local-diagnostic?          bfd-diagnostic
      |  +--ro remote-diagnostic?         bfd-diagnostic

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      |  +--ro detection-mode?            enumeration
      |  +--ro negotiated-tx-interval?    uint32
      |  +--ro negotiated-rx-interval?    uint32
      |  +--ro echo-tx-interval-in-use?   uint32
      |  +--ro detection-time?            uint32
      +--ro sesssion-statistics
      |  +--ro create-time?            yang:date-and-time
      |  +--ro last-down-time?         yang:date-and-time
      |  +--ro last-up-time?           yang:date-and-time
      |  +--ro down-count?             uint32
      |  +--ro admin-down-count?       uint32
      |  +--ro receive-packet-count?   uint64
      |  +--ro send-packet-count?      uint64
      |  +--ro receive-bad-packet?     uint64
      |  +--ro send-failed-packet?     uint64
      +--ro mpls-dest-address?      inet:ip-address
   notifications:
      +---n bfd-mpls-te-notification
         +--ro local-discr?              bfd-discriminator
         +--ro remote-discr?             bfd-discriminator
         +--ro new-state?                bfd-state
         +--ro state-change-reason?      string
         +--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 mpls-dest-address?        inet:ip-address
         +--ro tunnel-name?              string

2.11.  Examples

2.12.  Interaction with other YANG modules

   TBD.

2.13.  BFD top-level Yang Module

   <CODE BEGINS> file "ietf-bfd@2016-07-04.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";
     }

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

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

     import ietf-routing {
       prefix "rt";
     }

     import ietf-network-instance {
       prefix "ni";
     }

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

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

     revision 2016-07-04 {
       description "Initial revision.";
       reference "RFC XXXX: A YANG data model for BFD";
     }

     identity bfd {
       base "rt:routing-protocol";
       description "BFD protocol";
     }

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

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     }

     typedef 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 bfd-state {
       type enumeration {
         enum adminDown {
           value 0;

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           description "admindown";
         }
         enum down {
           value 1;
           description "down";
         }
         enum init {
           value 2;
           description "init";
         }
         enum up {
           value 3;
           description "up";
         }
       }
       description "BFD state";
     }

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

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

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

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     }
     identity bfd-path-mpls-lsp {
       base bfd-path-type;
       description "BFD on MPLS Label Switched Path";
     }
     identity bfd-path-lag {
       base bfd-path-type;
       description "Micro-BFD on LAG member links";
     }

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

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

     identity bfd-auth-replay-protection {
       description
         "Base identity for BFD authentication replay protection";
     }
     identity bfd-auth-replay-protection-non-meticulous {
       base bfd-auth-replay-protection;
       description "Non-meticulous (see RFC5880)";
     }
     identity bfd-auth-replay-protection-meticulous {
       base bfd-auth-replay-protection;
       description "Meticulous (see RFC5880)";
     }

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

         leaf key-chain {
           type kc:key-chain-ref;

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           description "Name of key-chain";
         }

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

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

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

           leaf required-min-rx-interval {
             type uint32;
             units microseconds;
             mandatory true;
             description
               "Required minimum receive interval of control packets";
           }
         }
         case single-interval {
           leaf min-interval {
             type uint32;
             units microseconds;
             mandatory true;
             description

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               "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 enable demand mode";
       }

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

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

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

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

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

     grouping bfd-all-session {
       description "BFD session operational information";
       leaf path-type {
         type identityref {
           base bfd-path-type;
         }
         description
           "BFD session type, this indicates the path type that BFD is
           running on";
       }
       leaf local-discriminator {
         type bfd-discriminator;
         description "Local discriminator";
       }
       leaf remote-discriminator {
         type bfd-discriminator;
         description "Remote discriminator";
       }
       leaf remote-multiplier {
         type 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";
       }

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       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 bfd-state;
           description "Local state";
         }
         leaf remote-state {
           type bfd-state;
           description "Remote state";
         }
         leaf local-diagnostic {
           type bfd-diagnostic;
           description "Local diagnostic";
         }
         leaf remote-diagnostic {
           type 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";

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         }
         leaf negotiated-rx-interval {
           type uint32;
           units microseconds;
           description "Negotiated receive interval";
         }
         leaf 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 "Echo transmit interval in use";
         }
         leaf detection-time {
           type uint32;
           units microseconds;
           description "Detection time";
         }
       }

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

         leaf create-time {
           type yang:date-and-time;
           description
             "Time and date when session was created";
         }
         leaf last-down-time {
           type yang:date-and-time;
           description
             "Time and date of last time the session went down";
         }
         leaf last-up-time {
           type yang:date-and-time;
           description
             "Time and date of last time the session went up";
         }
         leaf down-count {
           type uint32;
           description "Session Down Count";
         }
         leaf admin-down-count {
           type uint32;
           description "Session Admin-Down Count";
         }

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         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 {

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         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";
       }
     }

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     augment "/ni:network-instances/ni:network-instance" {
       description "BFD augmentation.";

       container bfd {
         presence "BFD";
         description "BFD top level container";
         container 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@2016-07-04.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 {

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       prefix "if";
     }

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

     import ietf-network-instance {
       prefix "ni";
     }

     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 2016-01-04 {
       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 "/ni:network-instances/ni:network-instance/bfd:bfd" {
       description "BFD augmentation for IP single-hop.";

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

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

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

             uses bfd:bfd-all-session;
           }
         }
       }
     }

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

       uses bfd:bfd-notification-parms;

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

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

   }
   <CODE ENDS>

2.15.  BFD IP multi-hop Yang Module

   <CODE BEGINS> file "ietf-bfd-ip-mh@2016-07-04.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";

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     }

     import ietf-network-instance {
       prefix "ni";
     }

     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 2016-07-04 {
       description "Initial revision.";
       reference "RFC XXXX: A YANG data model for BFD IP multi-hop";
     }

     augment "/bfd:bfd" {
       description "BFD augmentation for IP multi-hop";
       container ip-mh {
         description "BFD IP multi-hop top level container";

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

     augment "/ni:network-instances/ni:network-instance/bfd:bfd" {
       description "BFD augmentation for IP multi-hop.";

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

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             description "BFD IP multi-hop session configuration";

             list sessions {
               key "source-addr dest-addr";
               description "List of IP multi-hop sessions";

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

               leaf tx-ttl {
                 type bfd:ttl;
                 default 255;
                 description "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:bfd-session-statistics;
           }

           list 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, " +

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               "each session has a different field in UDP/IP hdr for " +
               "ECMP.";
             leaf source-addr {
               type inet:ip-address;
               description "BFD source address";
             }
             leaf dest-addr {
               type inet:ip-address;
               description "BFD peer address";
             }
             list sessions {
               key "local-discriminator";
               description
                 "The BFD sessions between a source and a. " +
                 "destination. Local discriminator is unique for " +
                 "each session in the group.";
               leaf ttl {
                 type bfd:ttl;
                 description "TTL of outgoing packets";
               }
               uses bfd:bfd-all-session;
             }
           }
         }
       }
     }

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

       uses bfd:bfd-notification-parms;

       leaf network-instance {
         type string;
         description "Network instance";
       }
     }
   }
   <CODE ENDS>

2.16.  BFD over LAG Yang Module

   <CODE BEGINS> file "ietf-bfd-lag@2016-02-17.yang"
   module ietf-bfd-lag {
     namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-lag";

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

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

     augment "/bfd:bfd" {
       description "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 sessions {
               key "lag-name";
               description "A LAG interface on which BFD is running";
               leaf lag-name {
                 type if:interface-ref ;
                 description "Name of the LAG";

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               }
               leaf ipv4-dest-addr {
                 type inet:ipv4-address;
                 description
                   "IPv4 address of the peer, for IPv4 micro-BFD.";
               }
               leaf ipv6-dest-addr {
                 type inet:ipv6-address;
                 description
                   "IPv6 address of the peer, for IPv6 micro-BFD.";
               }
               uses bfd:bfd-grouping-common-cfg-parms;
             }
           }
         }

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

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

           list session-lag {
             key "lag-name";
             description "A LAG interface on which BFD is running";
             leaf lag-name {
               type if:interface-ref ;
               description "Name of the LAG";
             }

             leaf use-ipv4 {
               type boolean;
               description "Using IPv4 micro-BFD.";
             }
             leaf use-ipv6 {
               type boolean;
               description "Using IPv6 micro-BFD.";
             }

             list member-links {
               key "member-link";

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               description
                 "Micro-BFD over LAG. This represents one member link";

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

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

       uses bfd:bfd-notification-parms;

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

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

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   }
   <CODE ENDS>

2.17.  BFD over MPLS Yang Module

   <CODE BEGINS> file "ietf-bfd-mpls@2016-07-04.yang"
   module ietf-bfd-mpls {
     namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-mpls";
     // replace with IANA namespace when assigned
     prefix "bfd-mpls";

     import ietf-bfd {
       prefix "bfd";
     }

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

     import ietf-network-instance {
       prefix "ni";
     }

     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 parameters for
        MPLS LSPs as per RFC5884.";

     revision 2016-07-04 {
       description "Initial revision.";
       reference "RFC XXXX: A YANG data model for BFD over MPLS LSPs";
     }

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

     identity bfd-encap-ip-gach {

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

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

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

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

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

     augment "/bfd:bfd" {
       description "BFD augmentation for 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;
           }
         }

         container oper {

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

     augment "/ni:network-instances/ni:network-instance/bfd:bfd" {
       description "BFD augmentation for MPLS.";

       container mpls {
         description "BFD MPLS container";

         container config {
           description "BFD MPLS configuration container";

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

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

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

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

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

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

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

       uses bfd:bfd-notification-parms;

       leaf network-instance {
         type string;
         description "Network instance";
       }

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

2.18.  BFD over MPLS-TE Yang Module

   <CODE BEGINS> file "ietf-bfd-mpls-te@2016-02-04.yang"
   module ietf-bfd-mpls-te {
     namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-mpls-te";
     // replace with IANA namespace when assigned
     prefix "bfd-mpls-te";

     import ietf-bfd {
       prefix "bfd";
     }

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

     import ietf-te {
       prefix "te";
     }

     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 parameters for
        MPLS Traffic Engineering as per RFC5884.";

     revision 2016-02-04 {
       description "Initial revision.";
       reference "RFC XXXX: A YANG data model for BFD over MPLS-TE";
     }

     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 container";

           container egress {
             description "Egress configuration";

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

             uses bfd:bfd-auth-parms;
           }
         }

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

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       }
     }

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

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

       uses bfd-mpls:bfd-encap-cfg;
     }

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

       uses bfd:bfd-all-session;

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

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

       uses bfd:bfd-notification-parms;

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

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

2.19.  Security Considerations

   The YANG module defined in this memo is designed to be accessed via
   the NETCONF protocol [RFC6241].  The lowest NETCONF layer is the
   secure transport layer and the mandatory to implement secure
   transport is SSH [RFC6242].  The NETCONF access control model
   [RFC6536] provides the means to restrict access for particular

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   NETCONF users to a pre-configured subset of all available NETCONF
   protocol operations and content.

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

2.20.  IANA Considerations

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

   URI:TBD

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>.

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   [RFC5882]  Katz, D. and D. Ward, "Generic Application of
              Bidirectional Forwarding Detection (BFD)", RFC 5882,
              DOI 10.17487/RFC5882, June 2010,
              <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-14 (work in
              progress), June 2016.

   [I-D.ietf-netmod-routing-cfg]
              Lhotka, L. and A. Lindem, "A YANG Data Model for Routing
              Management", draft-ietf-netmod-routing-cfg-22 (work in
              progress), July 2016.

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   [I-D.ietf-rtgwg-ni-model]
              Berger, L., Hopps, C., Lindem, A., and D. Bogdanovic,
              "Network Instance Model", draft-ietf-rtgwg-ni-model-00
              (work in progress), June 2016.

   [I-D.ietf-rtgwg-yang-key-chain]
              Lindem, A., Qu, Y., Yeung, D., Chen, I., Zhang, Z., and Y.
              Yang, "Routing Key Chain YANG Data Model", draft-ietf-
              rtgwg-yang-key-chain-06 (work in progress), June 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-03 (work in progress), March 2016.

Appendix A.  Change log

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

A.1.  Changes between versions -01 and -02

   o  Replace routing-instance, which has been removed from
      [I-D.ietf-netmod-routing-cfg], with network-instance from
      [I-D.ietf-rtgwg-ni-model]

A.2.  Changes between versions -00 and -01

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

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

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

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

Authors' Addresses

   Lianshu Zheng (editor)
   Huawei Technologies
   China

   Email: vero.zheng@huawei.com

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   Reshad Rahman (editor)
   Cisco Systems
   Canada

   Email: rrahman@cisco.com

   Santosh Pallagatti
   India

   Email: santosh.pallagatti@gmail.com

   Mahesh Jethanandani
   Cisco Systems

   Email: mjethanandani@gmail.com

   Greg Mirsky
   Ericsson

   Email: gregory.mirsky@ericsson.com

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