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Versions: 00 01 02 03 04 draft-ietf-bfd-yang

Network Working Group                                      L. Zheng, Ed.
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                          R. Rahman, Ed.
Expires: January 6, 2016                                   Cisco Systems
                                                           S. Pallagatti
                                                        Juniper Networks
                                                         M. Jethanandani
                                                           Cisco Systems
                                                               G. Mirsky
                                                                Ericsson
                                                           July 05, 2015


      Yang Data Model for Bidirectional Forwarding Detection (BFD)
                      draft-zheng-bfd-yang-04.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 6, 2016.








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Copyright Notice

   Copyright (c) 2015 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  . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Design of the Data Model  . . . . . . . . . . . . . . . . . .   3
     2.1.  Design of Configuration Model . . . . . . . . . . . . . .   4
       2.1.1.  Single-hop IP . . . . . . . . . . . . . . . . . . . .   4
       2.1.2.  Multi-hop IP  . . . . . . . . . . . . . . . . . . . .   5
       2.1.3.  Traffic Engineering Tunnels . . . . . . . . . . . . .   6
       2.1.4.  LDP Label Switched Paths  . . . . . . . . . . . . . .   6
       2.1.5.  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  . . . . . . . . . . . .   8
       2.5.1.  Centralized BFD Configuration . . . . . . . . . . . .   8
       2.5.2.  Configuration in BFD clients  . . . . . . . . . . . .   9
     2.6.  Operational Data Hierarchy  . . . . . . . . . . . . . . .  11
     2.7.  Notifications . . . . . . . . . . . . . . . . . . . . . .  14
     2.8.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .  16
     2.9.  Interaction with other YANG modules . . . . . . . . . . .  16
     2.10. BFD Yang Module . . . . . . . . . . . . . . . . . . . . .  16
     2.11. BFD Client Example Configuration Yang Module  . . . . . .  33
     2.12. Security Considerations . . . . . . . . . . . . . . . . .  34
     2.13. IANA Considerations . . . . . . . . . . . . . . . . . . .  34
     2.14. Acknowledgements  . . . . . . . . . . . . . . . . . . . .  35
   3.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  35
     3.1.  Normative References  . . . . . . . . . . . . . . . . . .  35
     3.2.  Informative References  . . . . . . . . . . . . . . . . .  35
   Appendix A.  Change log . . . . . . . . . . . . . . . . . . . . .  36
     A.1.  Changes between versions -03 and -04  . . . . . . . . . .  36
     A.2.  Changes between versions -02 and -03  . . . . . . . . . .  36



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     A.3.  Changes between versions -01 and -02  . . . . . . . . . .  36
     A.4.  Changes between versions -00 and -01  . . . . . . . . . .  36
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  36

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

1.1.  Contributors

2.  Design of the Data Model

   The BFD YANG data model follows a VRF-centric model by augmenting the
   "routing-protocol" data node in [I-D.ietf-netmod-routing-cfg].






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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 are to be used by BFD clients.  Other parameters
   which remain under BFD control, e.g. demand mode and authentication,
   are configured under BFD.

   We provide groupings, which contain the basic BFD session parameters,
   for applications to use.  This ensures consistency of BFD parameters
   across applications.

   Although [RFC5880] allows for different values for transmit and
   receive intervals, many 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 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".


2.1.1.  Single-hop IP

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

   - This provides consistency since the same grouping 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 the respective YANG modules.

   An application importing the BFD configuration grouping could do so
   in a hierarchical manner if it has multiple levels at which BFD



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   configuration can be applied.  In a subsequent section, we provide an
   example of how a BFD client would use the grouping in such a way.

   The configuration items are:

   enabled
           Set to true to enable BFD.

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

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

           OR

   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].

2.1.2.  Multi-hop IP

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

   required-min-rx-interval



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           This 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.

   tx-ttl
           TTL of outgoing BFD control packets.

   rx-ttl
           Minimum TTL of incoming BFD control packets.

2.1.3.  Traffic Engineering Tunnels

   For Traffic Engineering (TE) tunnels, BFD is configured under the 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 the TE application for the
   basic BFD parameters.  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 application.

2.1.4.  LDP Label Switched Paths

   For LDP LSPs, BFD is configured under the LDP FEC.  The grouping for
   BFD clients in Section 2.1.1 can be used by the LDP application for
   the basic BFD parameters.  For BFD parameters which are specific to
   the LDP application, if any, these parameters will be defined in the
   YANG model of the LDP application.

2.1.5.  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 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 of the peer system which can be reached by the LAG,




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   the parameters will be defined in the YANG model of the LAG
   application.

2.1.6.  Per-interface Configuration

   With multiplier and intervals configured under the BFD clients, 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 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].

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 of arbitrary
   paths, there is no uniform key to identify a BFD session.  E.g. a BFD
   single-hop IP session is uniquely identified by the combination of
   destination IP address and interface whereas a multihop IP session is
   uniquely identified by the combination of source IP address and
   destination IP address (in the context of a VRF).  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,
   mainly three categories of operational items are shown.  The
   fundamental information of a BFD session such as the local



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   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 and 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


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.


2.4.  RPC Operations

   TBD

2.5.  BFD Configuration Data Hierarchy

2.5.1.  Centralized BFD Configuration

   The following is the centralized configuration data hierarchy:

   We have a container which contains a list for each session type.
   This contains session configuration for only IP multi-hop sessions.

   We have per-interface configuration for authentication, demand-mode,
   etc.  This is used e.g. for IP single-hop sessions whose base BFD
   configuration belongs to the BFD clients.





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   module: ietf-bfd
   augment /rt:routing/rt:routing-instance/rt:routing-protocols/
            rt:routing-protocol:
      +--rw bfd
         +--rw bfd-cfg
         |  +--rw bfd-session-cfg
         |  |  +--rw session-ip-mh* [source-addr dest-addr]
         |  |     +--rw source-addr                 inet:ip-address
         |  |     +--rw dest-addr                   inet:ip-address
         |  |     +--rw admin-down?                 boolean
         |  |     +--rw local-multiplier?           multiplier
         |  |     +--rw (interval-config-type)?
         |  |     |  +--:(tx-rx-intervals)
         |  |     |  |  +--rw desired-min-tx-interval     uint32
         |  |     |  |  +--rw required-min-rx-interval    uint32
         |  |     |  +--:(single-interval)
         |  |     |     +--rw min-interval                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 tx-ttl?                     ttl
         |  |     +--rw rx-ttl                      ttl
         |  +--rw bfd-interface-cfg* [interface] {bfd-interface-config}?
         |     +--rw interface                        if:interface-ref
         |     +--rw local-multiplier?                multiplier
         |     +--rw (interval-config-type)?
         |     |  +--:(tx-rx-intervals)
         |     |  |  +--rw desired-min-tx-interval          uint32
         |     |  |  +--rw required-min-rx-interval         uint32
         |     |  +--:(single-interval)
         |     |     +--rw min-interval                     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?    uint32
         |     +--rw required-min-echo-rx-interval?   uint32

2.5.2.  Configuration in BFD clients

   The following is the configuration data hierarchy for a hypothetical
   BFD client called example-bfd-routing-app.  The BFD configuration is
   supported conditionally via use of if-feature.





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   We have a list of areas and in 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 is applied under an interface, that
   configuration takes precedence over any BFD configuration, if any, at
   the area level

   - If BFD configuration is applied 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 the BFD client implementation supports "interface all", then all
   the interfaces belonging to that area will inherit the BFD
   configuration under "interface all".  Additionally, if there is
   specific interface configuration, then the specific interface will
   override the "interface all" parameters.

   - The tx and rx intervals can be configured separately or a single
   interval can be configured.

   module: example-bfd-routing-app
      +--rw area* [area-id]
         +--rw area-id      uint32
         +--rw bfd-cfg
         |  +--rw enabled?                    boolean
         |  +--rw local-multiplier?           multiplier
         |  +--rw (interval-config-type)?
         |     +--:(tx-rx-intervals)
         |     |  +--rw desired-min-tx-interval     uint32
         |     |  +--rw required-min-rx-interval    uint32
         |     +--:(single-interval)
         |        +--rw min-interval                uint32
         +--rw interface* [interface]
            +--rw interface    if:interface-ref
            +--rw bfd-cfg
               +--rw enabled?                    boolean
               +--rw local-multiplier?           multiplier
               +--rw (interval-config-type)?
                  +--:(tx-rx-intervals)
                  |  +--rw desired-min-tx-interval     uint32
                  |  +--rw required-min-rx-interval    uint32
                  +--:(single-interval)
                     +--rw min-interval                uint32






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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:
      +--rw bfd
         +--ro bfd-oper
            +--ro bfd-session-statistics
            |  +--ro ip-sh-session-num?     uint32
            |  +--ro ip-mh-session-num?     uint32
            |  +--ro total-session-num?     uint32
            |  +--ro session-up-num?        uint32
            |  +--ro sess-down-num?         uint32
            |  +--ro sess-admin-down-num?   uint32
            +--ro bfd-session-lists
               +--ro session-ip-sh* [interface dest-addr]
               |  +--ro interface               if:interface-ref
               |  +--ro dest-addr               inet:ip-address
               |  +--ro source-addr?            inet:ip-address
               |  +--ro session-type?           bfd-session-type
               |  +--ro local-discriminator?    discriminator
               |  +--ro remote-discriminator?   discriminator
               |  +--ro remote-multiplier?      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?                   state
               |  |  +--ro remote-state?                  state
               |  |  +--ro local-diagnostic?              diagnostic
               |  |  +--ro remote-diagnostic?             diagnostic
               |  |  +--ro detection-mode?                enumeration
               |  |  +--ro negotiated-tx-interval?        uint32
               |  |  +--ro negotiated-rx-interval?        uint32
               |  |  +--ro negotiated-echo-tx-interval?   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



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               |     +--ro receive-packet-count?   uint64
               |     +--ro send-packet-count?      uint64
               |     +--ro receive-bad-packet?     uint64
               |     +--ro send-failed-packet?     uint64
               +--ro session-ip-mh-group* [source-addr dest-addr]
               |  +--ro source-addr      inet:ip-address
               |  +--ro dest-addr        inet:ip-address
               |  +--ro session-ip-mh* [source-port]
               |     +--ro ttl?                    ttl
               |     +--ro session-type?           bfd-session-type
               |     +--ro local-discriminator?    discriminator
               |     +--ro remote-discriminator?   discriminator
               |     +--ro remote-multiplier?      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?                   state
               |     |  +--ro remote-state?                  state
               |     |  +--ro local-diagnostic?              diagnostic
               |     |  +--ro remote-diagnostic?             diagnostic
               |     |  +--ro detection-mode?                enumeration
               |     |  +--ro negotiated-tx-interval?        uint32
               |     |  +--ro negotiated-rx-interval?        uint32
               |     |  +--ro negotiated-echo-tx-interval?   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 session-te-tunnel* [tunnel-name]
               |  +--ro tunnel-name             string
               |  +--ro session-type?           bfd-session-type
               |  +--ro local-discriminator?    discriminator
               |  +--ro remote-discriminator?   discriminator
               |  +--ro remote-multiplier?      multiplier
               |  +--ro out-interface?          if:interface-ref
               |  +--ro demand-capability?      boolean
               |  +--ro source-port?            inet:port-number
               |  +--ro dest-port?              inet:port-number



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               |  +--ro session-running*
               |  |  +--ro session-index?                 uint32
               |  |  +--ro local-state?                   state
               |  |  +--ro remote-state?                  state
               |  |  +--ro local-diagnostic?              diagnostic
               |  |  +--ro remote-diagnostic?             diagnostic
               |  |  +--ro detection-mode?                enumeration
               |  |  +--ro negotiated-tx-interval?        uint32
               |  |  +--ro negotiated-rx-interval?        uint32
               |  |  +--ro negotiated-echo-tx-interval?   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 session-ldp-lsp-group* [ldp-fec]
               |  +--ro ldp-fec            inet:ip-prefix
               |  +--ro session-ldp-lsp* [source-port]
               |     +--ro ttl?                    ttl
               |     +--ro session-type?           bfd-session-type
               |     +--ro local-discriminator?    discriminator
               |     +--ro remote-discriminator?   discriminator
               |     +--ro remote-multiplier?      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?                   state
               |     |  +--ro remote-state?                  state
               |     |  +--ro local-diagnostic?              diagnostic
               |     |  +--ro remote-diagnostic?             diagnostic
               |     |  +--ro detection-mode?                enumeration
               |     |  +--ro negotiated-tx-interval?        uint32
               |     |  +--ro negotiated-rx-interval?        uint32
               |     |  +--ro negotiated-echo-tx-interval?   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



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               |        +--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-lag* [lag-name]
                  +--ro lag-name             if:interface-ref
                  +--ro session-lag-micro* [member-link]
                     +--ro member-link             if:interface-ref
                     +--ro session-type?           bfd-session-type
                     +--ro local-discriminator?    discriminator
                     +--ro remote-discriminator?   discriminator
                     +--ro remote-multiplier?      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?                   state
                     |  +--ro remote-state?                  state
                     |  +--ro local-diagnostic?              diagnostic
                     |  +--ro remote-diagnostic?             diagnostic
                     |  +--ro detection-mode?                enumeration
                     |  +--ro negotiated-tx-interval?        uint32
                     |  +--ro negotiated-rx-interval?        uint32
                     |  +--ro negotiated-echo-tx-interval?   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


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/



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            rt:routing-protocol:
   notifications:
      +---n bfd-singlehop-notification
      |  +--ro local-discr?              discriminator
      |  +--ro remote-discr?             discriminator
      |  +--ro new-state?                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
      |  +--ro interface?                if:interface-ref
      |  +--ro echo-enabled?             boolean
      +---n bfd-multihop-notification
      |  +--ro local-discr?              discriminator
      |  +--ro remote-discr?             discriminator
      |  +--ro new-state?                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
      +---n bfd-te-tunnel-notification
      |  +--ro local-discr?              discriminator
      |  +--ro remote-discr?             discriminator
      |  +--ro new-state?                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
      |  +--ro tunnel-name?              string
      +---n bfd-ldp-lsp-notification
      |  +--ro local-discr?              discriminator
      |  +--ro remote-discr?             discriminator
      |  +--ro new-state?                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
      |  +--ro ldp-fec?                  inet:ip-prefix
      |  +--ro source-port?              inet:port-number
      +---n bfd-lag-notification



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         +--ro local-discr?              discriminator
         +--ro remote-discr?             discriminator
         +--ro new-state?                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.  Examples

2.9.  Interaction with other YANG modules

   TBD.

2.10.  BFD Yang Module

   <CODE BEGINS> file "ietf-bfd@2015-07-01.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";
     }

     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
        Editor:   Lianshu Zheng and Reshad Rahman";



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     description
       "This module contains the YANG definition for BFD parameters as
        per RFC5880, RFC5881 and RFC5883";

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

     typedef 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 {



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           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 {
       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 {
       type uint8 {
         range 1..255;
       }
       description "Multiplier";
     }

     typedef ttl {
       type uint8 {
         range 1..255;
       }



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       description "Time To Live";
     }

     typedef bfd-session-type {
       type enumeration {
         enum ip-single-hop {
           description "IP single hop";
         }
         enum ip-multi-hop {
           description "IP multi hop";
         }
         enum te-tunnel {
           description "Traffic Engineering tunnes";
         }
         enum ldp-lsp {
           description "LDP Label Switched Path";
         }
         enum lag {
           description "Micro-BFD on LAG member links";
         }
       }
       description
         "BFD session type, this indicates the path type that BFD is
          running on";
     }

     typedef bfd-auth-algorithm {
       type enumeration {
         enum simple-password {
           description
             "Simple password";
         }

         enum keyed-md5 {
           description
             "Keyed message Digest 5";
         }

         enum meticulous-keyed-md5 {
           description
             "Meticulous keyed message Digest 5";
         }

         enum keyed-sha-1 {
           description
             "Keyed secure hash algorithm (SHA1) ";
         }




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         enum meticulous-keyed-sha-1 {
           description
             "Meticulous keyed secure hash algorithm (SHA1) ";
         }
       }
       description "Authentication algorithm";
     }

     feature bfd-interface-config {
       description "BFD per-interface config supported";
     }
     feature bfd-authentication {
       description "BFD authentication supported";
     }

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

       choice interval-config-type {
         description
           "Two interval values or 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;



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             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 demand mode";
       }

       leaf enable-authentication {
         type boolean;
         default false;
         description
           "If set, the Authentication Section is present and the
            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";
           }



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           description "Authentication algorithm to be used";
         }
       }
     }

     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";

       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 {
         type bfd-session-type;
         description
           "BFD session type, this indicates the path type that BFD is
           running on";
       }



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



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         leaf remote-diagnostic {
           type 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 {
           type uint32;
           units microseconds;
           description "Negotiated echo transmit interval";
         }
         leaf detection-time {
           type uint32;
           units microseconds;
           description "Detection time";
         }
       }

       list sesssion-statistics {



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         description "BFD 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";
         }
       }
     }

     augment "/rt:routing/rt:routing-instance/rt:routing-protocols/"
       + "rt:routing-protocol" {
       when "rt:type = 'bfd:bfd'" {
         description



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           "This augment is only valid for a protocol instance
           of BFD.";
       }
       description "BFD augmentation.";

       container bfd {
         description "BFD top-level container";
         container bfd-cfg {
           description "BFD configuration";
           container bfd-session-cfg {
             description "BFD session configuration";

             list session-ip-mh {
               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";
               }
               leaf admin-down {
                 type boolean;
                 default false;
                 description
                   "Is the BFD session administratively down";
               }
               uses bfd-grouping-common-cfg-parms;

               leaf tx-ttl {
                 type ttl;
                 default 255;
                 description "TTL of outgoing BFD control packets";
               }
               leaf rx-ttl {
                 type ttl;
                 mandatory true;
                 description
                   "Minimum allowed TTL value for incoming BFD control
                    packets";
               }
             }
           }



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           list bfd-interface-cfg {
             if-feature bfd-interface-config;
             key interface;

             description "Per-interface BFD configuration";
             leaf interface {
               type if:interface-ref;
               description "Interface";

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

             uses bfd-grouping-echo-cfg-parms;

           }
         }

         container bfd-oper {
           config "false";
           description "BFD operational container";
           container bfd-session-statistics {
             description "BFD session counters";
             leaf ip-sh-session-num {
               type uint32;
               description "IP single hop session number";
             }
             leaf ip-mh-session-num {
               type uint32;
               description "IP multi hop session Number";
             }
             leaf total-session-num {
               type uint32;
               description "Total session number";
             }
             leaf session-up-num {
               type uint32;
               description "Session up number";
             }
             leaf sess-down-num {
               type uint32;
               description "Session down number";
             }
             leaf sess-admin-down-num {
               type uint32;
               description "Session admin-down number";
             }
           }




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           container bfd-session-lists {
             description
               "Contains multiple session lists, one per type";
             list session-ip-sh {
               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";
               }
               leaf source-addr {
                 type inet:ip-address;
                 description "BFD source address";
               }

               uses bfd-all-session;
             }

             list session-ip-mh-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 a different source UDP port 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 {
                 key "source-port";
                 description
                   "The BFD sessions between a source and a. " +
                   "destination. Source UDP port is unique for " +
                   "each session in the group.";
                 leaf ttl {
                   type ttl;
                   description "TTL of outgoing packets";
                 }



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                 uses bfd-all-session;
               }
             }

             list session-te-tunnel {
               key "tunnel-name";
               description "BFD over TE tunnel";

               leaf tunnel-name {
                 type string;
                 description "Name of TE tunnel";
               }
               uses bfd-all-session;
             }

             list session-ldp-lsp-group {
               key "ldp-fec";
               description
                 "BFD over LDP LSP group of sessions. A group of " +
                 "sessions is to one LDP FEC, each session uses a " +
                 "different source UDP port for ECMP.";

               leaf ldp-fec {
                 type inet:ip-prefix;
                 description "LDP FEC";
               }
               list session-ldp-lsp {
                 key "source-port";
                 description
                   "The BFD sessions on an LDP FEC. Source UDP " +
                   "port is unique for each session in the group.";
                 leaf ttl {
                   type ttl;
                   description "TTL of outgoing packets";
                 }
                 uses bfd-all-session;
               }
             }

             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";
               }

               list session-lag-micro {



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               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";
                 }
                 uses bfd-all-session;
               }
             }

           }
         }
       }

     }

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

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

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

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

       leaf state-change-reason {
         type string;
         description "BFD state change reason";
       }

       leaf time-in-previous-state {
         type string;
         description



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           "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 session-type {
         type bfd-session-type;
         description "BFD session type";
       }
     }

     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-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";
       }
     }


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



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         "session is continuously changing state.";

       uses bfd-notification-parms;
     }

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

       uses bfd-notification-parms;

       leaf tunnel-name {
         type string;
         description "TE tunnel to which this BFD session belongs to";
       }
     }


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

       uses bfd-notification-parms;

       leaf ldp-fec {
         type inet:ip-prefix;
         description "LDP FEC";
       }
       leaf source-port {
         type inet:port-number;
         description "Source UDP port";
       }
     }

     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-notification-parms;

       leaf lag-name {
         type if:interface-ref;



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         description "LAG interface name";
       }

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


   <CODE ENDS>

2.11.  BFD Client Example Configuration Yang Module

   module example-bfd-routing-app {
      namespace "urn:ietf:params:xml:ns:yang:example-bfd-routing-app";
      prefix bfd-routing-app;

      import ietf-bfd {
        prefix "bfd";
      }

      import ietf-interfaces {
        prefix "if";
      }

      organization
        "ACME";
      contact
        "acme@acme.com";

      description
        "Testing BFD grouping (simulating a routing application)";

      revision 2015-07-01 {
        description "Initial revision.";
        reference "RFC XXXX: An example BFD routing application";
      }

      feature routing-app-bfd {
        description "BFD configuration under routing-app";
      }

      list area {
        key "area-id";

        description "Specify a routing area.";



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        leaf area-id {
          type uint32;
          description "Area";
        }

        uses bfd:bfd-client-base-cfg-parms {
          if-feature routing-app-bfd;
        }

        list interface {
          key "interface";
          description "List of interfaces";
          leaf interface {
            type if:interface-ref;
            description "Interface";
          }
          uses bfd:bfd-client-base-cfg-parms {
            if-feature routing-app-bfd;
          }
        }

      }
   }


2.12.  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.  IANA Considerations

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

   URI:TBD



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2.14.  Acknowledgements

   We would also like to thank Nobo Akiya and Jeff Haas for their
   encouragement on this work.

3.  References

3.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, June 2010.

   [RFC5881]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, June
              2010.

   [RFC5882]  Katz, D. and D. Ward, "Generic Application of
              Bidirectional Forwarding Detection (BFD)", RFC 5882, June
              2010.

   [RFC5883]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for Multihop Paths", RFC 5883, June 2010.

   [RFC5884]  Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
              "Bidirectional Forwarding Detection (BFD) for MPLS Label
              Switched Paths (LSPs)", RFC 5884, June 2010.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)", RFC
              6241, June 2011.

   [RFC7130]  Bhatia, M., Chen, M., Boutros, S., Binderberger, M., and
              J. Haas, "Bidirectional Forwarding Detection (BFD) on Link
              Aggregation Group (LAG) Interfaces", RFC 7130, February
              2014.

3.2.  Informative References







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   [I-D.ietf-netconf-restconf]
              Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", draft-ietf-netconf-restconf-06 (work in
              progress), June 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 (work in
              progress), May 2015.

Appendix A.  Change log

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

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

   o  Follow VRF-centric model

   o  IP single-hop session configuration 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:

   o  Added missing filename

   o  Added missing CODE ENDS

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
   Juniper Networks
   India

   Email: santoshpk@juniper.net


   Mahesh Jethanandani
   Cisco Systems

   Email: mjethanandani@gmail.com


   Greg Mirsky
   Ericsson

   Email: gregory.mirsky@ericsson.com



























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