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Yang Data Model for Bidirectional Forwarding Detection (BFD)
draft-zheng-bfd-yang-03

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This is an older version of an Internet-Draft whose latest revision state is "Replaced".
Authors Lianshu Zheng , Reshad Rahman , Santosh Pallagatti , Mahesh Jethanandani , Greg Mirsky
Last updated 2015-06-11
Replaced by draft-ietf-bfd-yang, draft-ietf-bfd-yang, RFC 9127
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Send notices to draft-zheng-bfd-yang.ad@ietf.org, draft-zheng-bfd-yang@ietf.org, bfd-chairs@ietf.org, draft-zheng-bfd-yang.shepherd@ietf.org
draft-zheng-bfd-yang-03
Network Working Group                                      L. Zheng, Ed.
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                          R. Rahman, Ed.
Expires: December 11, 2015                                 Cisco Systems
                                                           S. Pallagatti
                                                        Juniper Networks
                                                         M. Jethanandani
                                                           Cisco Systems
                                                               G. Mirsky
                                                                Ericsson
                                                            June 9, 2015

      Yang Data Model for Bidirectional Forwarding Detection (BFD)
                      draft-zheng-bfd-yang-03.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 December 11, 2015.

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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.  Centralized BFD configuration . . . . . . . . . . . .   4
         2.1.1.1.  Common BFD configuration  . . . . . . . . . . . .   4
         2.1.1.2.  Single-hop IP . . . . . . . . . . . . . . . . . .   5
         2.1.1.3.  Multi-hop IP  . . . . . . . . . . . . . . . . . .   5
         2.1.1.4.  MPLS LSP  . . . . . . . . . . . . . . . . . . . .   6
         2.1.1.5.  Link Aggregation Group  . . . . . . . . . . . . .   6
         2.1.1.6.  Per-interface configuration . . . . . . . . . . .   6
       2.1.2.  Configuration in BFD clients  . . . . . . . . . . . .   6
     2.2.  Design of operational model . . . . . . . . . . . . . . .   7
     2.3.  Notifications . . . . . . . . . . . . . . . . . . . . . .   7
     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  . . . . . . . . . . . .  10
     2.6.  Operational Data Hierarchy  . . . . . . . . . . . . . . .  10
     2.7.  Notifications . . . . . . . . . . . . . . . . . . . . . .  12
     2.8.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .  13
     2.9.  Interaction with other YANG modules . . . . . . . . . . .  13
     2.10. BFD Yang Module . . . . . . . . . . . . . . . . . . . . .  13
     2.11. BFD Client Example Configuration Yang Module  . . . . . .  27
     2.12. Security Considerations . . . . . . . . . . . . . . . . .  28
     2.13. IANA Considerations . . . . . . . . . . . . . . . . . . .  29
     2.14. Acknowledgements  . . . . . . . . . . . . . . . . . . . .  29
   3.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  29
     3.1.  Normative References  . . . . . . . . . . . . . . . . . .  29
     3.2.  Informative References  . . . . . . . . . . . . . . . . .  30
   Appendix A.  Change log . . . . . . . . . . . . . . . . . . . . .  30

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     A.1.  Changes between versions -02 and -03  . . . . . . . . . .  30
     A.2.  Changes between versions -01 and -02  . . . . . . . . . .  30
     A.3.  Changes between versions -00 and -01  . . . . . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  30

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, aka 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

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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 configuration under the BFD client,
   e.g.  BFD configuration is under routing applications such as OSPF,
   IS-IS, BGP etc.  Other implementations have BFD configuration
   centralized, i.e outside the multiple BFD clients.  In the sections
   below we address both approaches.

2.1.1.  Centralized BFD configuration

   The BFD data model consists of configuring BFD sessions of different
   types (e.g. single-hop IP, multi-hop IP etc).  Since the different
   session types have different keys we have a list per session type,
   but we use a grouping to share the common configuration data between
   the different session types.

2.1.1.1.  Common BFD configuration

   The common BFD session configuration items are put in a grouping to
   be used in multiple places, these items 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].

   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).

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2.1.1.2.  Single-hop IP

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

   interface
           This is the interface on which the BFD packets for this
           session are transmitted and received.  Examples of an
           interface are physical media, virtual circuit, tunnel etc.

   destination address
           Address belonging to the peer system as per [RFC5881]

   The common configuration data in Section 2.1.1.1 is used for single-
   hop IP.  On top of that common data, we also need configuration data
   for echo:

   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
           The is the Required Min Echo RX Interval as defined in
           [RFC5880].

2.1.1.3.  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]

   VRF name
           VRF in which the BFD multi-hop session is running

   The common configuration data in Section 2.1.1.1 is used for multi-
   hop IP.On top of that common data, we also need TTL:

   ttl
           TTL of outgoing BFD control packets.

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2.1.1.4.  MPLS LSP

   TBD

2.1.1.5.  Link Aggregation Group

   TBD

2.1.1.6.  Per-interface configuration

   For implementations which have 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:

   Common parameters
           The common BFD parameters listed in Section 2.1.1.1

   Echo parameters
           The echo parameters listed in Section 2.1.1.2

2.1.2.  Configuration in BFD clients

   When BFD is configured in BFD clients, it is highly desirable to have
   BFD configuration consistency between those clients.  In this
   approach we have a grouping for BFD configuration which applications
   can import in their YANG module:

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

   - Since 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
   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 the detection time multiplier as defined in [RFC5880].

   desired-min-tx-interval

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

   required-min-rx-interval
           This the Required Min 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,
   destination IP address and 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 in which 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 discriminator, remote
   discriminator and the capability of supporting demand detect mode are
   shown in the first category.  A 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 this
   session, e.g. when the session went to up/down, how long it has been
   since the session is up/down.

2.3.  Notifications

   This YANG model defines a list of notifications to inform clients of
   BFD with important events detected during the protocol operation.
   Pair of local and remote discriminator identifies a BFD session on
   local system.  Notification also give more important details about
   BFD sessions e.g. new state, time in previous state, VRF and reason
   for BFD session state changed.

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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

   We have per-interface configuration

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  module: ietf-bfd
     +--rw bfd
        +--rw bfd-cfg
        |  +--rw bfd-session-cfg {bfd-centralized-session-config}?
        |  |  +--rw session-ip-sh* [interface dest-addr]
        |  |  |  +--rw interface                        if:interface-ref
        |  |  |  +--rw dest-addr                        inet:ip-address
        |  |  |  +--rw admin-down?                      boolean
        |  |  |  +--rw local-multiplier?                multiplier
        |  |  |  +--rw desired-min-tx-interval          uint32
        |  |  |  +--rw required-min-rx-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
        |  |  +--rw session-ip-mh* [vrf-name source-addr dest-addr]
        |  |     +--rw vrf-name                    vrfName
        |  |     +--rw source-addr                 inet:ip-address
        |  |     +--rw dest-addr                   inet:ip-address
        |  |     +--rw admin-down?                 boolean
        |  |     +--rw local-multiplier?           multiplier
        |  |     +--rw desired-min-tx-interval     uint32
        |  |     +--rw required-min-rx-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 desired-min-tx-interval          uint32
        |     +--rw required-min-rx-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

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2.5.2.  Configuration in BFD clients

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

   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".  Along with this if there are
   specific interface configuration then specific interface will
   override the "interface all" parameters.

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

2.6.  Operational Data Hierarchy

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

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   module: ietf-bfd
      +--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 bfd-session-lists
               +--ro session-ip-sh* [interface dest-addr]
               |  +--ro interface               if:interface-ref
               |  +--ro dest-addr               inet:ip-address
               |  +--ro sesssion-type?          enumeration
               |  +--ro local-discriminator?    discriminator
               |  +--ro remote-discriminator?   discriminator
               |  +--ro remote-multiplier?      multiplier
               |  +--ro out-interface?          if:interface-ref
               |  +--ro demand-capability?      boolean
               |  +--ro session-running*
               |  |  +--ro local-state?               state
               |  |  +--ro remote-state?              state
               |  |  +--ro local-diagnostic?          diagnostic
               |  |  +--ro remote-diagnostic?         diagnostic
               |  |  +--ro detect-Mode?               enumeration
               |  |  +--ro actual-tx-interval?        uint32
               |  |  +--ro actual-rx-interval?        uint32
               |  |  +--ro actual-echo-tx-interval?   uint32
               |  |  +--ro detect-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 receive-pkt?         uint64
               |     +--ro send-pkt?            uint64
               |     +--ro down-count?          uint32
               |     +--ro receive-bad-pkt?     uint64
               |     +--ro send-failed-pkt?     uint64
               |     +--ro short-break-count?   uint32
               +--ro session-ip-mh* [vrfName source-addr dest-addr]
                  +--ro vrfName                 vrfName
                  +--ro source-addr             inet:ip-address
                  +--ro dest-addr               inet:ip-address
                  +--ro ttl?                    TTL
                  +--ro sesssion-type?          enumeration
                  +--ro local-discriminator?    discriminator
                  +--ro remote-discriminator?   discriminator
                  +--ro remote-multiplier?      multiplier

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                  +--ro out-interface?          if:interface-ref
                  +--ro demand-capability?      boolean
                  +--ro session-running*
                  |  +--ro local-state?               state
                  |  +--ro remote-state?              state
                  |  +--ro local-diagnostic?          diagnostic
                  |  +--ro remote-diagnostic?         diagnostic
                  |  +--ro detect-Mode?               enumeration
                  |  +--ro actual-tx-interval?        uint32
                  |  +--ro actual-rx-interval?        uint32
                  |  +--ro actual-echo-tx-interval?   uint32
                  |  +--ro detect-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 receive-pkt?         uint64
                     +--ro send-pkt?            uint64
                     +--ro down-count?          uint32
                     +--ro receive-bad-pkt?     uint64
                     +--ro send-failed-pkt?     uint64
                     +--ro short-break-count?   uint32

2.7.  Notifications

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

   module: ietf-bfd
   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 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 vrf-name?                 vrfName
         +--ro source-addr?              inet:ip-address

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2.8.  Examples

2.9.  Interaction with other YANG modules

   TBD.

2.10.  BFD Yang Module

   <CODE BEGINS> file "ietf-bfd@2015-06-09.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";
     }

     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";

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

     revision 2015-06-09 {
       description "Initial revision.";
       reference "RFC XXXX: A YANG data model for BFD";
     }

     typedef discriminator {
       type uint32 {
         range 1..4294967295;
       }

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       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 {
           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 {

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           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;
       }
       description "Time To Live";
     }

     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";

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         }

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

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

     typedef vrfName {
       type string;
       description "VRF Name";
     }

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

     grouping bfd-grouping-common-cfg-parms {
       description "BFD grouping for common config parameters";

       leaf local-multiplier {
         type multiplier;
         default 3;
         description "Local multiplier";
       }

       leaf desired-min-tx-interval {
         type uint32;
         units microseconds;
         mandatory true;
         description
           "Desired minimum transmit interval of control packets";
       }

       leaf required-min-rx-interval {

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         type uint32;
         units microseconds;
         mandatory true;
         description
           "Required minimum receive interval of control packets";
       }

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

     grouping bfd-grouping-echo-cfg-parms {

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       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";
         }

         leaf local-multiplier {
           type multiplier;
           default 3;
           description "Multiplier transmitted by local system";
         }

         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

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             "Required minimum receive interval of control packets";
         }
       }
     }

     grouping bfd-client-full-cfg-parms {
       description
         "BFD grouping for complete 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-common-cfg-parms;

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

     grouping bfd-all-session {
       description "BFD session operational information";
       leaf sesssion-type {
         type enumeration {
           enum ip-single-hop {
             value "0";
             description "IP single hop";
           }
           enum ip-multi-hop {
             value "1";
             description "IP multi hop";
           }
         }
         description
           "BFD session type, this indicates the path type that BFD is
           running on";
       }
       leaf local-discriminator {
         type discriminator;
         description "Local discriminator";
       }
       leaf remote-discriminator {
         type discriminator;
         description "Remote discriminator";

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       }
       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";
       }

       list session-running {
         description "BFD session running information";
         leaf local-state {
           type state;
           description "Local state";
         }
         leaf remote-state {
           type state;
           description "Remote state";
         }
         leaf local-diagnostic {
           type diagnostic;
           description "Local diagnostic";
         }
         leaf remote-diagnostic {
           type diagnostic;
           description "Remote diagnostic";
         }
         leaf detect-Mode {
           type enumeration {
             enum async-with-echo {
               value "0";
               description "Async with echo";
             }
             enum async-without-echo {
               value "1";
               description "Async without echo";
             }
             enum demand-with-echo {
               value "2";
               description "Demand with echo";
             }
             enum demand-without-echo {
               value "3";

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               description "Demand without echo";
             }
           }
           description "Detect mode";
         }
         leaf actual-tx-interval {
           type uint32;
           units microseconds;
           description "Actual transmit interval";
         }
         leaf actual-rx-interval {
           type uint32;
           units microseconds;
           description "Actual receive interval";
         }
         leaf actual-echo-tx-interval {
           type uint32;
           units microseconds;
           description "Actual echo transmit interval";
         }
         leaf detect-time {
           type uint32;
           units microseconds;
           description "Detect time";
         }
       }

       list sesssion-statistics {
         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 receive-pkt {
           type uint64;
           description "Received Packet Count";

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         }
         leaf send-pkt {
           type uint64;
           description "Sent Packet Count";
         }
         leaf down-count {
           type uint32;
           description "Session Down Count";
         }
         leaf receive-bad-pkt {
           type uint64;
           description "Received bad packet count";
         }
         leaf send-failed-pkt {
           type uint64;
           description "Packet Failed to Send Count";
         }
         leaf short-break-count {
           type uint32;
           default "0";
           description "Shortbreak count";
         }
       }
     }

     container bfd {
       description "BFD top-level container";
       container bfd-cfg {
         description "BFD configuration";
         container bfd-session-cfg {
           if-feature bfd-centralized-session-config;
           description "BFD session configuration";
           list session-ip-sh {
             key "interface dest-addr";
             description "List of IP single-hop sessions";
             leaf interface {
               type if:interface-ref;
               description
                 "Interface on which the IP single-hop session is
                running.";
             }
             leaf dest-addr {
               type inet:ip-address;
               description
                 "IP address of the peer";
             }
             leaf admin-down {
               type boolean;

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               default false;
               description
                 "Is the BFD session administratively down";
             }
             uses bfd-grouping-common-cfg-parms;

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

           list session-ip-mh {
             key "vrf-name source-addr dest-addr";
             description "List of IP multi-hop sessions";

             leaf vrf-name {
               type vrfName;
               description "Routing instance";
             }
             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";
           }
         }

         container bfd-session-lists {
           description "Contains multiple session lists, one per type";

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           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";
             }

             uses bfd-all-session;
           }

           list session-ip-mh {
             key "vrfName source-addr dest-addr";
             description "BFD IP multi-hop sessions";
             leaf vrfName {
               type vrfName;
               description "VRF";
             }
             leaf source-addr {
               type inet:ip-address;
               description "BFD source address";
             }
             leaf dest-addr {
               type inet:ip-address;
               description "BFD peer address";
             }
             leaf ttl {
               type TTL;
               description "TTL of session";
             }
             uses bfd-all-session;
           }
         }
       }
     }

     grouping bfd-notification-params {
       description
         "This group describes common params that will be send
           as part of BFD notification";

       leaf local-discr {
         type discriminator;

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         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
           "How long the BFD session was in the previous state";
       }

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

     notification bfd-singlehop-notification {
       description
         "Notitification for BFD single-hop session state change";

       uses bfd-notification-params;

       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";
       }
     }

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     notification bfd-multihop-notification {
       description
         "Notitification for BFD multi-hop session state change";

       uses bfd-notification-params;

       leaf vrf-name {
         type vrfName;
         description "Routing instance";
       }

       leaf source-addr {
         type inet:ip-address;
         description "BFD local address";
       }
     }
   }
   <CODE ENDS>

2.11.  BFD Client Example Configuration Yang Module

   module example-bfd-routing-app {
      namespace "urn:cisco:params:xml:ns:yang:bfdroutingapp";
      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 2015-02-14 {
        description
          "Initial revision.";
      }

      feature routing-app-bfd {

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        description "BFD configuration under routing-app";
      }

      list area {
        description
          "Specify a routing area.";

        key "area-id";

        leaf area-id {
          type uint32;
        }

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

        list interface {
          key "interface";
          leaf interface {
            type if:interface-ref;
          }
          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.

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2.13.  IANA Considerations

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

   URI:TBD

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.

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   [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

   [I-D.ietf-netconf-restconf]
              Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", draft-ietf-netconf-restconf-05 (work in
              progress), June 2015.

Appendix A.  Change log

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

A.1.  Changes between versions -02 and -03

   o  Fixed date mismatch

   o  Updated authors

A.2.  Changes between versions -01 and -02

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

   o  Added appendix for "Change log"

A.3.  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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