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OPSAWG                                                         B. Claise
Internet-Draft                                               J. Quilbeuf
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: January 28, 2021                                     P. Lucente
                                                                     NTT
                                                               P. Fasano
                                                               TIM S.p.A
                                                           July 27, 2020


                   YANG Modules for Service Assurance
             draft-claise-opsawg-service-assurance-yang-05

Abstract

   This document proposes YANG modules for the Service Assurance for
   Intent-based Networking Architecture.

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 https://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 28, 2021.

Copyright Notice

   Copyright (c) 2020 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
   (https://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




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  YANG Models Overview  . . . . . . . . . . . . . . . . . . . .   3
   4.  Base ietf-service-assurance YANG module . . . . . . . . . . .   4
     4.1.  Tree View . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Concepts  . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Subservice Extension: ietf-service-assurance-device YANG
       module  . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     5.1.  Tree View . . . . . . . . . . . . . . . . . . . . . . . .  13
     5.2.  Complete Tree View  . . . . . . . . . . . . . . . . . . .  13
     5.3.  Concepts  . . . . . . . . . . . . . . . . . . . . . . . .  14
     5.4.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  15
   6.  Subservice Extension: ietf-service-assurance-interface YANG
       module  . . . . . . . . . . . . . . . . . . . . . . . . . . .  16
     6.1.  Tree View . . . . . . . . . . . . . . . . . . . . . . . .  16
     6.2.  Complete Tree View  . . . . . . . . . . . . . . . . . . .  17
     6.3.  Concepts  . . . . . . . . . . . . . . . . . . . . . . . .  18
     6.4.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  18
   7.  Vendor-specific Subservice Extension: example-service-
       assurance-device-acme YANG module . . . . . . . . . . . . . .  19
     7.1.  Tree View . . . . . . . . . . . . . . . . . . . . . . . .  19
     7.2.  Complete Tree View  . . . . . . . . . . . . . . . . . . .  20
     7.3.  Concepts  . . . . . . . . . . . . . . . . . . . . . . . .  21
     7.4.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  22
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  23
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
     9.1.  The IETF XML Registry . . . . . . . . . . . . . . . . . .  24
     9.2.  The YANG Module Names Registry  . . . . . . . . . . . . .  25
   10. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . .  25
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  25
     11.2.  Informative References . . . . . . . . . . . . . . . . .  26
   Appendix A.  Changes between revisions  . . . . . . . . . . . . .  26
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  27
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27

1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP




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   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   The terms used in this document are defined in draft-claise-opsawg-
   service-assurance-architecture IETF draft.

2.  Introduction

   The "Service Assurance for Intent-based Networking Architecture"
   draft-claise-opsawg-service-assurance-architecture, specifies the
   framework and all of its components for service assurance.  This
   document complements the architecture by providing open interfaces
   between components.  More specifically, the goal is to provide YANG
   modules for the purpose of service assurance in a format that is:

   o  machine readable

   o  vendor independent

   o  augmentable

3.  YANG Models Overview

   The main YANG module, ietf-service-assurance, defines objects for
   assuring network services based on their decomposition into so-called
   subservices.  The subservices are hierarchically organised by
   dependencies.  The subservices, along with the dependencies,
   constitute an assurance graph.  This module should be supported by an
   agent, able to interact with the devices in order to produce a health
   status and symptoms for each subservice in the assurance graph.  This
   module is intended for the following use cases:

   o  Assurance graph configuration:

      *  Subservices: configure a set of subservices to assure, by
         specifying their types and parameters.

      *  Dependencies: configure the dependencies between the
         subservices, along with their type.

   o  Assurance telemetry: export the health status of the subservices,
      along with the observed symptoms.

   The second YANG module, ietf-service-assurance-device, extends the
   ietf-service-assurance module to add support for the subservice
   DeviceHealthy.  Additional subservice types might be added the same
   way.




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   The third YANG module, example-service-assurance-device-acme, extends
   the ietf-service-assurance-device module as an example to add support
   for the subservice DeviceHealthy, with specifics for the fictional
   ACME Corporation.  Additional vendor-specific parameters might be
   added the same way.

4.  Base ietf-service-assurance YANG module

4.1.  Tree View

   The following tree diagram [RFC8340] provides an overview of the
   ietf-service-assurance data model.

module: ietf-service-assurance
  +--ro assurance-graph-version        yang:counter32
  +--ro assurance-graph-last-change    yang:date-and-time
  +--rw subservices
     +--rw subservice* [type id]
        +--rw type                                identityref
        +--rw id                                  string
        +--ro last-change?                        yang:date-and-time
        +--ro label?                              string
        +--rw under-maintenance?                  boolean
        +--rw maintenance-contact                 string
        +--rw (parameter)?
        |  +--:(service-instance-parameter)
        |     +--rw service-instance-parameter
        |        +--rw service?         string
        |        +--rw instance-name?   string
        +--ro health-score?                       uint8
        +--ro symptoms-history-start?             yang:date-and-time
        +--rw symptoms
        |  +--ro symptom* [start-date-time id]
        |     +--ro id                     string
        |     +--ro health-score-weight?   uint8
        |     +--ro description?           string
        |     +--ro start-date-time        yang:date-and-time
        |     +--ro stop-date-time?        yang:date-and-time
        +--rw dependencies
           +--rw dependency* [type id]
              +--rw type               -> /subservices/subservice/type
              +--rw id                 -> /subservices/subservice[type=current()/../type]/id
              +--rw dependency-type?   identityref








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4.2.  Concepts

   The ietf-service-assurance YANG model assumes an identified number of
   subservices, to be assured independently.  A subservice is a feature
   or a subpart of the network system that a given service instance
   might depend on.  Example of subservices include:

   o  DeviceHealthy: whether a device is healthy, and if not, what are
      the symptoms.  Potential symptoms are "CPU overloaded", "Out of
      RAM", or "Out of TCAM".

   o  ConnectivityHealthy: given two IP addresses owned by two devices,
      what is the quality of the connection between them.  Potential
      symptoms are "No route available" or "ECMP Imbalance".

   The first example is a subservice representing a subpart of the
   network system, while the second is a subservice representing a
   feature of the network, In both cases, these subservices might depend
   on other subservices, for instance, the connectivity might depend on
   a subservice representing the routing mechanism and on a subservice
   representing ECMP.

   The symptoms are listed for each subservice.  Each symptom is
   specified by a unique id and contains a health-score-weight (the
   impact to the health score incurred by this symptom), a label (text
   describing what the symptom is), and dates and times at which the
   symptom was detected and stopped being detected.  While the unique id
   is sufficient as an unique key list, the start-date-time second key
   help sorting and retrieving relevant symptoms.

   The assurance of a given service instance can be obtained by
   composing the assurance of the subservices that it depends on, via
   the dependency relations.

   In order to declare a subservice MUST provide:

   o  A type: identity inheriting of the base identity for subservice,

   o  An id: string uniquely identifying the subservice among those with
      the same identity,

   o  Some parameters, which should be specified in an augmenting model,
      as described in the next sections.

   The type and id uniquely identify a given subservice.  They are used
   to indicate the dependencies.  Dependencies have types as well.  Two
   types are specified in the model:




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   o  Impacting: such a dependency indicates an impact on the health of
      the dependent,

   o  Informational: such a dependency might explain why the dependent
      has issues but does not impact its health.

   To illustrate the difference between "impacting" and "informational",
   consider the subservice InterfaceHealthy, representing a network
   interface.  If the device to which the network interface belongs goes
   down, the network interface will transition to a down state as well.
   Therefore, the dependency of InterfaceHealthy towards DeviceHealthy
   is "impacting".  On the other hand, as a the dependency towards the
   ECMPLoad subservice, which checks that the load between ECMP remains
   ce remains stable throughout time, is only "informational".  Indeed,
   services might be perfectly healthy even if the load distribution
   between ECMP changed.  However, such an instability might be a
   relevant symptom for diagnosing the root cause of a problem.

   Service instances MUST be modeled as a particular type of subservice
   with two parameters, a type and an instance name.  The type is the
   name of the service defined in the network orchestrator, for instance
   "point-to-point-l2vpn".  The instance name is the name assigned to
   the particular instance that we are assuring, for instance the name
   of the customer using that instance.

   The "under-maintenance" and "maintenance-contact" flags inhibit the
   emission of symptoms for that subservice and subservices that depend
   on them.  See Section 3.7 of
   [draft-claise-opsawg-service-assurance-architecture] for a more
   detailed discussion.

   By specifying service instances and their dependencies in terms of
   subservices, one defines the whole assurance to apply for them.  An
   assurance agent supporting this model should then produce telemetry
   in return with, for each subservice: a health-status indicating how
   healthy the subservice is and when the subservice is not healthy, a
   list of symptoms explaining why the subservice is not healthy.

4.3.  YANG Module

   <CODE BEGINS> file "ietf-service-assurance@2020-01-13.yang"

module ietf-service-assurance {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-service-assurance";
  prefix service-assurance;

  import ietf-yang-types {



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    prefix yang;
  }

  organization
    "IETF NETCONF (Network Configuration) Working Group";
  contact
    "WG Web:   <https://datatracker.ietf.org/wg/netconf/>
     WG List:  <mailto:netconf@ietf.org>
     Author:   Benoit Claise  <mailto:bclaise@cisco.com>
     Author:   Jean Quilbeuf   <mailto:jquilbeu@cisco.com>";
  description
    "This module defines objects for assuring network services based on
    their decomposition into so-called subservices, according to the SAIN
    (Service Assurance for Intent-based Networking) architecture.

    The subservices hierarchically organised by dependencies constitute an
    assurance graph. This module should be supported by an assurance agent,
    able to interact with the devices in order to produce a health status
    and symptoms for each subservice in the assurance graph.

    This module is intended for the following use cases:
    * Assurance graph configuration:
      * subservices: configure a set of subservices to assure, by specifying
        their types and parameters.
      * dependencies: configure the dependencies between the subservices,
         along with their type.
    * Assurance telemetry: export the health status of the subservices, along
      with the observed symptoms.

    The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
    'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
    'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
    are to be interpreted as described in BCP 14 (RFC 2119)
    (RFC 8174) when, and only when, they appear in all
    capitals, as shown here.

    Copyright (c)2020 IETF Trust and the persons identified as
    authors of the code.  All rights reserved.

    Redistribution and use in source and binary forms, with or
    without modification, is permitted pursuant to, and subject
    to the license terms contained in, the Simplified BSD License
    set forth in Section 4.c of the IETF Trust's Legal Provisions
    Relating to IETF Documents
    (https://trustee.ietf.org/license-info).

    This version of this YANG module is part of RFC XXXX; see the
    RFC itself for full legal notices.



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    TO DO:
    - Better type (IETF or OC) for device-id, interface-id, etc.
    - Have a YANG module for IETF and one for OC?";

  revision 2020-01-13 {
    description
      "Added the maintenance window concept.";
    reference
      "RFC xxxx: Title to be completed";
  }

  revision 2019-11-16 {
    description
      "Initial revision.";
    reference
      "RFC xxxx: Title to be completed";
  }

  identity subservice-idty {
    description
      "Root identity for all subservice types.";
  }

  identity service-instance-idty {
    base subservice-idty;
    description
      "Identity representing a service instance.";
  }

  identity dependency-type {
    description
      "Base identity for representing dependency types.";
  }

  identity informational-dependency {
    base dependency-type;
    description
      "Indicates that symptoms of the dependency might be of interest for the
       dependent, but the status of the dependency should not have any
       impact on the dependent.";
  }

  identity impacting-dependency {
    base dependency-type;
    description
      "Indicates that the status of the dependency directly impacts the status
       of the dependent.";
  }



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  grouping symptom {
    description
      "Contains the list of symptoms for a specific subservice.";
    leaf id {
      type string;
      description
        "A unique identifier for the symptom.";
    }
    leaf health-score-weight {
      type uint8 {
        range "0 .. 100";
      }
      description
        "The weight to the health score incurred by this symptom. The higher the
         value, the more of an impact this symptom has. If a subservice health
         score is not 100, there must be at least one symptom with a health
         score weight larger than 0.";
    }
    leaf description {
      type string;
      description
        "Description of the symptom, i.e. text describing what the symptom is, to
         be computer-consumable and be displayed on a human interface. ";
    }
    leaf start-date-time {
      type yang:date-and-time;
      description
        "Date and time at which the symptom was detected.";
    }
    leaf stop-date-time {
      type yang:date-and-time;
      description
        "Date and time at which the symptom stopped being detected.";
    }
  }

  grouping subservice-dependency {
    description
      "Represent a dependency to another subservice.";
    leaf type {
      type leafref {
        path "/subservices/subservice/type";
      }
      description
        "The type of the subservice to refer to (e.g. DeviceHealthy).";
    }
    leaf id {
      type leafref {



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        path "/subservices/subservice[type=current()/../type]/id";
      }
      description
        "The identifier of the subservice to refer to.";
    }
    leaf dependency-type {
      type identityref {
        base dependency-type;
      }
      description
        "Represents the type of dependency (i.e. informational, impacting).";
    }
    // augment here if more info are needed (i.e. a percentage) depending on the dependency type.
  }

  leaf assurance-graph-version {
    type yang:counter32;
    mandatory true;
    config false;
    description
      "The assurance graph version, which increases by 1 for each new version, after the changes
       (dependencies and/or maintenance windows parameters) are applied to the subservice(s).";
  }
  leaf assurance-graph-last-change {
    type yang:date-and-time;
    mandatory true;
    config false;
    description
      "Date and time at which the assurance graph last changed after the changes (dependencies
       and/or maintenance windows parameters) are applied to the subservice(s). These date and time
       must be more recent or equal compared to the more recent value of any changed subservices
       last-change";
  }
  container subservices {
    description
      "Root container for the subservices.";
    list subservice {
      key "type id";
      description
        "List of subservice configured.";
      leaf type {
        type identityref {
          base subservice-idty;
        }
        description
          "Name of the subservice, e.g. DeviceHealthy.";
      }
      leaf id {



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        type string;
        description
          "Unique identifier of the subservice instance, for each type.";
      }
      leaf last-change {
        type yang:date-and-time;
        config false;
        description
          "Date and time at which the assurance graph for this subservice
           instance last changed, i.e. dependencies and/or maintenance windows parameters.";
      }
      leaf label {
        type string;
        config false;
        description
          "Label of the subservice, i.e. text describing what the subservice is to
           be displayed on a human interface.";
      }
      leaf under-maintenance {
        type boolean;
        default false;
        description
          "An optional flag indicating whether this particular subservice is under
          maintenance. Under this circumstance, the subservice symptoms and the
          symptoms of its dependencies in the assurance graph should not be taken
          into account. Instead, the subservice should send a 'Under Maintenance'
          single symptom.

          The operator changing the under-maintenance value must set the
          maintenance-contact variable.

          When the subservice is not under maintenance any longer, the
          under-maintenance flag must return to its default value and
          the under-maintenance-owner variable deleted.";
      }
      leaf maintenance-contact {
        when "../under-maintenance = 'true'";
        type string;
        mandatory true;
        description
          "A string used to model an administratively assigned name of the
          resource that changed the under-maintenance value to 'true.

          It is suggested that this name contain one or more of the following:
          IP address, management station name, network manager's name, location,
          or phone number. In some cases the agent itself will be the owner of
          an entry. In these cases, this string shall be set to a string
          starting with 'monitor'.";



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      }
      choice parameter {
        description
          "Specify the required parameters per subservice type.";
        container service-instance-parameter {
          when "derived-from-or-self(../type, 'service-assurance:service-instance-idty')";
          description
            "Specify the parameters of a service instance.";
          leaf service {
            type string;
            description "Name of the service.";
          }
          leaf instance-name{
            type string;
            description "Name of the instance for that service.";
          }
        }
        // Other modules can augment their own cases into here
      }
      leaf health-score {
        type uint8 {
          range "0 .. 100";
        }
        config false;
        description
           "Score value of the subservice health. A value of 100 means that
           subservice is healthy. A value of 0 means that the subservice is
           broken. A value between 0 and 100 means that the subservice is
           degraded.";
      }
       leaf symptoms-history-start {
        type yang:date-and-time;
        config false;
        description
           "Date and time at which the symptoms history starts for this
           subservice instance, either because the subservice instance
           started at that date and time or because the symptoms before that
           were removed due to a garbage collection process.";
      }
      container symptoms {
        description
          "Symptoms for the subservice.";
        list symptom {
          key "start-date-time id";
          config false;
          description
            "List of symptoms the subservice. While the start-date-time key is not
            necessary per se, this would get the entries sorted by start-date-time



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            for easy consumption.";
          uses symptom;
        }
      }
      container dependencies {
        description
          "configure the dependencies between the subservices, along with their types.";
        list dependency {
          key "type id";
          description
            "List of soft dependencies of the subservice.";
          uses subservice-dependency;
        }
      }
    }
  }
}

   <CODE ENDS>

5.  Subservice Extension: ietf-service-assurance-device YANG module

5.1.  Tree View

   The following tree diagram [RFC8340] provides an overview of the
   ietf-service-assurance-device data model.

module: ietf-service-assurance-device
  augment /service-assurance:subservices/service-assurance:subservice/service-assurance:parameter:
    +--rw device-idty
       +--rw device?   string

5.2.  Complete Tree View

   The following tree diagram [RFC8340] provides an overview of the
   ietf-service-assurance and ietf-service-assurance-device data models.















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module: ietf-service-assurance
  +--ro assurance-graph-version        yang:counter32
  +--ro assurance-graph-last-change    yang:date-and-time
  +--rw subservices
     +--rw subservice* [type id]
        +--rw type                                          identityref
        +--rw id                                            string
        +--ro last-change?                                  yang:date-and-time
        +--ro label?                                        string
        +--rw under-maintenance?                            boolean
        +--rw maintenance-contact                           string
        +--rw (parameter)?
        |  +--:(service-instance-parameter)
        |  |  +--rw service-instance-parameter
        |  |     +--rw service?         string
        |  |     +--rw instance-name?   string
        |  +--:(service-assurance-device:device-idty)
        |     +--rw service-assurance-device:device-idty
        |        +--rw service-assurance-device:device?   string
        +--ro health-score?                                 uint8
        +--ro symptoms-history-start?                       yang:date-and-time
        +--rw symptoms
        |  +--ro symptom* [start-date-time id]
        |     +--ro id                     string
        |     +--ro health-score-weight?   uint8
        |     +--ro description?           string
        |     +--ro start-date-time        yang:date-and-time
        |     +--ro stop-date-time?        yang:date-and-time
        +--rw dependencies
           +--rw dependency* [type id]
              +--rw type               -> /subservices/subservice/type
              +--rw id                 -> /subservices/subservice[type=current()/../type]/id
              +--rw dependency-type?   identityref

5.3.  Concepts

   As the number of subservices will grow over time, the YANG module is
   designed to be extensible.  A new subservice type requires the
   precise specifications of its type and expected parameters.  Let us
   illustrate the example of the new DeviceHealthy subservice type.  As
   the name implies, it monitors and reports the device health, along
   with some symptoms in case of degradation.

   For our DeviceHealthy subservice definition, the new device-idty is
   specified, as an inheritance from the base identity for subservices.
   This indicates to the assurance agent that we are now assuring the
   health of a device.




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   The typical parameter for the configuration of the DeviceHealthy
   subservice is the name of the device that we want to assure.  By
   augmenting the parameter choice from ietf-service-assurance YANG
   module for the case of the device-idty subservice type, this new
   parameter is specified.

5.4.  YANG Module

   <CODE BEGINS> file "ietf-service-assurance-device@2020-01-13.yang"

module ietf-service-assurance-device {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-service-assurance-device";
  prefix service-assurance-device;

  import ietf-service-assurance {
    prefix "service-assurance";
  }

  organization
    "IETF NETCONF (Network Configuration) Working Group";
  contact
    "WG Web:   <https://datatracker.ietf.org/wg/netconf/>
     WG List:  <mailto:netconf@ietf.org>
     Author:   Benoit Claise  <mailto:bclaise@cisco.com>
     Author:   Jean Quilbeuf   <mailto:jquilbeu@cisco.com>";
  description
   "This module extends the ietf-service-assurance module to add
    support for the subservice DeviceHealthy.

    Checks whether a network device is healthy.

    The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
    'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
    'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
    are to be interpreted as described in BCP 14 (RFC 2119)
    (RFC 8174) when, and only when, they appear in all
    capitals, as shown here.

    Copyright (c) 2020 IETF Trust and the persons identified as
    authors of the code.  All rights reserved.

    Redistribution and use in source and binary forms, with or
    without modification, is permitted pursuant to, and subject
    to the license terms contained in, the Simplified BSD License
    set forth in Section 4.c of the IETF Trust's Legal Provisions
    Relating to IETF Documents
    (https://trustee.ietf.org/license-info).



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    This version of this YANG module is part of RFC XXXX; see the
    RFC itself for full legal notices.  ";

  revision 2020-01-13 {
    description
      "Added the maintenance window concept.";
    reference
      "RFC xxxx: Title to be completed";
  }

  revision 2019-11-16 {
    description
      "Initial revision.";
    reference
        "RFC xxxx: Title to be completed";
  }

  identity device-idty {
    base service-assurance:subservice-idty;
    description "Network Device is healthy.";
  }

  augment /service-assurance:subservices/service-assurance:subservice/service-assurance:parameter {
       description
         "Specify the required parameters for a new subservice type";
       container device-idty{
           when "derived-from-or-self(../service-assurance:type, 'device-idty')";
           description
             "Specify the required parameters for the device-idty subservice type";

           leaf device {
               type string;
               description "The device to monitor.";
           }
       }
  }
}

   <CODE ENDS>

6.  Subservice Extension: ietf-service-assurance-interface YANG module

6.1.  Tree View

   The following tree diagram [RFC8340] provides an overview of the
   ietf-service-assurance-interface data model.





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module: ietf-service-assurance-interface
  augment /service-assurance:subservices/service-assurance:subservice/service-assurance:parameter:
    +--rw device?      string
    +--rw interface?   string

6.2.  Complete Tree View

   The following tree diagram [RFC8340] provides an overview of the
   ietf-service-assurance, ietf-service-assurance-device, and ietf-
   service-assurance-interface data models.

module: ietf-service-assurance
  +--ro assurance-graph-version        yang:counter32
  +--ro assurance-graph-last-change    yang:date-and-time
  +--rw subservices
     +--rw subservice* [type id]
        +--rw type                                           identityref
        +--rw id                                             string
        +--ro last-change?                                   yang:date-and-time
        +--ro label?                                         string
        +--rw under-maintenance?                             boolean
        +--rw maintenance-contact                            string
        +--rw (parameter)?
        |  +--:(service-instance-parameter)
        |  |  +--rw service-instance-parameter
        |  |     +--rw service?         string
        |  |     +--rw instance-name?   string
        |  +--:(service-assurance-device:device-idty)
        |  |  +--rw service-assurance-device:device-idty
        |  |     +--rw service-assurance-device:device?   string
        |  +--:(service-assurance-interface:device)
        |  |  +--rw service-assurance-interface:device?      string
        |  +--:(service-assurance-interface:interface)
        |     +--rw service-assurance-interface:interface?   string
        +--ro health-score?                                  uint8
        +--ro symptoms-history-start?                        yang:date-and-time
        +--rw symptoms
        |  +--ro symptom* [start-date-time id]
        |     +--ro id                     string
        |     +--ro health-score-weight?   uint8
        |     +--ro description?           string
        |     +--ro start-date-time        yang:date-and-time
        |     +--ro stop-date-time?        yang:date-and-time
        +--rw dependencies
           +--rw dependency* [type id]
              +--rw type               -> /subservices/subservice/type
              +--rw id                 -> /subservices/subservice[type=current()/../type]/id
              +--rw dependency-type?   identityref



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6.3.  Concepts

   For our InterafaceHealthy subservice definition, the new interface-
   idty is specified, as an inheritance from the base identity for
   subservices.  This indicates to the assurance agent that we are now
   assuring the health of an interface.

   The typical parameters for the configuration of the InterfaceHealthy
   subservice are the name of the device and, on that specific device, a
   specific interface.  By augmenting the parameter choice from ietf-
   service-assurance YANG module for the case of the interface-idty
   subservice type, those two new parameter are specified.

6.4.  YANG Module

   <CODE BEGINS> file "ietf-service-assurance-interface@2020-01-13.yang"

module ietf-service-assurance-interface {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-service-assurance-interface";
  prefix service-assurance-interface;

  import ietf-service-assurance {
    prefix "service-assurance";
  }

  organization
    "IETF OPSAWG Working Group";
  contact
    "WG Web:   <https://datatracker.ietf.org/wg/opsawg/>
     WG List:  <mailto:opsawg@ietf.org>
     Author:   Benoit Claise  <mailto:bclaise@cisco.com>
     Author:   Jean Quilbeuf   <mailto:jquilbeu@cisco.com>";
  description
   "This module extends the ietf-service-assurance module to add
    support for the subservice InterfaceHealthy.

    Checks whether an interface is healthy.

    The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
    'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
    'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
    are to be interpreted as described in BCP 14 (RFC 2119)
    (RFC 8174) when, and only when, they appear in all
    capitals, as shown here.

    Copyright (c) 2020 IETF Trust and the persons identified as
    authors of the code.  All rights reserved.



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    Redistribution and use in source and binary forms, with or
    without modification, is permitted pursuant to, and subject
    to the license terms contained in, the Simplified BSD License
    set forth in Section 4.c of the IETF Trust's Legal Provisions
    Relating to IETF Documents
    (https://trustee.ietf.org/license-info).

    This version of this YANG module is part of RFC XXXX; see the
    RFC itself for full legal notices.  ";

  revision 2020-01-13 {
    description
      "Initial revision.";
    reference
        "RFC xxxx: Title to be completed";
  }

  identity interface-idty {
    base service-assurance:subservice-idty;
    description "Checks whether an interface is healthy.";
  }

  augment /service-assurance:subservices/service-assurance:subservice/service-assurance:parameter {
       when "derived-from-or-self(service-assurance:type, 'interface-idty')";
       description
         "Specify the required parameters for the interface-idty subservice type";

       leaf device {
           type string;
           description "Device supporting the interface.";
       }
       leaf interface {
           type string;
           description "Name of the interface.";
       }
  }
}

   <CODE ENDS>

7.  Vendor-specific Subservice Extension: example-service-assurance-
    device-acme YANG module

7.1.  Tree View

   The following tree diagram [RFC8340] provides an overview of the
   example-service-assurance-device-acme data model.




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module: example-service-assurance-device-acme
  augment /service-assurance:subservices/service-assurance:subservice/service-assurance:parameter:
    +--rw acme-device-idty
       +--rw device?                    string
       +--rw acme-specific-parameter?   string

7.2.  Complete Tree View

   The following tree diagram [RFC8340] provides an overview of the
   ietf-service-assurance, ietf-service-assurance-device, and example-
   service-assurance-device-acme data models.








































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module: ietf-service-assurance
  +--ro assurance-graph-version        yang:counter32
  +--ro assurance-graph-last-change    yang:date-and-time
  +--rw subservices
     +--rw subservice* [type id]
        +--rw type                                                            identityref
        +--rw id                                                              string
        +--ro last-change?                                                    yang:date-and-time
        +--ro label?                                                          string
        +--rw under-maintenance?                                              boolean
        +--rw maintenance-contact                                             string
        +--rw (parameter)?
        |  +--:(service-instance-parameter)
        |  |  +--rw service-instance-parameter
        |  |     +--rw service?         string
        |  |     +--rw instance-name?   string
        |  +--:(service-assurance-device:device-idty)
        |  |  +--rw service-assurance-device:device-idty
        |  |     +--rw service-assurance-device:device?   string
        |  +--:(service-assurance-interface:device)
        |  |  +--rw service-assurance-interface:device?                       string
        |  +--:(service-assurance-interface:interface)
        |  |  +--rw service-assurance-interface:interface?                    string
        |  +--:(example-service-assurance-device-acme:acme-device-idty)
        |     +--rw example-service-assurance-device-acme:acme-device-idty
        |        +--rw example-service-assurance-device-acme:device?                    string
        |        +--rw example-service-assurance-device-acme:acme-specific-parameter?   string
        +--ro health-score?                                                   uint8
        +--ro symptoms-history-start?                                         yang:date-and-time
        +--rw symptoms
        |  +--ro symptom* [start-date-time id]
        |     +--ro id                     string
        |     +--ro health-score-weight?   uint8
        |     +--ro description?           string
        |     +--ro start-date-time        yang:date-and-time
        |     +--ro stop-date-time?        yang:date-and-time
        +--rw dependencies
           +--rw dependency* [type id]
              +--rw type               -> /subservices/subservice/type
              +--rw id                 -> /subservices/subservice[type=current()/../type]/id
              +--rw dependency-type?   identityref

7.3.  Concepts

   Under some circumstances, vendor-specific subservice types might be
   required.  As an example of this vendor-specific implementation, this
   section shows how to augment the ietf-service-assurance-device module




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   to add support for the subservice DeviceHealthy, specific to the ACME
   Corporation.  The new parameter is acme-specific-parameter.

7.4.  YANG Module

module example-service-assurance-device-acme {
  yang-version 1.1;
  namespace "urn:example:example-service-assurance-device-acme";
  prefix example-service-assurance-device-acme;

  import ietf-service-assurance {
    prefix "service-assurance";
  }

  import ietf-service-assurance-device {
    prefix "service-assurance-device";
  }

  organization
    "IETF NETCONF (Network Configuration) Working Group";
  contact
    "WG Web:   <https://datatracker.ietf.org/wg/netconf/>
     WG List:  <mailto:netconf@ietf.org>
     Author:   Benoit Claise  <mailto:bclaise@cisco.com>
     Author:   Jean Quilbeuf   <mailto:jquilbeu@cisco.com>";
  description
   "This module extends the ietf-service-assurance-device module to add
    support for the subservice DeviceHealthy, specific to the ACME Corporation.

    ACME Network Device is healthy.

    The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
    'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
    'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
    are to be interpreted as described in BCP 14 (RFC 2119)
    (RFC 8174) when, and only when, they appear in all
    capitals, as shown here.

    Copyright (c) 2019 IETF Trust and the persons identified as
    authors of the code.  All rights reserved.

    Redistribution and use in source and binary forms, with or
    without modification, is permitted pursuant to, and subject
    to the license terms contained in, the Simplified BSD License
    set forth in Section 4.c of the IETF Trust's Legal Provisions
    Relating to IETF Documents
    (https://trustee.ietf.org/license-info).




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    This version of this YANG module is part of RFC XXXX; see the
    RFC itself for full legal notices.  ";

  revision 2020-01-13 {
    description
      "Added the maintenance window concept.";
    reference
      "RFC xxxx: Title to be completed";
  }

  revision 2019-11-16 {
    description
      "Initial revision.";
    reference
        "RFC xxxx: Title to be completed";
  }

  identity device-acme-idty {
    base service-assurance-device:device-idty;
    description "Network Device is healthy.";
  }

  augment /service-assurance:subservices/service-assurance:subservice/service-assurance:parameter {
       description
         "Specify the required parameters for a new subservice type";
       container acme-device-idty{
           when "derived-from-or-self(../service-assurance:type, 'device-acme-idty')";
           description
             "Specify the required parameters for the device-acme-idty subservice type";

           leaf device {
               type string;
               description "The device to monitor.";
           }

           leaf acme-specific-parameter {
               type string;
               description "The ACME Corporation sepcific parameter.";
           }
       }
  }
}

8.  Security Considerations

   The YANG module specified in this document defines a schema for data
   that is designed to be accessed via network management protocols such
   as NETCONF [RFC6241] or RESTCONF [RFC8040].  The lowest NETCONF layer



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   is the secure transport layer, and the mandatory-to-implement secure
   transport is Secure Shell (SSH) [RFC6242].  The lowest RESTCONF layer
   is HTTPS, and the mandatory-to-implement secure transport is TLS
   [RFC8446].

   The Network Configuration Access Control Model (NACM) [RFC8341]
   provides the means to restrict access for particular NETCONF or
   RESTCONF users to a preconfigured subset of all available NETCONF or
   RESTCONF protocol operations and content.

   There are a number of data nodes defined in this YANG module that are
   writable/ creatable/deletable (i.e., config true, which is the
   default).  These data nodes may be considered sensitive or vulnerable
   in some network environments.  Write operations (e.g., edit-config)
   to these data nodes without proper protection can have a negative
   effect on network operations.  These are the subtrees and data nodes
   and their sensitivity/vulnerability:

   o  /subservices/subservice/type

   o  /subservices/subservice/id

   o  /subservices/subservice/under-maintenance

   o  /subservices/subservice/maintenance-contact

9.  IANA Considerations

9.1.  The IETF XML Registry

   This document registers two URIs in the IETF XML registry [RFC3688].
   Following the format in [RFC3688], the following registrations are
   requested:

      URI: urn:ietf:params:xml:ns:yang:ietf-service-assurance
      Registrant Contact: The NETCONF WG of the IETF.
      XML: N/A, the requested URI is an XML namespace.

      URI: urn:ietf:params:xml:ns:yang:ietf-service-assurance-device
      Registrant Contact: The NETCONF WG of the IETF.
      XML: N/A, the requested URI is an XML namespace.

      URI: urn:ietf:params:xml:ns:yang:ietf-service-assurance-interface
      Registrant Contact: The NETCONF WG of the IETF.
      XML: N/A, the requested URI is an XML namespace.






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9.2.  The YANG Module Names Registry

   This document registers three YANG modules in the YANG Module Names
   registry [RFC7950].  Following the format in [RFC7950], the the
   following registrations are requested:

  name:       ietf-service-assurance
  namespace:  urn:ietf:params:xml:ns:yang:ietf-service-assurance
  prefix:     inc
  reference:  RFC XXXX

  name:       ietf-service-assurance-device
  namespace:  urn:ietf:params:xml:ns:yang:ietf-service-assurance-device
  prefix:     inc
  reference:  RFC XXXX

  name:       ietf-service-assurance-interface
  namespace:  urn:ietf:params:xml:ns:yang:ietf-service-assurance-interface
  prefix:     inc
  reference:  RFC XXXX

10.  Open Issues

      -None

11.  References

11.1.  Normative References

   [draft-claise-opsawg-service-assurance-architecture]
              Claise, B. and J. Quilbeuf, "draft-claise-opsawg-service-
              assurance-architecture", 2020.

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

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.






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

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

11.2.  Informative References

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

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

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

Appendix A.  Changes between revisions

   v04 - v05

   o  Added the concept of symptoms-history-start

   o  Changed label to description, under symptoms.  This was confusing
      as there was two labels in the models

   v03 - v04

   o  Add the interface subservice, with two parameters

   v02 - v03

   o  Added the maintenace window concepts



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   v01 - v02

   o  Improved leaf naming

   o  Clarified some concepts: symptoms, dependency

   v00 - v01

   o  Terminology clarifications

   o  Provide example of impacting versus impacted dependencies

Acknowledgements

   The authors would like to thank Jan Lindblad for his help during the
   design of these YANG modules.  The authors would like to thank
   Stephane Litkowski and Charles Eckel for their reviews.

Authors' Addresses

   Benoit Claise
   Cisco Systems, Inc.
   De Kleetlaan 6a b1
   1831 Diegem
   Belgium

   Email: bclaise@cisco.com


   Jean Quilbeuf
   Cisco Systems, Inc.
   1, rue Camille Desmoulins
   92782 Issy Les Moulineaux
   France

   Email: jquilbeu@cisco.com


   Paolo Lucente
   NTT
   Siriusdreef 70-72
   Hoofddorp, WT  2132
   Netherlands

   Email: paolo@ntt.net






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   Paolo Fasano
   TIM S.p.A
   via G. Reiss Romoli, 274
   10148 Torino
   Italy

   Email: paolo2.fasano@telecomitalia.it












































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