NETCONF                                                       B. Lengyel
Internet-Draft                                                  Ericsson
Intended status: Standards Track                                A. Clemm
Expires: March 7, April 25, 2020                                        Futurewei
                                                               B. Claise
                                                     Cisco Systems, Inc.
                                                       September 4,
                                                        October 23, 2019

                  Yang-Push

                  YANG-Push Notification Capabilities
            draft-ietf-netconf-notification-capabilities-04
            draft-ietf-netconf-notification-capabilities-05

Abstract

   This document proposes a YANG module that allows a server publisher to
   specify
   server capabilities related to "Subscription to YANG Datastores"
   (Yang-Push).
   (YANG-Push).  It proposes to use YANG Instance Data to document this
   information and make it already available at implementation time, implementation-time, but
   also allow it to be reported at run-time.

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 March 7, April 25, 2020.

Copyright Notice

   Copyright (c) 2019 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
   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.  Notification Capability Model . . . . . . . . . . . . . . . .   4   5
     3.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .   5   6
     3.2.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
     5.1.  The IETF XML Registry . . . . . . . . . . . . . . . . . .  12  13
     5.2.  The YANG Module Names Registry  . . . . . . . . . . . . .  12  13
   6.  Open Issues . . . . . . . . . . . . . . . . . . . . . . . . .  12
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     7.1.
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     7.2.
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  13  14
   Appendix A.  Instance data examples . . . . . . . . . . . . . . .  14
   Appendix B.  Changes between revisions  . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

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

   The terms Yang-Push, YANG-Push, On-change subscription and Periodic subscription
   are used as defined in [I-D.ietf-netconf-yang-push] [RFC8641]

   The terms Subscriber, Publisher and Receiver are used as defined in
   [RFC8639]

   On-change Notification Capability: The capability of the server publisher to
   support On-change subscriptions.
   send on-change notifications for a specific datastore or a specific
   data node.

   The term Server is used as defined in [RFC8342]

   Implementation-time information: Information about the server's publisher's
   behavior that is made available during the implementation of the
   server,
   publisher, available from a source other then a running server. server
   implementing the publisher.

   Run-time information: Information about the server's publisher's behavior that
   is available from the running server (implementing the publisher) via
   management protocols such as NETCONF [RFC6241] or RESTCONF [RFC8040].

2.  Introduction

   As defined in [I-D.ietf-netconf-yang-push] [RFC8641] a server publisher may allow clients subscribers to
   subscribe to updates from a datastore and subsequently push such
   update notifications to the client. receiver.  Notifications may be sent
   periodically or on-change (more or less immediately after each
   change).

   A server publisher supporting YANG-Push has a number of capabilities defined
   in
   [I-D.ietf-netconf-yang-push] [RFC8641] that are often determined during the implementation of
   the server. publisher.  These include:

   o  Supported (reporting) periods for periodic subscriptions

   o  Maximum number of objects that can be sent in an update

   o  The set of datastores or data nodes for which periodic
      notification is supported

   If the optional on-change feature is supported, additionally:

   o  Supported dampening periods for on-change subscriptions

   o  The set of datastores or data nodes for which on-change
      notification is supported

   Servers

   Publishers MAY have limitations in how many update notifications and
   how many datastore node updates they can send out in a certain time-
   period.

   Publishers might not support periodic subscriptions to all
   datastores.

   In some cases, a publisher supporting on-change notifications will
   not be able to push updates for some object types on-change.  Reasons
   for this might be that the value of the datastore node changes
   frequently (e.g. in-octets counter), that small object changes are
   frequent and meaningless irrelevant to the receiver (e.g., a temperature gauge
   changing 0.1
   degrees), degrees within a predetermined and acceptable range), or
   that the implementation is not capable of on-change notification for
   a particular object.  In those cases, it will be important for client
   subscriber applications to have a way to identify for which objects on-change on-
   change notifications are supported and for which ones not.

   Faced with the reality that support for on-change notification does
   not mean that such notifications will be sent for any specific data
   node, client/management subscriber/management applications can not rely on the on-change on-
   change functionality unless the client subscriber has some means to identify for
   which objects on-change notifications are supported.  YANG models are
   meant to be used as an interface contract.  Without identification of
   the data nodes actually supporting on-change, this contract would be
   incomplete.

   This document proposes a YANG module that allows a client subscriber to
   discover YANG-Push related capabilities both at implementation-time
   and run-
   time.

   Implementation time run-time.

   Implementation-time information is needed by Network Management
   System (NMS) implementers.  During  A NMS implementation for any
   functionality that depends on the notifications wants to
   support notifications, needs the information about
   on change on-change
   notification capability is needed. capability.  If the information is not available early documented in some document, a
   way available to the NMS designer, but only as instance data from the
   network node once it is deployed, the NMS implementation will be
   delayed, because it has to wait for the network node to be ready.  In
   addition, the assumption that all NMS implementers will have a
   correctly configured network node available to retrieve data from, from is
   an expensive proposition and may not always hold.  (An NMS may need
   to be able to handle many dozens of network node types.)  Often a
   fully functional NMS is a requirement for introducing a new network
   node type into a network, so delaying NMS readiness effectively also
   delays the time at which a new network node type can be introduced
   into the network.

   Implementation time

   Implementation-time information is needed by system integrators.
   When introducing a network node type into their network, operators
   often need to integrate the node type into their own management
   system.  The NMS may have management functions that depend on on-
   change notifications.  The network operator needs to plan his
   management practices and NMS implementation before he even decides to
   buy the specific network node type.  Moreover the decision to buy the
   node type sometimes depends on these management possibilities.

   Run-time information is needed:

   o  for any "purely model driven" client, application, e.g. a NETCONF-browser.  As
      long as it has a valid model
      Such applications depend on reading models, capabilities in run-
      time to read support all the capability information,
      it does not care which data nodes send notification, it will just
      handle what is available. publisher's available functionality.

   o  in case the capability might change during run-time e.g. due to
      licensing, HW constraints etc.

   o  to check that early, implementation time capability information
      about the capabilities provided early, already in
      implementation-time is indeed what the server publisher implements (is
      the supplied documentation correct?)

3.  Notification Capability Model

   It is a goal to provide Yang-Push YANG-Push notification capability information
   in a format that is:

   o  vendor independent

   o  formal  machine readable

   o  identical for implementation-time and run-time

   The YANG module ietf-notification-capabilities is defined to provide
   the information.  It contains:

   o  a set of capabilities related to the amount throughput of notifications notification
      data the
      server publisher can send out

   o  specification of which data nodes support on-change notifications.

   Capability values can be specified on server publisher level, datastore
   level or on specific data nodes (and their contained sub-tree) of a
   specific datastore.  Capability values on a smaller, more specific
   part of the server's publisher's data always override more generic values.

   On-change capability is not specified on a server publisher level as
   different datastores usually have different on-change capabilities.
   On a datastore level on-change capability for configuration and state
   data can be specified separately.

   The information SHALL SHOULD be provided in two ways both following the
   ietf-notification-capabilities module:

   o  For the implementation-time use-case: It SHALL be provided by the
      implementer as YANG instance data file complying to
      [I-D.ietf-netmod-yang-instance-file-format].  The file SHALL be
      available already in implementation time implementation-time retrievable in a way that
      does not depend on a live network node.  E.g. download from
      product Website.

   o  For the run-time use-case: It SHALL MUST be available via NETCONF
      [RFC6241] or RESTCONF [RFC8040] from the live server (implementing
      the publisher) during run-
      time. run-time.  Implementations which support
      changing these capabilities at run-time SHOULD support on-change
      notifications about the
      datastore-subscription-capabilities publisher-subscription-capabilities
      container.

3.1.  Tree Diagram

   The following tree diagram [RFC8340] provides an overview of the data
   model.

module: ietf-notification-capabilities
  +--ro datastore-subscription-capabilities publisher-subscription-capabilities
     +--ro (update-period)?
     |  +--:(minimum-update-period)
     |  |  +--ro minimum-update-period?        uint32
     |  +--:(supported-update-period)
     |     +--ro supported-update-period*      uint32
     +--ro max-objects-per-update?             uint32
     +--ro minimum-dampening-period?           uint32 {yp:on-change}?
     +--ro datastore-capabilities* [datastore]
        +--ro datastore                          union
        +--ro (update-period)?
        |  +--:(minimum-update-period)
        |  |  +--ro minimum-update-period?       uint32
        |  +--:(supported-update-period) on-change-supported?                notification-support
     |                                                {yp:on-change}?
     +--ro supported-update-period*     uint32
        +--ro max-objects-per-update?            uint32 periodic-notifications-supported?   notification-support
     +--ro minimum-dampening-period?          uint32 supported-excluded-change-type*     union {yp:on-change}?
     +--ro on-change-supported-for-config?    boolean {yp:on-change}? datastore-capabilities* [datastore]
        +--ro on-change-supported-for-state?     boolean {yp:on-change}? datastore          -> /yanglib:yang-library/datastore/name
        +--ro per-node-capabilities* [node-selector]
           +--ro node-selector             nacm:node-instance-identifier
           +--ro (update-period)?
           |  +--:(minimum-update-period)
           |  |  +--ro minimum-update-period?        uint32
           |  +--:(supported-update-period)
           |     +--ro supported-update-period*      uint32
           +--ro max-objects-per-update?             uint32
           +--ro minimum-dampening-period?           uint32
           |                                             {yp:on-change}?
           +--ro on-change-supported             boolean on-change-supported?              notification-support
           |                                             {yp:on-change}?
           +--ro periodic-notifications-supported? notification-support
           +--ro supported-excluded-change-type*   union {yp:on-change}?

3.2.  YANG Module

   <CODE BEGINS> file "ietf-notification-capabilities@2019-08-13.yang" "ietf-notification-capabilities@2019-10-22.yang"

 module ietf-notification-capabilities {
   yang-version 1.1;
   namespace
     "urn:ietf:params:xml:ns:yang:ietf-notification-capabilities";
   prefix inc;
   import ietf-netconf-acm  { prefix nacm; }
   import ietf-yang-push    { prefix yp; }
   import ietf-yang-library {
     prefix yanglib;
     description
       "Requires revision 2019-01-04 or a revision derived from it.";
   }

   organization
     "IETF NETCONF (Network Configuration) Working Group";
   contact
     "WG Web:   <https://datatracker.ietf.org/wg/netconf/>
      WG List:  <mailto:netconf@ietf.org>

      Editor:   Balazs Lengyel
                <mailto:balazs.lengyel@ericsson.com>";
   description
     "This module specifies YANG-Push related server publisher
      capabilities.

      The module contains
      - capabilities related to the amount throughput of notifications notification data the
     server
      publisher can send out. support. (Note that for a specific subscription
      the server publisher MAY still allow only longer periods or smaller
      updates depending on e.g. actual load conditions.)
      - specification of which data nodes support on-change or periodic
      notifications.

      Capability values can be specified on publisher level, datastore
      level or on a
     smaller, more specific part data nodes (and their contained sub-tree) of
      a specific datastore.
      If a capability is specified on multiple levels, the server's data always override
      specification on a more specific level overrides more
      generic values. The hierarchy of specifications from generic
     to capability specifications; thus
      - a publisher level specification is overridden by any other
      specification
      - a datastore level specification (with a node-selector '/') is
      overridden by a specification with a more specific is:
      1) top level values valid for all datastores
      2) values node-selector.
      - a specification for a specific datastore (including and node-selector
      is overridden by a specification for the special
        'all' same datastore identifier)
      3) Value with
      a node-slector that describes more levels of containing lists
      and containers.

      If for a specific data node and its contained sub-tree
        in one of the datastores. Such capability different values are indicated
      for different nodes in a subscription, then only values
      acceptable for every node are inherited
        down guaranteed to be acceptable
      for the containment tree unless subscription.

      To find a more specific capability value is
        provided, as described in 4)
      4) A contained, smaller, more for a specific sub-tree node in a
      specific datastore (could be a single leaf)

      Any capability value MAY be absent the user SHALL
      1) consider the publisher level capabilities under the
      publisher-subscription-capabilities container if such exist
      2) search for a more generic datastore-capabilities list entry for
      the specific datastore
      3) within that datastore entry search for a
      per-node-capabilities entry that specifies the specific
      capability
      value is already provided or if and that has the server node-selector selecting the
      specific data node and that specifies the most levels of
      containing containers and lists.
      4) If no entries are found in the previous steps the
      publisher is not capable of providing a value. value because
      it is unknown, the capability is changing for some reason,
      there is no specified limit etc. In this case the
      publisher's behavior is unspecified.

      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
      (http://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 2019-08-13 2019-10-22 {
     description
       "Initial version";
     reference
       "RFC XXX: Yang-Push YANG-Push Notification Capabilities";
   }

  container datastore-subscription-capabilities

   grouping subscription-capabilities {
    config false;
     description
      "YANG-Push "Capabilities related server capabilities";

    grouping datastore-subscription-throughput-capabilities to Yang-Push notifications";

     typedef notification-support {
       type enumeration {
         enum no-notifications-supported {
           description "Capability values that affect the amount of
        notifications the server can send out."; "The publisher is not capable of sending any
             notifications for the relevant scope and subscription
             type." ;
         }
         enum notifications-for-config-changes-supported {
           description "The publisher is capable of sending
             notifications for config=true nodes, but not
             for config=false nodes for the relevant scope
             and subscription type." ;
         }
         enum notifications-for-state-changes-supported {
           description "The publisher is capable of sending
             notifications for config=false nodes, but not
             for config=true nodes for the relevant scope
             and subscription type." ;
         }
         enum notifications-for-all-changes-supported {
           description "The publisher is capable of sending
             notifications for both config=false and config=true
             nodes for the relevant scope and subscription type." ;
         }
       }
       description "Type for defining whether on-change or
         periodic notifications are supported for no, only config=true,
         only config=false or all data nodes.";
     }

     choice update-period {
       description "Supported update-period values.";
       leaf minimum-update-period {
         type uint32;
         units "centiseconds";
         description
            "Minimum "Indicates the minimal update period that is
           supported for a periodic subscription."; subscription.
           A periodic subscription to the selected data nodes must
           specify a value that is at least as large or greater than
           this";
       }

       leaf-list supported-update-period {
         type uint32;
         units "centiseconds";
         description "Supported update period values for a
           periodic subscription.
           A periodic subscription (used if only these specific to the selected data nodes must
           specify one of the values in the list; other values
           are supported)."; not supported.";
       }
     }

     leaf max-objects-per-update {
       type uint32 {
             range "1..max";
       }
       description
         "Maximum number of objects that can be sent
          in an update."; update for the selected data nodes.";
     }

     leaf minimum-dampening-period {
       if-feature yp:on-change ; yp:on-change;
       type uint32;
       units "centiseconds";
       description
         "The minimum dampening period supported for on-change
           subscriptions.";
      }
    }

    uses datastore-subscription-throughput-capabilities {
      description "Top level throughput capabilities.
        These values can be overridden by values provided per
        datastore or
          subscriptions for individual the selected data nodes in a datastore."; nodes.";
     }

    list datastore-capabilities

     leaf on-change-supported {
      key datastore ;
       if-feature yp:on-change;
       type notification-support;
       description "Capabilities values per datastore.
        For non-NMDA servers
         "Specifies whether the config=false data publisher is considered
        as if it was part capable of
          sending on-change notifications for the running datastore.

        Indicates per datastore throughput capabilities.

        Indicates per datastore the selected
          data store or data nodes for which and the
        server subtree below them.";
     }

     leaf periodic-notifications-supported {
       type notification-support;
       description
         "Specifies whether the publisher is capable of
          sending on-change notifications.
        If a datastore implemented by periodic notifications for the server is not specified
        in this list and there is no list element for 'all' datastores
        the datastore does not support any on-change notifications.

        On-change notifications SHALL be sent for a config=true selected
          data node if one of the following is true:
        - if it is a top level data-node and is not specified in the
        per-node-capabilities list and on-change-supported-for-config
        is true; store or
        - notifications are sent for its parent data node nodes and it is
        not specified in the per-node-capabilities list; or
        - it is specified in subtree below them.";
     }

     leaf-list supported-excluded-change-type {
       if-feature yp:on-change;
       type union {
         type enumeration {
           enum none {
             description "None of the per-node-capabilities list and has
        an on-change-supported value true.

        On-change notifications SHALL change types can be sent for a config=false
        data node if one excluded.";
           }
           enum all {
             description
               "Any combination of the following is true:
        - if it is a top level data-node (a config=false data node with
        a config=true parent SHALL change types can be treated as a top excluded.";
           }
         }
         type yp:change-type;
       }
       description "The change types that can be excluded in
         YANG-Push subscriptions.";
     }
   }

   container publisher-subscription-capabilities {
     config false;
     description "YANG-Push related publisher capabilities.
       Capability values specified here at the publisher level data node)
       are valid for all datastores and
       are used when the capability is not specified in on the per-node-capabilities list and
        on-change-supported-for-state is true;
       datastore level or
        - notifications are sent for its parent specific data node
        which is also nodes. ";

     uses subscription-capabilities {
       refine supported-excluded-change-type {
         default none;
       }
     }

     list datastore-capabilities {
       key datastore;

       description "Capabilities values per datastore.
         For non-NMDA servers/publishers the config=false and it data is not specified in the
        per-node-capabilities list; or
        -
         considered as if it is specified in was part of the per-node-capabilities list and has
        an on-change-supported value true"; running datastore.";

       leaf datastore {
         type union {
          type leafref {
           path /yanglib:yang-library/yanglib:datastore/yanglib:name ;
          }
          type enumeration {
            enum all ;
          }
        }
        must '. != "all" or count(..) = "1" ' {
          error-message
            "If 'all' is present individual datastores cannot be " +
              "specified."; /yanglib:yang-library/yanglib:datastore/yanglib:name;
         }
         description "The datastore for which capabilities are defined.";
      }

      uses datastore-subscription-throughput-capabilities {
        description "Throughput capabilities for a datastore.
          These values will override top level values and defined.
           Only individual datastores can be
          overridden by values provided for individual data nodes
          in a datastore.";
      }

      leaf on-change-supported-for-config {
        if-feature yp:on-change ;
        type boolean;
        default "true";
        description
          "Specifies the default value for
           top level config=true data nodes for the
           on-change-supported capability.";
      }

      leaf on-change-supported-for-state {
        if-feature yp:on-change ;
        type boolean;
        default "false";
        description
          "Specifies the default value for
           top level config=false data nodes for the
           on-change-supported capability."; specified
           e.g. ds:conventional is not allowed.";
       }

       list per-node-capabilities {
         key "node-selector";
         description
          "A
           "Each list of data nodes that have either a throughput or
           on-change-notification capability specifically defined.

           Should be used only when specific data nodes support
           capabilities that are different from entry specifies notification capabilities
           of their parent nodes or
            for the default selected data nodes. The same capabilities apply for
            the datastore."; data nodes in the subtree below them unless another list
            entry with a more specific node selector is present.";

         leaf node-selector {
           type nacm:node-instance-identifier;
           description
             "Selects the data nodes for which
             a capability is specified.";
        }

        uses datastore-subscription-throughput-capabilities {
          description "Throughput capabilities for a specific are
              specified. The special value '/' denotes all data node.
            These values will override top level or datastore
            specific values.";
        }

        leaf on-change-supported {
          if-feature yp:on-change ;
          type boolean;
          mandatory true;
          description
            "Specifies whether nodes
              in the server is capable datastore.
              The system SHOULD order list entries according to
              the tree structure of
             sending on-change notifications for the selected data nodes."; models to make
              reading/parsing the data model more simple.";
         }

         uses subscription-capabilities;
       }
     }
   }
 }

   <CODE ENDS>

4.  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
   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.

   All protocol-accessible data are read-only and cannot be modified.
   The data in this module is not security sensitive.  Access control
   may be configured, to avoid exposing the read-only data.

   When that data is in file format, data should be protected against
   modification or unauthorized access using normal file handling and
   secure and mutually authenticated file transport mechanisms.

5.  IANA Considerations
5.1.  The IETF XML Registry

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

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

5.2.  The YANG Module Names Registry

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

  name:       ietf-notification-capabilities
  namespace:  urn:ietf:params:xml:ns:yang:ietf-notification-capabilities
  prefix:     inc
  reference:  RFC XXXX

6.  Open Issues

      -

7.  References

7.1.

6.1.  Normative References

   [I-D.ietf-netconf-yang-push]
              Clemm, A. and E. Voit, "Subscription to YANG Datastores",
              draft-ietf-netconf-yang-push-25 (work in progress), May
              2019.

   [I-D.ietf-netmod-yang-instance-file-format]
              Lengyel, B. and B. Claise, "YANG Instance Data File
              Format", draft-ietf-netmod-yang-instance-file-format-04
              (work in progress), August 2019.

   [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>.

   [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>.

   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore Architecture
              (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
              <https://www.rfc-editor.org/info/rfc8342>.

   [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>.

7.2.

   [RFC8639]  Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
              E., and A. Tripathy, "Subscription to YANG Notifications",
              RFC 8639, DOI 10.17487/RFC8639, September 2019,
              <https://www.rfc-editor.org/info/rfc8639>.

   [RFC8641]  Clemm, A. and E. Voit, "Subscription to YANG Notifications
              for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641,
              September 2019, <https://www.rfc-editor.org/info/rfc8641>.

6.2.  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.  Instance data examples

   The following example is instance-data describing the notification
   capabilities of a hypothetical "acme-switch".  The switch implements
   the running, candidate and operational datastores.  Every change can
   be reported on-change from running, nothing from candidate and all
   config=false data from operational.  Periodic subscriptions are
   supported for running and operational, but not for candidate.

<?xml version="1.0" encoding="UTF-8"?>
<instance-data-set xmlns=
    "urn:ietf:params:xml:ns:yang:ietf-yang-instance-data">
  <name>acme-switch-notification-capabilities</name>
   <module>ietf-notification-capabilities@2019-08-13.yang</module>
  <module>ietf-notification-capabilities@2019-10-22.yang</module>
  <!-- revision date, contact, etc. -->
  <description>Notification capabilities of acme-switch.
    Acme-switch implements the running, candidate and operational
    datastores. Every change can be reported on-change from running,
    nothing from candidate and all config=false data from operational.
    Periodic subscriptions are supported for running and
    operational, but not for candidate.
  </description>
  <content-data>
     <datastore-subscription-capabilities>
    <publisher-subscription-capabilities
      xmlns="urn:ietf:params:xml:ns:yang:ietf-notification-capabilities"
      xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
      <minimum-update-period>500</minimum-update-period>
      <max-objects-per-update>2000</max-objects-per-update>
      <minimum-dampening-period>100</minimum-dampening-period>
      <periodic-notifications-supported>
        notifications-for-all-changes-supported
      </periodic-notifications-supported>
      <datastore-capabilities>
         <datastore xmlns="urn:ietf:params:xml:ns:yang:ietf-datastores">
           running
         </datastore>
         <!-- Neither on-change-supported-for-config nor
         on-change-supported-for-state are present as the
         default values are in effect. -->
        <datastore>ds:operational</datastore>
        <per-node-capabilities>
          <node-selector>/</node-selector>
          <on-change-supported>
            notifications-for-state-changes-supported
          </on-change-supported>
        </per-node-capabilities>
      </datastore-capabilities>
       <!-- The candidate datastore is implemented, but not present
       here as it does not support any on-change notifications. -->
      <datastore-capabilities>
         <datastore xmlns="urn:ietf:params:xml:ns:yang:ietf-datastores">
           operational
         </datastore>
         <on-change-supported-for-config>
           false
         </on-change-supported-for-config>
         <on-change-supported-for-state>
           true
         </on-change-supported-for-state>
        <datastore>ds:candidate</datastore>
        <per-node-capabilities>
          <node-selector>/</node-selector>
          <on-change-supported>no-notifications-supported
            </on-change-supported>
          <periodic-notifications-supported>no-notifications-supported
            </periodic-notifications-supported>
        </per-node-capabilities>
      </datastore-capabilities>
      <datastore-capabilities>
        <datastore>ds:running</datastore>
        <per-node-capabilities>
          <node-selector>/</node-selector>
          <on-change-supported>notifications-for-all-changes-supported
            </on-change-supported>
        </per-node-capabilities>
      </datastore-capabilities>
     </datastore-subscription-capabilities>

    </publisher-subscription-capabilities>
  </content-data>
</instance-data-set>

     Figure 1: Notification Capabilities with default datastore level settings

   The following is the instance-data describing the notification
   capabilities of a hypothetical "acme-router".  The router implements
   the running, and operational datastores.  Every change can be
   reported on-change from running, but only config=true nodes and some
   config=false data from operational.  Interface statistics are not
   reported on-change only 2 important counters.  Datastore subscription
   capabilities are not reported on-change as they never change on the
   acme-router during run-time.

<?xml version="1.0" encoding="UTF-8"?>
<instance-data-set xmlns=
    "urn:ietf:params:xml:ns:yang:ietf-yang-instance-data">
  <name>acme-router-notification-capabilities</name>
  <module>ietf-notification-capabilities@2019-08-13.yang</module>
  <module>ietf-notification-capabilities@2019-10-22.yang</module>
  <!-- revision date, contact, etc. -->
  <description>Defines the notification capabilities of an acme-router.
    The router only has running, and operational datastores.
    Every change can be reported on-change from running, but
    only config=true nodes and some config=false data from operational.
    Statistics are not reported on-change only 2 important counters,
    for these a smaller dampening period is possible.
      </description>
  <content-data>
    <datastore-subscription-capabilities
     xmlns="urn:ietf:params:xml:ns:yang:ietf-notification-capabilities">
    <publisher-subscription-capabilities
      xmlns="urn:ietf:params:xml:ns:yang:ietf-notification-capabilities"
      xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
      <minimum-update-period>500</minimum-update-period>
      <max-objects-per-update>2000</max-objects-per-update>
      <minimum-dampening-period>100</minimum-dampening-period>
      <periodic-notifications-supported>
        notifications-for-all-changes-supported
      </periodic-notifications-supported>
      <on-change-supported>
        notifications-for-all-changes-supported
      </on-change-supported>
      <supported-excluded-change-type>
        all
      </supported-excluded-change-type>
      <datastore-capabilities>
        <datastore xmlns="urn:ietf:params:xml:ns:yang:ietf-datastores">
          running
        </datastore>
      </datastore-capabilities>
      <datastore-capabilities>
        <datastore xmlns="urn:ietf:params:xml:ns:yang:ietf-datastores">
          operational
          ds:operational
        </datastore>
        <on-change-supported-for-state>
          true
        </on-change-supported-for-state>
        <per-node-capabilities>
          <node-selector>
            /inc:datastore-subscription-capabilities</node-selector>
          <on-change-supported>false</on-change-supported>
        </per-node-capabilities>
        <per-node-capabilities>
          <node-selector>
              /if:interfaces/if:interface/if:statistics</node-selector>
          <on-change-supported>false</on-change-supported>
          <on-change-supported>
            no-notifications-supported
          </on-change-supported>
        </per-node-capabilities>
        <per-node-capabilities>
          <node-selector>
              /if:interfaces/if:interface/if:statistics/if:in-octets
          </node-selector>
          <minimum-dampening-period>10</minimum-dampening-period>
          <on-change-supported>true</on-change-supported>
          <on-change-supported>
            notifications-for-all-changes-supported
          </on-change-supported>
        </per-node-capabilities>
        <per-node-capabilities>
          <node-selector>
              /if:interfaces/if:interface/if:statistics/if:out-octets
          </node-selector>
          <on-change-supported>true</on-change-supported>
          <minimum-dampening-period>10</minimum-dampening-period>
          <on-change-supported>
            notifications-for-all-changes-supported
          </on-change-supported>
        </per-node-capabilities>
      </datastore-capabilities>
    </datastore-subscription-capabilities>
    </publisher-subscription-capabilities>
  </content-data>
</instance-data-set>

   Figure 2: Notification Capabilities with data node specific settings

Appendix B.  Changes between revisions

   v04 - v05

   o  Added new capabilities periodic-notifications-supported and
      supported-excluded-change-type.

   o  Restructured YANG module to make the node-selector's usage similar
      to how NACM uses it: "/" means the whole datastore.

   o  Small corrections, spelling, rewording

   o  Replaced the term server with the term publisher except in cases
      where we speak about datastores and functionality based on get,
      getconfig operations.  In this latter case it is really the server
      functionality that is discussed

   v03 - v04

   o  Clarified recommended support for on-change notifications about
      the datastore-subscription-capabilities.

   v02 - v03

   o  Allow throughput related capabilities to be defined on top,
      datastore or data node level.  Described that specific capability
      values always override generic ones.

   o  Indicate that non-NMDA servers can also use this model.

   o  Updated according to draft-ietf-netmod-yang-instance-file-
      format-04

   v01 - v02

   o  Added instance data examples

   o  On-change capability can be defined per datastore

   o  Added "if-feature yp:on-change" where relevant

   o  Unified units used

   v00 - v01

   o  Add more capabilities: minimum period, supported period max-number
      of objects, min dampening period, dampening supported

Authors' Addresses

   Balazs Lengyel
   Ericsson
   Magyar Tudosok korutja 11
   1117 Budapest
   Hungary

   Email: balazs.lengyel@ericsson.com
   Alexander Clemm
   Futurewei
   2330 Central Expressway
   Santa Clara, CA 95050
   USA

   Email: ludwig@clemm.org

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

   Email: bclaise@cisco.com