NETCONF                                                       B. Lengyel
Internet-Draft                                                  Ericsson
Intended status: Standards Track                                A. Clemm
Expires: July 10, 18, 2020                                         Futurewei
                                                               B. Claise
                                                     Cisco Systems, Inc.
                                                        January 7, 15, 2020

  Generic YANG-related System Capabilities and YANG-Push Notification
                              Capabilities
            draft-ietf-netconf-notification-capabilities-09
            draft-ietf-netconf-notification-capabilities-10

Abstract

   This document proposes two YANG modules.  The module ietf-system-
   capabilities provides a structure that can be used to specify any
   YANG related system capability.

   The module ietf-notification-capabilities allows a publisher to
   specify capabilities related to "Subscription to YANG Datastores"
   (YANG-Push).  It proposes to use YANG Instance Data to document this
   information and make it already available at 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 July 10, 18, 2020.

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
   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
     2.1.  YANG-Push Notification Capabilities . . . . . . . . . . .   3
   3.  Providing System Capability Information . . . . . . . . . . .   5
   4.  System Capabilities Model . . . . . . . . . . . . . . . . . .   6
     4.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Notification Capabilities Model . . . . . . . . . . . . . . .  10
     5.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .  10
     5.2.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  11
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  16  15
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16  15
     7.1.  The IETF XML Registry . . . . . . . . . . . . . . . . . .  16  15
     7.2.  The YANG Module Names Registry  . . . . . . . . . . . . .  17  16
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  17  16
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  17  16
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  18  17
   Appendix A.  Instance data examples . . . . . . . . . . . . . . .  18  17
   Appendix B.  Changes between revisions  . . . . . . . . . . . . .  22  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24  23

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, On-change subscription and Periodic subscription
   are used as defined in [RFC8641]

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

   The term Server is used as defined in [RFC8342]
   On-change Notification Capability: The capability of the publisher to
   send on-change notifications for a specific datastore or a specific
   data node.

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

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

2.  Introduction

   Systems implementing a server and/or a publisher often have
   capabilities that are not defined by the YANG model itself.  There is
   a need to publish this capability information as it part of the
   contract between the server and client.  Examples include: maximum
   size of data that can be stored or transferred, information about
   counters (whether a node supports on-change telemetry), etc.  Such
   capabilities are often dependent on a vendor's implementation or the
   available resources at deployment.  Many such capabilities are
   specific to either the complete system, individual YANG datastores or
   specific parts of the YANG schema, or even to individual data nodes.
   It is a goal of this document to provide a common way of representing
   such capabilities in a format that is:

   o  vendor independent

   o  machine readable

   o  available in identical format both in implementation-time and run-
      time

2.1.  YANG-Push Notification Capabilities

   A specific case where we need to specify capabilities is the YANG-
   Push functionality.  As defined in [RFC8641] a publisher may allow
   subscribers to subscribe to updates from a datastore and subsequently
   push such update notifications to the receiver.  Notifications may be
   sent periodically or on-change (more or less immediately after each
   change).

   A publisher supporting YANG-Push has a number of capabilities defined
   in [RFC8641] that are often determined during the implementation of
   the 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

   Additional capabilities if the optional on-change feature is
   supported include:

   o  Supported dampening periods for on-change subscriptions

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

   Publishers 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 irrelevant to the receiver (e.g., a temperature gauge
   changing 0.1 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
   subscriber applications to have a way to identify which objects 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, subscriber/management applications can not rely on the on-
   change functionality unless the subscriber has some means to identify
   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.

   Clients of a server, subscribers to a publisher need a method to
   gather capability information.

   Implementation-time information is needed by Network Management
   System (NMS) implementers.  A NMS implementation that wants to
   support notifications, needs the information about on-change
   notification capability.  If the information is not documented in 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 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 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" application, e.g., a NETCONF-
      browser.  Such applications depend on reading models and
      capabilities in run-time to support all the 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 capability information provided early, already in
      implementation-time is indeed what the publisher implements (is
      the supplied documentation correct?)

3.  Providing System Capability Information

   Capability information is represented by instance-data based on one
   or more "capability defining YANG modules".  This allows a user to
   discover capabilities both at implementation-time and run-time.

   o  For the implementation-time use-case: Capabilities SHOULD be
      provided by the implementer as YANG instance data files complying
      to [I-D.ietf-netmod-yang-instance-file-format].  The file SHALL be
      available already in 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: Capabilities SHOULD be available via
      NETCONF [RFC6241] or RESTCONF [RFC8040] from the live server
      (implementing the publisher) during run-time.  Implementations
      which support changing these capabilities at run-time SHOULD
      support on-change notifications about the system-capabilities
      container.

   The module ietf-system-capabilities is defined to provide a structure
   that can be used to specify any YANG related system capability.

   The module ietf-notification-capabilities is defined to allow a
   publisher to specify capabilities related to "Subscription to YANG
   Datastores" (YANG-Push) augmenting ietf-system-capabilities.

4.  System Capabilities Model

   The module ietf-system-capabilities is defined to provide a structure
   that can be used to specify any YANG related system capability.

   Capability values can be specified on system/publisher level,
   datastore level (by selecting all nodes in the datastore) or for
   specific data nodes of a specific datastore (and their contained sub-
   tree) of a specific datastore.
   trees).  Capability values on specified for a smaller, more specific part of the system's data always datastore or
   node-set override more generic
   values. values specified on the system/publisher level.

   This module itself does not contain any capabilities.  It SHOULD be
   used by other modules to augment-in specific capability information.
   Every set of such capabilities SHOULD be wrapped in a container under
   the augment statement to cleanly separate different groups of
   capabilities.  These "wrapper containers" SHALL be augmented in at
   /sysc:system-capabilities and /sysc:system-capabilities/
   sysc:datastore-capabilities/sysc:per-node-capabilities.

   Note: The solution is usable for both NMDA and non-NMDA systems.  For
   non-NMDA servers/publishers config=false data is considered as if it
   was part of the running datastore.

4.1.  Tree Diagram

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

 module: ietf-system-capabilities
   +--ro system-capabilities
      +--ro datastore-capabilities* [datastore]
         +--ro datastore         -> /yanglib:yang-library/datastore/name
         +--ro per-node-capabilities* [node-selector] []
            +--ro node-selector (node-selection)?
               +--:(node-selector)
                  +--ro node-selector?   nacm:node-instance-identifier

4.2.  YANG Module

   <CODE BEGINS> file "ietf-system-capabilities@2020-01-02.yang" "ietf-system-capabilities@2020-01-14.yang"

module ietf-system-capabilities {
  yang-version 1.1;
  namespace
    "urn:ietf:params:xml:ns:yang:ietf-system-capabilities";
  prefix sysc;

  import ietf-netconf-acm { prefix nacm;
     description
        "The module ietf-netconf-acm is OPTIONAL to implement."; }

  import ietf-yang-library {
    prefix yanglib;
    description "The module ietf-yang-library is REQUIRED to
       be implemented. Revision "Revision 2019-01-04 or a
      revision derived from it is REQUIRED.";
  }

  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 a module intended to contain system
      capabilities. System capabilities may include capabilities of a
      NETCONF or RESTCONF server or a notification publisher.

     This module does not contain any specific capabilities it only
     provides a structure where containers containing the actual
     capabilities should be augmented in.

     Capability values can be specified on system level,
     datastore level (by selecting all nodes in the datastore) or
     for specific data nodes (and their contained
      sub-tree) of a specific datastore.
      If a capability is specified on multiple levels, the
      specification on a more specific level overrides more
      generic capability specifications; thus
      - a system 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 node-selector.
      - a specification (and their
     contained sub-trees).

     Capability values specified for a specific datastore and node-selector
      is overridden by a specification for the same datastore with
      a node-selector that describes more levels of containing lists
      and containers.
      It is not allowed to have multiple node selectors which
      - are defined for the same datastore AND
      - have or
     node-set override values specified on the same number of containment levels AND
      - select an overlapping set of nodes. system/publisher level.

     To find a capability value for a specific data node in a
     specific datastore the user SHALL
     1) consider the system level capabilities under the
      system-capabilities container if the
      capability value is specified.
      2) search for a datastore-capabilities list entry for
     the specific datastore.
      3)
     2) If the datastore entry is found within that datastore entry search for a process all
     per-node-capabilities entries in the order they appear in the list.
     The first entry that specifies the specific capability and that has the a
     node-selector selecting the specific data node and that specifies defines the most levels of
      containing containers
     capability value.
     3) If the capability value is not found above and lists. the specific
     capability is specified under the system-capabilities container
     (outside the datastore-capabilities list) this value shall be used.
     4) If no entries values are found in the previous steps the
      publisher
     system/publisher is not capable of providing a value because
     it is unknown, the capability is changing for some reason,
     there is no specified limit etc. In this case the
     system'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) 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
     (http://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC XXXX
     (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
     for full legal notices.";

  revision 2020-01-02 2020-01-14 {
    description
      "Initial version";
    reference
      "RFC XXX: YANG-Push Notification Capabilities";
  }
  container system-capabilities {
    config false;
    description "System capabilities.
      Capability values specified here at the system level
      are valid for all datastores and
      are used when the capability is not specified on the
      datastore level or for specific data nodes.";

    // augmentation point for system level capabilities

    list datastore-capabilities {
      key datastore;

      description "Capabilities values per datastore.
        For non-NMDA servers/publishers config=false data is
        considered as if it was part of the running datastore.";

      leaf datastore {
        type leafref {
          path /yanglib:yang-library/yanglib:datastore/yanglib:name;
        }
        description "The datastore for which capabilities are defined.
          Only individual datastores can be specified
          e.g., ds:conventional is not allowed.";
      }

      list per-node-capabilities {
         key "node-selector";
        description
          "Each list entry specifies capabilities for the selected
           data nodes. The same capabilities apply for the data nodes
           in the subtree below them unless another list
            entry with a more specific node selector specifying the same
            capability is present.";

         leaf node-selector {
           type nacm:node-instance-identifier;
           description
             "Selects the selected nodes.
           The system SHALL order the entries according to their
           precedence. The order of the entries MUST NOT change unless
           the underlying capabilities also change.";

        choice node-selection {
          description
            "A method to select all or some nodes within a datastore.";

          leaf node-selector {
            type nacm:node-instance-identifier;
            description
              "Selects the data nodes for which capabilities are
               specified. The special value '/' denotes all data nodes
               in the datastore.
              The system SHOULD order list entries according to
              the tree structure of the data models to make
              reading/parsing the data more simple."; datastore.";
          }
        }
        // augmentation point for datastore or data node level
        // capabilities
      }
    }
  }
}

   <CODE ENDS>

5.  Notification Capabilities Model

   The YANG module ietf-notification-capabilities is defined to provide
   YANG-Push related capability information.

5.1.  Tree Diagram

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

 module: ietf-notification-capabilities
   augment /sysc:system-capabilities:
     +--ro 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? max-nodes-per-update?               uint32
        +--ro minimum-dampening-period?           uint32 {yp:on-change}?
        +--ro on-change-supported?                notification-support
        |                                                {yp:on-change}?
        +--ro periodic-notifications-supported?   notification-support
        +--ro supported-excluded-change-type*     union {yp:on-change}?
   augment /sysc:system-capabilities/sysc:datastore-capabilities/ +
     |                                 sysc:per-node-capabilities:
     +--ro 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? max-nodes-per-update?               uint32
        +--ro minimum-dampening-period?           uint32 {yp:on-change}?
        +--ro on-change-supported?                notification-support
        |                                                {yp:on-change}?
        +--ro periodic-notifications-supported?   notification-support
        +--ro supported-excluded-change-type*     union {yp:on-change}?

5.2.  YANG Module

   <CODE BEGINS> file "ietf-notification-capabilities@2020-01-02.yang" "ietf-notification-capabilities@2020-01-14.yang"

 module ietf-notification-capabilities {
   yang-version 1.1;
   namespace
     "urn:ietf:params:xml:ns:yang:ietf-notification-capabilities";
   prefix inc;

   import ietf-yang-push { prefix yp;
    description
      "The module ietf-yang-push is REQUIRED to be
        implemented."; }
   import ietf-system-capabilities { prefix sysc;
    description
      "The module ietf-system-capabilities is REQUIRED to be
        implemented."; }

   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 publisher capabilities.

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

      Capability values can be specified on system/publisher level,
      datastore level or for specific data nodes (and their contained
     sub-tree) of a specific datastore, datastore
      (and their contained sub-trees), as defined in the
      ietf-system-capabilities module.

      If, different data nodes covered by a single subscription
      have different values for a specific capability, then using values
      that are only acceptable for some of these data nodes, but not for
      others, may result in the rejection of the subscription.

      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
      (http://trustee.ietf.org/license-info).

      This version of this YANG module is part of RFC XXXX
      (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
      for full legal notices.";

   revision 2020-01-02 2020-01-14 {
     description
       "Initial version";
     reference
       "RFC XXX: YANG-Push Notification Capabilities";
   }

   grouping subscription-capabilities {
     description  "Capabilities related to YANG-Push subscriptions
       and notifications";

     container subscription-capabilities {
       description "Capabilities related to YANG-Push subscriptions
         and notifications";

       typedef notification-support {
         type enumeration {
          enum no-notifications-supported {
            description "The publisher is not capable of sending any
              notifications for the relevant scope and subscription
              type." ;
          }
          enum notifications-for-config-changes-supported bits {
            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
           bit config-changes {
             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
           bit state-changes {
             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, none, only
           config=true, only config=false or all data nodes.";
       }

       choice update-period {
         description "Supported update period value or values for
           periodic subscriptions.";
         leaf minimum-update-period {
           type uint32;
           units "centiseconds";
           description "Indicates the minimal update period that is
             supported for a periodic subscription.
             A periodic subscription request to the selected data
             nodes must
            specify with a value that is at least as large or greater smaller period than
            this"; what this leaf specifies
             will result in a 'period-unsupported' error.";
           reference
             "The period leaf in RFC 8641 ietf-yang-push YANG module";
         }

         leaf-list supported-update-period {
           type uint32;
           units "centiseconds";
           description "Supported update period values for a
             periodic subscription.
             A periodic subscription request to the selected data nodes must
            specify one of the values with a
             period not included in the list; other values
            are not supported."; leaf-list will result in a
             'period-unsupported' error.";
           reference
             "The period leaf in RFC 8641 ietf-yang-push YANG module";
         }
       }

       leaf max-objects-per-update max-nodes-per-update {
         type uint32 {
               range "1..max";
         }
         description
           "Maximum number of objects data nodes that can be sent
            in an update for the selected update. The publisher MAY support more data nodes."; nodes,
            but SHOULD support at least this number.";
       }

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

       leaf on-change-supported {
         if-feature yp:on-change;
         type notification-support;
         description
           "Specifies whether the publisher is capable of
            sending on-change notifications for the selected
            data store or data nodes and the subtree below them.";
       }

       leaf periodic-notifications-supported {
         type notification-support;
         description
           "Specifies whether the publisher is capable of
            sending periodic notifications for the selected
            data store or data nodes and the subtree below them.";
       }

       leaf-list supported-excluded-change-type {
         if-feature yp:on-change;
         type union {
           type enumeration {
             enum none {
               value -2 ;
               description "None of the change types can be excluded.";
             }
             enum all {
               value -1 ;
               description
                 "Any combination of change types can be excluded.";
             }
           }
           type yp:change-type;
         }
         description "The change types that can be excluded in
           YANG-Push subscriptions.";
       }
     }
   }

   augment /sysc:system-capabilities {
     description "Add system level capabilities";
     uses subscription-capabilities {
       refine subscription-capabilities/supported-excluded-change-type {
         default none;
       }
     }
   }

   augment "/sysc:system-capabilities/sysc:datastore-capabilities" +
       "/sysc:per-node-capabilities" {

     description "Add datastore and node level capabilities";
     uses subscription-capabilities {
       refine subscription-capabilities/supported-excluded-change-type {
         default none;
       }
     }
   }
 }

   <CODE ENDS>

6.  Security Considerations

   The YANG modules specified in this document define 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 nodes are read-only and cannot be
   modified.  The data in these modules 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
   mechanisms.

7.  IANA Considerations

7.1.  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-system-capabilities
      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-notification-capabilities
      Registrant Contact: The NETCONF WG of the IETF.
      XML: N/A, the requested URI is an XML namespace.

7.2.  The YANG Module Names Registry

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

     name:       ietf-system-capabilities
     namespace:  urn:ietf:params:xml:ns:yang:ietf-system-capabilities
     prefix:     sysc
     reference:  RFC XXXX

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

8.  References

8.1.  Normative References

   [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-06
              (work in progress), December 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>.

   [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>.

8.2.  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>.

   [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>.

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>
  <yid-version>1</yid-version>
  <content-schema>
    <module>ietf-system-capabilities@2020-01-02</module>
    <module>ietf-notification-capabilities@2020-01-02</module>
    <module>ietf-system-capabilities@2020-01-14</module>
    <module>ietf-notification-capabilities@2020-01-14</module>
  </content-schema>
  <!-- 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>
    <system-capabilities
      xmlns="urn:ietf:params:xml:ns:yang:ietf-system-capabilities"
      xmlns:inc=
        "urn:ietf:params:xml:ns:yang:ietf-notification-capabilities"
      xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
      <inc:subscription-capabilities>
        <inc:minimum-update-period>500</inc:minimum-update-period>
        <inc:max-objects-per-update>2000</inc:max-objects-per-update>
        <inc:max-nodes-per-update>2000</inc:max-nodes-per-update>
        <inc:minimum-dampening-period>100</inc:minimum-dampening-period>
        <inc:periodic-notifications-supported>
          notifications-for-all-changes-supported
          config-changes state-changes
        </inc:periodic-notifications-supported>
      </inc:subscription-capabilities>
      <datastore-capabilities>
        <datastore>ds:operational</datastore>
        <per-node-capabilities>
          <node-selector>/</node-selector>
          <inc:subscription-capabilities>
            <inc:on-change-supported>
              notifications-for-state-changes-supported
              state-changes
            </inc:on-change-supported>
          </inc:subscription-capabilities>
        </per-node-capabilities>
        </datastore-capabilities>
      <datastore-capabilities>
        <datastore>ds:candidate</datastore>
        <per-node-capabilities>
          <node-selector>/</node-selector>
          <inc:subscription-capabilities>
            <inc:on-change-supported>no-notifications-supported
            </inc:on-change-supported>
            <inc:periodic-notifications-supported>
              no-notifications-supported
            </inc:periodic-notifications-supported>
            <inc:on-change-supported/>
            <inc:periodic-notifications-supported/>
          </inc:subscription-capabilities>
        </per-node-capabilities>
      </datastore-capabilities>
      <datastore-capabilities>
        <datastore>ds:running</datastore>
        <per-node-capabilities>
          <node-selector>/</node-selector>
          <inc:subscription-capabilities>
            <inc:on-change-supported>
              notifications-for-all-changes-supported
              config-changes state-changes
            </inc:on-change-supported>
          </inc:subscription-capabilities>
        </per-node-capabilities>
      </datastore-capabilities>
    </system-capabilities>
  </content-data>
</instance-data-set>

     Figure 1: Notification Capabilities with 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>
  <yid-version>1</yid-version>
  <content-schema>
    <module>ietf-system-capabilities@2020-01-02</module>
    <module>ietf-notification-capabilities@2020-01-02</module>
    <module>ietf-system-capabilities@2020-01-14</module>
    <module>ietf-notification-capabilities@2020-01-14</module>
  </content-schema>
  <!-- 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>
    <system-capabilities
      xmlns="urn:ietf:params:xml:ns:yang:ietf-system-capabilities"
      xmlns:inc=
        "urn:ietf:params:xml:ns:yang:ietf-notification-capabilities"
      xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
      <inc:subscription-capabilities>
        <inc:minimum-update-period>500</inc:minimum-update-period>
        <inc:max-objects-per-update>2000</inc:max-objects-per-update>
        <inc:max-nodes-per-update>2000</inc:max-nodes-per-update>
        <inc:minimum-dampening-period>100</inc:minimum-dampening-period>
        <inc:periodic-notifications-supported>
          notifications-for-all-changes-supported
          config-changes state-changes
        </inc:periodic-notifications-supported>
        <inc:on-change-supported>
          notifications-for-all-changes-supported
          config-changes state-changes
        </inc:on-change-supported>
        <inc:supported-excluded-change-type>
          all
        </inc:supported-excluded-change-type>
      </inc:subscription-capabilities>
      <datastore-capabilities>
        <datastore>ds:operational</datastore>
        <per-node-capabilities>
          <node-selector>
              /if:interfaces/if:interface/if:statistics</node-selector>
          <inc:subscription-capabilities>
            <inc:on-change-supported>
              no-notifications-supported
            </inc:on-change-supported>
          </inc:subscription-capabilities>
        </per-node-capabilities>
        <per-node-capabilities>
          <node-selector>
              /if:interfaces/if:interface/if:statistics/if:in-octets
          </node-selector>
          <inc:subscription-capabilities>
            <inc:minimum-dampening-period>10
              </inc:minimum-dampening-period>
            <inc:on-change-supported>
              notifications-for-all-changes-supported
              config-changes state-changes
            </inc:on-change-supported>
          </inc:subscription-capabilities>
        </per-node-capabilities>
        <per-node-capabilities>
          <node-selector>
              /if:interfaces/if:interface/if:statistics/if:out-octets
          </node-selector>
          <inc:subscription-capabilities>
            <inc:minimum-dampening-period>10
              </inc:minimum-dampening-period>
            <inc:on-change-supported>
              notifications-for-all-changes-supported
              config-changes state-changes
            </inc:on-change-supported>
          </inc:subscription-capabilities>
        </per-node-capabilities>
        <per-node-capabilities>
          <node-selector>
              /if:interfaces/if:interface/if:statistics</node-selector>
          <inc:subscription-capabilities>
            <inc:on-change-supported/>
          </inc:subscription-capabilities>
        </per-node-capabilities>
      </datastore-capabilities>
    </system-capabilities>
  </content-data>
</instance-data-set>

   Figure 2: Notification Capabilities with data node specific settings

Appendix B.  Changes between revisions

   v09 - v10

   o  Removed description text from imports about the need for
      implementing the imported module.

   o  Changed notification-support to bits with shorter names

   o  Assigned enum values to supported-excluded-change-type

   o  Made node-selector a choice to allow for future alternative
      selection methods.

   o  Changed precedence of per-node-capabilities entries.  Precedence
      is now according to the position of entries in the list.

   v08 - v09

   o  Split the YANG module into two: ietf-system-capabilities and ietf-
      notification-capabilities.  Restructured/updated the draft
      accordingly.

   v07 - v08

   o  Prepared the YANG model to include other non-YANG-Push related
      capabilities.

   o  Renamed the top level container to system-capabilities

   o  Added a container subscription-capabilities to the grouping
      subscription-capabilities to contain all subscription related
      capabilities

   o  Updated examples according to draft-ietf-netmod-yang-instance-
      file-format-06.

   v06 - v07

   o  Updated examples according to draft-ietf-netmod-yang-instance-
      file-format-05.

   v05 - v06

   o  Providing the capability data is only a "SHOULD" recommendation.
      Some reviewers wanted MUST some wanted much less.

   o  The YANG module import statements now indicate the imported
      modules that must be implemented not just available as import as
      requested by the YangDoctors review.

   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