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Versions: (draft-lengyel-netconf-notification-capabilities) 00 01 02 03 04 05 06 07 08 09 10 11 12 13

NETCONF                                                       B. Lengyel
Internet-Draft                                                  Ericsson
Intended status: Standards Track                                A. Clemm
Expires: September 24, 2020                                    Futurewei
                                                               B. Claise
                                                     Cisco Systems, Inc.
                                                          March 23, 2020


     YANG Modules for describing System Capabilities and Yang-Push
                       Notification Capabilities
            draft-ietf-netconf-notification-capabilities-13

Abstract

   This document defines two YANG modules:

   The module ietf-system-capabilities provides a structure that can be
   used to specify YANG related system capabilities for servers.  The
   module can be used in conjunction with YANG Instance Data to make
   this information available at implementation-time.  The module can
   also be used to report capability information from the server at run-
   time.

   The module ietf-notification-capabilities augments ietf-system-
   capabilities to specify capabilities related to "Subscription to YANG
   Datastores" (YANG-Push).

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 September 24, 2020.







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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 . . . . . . . . . . .   4
   3.  Providing System Capability Information . . . . . . . . . . .   6
   4.  System Capabilities Model . . . . . . . . . . . . . . . . . .   6
     4.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Notification Capabilities Model . . . . . . . . . . . . . . .  10
     5.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .  10
     5.2.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  11
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     7.1.  The IETF XML Registry . . . . . . . . . . . . . . . . . .  17
     7.2.  The YANG Module Names Registry  . . . . . . . . . . . . .  17
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  18
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  18
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  19
   Appendix A.  Instance data examples . . . . . . . . . . . . . . .  19
   Appendix B.  Changes between revisions  . . . . . . . . . . . . .  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

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.





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   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].

   The terms Instance Data and Instance Data Set are used as defined in
   [I-D.ietf-netmod-yang-instance-file-format].

   In addition, this document defines the following terms:

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

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

   On-change notification capability: The capability of the publisher to
   send on-change notifications for a specific datastore or a specific
   data node.

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 is 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 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 at implementation-time and run-
      time





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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



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   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 at 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 earlier, at
      implementation-time is what the publisher has implemented.




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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 MUST be
      available already at 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.

   The YANG data models in this document conform to the Network
   Management Datastore Architecture (NMDA) defined in [RFC8342].

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-
   trees).  Capability values specified for a specific datastore or
   node-set override 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.



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   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* []
            +--ro (node-selection)?
               +--:(node-selector)
                  +--ro node-selector?   nacm:node-instance-identifier

4.2.  YANG Module

   This YANG module imports typedefs from [RFC8341] and a reference path
   from [RFC8525].

<CODE BEGINS> file "ietf-system-capabilities@2020-03-23.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;
    reference
      "RFC 8341: Network Configuration Access Control Model";
  }
  import ietf-yang-library {
    prefix yanglib;
    description
      "Revision 2019-01-04 or a
       revision derived from it is REQUIRED.";
    reference
      "RFC RFC8525: YANG Library";
  }

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



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     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 of a specific datastore (and their
     contained sub-trees).
     Capability values specified for a specific datastore or
     node-set override values specified on the system/publisher level.

     To find a capability value for a specific data node in a
     specific datastore the user SHALL
     1) search for a datastore-capabilities list entry for
     the specific datastore.
     2) If the datastore entry is found within that entry process all
     per-node-capabilities entries in the order they appear in the list.
     The first entry that specifies the specific capability and has a
     node-selector selecting the specific data node defines the
     capability value.
     3) If the capability value is not found above and the specific
     capability is specified under the system-capabilities container
     (outside the datastore-capabilities list) this value shall be used.
     4) If no values are found in the previous steps the
     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.




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

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

  revision 2020-03-23 {
    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 {
        description
          "Each list entry specifies capabilities for the selected
           data nodes. The same capabilities apply for the data nodes
           in the subtree below the selected nodes.



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           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.";
          }
        }
        // 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.



















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

5.2.  YANG Module

   This YANG module imports a feature and typedefs from [RFC8641].

   <CODE BEGINS> file "ietf-notification-capabilities@2020-03-23.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;
       reference



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         "RFC 8641: Subscription to YANG Notifications for Datastore
           Updates";
     }
     import ietf-system-capabilities {
       prefix sysc;
       reference
         "RFC XXXX: YANG Modules for describing System Capabilities
           and Yang-Push Notification Capabilities";
     }

     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 [RFC 8641] 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 of a specific
        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.




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        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 2020-03-23 {
       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 bits {
             bit config-changes {
               description
                 "The publisher is capable of sending
                  notifications for config=true nodes for the relevant
                  scope and subscription type.";
             }
             bit state-changes {
               description
                 "The publisher is capable of sending
                  notifications for config=false nodes for the relevant
                  scope and subscription type.";
             }
           }
           description
             "Type for defining whether on-change or
              periodic notifications are supported for none, only
              config=true, only config=false or all data nodes.



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              If the bit config-changes or state-changes is set
              for a datastore or a set of nodes that does not contain
              nodes with the indicated config value,
              this has no effect, as if no support was declared.
              E.g. indicating support for state-changes for
              a candidate datastore has no effect.";
         }

         leaf max-nodes-per-update {
           type uint32 {
             range "1..max";
           }
           description
             "Maximum number of data nodes that can be sent
              in an update. The publisher MAY support more data nodes,
              but SHOULD support at least this number.
              May be used to avoid the update-too-big error
              during subscription.";
           reference "The update-too-big error/identity in RFC 8641";
         }
         leaf periodic-notifications-supported {
           type notification-support;
           description
             "Specifies whether the publisher is capable of
              sending periodic notifications for the selected
              data nodes and the subtree below them.";
           reference
             "Periodic subscription concept in RFC 8641";
         }
         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 subscription request to the selected data
                nodes with a smaller period than 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";



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             description
               "Supported update period values for a
                periodic subscription.
                A subscription request to the selected data nodes with a
                period not included in the leaf-list will result in a
                'period-unsupported' error.";
             reference
               "The period leaf in RFC 8641 ietf-yang-push YANG module";
           }
         }
         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 nodes and the subtree below them.";
           reference
             "On-change concept in RFC 8641";
         }
         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.
              If this value is present and greater than zero,
              that implies dampening is mandatory.";
           reference
             "The dampening-period leaf in RFC 8641 ietf-yang-push
              YANG module";
         }
         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.";
               }
             }



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             type yp:change-type;
           }
           description
             "The change types that can be excluded in
              YANG-Push subscriptions.";
           reference
             "The change-type typedef in RFC 8641 ietf-yang-push
              YANG module";
         }
       }
     }

     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].




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   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





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8.  Acknowledgments

   For their valuable comments, discussions, and feedback, we wish to
   acknowledge Andy Bierman, Juergen Schoenwaelder, Rob Wilton, Kent
   Watsen, Eric Voit, Joe Clarke, Martin Bjorklund, Ladislav Lhotka, Qin
   Wu, Mahesh Jethanandani, Ran Tao, Reshad Rahman and other members of
   the Netmod WG.

9.  References

9.1.  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-08
              (work in progress), March 2020.

   [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>.

   [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>.

   [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>.

   [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>.

   [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>.

   [RFC8525]  Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K.,
              and R. Wilton, "YANG Library", RFC 8525,
              DOI 10.17487/RFC8525, March 2019,
              <https://www.rfc-editor.org/info/rfc8525>.







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   [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>.

9.2.  Informative References

   [I-D.ietf-netmod-artwork-folding]
              Watsen, K., Auerswald, E., Farrel, A., and Q. WU,
              "Handling Long Lines in Inclusions in Internet-Drafts and
              RFCs", draft-ietf-netmod-artwork-folding-12 (work in
              progress), January 2020.

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

   [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>.

   [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>.

   [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>.

   [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>.

Appendix A.  Instance data examples

   The following examples use artwork folding
   [I-D.ietf-netmod-artwork-folding] for better formatting.





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   The following instance-data example describes 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.

<CODE BEGINS> file "acme-switch-notification-capabilities.xml"
========== NOTE: '\' line wrapping per BCP YYY (RFC YYYY) ===========

<?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>
  <content-schema>
    <module>ietf-system-capabilities@2020-03-23</module>
    <module>ietf-notification-capabilities@2020-03-23</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-nodes-per-update>2000</inc:max-nodes-per-update>
        <inc:minimum-dampening-period>100</inc:minimum-dampening-period>
        <inc:periodic-notifications-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>\
              state-changes\
            </inc:on-change-supported>



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          </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/>
            <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>\
              config-changes\
            </inc:on-change-supported>
          </inc:subscription-capabilities>
        </per-node-capabilities>
      </datastore-capabilities>
    </system-capabilities>
  </content-data>
</instance-data-set>
<CODE ENDS>

     Figure 1: Notification Capabilities with datastore level settings

   The following instance-data example describes 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.

<CODE BEGINS> file "acme-router-notification-capabilities.xml"
========== NOTE: '\' line wrapping per BCP YYY (RFC YYYY) ===========

<?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>
  <content-schema>



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    <module>ietf-system-capabilities@2020-03-23</module>
    <module>ietf-notification-capabilities@2020-03-23</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-nodes-per-update>2000</inc:max-nodes-per-update>
        <inc:minimum-dampening-period>100</inc:minimum-dampening-period>
        <inc:periodic-notifications-supported>\
          config-changes state-changes\
        </inc:periodic-notifications-supported>
        <inc:on-change-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:name='lo']\
          </node-selector>
          <inc:subscription-capabilities>
            <inc:on-change-supported/>
            <inc:periodic-notifications-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



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              </inc:minimum-dampening-period>
            <inc:on-change-supported>\
              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>\
              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>
<CODE ENDS>

   Figure 2: Notification Capabilities with data node specific settings

Appendix B.  Changes between revisions

   Note to RFC Editor (To be removed by RFC Editor)

   v12 - v13

   o  Rearranged order of notification capability leafs into 3 groups:
      generic, specific to periodic subscriptions, specific to on-
      change.

   o  Introduced artwork folding in the examples

   o  Updated to follow draft-ietf-netmod-yang-instance-file-format-10




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   o  Various editing changes

   v11 - v12

   o  Updated max-nodes-per-update description

   o  Reformatted YANG models with pyang -f yang --keep-comments --yang-
      line-length 69

   v10 - v11

   o  Updated examples

   o  Updated typedef notification-support

   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





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   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




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   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









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