Netconf B. Lengyel
Internet-Draft Ericsson
Intended status: Standards Track A. Clemm
Expires: September 2, 2019 Huawei USA
March 1, 2019

YangPush Notification Capabilities


This document proposes a YANG module that allows a YANG server to specify server capabilities related to "Subscription to YANG Datastores" (YangPush). It proposes to use YANG Instance Data to document this information already in implementation time.

Status of This Memo

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This Internet-Draft will expire on September 2, 2019.

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Table of Contents

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 [I-D.ietf-netconf-yang-push]

On-change Notification Capability: The capability of the YANG server to support On-change subscriptions.

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

Rutime-information: Information about the YANG server's behavior that is available from the running YANG server via a protocol like NETCONF, RESTCONF or HTTPS.

2. Introduction

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

A YANG server supporting YANG-Push has a number of capabilities that are determined during the implementation of the server. These include:

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

In some cases, a publisher supporting on-change notifications will not be able to push updates for some object types on-change. Reasons for this might be that the value of the datastore node changes frequently (e.g. in-octets counter), that small object changes are frequent and meaningless (e.g., a temperature gauge changing 0.1 degrees), or that the implementation is not capable of on-change notification for a particular object. In those cases, it will be important for client applications to have a way to identify for 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, client/management applications can not rely on the on-change functionality unless the client has some means to identify for which objects on-change notifications are supported. YANG models are meant to be used as an interface contract. Without identification of data nodes supporting on-change, this contract would only state the YANG server may (or may not) send on-change notifications for a data node specified in a YANG module.

This document proposes a YANG module that allows a client to discover YANG-Push related capabilities.

YANG-Push related capability information will be needed both in implementation-time and run-time.

Implementation time information is needed by Network Management System (NMS) implementers. During NMS implementation for any functionality that depends on the notifications the information about on change notification capability is needed. If the information is not available early in some document, but only as instance data from the network node, the NMS implementation will be delayed, because it has to wait for the network node to be ready. Also assuming that all NMS implementers will have a correctly configured network node available to retrieve data from, is an expensive proposition. (An NMS may handle 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 the NMS effectively delays the availability of the network node as well.

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

3. Notification Capability Model

It is a goal to provide YangPush notification capability information in a format that is

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

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

3.1. Tree Diagram

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

module: ietf-notification-capabilities
  +--ro yangpush-notification-capabilities
     +--ro minimum-dampening-period?               uint32
     +--ro (update-period)?
     |  +--:(minimum-update-period)
     |  |  +--ro minimum-update-period?                  uint32
     |  +--:(supported-update-period)
     |     +--ro supported-update-period*                uint32
     +--ro max-objects-per-update?                 uint32
     +--ro notification-sent-for-config-default?   boolean
     +--ro notification-sent-for-state-default?    boolean
     +--ro on-change-notification-capability* [node-selector]
        +--ro node-selector               nacm:node-instance-identifier
        +--ro on-change-notification-sent    boolean

3.2. YANG Module

<CODE BEGINS> file "ietf-notification-capabilities.yang"

module ietf-notification-capabilities {
  yang-version 1.1;
  prefix inc;

  import ietf-netconf-acm { prefix nacm; }

    "IETF NETCONF (Network Configuration) Working Group";

    "WG Web:   <>
     WG List:  <>

     WG Chair: Kent Watsen

     WG Chair: Mahesh Jethanandani

     Editor:   Balazs Lengyel

  description "This module specifies YANG-Push related server 
    capabilities. It contains 
    - capabilities related to the amount of notifications the 
    server can send out
    - default and schema node specific information specifying 
    the set of data nodes for which the YANG server is capable 
    of sending on-change notifications.

    On-change notification capability is marked as true or false.
    This marking is inherited from the parent down the data tree
    unless explicitly marked otherwise.

    On-change notifications SHALL be sent for a config=true 
    data node if one of the following is true:
    - if it is a top level data-node and is not specified in the
    on-change-notification-capability list and the
    notification-sent-for-config-default is true; or
    - notifications are sent for its parent data node and it is
    not specified in the on-change-notification-capability list; or
    - it is specified in the on-change-notification-capability
    list and has a on-change-notification-sent value true.

    On-change notifications SHALL be sent for a config=false 
    data node if one of the following is true:
    - if it is a top level data-node or has a config=true parent 
    data node and is not specified in the 
    on-change-notification-capability list and the
    notification-sent-for-state-default is true; or
    - notifications are sent for its parent data node 
    which is also config=false and it is
    not specified in the on-change-notification-capability list; or
    - it is specified in the on-change-notification-capability
    list and has an on-change-notification-sent value true or
  revision 2019-02-28 {
    description "Initial version";
      "RFC XXX: YangPush Notification Capabilities";

  container yangpush-notification-capabilities {
    config false;
    description "YANG-Push related server capabilities";
    leaf minimum-dampening-period {
      type uint32;
      units msec;
      description "The minimum dampening period supported for on-change 

    choice update-period {
      description "Supported period values.";
      leaf minimum-update-period {
        type uint32;
        units centiseconds;
        description "Minimum update period supported for a 
          periodic subscription.";
      leaf-list supported-update-period {
        type uint32;
        units centiseconds;
        description "Specific supported update period values  
          for a periodic subscription";       

    leaf max-objects-per-update {
      type uint32;
      description "Maximum number of objects that can be sent 
        in an update";
    leaf notification-sent-for-config-default {
      type boolean;
      default true;
      description "Specifies the default value for 
        top level configuration data nodes for the
        on-change-notification-sent capability.";

    leaf notification-sent-for-state-default {
      type boolean;
      default false;
      description "Specifies the default value 
        top level state data nodes for the
        on-change-notification-sent capability.";

    list on-change-notification-capability {
      key node-selector ;
      description "A list of data nodes that have the
         on-change-notification-capability specifically defined.
         Should be used when specific data nodes support 
         on-change notification in a module/subtree that 
         generally does not support it or when some data nodes 
         do not support the notification in a module/subtree 
         that generally supports on-change notifications.";

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

      leaf on-change-notification-sent {
        type boolean;
        mandatory true;
        description "Specifies whether the YANG server will
          send on-change notifications for the selected 
          data nodes.";


4. Security Considerations

The YANG module defined in this document is designed to be accessed via YANG based management protocols, such as NETCONF and RESTCONF. Both of these protocols have mandatory-to- implement secure transport layers (e.g., SSH, TLS) with mutual authentication.

The NETCONF access control model (NACM) provides the means to restrict access for particular users to a pre-configured subset of all available protocol operations and content.

The data in this module is not security sensitive.

5. IANA Considerations

5.1. The IETF XML Registry

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

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

5.2. The YANG Module Names Registry

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

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

6. Open Issues

7. References

7.1. Normative References

[I-D.ietf-netconf-yang-push] Clemm, A., Voit, E., Prieto, A., Tripathy, A., Nilsen-Nygaard, E., Bierman, A. and B. Lengyel, "Subscription to YANG Datastores", Internet-Draft draft-ietf-netconf-yang-push-22, February 2019.
[I-D.lengyel-netmod-yang-instance-data] Lengyel, B. and B. Claise, "YANG Based Instance Data Files Format", Internet-Draft draft-lengyel-netmod-yang-instance-data-05, October 2018.
[RFC7950] Bjorklund, M., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016.

7.2. 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.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[RFC8340] Bjorklund, M. and L. Berger, "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018.

Appendix A. Changes between revisions

v00 - v01

Authors' Addresses

Balazs Lengyel Ericsson Magyar Tudosok korutja 11 1117 Budapest, Hungary EMail:
Alexander Clemm Huawei USA 2330 Central Expressway Santa Clara, CA 95050, USA EMail: