NETCONF A. Gonzalez Prieto
Internet-Draft Cisco Systems
Intended status: Standards Track A. Clemm
Expires: November 2, 2017 Huawei
E. Voit
E. Nilsen-Nygaard
A. Tripathy
Cisco Systems
S. Chisholm
Ciena
H. Trevino
Cisco Systems
May 1, 2017

NETCONF Support for Event Notifications
draft-ietf-netconf-netconf-event-notifications-02

Abstract

This document defines the support of [event-notifications] by the Network Configuration protocol (NETCONF). [event-notifications] describes capabilities and operations for providing asynchronous message notification delivery. This document discusses how to provide them on top of NETCONF. The capabilities and operations defined between this document and [event-notifications] are intended to obsolete RFC 5277.

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 http://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 November 2, 2017.

Copyright Notice

Copyright (c) 2017 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 (http://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. Introduction

[RFC6241] can be conceptually partitioned into four layers:

            Layer                 Example
       +-------------+      +-----------------+      +----------------+
   (4) |   Content   |      |  Configuration  |      |  Notification  |
       |             |      |      data       |      |      data      |
       +-------------+      +-----------------+      +----------------+
              |                       |                      |
       +-------------+      +-----------------+              |
   (3) | Operations  |      |  <edit-config>  |              |
       |             |      |                 |              |
       +-------------+      +-----------------+              |
              |                       |                      |
       +-------------+      +-----------------+      +----------------+
   (2) |  Messages   |      |     <rpc>,      |      | <notification> |
       |             |      |   <rpc-reply>   |      |                |
       +-------------+      +-----------------+      +----------------+
              |                       |                      |
       +-------------+      +-----------------------------------------+
   (1) |   Secure    |      |       SSH, TLS, SOAP/HTTP/TLS, ...      |
       |  Transport  |      |                                         |
       +-------------+      +-----------------------------------------+
          

Figure 1: NETCONF layer architecture

This document defines mechanisms that provide an asynchronous message notification delivery service for the NETCONF protocol [RFC6241] based on [event-notifications]. This is an optional capability built on top of the base NETCONF definition.

[event-notifications] and this document enhance the capabilities of RFC 5277 while maintaining backwards capability with existing implementations. It is intended that a final version of this document might obsolete [RFC5277]. The enhancements include the ability to terminate subscriptions without terminating the client session, to modify existing subscriptions, and to have multiple subscriptions on a NETCONF session. [RFC5277] clients that do not require these enhancements are not affected by them.

[event-notifications] covers the following functionality:

To support this functionality, NETCONF agents must implement the operations, configuration and operational state defined in [event-notifications]. In addition, they need to:

1.1. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].

1.1.1. NETCONF

The following terms are defined in [RFC6241] :

1.1.2. Event Notifications

The following terms are defined in [event-notifications]:

Note that a publisher in [event-notifications] corresponds to a server in [RFC6241]. Similarly, a subscribers corresponds to a client. A receiver is also a client. In the remainder of this document, we will use the terminology in [RFC6241].

1.1.3. NETCONF Access Control

The following terms are defined in [RFC6536] :

1.2. Solution Overview

[event-notifications] defines mechanisms that provide an asynchronous message notification delivery service. This document discusses its realization on top of the NETCONF protocol [RFC6241].

The functionality to support is defined in [event-notifications]. It is formalized in a set of yang models. The mapping of yang constructs into NETCONF is described in [RFC6020].

Supporting [event-notifications] requires enhancements and modifications in NETCONF. The key enhacement is suporting multiple subscriptions on a NETCONF session. A key modification is the definition of the NETCONF stream.

These enhancements do not affect [RFC5277] clients that do not support [event-notifications].

2. Solution

In this section, we describe and exemplify how [event-notifications] must be supported over NETCONF.

2.1. Event Streams

In the context of NETCONF, an event stream is a set of events available for subscription from a NETCONF server. It is out of the scope of this document to identify a) how streams are defined, b) how events are defined/generated, and c) how events are assigned to streams.

The following is a high-level description of the flow of a notification. Note that it does not mandate and/or preclude an implementation. As events are raised, they are assigned to streams. An event may be assigned to multiple streams. The event is distributed to subscribers and receivers based on the current subscriptions and access control. Access control is needed because if any receiver of that subscription does not have permission to receive an event, then it never makes it into a notification, and processing of the event is completed for that subscription.

2.2. Event Stream Discovery

A NETCONF client can retrieve the list of available event streams from a NETCONF server using the <get> operation. The reply contains the elements defined in the YANG model under the container "/streams", which includes the stream identifier.

The following example ilustrates the retrieval of the list of available event streams using the <get> operation.

<rpc message-id="101" 
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <get>
    <filter type="subtree">
      <streams 
       xmlns="urn:ietf:params:xml:ns:yang:ietf-event-notifications"/>
      </filter>
  </get>
</rpc>
                    

Figure 2: Get streams

The NETCONF server returns a list of event streams available for subscription. In this example, the list contains the NETCONF, SNMP, and syslog-critical streams.

<rpc-reply message-id="101" 
        xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <data>
    <streams  
        xmlns="urn:ietf:params:xml:ns:yang:ietf-event-notifications">
      <stream>NETCONF</stream>
      <stream>SNMP</stream>
      <stream>syslog-critical</stream>
      <stream>NETCONF</stream>
      </streams>
  </data>
</rpc-reply>
                    

Figure 3: Get streams response

2.2.1. Backwards Compatibility

In order to maintain backwards compatibility, clients that only support [RFC5277] can retrieve the list of available event streams executing a <get> operation against the container "/netconf/streams".

The following example ilustrates this mechanism.

<rpc message-id="101" 
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <get>
    <filter type="subtree">
      <netconf 
            xmlns="urn:ietf:params:xml:ns:netmod:notification">
        <streams/>
      </netconf>
    </filter>
  </get>
</rpc>
                        

Figure 4: Get streams (backwards compatibility)

The NETCONF server returns a list of event streams available for subscription. In this example, the list contains the NETCONF, SNMP, and syslog-critical streams.

<rpc-reply message-id="101" 
        xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <data>
    <netconf  
            xmlns="urn:ietf:params:xml:ns:netmod:notification">
      <streams>
        <stream>
          <name>
            NETCONF
          </name>
          <description>
            default NETCONF event stream
          </description>
          <replaySupport>
            true
          </replaySupport>
          <replayLogCreationTime>
            2016-02-05T00:00:00Z
          </replayLogCreationTime>
        </stream>
        <stream>
          <name>
            SNMP
          </name>
          <description>
            SNMP notifications
          </description>
          <replaySupport>
            false
          </replaySupport>
        </stream>
        <stream>
          <name>
            syslog-critical
          </name>
          <description>
            Critical and higher severity
          </description>
          <replaySupport>
            true
          </replaySupport>
          <replayLogCreationTime>
            2007-07-01T00:00:00Z
          </replayLogCreationTime>
        </stream>
      </streams>
    </netconf>
  </data>
</rpc-reply>
                        

Figure 5: Get streams response (backwards compatibility)

2.3. Default Event Stream

A NETCONF server implementation supporting the notification capability MUST support the "NETCONF" notification event stream. This stream contains all NETCONF XML event notifications supported by the NETCONF server, except for those belonging only to streams that explicitly indicate that they must be excluded from the NETCONF stream. The exact string "NETCONF" is used during the advertisement of stream support during the <get> operation on <streams> and during the <create-subscription> and <establish-subscription> operations.

2.4. Creating a Subscription

This operation was fully defined in [RFC5277].

2.4.1. Usage Example

The following demonstrates dynamically creating a subscription.

<netconf:rpc message-id="101" 
       xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
  <create-subscription 
        xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
  </create-subscription>
</netconf:rpc>
                        

Figure 6: Create subscription

2.4.2. Positive Response

If the NETCONF server can satisfy the request, the server sends an <ok> element.

<netconf:rpc netconf:message-id="102" 
       xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
  <create-subscription 
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
    <filter netconf:type="xpath" 
                xmlns:ex="http://example.com/event/1.0"
             select="/ex:event[ex:eventClass='fault' and 
                      (ex:severity='minor' or ex:severity='major'
                       or ex:severity='critical')]"/>
  </create-subscription>
</netconf:rpc>

<rpc-reply message-id="102" 
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <ok/>
</rpc-reply>
                        

Figure 7: Successful create subscription

2.4.3. Negative Response

If the request cannot be completed for any reason, an <rpc-error> element is included within the <rpc-reply>. Subscription requests can fail for several reasons including if a filter with invalid syntax is provided or if the name of a non-existent stream is provided.

If a stopTime is specified in a request without having specified a startTime, the following error is returned:

Tag: missing-element
Error-type: protocol
Severity: error
Error-info: <bad-element>: startTime
Description: An expected element is missing.
                        

Figure 8: Create subscription missing an element

If the optional replay feature is requested but the NETCONF server does not support it, the following error is returned:

Tag: operation-failed
Error-type: protocol
Severity: error
Error-info: none
Description: Request could not be completed because the
             requested operation failed for some reason 
             not covered by any other error condition.
                        

Figure 9: Create subscription operation failed

If a stopTime is requested that is earlier than the specified startTime, the following error is returned:

Tag: bad-element
Error-type: protocol
Severity: error
Error-info: <bad-element>: stopTime
Description: An element value is not correct; 
             e.g., wrong type, out of range, pattern mismatch.
                        

Figure 10: Create subscription incorrect stopTime

If a startTime is requested that is later than the current time, the following error is returned:

Tag: bad-element
Error-type: protocol
Severity: error
Error-info: <bad-element>: startTime
Description: An element value is not correct; 
             e.g., wrong type, out of range, pattern mismatch.
                        

Figure 11: Create subscription incorrect startTime

2.5. Establishing a Subscription

This operation is defined in [event-notifications].

2.5.1. Usage Example

The following illustrates the establishment of a simple subscription.

<netconf:rpc message-id="101" 
       xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
  <establish-subscription 
          xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
  </establish-subscription>
</netconf:rpc>
                        

Figure 12: Establish subscription

2.5.2. Positive Response

If the NETCONF server can satisfy the request, the server sends a positive <subscription-result> element, and the subscription-id of the accepted subscription.

<netconf:rpc netconf:message-id="102" 
       xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
  <establish-subscription 
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    <filter netconf:type="xpath" 
                xmlns:ex="http://example.com/event/1.0"
             select="/ex:event[ex:eventClass='fault' and 
                      (ex:severity='minor' or ex:severity='major'
                       or ex:severity='critical')]"/>
  </establish-subscription>
</netconf:rpc>

<rpc-reply message-id="102" 
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <subscription-result 
          xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    ok
  </subscription-result>
  <subscription-id 
          xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    52
  </subscription-id>
</rpc-reply>        
                        

Figure 13: Successful establish-subscription

2.5.3. Negative Response

If the NETCONF server cannot satisfy the request, the server sends a negative <subscription-result> element.

If the client has no authorization to establish the subscription, the <subscription-result> indicates an authorization error. For instance:

<netconf:rpc netconf:message-id="103" 
       xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
  <establish-subscription 
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    <stream>foo</stream>
  </establish-subscription>
</netconf:rpc>

<rpc-reply message-id="103" 
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <subscription-result 
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    error-data-not-authorized
  </subscription-result>
</rpc-reply>
                        

Figure 14: Unsuccessful establish subscription

If the request is rejected because the server is not able to serve it, the server SHOULD include in the returned error what subscription parameters would have been accepted for the request when it was processed. However, they are no guarantee that subsequent requests with those parameters for this client or others will be accepted. For instance, consider a subscription from [yang-push], which augments the establish-subscription with some additional parameters, including "period". If the client requests a period the NETCONF server cannot serve, the exchange may be:

<netconf:rpc message-id="101" 
         xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
  <establish-subscription 
            xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    <stream>push-update</stream>
    <filter netconf:type="xpath"
            xmlns:ex="http://example.com/sample-data/1.0"
            select="/ex:foo"/>
    <period xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
      500
    </period>
    <encoding>encode-xml</encoding>
  </establish-subscription>
</netconf:rpc>


<rpc-reply message-id="101"
      xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <subscription-result 
        xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    error-insufficient-resources
  </subscription-result>
  <period 
        xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
    2000
  </period>
</rpc-reply>
                        

Figure 15: Subscription establishment negotiation

Subscription requests will fail if a filter with invalid syntax is provided or if the name of a non-existent stream is provided.

2.5.4. Multiple Subscriptions over a Single NETCONF Session

Note that [event-notifications] requires supporting multiple subscription establishments over a single NETCONF session. In contrast, [RFC5277] mandated servers to return an error when a create-subscription was sent while a subscription was active on that session. Note that servers are not required to support multiple create-subscription over a single session, but they MUST support multiple establish-subscription over one session.

2.5.5. Message Flow Examples

                               
+------------+                 +-----------+      
|   Client   |                 |   Server  |      
+------------+                 +-----------+      
      |                              |            
      |    Capability Exchange       |            
      |<---------------------------->|            
      |                              |            
      |                              |            
      |    Establish Subscription    |            
      |----------------------------->|            
      | RPC Reply: OK, subs-id = 22  |            
      |<-----------------------------|            
      |                              |            
      |  Notification (subs-id 22)   |            
      |<-----------------------------|            
      |                              |            
      |                              |            
      |  Notification (subs-id 22)   |            
      |<-----------------------------|            
      |  Notification (subs-id 22)   |            
      |<-----------------------------|            
      |                              |            
      |                              |            

                        

Figure 16: Message flow for subscription establishment

                               
+------------+                 +-----------+      
|   Client   |                 |   Server  |      
+------------+                 +-----------+      
      |                              |            
      |    Capability Exchange       |            
      |<---------------------------->|            
      |                              |            
      |                              |            
      |    Establish Subscription    |            
      |----------------------------->|            
      | RPC Reply: OK, subs-id = 22  |            
      |<-----------------------------|            
      |                              |            
      |  Notification (subs-id 22)   |            
      |<-----------------------------|            
      |                              |            
      |                              |            
      |    Establish Subscription    |            
      |----------------------------->|            
      | RPC Reply: OK, subs-id = 23  |            
      |<-----------------------------|            
      |                              |            
      |  Notification (subs-id 22)   |            
      |<-----------------------------|            
      |                              |            
      |                              |            
      |  Notification (subs-id 22)   |            
      |<-----------------------------|    
      |  Notification (subs-id 23)   |            
      |<-----------------------------|            
      |                              |            
      |                              |                    

                        

Figure 17: Message Flow for multiple subscription establishments over a single session

2.6. Modifying a Subscription

This operation is defined in [event-notifications].

2.6.1. Usage Example

The following demonstrates modifying a subscription. Consider a subscription from [yang-push], which augments the establish-subscription with some additional parameters, including "period". A subscription may be established as follows.

<netconf:rpc message-id="101" 
       xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
  <establish-subscription 
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    <stream>push-update</stream>
    <filter netconf:type="xpath" 
            xmlns:ex="http://example.com/sample-data/1.0" 
            select="/ex:foo"/>
    <period xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
      500
    </period>
    <encoding>encode-xml</encoding>
  </establish-subscription>
</netconf:rpc>

<rpc-reply message-id="101" 
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <subscription-result 
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    ok
  </subscription-result>
  <subscription-id 
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    1922
  </subscription-id>
</rpc-reply>
                        

Figure 18: Establish subscription to be modified

The subscription may be modified with:

<netconf:rpc message-id="102" 
       xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
  <modify-subscription 
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    <subscription-id>1922</subscription-id>
    <period>1000</period>
  </modify-subscription >
</netconf:rpc>

<rpc-reply message-id="102" 
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <subscription-result 
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    ok
  </subscription-result>
  <subscription-id 
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    1922
  </subscription-id>
</rpc-reply>
                        

Figure 19: Modify subscription

2.6.2. Positive Response

If the NETCONF server can satisfy the request, the server sends a positive <subscription-result> element. This response is like that to an establish-subscription request, but without the subscription-id (which would be redundant).

<netconf:rpc message-id="102" 
       xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
  <modify-subscription 
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    <subscription-id>1922</subscription-id>
    <period 
              xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
      1000
    </period>
  </modify-subscription >
</netconf:rpc>

<rpc-reply message-id="102" 
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <subscription-result 
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    ok
  </subscription-result>
</rpc-reply>
                        

Figure 20: Successful modify subscription

2.6.3. Negative Response

If the NETCONF server cannot satisfy the request, the server sends a negative <subscription-result> element. Its contents and semantics are identical to those in an establish-subscription request. For instance:

<netconf:rpc message-id="102" 
       xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
  <modify-subscription 
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    <subscription-id>1922</subscription-id>
    <period xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
      100
    </period>
  </modify-subscription>
</netconf:rpc>

<rpc-reply message-id="102" 
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <subscription-result 
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    error-insufficient-resources
  </subscription-result>
  <period>500</period>
</rpc-reply>
                        

Figure 21: Unsuccessful modify subscription

2.6.4. Message Flow Example

                               
+------------+                 +-----------+      
|   Client   |                 |   Server  |      
+------------+                 +-----------+      
      |                              |            
      |    Capability Exchange       |            
      |<---------------------------->|            
      |                              |            
      |                              |            
      |    Establish Subscription    |            
      |----------------------------->|            
      | RPC Reply: OK, subs-id = 22  |            
      |<-----------------------------|            
      |                              |            
      |  Notification (subs-id 22)   |            
      |<-----------------------------|            
      |                              |            
      |                              |            
      |                              |            
      |                              |            
      |     Modify Subscription      |            
      |----------------------------->|            
      |                              |            
      |                              |            
      |  Notification (subs-id 22)   |            
      |<-----------------------------|            
      |  Notification (subs-id 22)   |            
      |<-----------------------------|            
      |                              |            
      |                              |            

                        

Figure 22: Message flow for subscription modification

2.7. Deleting a Subscription

This operation is defined in [event-notifications].

2.7.1. Usage Example

The following demonstrates deleting a subscription.

<netconf:rpc message-id="101" 
       xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
  <delete-subscription 
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    <subscription-id>1922</subscription-id>
  </delete-subscription>
</netconf:rpc>    
                        

Figure 23: Delete subscription

2.7.2. Positive Response

If the NETCONF server can satisfy the request, the server sends an OK element. For example:

<netconf:rpc message-id="103" 
       xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
  <delete-subscription 
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    <subscription-id>1922</subscription-id>
  </delete-subscription>
</netconf:rpc>

<rpc-reply message-id="103" 
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <ok/>
</rpc-reply>
                        

Figure 24: Successful delete subscription

2.7.3. Negative Response

If the NETCONF server cannot satisfy the request, the server sends an error-rpc element. For example:

<netconf:rpc message-id="103" 
       xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
  <delete-subscription 
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
    <subscription-id>2017</subscription-id>
  </delete-subscription>
</netconf:rpc>
                            
<rpc-reply message-id="101" 
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <rpc-error>
    <error-type>application</error-type>
    <error-tag>invalid-value</error-tag>
    <error-severity>error</error-severity>
    <error-path 
           xmlns:t="urn:ietf:params:xml:ns:netconf:notification:1.1">
      /t:subscription-id
    </error-path>
    <error-message xml:lang="en">
      Subscription-id 2017 does not exist
    </error-message>
  </rpc-error>
</rpc-reply>
                        

Figure 25: Unsuccessful delete subscription

2.7.4. Message Flow Example

                               
+------------+                 +-----------+      
|   Client   |                 |   Server  |      
+------------+                 +-----------+      
      |                              |            
      |    Capability Exchange       |            
      |<---------------------------->|            
      |                              |            
      |                              |            
      |    Establish Subscription    |            
      |----------------------------->|            
      | RPC Reply: OK, subs-id = 22  |            
      |<-----------------------------|            
      |                              |            
      |  Notification (subs-id 22)   |            
      |<-----------------------------|            
      |                              |            
      |                              |            
      |  Notification (subs-id 22)   |            
      |<-----------------------------|            
      |  Notification (subs-id 22)   |            
      |<-----------------------------|            
      |                              |            
      |                              |            
      |     Delete Subscription      |            
      |----------------------------->|            
      |                              |            
      |                              |            
      |                              |            
      |                              |            

                        

Figure 26: Message flow for subscription deletion

2.8. Configured Subscriptions

A configured subscription is a subscription installed via a configuration interface. Configured subscriptions do not support negotiation.

Supporting configured subscriptions is optional and advertised during the capabilities exchange using the "configured-subscriptions" feature.

Configured susbscriptions are supported by NETCONF servers using NETCONF Call Home [call-home]

In this section, we present examples of how to manage configuration subscriptions using a NETCONF client.

2.8.1. Call Home for Configured Subscriptions

Configured subscriptions are established, modified, and deleted using configuration operations against the top-level subtree subscription-config. Once the configuration is set, the server initiates a Call Home to each of the receivers in the subscription on the address and port specified. Once the NETCONF session between the server and the receiver is established, the server will issue a "subscription-started" notification. After that, the server will send notifications to the receiver as per the subscription.

Note that the server assumes the receiver is aware that calls on the configured port are intended only for pushing notifications. It also assumes that the receiver is ready to accept notifications on the session created as part of the Call Home as soon as the NETCONF session is established. This may require coordination between the client that configures the subscription and the clients for which the notifications are intended. This coordination is out of the scope of this document.

2.8.2. Establishing a Configured Subscription

Subscriptions are established using configuration operations against the top-level subtree subscription-config.

For example at subscription establishment, a NETCONF client may send:

<rpc message-id="101" 
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0" 
       xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0">
  <edit-config>
    <target>
      <running/>
    </target>
    <subscription-config 
            xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
      <subscription>
        <subscription-id>
          1922
        </subscription-id>
        <stream>
          foo
        </stream>
        <receiver>
          <address>
            1.2.3.4
          </address>
          <port>
            1234
          </port>
        </receiver>
      </subscription>
    </subscription-config>
  </edit-config>
</rpc>
                        

Figure 27: Establish static subscription

if the request is accepted, the server would reply:

<rpc-reply message-id="101" 
          xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <ok/>
</rpc-reply>
                        

Figure 28: Response to a successful static subscription establishment

if the request is not accepted because the server cannot serve it, the server may reply:

<rpc-reply xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <rpc-error>
    <error-type>application</error-type>
      <error-tag>resource-denied</error-tag>
      <error-severity>error</error-severity>
      <error-message xml:lang="en">
        Temporarily the server cannot serve this 
        subscription due to the current workload.
    </error-message>       
  </rpc-error>
</rpc-reply>
                        

Figure 29: Response to a failed static subscription establishment

2.8.2.1. Message Flow Example

                               
+----------+                 +-----------+     +---------+  +---------+
|  Client  |                 |   Server  |     | Rcver A |  | Rcver B |       
+----------+                 +-----------+     +---------+  +---------+
      |                            |                |            |
      |    Capability Exchange     |                |            |            
      |<-------------------------->|                |            |            
      |                            |                |            |            
      |                            |                |            |            
      |        Edit-config         |                |            |            
      |--------------------------->|                |            |            
      |       RPC Reply: OK        |                |            |            
      |<---------------------------|                |            |  
      |                            |   Call Home    |            |            
      |                            |<-------------->|            |
      |                            |<--------------------------->|            
      |                            |                |            |            
      |                            |  Subscription  |            |            
      |                            |  Started       |            |    
      |                            |  (subs-id 22)  |            |            
      |                            |--------------->|            |            
      |                            |---------------------------->|
      |                            |                |            |            
      |                            |  Notification  |            |            
      |                            |  (subs-id 22)  |            |            
      |                            |--------------->|            |            
      |                            |---------------------------->|
      |                            |                |            |            
      |                            |                |            |            
      |                            |                |            |            
      |                            |                |            |            
      |                            |                |            |            
      |                            |  Notification  |            | 
      |                            |  (subs-id 22)  |            |            
      |                            |--------------->|            |            
      |                            |---------------------------->|
      |                            |                |            |            
      |                            |  Notification  |            |
      |                            |  (subs-id 22)  |            |            
      |                            |--------------->|            |            
      |                            |---------------------------->|
      |                            |                |            |            


                        

Figure 30: Message flow for subscription establishment (configured subscription)

2.8.3. Modifying a Configured Subscription

Configured subscriptions can be modified using configuration operations against the top-level subtree subscription-config.

For example, the subscription established in the previous section could be modified as follows, choosing a different receiver:

<rpc message-id="102" 
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0" 
       xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0">
  <edit-config>
    <target>
      <running/>
    </target>
    <subscription-config 
            xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
      <subscription>
        <subscription-id>
          1922
        </subscription-id>
        <stream>
          foo
        </stream>
        <receiver>
          <address>
            1.2.3.5
          </address>
          <port>
            1234
          </port>
        </receiver>
      </subscription>
    </subscription-config>
  </edit-config>
</rpc>
                        

Figure 31: Modify configured subscription

if the request is accepted, the server would reply:

<rpc-reply message-id="102" 
          xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <ok/>
</rpc-reply>
                        

Figure 32: Response to a successful configured subscription modification

2.8.3.1. Message Flow Example

                               
+----------+                 +-----------+     +---------+  +---------+
|  Client  |                 |   Server  |     | Rcver A |  | Rcver B |       
+----------+                 +-----------+     +---------+  +---------+
      |                            |                |            |
      |    Capability Exchange     |                |            |            
      |<-------------------------->|                |            |            
      |                            |                |            |            
      |                            |                |            |            
      |        Edit-config         |                |            |            
      |--------------------------->|                |            |            
      |       RPC Reply: OK        |                |            |            
      |<---------------------------|                |            |  
      |                            |   Call Home    |            |            
      |                            |<-------------->|            |
      |                            |<--------------------------->|            
      |                            |                |            |            
      |                            |  Subscription  |            |            
      |                            |  Started       |            |   
      |                            |  (subs-id 22)  |            |            
      |                            |--------------->|            |            
      |                            |---------------------------->|
      |                            |                |            |            
      |                            |  Notification  |            | 
      |                            |  (subs-id 22)  |            |                       
      |                            |--------------->|            |            
      |                            |---------------------------->|
      |                            |                |            |            
      |                            |                |            |            
      |                            |                |            |            
      |        Edit-config         |                |            |            
      |--------------------------->|                |            |            
      |       RPC Reply: OK        |                |            |            
      |<---------------------------|                |            |            
      |                            |                |            |            
      |                            |                |            |            
      |                            |  Subscription  |            |            
      |                            |  Modified      |            |    
      |                            |  (subs-id 22)  |            |            
      |                            |--------------->|            |            
      |                            |---------------------------->|
      |                            |                |            |            
      |                            |  Notification  |            |            
      |                            |  (subs-id 22)  |            |            
      |                            |--------------->|            |            
      |                            |---------------------------->|
      |                            |                |            |            


                            

Figure 33: Message flow for subscription modification (configured subscription)

2.8.4. Deleting a Configured Subscription

Subscriptions can be deleted using configuration operations against the top-level subtree subscription-config. For example:

<rpc message-id="103" 
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <edit-config>
    <target>
      <running/>
    </target>
    <subscription-config 
        xmlns:xc="urn:ietf:params:xml:ns:netconf:notification:1.1">
      <subscription xc:operation="delete">
        <subscription-id>
          1922
        </subscription-id>
      </subscription>
    </subscription-config>
  </edit-config>
</rpc>

<rpc-reply message-id="103" 
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <ok/>
</rpc-reply>

                        

Figure 34: Deleting a configured subscription

2.8.4.1. Message Flow Example

                               
+----------+                 +-----------+     +---------+  +---------+
|  Client  |                 |   Server  |     | Rcver A |  | Rcver B |       
+----------+                 +-----------+     +---------+  +---------+
      |                            |                |            |
      |    Capability Exchange     |                |            |            
      |<-------------------------->|                |            |            
      |                            |                |            |            
      |                            |                |            |            
      |        Edit-config         |                |            |            
      |--------------------------->|                |            |            
      |       RPC Reply: OK        |                |            |            
      |<---------------------------|                |            |  
      |                            |   Call Home    |            |            
      |                            |<-------------->|            |
      |                            |<--------------------------->|            
      |                            |                |            |            
      |                            |  Subscription  |            |            
      |                            |  Started       |            |       
      |                            |  (subs-id 22)  |            |            
      |                            |--------------->|            |            
      |                            |---------------------------->|
      |                            |                |            |
      |                            |  Notification  |            |
      |                            |  (subs-id 22)  |            |            
      |                            |--------------->|            |            
      |                            |---------------------------->|
      |                            |                |            |            
      |                            |                |            |
      |                            |                |            |
      |                            |                |            |
      |                            |                |            |  
      |                            |  Notification  |            |            
      |                            |  (subs-id 22)  |            |            
      |                            |--------------->|            |            
      |                            |---------------------------->|
      |                            |                |            |            
      |        Edit-config         |                |            |            
      |--------------------------->|                |            |            
      |       RPC Reply: OK        |                |            |            
      |<---------------------------|                |            |            
      |                            |                |            |            
      |                            |                |            |            
      |                            |  Subscription  |            |            
      |                            |  Terminated    |            |    
      |                            |  (subs-id 22)  |            |            
      |                            |--------------->|            |            
      |                            |---------------------------->|
      |                            |                |            |            
      |                            |                |            |            
      |                            |                |            |            
      |                            |                |            |            

                            

Figure 35: Message flow for subscription deletion (configured subscription)

2.9. Event (Data Plane) Notifications

Once a subscription has been set up, the NETCONF server sends (asynchronously) the event notifications from the subscribed stream. We refer to these as data plane notifications. For dynamic subscriptions set up via RPC operations, event notifications are sent over the NETCONF session used to create or establish the subscription. For static subscriptions, event notifications are sent over the specified connections.

An event notification is sent to the receiver(s) when an event of interest (i.e., meeting the specified filtering criteria) has occurred. An event notification is a complete and well-formed XML document. Note that <notification> is not a Remote Procedure Call (RPC) method but rather the top-level element identifying the one-way message as a notification. Note that event notifications never trigger responses.

The event notification always includes an <eventTime> element. It is the time the event was generated by the event source. This parameter is of type dateTime and compliant to [RFC3339]. Implementations must support time zones.

The event notification also contains notification-specific tagged content, if any. With the exception of <eventTime>, the content of the notification is beyond the scope of this document.

For encodings other than XML, notifications include an additional XML element so that the notification is a well-formed XML. The element is <notification-contents-{encoding}>, E.g., <notification-contents-json>. That element contains the notification contents in the desired encoding

The following is an example of an event notification from [RFC6020]: