NETCONF E. Voit
Internet-Draft Cisco Systems
Intended status: Standards Track A. Clemm
Expires: November 20, 2019 Huawei
A. Gonzalez Prieto
Microsoft
E. Nilsen-Nygaard
A. Tripathy
Cisco Systems
May 19, 2019

Dynamic subscription to YANG Events and Datastores over NETCONF
draft-ietf-netconf-netconf-event-notifications-22

Abstract

This document provides a Network Configuration Protocol (NETCONF) binding to the dynamic subscription capability of both subscribed notifications and YANG-Push.

RFC Editor note: please replace the references to pre-RFC normative drafts with the actual assigned RFC numbers.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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Table of Contents

1. Introduction

This document specifies the binding of a stream of events which form part of a dynamic subscription to the NETCONF protocol [RFC6241]. Dynamic subscriptions are defined in [I-D.draft-ietf-netconf-subscribed-notifications]. In addition, as [I-D.draft-ietf-netconf-yang-push] is itself built upon [I-D.draft-ietf-netconf-subscribed-notifications], this document enables a NETCONF client to request via a dynamic subscription and receive updates from a YANG datastore located on a NETCONF server.

This document assumes that the reader is familiar with the terminology and concepts defined in [I-D.draft-ietf-netconf-subscribed-notifications].

2. 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 following terms are defined in [I-D.draft-ietf-netconf-subscribed-notifications]: dynamic subscription, event stream, notification message, publisher, receiver, subscriber, subscription. No additional terms are defined.

3. Compatibility with RFC-5277's create-subscription

A publisher is allowed to concurrently support dynamic subscription RPCs of [I-D.draft-ietf-netconf-subscribed-notifications] at the same time as [RFC5277]'s "create-subscription" RPC. However a single NETCONF transport session MUST NOT support both this specification and a subscription established by [RFC5277]'s "create-subscription" RPC. To protect against any attempts to use a single NETCONF transport session in this way:

If a publisher supports this specification but not subscriptions via [RFC5277], the publisher MUST NOT advertise "urn:ietf:params:netconf:capability:notification:1.0".

4. Mandatory XML, event stream and datastore support

The "encode-xml" feature of [I-D.draft-ietf-netconf-subscribed-notifications] MUST be supported. This indicates that XML is a valid encoding for RPCs, state change notifications, and subscribed content.

A NETCONF publisher supporting event stream subscription via [I-D.draft-ietf-netconf-subscribed-notifications] MUST support the "NETCONF" event stream identified in that document.

5. NETCONF connectivity and the Dynamic Subscriptions

Management of dynamic subscriptions occurs via RPCs as defined in [I-D.draft-ietf-netconf-yang-push] and [I-D.draft-ietf-netconf-subscribed-notifications]. For a dynamic subscription, if the NETCONF session involved with the "establish-subscription" terminates, the subscription MUST be terminated.

For a dynamic subscription, any "modify-subscription", "delete-subscription", or "resync-subscription" RPCs MUST be sent using the same NETCONF session upon which the referenced subscription was established.

6. Notification Messages

Notification messages transported over the NETCONF protocol MUST be encoded in a <notification> message as defined within [RFC5277], Section 4. And per [RFC5277]'s "eventTime" object definition, the "eventTime" is populated with the event occurrence time.

For dynamic subscriptions, all notification messages MUST use the NETCONF transport session used by the "establish-subscription" RPC.

7. Dynamic Subscriptions and RPC Error Responses

When an RPC error occurs as defined in [I-D.draft-ietf-netconf-subscribed-notifications] Section 2.4.6 and [I-D.draft-ietf-netconf-yang-push] Appendix A, the NETCONF RPC reply MUST include an "rpc-error" element per [RFC6241] with the error information populated as follows:

      
          error identity         uses error-tag
          ---------------------- --------------
          dscp-unavailable       invalid-value
          encoding-unsupported   invalid-value 
          filter-unsupported     invalid-value
          insufficient-resources resource-denied 
          no-such-subscription   invalid-value
          replay-unsupported     operation-not-supported
       

       
          error identity              uses error-tag
          ----------------------      --------------
          cant-exclude                operation-not-supported
          datastore-not-subscribable  invalid-value
          no-such-subscription-resync invalid-value
          on-change-unsupported       operation-not-supported
          on-change-sync-unsupported  operation-not-supported
          period-unsupported          invalid-value
          update-too-big              too-big
          sync-too-big                too-big
          unchanging-selection        operation-failed
       

         RPC                     have base identity
         ----------------------  ----------------------------
         establish-subscription  establish-subscription-error     
         modify-subscription     modify-subscription-error
         delete-subscription     delete-subscription-error    
         kill-subscription       delete-subscription-error
         resync-subscription     resync-subscription-error
            

    
      establish-subscription returns hints in yang-data structure
      ---------------------- ------------------------------------         
      target: event stream   establish-subscription-stream-error-info
      target: datastore      establish-subscription-datastore-error-info
            
      modify-subscription    returns hints in yang-data structure
      ---------------------- ------------------------------------         
      target: event stream   modify-subscription-stream-error-info
      target: datastore      modify-subscription-datastore-error-info
      
      The yang-data included within "error-info" SHOULD NOT include the
      optional leaf "reason", as such a leaf would be redundant
      with information that is already placed within the
      "error-app-tag".
            

In case of an rpc error resulting from a "delete-subscription", "kill-subscription", or "resync-subscription" request, no "error-info" needs to be included, as the "subscription-id" is the only RPC input parameter and no hints regarding this RPC input parameters need to be provided.

8. Security Considerations

This document does not introduce additional Security Considerations for dynamic subscriptions beyond those discussed in [I-D.draft-ietf-netconf-subscribed-notifications]. But there is one consideration worthy of more refinement based on the connection oriented nature of the NETCONF protocol. Specifically, if a buggy or compromised NETCONF subscriber sends a number of "establish-subscription" requests, then these subscriptions accumulate and may use up system resources. In such a situation, subscriptions MAY be terminated by terminating the underlying NETCONF session. The publisher MAY also suspend or terminate a subset of the active subscriptions on that NETCONF session in order to reclaim resources and preserve normal operation for the other subscriptions.

9. IANA Considerations

This document has no actions for IANA.

10. Acknowledgments

We wish to acknowledge the helpful contributions, comments, and suggestions that were received from: Andy Bierman, Yan Gang, Sharon Chisholm, Hector Trevino, Peipei Guo, Susan Hares, Tim Jenkins, Balazs Lengyel, Martin Bjorklund, Mahesh Jethanandani, Kent Watsen, Qin Wu, and Guangying Zheng.

11. References

11.1. Normative References

[I-D.draft-ietf-netconf-subscribed-notifications] Voit, E., Clemm, A., Gonzalez Prieto, A., Tripathy, A. and E. Nilsen-Nygaard, "Customized Subscriptions to a Publisher's Event Streams", September 2018.
[I-D.draft-ietf-netconf-yang-push] Clemm, Alexander., Voit, Eric., Gonzalez Prieto, Alberto., Tripathy, A., Nilsen-Nygaard, E., Bierman, A. and B. Lengyel, "YANG Datastore Subscription", September 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event Notifications", RFC 5277, DOI 10.17487/RFC5277, July 2008.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J. and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.

11.2. Informative References

[RFC8347] Liu, X., Kyparlis, A., Parikh, R., Lindem, A. and M. Zhang, "A YANG Data Model for the Virtual Router Redundancy Protocol (VRRP)", RFC 8347, DOI 10.17487/RFC8347, March 2018.
[XPATH] Clark, J. and S. DeRose, "XML Path Language (XPath) Version 1.0", November 1999.

Appendix A. Examples

This section is non-normative. Additionally the subscription "id" values of 22, 23, and 39 used below are just examples. In production, the actual values of "id" may not be small integers.

A.1. Event Stream Discovery

As defined in [I-D.draft-ietf-netconf-subscribed-notifications] an event stream exposes a continuous set of events available for subscription. A NETCONF client can retrieve the list of available event streams from a NETCONF publisher using the "get" operation against the top-level container "/streams" defined in [I-D.draft-ietf-netconf-subscribed-notifications] Section 3.1.

The following example illustrates the retrieval of the list of available event streams:

<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-subscribed-notifications"/>
    </filter>
  </get>
</rpc>
            

Figure 1: Get streams request

After such a request, the NETCONF publisher returns a list of event streams available, as well as additional information which might exist in the container.

A.2. Dynamic Subscriptions

A.2.1. Establishing Dynamic Subscriptions

The following figure shows two successful "establish-subscription" RPC requests as per [I-D.draft-ietf-netconf-subscribed-notifications]. The first request is given a subscription "id" of 22, the second, an "id" of 23.

   +------------+                 +-----------+
   | Subscriber |                 | Publisher |
   +------------+                 +-----------+
         |                              |
         |    Capability Exchange       |
         |<---------------------------->|
         |                              |
         |                              |
         |    establish-subscription    |
         |----------------------------->|  (a)
         | RPC Reply: OK, id = 22       |
         |<-----------------------------|  (b)
         |                              |
         | notification message (for 22)|
         |<-----------------------------|
         |                              |
         |                              |
         |    establish-subscription    |
         |----------------------------->|
         | notification message (for 22)|
         |<-----------------------------|
         | RPC Reply: OK, id = 23       |
         |<-----------------------------|
         |                              |
         |                              |
         | notification message (for 22)|
         |<-----------------------------|
         | notification message (for 23)|
         |<-----------------------------|
         |                              |                
          

Figure 2: Multiple subscriptions over a NETCONF session

To provide examples of the information being transported, example messages for interactions (a) and (b) in Figure 2 are detailed below:

<rpc message-id="102" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <establish-subscription 
      xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
    <stream-xpath-filter xmlns:ex="http://example.com/events">
      /ex:foo/
    </stream-xpath-filter>
    <stream>NETCONF</stream>
    <dscp>10</dscp>
  </establish-subscription>
</rpc>
            

Figure 3: establish-subscription request (a)

As NETCONF publisher was able to fully satisfy the request (a), the publisher sends the subscription "id" of the accepted subscription within message (b):

<rpc-reply message-id="102" 
  xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <id 
    xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
    22
  </id>
</rpc-reply>
           

Figure 4: establish-subscription success (b)

If the NETCONF publisher had not been able to fully satisfy the request, or subscriber has no authorization to establish the subscription, the publisher would have sent an RPC error response. For instance, if the "dscp" value of 10 asserted by the subscriber in Figure 3 proved unacceptable, the publisher may have returned:

<rpc-reply message-id="102" 
  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-app-tag>
     ietf-subscribed-notifications:dscp-unavailable
   </error-app-tag>    
  </rpc-error>
</rpc-reply>
          

Figure 5: an unsuccessful establish subscription

The subscriber can use this information in future attempts to establish a subscription.

A.2.2. Modifying Dynamic Subscriptions

An existing subscription may be modified. The following exchange shows a negotiation of such a modification via several exchanges between a subscriber and a publisher. This negotiation consists of a failed RPC modification request/response, followed by a successful one.

                  
   +------------+                 +-----------+
   | Subscriber |                 | Publisher |
   +------------+                 +-----------+
         |                              |
         | notification message (for 23)|
         |<-----------------------------|
         |                              |
         | modify-subscription (id = 23)|
         |----------------------------->|  (c)
         | RPC error (with hint)        |
         |<-----------------------------|  (d)
         |                              |
         | modify-subscription (id = 23)|
         |----------------------------->|
         | RPC Reply: OK                |
         |<-----------------------------|
         |                              |
         | notification message (for 23)|
         |<-----------------------------|
         |                              |          
          

Figure 6: Interaction model for successful subscription modification

If the subscription being modified in Figure 6 is a datastore subscription as per [I-D.draft-ietf-netconf-yang-push], the modification request made in (c) may look like that shown in Figure 7. As can be seen, the modifications being attempted are the application of a new XPath filter as well as the setting of a new periodic time interval.

<rpc message-id="303"
  xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <modify-subscription
       xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
       xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
    <id>23</id>
    <yp:datastore-xpath-filter xmlns:ex="http://example.com/datastore">  
        /ex:foo/ex:bar
    </yp:datastore-xpath-filter>
    <yp:periodic>
      <yp:period>500</yp:period>
    </yp:periodic> 
  </modify-subscription>
</rpc>
          

Figure 7: Subscription modification request (c)

If the NETCONF publisher can satisfy both changes, the publisher sends a positive result for the RPC. If the NETCONF publisher cannot satisfy either of the proposed changes, the publisher sends an RPC error response (d). The following is an example RPC error response for (d) which includes a hint. This hint is an alternative time period value which might have resulted in a successful modification:

<rpc-reply message-id="303"
  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-app-tag>
        ietf-yang-push:period-unsupported 
    </error-app-tag>
    <error-info>
      <modify-subscription-datastore-error-info
          xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push">
        <period-hint>
            3000
        </period-hint>
      </modify-subscription-datastore-error-info>
    </error-info>
  </rpc-error>
</rpc-reply>
          

Figure 8: Modify subscription failure with hint (d)

A.2.3. Deleting Dynamic Subscriptions

The following demonstrates deleting a subscription. This subscription may have been to either a stream or a datastore.

<rpc message-id="103"
  xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <delete-subscription
    xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
    <id>22</id>
  </delete-subscription>
</rpc> 
        

Figure 9: Delete subscription

If the NETCONF publisher can satisfy the request, the publisher replies with success to the RPC request.

If the NETCONF publisher cannot satisfy the request, the publisher sends an error-rpc element indicating the modification didn't work. Figure 10 shows a valid response for existing valid subscription "id", but that subscription "id" was created on a different NETCONF transport session:

<rpc-reply message-id="103"
  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-app-tag>
        ietf-subscribed-notifications:no-such-subscription
    </error-app-tag>
  </rpc-error>
</rpc-reply>
          

Figure 10: Unsuccessful delete subscription

A.3. Subscription State Notifications

A publisher will send subscription state notifications for dynamic subscriptions according to the definitions within [I-D.draft-ietf-netconf-subscribed-notifications].

A.3.1. subscription-modified

As per Section 2.7.2 of [I-D.draft-ietf-netconf-subscribed-notifications], a "subscription-modified" might be sent over NETCONF if the definition of a configured filter changes. A subscription state notification encoded in XML would look like:

<notification xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
  <eventTime>2007-09-01T10:00:00Z</eventTime>
  <subscription-modified 
      xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
    <id>39</id>
    <stream-xpath-filter xmlns:ex="http://example.com/events">
      /ex:foo
    </stream-xpath-filter>
    <stream>NETCONF</stream>
  </subscription-modified>
</notification>
           

Figure 11: subscription-modified subscription state notification

A.3.2. subscription-resumed, and replay-complete

A "subscription-resumed" would look like:

<notification
  xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
  <eventTime>2007-09-01T10:00:00Z</eventTime>
  <subscription-resumed
    xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
    <id>39</id>
  </subscription-resumed>
</notification>
           

Figure 12: subscription-resumed notification in XML

The "replay-complete" is virtually identical, with "subscription-resumed" simply being replaced by "replay-complete".

A.3.3. subscription-terminated and subscription-suspended

A "subscription-terminated" would look like:

<notification
  xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
  <eventTime>2007-09-01T10:00:00Z</eventTime>
  <subscription-terminated
    xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
    <id>39</id>
    <reason>
       suspension-timeout
    </reason>
  </subscription-terminated>
</notification>
          

Figure 13: subscription-terminated subscription state notification

The "subscription-suspended" is virtually identical, with "subscription-terminated" simply being replaced by "subscription-suspended".

A.4. Filter Examples

This section provides examples which illustrate both XPath and subtree methods of filtering event record contents. The examples are based on the YANG notification "vrrp-protocol-error-event" as defined per the ietf-vrrp.yang model within [RFC8347]. Event records based on this specification which are generated by the publisher might appear as:

<notification xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
  <eventTime>2018-09-14T08:22:33.44Z</eventTime>
  <vrrp-protocol-error-event 
       xmlns="urn:ietf:params:xml:ns:yang:ietf-vrrp">
     <protocol-error-reason>checksum-error</protocol-error-reason>  
  </vrrp-protocol-error-event>
</notification>
         

Figure 14: RFC 8347 (VRRP) - Example Notification

Suppose a subscriber wanted to establish a subscription which only passes instances of event records where there is a "checksum-error" as part of a VRRP protocol event. Also assume the publisher places such event records into the NETCONF stream. To get a continuous series of matching event records, the subscriber might request the application of an XPath filter against the NETCONF stream. An "establish-subscription" RPC to meet this objective might be:

<rpc message-id="601" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <establish-subscription
    xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
    <stream>NETCONF</stream>
    <stream-xpath-filter xmlns="urn:ietf:params:xml:ns:yang:ietf-vrrp">
      /vrrp-protocol-error-event[
         vrrp:protocol-error-reason="vrrp:checksum-error"]
    </stream-xpath-filter>
  </establish-subscription>
</rpc>
         

Figure 15: Establishing a subscription error reason via XPath

For more examples of XPath filters, see [XPATH].

Suppose the "establish-subscription" in Figure 15 was accepted. And suppose later a subscriber decided they wanted to broaden this subscription cover to all VRRP protocol events (i.e., not just those with a "checksum error"). The subscriber might attempt to modify the subscription in a way which replaces the XPath filter with a subtree filter which sends all VRRP protocol events to a subscriber. Such a "modify-subscription" RPC might look like:

 
<rpc message-id="602" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <modify-subscription
     xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
    <id>99</id>
    <stream-subtree-filter>
     <vrrp-protocol-error-event 
            xmlns="urn:ietf:params:xml:ns:yang:ietf-vrrp"/>
    </stream-subtree-filter>
  </modify-subscription>
</rpc>
         

Figure 16

For more examples of subtree filters, see [RFC6241], section 6.4.

Appendix B. Changes between revisions

(To be removed by RFC editor prior to publication)

B.1. v21 to v22

B.2. v20 to v21

B.3. v19 to v20

B.4. v17 to v19

B.5. v16 to v17

B.6. v15 to v16

B.7. v14 to v15

B.8. v13 to v14

B.9. v11 to v13

B.10. v10 to v11

B.11. v09 to v10

B.12. v08 to v09

B.13. v07 to v08

B.14. v06 to v07

B.15. v05 to v06

B.16. v03 to v04

B.17. v01 to v03

B.18. v00 to v01

Authors' Addresses

Eric Voit Cisco Systems EMail: evoit@cisco.com
Alexander Clemm Huawei EMail: ludwig@clemm.org
Alberto Gonzalez Prieto Microsoft EMail: alberto.gonzalez@microsoft.com
Einar Nilsen-Nygaard Cisco Systems EMail: einarnn@cisco.com
Ambika Prasad Tripathy Cisco Systems EMail: ambtripa@cisco.com