| 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
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.
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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].
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.
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".
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.
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.
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.
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.
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.
This document has no actions for IANA.
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.
| [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. |
| [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. |
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.
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.
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.
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)
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 publisher will send subscription state notifications for dynamic subscriptions according to the definitions within [I-D.draft-ietf-netconf-subscribed-notifications].
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 "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 "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".
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.
(To be removed by RFC editor prior to publication)