Internet Engineering Task Force (IETF) E. Voit Request for Comments: 9999 Cisco Systems Category: Standards Track A. Clemm ISSN: 2070-1721 Huawei A. Gonzalez Prieto Microsoft E. Nilsen-Nygaard A. Tripathy Cisco Systems July 2019 Dynamic Subscription to YANG Events and Datastores over NETCONF Abstract This document provides a Network Configuration Protocol (NETCONF) binding to the dynamic subscription capability of both subscribed notifications and YANG-Push. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9999. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Table of Contents 1. Introduction 2. Terminology 3. Compatibility with RFC-5277's create-subscription 4. Mandatory XML, event stream and datastore support 5. NETCONF connectivity and the Dynamic Subscriptions 6. Notification Messages 7. Dynamic Subscriptions and RPC Error Responses 8. Security Considerations 9. IANA Considerations 10. References 10.1. Normative References 10.2. Informative References Appendix A. Examples A.1. Event Stream Discovery A.2. Dynamic Subscriptions A.3. Subscription State Notifications A.4. Filter Examples Acknowledgments Authors' Addresses 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 [RFCYYYY]. In addition, as [RFCZZZZ] is itself built upon [RFCYYYY], 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 [RFCYYYY]. 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 [RFCYYYY]: 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 [RFCYYYY] 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: * A solution MUST reply with the [RFC6241] "rpc-error" element containing the "error-tag" value of "operation-not-supported" if a "create-subscription" RPC is received on a NETCONF session where an [RFCYYYY] established subscription exists. * A solution MUST reply with the [RFC6241] "rpc-error" element containing the "error-tag" value of "operation-not-supported" if an "establish-subscription" request has been received on a NETCONF session where the "create-subscription" RPC has successfully [RFC5277] created a subscription. 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 [RFCYYYY] 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 [RFCYYYY] 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 [RFCZZZZ] and [RFCYYYY]. 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 message as defined within [RFC5277]. 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 [RFCYYYY] Section 2.4.6 and [RFCZZZZ] Appendix A, the NETCONF RPC reply MUST include an "rpc- error" element per [RFC6241] with the error information populated as follows: * An "error-type" node of "application". * An "error-tag" node with the value being a string that corresponds to an identity associated with the error. For the mechanisms specified in this document, this "error-tag" will come from one of two places. Either it will correspond to the error identities within [RFCYYYY] section 2.4.6 for general subscription errors: 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 * Or this "error-tag" will correspond to the error identities within [RFCZZZZ] Appendix A.1 for subscription errors specific to YANG datastores: 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 * an "error-severity" of "error" (this MAY be included). * an "error-app-tag" node with the value being a string that corresponds to an identity associated with the error, as defined in [RFCYYYY] section 2.4.6 for general subscriptions, and [RFCZZZZ] Appendix A.1, for datastore subscriptions. The specific identity to use depends on the RPC for which the error occurred. Each error identity will be inserted as the "error-app-tag" following the form :. An example of such as valid encoding would be "ietf-subscribed-notifications:no- such-subscription". Viable errors for different RPCs are as follows: 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 * In case of error responses to an "establish-subscription" or "modify-subscription" request there is the option of including an "error-info" node. This node may contain XML-encoded data with hints for parameter settings that might lead to successful RPC requests in the future. Following are the yang-data structures from [RFCYYYY] and [RFCZZZZ] which may be returned: 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 [RFCYYYY]. 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 IANA actions. 10. References 10.1. Normative References [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., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "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, . [RFCYYYY] Voit, E., Clemm, A., Gonzalez Prieto, A., Tripathy, A., and E. Nilsen-Nygaard, "A YANG Data Model for Subscriptions to Event Notifications", RFC YYYY, DOI 10.17487/RFCYYYY, July 2019, . [RFCZZZZ] Clemm, Alexander. and Eric. Voit, "A YANG Data Model for Subscriptions to YANG Datastores", RFC ZZZZ, DOI 10.17487/RFCZZZZ, July 2019, . 10.2. Informative References [RFC8347] Liu, X., Ed., 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 [RFCYYYY] 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 [RFCYYYY] Section 3.1. The following example illustrates the retrieval of the list of available event streams: 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 [RFCYYYY]. 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: /ex:foo/ NETCONF 10 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): 22 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: application invalid-value error ietf-subscribed-notifications:dscp-unavailable 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 [RFCZZZZ], 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. 23 /ex:foo/ex:bar 500 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: application invalid-value error ietf-yang-push:period-unsupported 3000 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. 22 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: application invalid-value error ietf-subscribed-notifications:no-such-subscription 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 [RFCYYYY]. A.3.1. subscription-modified As per Section 2.7.2 of [RFCYYYY], 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: 2007-09-01T10:00:00Z 39 /ex:foo NETCONF Figure 11: "subscription-modified" Subscription State Notification A.3.2. subscription-resumed, and replay-complete A "subscription-resumed" would look like: 2007-09-01T10:00:00Z 39 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: 2007-09-01T10:00:00Z 39 suspension-timeout 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: 2018-09-14T08:22:33.44Z checksum-error 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: NETCONF /vrrp-protocol-error-event[ vrrp:protocol-error-reason="vrrp:checksum-error"] 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: 99 Figure 16: "Example "modify-subscription" RPC" For more examples of subtree filters, see [RFC6241], section 6.4. 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. 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