NETCONF A. Clemm Internet-Draft Huawei USA Intended status: Standards Track E. Voit Expires: August 8, 2019 Cisco Systems A. Gonzalez Prieto Microsoft A. Tripathy E. Nilsen-Nygaard Cisco Systems A. Bierman YumaWorks B. Lengyel Ericsson February 4, 2019 Subscription to YANG Datastores draft-ietf-netconf-yang-push-22 Abstract Via the mechanism described in this document, subscriber applications may request a continuous, customized stream of updates from a YANG datastore. Providing such visibility into updates enables new capabilities based on the remote mirroring and monitoring of configuration and operational state. 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 https://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 August 8, 2019. Clemm, et al. Expires August 8, 2019 [Page 1] Internet-Draft YANG-Push February 2019 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 . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Definitions and Acronyms . . . . . . . . . . . . . . . . . . 4 3. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Subscription Model . . . . . . . . . . . . . . . . . . . 5 3.2. Negotiation of Subscription Policies . . . . . . . . . . 6 3.3. On-Change Considerations . . . . . . . . . . . . . . . . 7 3.4. Reliability Considerations . . . . . . . . . . . . . . . 8 3.5. Data Encodings . . . . . . . . . . . . . . . . . . . . . 9 3.6. Defining the Selection with a Datastore . . . . . . . . . 10 3.7. Streaming Updates . . . . . . . . . . . . . . . . . . . . 11 3.8. Subscription Management . . . . . . . . . . . . . . . . . 13 3.9. Receiver Authorization . . . . . . . . . . . . . . . . . 15 3.10. On-Change Notifiable Datastore Nodes . . . . . . . . . . 16 3.11. Other Considerations . . . . . . . . . . . . . . . . . . 17 4. A YANG Data Model for Management of Datastore Push Subscriptions . . . . . . . . . . . . . . . . . . . . . . . . 18 4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 18 4.2. Subscription Configuration . . . . . . . . . . . . . . . 24 4.3. YANG Notifications . . . . . . . . . . . . . . . . . . . 25 Clemm, et al. Expires August 8, 2019 [Page 2] Internet-Draft YANG-Push February 2019 4.4. YANG RPCs . . . . . . . . . . . . . . . . . . . . . . . . 26 5. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . . 31 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 48 7. Security Considerations . . . . . . . . . . . . . . . . . . . 48 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 49 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 50 9.1. Normative References . . . . . . . . . . . . . . . . . . 50 9.2. Informative References . . . . . . . . . . . . . . . . . 51 Appendix A. Appendix A: Subscription Errors . . . . . . . . . . 51 A.1. RPC Failures . . . . . . . . . . . . . . . . . . . . . . 52 A.2. Notifications of Failure . . . . . . . . . . . . . . . . 53 Appendix B. Changes Between Revisions . . . . . . . . . . . . . 53 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 57 1. Introduction Traditional approaches to providing visibility into managed entities from remote have been built on polling. With polling, data is periodically requested and retrieved by a client from a server to stay up-to-date. However, there are issues associated with polling- based management: o Polling incurs significant latency. This latency prohibits many application types. o Polling cycles may be missed, requests may be delayed or get lost, often when the network is under stress and the need for the data is the greatest. o Polling requests may undergo slight fluctuations, resulting in intervals of different lengths. The resulting data is difficult to calibrate and compare. o For applications that monitor for changes, many remote polling cycles place unwanted and ultimately wasteful load on the network, devices, and applications, particularly when changes occur only infrequently. A more effective alternative to polling is for an application to receive automatic and continuous updates from a targeted subset of a datastore. Accordingly, there is a need for a service that allows applications to subscribe to updates from a datastore and that enables the server (also referred to as publisher) to push and in effect stream those updates. The requirements for such a service have been documented in [RFC7923]. This document defines a corresponding solution that is built on top of "Custom Subscription to Event Streams" Clemm, et al. Expires August 8, 2019 [Page 3] Internet-Draft YANG-Push February 2019 [I-D.draft-ietf-netconf-subscribed-notifications]. Supplementing that work are YANG data model augmentations, extended RPCs, and new datastore specific update notifications. Transport options for [I-D.draft-ietf-netconf-subscribed-notifications] will work seamlessly with this solution. 2. Definitions and Acronyms 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. This document uses the terminology defined in [RFC7950], [RFC8341], [RFC8342], and [I-D.draft-ietf-netconf-subscribed-notifications]. In addition, the following terms are introduced: o Datastore node: A node in the instantiated YANG data tree associated with a datastore. In this document, datastore nodes are often also simply referred to as "objects" o Datastore node update: A data item containing the current value of a datastore node at the time the datastore node update was created, as well as the path to the datastore node. o Datastore subscription: A subscription to a stream of datastore node updates. o Datastore subtree: A datastore node and all its descendant datastore nodes o On-change subscription: A datastore subscription with updates that are triggered when changes in subscribed datastore nodes are detected. o Periodic subscription: A datastore subscription with updates that are triggered periodically according to some time interval. o Selection filter: Evaluation and/or selection criteria, which may be applied against a targeted set of objects. o Update record: A representation of one or more datastore node updates. In addition, an update record may contain which type of update led to the datastore node update (e.g., whether the datastore node was added, changed, deleted). Also included in the update record may be other metadata, such as a subscription id of the subscription as part of which the update record was generated. Clemm, et al. Expires August 8, 2019 [Page 4] Internet-Draft YANG-Push February 2019 In this document, update records are often also simply referred to as "updates". o Update trigger: A mechanism that determines when an update record needs to be generated. o YANG-Push: The subscription and push mechanism for datastore updates that is specified in this document. 3. Solution Overview This document specifies a solution that provides a subscription service for updates from a datastore. This solution supports dynamic as well as configured subscriptions to updates of datastore nodes. Subscriptions specify when notification messages (also referred to as "push updates") should be sent and what data to include in update records. Datastore node updates are subsequently pushed from the publisher to the receiver per the terms of the subscription. 3.1. Subscription Model YANG-push subscriptions are defined using a YANG data model. This model enhances the subscription model defined in [I-D.draft-ietf-netconf-subscribed-notifications] with capabilities that allow subscribers to subscribe to datastore node updates, specifically to specify the update triggers defining when to generate update records as well as what to include in an update record. Key enhancements include: o Specification of selection filters which identify targeted YANG datastore nodes and/or datastore subtrees for which updates are to be pushed. o Specification of update policies contain conditions which trigger the generation and pushing of new update records. There are two types of subscriptions, distinguished by how updates are triggered: periodic and on-change. * For periodic subscriptions, the update trigger is specified by two parameters that define when updates are to be pushed. These parameters are the period interval with which to report updates, and an "anchor time", i.e. a reference point in time that can be used to calculate at which points in time periodic updates need to be assembled and sent. * For on-change subscriptions, an update trigger occurs whenever a change in the subscribed information is detected. Included are additional parameters that include: Clemm, et al. Expires August 8, 2019 [Page 5] Internet-Draft YANG-Push February 2019 + Dampening period: In an on-change subscription, detected object changes should be sent as quickly as possible. However it may be undesirable to send a rapid series of object changes. Such behavior has the potential to exhaust resources in the publisher or receiver. In order to protect against that, a dampening period MAY be used to specify the interval which has to pass before successive update records for the same subscription are generated for a receiver. The dampening period collectively applies to the set of all datastore nodes selected by a single subscription. This means that when there is a change to one or more subscribed objects, an update record containing those objects is created immediately (when no dampening period is in effect) or at the end of a dampening period (when a dampening period is in fact in effect). If multiple changes to a single object occur during a dampening period, only the value that is in effect at the time when the update record is created is included. The dampening period goes into effect every time an update record completes assembly. + Change type: This parameter can be used to reduce the types of datastore changes for which updates are sent (e.g., you might only send an update when an object is created or deleted, but not when an object value changes). + Sync on start: defines whether or not a complete push-update of all subscribed data will be sent at the beginning of a subscription. Such early synchronization establishes the frame of reference for subsequent updates. o An encoding (using anydata) for the contents of periodic and on- change push updates. 3.2. Negotiation of Subscription Policies A dynamic subscription request SHOULD be declined if a publisher's assessment is that it may be unable to provide update records meeting the terms of an "establish-subscription" or "modify-subscription" RPC request. In this case, a subscriber may quickly follow up with a new RPC request using different parameters. Random guessing of different parameters by a subscriber is to be discouraged. Therefore, in order to minimize the number of subscription iterations between subscriber and publisher, a dynamic subscription supports a simple negotiation between subscribers and publishers for subscription parameters. This negotiation is in the form of supplemental information which should be inserted within error responses to a failed RPC request. This returned error Clemm, et al. Expires August 8, 2019 [Page 6] Internet-Draft YANG-Push February 2019 response information, when considered, should increase the likelihood of success for subsequent RPC requests. Such hints include suggested periodic time intervals, acceptable dampening periods, and size estimates for the number or objects which would be returned from a proposed selection filter. However, there are no guarantees that subsequent requests which consider these hints will be accepted. 3.3. On-Change Considerations On-change subscriptions allow receivers to receive updates whenever changes to targeted objects occur. As such, on-change subscriptions are particularly effective for data that changes infrequently, yet for which applications need to be quickly notified whenever a change does occur with minimal delay. On-change subscriptions tend to be more difficult to implement than periodic subscriptions. Accordingly, on-change subscriptions may not be supported by all implementations or for every object. Whether or not to accept or reject on-change subscription requests when the scope of the subscription contains objects for which on- change is not supported is up to the publisher implementation. A publisher MAY accept an on-change subscription even when the scope of the subscription contains objects for which on-change is not supported. In that case, updates are sent only for those objects within the scope that do support on-change updates, whereas other objects are excluded from update records, even if their values change. In order for a subscriber to determine whether objects support on-change subscriptions, objects are marked accordingly on a publisher. Accordingly, when subscribing, it is the responsibility of the subscriber to ensure it is aware of which objects support on- change and which do not. For more on how objects are so marked, see Section 3.10. Alternatively, a publisher MAY decide to simply reject an on-change subscription in case the scope of the subscription contains objects for which on-change is not supported. In case of a configured subscription, the publisher MAY suspend the subscription. To avoid flooding receivers with repeated updates for subscriptions containing fast-changing objects, or objects with oscillating values, an on-change subscription allows for the definition of a dampening period. Once an update record for a given object is generated, no other updates for this particular subscription will be created until the end of the dampening period. Values sent at the end of the dampening period are the values that are current at the end of the dampening period of all changed objects. Changed objects include those which were deleted or newly created during that dampening Clemm, et al. Expires August 8, 2019 [Page 7] Internet-Draft YANG-Push February 2019 period. If an object has returned to its original value (or even has been created and then deleted) during the dampening-period, that value (and not the interim change) will still be sent. This will indicate churn is occurring on that object. On-change subscriptions can be refined to let users subscribe only to certain types of changes. For example, a subscriber might only want object creations and deletions, but not modifications of object values. Putting it all together, following is the conceptual process for creating an update record as part of an on-change subscription: 1. Just before a change, or at the start of a dampening period, evaluate any filtering and any access control rules to ensure receiver is authorized to view all subscribed datastore nodes (filtering out any nodes for which this is not the case). The result is a set "A" of datastore nodes and subtrees. 2. Just after a change, or at the end of a dampening period, evaluate any filtering and any (possibly new) access control rules. The result is a set "B" of datastore nodes and subtrees. 3. Construct an update record, which takes the form of YANG patch record [RFC8072] for going from A to B. 4. If there were any changes made between A and B which canceled each other out, insert into the YANG patch record the last change made, even if the new value is no different from the original value (since changes that were made in the interim were canceled out). In case the changes involve creating a new datastore node, then deleting it, the YANG patch record will indicate deletion of the datastore node. Similarly, in case the changes involve deleting a new datastore node, then recreating it, the YANG patch record will indicate creation of the datastore node. 5. If the resulting patch record is non-empty, send it to the receiver. Note: In cases where a subscriber wants to have separate dampening periods for different objects, the subscriber has the option to create multiple subscriptions with different selection filters. 3.4. Reliability Considerations A subscription to updates from a datastore is intended to obviate the need for polling. However, in order to do so, it is critical that subscribers can rely on the subscription and have confidence that Clemm, et al. Expires August 8, 2019 [Page 8] Internet-Draft YANG-Push February 2019 they will indeed receive the subscribed updates without having to worry about updates being silently dropped. In other words, a subscription constitutes a promise on the side of the publisher to provide the receivers with updates per the terms of the subscription. Now, there are many reasons why a publisher may at some point no longer be able to fulfill the terms of the subscription, even if the subscription had been entered into with good faith. For example, the volume of datastore nodes may be larger than anticipated, the interval may prove too short to send full updates in rapid succession, or an internal problem may prevent objects from being collected. For this reason, the solution that is defined in this document mandates that a publisher notifies receivers immediately and reliably whenever it encounters a situation in which it is unable to keep the terms of the subscription, and provides the publisher with the option to suspend the subscription in such a case. This includes indicating the fact that an update is incomplete as part of a push- update or push-change-update notification, as well as emitting a subscription-suspended notification as applicable. This is described further in Section 3.11.1. A publisher SHOULD reject a request for a subscription if it is unlikely that the publisher will be able to fulfill the terms of that subscription request. In such cases, it is preferable to have a subscriber request a less resource intensive subscription than to deal with frequently degraded behavior. 3.5. Data Encodings 3.5.1. Periodic Subscriptions In a periodic subscription, the data included as part of an update record corresponds to data that could have been read using a retrieval operation. 3.5.2. On-Change Subscriptions In an on-change subscription, update records need to indicate not only values of changed datastore nodes but also the types of changes that occurred since the last update. Therefore, encoding rules for data in on-change updates will generally follow YANG-patch operation as specified in [RFC8072]. The YANG-patch will describe what needs to be applied to the earlier state reported by the preceding update, to result in the now-current state. Note that contrary to [RFC8072], objects encapsulated are not restricted to only configuration objects. Clemm, et al. Expires August 8, 2019 [Page 9] Internet-Draft YANG-Push February 2019 A publisher indicates the type of change to a datastore node using the different YANG patch operations: the "create" operation is used for newly created objects (except entries in a user-ordered list), the "delete" operation is used for deleted objects (including in user-ordered lists), the "replace" operation is used when only the object value changes, the "insert" operation is used when a new entry is inserted in a list, and the "move" operation is used when an existing entry in a user-ordered list is moved. However, a patch must be able to do more than just describe the delta from the previous state to the current state. As per Section 3.3, it must also be able to identify whether transient changes have occurred on an object during a dampening period. To support this, it is valid to encode a YANG patch operation so that its application would result in no change between the previous and current state. This indicates that some churn has occurred on the object. An example of this would be a patch that indicates a "create" operation for a datastore node where the receiver believes one already exists, or a "replace" operation which replaces a previous value with the same value. Note that this means that the "create" and "delete" errors described in [RFC8072] section 2.5 are not errors, and are valid operations with YANG-Push. 3.6. Defining the Selection with a Datastore A subscription must specify both the selection filters and the datastore against which these selection filters will be applied. This information is used to choose and subsequently push data from the publisher's datastore to the receivers. Only a single selection filter can be applied to a subscription at a time. An RPC request proposing a new selection filter replaces any existing filter. The following selection filter types are included in the yang-push data model, and may be applied against a datastore: o subtree: A subtree selection filter identifies one or more datastore subtrees. When specified, update records will only come from the datastore nodes of selected datastore subtree(s). The syntax and semantics correspond to that specified for [RFC6241] section 6. o xpath: An "xpath" selection filter is an XPath expression that returns a node set. When specified, updates will only come from the selected datastore nodes. These filters are intended to be used as selectors that define which objects are within the scope of a subscription. A publisher MUST support at least one type of selection filter. Clemm, et al. Expires August 8, 2019 [Page 10] Internet-Draft YANG-Push February 2019 XPath itself provides powerful filtering constructs and care must be used in filter definition. Consider an XPath filter which only passes a datastore node when an interface is up. It is up to the receiver to understand implications of the presence or absence of objects in each update. When the set of selection filtering criteria is applied for a periodic subscription, then they are applied whenever a periodic update record is constructed, and only datastore nodes that pass the filter and to which a receiver has access are provided to that receiver. If the same filtering criteria is applied to an on-change subscription, only the subset of those datastore nodes supporting on- change is provided. A datastore node which doesn't support on-change is never sent as part of an on-change subscription's "push-update" or "push-change-update" (see Section 3.7). 3.7. Streaming Updates Contrary to traditional data retrieval requests, datastore subscription enables an unbounded series of update records to be streamed over time. Two generic YANG notifications for update records have been defined for this: "push-update" and "push-change- update". A "push-update" notification defines a complete, filtered update of the datastore per the terms of a subscription. This type of YANG notification is used for continuous updates of periodic subscriptions. A "push-update" notification can also be used for the on-change subscriptions in two cases. First, it MUST be used as the initial "push-update" if there is a need to synchronize the receiver at the start of a new subscription. It also MAY be sent if the publisher later chooses to resync an on-change subscription. The "push-update" update record contains an instantiated datastore subtree with all of the subscribed contents. The content of the update record is equivalent to the contents that would be obtained had the same data been explicitly retrieved using a datastore retrieval operation using the same transport with the same filters applied. A "push-change-update" notification is the most common type of update for on-change subscriptions. The update record in this case contains the set of changes that datastore nodes have undergone since the last notification message. In other words, this indicates which datastore nodes have been created, deleted, or have had changes to their values. In cases where multiple changes have occurred over the course of a dampening period and the object has not been deleted, the object's most current value is reported. (In other words, for each Clemm, et al. Expires August 8, 2019 [Page 11] Internet-Draft YANG-Push February 2019 object, only one change is reported, not its entire history. Doing so would defeat the purpose of the dampening period.) "Push-update" and "push-change-update" are encoded and placed within notification messages, and ultimately queued for egress over the specified transport. The following is an example of a notification message for a subscription tracking the operational status of a single Ethernet interface (per [RFC8343]). This notification message is encoded XML over NETCONF as per [I-D.draft-ietf-netconf-netconf-event-notifications]. 2017-10-25T08:00:11.22Z 1011 eth0 up Figure 1: Push example The following is an example of an on-change notification message for the same subscription. Clemm, et al. Expires August 8, 2019 [Page 12] Internet-Draft YANG-Push February 2019 2017-10-25T08:22:33.44Z 89 0 edit1 replace /ietf-interfaces:interfaces eth0 down Figure 2: Push example for on change Of note in the above example is the 'patch-id' with a value of '0'. Per [RFC8072], the 'patch-id' is an arbitrary string. With YANG Push, the publisher SHOULD put into the 'patch-id' a counter starting at '0' which increments with every 'push-change-update' generated for a subscription. If used as a counter, this counter MUST be reset to '0' anytime a resynchronization occurs (i.e., with the sending of a 'push-update'). Also if used as a counter, the counter MUST be reset to '0' after passing a maximum value of '4294967295' (i.e. maximum value that can be represented using uint32 data type). Such a mechanism allows easy identification of lost or out-of-sequence update records. 3.8. Subscription Management The RPCs defined within [I-D.draft-ietf-netconf-subscribed-notifications] have been enhanced to support datastore subscription negotiation. Also, new error codes have been added that are able to indicate why a datastore subscription attempt has failed, along with new yang-data that MAY be Clemm, et al. Expires August 8, 2019 [Page 13] Internet-Draft YANG-Push February 2019 used to include details on input parameters that might result in a successful subsequent RPC invocation. The establishment or modification of a datastore subscription can be rejected for multiple reasons. This includes a too large subtree request, or the inability of the publisher to push update records as frequently as requested. In such cases, no subscription is established. Instead, the subscription-result with the failure reason is returned as part of the RPC response. As part of this response, a set of alternative subscription parameters MAY be returned that would likely have resulted in acceptance of the subscription request. The subscriber may consider these as part of future subscription attempts. In the case of a rejected request for an establishment of a datastore subscription, if there are hints, the hints SHOULD be transported within a yang-data "establish-subscription-datastore-error-info" container inserted into the RPC error response, in lieu of the "establish-subscription-stream-error-info" that is inserted in case of a stream subscription. Below is a tree diagram for "establish-subscription-datastore-error- info". All tree diagrams used in this document follow the notation defined in [RFC8340] yang-data establish-subscription-datastore-error-info +--ro establish-subscription-datastore-error-info +--ro reason? identityref +--ro period-hint? centiseconds +--ro filter-failure-hint? string +--ro object-count-estimate? uint32 +--ro object-count-limit? uint32 +--ro kilobytes-estimate? uint32 +--ro kilobytes-limit? uint32 Figure 3: Tree diagram for establish-subscription-datastore-error- info Similarly, in the case of a rejected request for modification of a datastore subscription, if there are hints, the hints SHOULD be transported within a yang-data "modify-subscription-datastore-error- info" container inserted into the RPC error response, in lieu of the "modify-subscription-stream-error-info" that is inserted in case of a stream subscription. Below is a tree diagram for "modify-subscription-datastore-error- info". Clemm, et al. Expires August 8, 2019 [Page 14] Internet-Draft YANG-Push February 2019 yang-data modify-subscription-datastore-error-info +--ro modify-subscription-datasore-error-info +--ro reason? identityref +--ro period-hint? centiseconds +--ro filter-failure-hint? string +--ro object-count-estimate? uint32 +--ro object-count-limit? uint32 +--ro kilobytes-estimate? uint32 +--ro kilobytes-limit? uint32 Figure 4: Tree diagram for modify-subscription-datastore-error-info 3.9. Receiver Authorization A receiver of subscription data MUST only be sent updates for which it has proper authorization. A publisher MUST ensure that no non- authorized data is included in push updates. To do so, it needs to apply all corresponding checks applicable at the time of a specific pushed update and if necessary silently remove any non-authorized data from datastore subtrees. This enables YANG data pushed based on subscriptions to be authorized equivalently to a regular data retrieval (get) operation. Each "push-update" and "push-change-update" MUST have access control applied, as is depicted in the following diagram. This includes validating that read access is permitted for any new objects selected since the last notification message was sent to a particular receiver. To accomplish this, implementations SHOULD support the conceptual authorization model of [RFC8341], specifically section 3.2.4. +-----------------+ +--------------------+ push-update or --> | datastore node | yes | add datastore node | push-change-update | access allowed? | ---> | to update record | +-----------------+ +--------------------+ Figure 5: Updated [RFC8341] access control for push updates A publisher MUST allow for the possibility that a subscription's selection filter references non-existent data or data that a receiver is not allowed to access. Such support permits a receiver the ability to monitor the entire lifecyle of some datastore tree without needing to explicitly enumerate every individual datastore node. If, after access control has been applied, there are no objects remaining in an update record, then (in case of a periodic subscription) only a single empty "push-update" notification MUST be sent. Empty "push- change-update" messages (in case of an on-change subscription) MUST NOT be sent. This is required to ensure that clients cannot Clemm, et al. Expires August 8, 2019 [Page 15] Internet-Draft YANG-Push February 2019 surreptitiously monitor objects that they do not have access to via carefully crafted selection filters. By the same token, changes to objects that are filtered MUST NOT affect any dampening intervals. A publisher MAY choose to reject an establish-subscription request which selects non-existent data or data that a receiver is not allowed to access. As reason, the error identity "unchanging- selection" SHOULD be returned. In addition, a publisher MAY choose to terminate a dynamic subscription or suspend a configured receiver when the authorization privileges of a receiver change, or the access controls for subscribed objects change. In that case, the publisher SHOULD include the error identity "unchanging-selection" as reason when sending the "subscription-terminated" respectively "subscription-suspended" notification. Such a capability enables the publisher to avoid having to support continuous and total filtering of a subscription's content for every update record. It also reduces the possibility of leakage of access-controlled objects. If read access into previously accessible nodes has been lost due to a receiver permissions change, this SHOULD be reported as a patch "delete" operation for on-change subscriptions. If not capable of handling such receiver permission changes with such a "delete", publisher implementations MUST force dynamic subscription re- establishment or configured subscription re-initialization so that appropriate filtering is installed. 3.10. On-Change Notifiable Datastore Nodes In some cases, a publisher supporting on-change notifications may not be able to push on-change updates for some object types. Reasons for this might be that the value of the datastore node changes frequently (e.g., [RFC8343]'s in-octets counter), that small object changes are frequent and meaningless (e.g., a temperature gauge changing 0.1 degrees), or that the implementation is not capable of on-change notification for a particular object. In those cases, it will be important for client applications to have a way to identify for which objects on-change notifications are supported and for which ones they are not supported. Otherwise client applications will have no way of knowing whether they can indeed rely on their on-change subscription to provide them with the change updates that they are interested in. In other words, if implementations do not provide a solution and do not support comprehensive on-change notifiability, clients of those implementations will have no way of knowing what their on-change subscription actually covers. Clemm, et al. Expires August 8, 2019 [Page 16] Internet-Draft YANG-Push February 2019 Implementations are therefore strongly advised to provide a solution to this problem. It is expected that such a solution will be standardized at some point in the future. In the meantime and until this occurs, implementations SHOULD provide their own solution. 3.11. Other Considerations 3.11.1. Robustness and reliability Particularly in the case of on-change updates, it is important that these updates do not get lost. In case the loss of an update is unavoidable, it is critical that the receiver is notified accordingly. Update records for a single subscription MUST NOT be resequenced prior to transport. It is conceivable that under certain circumstances, a publisher will recognize that it is unable to include within an update record the full set of objects desired per the terms of a subscription. In this case, the publisher MUST act as follows. o The publisher MUST set the "incomplete-update" flag on any update record which is known to be missing information. o The publisher MAY choose to suspend the subscription as per [I-D.draft-ietf-netconf-subscribed-notifications]. If the publisher does not create an update record at all, it MUST suspend the subscription. o When resuming an on-change subscription, the publisher SHOULD generate a complete patch from the previous update record. If this is not possible and the "sync-on-start" option is true for the subscription, then the full datastore contents MAY be sent via a "push-update" instead (effectively replacing the previous contents). If neither of these are possible, then an "incomplete- update" flag MUST be included on the next "push-change-update". Note: It is perfectly acceptable to have a series of "push-change- update" notifications (and even "push update" notifications) serially queued at the transport layer awaiting transmission. It is not required for the publisher to merge pending update records sent at the same time. Clemm, et al. Expires August 8, 2019 [Page 17] Internet-Draft YANG-Push February 2019 3.11.2. Publisher capacity It is far preferable to decline a subscription request than to accept such a request when it cannot be met. Whether or not a subscription can be supported will be determined by a combination of several factors such as the subscription update trigger (on-change or periodic), the period in which to report changes (one second periods will consume more resources than one hour periods), the amount of data in the datastore subtree that is being subscribed to, and the number and combination of other subscriptions that are concurrently being serviced. 4. A YANG Data Model for Management of Datastore Push Subscriptions 4.1. Overview The YANG data model for datastore push subscriptions is depicted in the following figures. The tree diagram that is used follows the notation defined in [RFC8340]. New schema objects defined here (i.e., beyond those from [I-D.draft-ietf-netconf-subscribed-notifications]) are identified with "yp". For the reader's convenience, in order to compact the tree representation, some nodes that are defined in ietf-subscribed- notifications and that are not essential to the understanding of the data model defined here have been removed. This is indicated by "..." in the diagram where applicable. Because the tree diagram is quite large, its depiction is broken up into several figures. The first figure depicts the augmentations that are introduced in module ietf-yang-push to subscription configuration specified in module ietf-subscribed-notifications. Clemm, et al. Expires August 8, 2019 [Page 18] Internet-Draft YANG-Push February 2019 module: ietf-subscribed-notifications ... +--rw filters | ... | +--rw yp:selection-filter* [filter-id] | +--rw yp:filter-id string | +--rw (yp:filter-spec)? | +--:(yp:datastore-subtree-filter) | | +--rw yp:datastore-subtree-filter? | | {sn:subtree}? | +--:(yp:datastore-xpath-filter) | +--rw yp:datastore-xpath-filter? yang:xpath1.0 | {sn:xpath}? +--rw subscriptions +--rw subscription* [id] | ... +--rw (target) | +--:(stream) | | ... | +--:(yp:datastore) | +--rw yp:datastore identityref | +--rw (yp:selection-filter)? | +--:(yp:by-reference) | | +--rw yp:selection-filter-ref | | selection-filter-ref | +--:(yp:within-subscription) | +--rw (yp:filter-spec)? | +--:(yp:datastore-subtree-filter) | | +--rw yp:datastore-subtree-filter? | | {sn:subtree}? | +--:(yp:datastore-xpath-filter) | +--rw yp:datastore-xpath-filter? | yang:xpath1.0 {sn:xpath}? | ... +--rw (yp:update-trigger) +--:(yp:periodic) | +--rw yp:periodic! | +--rw yp:period centiseconds | +--rw yp:anchor-time? yang:date-and-time +--:(yp:on-change) {on-change}? +--rw yp:on-change! +--rw yp:dampening-period? centiseconds +--rw yp:sync-on-start? boolean +--rw yp:excluded-change* change-type Figure 6: Model structure: subscription configuration Clemm, et al. Expires August 8, 2019 [Page 19] Internet-Draft YANG-Push February 2019 The next figure depicts the augmentations of module ietf-yang-push made to RPCs specified in module ietf-subscribed-notifications. Specifically, these augmentations concern the establish-subscription and modify-subscription RPCs, which are augmented with parameters that are needed to specify datastore push subscriptions. rpcs: +---x establish-subscription | +---w input | | ... | | +---w (target) | | | +--:(stream) | | | | ... | | | +--:(yp:datastore) | | | +---w yp:datastore identityref | | | +---w (yp:selection-filter)? | | | +--:(yp:by-reference) | | | | +---w yp:selection-filter-ref | | | | selection-filter-ref | | | +--:(yp:within-subscription) | | | +---w (yp:filter-spec)? | | | +--:(yp:datastore-subtree-filter) | | | | +---w yp:datastore-subtree-filter? | | | | {sn:subtree}? | | | +--:(yp:datastore-xpath-filter) | | | +---w yp:datastore-xpath-filter? | | | yang:xpath1.0 {sn:xpath}? | | | ... | | +---w (yp:update-trigger) | | +--:(yp:periodic) | | | +---w yp:periodic! | | | +---w yp:period centiseconds | | | +---w yp:anchor-time? yang:date-and-time | | +--:(yp:on-change) {on-change}? | | +---w yp:on-change! | | +---w yp:dampening-period? centiseconds | | +---w yp:sync-on-start? boolean | | +---w yp:excluded-change* change-type | +--ro output | +--ro id subscription-id | +--ro replay-start-time-revision? yang:date-and-time | {replay}? +---x modify-subscription | +---w input | ... | +---w (target) | | ... Clemm, et al. Expires August 8, 2019 [Page 20] Internet-Draft YANG-Push February 2019 | | +--:(yp:datastore) | | +---w yp:datastore identityref | | +---w (yp:selection-filter)? | | +--:(yp:by-reference) | | | +---w yp:selection-filter-ref | | | selection-filter-ref | | +--:(yp:within-subscription) | | +---w (yp:filter-spec)? | | +--:(yp:datastore-subtree-filter) | | | +---w yp:datastore-subtree-filter? | | | {sn:subtree}? | | +--:(yp:datastore-xpath-filter) | | +---w yp:datastore-xpath-filter? | | yang:xpath1.0 {sn:xpath}? | | ... | +---w (yp:update-trigger) | +--:(yp:periodic) | | +---w yp:periodic! | | +---w yp:period centiseconds | | +---w yp:anchor-time? yang:date-and-time | +--:(yp:on-change) {on-change}? | +---w yp:on-change! | +---w yp:dampening-period? centiseconds +---x delete-subscription | ... +---x kill-subscription ... yang-data (for placement into rpc error responses) ... Figure 7: Model structure: RPCs The next figure depicts augmentations of module ietf-yang-push to the notifications that are specified in module ietf-subscribed- notifications. The augmentations allow to include subscription configuration parameters that are specific to datastore push subscriptions as part of subscription-started and subscription- modified notifications. notifications: +---n replay-completed {replay}? | ... +---n subscription-completed | ... +---n subscription-started {configured}? | | ... | +--ro (target) Clemm, et al. Expires August 8, 2019 [Page 21] Internet-Draft YANG-Push February 2019 | | ... | | +--:(yp:datastore) | | +--ro yp:datastore identityref | | +--ro (yp:selection-filter)? | | +--:(yp:by-reference) | | | +--ro yp:selection-filter-ref | | | selection-filter-ref | | +--:(yp:within-subscription) | | +--ro (yp:filter-spec)? | | +--:(yp:datastore-subtree-filter) | | | +--ro yp:datastore-subtree-filter? | | | {sn:subtree}? | | +--:(yp:datastore-xpath-filter) | | +--ro yp:datastore-xpath-filter? | | yang:xpath1.0 {sn:xpath}? | ... | +--ro (yp:update-trigger) | +--:(yp:periodic) | | +--ro yp:periodic! | | +--ro yp:period centiseconds | | +--ro yp:anchor-time? yang:date-and-time | +--:(yp:on-change) {on-change}? | +--ro yp:on-change! | +--ro yp:dampening-period? centiseconds | +--ro yp:sync-on-start? boolean | +--ro yp:excluded-change* change-type +---n subscription-resumed | ... +---n subscription-modified | ... | +--ro (target) | | | ... | | +--:(yp:datastore) | | +--ro yp:datastore identityref | | +--ro (yp:selection-filter)? | | +--:(yp:by-reference) | | | +--ro yp:selection-filter-ref | | | selection-filter-ref | | +--:(yp:within-subscription) | | +--ro (yp:filter-spec)? | | +--:(yp:datastore-subtree-filter) | | | +--ro yp:datastore-subtree-filter? | | | {sn:subtree}? | | +--:(yp:datastore-xpath-filter) | | +--ro yp:datastore-xpath-filter? | | yang:xpath1.0 {sn:xpath}? | ... | +--ro (yp:update-trigger)? Clemm, et al. Expires August 8, 2019 [Page 22] Internet-Draft YANG-Push February 2019 | +--:(yp:periodic) | | +--ro yp:periodic! | | +--ro yp:period centiseconds | | +--ro yp:anchor-time? yang:date-and-time | +--:(yp:on-change) {on-change}? | +--ro yp:on-change! | +--ro yp:dampening-period? centiseconds | +--ro yp:sync-on-start? boolean | +--ro yp:excluded-change* change-type +---n subscription-terminated | ... +---n subscription-suspended ... Figure 8: Model structure: Notifications The final figure in this section depicts the parts of module ietf- yang-push that are not simply augmentations to another module, but that are newly introduced. module: ietf-yang-push rpcs: +---x resync-subscription {on-change}? +---w input +---w id sn:subscription-id yang-data: (for placement into rpc error responses) +-- resync-subscription-error | +--ro reason? identityref | +--ro period-hint? centiseconds | +--ro filter-failure-hint? string | +--ro object-count-estimate? uint32 | +--ro object-count-limit? uint32 | +--ro kilobytes-estimate? uint32 | +--ro kilobytes-limit? uint32 +-- establish-subscription-error-datastore | +--ro reason? identityref | +--ro period-hint? centiseconds | +--ro filter-failure-hint? string | +--ro object-count-estimate? uint32 | +--ro object-count-limit? uint32 | +--ro kilobytes-estimate? uint32 | +--ro kilobytes-limit? uint32 +-- modify-subscription-error-datastore +--ro reason? identityref Clemm, et al. Expires August 8, 2019 [Page 23] Internet-Draft YANG-Push February 2019 +--ro period-hint? centiseconds +--ro filter-failure-hint? string +--ro object-count-estimate? uint32 +--ro object-count-limit? uint32 +--ro kilobytes-estimate? uint32 +--ro kilobytes-limit? uint32 notifications: +---n push-update | +--ro id? sn:subscription-id | +--ro datastore-contents? | +--ro incomplete-update? empty +---n push-change-update {on-change}? +--ro id? sn:subscription-id +--ro datastore-changes | +--ro yang-patch | +--ro patch-id string | +--ro comment? string | +--ro edit* [edit-id] | +--ro edit-id string | +--ro operation enumeration | +--ro target target-resource-offset | +--ro point? target-resource-offset | +--ro where? enumeration | +--ro value? +--ro incomplete-update? empty Figure 9: Model structure (non-augmentation portions Selected components of the model are summarized below. 4.2. Subscription Configuration Both configured and dynamic subscriptions are represented within the list "subscription". New parameters extending the basic subscription data model in [I-D.draft-ietf-netconf-subscribed-notifications] include: o The targeted datastore from which the selection is being made. The potential datastores include those from [RFC8341]. A platform may also choose to support a custom datastore. o A selection filter identifying yang nodes of interest within a datastore. Filter contents are specified via a reference to an existing filter, or via an in-line definition for only that subscription. Referenced filters allows an implementation to avoid evaluating filter acceptability during a dynamic Clemm, et al. Expires August 8, 2019 [Page 24] Internet-Draft YANG-Push February 2019 subscription request. The case statement differentiates the options. o For periodic subscriptions, triggered updates will occur at the boundaries of a specified time interval. These boundaries can be calculated from the periodic parameters: * a "period" which defines the duration between push updates. * an "anchor-time"; update intervals fall on the points in time that are a multiple of a "period" from an "anchor-time". If "anchor-time" is not provided, then the "anchor-time" MUST be set with the creation time of the initial update record. o For on-change subscriptions, assuming any dampening period has completed, triggering occurs whenever a change in the subscribed information is detected. On-change subscriptions have more complex semantics that is guided by its own set of parameters: * a "dampening-period" specifies the interval that must pass before a successive update for the subscription is sent. If no dampening period is in effect, the update is sent immediately. If a subsequent change is detected, another update is only sent once the dampening period has passed for this subscription. * an "excluded-change" parameter which allows restriction of the types of changes for which updates should be sent (e.g., only add to an update record on object creation). * a "sync-on-start" specifies whether a complete update with all the subscribed data is to be sent at the beginning of a subscription. 4.3. YANG Notifications 4.3.1. State Change Notifications Subscription state notifications and mechanism are reused from [I-D.draft-ietf-netconf-subscribed-notifications]. Notifications "subscription-started" and "subscription-modified" have been augmented to include the datastore specific objects. 4.3.2. Notifications for Subscribed Content Along with the subscribed content, there are other objects which might be part of a "push-update" or "push-change-update" notification. Clemm, et al. Expires August 8, 2019 [Page 25] Internet-Draft YANG-Push February 2019 An "id" (that identifies the subscription) MUST be transported along with the subscribed contents. This allows a receiver to differentiate which subscription resulted in a particular update record. A "time-of-update" which represents the time an update record snapshot was generated. A receiver MAY assume that at this point in time a publisher's objects have the values that were pushed. An "incomplete-update" leaf. This leaf indicates that not all changes which have occurred since the last update are actually included with this update. In other words, the publisher has failed to fulfill its full subscription obligations. (For example a datastore was unable to provide the full set of datastore nodes to a publisher process.) To facilitate re-synchronization of on-change subscriptions, a publisher MAY subsequently send a "push-update" containing a full selection snapshot of subscribed data. 4.4. YANG RPCs YANG-Push subscriptions are established, modified, and deleted using RPCs augmented from [I-D.draft-ietf-netconf-subscribed-notifications]. 4.4.1. Establish-subscription RPC The subscriber sends an establish-subscription RPC with the parameters in section 3.1. An example might look like: Clemm, et al. Expires August 8, 2019 [Page 26] Internet-Draft YANG-Push February 2019 ds:operational /ex:foo 500 Figure 10: Establish-subscription RPC A positive response includes the "id" of the accepted subscription. In that case a publisher may respond: 52 Figure 11: Establish-subscription positive RPC response A subscription can be rejected for multiple reasons, including the lack of authorization to establish a subscription, no capacity to serve the subscription at the publisher, or the inability of the publisher to select datastore content at the requested cadence. If a request is rejected because the publisher is not able to serve it, the publisher SHOULD include in the returned error hints which help a subscriber understand subscription parameters might have been accepted for the request. These hints would be included within the yang-data structure "establish-subscription-error-datastore". However even with these hints, there are no guarantee that subsequent requests will in fact be accepted. Clemm, et al. Expires August 8, 2019 [Page 27] Internet-Draft YANG-Push February 2019 The specific parameters to be returned as part of the RPC error response depend on the specific transport that is used to manage the subscription. For NETCONF, those parameters are defined in [I-D.draft-ietf-netconf-netconf-event-notifications]. For example, for the following NETCONF request: ds:operational /ex:foo 100 Figure 12: Establish-subscription request example 2 a publisher that cannot serve on-change updates but periodic updates might return the following NETCONF response: application operation-failed error /yp:periodic/yp:period yp:on-change-unsupported Figure 13: Establish-subscription error response example 2 Clemm, et al. Expires August 8, 2019 [Page 28] Internet-Draft YANG-Push February 2019 4.4.2. Modify-subscription RPC The subscriber MAY invoke the "modify-subscription" RPC for a subscription it previously established. The subscriber will include newly desired values in the "modify-subscription" RPC. Parameters not included MUST remain unmodified. Below is an example where a subscriber attempts to modify the period and datastore XPath filter of a subscription using NETCONF. 1011 ds:operational /ex:bar 250 Figure 14: Modify subscription request The publisher MUST respond to the subscription modification request. If the request is rejected, the existing subscription is left unchanged, and the publisher MUST send an RPC error response. This response might have hints encapsulated within the yang-data structure "modify-subscription-error-datastore". A subscription MAY be modified multiple times. The specific parameters to be returned in as part of the RPC error response depend on the specific transport that is used to manage the subscription. For NETCONF, those parameters are specified in [I-D.draft-ietf-netconf-netconf-event-notifications]. A configured subscription cannot be modified using "modify- subscription" RPC. Instead, the configuration needs to be edited as needed. Clemm, et al. Expires August 8, 2019 [Page 29] Internet-Draft YANG-Push February 2019 4.4.3. Delete-subscription RPC To stop receiving updates from a subscription and effectively delete a subscription that had previously been established using an "establish-subscription" RPC, a subscriber can send a "delete- subscription" RPC, which takes as only input the subscription's "id". This RPC is unmodified from [I-D.draft-ietf-netconf-subscribed-notifications]. 4.4.4. Resync-subscription RPC This RPC is supported only for on-change subscriptions previously established using an "establish-subscription" RPC. For example: 1011 Figure 15: Resync subscription On receipt, a publisher must either accept the request and quickly follow with a "push-update", or send an appropriate error within an rpc error response. Within an error response, the publisher MAY include supplemental information about the reasons within the yang- data structure "resync-subscription-error". 4.4.5. YANG Module Synchronization To make subscription requests, the subscriber needs to know the YANG datastore schemas used by the publisher, which are available via the YANG Library module, ietf-yang-library.yang from [RFC7895]. The receiver is expected to know the YANG library information before starting a subscription. The set of modules, revisions, features, and deviations can change at run-time (if supported by the publisher implementation). For this purpose, the YANG library provides a simple "yang-library-change" notification that informs the subscriber that the library has changed. In this case, a subscription may need to be updated to take the updates into account. The receiver may also need to be informed of module changes in order to process updates regarding datastore nodes from changed modules correctly. Clemm, et al. Expires August 8, 2019 [Page 30] Internet-Draft YANG-Push February 2019 5. YANG Module This YANG module imports typedefs from [RFC6991], identities from [RFC8342], the yang-data extension from [RFC8040], and the yang-patch grouping from [RFC8072]. In addition, it imports and augments many definitions from [I-D.draft-ietf-netconf-subscribed-notifications]. file "ietf-yang-push@2019-02-04.yang" module ietf-yang-push { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-yang-push"; prefix yp; import ietf-yang-types { prefix yang; reference "RFC 6991: Common YANG Data Types"; } import ietf-subscribed-notifications { prefix sn; reference "draft-ietf-netconf-subscribed-notifications: Customized Subscriptions to a Publisher's Event Streams NOTE TO RFC Editor: Please replace above reference to draft-ietf-netconf-subscribed-notifications with RFC number when published (i.e. RFC xxxx)."; } import ietf-datastores { prefix ds; reference "RFC 8342: Network Management Datastore Architecture (NMDA)"; } import ietf-restconf { prefix rc; reference "RFC 8040: RESTCONF Protocol"; } import ietf-yang-patch { prefix ypatch; reference "RFC 8072: YANG Patch Media Type"; } organization "IETF NETCONF Working Group"; contact "WG Web: Clemm, et al. Expires August 8, 2019 [Page 31] Internet-Draft YANG-Push February 2019 WG List: Editor: Alexander Clemm Editor: Eric Voit Editor: Alberto Gonzalez Prieto Editor: Ambika Prasad Tripathy Editor: Einar Nilsen-Nygaard Editor: Andy Bierman Editor: Balazs Lengyel "; description "This module contains YANG specifications for YANG push. 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 (RFC 2119) (RFC 8174) when, and only when, they appear in all capitals, as shown here. Copyright (c) 2019 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Simplified BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX; see the RFC itself for full legal notices."; // RFC Ed.: replace XXXX with actual RFC number and remove this // note. revision 2019-02-04 { description "Initial revision. NOTE TO RFC EDITOR: (1)Please replace the above revision date to the date of RFC publication when published. (2) Please replace the date in the file name Clemm, et al. Expires August 8, 2019 [Page 32] Internet-Draft YANG-Push February 2019 (ietf-yang-push@2019-02-04.yang) to the date of RFC publication. (3) Please replace the following reference to draft-ietf-netconf-yang-push-22 with RFC number when published (i.e. RFC xxxx)."; reference "draft-ietf-netconf-yang-push-22"; } /* * FEATURES */ feature on-change { description "This feature indicates that on-change triggered subscriptions are supported."; } /* * IDENTITIES */ /* Error type identities for datastore subscription */ identity resync-subscription-error { description "Problem found while attempting to fulfill an 'resync-subscription' RPC request."; } identity cant-exclude { base sn:establish-subscription-error; description "Unable to remove the set of 'excluded-changes'. This means the publisher is unable to restrict 'push-change-update's to just the change types requested for this subscription."; } identity datastore-not-subscribable { base sn:establish-subscription-error; base sn:subscription-terminated-reason; description "This is not a subscribable datastore."; } identity no-such-subscription-resync { base resync-subscription-error; Clemm, et al. Expires August 8, 2019 [Page 33] Internet-Draft YANG-Push February 2019 description "Referenced subscription doesn't exist. This may be as a result of a non-existent subscription ID, an ID which belongs to another subscriber, or an ID for configured subscription."; } identity on-change-unsupported { base sn:establish-subscription-error; description "On-change is not supported for any objects which are selectable by this filter."; } identity on-change-sync-unsupported { base sn:establish-subscription-error; description "Neither sync on start nor resynchronization are supported for this subscription. This error will be used for two reasons. First if an 'establish-subscription' RPC includes 'sync-on-start', yet the publisher can't support sending a 'push-update' for this subscription for reasons other than 'on-change-unsupported' or 'sync-too-big'. And second, if the 'resync-subscription' RPC is invoked either for an existing periodic subscription, or for an on-change subscription which can't support resynchronization."; } identity period-unsupported { base sn:establish-subscription-error; base sn:modify-subscription-error; base sn:subscription-suspended-reason; description "Requested time period or dampening-period is too short. This can be for both periodic and on-change subscriptions (with or without dampening.) Hints suggesting alternative periods may be returned as supplemental information."; } identity update-too-big { base sn:establish-subscription-error; base sn:modify-subscription-error; base sn:subscription-suspended-reason; description "Periodic or on-change push update datatrees exceed a maximum size limit. Hints on estimated size of what was too big may be returned as supplemental information."; } Clemm, et al. Expires August 8, 2019 [Page 34] Internet-Draft YANG-Push February 2019 identity sync-too-big { base sn:establish-subscription-error; base sn:modify-subscription-error; base resync-subscription-error; base sn:subscription-suspended-reason; description "Sync-on-start or resynchronization datatree exceeds a maximum size limit. Hints on estimated size of what was too big may be returned as supplemental information."; } identity unchanging-selection { base sn:establish-subscription-error; base sn:modify-subscription-error; base sn:subscription-terminated-reason; description "Selection filter is unlikely to ever select datatree nodes. This means that based on the subscriber's current access rights, the publisher recognizes that the selection filter is unlikely to ever select datatree nodes which change. Examples for this might be that node or subtree doesn't exist, read access is not permitted for a receiver, or static objects that only change at reboot have been chosen."; } /* * TYPE DEFINITIONS */ typedef change-type { type enumeration { enum create { description "A change that refers to the creation of a new datastore node."; } enum delete { description "A change that refers to the deletion of a datastore node."; } enum insert { description "A change that refers to the insertion of a new user-ordered datastore node."; } enum move { description Clemm, et al. Expires August 8, 2019 [Page 35] Internet-Draft YANG-Push February 2019 "A change that refers to a reordering of the target datastore node."; } enum replace { description "A change that refers to a replacement of the target datastore node's value."; } } description "Specifies different types of datastore changes. This type is based on the edit operations defined for YANG Patch, with the difference that it is valid for a receiver to process an update record which performs a create operation on a datastore node the receiver believes exists, or to process a delete on a datastore node the receiver believes is missing."; reference "RFC 8072: YANG Patch Media Type, section 2.5"; } typedef selection-filter-ref { type leafref { path "/sn:filters/yp:selection-filter/yp:filter-id"; } description "This type is used to reference a selection filter."; } typedef centiseconds { type uint32; description "A period of time, measured in units of 0.01 seconds."; } /* * GROUP DEFINITIONS */ grouping datastore-criteria { description "A grouping to define criteria for which selected objects from a targeted datastore should be included in push updates."; leaf datastore { type identityref { base ds:datastore; Clemm, et al. Expires August 8, 2019 [Page 36] Internet-Draft YANG-Push February 2019 } mandatory true; description "Datastore from which to retrieve data."; } uses selection-filter-objects; } grouping selection-filter-types { description "This grouping defines the types of selectors for objects from a datastore."; choice filter-spec { description "The content filter specification for this request."; anydata datastore-subtree-filter { if-feature "sn:subtree"; description "This parameter identifies the portions of the target datastore to retrieve."; reference "RFC 6241: Network Configuration Protocol, Section 6."; } leaf datastore-xpath-filter { if-feature "sn:xpath"; type yang:xpath1.0; description "This parameter contains an XPath expression identifying the portions of the target datastore to retrieve. If the expression returns a node-set, all nodes in the node-set are selected by the filter. Otherwise, if the expression does not return a node-set, the filter doesn't select any nodes. The expression is evaluated in the following XPath context: o The set of namespace declarations is the set of prefix and namespace pairs for all YANG modules implemented by the server, where the prefix is the YANG module name and the namespace is as defined by the 'namespace' statement in the YANG module. If the leaf is encoded in XML, all namespace declarations in scope on the 'stream-xpath-filter' leaf element are added to the set of namespace declarations. If a prefix found in the XML is Clemm, et al. Expires August 8, 2019 [Page 37] Internet-Draft YANG-Push February 2019 already present in the set of namespace declarations, the namespace in the XML is used. o The set of variable bindings is empty. o The function library is the core function library, and the XPath functions defined in section 10 in RFC 7950. o The context node is the root node of the target datastore."; } } } grouping selection-filter-objects { description "This grouping defines a selector for objects from a datastore."; choice selection-filter { description "The source of the selection filter applied to the subscription. This will come either referenced from a global list, or be provided within the subscription itself."; case by-reference { description "Incorporate a filter that has been configured separately."; leaf selection-filter-ref { type selection-filter-ref; mandatory true; description "References an existing selection filter which is to be applied to the subscription."; } } case within-subscription { description "Local definition allows a filter to have the same lifecycle as the subscription."; uses selection-filter-types; } } } grouping update-policy-modifiable { description "This grouping describes the datastore specific subscription conditions that can be changed during the lifetime of the Clemm, et al. Expires August 8, 2019 [Page 38] Internet-Draft YANG-Push February 2019 subscription."; choice update-trigger { description "Defines necessary conditions for sending an event record to the subscriber."; case periodic { container periodic { presence "indicates a periodic subscription"; description "The publisher is requested to notify periodically the current values of the datastore as defined by the selection filter."; leaf period { type centiseconds; mandatory true; description "Duration of time which should occur between periodic push updates, in one hundredths of a second."; } leaf anchor-time { type yang:date-and-time; description "Designates a timestamp before or after which a series of periodic push updates are determined. The next update will take place at a whole multiple interval from the anchor time. For example, for an anchor time is set for the top of a particular minute and a period interval of a minute, updates will be sent at the top of every minute this subscription is active."; } } } case on-change { if-feature "on-change"; container on-change { presence "indicates an on-change subscription"; description "The publisher is requested to notify changes in values in the datastore subset as defined by a selection filter."; leaf dampening-period { type centiseconds; default "0"; description "Specifies the minimum interval between the assembly of successive update records for a single receiver of a subscription. Whenever subscribed objects change, and a dampening period interval (which may be zero) has Clemm, et al. Expires August 8, 2019 [Page 39] Internet-Draft YANG-Push February 2019 elapsed since the previous update record creation for a receiver, then any subscribed objects and properties which have changed since the previous update record will have their current values marshalled and placed into a new update record."; } } } } } grouping update-policy { description "This grouping describes the datastore-specific subscription conditions of a subscription."; uses update-policy-modifiable { augment "update-trigger/on-change/on-change" { description "Includes objects not modifiable once subscription is established."; leaf sync-on-start { type boolean; default "true"; description "When this object is set to false, it restricts an on-change subscription from sending push-update notifications. When false, pushing a full selection per the terms of the selection filter MUST NOT be done for this subscription. Only updates about changes, i.e. only push-change-update notifications are sent. When true (default behavior), in order to facilitate a receiver's synchronization, a full update is sent when the subscription starts using a push-update notification. After that, push-change-update notifications are exclusively sent unless the publisher chooses to resync the subscription via a new push-update notification."; } leaf-list excluded-change { type change-type; description "Use to restrict which changes trigger an update. For example, if modify is excluded, only creation and deletion of objects is reported."; } } } } Clemm, et al. Expires August 8, 2019 [Page 40] Internet-Draft YANG-Push February 2019 grouping hints { description "Parameters associated with some error for a subscription made upon a datastore."; leaf period-hint { type centiseconds; description "Returned when the requested time period is too short. This hint can assert a viable period for either a periodic push cadence or an on-change dampening interval."; } leaf filter-failure-hint { type string; description "Information describing where and/or why a provided filter was unsupportable for a subscription."; } leaf object-count-estimate { type uint32; description "If there are too many objects which could potentially be returned by the selection filter, this identifies the estimate of the number of objects which the filter would potentially pass."; } leaf object-count-limit { type uint32; description "If there are too many objects which could be returned by the selection filter, this identifies the upper limit of the publisher's ability to service for this subscription."; } leaf kilobytes-estimate { type uint32; description "If the returned information could be beyond the capacity of the publisher, this would identify the data size which could result from this selection filter."; } leaf kilobytes-limit { type uint32; description "If the returned information would be beyond the capacity of the publisher, this identifies the upper limit of the publisher's ability to service for this subscription."; } } Clemm, et al. Expires August 8, 2019 [Page 41] Internet-Draft YANG-Push February 2019 /* * RPCs */ rpc resync-subscription { if-feature "on-change"; description "This RPC allows a subscriber of an active on-change subscription to request a full push of objects. A successful invocation results in a push-update of all datastore nodes that the subscriber is permitted to access. This RPC can only be invoked on the same session on which the subscription is currently active. In case of an error, a resync-subscription-error is sent as part of an error response."; input { leaf id { type sn:subscription-id; mandatory true; description "Identifier of the subscription that is to be resynced."; } } } rc:yang-data resync-subscription-error { container resync-subscription-error { description "If a 'resync-subscription' RPC fails, the subscription is not resynced and the RPC error response MUST indicate the reason for this failure. This yang-data MAY be inserted as structured data within a subscription's RPC error response to indicate the failure reason."; leaf reason { type identityref { base resync-subscription-error; } mandatory true; description "Indicates the reason why the publisher has declined a request for subscription resynchronization."; } uses hints; } } augment "/sn:establish-subscription/sn:input" { Clemm, et al. Expires August 8, 2019 [Page 42] Internet-Draft YANG-Push February 2019 description "This augmentation adds additional subscription parameters that apply specifically to datastore updates to RPC input."; uses update-policy; } augment "/sn:establish-subscription/sn:input/sn:target" { description "This augmentation adds the datastore as a valid target for the subscription to RPC input."; case datastore { description "Information specifying the parameters of an request for a datastore subscription."; uses datastore-criteria; } } rc:yang-data establish-subscription-datastore-error-info { container establish-subscription-datastore-error-info { description "If any 'establish-subscription' RPC parameters are unsupportable against the datastore, a subscription is not created and the RPC error response MUST indicate the reason why the subscription failed to be created. This yang-data MAY be inserted as structured data within a subscription's RPC error response to indicate the failure reason. This yang-data MUST be inserted if hints are to be provided back to the subscriber."; leaf reason { type identityref { base sn:establish-subscription-error; } description "Indicates the reason why the subscription has failed to be created to a targeted datastore."; } uses hints; } } augment "/sn:modify-subscription/sn:input" { description "This augmentation adds additional subscription parameters specific to datastore updates."; uses update-policy-modifiable; } Clemm, et al. Expires August 8, 2019 [Page 43] Internet-Draft YANG-Push February 2019 augment "/sn:modify-subscription/sn:input/sn:target" { description "This augmentation adds the datastore as a valid target for the subscription to RPC input."; case datastore { description "Information specifying the parameters of an request for a datastore subscription."; uses datastore-criteria; } } rc:yang-data modify-subscription-datastore-error-info { container modify-subscription-datastore-error-info { description "This yang-data MAY be provided as part of a subscription's RPC error response when there is a failure of a 'modify-subscription' RPC which has been made against a datastore. This yang-data MUST be used if hints are to be provides back to the subscriber."; leaf reason { type identityref { base sn:modify-subscription-error; } description "Indicates the reason why the subscription has failed to be modified."; } uses hints; } } /* * NOTIFICATIONS */ notification push-update { description "This notification contains a push update, containing data subscribed to via a subscription. This notification is sent for periodic updates, for a periodic subscription. It can also be used for synchronization updates of an on-change subscription. This notification shall only be sent to receivers of a subscription. It does not constitute a general-purpose notification that would be subscribable as part of the NETCONF event stream by any receiver."; leaf id { type sn:subscription-id; Clemm, et al. Expires August 8, 2019 [Page 44] Internet-Draft YANG-Push February 2019 description "This references the subscription which drove the notification to be sent."; } anydata datastore-contents { description "This contains the updated data. It constitutes a snapshot at the time-of-update of the set of data that has been subscribed to. The snapshot corresponds to the same snapshot that would be returned in a corresponding get operation with the same selection filter parameters applied."; } leaf incomplete-update { type empty; description "This is a flag which indicates that not all datastore nodes subscribed to are included with this update. In other words, the publisher has failed to fulfill its full subscription obligations, and despite its best efforts is providing an incomplete set of objects."; } } notification push-change-update { if-feature "on-change"; description "This notification contains an on-change push update. This notification shall only be sent to the receivers of a subscription; it does not constitute a general-purpose notification."; leaf id { type sn:subscription-id; description "This references the subscription which drove the notification to be sent."; } container datastore-changes { description "This contains the set of datastore changes of the target datastore starting at the time of the previous update, per the terms of the subscription."; uses ypatch:yang-patch; } leaf incomplete-update { type empty; description "The presence of this object indicates not all changes which Clemm, et al. Expires August 8, 2019 [Page 45] Internet-Draft YANG-Push February 2019 have occurred since the last update are included with this update. In other words, the publisher has failed to fulfill its full subscription obligations, for example in cases where it was not able to keep up with a change burst."; } } augment "/sn:subscription-started" { description "This augmentation adds datastore-specific objects to the notification that a subscription has started."; uses update-policy; } augment "/sn:subscription-started/sn:target" { description "This augmentation allows the datastore to be included as part of the notification that a subscription has started."; case datastore { uses datastore-criteria { refine "selection-filter/within-subscription" { description "Specifies the selection filter and where it originated from. If the 'selection-filter-ref' is populated, the filter within the subscription came from the 'filters' container. Otherwise it is populated in-line as part of the subscription itself."; } } } } augment "/sn:subscription-modified" { description "This augmentation adds datastore-specific objects to the notification that a subscription has been modified."; uses update-policy; } augment "/sn:subscription-modified/sn:target" { description "This augmentation allows the datastore to be included as part of the notification that a subscription has been modified."; case datastore { uses datastore-criteria { refine "selection-filter/within-subscription" { Clemm, et al. Expires August 8, 2019 [Page 46] Internet-Draft YANG-Push February 2019 description "Specifies where the selection filter, and where it came from within the subscription and then populated within this notification. If the 'selection-filter-ref' is populated, the filter within the subscription came from the 'filters' container. Otherwise it is populated in-line as part of the subscription itself."; } } } } /* * DATA NODES */ augment "/sn:filters" { description "This augmentation allows the datastore to be included as part of the selection filtering criteria for a subscription."; list selection-filter { key "filter-id"; description "A list of pre-configured filters that can be applied to datastore subscriptions."; leaf filter-id { type string; description "An identifier to differentiate between selection filters."; } uses selection-filter-types; } } augment "/sn:subscriptions/sn:subscription" { when 'yp:datastore'; description "This augmentation adds many datastore specific objects to a subscription."; uses update-policy; } augment "/sn:subscriptions/sn:subscription/sn:target" { description "This augmentation allows the datastore to be included as part of the selection filtering criteria for a subscription."; case datastore { Clemm, et al. Expires August 8, 2019 [Page 47] Internet-Draft YANG-Push February 2019 uses datastore-criteria; } } } 6. IANA Considerations This document registers the following namespace URI in the "IETF XML Registry" [RFC3688]: URI: urn:ietf:params:xml:ns:yang:ietf-yang-push Registrant Contact: The IESG. XML: N/A; the requested URI is an XML namespace. This document registers the following YANG module in the "YANG Module Names" registry [RFC6020]: Name: ietf-yang-push Namespace: urn:ietf:params:xml:ns:yang:ietf-yang-push Prefix: yp Reference: draft-ietf-netconf-yang-push-21.txt (RFC form) 7. Security Considerations The YANG module specified in this document defines a schema for data that is designed to be accessed via network management protocols such as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS [RFC8446]. The Network Configuration Access Control Model (NACM) [RFC8341] provides the means to restrict access for particular NETCONF or RESTCONF users to a preconfigured subset of all available NETCONF or RESTCONF protocol operations and content. There are a number of data nodes defined in this YANG module that are writable/creatable/deletable (i.e., config true, which is the default). These data nodes may be considered sensitive or vulnerable in some network environments. Write operations (e.g., edit-config) to these data nodes without proper protection can have a negative effect on network operations. These are the subtrees and data nodes and their sensitivity/vulnerability. (It should be noted that the YANG module augments the YANG module from Clemm, et al. Expires August 8, 2019 [Page 48] Internet-Draft YANG-Push February 2019 [I-D.draft-ietf-netconf-subscribed-notifications]. All security considerations that are listed there are relevant also for datastore subscriptions. In the following, we focus on the data nodes that are newly introduced here.) o Subtree "selection-filter" under container "filters": This subtree allows to specify which objects or subtrees to include in a datastore subscription. An attacker could attempt to modify the filter. For example, the filter might be modified to result in very few objects being filtered in order to attempt to overwhelm the receiver. Alternatively, the filter might be modified to result in certain objects to be excluded from updates, in order to have certain changes go unnoticed. o Subtree "datastore" in choice "target" in list "subscription": Analogous to "selection filter", an attacker might attempt to modify the objects being filtered in order to overwhelm a receiver with a larger volume of object updates than expected, or to have certain changes go unnoticed. o Choice "update-trigger" in list "subscription": By modifying the update trigger, an attacker might alter the updates that are being sent in order to confuse a receiver, to withhold certain updates to be sent to the receiver, and/or to overwhelm a receiver. For example, an attacker might modify the period with which updates are reported for a periodic subscription, or it might modify the dampening period for an on-change subscription, resulting in greater delay of successive updates (potentially affecting responsiveness of applications that depend on the updates) or in a high volume of updates (to exhaust receiver resources). o RPC "resync-subscription": This RPC allows a subscriber of an on- change subscription to request a full push of objects in the subscription's scope. This can result in a large volume of data. An attacker could attempt to use this RPC to exhaust resources on the server to generate the data, and attempt to overwhelm a receiver with the resulting data volume. 8. Acknowledgments For their valuable comments, discussions, and feedback, we wish to acknowledge Tim Jenkins, Martin Bjorklund, Kent Watsen, Susan Hares, Yang Geng, Peipei Guo, Michael Scharf, Guangying Zheng, Tom Petch, Henk Birkholz, Reshad Rahman, Qin Wu, Rohit Ranade, and Rob Wilton. Clemm, et al. Expires August 8, 2019 [Page 49] Internet-Draft YANG-Push February 2019 9. References 9.1. Normative References [I-D.draft-ietf-netconf-subscribed-notifications] Voit, E., Clemm, A., Gonzalez Prieto, A., Tripathy, A., and E. Nilsen-Nygaard, "Subscription to YANG Event NOtifications", draft-ietf-netconf-subscribed- notifications-22 (work in progress), January 2019. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, . [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, . [RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, July 2013, . [RFC7895] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Module Library", RFC 7895, DOI 10.17487/RFC7895, June 2016, . [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, . [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, . [RFC8072] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Patch Media Type", RFC 8072, DOI 10.17487/RFC8072, February 2017, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Clemm, et al. Expires August 8, 2019 [Page 50] Internet-Draft YANG-Push February 2019 [RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, March 2018, . [RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K., and R. Wilton, "Network Management Datastore Architecture (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018, . 9.2. Informative References [I-D.draft-ietf-netconf-netconf-event-notifications] Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard, E., and A. Tripathy, "Dynamic subscription to YANG Events and DAtastores over NETCONF", January 2019. [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, . [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011, . [RFC7923] Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements for Subscription to YANG Datastores", RFC 7923, DOI 10.17487/RFC7923, June 2016, . [RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, . [RFC8343] Bjorklund, M., "A YANG Data Model for Interface Management", RFC 8343, DOI 10.17487/RFC8343, March 2018, . [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . Appendix A. Appendix A: Subscription Errors Clemm, et al. Expires August 8, 2019 [Page 51] Internet-Draft YANG-Push February 2019 A.1. RPC Failures Rejection of an RPC for any reason is indicated by via RPC error response from the publisher. Valid RPC errors returned include both existing transport layer RPC error codes, such as those seen with NETCONF in [RFC6241], as well as subscription specific errors such as those defined within the YANG model. As a result, how subscription errors are encoded within an RPC error response is transport dependent. References to specific identities in the ietf-subscribed- notifications YANG model or the ietf-yang-push YANG model may be returned as part of the error responses resulting from failed attempts at datastore subscription. For errors defined as part of ietf-subscribed-notifications, please refer to [I-D.draft-ietf-netconf-subscribed-notifications]. The errors introduced in this document, grouped per RPC, are as follows: establish-subscription modify-subscription ---------------------- ------------------- cant-exclude period-unsupported datastore-not-subscribable update-too-big on-change-unsupported sync-too-big on-change-sync-unsupported unchanging-selection period-unsupported update-too-big resync-subscription sync-too-big -------------------- unchanging-selection no-such-subscription-resync sync-too-big There is one final set of transport independent RPC error elements included in the YANG model. These are the following four yang-data structures for failed datastore subscriptions: Clemm, et al. Expires August 8, 2019 [Page 52] Internet-Draft YANG-Push February 2019 1. yang-data establish-subscription-error-datastore This MUST be returned if information identifying the reason for an RPC error has not been placed elsewhere within the transport portion of a failed "establish-subscription" RPC response. This MUST be sent if hints are included. 2. yang-data modify-subscription-error-datastore This MUST be returned if information identifying the reason for an RPC error has not been placed elsewhere within the transport portion of a failed "modifiy-subscription" RPC response. This MUST be sent if hints are included. 3. yang-data sn:delete-subscription-error This MUST be returned if information identifying the reason for an RPC error has not been placed elsewhere within the transport portion of a failed "delete-subscription" or "kill-subscription" RPC response. 4. yang-data resync-subscription-error This MUST be returned if information identifying the reason for an RPC error has not been placed elsewhere within the transport portion of a failed "resync-subscription" RPC response. A.2. Notifications of Failure A subscription may be unexpectedly terminated or suspended independent of any RPC or configuration operation. In such cases, indications of such a failure MUST be provided. To accomplish this, a number of errors can be returned as part of the corresponding subscription state change notification. For this purpose, the following error identities have been introduced in this document, in addition to those that were already defined in [I-D.draft-ietf-netconf-subscribed-notifications]: subscription-terminated subscription-suspended ----------------------- ---------------------- datastore-not-subscribable period-unsupported unchanging-selection update-too-big synchronization-size Appendix B. Changes Between Revisions (To be removed by RFC editor prior to publication) v21 - v22 Clemm, et al. Expires August 8, 2019 [Page 53] Internet-Draft YANG-Push February 2019 o Minor updates per Martin Bjorklund's YANG doctor review. v20 - v21 o Minor updates, simplifying RPC input conditions. v19 - v20 o Minor updates per WGLC comments. v18 - v19 o Minor updates per WGLC comments. v17 - v18 o Minor updates per WGLC comments. v16 - v17 o Minor updates to YANG module, incorporating comments from Tom Petch. o Updated references. v15 - v16 o Updated security considerations. o Updated references. o Addressed comments from last call review, specifically comments received from Martin Bjorklund. v14 - v15 o Minor text fixes. Includes a fix to on-change update calculation to cover churn when an object changes to and from a value during a dampening period. v13 - v14 o Minor text fixes. v12 - v13 o Hint negotiation models now show error examples. Clemm, et al. Expires August 8, 2019 [Page 54] Internet-Draft YANG-Push February 2019 o yang-data structures for rpc errors. v11 - v12 o Included Martin's review clarifications. o QoS moved to subscribed-notifications o time-of-update removed as it is redundant with RFC5277's eventTime, and other times from notification-messages. o Error model moved to match existing implementations o On-change notifiable removed, how to do this is implementation specific. o NMDA model supported. Non NMDA version at https://github.com/ netconf-wg/yang-push/ v10 - v11 o Promise model reference added. o Error added for no-such-datastore o Inherited changes from subscribed notifications (such as optional feature definitions). o scrubbed the examples for proper encodings v09 - v10 o Returned to the explicit filter subtyping of v00-v05 o identityref to ds:datastore made explicit o Returned ability to modify a selection filter via RPC. v08 - v09 o Minor tweaks cleaning up text, removing appendicies, and making reference to revised-datastores. o Subscription-id (now:id) optional in push updates, except when encoded in RFC5277, Section 4 one-way notification. o Finished adding the text descibing the resync subscription RPC. Clemm, et al. Expires August 8, 2019 [Page 55] Internet-Draft YANG-Push February 2019 o Removed relationships to other drafts and future technology appendicies as this work is being explored elsewhere. o Deferred the multi-line card issue to new drafts o Simplified the NACM interactions. v07 - v08 o Updated YANG models with minor tweaks to accommodate changes of ietf-subscribed-notifications. v06 - v07 o Clarifying text tweaks. o Clarification that filters act as selectors for subscribed datastore nodes; support for value filters not included but possible as a future extension o Filters don't have to be matched to existing YANG objects v05 - v06 o Security considerations updated. o Base YANG model in [subscribe] updated as part of move to identities, YANG augmentations in this doc matched up o Terms refined and text updates throughout o Appendix talking about relationship to other drafts added. o Datastore replaces stream o Definitions of filters improved v04 to v05 o Referenced based subscription document changed to Subscribed Notifications from 5277bis. o Getting operational data from filters o Extension notifiable-on-change added o New appendix on potential futures. Moved text into there from several drafts. Clemm, et al. Expires August 8, 2019 [Page 56] Internet-Draft YANG-Push February 2019 o Subscription configuration section now just includes changed parameters from Subscribed Notifications o Subscription monitoring moved into Subscribed Notifications o New error and hint mechanisms included in text and in the yang model. o Updated examples based on the error definitions o Groupings updated for consistency o Text updates throughout v03 to v04 o Updates-not-sent flag added o Not notifiable extension added o Dampening period is for whole subscription, not single objects o Moved start/stop into rfc5277bis o Client and Server changed to subscriber, publisher, and receiver o Anchor time for periodic o Message format for synchronization (i.e. sync-on-start) o Material moved into 5277bis o QoS parameters supported, by not allowed to be modified by RPC o Text updates throughout Authors' Addresses Alexander Clemm Huawei USA Email: ludwig@clemm.org Eric Voit Cisco Systems Email: evoit@cisco.com Clemm, et al. Expires August 8, 2019 [Page 57] Internet-Draft YANG-Push February 2019 Alberto Gonzalez Prieto Microsoft Email: albgonz@microsoft.com Ambika Prasad Tripathy Cisco Systems Email: ambtripa@cisco.com Einar Nilsen-Nygaard Cisco Systems Email: einarnn@cisco.com Andy Bierman YumaWorks Email: andy@yumaworks.com Balazs Lengyel Ericsson Email: balazs.lengyel@ericsson.com Clemm, et al. Expires August 8, 2019 [Page 58]