YANG Datastore SubscriptionHuaweiludwig@clemm.orgCisco Systemsevoit@cisco.comVMwareagonzalezpri@vmware.comCisco Systemsambtripa@cisco.comCisco Systemseinarnn@cisco.comYumaWorksandy@yumaworks.comEricssonbalazs.lengyel@ericsson.com
Operations & Management
NETCONFDraftVia the mechanism described in this document, subscriber applications may request a continuous, customized stream of updates from a YANG datastore. Providing such visibility into changes made upon YANG configuration and operational objects enables new capabilities based on the remote mirroring of configuration and operational state.Traditional approaches to remote visibility 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:
Polling incurs significant latency. This latency prohibits many application types.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.Polling requests may undergo slight fluctuations, resulting in intervals of different lengths. The resulting data is difficult to calibrate and compare.For applications that monitor for changes, many remote polling cycles place ultimately fruitless load on the network, devices, and applications.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 publisher to push and in effect stream those updates. The requirements for such a service have been documented in . This document defines a corresponding solution that is built on top of "Custom Subscription to Event Streams" . Supplementing that work are YANG data model augmentations, extended RPCs, and new datastore specific update notifications. Transport options for will work seamlessly with this solution. The terms below supplement those defined in . In addition, the term "datastore" is defined in .Datastore node: An instance of management information in a datastore. Also known as "object".Datastore node update: A data item containing the current value/property of a datastore node at the time the datastore node update was created.Datastore subtree: An instantiated datastore node and the datastore nodes that are hierarchically contained within it.Update record: A representation datastore node update(s) resulting from the application of a selection filter for a subscription. An update record will include the value/property of one or more datastore nodes at a point in time. It may contain the update type for each datastore node (e.g., add, change, delete). Also included may be metadata/headers such as a subscription identifier.Selection filter: Evaluation and/or selection criteria, which may be applied against a targeted set of objects.Update trigger: A mechanism that determines when an update record needs to be generated. YANG-Push: The subscription and push mechanism for datastore updates that is specified in this document.This document specifies a solution for a push update subscription service.
This solution supports dynamic as well as configured subscriptions to information updates from datastores.
Subscriptions specify when notification messages should be sent and what data to include in update records.
YANG objects are subsequently pushed from the publisher to the receiver per the terms of the subscription.YANG-push subscriptions are defined using a data model that is itself defined in YANG.
This model enhances the subscription model defined in
with capabilities that allow subscribers to subscribe to datastore node updates,
specifically to specify the triggers defining when to generate update records as well as what to include in an update record.
Key enhancements include:Specification of selection filters which identify targeted YANG datastore nodes and/or subtrees within a datastore for which updates are to be pushed.An encoding (using anydata) for the contents of periodic and on-change push updates.Specification of update policies contain conditions which trigger the generation and pushing of new update records. There are two types of triggers for subscriptions: periodic and on-change.
For periodic subscriptions, the 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 which can be used to calculate at which point in time updates need to be assembled and sent.For on-change subscriptions, a trigger occurs whenever a change in the subscribed information is detected. Included are additional parameters such as:
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 of resources in the publisher or receiver. In order to protect against that, a dampening period MAY be used to specify the interval which must 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 and sent to a single receiver. This means that when there is a change to one or more subscribed objects, an update record containing those objects is created either immediately when no dampening period is in effect, or at the end of a dampening period. If multiple changes to a single object occur during a dampening period, only the value that is in effect at the time 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 when an object is created or deleted, but not when an object value changes).No Synch 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.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 at different parameters by a subscriber is to be discouraged. Therefore, in order to minimize the number of subscription iterations between subscriber and publisher,
dynamic subscription supports a simple negotiation between subscribers and publishers for subscription parameters. This negotiation is in the form of supplemental information which may be inserted within error responses to a failed rpc request. This returned error 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.
On-change subscriptions allow subscribers 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, whether or not their values actually 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 .
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 subscription MAY be suspended.
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 current values of all changed objects which are current at the time the dampening period expires. Changed objects include those which were deleted or newly created during that dampening period. If an object has returned to its original value (or even has been created and then deleted) during the dampening-period, the last 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 push-change-update notification:
Just before a change, or at the start of a dampening period, evaluate any filtering and any access control rules. The result is a set "A" of datastore nodes and subtrees.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.Construct a YANG patch record for going from A to B. If the record is non-empty, send it to the receiver.Note: In cases where a subscriber wants to have separate dampening periods for different objects, multiple subscriptions with different objects in a selection filter can be created.
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 they will indeed receive the subscribed updates without having to worry 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 data objects 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. If for some reason the publisher of a subscription is not able to keep its promise, receivers MUST be notified immediately and reliably. The publisher MAY also suspend the subscription.
A publisher SHOULD reject a request for a subscription if it is unlikely that the publisher will be able 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.
In a periodic subscription, the data included as part of an update corresponds to data that could have been read using a retrieval operation.In an on-change subscription, updates 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 . 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 , objects encapsulated are not restricted to configuration objects only. However a patch must be able to do more than just describe the delta from the previous state to the current state. As per , it must also be able to identify if 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 a 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 does a "create" operation for a datastore node where the receiver believes one already exists, or a "merge" operation which replaces a previous value with the same value. Note that this means that the "create" and "delete" errors described in section 2.5 are not errors, and are valid operations with YANG push.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 MUST remove any existing filter. The following selection filter types are included in the yang-push data model, and may be applied against a datastore: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 section 6.xpath: An xpath selection filter is an XPath expression that returns a node set. When specified, updates will only come from the selected data 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.Xpath itself provides powerful filtering constructs and care must be used in filter definition. As an example, consider an xpath filter with a boolean result; such a result will not provide an easily interpretable subset of a datastore. Beyond the boolean example, it is quite possible to define an xpath filter where results are easy for an application to mis-interpret. Consider an xpath filter which only passes a datastore object 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 periodic subscription, all selected datastore nodes to which a receiver has access are provided to a 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".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 will 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 resynch an on-change subscription. The "push-update" update record contains a data snippet that 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 e.g., a NETCONF "get" operation, 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 a data snippet that indicates 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 and the object has not been deleted, the object's most current value is reported. (In other words, for each object, only one change is reported, not its entire history. Doing so would defeat the purpose of the dampening period.)These new "push-update" or "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 port (per ). This notification message is encoded XML over NETCONF as per .The following is an example of an on-change notification message for the same subscription.Of note in the above example is the 'patch-id' with a value of '1'. Per , the 'patch-id' is an arbitrary string. With YANG Push, the publisher SHOULD put into the 'patch-id' a counter starting at '1' which increments with every 'push-change-update' generated for a subscription. If used as a counter, this counter MUST be reset to '1' 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 '1' the after passing a maximum value of '99999'. Such a mechanism allows easy identification of lost or out-of-sequence update records.The RPCs defined within have been enhanced to support datastore subscription negotiation. Included in these enhancements are error codes which can indicate why a datastore subscription attempt has failed.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.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. In the case of NETCONF
, the NETCONF RPC reply
MUST include an "rpc-error" element with the following additional elements:
"error-type" of "application". "error-tag" of "operation-failed". Optionally, an "error-severity" of "error" (this MAY but does not have to be included). "error-app-tag" with the value being a string that corresponds
to an identity with a base of "establish-subscription-error" (for error responses to an establish-subscription request), "modify-subscription-error" (for error responses to a modify-subscription request), "delete-subscription-error" (for error responses to a delete-subscription request), "resynch-subscription-error" (for error responses to resynch-subscription request), or "kill-subscription-error" (for error responses to a kill-subscription request), respectively. In case of error responses to an establish-subscription or modify-subscription request:
optionally, "error-info" containing XML-encoded data with hints regarding parameter settings
that might lead to successful requests in the future,
per yang-data definitions "establish-subscription-error-datastore" (for error responses to an establish-subscription request) or "modify-subscription-error-datastore (for error responses to a modify-subscription request), respectively. In case of an rpc error as a result of a delete-subscription, or a kill-subscription, or a resynch-subscription request, no error-info needs to be included, as the subscription-id is the only RPC input parameter and no hints regarding RPC input parameters need to be provided.
For instance, for the following request:the publisher might return:A receiver of subscription data MUST only be sent updates for which they have 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.A publisher MUST allow for the possibility that a subscription's selection filter references non-existent or access-protected data. Such support permits a receiver the ability to monitor the entire lifecyle of some datastore tree. In this case, all "push-update" notifications must be sent empty, and no "push-change-update" notifications will be sent until some data becomes visible for a receiver.A publisher MAY choose reject an establish-subscription request which selects non-existent or access-protected data. 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. Such a capability enables the publisher to avoid having to support a continuous, and total filtering of an entire subscription's content.In these cases above, the error identity "unchanging-selection" SHOULD be returned. This reduces the possibility of leakage of access controlled objects.Each "push-update" and "push-change-update" MUST have access control applied. This includes validating that read access is permitted for any new objects selected since the last notification message was sent to a particular each receiver. To accomplish this, implementations SHOULD support the conceptual authorization model of , Section 3.2.4.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.In some cases, a publisher supporting on-change notifications may not be able to push updates for some object types on-change. Reasons for this might be that the value of the datastore node changes frequently (e.g., '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.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 will be expected to provide their own solution.Particularly in the case of on-change updates, it is important that these updates do not get lost. Or in case the loss of an update is unavoidable, it is critical that the receiver is notified accordingly.Update records for a single subscription MAY 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 take one or more of the following actions.
A publisher MUST set the "updates-not-sent" flag on any update record which is known to be missing information.It MAY choose to suspend a subscription as per .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 "no-synch-on-start" option is not present 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 "updates-not-sent" 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 to merge pending update messages. I.e., the dampening period applies to update record creation, not transmission.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 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.The YANG data model for datastore push subscriptions is depicted in the following figure. Following YANG tree convention in the depiction, brackets enclose list keys, "rw" means configuration, "ro" operational state data, "?" designates optional nodes, "*" designates nodes that can have multiple instances. Parentheses with a name in the middle enclose choice and case nodes. New schema objects defined here (i.e., beyond those from ) are identified with "yp". Selected components of the model are summarized below.Both configured and dynamic subscriptions are represented within the list subscription. But only configured subscriptions are listed within list subscription-config. In both lists, each subscription has own list elements. New and enhanced parameters extending the basic subscription data model in include:
The targeted datastore from which the selection is being made. The potential datastores include those from . A platform may also choose to support a custom datastore.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 subscription request. The case statement differentiates the options.For periodic subscriptions, triggered updates will occur at the boundaries of a specified time interval. These boundaries many be calculated from the periodic parameters:
a "period" which defines duration between period push updates. an "anchor-time"; update intervals always 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.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" flag 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 "no-synch-on-start" flag which specifies whether a complete update with all the subscribed data is to be sent at the beginning of a subscription.Subscription state notifications and mechanism are reused from . Some have been augmented to include the datastore specific objects.Along with the subscribed content, there are other objects which might be part of a "push-update" or "push-change-update"A "subscription-id" MUST be transported along with the subscribed contents. An Section 4 one-way notification MAY be used for encoding updates. Where it is, the relevant "subscription-id" MUST be encoded as the first element within each "push-update" or "push-change-update". This allows a receiver to differentiate which subscription resulted in a particular push. A "time-of-update" which represents the time an update record snapshot was generated. A receiver MAY assume that a publisher's objects have these pushed values at this point in time.An "updates-not-sent" object. This object 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 providing 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.YANG-Push subscriptions are established, modified, and deleted using RPCs augmented from .The subscriber sends an establish-subscription RPC with the parameters in section 3.1. An example might look like:The publisher MUST respond explicitly positively (i.e., subscription accepted) or negatively (i.e., subscription rejected) to the request. Positive responses include the "identifier" of the accepted subscription. In that case a publisher MAY respond: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.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. In the case of NETCONF
, when a subscription
request is rejected, the NETCONF RPC reply
MUST include an "rpc-error" element with the following elements:
"error-type" of "application". "error-tag" of "operation-failed". Optionally, an "error-severity" of "error" (this MAY but does not have to be included). "error-app-tag" with the value being a string that corresponds
to an identity with a base of "establish-subscription-error". Optionally, "error-info" containing XML-encoded data with hints for parameter settings
that might result in future RPC success per yang-data definition "establish-subscription-error-datastore".
For example, for the following request:a publisher that cannot serve on-change updates but periodic updates might return the following: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" of a subscription.The publisher MUST respond explicitly positively or negatively to the request. If the subscription modification is rejected, the subscription is maintained as it was before the modification request. In addition, the publisher MUST send an rpc error response. This rpc error response may contain 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. In the case of NETCONF
, when a subscription
request is rejected, the NETCONF RPC reply
MUST include an "rpc-error" element with the following elements:
"error-type" of "application". "error-tag" of "operation-failed". Optionally, an "error-severity" of "error" (this MAY but does not have to be included). "error-app-tag" with the value being a string that corresponds
to an identity with a base of "modify-subscription-error". "error-path" pointing to the object or parameter that caused the rejection. Optionally, "error-info" containing XML-encoded data with hints for parameter settings
that might result in future RPC success per yang-data definition "modify-subscription-error-datastore".
A configured subscription cannot be modified using "modify-subscription" RPC. Instead, the configuration needs to be edited as needed.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 "identifier". Configured subscriptions cannot be deleted via RPC, but have to be removed from the configuration. This RPC is identical to the RPC from .This RPC is only applicable only for on-change subscriptions previously been established using an "establish-subscription" RPC. For example: 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 "resynch-subscription-error".To make subscription requests, the subscriber needs to know the YANG module library available on the publisher. The YANG 1.0 module library information is sent by a NETCONF server in the NETCONF "hello" message. For YANG 1.1 modules and all modules used with the RESTCONF protocol, this information is provided by the YANG Library module (ietf-yang-library.yang from . This YANG library information is important for the receiver to reproduce the set of object definitions used within the publisher. The YANG library includes a module list with the name, revision, enabled features, and applied deviations for each YANG module implemented by the publisher. The receiver is expected to know the YANG library information before starting a subscription. The "/modules-state/module-set-id" leaf in the "ietf-yang-library" module can be used to cache the YANG library information.The set of modules, revisions, features, and deviations can change at run-time (if supported by the publisher implementation). In this case, the receiver needs to be informed of module changes before datastore nodes from changed modules can be processed correctly. The YANG library provides a simple "yang-library-change" notification that informs the subscriber that the library has changed. The receiver then needs to re-read the entire YANG library data for the replicated publisher in order to detect the specific YANG library changes. The "ietf-netconf-notifications" module defined in contains a "netconf-capability-change" notification that can identify specific module changes. For example, the module URI capability of a newly loaded module will be listed in the "added-capability" leaf-list, and the module URI capability of an removed module will be listed in the "deleted-capability" leaf-list.
This document registers the following namespace URI in the "IETF XML
Registry" :
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 :
Name: ietf-yang-push
Namespace: urn:ietf:params:xml:ns:yang:ietf-yang-push
Prefix: yp
Reference: draft-ietf-netconf-yang-push-12.txt (RFC form)
All security considerations from are relevant for datastores. In addition there are specific security considerations for receivers defined in If the access control permissions on subscribed YANG nodes change during the lifecycle of a subscription, a publisher MUST either transparently conform to the new access control permissions, or must terminate or restart the subscriptions so that new access control permissions are re-established. The NETCONF Authorization Control Model SHOULD be used to restrict the delivery of YANG nodes for which the receiver has no access.For their valuable comments, discussions, and feedback, we wish to acknowledge Tim Jenkins, Kent Watsen, Susan Hares, Yang Geng, Peipei Guo, Michael Scharf, Martin Bjorklund, and Guangying Zheng.Network Configuration Protocol (NETCONF) Access Control ModelCustom Subscription to Event StreamsNetwork Management Datastore ArchitectureNETCONF Support for Event NotificationsRejection 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 , 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 within the either the subscribed-notifications YANG model or the yang-push YANG model may be returned as part of the error responses resulting from failed attempts at datastore subscription. Following are valid errors per RPC (note: throughout this section the prefix 'sn' indicates an item imported from the subscribed-notifications.yang model):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: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, the following types of error identities may be returned within the corresponding subscription state change notification:(To be removed by RFC editor prior to publication)v13 - v14
Minor text fixes.v12 - v13
Hint negotiation models now show error examples.yang-data structures for rpc errors.v11 - v12
Included Martin's review clarifications.QoS moved to subscribed-notificationstime-of-update removed as it is redundant with RFC5277's eventTime, and other times from notification-messages.Error model moved to match existing implementationsOn-change notifiable removed, how to do this is implementation specific.NMDA model supported. Non NMDA version at https://github.com/netconf-wg/yang-push/v10 - v11
Promise model reference added.Error added for no-such-datastoreInherited changes from subscribed notifications (such as optional feature definitions).scrubbed the examples for proper encodingsv09 - v10
Returned to the explicit filter subtyping of v00-v05identityref to ds:datastore made explicitReturned ability to modify a selection filter via RPC.v08 - v09
Minor tweaks cleaning up text, removing appendicies, and making reference to revised-datastores.Subscription-id optional in push updates, except when encoded in RFC5277, Section 4 one-way notification.Finished adding the text descibing the resynch subscription RPC.Removed relationships to other drafts and future technology appendicies as this work is being explored elsewhere.Deferred the multi-line card issue to new draftsSimplified the NACM interactions.v07 - v08
Updated YANG models with minor tweaks to accommodate changes of ietf-subscribed-notifications.v06 - v07
Clarifying text tweaks.Clarification that filters act as selectors for subscribed datastore nodes; support for value filters not included but possible as a future extensionFilters don't have to be matched to existing YANG objectsv05 - v06
Security considerations updated.Base YANG model in [subscribe] updated as part of move to identities, YANG augmentations in this doc matched upTerms refined and text updates throughoutAppendix talking about relationship to other drafts added.Datastore replaces streamDefinitions of filters improvedv04 to v05
Referenced based subscription document changed to Subscribed Notifications from 5277bis.Getting operational data from filtersExtension notifiable-on-change addedNew appendix on potential futures. Moved text into there from several drafts.Subscription configuration section now just includes changed parameters from Subscribed NotificationsSubscription monitoring moved into Subscribed NotificationsNew error and hint mechanisms included in text and in the yang model.Updated examples based on the error definitionsGroupings updated for consistencyText updates throughoutv03 to v04
Updates-not-sent flag addedNot notifiable extension addedDampening period is for whole subscription, not single objectsMoved start/stop into rfc5277bisClient and Server changed to subscriber, publisher, and receiverAnchor time for periodicMessage format for synchronization (i.e. synch-on-start)Material moved into 5277bisQoS parameters supported, by not allowed to be modified by RPCText updates throughout