Network Working Group A. Clemm Internet-Draft A. Gonzalez Prieto Intended status: Standards Track E. Voit Expires: September 10, 2015 Cisco Systems March 9, 2015 Subscribing to YANG datastore push updates draft-clemm-netconf-yang-push-00.txt Abstract This document defines a subscription and push mechanism for YANG datastores. This mechanism allows client applications to request updates from a YANG datastore, which are then pushed by the server to the client per a subscription policy, without requiring additional client requests. 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 http://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 September 10, 2015. Copyright Notice Copyright (c) 2015 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 (http://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 Clemm, et al. Expires September 10, 2015 [Page 1] Internet-Draft Datastore-Push March 2015 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Definitions and Acronyms . . . . . . . . . . . . . . . . . . 5 3. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 6 3.1. Subscription Model . . . . . . . . . . . . . . . . . . . 6 3.2. Negotiation of Subscription Policies . . . . . . . . . . 8 3.3. Custom Datastreams . . . . . . . . . . . . . . . . . . . 8 3.4. Push Data Stream and Transport Mapping . . . . . . . . . 9 3.5. Subscription operations . . . . . . . . . . . . . . . . . 10 3.6. A YANG data model for management of datastore push subscriptions . . . . . . . . . . . . . . . . . . . . . . 13 3.7. Other considerations . . . . . . . . . . . . . . . . . . 15 3.7.1. Authorization . . . . . . . . . . . . . . . . . . . . 15 3.7.2. Additional subscription primitives . . . . . . . . . 15 3.7.3. Robustness and reliability considerations . . . . . . 16 3.7.4. Implementation considerations . . . . . . . . . . . . 16 4. YANG module . . . . . . . . . . . . . . . . . . . . . . . . . 16 5. Security Considerations . . . . . . . . . . . . . . . . . . . 24 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 6.1. Normative References . . . . . . . . . . . . . . . . . . 24 6.2. Informative References . . . . . . . . . . . . . . . . . 25 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 1. Introduction YANG [RFC6020] was originally designed for the Netconf protocol [RFC6241], which originally put most emphasis on configuration. However, YANG is not restricted to configuration data. YANG datastores, i.e. datastores that contain data modeled according using YANG , can contain configuration as well as contain operational data. It is therefore reasonable to expect that data in YANG datastores will increasingly be used to support applications that are not Clemm, et al. Expires September 10, 2015 [Page 2] Internet-Draft Datastore-Push March 2015 focused on managing configurations but that are, for example, related to service assurance. Service assurance applications typically involve monitoring operational state of networks and devices; of particular interest are changes that this data undergoes over time. Likewise, there are applications in which data and objects from one datastore need to be made available both to applications in other systems and to remote datastores [peermount-req][peermount]. This requires mechanisms that allow remote systems to become quickly aware of any updates to allow to validate and maintain cross-network integrity and consistency. Traditional approaches rely heavily on polling, in which data is periodically explicitly retrieved by a client from a server to stay up-to-date. There are various issues associated with polling-based management: o It introduces additional load on network and devices. Each polling cycle requires a separate yet arguably redundant request that results in an interrupt, requires parsing, consumes bandwidth. o It lacks robustness. Polling cycles may be missed, requests may be delayed or get lost, often particularly in cases when the network is under stress and hence exactly when the need for the data is the greatest. o Data may be difficult to calibrate and compare. Polling requests may undergo slight fluctuations, resulting in intervals of different lengths which makes data hard to compare. Likewise, pollers may have difficulty issuing requests that reach all devices at the same time, resulting in offset polling intervals which again make data hard to compare. More effective is an alternative in which an application can request to be automatically updated of current content of the datastore (such as a subtree, or data in a subtree that meets a certain filter condition), and in which the server that maintains the datastore subsequently pushes those updates. However, such a solution does not currently exist. The need to perform polling-based management is typically considered an important shortcoming of management applications that rely on MIBs polled using SNMP [RFC1157]. However, without a provision to support a push-based alternative, there is no reason to believe that management applications that operate on YANG datastores using protocols such as NETCONF [RFC6241] or RESTconf [restconf] will be Clemm, et al. Expires September 10, 2015 [Page 3] Internet-Draft Datastore-Push March 2015 any more effective, as they would follow the same request/response pattern. While YANG allows the definition of notifications, such notifications are generally intended to indicate the occurrence of certain well- specified event conditions, such as a the onset of an alarm condition or the occurrence of an error. A capability to subscribe to and deliver event notifications has been defined in [RFC5277]. In addition, configuration change notifications have been defined in [RFC6470]. These change notifications pertain only to configuration information, not to operational state, and convey the root of the subtree to which changes were applied along with the edits, but not the modified data nodes and their values. Accordingly, there is a need for a service that allows client applications to subscribe to updates of a YANG datastore and that allows the server to push those updates. The requirements for such a service are documented in [pub-sub-reqs]. This document proposes a solution that addresses those requirements. The solution features the following: o A mechanism that allows clients to subscribe to automatic datastore updates, and the means to manage those subscription. The subscription allows clients to specify which data they are interested in, and to provide optional filters with criteria that data must meet for updates to be sent. Furthemore, subscription can specify a policy that directs when updates are provided. For example, a client may request to be updated periodically in certain intervals, or whenever data changes occur. o The ability to negotiate subscription parameters. Because not every server may support every requested interval for every piece of data, it is necessary for a server to be able to indicate whether or not it is capable of supporting a requested subscription, and possibly allow to negotiate subscription parameters. o A mechanism is to communicate the updates themselves. For this, the proposal leverages and extends existing YANG/Netconf/Restconf mechanisms, defining special notifications that carry updates. This document specifies a YANG data model to manage subscriptions to data in YANG datastores, and to configure associated filters and data streams. It defines extensions to RPCs defined in [RFC5277] that allow to extend notification subscriptions to subscriptions for datastore updates. It also defines a notification that can be used to carry data updates and thus serve as push mechanism. Clemm, et al. Expires September 10, 2015 [Page 4] Internet-Draft Datastore-Push March 2015 2. Definitions and Acronyms Data node: An instance of management information in a YANG datastore. Data record: A record containing a set of one or more data node instances and their associated values. Datastore: A conceptual store of instantiated management information, with individual data items represented by data nodes which are arranged in hierarchical manner. Datastream: A continuous stream of data records, each including a set of updates, i.e. data node instances and their associated values. Data subtree: An instantiated data node and the data nodes that are hierarchically contained within it. NACM: NETCONF Access Control Model NETCONF: Network Configuration Protocol Push-update stream: A conceptual data stream of a datastore that streams the entire datastore contents continuously and perpetually. RPC: Remote Procedure Call SNMP: Simple Network Management Protocol Subscription: A contract between a client ("subscriber") and a server ("publisher"), stipulating which information the client wishes to receive from the server (and which information the server has to provide to the client) without the need for further solicitation. Subscription filter: A filter that contains evaluation criteria which are evaluated against YANG objects of a subscription. An update is only published if the object meets the specified filter criteria. Subscription policy: A policy that specifies under what circumstances to push an update, e.g. whether updates are to be provided periodically or only whenever changes occur. Update: A data item containing the current value of a data node. Update trigger: A trigger, as specified by a subscription policy, that causes an update to be sent, respectively a data record to be generated. An example of a trigger is a change trigger, invoked when the value of a data node changes or a data node is created or Clemm, et al. Expires September 10, 2015 [Page 5] Internet-Draft Datastore-Push March 2015 deleted, or a time trigger, invoked after the laps of a periodic time interval. URI: Uniform Resource Identifier YANG: A data definition language for NETCONF 3. Solution Overview This document specifies a solution that allows clients to subscribe to information updates in a YANG datastore, which are subsequently pushed from the server to the client. Subscriptions are initiated by clients. Servers respond to a subscription request explicitly positively or negatively. Negative responses include information about why the subscription was not accepted, in order to facilitate converging on an accepable set of subscription parameters. Once a subscription has been established, datastore push updates are pushed from the server to the subscribing client until the subscription ends. Accordingly, the solution encompasses several components: o The subscription model for configuration and management of the subscriptions, with a set of associated services. o The ability to negotiate subscription parameters, in cases where a subscription desired by a client cannot currently be served. o The stream of datastore push updates. In addition, there are a number of additional considerations, such as the tie-in of the mechanisms with security mechanisms. Each of those aspects will be discussed in the following subsections. 3.1. Subscription Model Yang-push subscriptions are defined using a data model. This model is based on the subscriptions defined in [RFC-5277], which is also reused in RESTconf. The model is extended with several parameters, including a subscription type and a subscription ID. A subscription refers to a datastream. The subscription model assumes the presence of a conceptual perpetual datastream "push- update" of continuous datastore updates of infinite time resolution. A subscription refers to this datastream and specifies filters that are to be applied to, it for example, to provide only those subsets of the information that match a filter criteria. In addition, a Clemm, et al. Expires September 10, 2015 [Page 6] Internet-Draft Datastore-Push March 2015 subscription specifies a subscription policy that defines the trigger when data records should be sent, for example at periodic intervals or whenever underlying data items change. The complete set of subscription parameters is as follows: o The name of the stream to subscribe to. The subscription model always assumes the presence of a perpetual and continuous stream of updates. The stream is called "push-update". However, as mentioned, it is possible to subscribe to other datastreams, such as custom datastreams which are separately configured. o Optional filter(s), describing the subset of data items in the stream's data records that are of interest to the subscriber. The server should only send to the subscriber the data items that match the filter(s), when present. The absence of a filter indicates that all data items from the stream are of interest to the subscriber and all data records must be sent in their entirety to the subscriber. Two filtering mechanisms are provided: subtree filtering and Xpath filtering, with the semantics described in [RFC 5277 Section 3.6]. (Additional filter types can be added through extensions.) o An identifier for the subscription. o An optional start time. Used to trigger replays starting at the provided time. Its semantics are those in [RFC 5277]. o An optional stop time. Used to limit temporarily the events of interest. Its semantics are those in [RFC 5277]. o For subscriptions to "push-update", a subscription policy definition regarding the update trigger to send new updates. The trigger can be periodic or based on change. For periodic subscriptions, the trigger is defines by the interval with which to push updates. For on-change subscriptions, the trigger is defined using the dampening interval with which to push repeated changes, an indicator for the magnitude of changes, etc. It is conceivable that additional subscription parameters might be added in the future. For example, a parameter might be introduced that allows to specify which encoding method for updates to use. The list could accordingly be extended and augmented in the future. Clemm, et al. Expires September 10, 2015 [Page 7] Internet-Draft Datastore-Push March 2015 3.2. Negotiation of Subscription Policies A subscription rejection can be caused by the inability of the server to provide a stream with the requested semantics. Providing "on- change" updates for operational data can be computationally expensive and an agent may decide not to support them or supporting them for a small number of subscribers or for a limited set of data nodes. Yang-push supports a simple negotiation between clients and servers for subscription parameters. The negotiation is limited to a single pair of subscription request and response. For negative responses, the server SHOULD include in the returned error what subscription parameters would have been accepted for the request. The returned acceptable parameters are no guarantee for subsequent requests for this client or others. 3.3. Custom Datastreams Optionally, it is possible to introduce other datastreams (beyond the datastore-push datastream) with custom semantics. Some datastreams can be custom configured. The support of this is tied to a separate feature. The configuration of a custom datastream specifies the trigger conditions under which new data records for the stream are generated, and which updates the corresponding data records contain. For example, the configuration of a datastream can specify which subsets of data nodes in a datastore the datastream should contain, which filter criteria the updates need to meet, and under what conditions to create updates - for example, periodically or whenever a data item changes. A subscription that refers to a custom datastream can specify a set of filters, like for the "push-update" datastream. However, the policy as to when updates are triggered (periodically or on change) needs to be the same as the policy of the datastream and cannot be modified. It is not possible, for example, to define a custom datastream which creates on-change updates, yet subscribe to that datastream with periodic updates. While conceptually similar, the choice between subscribing to datastream "push-update" or configuring and subscribing to a custom datastream can be thought of as analogous to the choice between operating a nozzle that is connected to a hose, or controlling the faucet (custom datastream). Operating the nozzle is for most uses simpler; however, the option to operate the faucet instead can provide additional flexibility in some scenarios. Clemm, et al. Expires September 10, 2015 [Page 8] Internet-Draft Datastore-Push March 2015 3.4. Push Data Stream and Transport Mapping Pushing data based on a subscription could be considered analogous to a response to a data retrieval request, e.g. a "get" request. However, contrary to such a request, multiple responses to the same request may get sent over a longer period of time. A more suitable mechanism is therefore that of a notification. Contrary to notifications associated with alarms and unexpected event occurrences, push updates are solicited, i.e. tied tied to a particular subscription which triggered the notification. (An alternative conceptual model would consider a subscription an "opt- in" filter on a continuous stream of updates.) The notification contains several parameters: o A subscription correlator, referencing the name of the subscription on whose behalf the notification is sent. o A data node that contains a representation of the datastore subtree containing the updates. The subtree is filtered per access control rules to contain only data that the subscriber is authorized to see. Also, depending on the subscription type, i.e., specifically for on-change subscriptions, the subtree contains only the data nodes that contain actual changes. (This can be simply a node of type string or, for XML-based encoding, anyxml.) Notifications are sent using elements as defined in [RFC5277]. Alternative transports are conceivable but outside the scope of this specification. The solution specified in this document uses notifications to communicate datastore updates. The contents of the notification includes a set of explicitly defined data nodes. For this purpose, a new generic notification is introduced, "push-update" notification. This notification is used to carry a data record with updates of datastore contents as specified by a subscription. The update record consists of a data snippet that contains an instantiated datastore subtree with the subscribed contents. Data nodes that do not match filter criteria are removed. Likewise, in the case of a subscription with "on-change" subscription policy, data nodes that have not undergone change are omitted. The contents 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. Clemm, et al. Expires September 10, 2015 [Page 9] Internet-Draft Datastore-Push March 2015 The contents of the notification conceptually represents the union of all data nodes in the yang modules supported by the server, excluding the following statements: "mandatory", "must", "min-elements", "max- elements", "when", and "default". However, in a YANG data model, it is not practical to model the precise data contained in the updates as part of the notification, because the specific data nodes supported depends on the implementing system and may even vary dynamically. Therefore, to capture this data, a single parameter that can represent any datastore contents is used, not parameters that represent data nodes one at a time. The following is an example of push notification. It contains an update for subscription my-sub, including a subtree with root foo that contains a leaf, bar: my-sub 2015-03-09T19:14:56Z some_string Figure 1: Push example 3.5. Subscription operations There are several operations associated with subscriptions. At the most basic level, clients need to be able to create subscriptions, as well as delete subscriptions when they are no longer needed. RFC 5277 specifies an operation to create subscriptions for event streams, . This operation is leveraged and extended to create datastore-push subscriptions. Specifically, an additional parameter is added to allow for the specification of trigger policy. To support datastore push, a server MUST support the interleave capability specified in [RFC5277]. This is required to allow for Clemm, et al. Expires September 10, 2015 [Page 10] Internet-Draft Datastore-Push March 2015 modification of what data is being subscribed to without needing to establish a separate Netconf session. The example below illustrates a subscription for a periodic push of all data under a container called foo. push-update my-sub 500 Figure 2: Subscription example The example below illustrates a subscription response, where an agent does not support frequent periodic updates, and suggests a different sampling rate to the client. application operation-not-supported error 3000 Figure 3: Subscription negotiation example RFC 5277 does not specify operations to delete subscriptions. Instead, it assumes that an event subscription is associated with its Clemm, et al. Expires September 10, 2015 [Page 11] Internet-Draft Datastore-Push March 2015 own Netconf session. When the session is torn down, the subscription is implicitly deleted. Likewise, there is no operation to modify a subscription. Modifying a subscription requires tearing down a Netconf session, starting a new one, and creating a new subscription. Furthermore, each session only supports a single subscription. Establishing multiple subscriptions requires multiple concurrent Netconf sessions. To facilitate datastore-push subscriptions, an additional RPC is introduced, . The operation takes as parameter a subscription ID. As a result of the operation, the subscription is removed and no more data records will be sent. my-sub Figure 4: Subscription deletion Finally, a separate operation to modify a subscription is introduced, . This operation takes the same parameters as , but refers to an existing subscription. Of course, a subscription could also be deleted and another be created. However, modify operation avoids issues regarding the synchronization of creation and deletion operations, such as potential loss or duplication of updates. Also, a modify operation allows to simply extend an existing subscription beyond the initial subscription end time. Clemm, et al. Expires September 10, 2015 [Page 12] Internet-Draft Datastore-Push March 2015 push-update my-sub 3000 Figure 5: Modify subscription 3.6. A YANG data model for management of datastore push subscriptions Subscriptions as well as datastreams can be subjected to management themselves. For example, it is possible that a server may no longer be able to serve a subscription that it had previously accepted. Perhaps it has run out of resources, or internal errors may have occurred. When this is the case, a server needs to be able to temporarily suspend the subscription, or even to terminate it. More generally, the server should provide a means by which the status of subscriptions can be monitored. When custom datastreams are supported, those datastreams need to be configured and monitored as well. For this purpose, a YANG data model is introduced, which is depicted in the following figure. Clemm, et al. Expires September 10, 2015 [Page 13] Internet-Draft Datastore-Push March 2015 module: ietf-datastore-push +--rw streams {custom-streams}? | +--rw stream* [stream-name] | +--rw stream-name string | +--ro stream-status? identityref | +--rw subtree-filter? subtree-filter | +--rw xpath-filter? yang:xpath1.0 | +--rw (update-trigger)? | +--:(periodic) | | +--rw period? yang:timeticks | +--:(on-change) | +--rw dampening-period yang:timeticks | +--rw (change-policy)? | +--:(delta-policy) | +--rw delta? uint32 +--rw subscriptions +--ro datastore-push-subscription* [subscription-id] +--ro subscription-id subscription-identifier +--ro subscription-status? identityref +--ro stream? string +--ro start-time? yang:date-and-time +--ro stop-time? yang:date-and-time +--ro subtree-filter? subtree-filter +--ro xpath-filter? yang:xpath1.0 +--ro (update-trigger)? +--:(periodic) | +--ro period? yang:timeticks +--:(on-change) +--ro dampening-period yang:timeticks +--ro (change-policy)? +--:(delta-policy) +--ro delta? uint32 Figure 6: Model structure Each subscription is represented as a list element "datastore-push- subscription". The associated information includes an identifier for the subscription, a subscription status, as well as the various subscription paramters. The subscription status indicates whether the subscription is currently active and healthy, or if it is degraded in some form. Subscriptions are automatically removed from the list once they expire or are terminated. Because subscriptions are managed using their own set of operation primitives, they are read-only. An optional feature, custom-streams, is introduced to allow for the configuration of custom datastreams. Custom datastreams are represented through a separate list, consisting of information used Clemm, et al. Expires September 10, 2015 [Page 14] Internet-Draft Datastore-Push March 2015 to configure those datastreams. This information consititutes mostly configuration information, with the exception of parameters used to indicate the status and health of the datastream. In addition, a server needs to indicate any changes in status to the subscriber through a notification. Specifically, subscribers need to be informed of the following: o A subscription has been temporarily suspended(including the reason) o A subscription (that had been suspended earlier) is once again operational o A subscription has been abnormally terminated (including the reason) o A subscription has been modified (including the current set of subscription parameters in effect) Finally, a server might provide additional information about subscriptions, such as statistics about the number of data updates that were sent. However, such information is currently outside the scope of this specification. 3.7. Other considerations 3.7.1. Authorization A client may only receive updates to data that the client has proper authorization for. Normal authorization rules apply. Data that is being pushed therefore needs to be subjected to a filter that applies the corresponding rules, removing any non-authorized data as applicable. The authorization model for data in YANG datastores is described in the Netconf Access Control Model [RFC6536]. 3.7.2. Additional subscription primitives Other possible operations include the ability to suspend and resume subscriptions. However, those operations are not viewed as essential, as it is always possible to alternatively simply remove a subscription and recreate it when needed. Clemm, et al. Expires September 10, 2015 [Page 15] Internet-Draft Datastore-Push March 2015 3.7.3. Robustness and reliability considerations Particularly in the case of on-change push updates, it is important that push updates do not get lost. However, datastore-push uses a secure and reliable transport. Notifations are not getting reordered, and in addition contain a time stamp. For those reasons, we believe that additional reliability mechanisms at the application level, such as sequence numbers for push updates, are not required. 3.7.4. Implementation considerations Implementation specifics are outside the scope of this specification. That said,it should be noted that monitoring of operational state changes inside a system can be associated with significant implementation challenges. Even periodic retrieval of operational state alone, to be able to push it, can consume considerable system resources. Configuration data may in many cases be persisted in an actual database or a configuration file, where retrieval of the database content or the file itself is reasonably straightforward and computationally inexpensive. However, retrieval of operational data may, depending on the implementation, require invocation of APIs, possibly on an object-by-object basis, possibly involving additional internal interrupts, etc. For those reasons, if is important for an implementation to understand what subscriptions it can or cannot support. It is far preferrable to decline a subscription request, than to accept it only to result in subsequent failure later. Whether or not a subscription can be supported will in general be determined by a combination of several factors, including the subscription policy (on-change or periodic, with on-change in general being the more challenging of the two), the period in which to report changes (1 second periods will consume more resources than 1 hour periods), the amount of data in the subtree that is being subscribed to, and the number and combination of other subscriptions that are concurrently being serviced. 4. YANG module file "ietf-datastore-push@2014-03-09.yang" module ietf-datastore-push { namespace "urn:XXXX:params:xml:ns:yang:ietf-datastore-push"; prefix datastore-push; Clemm, et al. Expires September 10, 2015 [Page 16] Internet-Draft Datastore-Push March 2015 import ietf-yang-types { prefix yang; } organization "IETF"; contact "Editor: Alexander Clemm Editor: Alberto Gonzalez Prieto Editor: Eric Voit "; description "This module contains conceptual YANG specifications for datastore push."; revision 2014-03-09 { description "Initial revision."; reference "Datastore push."; } feature custom-streams { description "This feature allows users to configure datastore update streams in addition to the stream provided by default, datastore-push."; } identity subscription-stream-status { description "Base identity for the status of subscriptions and datastreams."; } identity active { base subscription-stream-status; description "Status is active and healthy."; } identity inactive { base subscription-stream-status; description "Status is inactive, for example outside the interval between start time and stop time."; Clemm, et al. Expires September 10, 2015 [Page 17] Internet-Draft Datastore-Push March 2015 } identity in-error { base subscription-stream-status; description "The status is in error or degraded, meaning that stream and/or subscription are currently unable to provide the negotiated updates."; } identity subscription-errors { description "Base identity for subscription errors."; } identity internal-error { base subscription-errors; description "Subscription failures caused by server internal error."; } identity no-resources { base subscription-errors; description "Lack of resources, e.g. CPU, memory, bandwidth"; } identity other { base subscription-errors; description "Fallback reason - any other reason"; } typedef datastore-contents { type string; description "This type is be used to represent datastore contents, including a filtered datastore subtree per a set of subscription parameters. "; } typedef subtree-filter { type string; description "This type is used to define a subtree filter. Its precise syntax is TBD."; } Clemm, et al. Expires September 10, 2015 [Page 18] Internet-Draft Datastore-Push March 2015 typedef subscription-identifier { type string { length "1 .. max"; } description "A client-provided identifier for the subscription."; } typedef subscription-term-reason { type identityref { base subscription-errors; } description "Reason for a server to terminate a subscription."; } typedef subscription-susp-reason { type identityref { base subscription-errors; } description "Reason for a server to suspend a subscription."; } grouping subscription-stream-policy { description "This grouping contains the parameters which describe the policy which data is pushed as part of a subscription or a data stream."; leaf subtree-filter { description "Datastore subtree of interest."; type subtree-filter; } leaf xpath-filter { type yang:xpath1.0; description "Xpath defining the data items of interest."; } choice update-trigger { description "Defines necessary conditions for sending an event to the subscriber."; case periodic { description "The agent is requested to notify periodically the current values of the datastore or the subset defined by the filter."; Clemm, et al. Expires September 10, 2015 [Page 19] Internet-Draft Datastore-Push March 2015 leaf period { type yang:timeticks; description "Elapsed time between notifications."; } } case on-change { description "The agent is requested to notify changes in values in the datastore or a subset of it defined by a filter."; leaf dampening-period { type yang:timeticks; mandatory true; description "Minimum amount of time that needs to have passed since the last time an update was provided."; } choice change-policy { description "Policy describing necessary conditions for sending an event to the subscriber."; case delta-policy { leaf delta { type uint32; description "For integer, minimum difference between current and last reports values that can trigger an update."; } } } } } } grouping subscription-info { description "This grouping describes basic information concerning a subscription, without the subscription policy which is defined separately to be shareable with the definition of a datastream."; leaf stream { type string; description "The name of the stream subscribed to."; } Clemm, et al. Expires September 10, 2015 [Page 20] Internet-Draft Datastore-Push March 2015 leaf start-time { type yang:date-and-time; description "Starting time for replays."; reference "RFC 5277, Section 2.1.1"; } leaf stop-time { type yang:date-and-time; description "Time limit for events of interest."; reference "RFC 5277, Section 2.1.1"; } } notification push-update { description "This notification contains an update from a datastore"; leaf subscription-id { type subscription-identifier; mandatory true; description "This references the subscription because of which the notification is sent."; } leaf datastore-contents { type datastore-contents; description "This contains datastore contents per the subscription."; } } notification subscription-suspended { description "This notification indicates that a suspension of the subscription by the server has occurred. No further datastore updates will be sent until subscription resumes."; leaf subscription-id { type subscription-identifier; mandatory true; description "This references the affected subscription."; } leaf reason { type subscription-susp-reason; description "Provides a reason for why the subscription was suspended."; Clemm, et al. Expires September 10, 2015 [Page 21] Internet-Draft Datastore-Push March 2015 } } notification subscription-resumed { description "This notification indicates that a subscription that had previously been suspended has resumed. Datastore updates will once again be sent."; leaf subscription-id { type subscription-identifier; mandatory true; description "This references the affected subscription."; } } notification subscription-modified { description "This notification indicates that a subscription has been modified. Datastore updates sent from this point on will conform to the modified terms of the subscription."; leaf subscription-id { type subscription-identifier; mandatory true; description "This references the affected subscription."; } uses subscription-info; uses subscription-stream-policy; } notification subscription-terminated { description "This notification indicates that a subscription has been terminated."; leaf subscription-id { type subscription-identifier; mandatory true; description "This references the affected subscription."; } leaf reason { type subscription-term-reason; description "Provides a reason for why the subscription was terminated."; } } container streams { if-feature custom-streams; Clemm, et al. Expires September 10, 2015 [Page 22] Internet-Draft Datastore-Push March 2015 list stream { key "stream-name"; description "A user-definable stream."; leaf stream-name { type string; mandatory true; description "The name assigned to the stream."; } leaf stream-status { type identityref { base subscription-stream-status; } config false; } uses subscription-stream-policy; } } container subscriptions { list datastore-push-subscription { description "Content of a yang-push subscription. Subscriptions are created using a dedicated RPC, hence they do not constitute configuration information."; config false; key "subscription-id"; leaf subscription-id { type subscription-identifier; description "Identifier to use for this subscription."; } leaf subscription-status { type identityref { base subscription-stream-status; } description "The status of the subscription."; } uses subscription-info; uses subscription-stream-policy; } } } Clemm, et al. Expires September 10, 2015 [Page 23] Internet-Draft Datastore-Push March 2015 5. Security Considerations Subscriptions could be used to attempt to overload servers of YANG datastores. For this reason, it is important that the server has the ability to decline a subscription request if it would deplete its resources. In addition, a server needs to be able to suspend an existing subscription when needed. When this occur, the subscription status is updated accordingly and the clients are notified. Likewise, requests for subscriptions need to be properly authorized. A subscription could be used to retrieve data in subtrees that a client has not authorized access to. Therefore it is important that data pushed based on subscriptions is authorized in the same way that regular data retrieval operations are. Data being pushed to a client needs therefore to be filtered accordingly, just like if the data were being retrieved on-demand. The Netconf Authorization Control Model applies. 6. References 6.1. Normative References [RFC1157] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple Network Management Protocol (SNMP)", STD 15, RFC 1157, May 1990. [RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event Notifications", RFC 5277, July 2008. [RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, October 2010. [RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J., and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, June 2011. [RFC6470] Bierman, A., "Network Configuration Protocol (NETCONF) Base Notifications", RFC 5277, February 2012. [RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration Protocol (NETCONF) Access Control Model", RFC 6536, March 2012. Clemm, et al. Expires September 10, 2015 [Page 24] Internet-Draft Datastore-Push March 2015 6.2. Informative References [peermount] Clemm, A., Medved, J., and E. Voit, "Mounting YANG-defined information from remote datastores", draft-clemm-netmod- mount-02 (work in progress), October 2014. [peermount-req] Voit, E., Clemm, A., Bansal, S., Tripathy, A., and P. Yellai, "Requirements for Peer Mounting of YANG subtrees from Remote Datastores", draft-voit-netmod-peer-mount- requirements-00 (work in progress), September 2014. [pub-sub-reqs] Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements for Subscription to YANG Datastores", draft-ietf-i2rs-pub- sub-requirements-00 (work in progress), March 2015. [restconf] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", I-D draft-ietf-netconf-restconf-03, October 2014. Authors' Addresses Alexander Clemm Cisco Systems EMail: alex@cisco.com Alberto Gonzalez Prieto Cisco Systems EMail: albertgo@cisco.com Eric Voit Cisco Systems EMail: evoit@cisco.com Clemm, et al. Expires September 10, 2015 [Page 25]