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2 NETCONF A. Clemm
3 Internet-Draft Huawei USA
4 Intended status: Standards Track E. Voit
5 Expires: November 1, 2019 Cisco Systems
6 A. Gonzalez Prieto
7 Microsoft
8 A. Tripathy
9 E. Nilsen-Nygaard
10 Cisco Systems
11 A. Bierman
12 YumaWorks
13 B. Lengyel
14 Ericsson
15 April 30, 2019
17 Subscription to YANG Datastores
18 draft-ietf-netconf-yang-push-23
20 Abstract
22 Via the mechanism described in this document, subscriber applications
23 may request a continuous, customized stream of updates from a YANG
24 datastore. Providing such visibility into updates enables new
25 capabilities based on the remote mirroring and monitoring of
26 configuration and operational state.
28 Status of This Memo
30 This Internet-Draft is submitted in full conformance with the
31 provisions of BCP 78 and BCP 79.
33 Internet-Drafts are working documents of the Internet Engineering
34 Task Force (IETF). Note that other groups may also distribute
35 working documents as Internet-Drafts. The list of current Internet-
36 Drafts is at https://datatracker.ietf.org/drafts/current/.
38 Internet-Drafts are draft documents valid for a maximum of six months
39 and may be updated, replaced, or obsoleted by other documents at any
40 time. It is inappropriate to use Internet-Drafts as reference
41 material or to cite them other than as "work in progress."
43 This Internet-Draft will expire on November 1, 2019.
45 Copyright Notice
47 Copyright (c) 2019 IETF Trust and the persons identified as the
48 document authors. All rights reserved.
50 This document is subject to BCP 78 and the IETF Trust's Legal
51 Provisions Relating to IETF Documents
52 (https://trustee.ietf.org/license-info) in effect on the date of
53 publication of this document. Please review these documents
54 carefully, as they describe your rights and restrictions with respect
55 to this document. Code Components extracted from this document must
56 include Simplified BSD License text as described in Section 4.e of
57 the Trust Legal Provisions and are provided without warranty as
58 described in the Simplified BSD License.
60 This document may contain material from IETF Documents or IETF
61 Contributions published or made publicly available before November
62 10, 2008. The person(s) controlling the copyright in some of this
63 material may not have granted the IETF Trust the right to allow
64 modifications of such material outside the IETF Standards Process.
65 Without obtaining an adequate license from the person(s) controlling
66 the copyright in such materials, this document may not be modified
67 outside the IETF Standards Process, and derivative works of it may
68 not be created outside the IETF Standards Process, except to format
69 it for publication as an RFC or to translate it into languages other
70 than English.
72 Table of Contents
74 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
75 2. Definitions and Acronyms . . . . . . . . . . . . . . . . . . 4
76 3. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 5
77 3.1. Subscription Model . . . . . . . . . . . . . . . . . . . 5
78 3.2. Negotiation of Subscription Policies . . . . . . . . . . 6
79 3.3. On-Change Considerations . . . . . . . . . . . . . . . . 7
80 3.4. Reliability Considerations . . . . . . . . . . . . . . . 8
81 3.5. Data Encodings . . . . . . . . . . . . . . . . . . . . . 9
82 3.6. Defining the Selection with a Datastore . . . . . . . . . 10
83 3.7. Streaming Updates . . . . . . . . . . . . . . . . . . . . 11
84 3.8. Subscription Management . . . . . . . . . . . . . . . . . 13
85 3.9. Receiver Authorization . . . . . . . . . . . . . . . . . 15
86 3.10. On-Change Notifiable Datastore Nodes . . . . . . . . . . 16
87 3.11. Other Considerations . . . . . . . . . . . . . . . . . . 17
88 4. A YANG Data Model for Management of Datastore Push
89 Subscriptions . . . . . . . . . . . . . . . . . . . . . . . . 18
90 4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 18
91 4.2. Subscription Configuration . . . . . . . . . . . . . . . 24
92 4.3. YANG Notifications . . . . . . . . . . . . . . . . . . . 25
93 4.4. YANG RPCs . . . . . . . . . . . . . . . . . . . . . . . . 26
94 5. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . . 31
95 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 48
96 7. Security Considerations . . . . . . . . . . . . . . . . . . . 48
97 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 50
98 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 50
99 9.1. Normative References . . . . . . . . . . . . . . . . . . 50
100 9.2. Informative References . . . . . . . . . . . . . . . . . 51
101 Appendix A. Appendix A: Subscription Errors . . . . . . . . . . 52
102 A.1. RPC Failures . . . . . . . . . . . . . . . . . . . . . . 52
103 A.2. Notifications of Failure . . . . . . . . . . . . . . . . 53
104 Appendix B. Changes Between Revisions . . . . . . . . . . . . . 53
105 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 57
107 1. Introduction
109 Traditional approaches to providing visibility into managed entities
110 from a remote system have been built on polling. With polling, data
111 is periodically requested and retrieved by a client from a server to
112 stay up-to-date. However, there are issues associated with polling-
113 based management:
115 o Polling incurs significant latency. This latency prohibits many
116 application types.
118 o Polling cycles may be missed, requests may be delayed or get lost,
119 often when the network is under stress and the need for the data
120 is the greatest.
122 o Polling requests may undergo slight fluctuations, resulting in
123 intervals of different lengths. The resulting data is difficult
124 to calibrate and compare.
126 o For applications that monitor for changes, many remote polling
127 cycles place unwanted and ultimately wasteful load on the network,
128 devices, and applications, particularly when changes occur only
129 infrequently.
131 A more effective alternative to polling is for an application to
132 receive automatic and continuous updates from a targeted subset of a
133 datastore. Accordingly, there is a need for a service that allows
134 applications to subscribe to updates from a datastore and that
135 enables the server (also referred to as publisher) to push and in
136 effect stream those updates. The requirements for such a service
137 have been documented in [RFC7923].
139 This document defines a corresponding solution that is built on top
140 of "Custom Subscription to Event Streams"
142 [I-D.draft-ietf-netconf-subscribed-notifications]. Supplementing
143 that work are YANG data model augmentations, extended RPCs, and new
144 datastore specific update notifications. Transport options for
145 [I-D.draft-ietf-netconf-subscribed-notifications] will work
146 seamlessly with this solution.
148 2. Definitions and Acronyms
150 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
151 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
152 "OPTIONAL" in this document are to be interpreted as described in BCP
153 14 [RFC2119] [RFC8174] when, and only when, they appear in all
154 capitals, as shown here.
156 This document uses the terminology defined in [RFC7950], [RFC8341],
157 [RFC8342], and [I-D.draft-ietf-netconf-subscribed-notifications]. In
158 addition, the following terms are introduced:
160 o Datastore node: A node in the instantiated YANG data tree
161 associated with a datastore. In this document, datastore nodes
162 are often also simply referred to as "objects"
164 o Datastore node update: A data item containing the current value of
165 a datastore node at the time the datastore node update was
166 created, as well as the path to the datastore node.
168 o Datastore subscription: A subscription to a stream of datastore
169 node updates.
171 o Datastore subtree: A datastore node and all its descendant
172 datastore nodes
174 o On-change subscription: A datastore subscription with updates that
175 are triggered when changes in subscribed datastore nodes are
176 detected.
178 o Periodic subscription: A datastore subscription with updates that
179 are triggered periodically according to some time interval.
181 o Selection filter: Evaluation and/or selection criteria, which may
182 be applied against a targeted set of objects.
184 o Update record: A representation of one or more datastore node
185 updates. In addition, an update record may contain which type of
186 update led to the datastore node update (e.g., whether the
187 datastore node was added, changed, deleted). Also included in the
188 update record may be other metadata, such as a subscription id of
189 the subscription as part of which the update record was generated.
191 In this document, update records are often also simply referred to
192 as "updates".
194 o Update trigger: A mechanism that determines when an update record
195 needs to be generated.
197 o YANG-Push: The subscription and push mechanism for datastore
198 updates that is specified in this document.
200 3. Solution Overview
202 This document specifies a solution that provides a subscription
203 service for updates from a datastore. This solution supports dynamic
204 as well as configured subscriptions to updates of datastore nodes.
205 Subscriptions specify when notification messages (also referred to as
206 "push updates") should be sent and what data to include in update
207 records. Datastore node updates are subsequently pushed from the
208 publisher to the receiver per the terms of the subscription.
210 3.1. Subscription Model
212 YANG-push subscriptions are defined using a YANG data model. This
213 model enhances the subscription model defined in
214 [I-D.draft-ietf-netconf-subscribed-notifications] with capabilities
215 that allow subscribers to subscribe to datastore node updates,
216 specifically to specify the update triggers defining when to generate
217 update records as well as what to include in an update record. Key
218 enhancements include:
220 o Specification of selection filters which identify targeted YANG
221 datastore nodes and/or datastore subtrees for which updates are to
222 be pushed.
224 o Specification of update policies contain conditions which trigger
225 the generation and pushing of new update records. There are two
226 types of subscriptions, distinguished by how updates are
227 triggered: periodic and on-change.
229 * For periodic subscriptions, the update trigger is specified by
230 two parameters that define when updates are to be pushed.
231 These parameters are the period interval with which to report
232 updates, and an "anchor time", i.e. a reference point in time
233 that can be used to calculate at which points in time periodic
234 updates need to be assembled and sent.
236 * For on-change subscriptions, an update trigger occurs whenever
237 a change in the subscribed information is detected. Included
238 are additional parameters that include:
240 + Dampening period: In an on-change subscription, detected
241 object changes should be sent as quickly as possible.
242 However it may be undesirable to send a rapid series of
243 object changes. Such behavior has the potential to exhaust
244 resources in the publisher or receiver. In order to protect
245 against that, a dampening period MAY be used to specify the
246 interval which has to pass before successive update records
247 for the same subscription are generated for a receiver. The
248 dampening period collectively applies to the set of all
249 datastore nodes selected by a single subscription. This
250 means that when there is a change to one or more subscribed
251 objects, an update record containing those objects is
252 created immediately (when no dampening period is in effect)
253 or at the end of a dampening period (when a dampening period
254 is in fact in effect). If multiple changes to a single
255 object occur during a dampening period, only the value that
256 is in effect at the time when the update record is created
257 is included. The dampening period goes into effect every
258 time an update record completes assembly.
260 + Change type: This parameter can be used to reduce the types
261 of datastore changes for which updates are sent (e.g., you
262 might only send an update when an object is created or
263 deleted, but not when an object value changes).
265 + Sync on start: defines whether or not a complete push-update
266 of all subscribed data will be sent at the beginning of a
267 subscription. Such early synchronization establishes the
268 frame of reference for subsequent updates.
270 o An encoding (using anydata) for the contents of periodic and on-
271 change push updates.
273 3.2. Negotiation of Subscription Policies
275 A dynamic subscription request SHOULD be declined if a publisher's
276 assessment is that it may be unable to provide update records meeting
277 the terms of an "establish-subscription" or "modify-subscription" RPC
278 request. In this case, a subscriber may quickly follow up with a new
279 RPC request using different parameters.
281 Random guessing of different parameters by a subscriber is to be
282 discouraged. Therefore, in order to minimize the number of
283 subscription iterations between subscriber and publisher, a dynamic
284 subscription supports a simple negotiation between subscribers and
285 publishers for subscription parameters. This negotiation is in the
286 form of supplemental information which should be inserted within
287 error responses to a failed RPC request. This returned error
288 response information, when considered, should increase the likelihood
289 of success for subsequent RPC requests. Such hints include suggested
290 periodic time intervals, acceptable dampening periods, and size
291 estimates for the number or objects which would be returned from a
292 proposed selection filter. However, there are no guarantees that
293 subsequent requests which consider these hints will be accepted.
295 3.3. On-Change Considerations
297 On-change subscriptions allow receivers to receive updates whenever
298 changes to targeted objects occur. As such, on-change subscriptions
299 are particularly effective for data that changes infrequently, yet
300 for which applications need to be quickly notified whenever a change
301 does occur with minimal delay.
303 On-change subscriptions tend to be more difficult to implement than
304 periodic subscriptions. Accordingly, on-change subscriptions may not
305 be supported by all implementations or for every object.
307 Whether or not to accept or reject on-change subscription requests
308 when the scope of the subscription contains objects for which on-
309 change is not supported is up to the publisher implementation. A
310 publisher MAY accept an on-change subscription even when the scope of
311 the subscription contains objects for which on-change is not
312 supported. In that case, updates are sent only for those objects
313 within the scope that do support on-change updates, whereas other
314 objects are excluded from update records, even if their values
315 change. In order for a subscriber to determine whether objects
316 support on-change subscriptions, objects are marked accordingly on a
317 publisher. Accordingly, when subscribing, it is the responsibility
318 of the subscriber to ensure it is aware of which objects support on-
319 change and which do not. For more on how objects are so marked, see
320 Section 3.10.
322 Alternatively, a publisher MAY decide to simply reject an on-change
323 subscription in case the scope of the subscription contains objects
324 for which on-change is not supported. In case of a configured
325 subscription, the publisher MAY suspend the subscription.
327 To avoid flooding receivers with repeated updates for subscriptions
328 containing fast-changing objects, or objects with oscillating values,
329 an on-change subscription allows for the definition of a dampening
330 period. Once an update record for a given object is generated, no
331 other updates for this particular subscription will be created until
332 the end of the dampening period. Values sent at the end of the
333 dampening period are the values that are current at the end of the
334 dampening period of all changed objects. Changed objects include
335 those which were deleted or newly created during that dampening
336 period. If an object has returned to its original value (or even has
337 been created and then deleted) during the dampening-period, that
338 value (and not the interim change) will still be sent. This will
339 indicate churn is occurring on that object.
341 On-change subscriptions can be refined to let users subscribe only to
342 certain types of changes. For example, a subscriber might only want
343 object creations and deletions, but not modifications of object
344 values.
346 Putting it all together, following is the conceptual process for
347 creating an update record as part of an on-change subscription:
349 1. Just before a change, or at the start of a dampening period,
350 evaluate any filtering and any access control rules to ensure
351 receiver is authorized to view all subscribed datastore nodes
352 (filtering out any nodes for which this is not the case). The
353 result is a set "A" of datastore nodes and subtrees.
355 2. Just after a change, or at the end of a dampening period,
356 evaluate any filtering and any (possibly new) access control
357 rules. The result is a set "B" of datastore nodes and subtrees.
359 3. Construct an update record, which takes the form of YANG patch
360 record [RFC8072] for going from A to B.
362 4. If there were any changes made between A and B which canceled
363 each other out, insert into the YANG patch record the last change
364 made, even if the new value is no different from the original
365 value (since changes that were made in the interim were canceled
366 out). In case the changes involve creating a new datastore node,
367 then deleting it, the YANG patch record will indicate deletion of
368 the datastore node. Similarly, in case the changes involve
369 deleting a new datastore node, then recreating it, the YANG patch
370 record will indicate creation of the datastore node.
372 5. If the resulting patch record is non-empty, send it to the
373 receiver.
375 Note: In cases where a subscriber wants to have separate dampening
376 periods for different objects, the subscriber has the option to
377 create multiple subscriptions with different selection filters.
379 3.4. Reliability Considerations
381 A subscription to updates from a datastore is intended to obviate the
382 need for polling. However, in order to do so, it is critical that
383 subscribers can rely on the subscription and have confidence that
384 they will indeed receive the subscribed updates without having to
385 worry about updates being silently dropped. In other words, a
386 subscription constitutes a promise on the side of the publisher to
387 provide the receivers with updates per the terms of the subscription.
389 Now, there are many reasons why a publisher may at some point no
390 longer be able to fulfill the terms of the subscription, even if the
391 subscription had been entered into with good faith. For example, the
392 volume of datastore nodes may be larger than anticipated, the
393 interval may prove too short to send full updates in rapid
394 succession, or an internal problem may prevent objects from being
395 collected. For this reason, the solution that is defined in this
396 document mandates that a publisher notifies receivers immediately and
397 reliably whenever it encounters a situation in which it is unable to
398 keep the terms of the subscription, and provides the publisher with
399 the option to suspend the subscription in such a case. This includes
400 indicating the fact that an update is incomplete as part of a push-
401 update or push-change-update notification, as well as emitting a
402 subscription-suspended notification as applicable. This is described
403 further in Section 3.11.1.
405 A publisher SHOULD reject a request for a subscription if it is
406 unlikely that the publisher will be able to fulfill the terms of that
407 subscription request. In such cases, it is preferable to have a
408 subscriber request a less resource intensive subscription than to
409 deal with frequently degraded behavior.
411 The solution builds on
412 [I-D.draft-ietf-netconf-subscribed-notifications]. As defined there,
413 any loss of underlying transport connection will be detected and
414 result in subscription termination (in case of dynamic subscriptions)
415 or suspension (in case of configured subscriptions), ensuring that
416 situations will not occur in which the loss of update notifications
417 would go unnoticed.
419 3.5. Data Encodings
421 3.5.1. Periodic Subscriptions
423 In a periodic subscription, the data included as part of an update
424 record corresponds to data that could have been read using a
425 retrieval operation.
427 3.5.2. On-Change Subscriptions
429 In an on-change subscription, update records need to indicate not
430 only values of changed datastore nodes but also the types of changes
431 that occurred since the last update. Therefore, encoding rules for
432 data in on-change updates will generally follow YANG-patch operation
433 as specified in [RFC8072]. The YANG-patch will describe what needs
434 to be applied to the earlier state reported by the preceding update,
435 to result in the now-current state. Note that contrary to [RFC8072],
436 objects encapsulated are not restricted to only configuration
437 objects.
439 A publisher indicates the type of change to a datastore node using
440 the different YANG patch operations: the "create" operation is used
441 for newly created objects (except entries in a user-ordered list),
442 the "delete" operation is used for deleted objects (including in
443 user-ordered lists), the "replace" operation is used when only the
444 object value changes, the "insert" operation is used when a new entry
445 is inserted in a list, and the "move" operation is used when an
446 existing entry in a user-ordered list is moved.
448 However, a patch must be able to do more than just describe the delta
449 from the previous state to the current state. As per Section 3.3, it
450 must also be able to identify whether transient changes have occurred
451 on an object during a dampening period. To support this, it is valid
452 to encode a YANG patch operation so that its application would result
453 in no change between the previous and current state. This indicates
454 that some churn has occurred on the object. An example of this would
455 be a patch that indicates a "create" operation for a datastore node
456 where the receiver believes one already exists, or a "replace"
457 operation which replaces a previous value with the same value. Note
458 that this means that the "create" and "delete" errors described in
459 [RFC8072] section 2.5 are not errors, and are valid operations with
460 YANG-Push.
462 3.6. Defining the Selection with a Datastore
464 A subscription must specify both the selection filters and the
465 datastore against which these selection filters will be applied.
466 This information is used to choose and subsequently push data from
467 the publisher's datastore to the receivers.
469 Only a single selection filter can be applied to a subscription at a
470 time. An RPC request proposing a new selection filter replaces any
471 existing filter. The following selection filter types are included
472 in the YANG-push data model, and may be applied against a datastore:
474 o subtree: A subtree selection filter identifies one or more
475 datastore subtrees. When specified, update records will only come
476 from the datastore nodes of selected datastore subtree(s). The
477 syntax and semantics correspond to that specified for [RFC6241]
478 section 6.
480 o xpath: An "xpath" selection filter is an XPath expression that
481 returns a node set. (XPath is a query language for selecting
482 nodes in an XML document.) When specified, updates will only come
483 from the selected datastore nodes.
485 These filters are intended to be used as selectors that define which
486 objects are within the scope of a subscription. A publisher MUST
487 support at least one type of selection filter.
489 XPath itself provides powerful filtering constructs and care must be
490 used in filter definition. Consider an XPath filter which only
491 passes a datastore node when an interface is up. It is up to the
492 receiver to understand implications of the presence or absence of
493 objects in each update.
495 When the set of selection filtering criteria is applied for a
496 periodic subscription, then they are applied whenever a periodic
497 update record is constructed, and only datastore nodes that pass the
498 filter and to which a receiver has access are provided to that
499 receiver. If the same filtering criteria is applied to an on-change
500 subscription, only the subset of those datastore nodes supporting on-
501 change is provided. A datastore node which doesn't support on-change
502 is never sent as part of an on-change subscription's "push-update" or
503 "push-change-update" (see Section 3.7).
505 3.7. Streaming Updates
507 Contrary to traditional data retrieval requests, datastore
508 subscription enables an unbounded series of update records to be
509 streamed over time. Two generic YANG notifications for update
510 records have been defined for this: "push-update" and "push-change-
511 update".
513 A "push-update" notification defines a complete, filtered update of
514 the datastore per the terms of a subscription. This type of YANG
515 notification is used for continuous updates of periodic
516 subscriptions. A "push-update" notification can also be used for the
517 on-change subscriptions in two cases. First, it MUST be used as the
518 initial "push-update" if there is a need to synchronize the receiver
519 at the start of a new subscription. It also MAY be sent if the
520 publisher later chooses to resync an on-change subscription. The
521 "push-update" update record contains an instantiated datastore
522 subtree with all of the subscribed contents. The content of the
523 update record is equivalent to the contents that would be obtained
524 had the same data been explicitly retrieved using a datastore
525 retrieval operation using the same transport with the same filters
526 applied.
528 A "push-change-update" notification is the most common type of update
529 for on-change subscriptions. The update record in this case contains
530 the set of changes that datastore nodes have undergone since the last
531 notification message. In other words, this indicates which datastore
532 nodes have been created, deleted, or have had changes to their
533 values. In cases where multiple changes have occurred over the
534 course of a dampening period and the object has not been deleted, the
535 object's most current value is reported. (In other words, for each
536 object, only one change is reported, not its entire history. Doing
537 so would defeat the purpose of the dampening period.)
539 "Push-update" and "push-change-update" are encoded and placed within
540 notification messages, and ultimately queued for egress over the
541 specified transport.
543 The following is an example of a notification message for a
544 subscription tracking the operational status of a single Ethernet
545 interface (per [RFC8343]). This notification message is encoded XML
546 over NETCONF as per
547 [I-D.draft-ietf-netconf-netconf-event-notifications].
549
550 2017-10-25T08:00:11.22Z
551
552 1011
553
554
555
556 eth0
557 up
558
559
560
561
562
564 Figure 1: Push example
566 The following is an example of an on-change notification message for
567 the same subscription.
569
570 2017-10-25T08:22:33.44Z
571
573 89
574
575
576 0
577
578 edit1
579 replace
580 /ietf-interfaces:interfaces
581
582
584
585 eth0
586 down
587
588
589
590
591
592
593
594
596 Figure 2: Push example for on change
598 Of note in the above example is the 'patch-id' with a value of '0'.
599 Per [RFC8072], the 'patch-id' is an arbitrary string. With YANG
600 Push, the publisher SHOULD put into the 'patch-id' a counter starting
601 at '0' which increments with every 'push-change-update' generated for
602 a subscription. If used as a counter, this counter MUST be reset to
603 '0' anytime a resynchronization occurs (i.e., with the sending of a
604 'push-update'). Also if used as a counter, the counter MUST be reset
605 to '0' after passing a maximum value of '4294967295' (i.e. maximum
606 value that can be represented using uint32 data type). Such a
607 mechanism allows easy identification of lost or out-of-sequence
608 update records.
610 3.8. Subscription Management
612 The RPCs defined within
613 [I-D.draft-ietf-netconf-subscribed-notifications] have been enhanced
614 to support datastore subscription negotiation. Also, new error codes
615 have been added that are able to indicate why a datastore
616 subscription attempt has failed, along with new YANG-data that MAY be
617 used to include details on input parameters that might result in a
618 successful subsequent RPC invocation.
620 The establishment or modification of a datastore subscription can be
621 rejected for multiple reasons. This includes a too large subtree
622 request, or the inability of the publisher to push update records as
623 frequently as requested. In such cases, no subscription is
624 established. Instead, the subscription-result with the failure
625 reason is returned as part of the RPC response. As part of this
626 response, a set of alternative subscription parameters MAY be
627 returned that would likely have resulted in acceptance of the
628 subscription request. The subscriber may consider these as part of
629 future subscription attempts.
631 In the case of a rejected request for an establishment of a datastore
632 subscription, if there are hints, the hints SHOULD be transported
633 within a YANG-data "establish-subscription-datastore-error-info"
634 container inserted into the RPC error response, in lieu of the
635 "establish-subscription-stream-error-info" that is inserted in case
636 of a stream subscription.
638 Below is a tree diagram for "establish-subscription-datastore-error-
639 info". All tree diagrams used in this document follow the notation
640 defined in [RFC8340]
642 YANG-data establish-subscription-datastore-error-info
643 +--ro establish-subscription-datastore-error-info
644 +--ro reason? identityref
645 +--ro period-hint? centiseconds
646 +--ro filter-failure-hint? string
647 +--ro object-count-estimate? uint32
648 +--ro object-count-limit? uint32
649 +--ro kilobytes-estimate? uint32
650 +--ro kilobytes-limit? uint32
652 Figure 3: Tree diagram for establish-subscription-datastore-error-
653 info
655 Similarly, in the case of a rejected request for modification of a
656 datastore subscription, if there are hints, the hints SHOULD be
657 transported within a YANG-data "modify-subscription-datastore-error-
658 info" container inserted into the RPC error response, in lieu of the
659 "modify-subscription-stream-error-info" that is inserted in case of a
660 stream subscription.
662 Below is a tree diagram for "modify-subscription-datastore-error-
663 info".
665 YANG-data modify-subscription-datastore-error-info
666 +--ro modify-subscription-datasore-error-info
667 +--ro reason? identityref
668 +--ro period-hint? centiseconds
669 +--ro filter-failure-hint? string
670 +--ro object-count-estimate? uint32
671 +--ro object-count-limit? uint32
672 +--ro kilobytes-estimate? uint32
673 +--ro kilobytes-limit? uint32
675 Figure 4: Tree diagram for modify-subscription-datastore-error-info
677 3.9. Receiver Authorization
679 A receiver of subscription data MUST only be sent updates for which
680 it has proper authorization. A publisher MUST ensure that no non-
681 authorized data is included in push updates. To do so, it needs to
682 apply all corresponding checks applicable at the time of a specific
683 pushed update and if necessary silently remove any non-authorized
684 data from datastore subtrees. This enables YANG data pushed based on
685 subscriptions to be authorized equivalently to a regular data
686 retrieval (get) operation.
688 Each "push-update" and "push-change-update" MUST have access control
689 applied, as is depicted in the following diagram. This includes
690 validating that read access is permitted for any new objects selected
691 since the last notification message was sent to a particular
692 receiver. To accomplish this, implementations SHOULD support the
693 conceptual authorization model of [RFC8341], specifically section
694 3.2.4.
696 +-----------------+ +--------------------+
697 push-update or --> | datastore node | yes | add datastore node |
698 push-change-update | access allowed? | ---> | to update record |
699 +-----------------+ +--------------------+
701 Figure 5: Updated [RFC8341] access control for push updates
703 A publisher MUST allow for the possibility that a subscription's
704 selection filter references non-existent data or data that a receiver
705 is not allowed to access. Such support permits a receiver the
706 ability to monitor the entire lifecyle of some datastore tree without
707 needing to explicitly enumerate every individual datastore node. If,
708 after access control has been applied, there are no objects remaining
709 in an update record, then (in case of a periodic subscription) only a
710 single empty "push-update" notification MUST be sent. Empty "push-
711 change-update" messages (in case of an on-change subscription) MUST
712 NOT be sent. This is required to ensure that clients cannot
713 surreptitiously monitor objects that they do not have access to via
714 carefully crafted selection filters. By the same token, changes to
715 objects that are filtered MUST NOT affect any dampening intervals.
717 A publisher MAY choose to reject an establish-subscription request
718 which selects non-existent data or data that a receiver is not
719 allowed to access. As reason, the error identity "unchanging-
720 selection" SHOULD be returned. In addition, a publisher MAY choose
721 to terminate a dynamic subscription or suspend a configured receiver
722 when the authorization privileges of a receiver change, or the access
723 controls for subscribed objects change. In that case, the publisher
724 SHOULD include the error identity "unchanging-selection" as reason
725 when sending the "subscription-terminated" respectively
726 "subscription-suspended" notification. Such a capability enables the
727 publisher to avoid having to support continuous and total filtering
728 of a subscription's content for every update record. It also reduces
729 the possibility of leakage of access-controlled objects.
731 If read access into previously accessible nodes has been lost due to
732 a receiver permissions change, this SHOULD be reported as a patch
733 "delete" operation for on-change subscriptions. If not capable of
734 handling such receiver permission changes with such a "delete",
735 publisher implementations MUST force dynamic subscription re-
736 establishment or configured subscription re-initialization so that
737 appropriate filtering is installed.
739 3.10. On-Change Notifiable Datastore Nodes
741 In some cases, a publisher supporting on-change notifications may not
742 be able to push on-change updates for some object types. Reasons for
743 this might be that the value of the datastore node changes frequently
744 (e.g., [RFC8343]'s in-octets counter), that small object changes are
745 frequent and meaningless (e.g., a temperature gauge changing 0.1
746 degrees), or that the implementation is not capable of on-change
747 notification for a particular object.
749 In those cases, it will be important for client applications to have
750 a way to identify for which objects on-change notifications are
751 supported and for which ones they are not supported. Otherwise
752 client applications will have no way of knowing whether they can
753 indeed rely on their on-change subscription to provide them with the
754 change updates that they are interested in. In other words, if
755 implementations do not provide a solution and do not support
756 comprehensive on-change notifiability, clients of those
757 implementations will have no way of knowing what their on-change
758 subscription actually covers.
760 Implementations are therefore strongly advised to provide a solution
761 to this problem. For example, a solution might involve making
762 discoverable to clients which objects are on-change notifiable,
763 specified using another YANG data model. It is expected that such a
764 solution will be standardized at some point in the future. In the
765 meantime and until this occurs, implementations SHOULD provide their
766 own solution.
768 3.11. Other Considerations
770 3.11.1. Robustness and reliability
772 Particularly in the case of on-change updates, it is important that
773 these updates do not get lost. In case the loss of an update is
774 unavoidable, it is critical that the receiver is notified
775 accordingly.
777 Update records for a single subscription MUST NOT be resequenced
778 prior to transport.
780 It is conceivable that under certain circumstances, a publisher will
781 recognize that it is unable to include within an update record the
782 full set of objects desired per the terms of a subscription. In this
783 case, the publisher MUST act as follows.
785 o The publisher MUST set the "incomplete-update" flag on any update
786 record which is known to be missing information.
788 o The publisher MAY choose to suspend the subscription as per
789 [I-D.draft-ietf-netconf-subscribed-notifications]. If the
790 publisher does not create an update record at all, it MUST suspend
791 the subscription.
793 o When resuming an on-change subscription, the publisher SHOULD
794 generate a complete patch from the previous update record. If
795 this is not possible and the "sync-on-start" option is true for
796 the subscription, then the full datastore contents MAY be sent via
797 a "push-update" instead (effectively replacing the previous
798 contents). If neither of these are possible, then an "incomplete-
799 update" flag MUST be included on the next "push-change-update".
801 Note: It is perfectly acceptable to have a series of "push-change-
802 update" notifications (and even "push update" notifications) serially
803 queued at the transport layer awaiting transmission. It is not
804 required for the publisher to merge pending update records sent at
805 the same time.
807 On the receiver side, what action to take when a record with an
808 incomplete-update flag is received depends on the application. It
809 could simply choose to wait and do nothing. It could choose to
810 resynch, actively retrieving all subscribed information. It could
811 also choose to tear down the subscription and start a new one,
812 perhaps with a lesser scope that contains less objects.
814 3.11.2. Publisher capacity
816 It is far preferable to decline a subscription request than to accept
817 such a request when it cannot be met.
819 Whether or not a subscription can be supported will be determined by
820 a combination of several factors such as the subscription update
821 trigger (on-change or periodic), the period in which to report
822 changes (one second periods will consume more resources than one hour
823 periods), the amount of data in the datastore subtree that is being
824 subscribed to, and the number and combination of other subscriptions
825 that are concurrently being serviced.
827 4. A YANG Data Model for Management of Datastore Push Subscriptions
829 4.1. Overview
831 The YANG data model for datastore push subscriptions is depicted in
832 the following figures. The tree diagram that is used follows the
833 notation defined in [RFC8340]. New schema objects defined here
834 (i.e., beyond those from
835 [I-D.draft-ietf-netconf-subscribed-notifications]) are identified
836 with "yp". For the reader's convenience, in order to compact the
837 tree representation, some nodes that are defined in ietf-subscribed-
838 notifications and that are not essential to the understanding of the
839 data model defined here have been removed. This is indicated by
840 "..." in the diagram where applicable.
842 Because the tree diagram is quite large, its depiction is broken up
843 into several figures. The first figure depicts the augmentations
844 that are introduced in module ietf-yang-push to subscription
845 configuration specified in module ietf-subscribed-notifications.
847 module: ietf-subscribed-notifications
848 ...
849 +--rw filters
850 | ...
851 | +--rw yp:selection-filter* [filter-id]
852 | +--rw yp:filter-id string
853 | +--rw (yp:filter-spec)?
854 | +--:(yp:datastore-subtree-filter)
855 | | +--rw yp:datastore-subtree-filter?
856 | | {sn:subtree}?
857 | +--:(yp:datastore-xpath-filter)
858 | +--rw yp:datastore-xpath-filter? yang:xpath1.0
859 | {sn:xpath}?
860 +--rw subscriptions
861 +--rw subscription* [id]
862 | ...
863 +--rw (target)
864 | +--:(stream)
865 | | ...
866 | +--:(yp:datastore)
867 | +--rw yp:datastore identityref
868 | +--rw (yp:selection-filter)?
869 | +--:(yp:by-reference)
870 | | +--rw yp:selection-filter-ref
871 | | selection-filter-ref
872 | +--:(yp:within-subscription)
873 | +--rw (yp:filter-spec)?
874 | +--:(yp:datastore-subtree-filter)
875 | | +--rw yp:datastore-subtree-filter?
876 | | {sn:subtree}?
877 | +--:(yp:datastore-xpath-filter)
878 | +--rw yp:datastore-xpath-filter?
879 | yang:xpath1.0 {sn:xpath}?
880 | ...
881 +--rw (yp:update-trigger)
882 +--:(yp:periodic)
883 | +--rw yp:periodic!
884 | +--rw yp:period centiseconds
885 | +--rw yp:anchor-time? yang:date-and-time
886 +--:(yp:on-change) {on-change}?
887 +--rw yp:on-change!
888 +--rw yp:dampening-period? centiseconds
889 +--rw yp:sync-on-start? boolean
890 +--rw yp:excluded-change* change-type
892 Figure 6: Model structure: subscription configuration
894 The next figure depicts the augmentations of module ietf-yang-push
895 made to RPCs specified in module ietf-subscribed-notifications.
896 Specifically, these augmentations concern the establish-subscription
897 and modify-subscription RPCs, which are augmented with parameters
898 that are needed to specify datastore push subscriptions.
900 rpcs:
901 +---x establish-subscription
902 | +---w input
903 | | ...
904 | | +---w (target)
905 | | | +--:(stream)
906 | | | | ...
907 | | | +--:(yp:datastore)
908 | | | +---w yp:datastore identityref
909 | | | +---w (yp:selection-filter)?
910 | | | +--:(yp:by-reference)
911 | | | | +---w yp:selection-filter-ref
912 | | | | selection-filter-ref
913 | | | +--:(yp:within-subscription)
914 | | | +---w (yp:filter-spec)?
915 | | | +--:(yp:datastore-subtree-filter)
916 | | | | +---w yp:datastore-subtree-filter?
917 | | | | {sn:subtree}?
918 | | | +--:(yp:datastore-xpath-filter)
919 | | | +---w yp:datastore-xpath-filter?
920 | | | yang:xpath1.0 {sn:xpath}?
921 | | | ...
922 | | +---w (yp:update-trigger)
923 | | +--:(yp:periodic)
924 | | | +---w yp:periodic!
925 | | | +---w yp:period centiseconds
926 | | | +---w yp:anchor-time? yang:date-and-time
927 | | +--:(yp:on-change) {on-change}?
928 | | +---w yp:on-change!
929 | | +---w yp:dampening-period? centiseconds
930 | | +---w yp:sync-on-start? boolean
931 | | +---w yp:excluded-change* change-type
932 | +--ro output
933 | +--ro id subscription-id
934 | +--ro replay-start-time-revision? yang:date-and-time
935 | {replay}?
936 +---x modify-subscription
937 | +---w input
938 | ...
939 | +---w (target)
940 | | ...
942 | | +--:(yp:datastore)
943 | | +---w yp:datastore identityref
944 | | +---w (yp:selection-filter)?
945 | | +--:(yp:by-reference)
946 | | | +---w yp:selection-filter-ref
947 | | | selection-filter-ref
948 | | +--:(yp:within-subscription)
949 | | +---w (yp:filter-spec)?
950 | | +--:(yp:datastore-subtree-filter)
951 | | | +---w yp:datastore-subtree-filter?
952 | | | {sn:subtree}?
953 | | +--:(yp:datastore-xpath-filter)
954 | | +---w yp:datastore-xpath-filter?
955 | | yang:xpath1.0 {sn:xpath}?
956 | | ...
957 | +---w (yp:update-trigger)
958 | +--:(yp:periodic)
959 | | +---w yp:periodic!
960 | | +---w yp:period centiseconds
961 | | +---w yp:anchor-time? yang:date-and-time
962 | +--:(yp:on-change) {on-change}?
963 | +---w yp:on-change!
964 | +---w yp:dampening-period? centiseconds
965 +---x delete-subscription
966 | ...
967 +---x kill-subscription
968 ...
970 YANG-data (for placement into rpc error responses)
971 ...
973 Figure 7: Model structure: RPCs
975 The next figure depicts augmentations of module ietf-yang-push to the
976 notifications that are specified in module ietf-subscribed-
977 notifications. The augmentations allow the inclusion of subscription
978 configuration parameters that are specific to datastore push
979 subscriptions as part of subscription-started and subscription-
980 modified notifications.
982 notifications:
983 +---n replay-completed {replay}?
984 | ...
985 +---n subscription-completed
986 | ...
987 +---n subscription-started {configured}?
988 | | ...
989 | +--ro (target)
990 | | ...
991 | | +--:(yp:datastore)
992 | | +--ro yp:datastore identityref
993 | | +--ro (yp:selection-filter)?
994 | | +--:(yp:by-reference)
995 | | | +--ro yp:selection-filter-ref
996 | | | selection-filter-ref
997 | | +--:(yp:within-subscription)
998 | | +--ro (yp:filter-spec)?
999 | | +--:(yp:datastore-subtree-filter)
1000 | | | +--ro yp:datastore-subtree-filter?
1001 | | | {sn:subtree}?
1002 | | +--:(yp:datastore-xpath-filter)
1003 | | +--ro yp:datastore-xpath-filter?
1004 | | yang:xpath1.0 {sn:xpath}?
1005 | ...
1006 | +--ro (yp:update-trigger)
1007 | +--:(yp:periodic)
1008 | | +--ro yp:periodic!
1009 | | +--ro yp:period centiseconds
1010 | | +--ro yp:anchor-time? yang:date-and-time
1011 | +--:(yp:on-change) {on-change}?
1012 | +--ro yp:on-change!
1013 | +--ro yp:dampening-period? centiseconds
1014 | +--ro yp:sync-on-start? boolean
1015 | +--ro yp:excluded-change* change-type
1016 +---n subscription-resumed
1017 | ...
1018 +---n subscription-modified
1019 | ...
1020 | +--ro (target)
1021 | | | ...
1022 | | +--:(yp:datastore)
1023 | | +--ro yp:datastore identityref
1024 | | +--ro (yp:selection-filter)?
1025 | | +--:(yp:by-reference)
1026 | | | +--ro yp:selection-filter-ref
1027 | | | selection-filter-ref
1028 | | +--:(yp:within-subscription)
1029 | | +--ro (yp:filter-spec)?
1030 | | +--:(yp:datastore-subtree-filter)
1031 | | | +--ro yp:datastore-subtree-filter?
1032 | | | {sn:subtree}?
1033 | | +--:(yp:datastore-xpath-filter)
1034 | | +--ro yp:datastore-xpath-filter?
1035 | | yang:xpath1.0 {sn:xpath}?
1036 | ...
1037 | +--ro (yp:update-trigger)?
1038 | +--:(yp:periodic)
1039 | | +--ro yp:periodic!
1040 | | +--ro yp:period centiseconds
1041 | | +--ro yp:anchor-time? yang:date-and-time
1042 | +--:(yp:on-change) {on-change}?
1043 | +--ro yp:on-change!
1044 | +--ro yp:dampening-period? centiseconds
1045 | +--ro yp:sync-on-start? boolean
1046 | +--ro yp:excluded-change* change-type
1047 +---n subscription-terminated
1048 | ...
1049 +---n subscription-suspended
1050 ...
1052 Figure 8: Model structure: Notifications
1054 The final figure in this section depicts the parts of module ietf-
1055 yang-push that are not simply augmentations to another module, but
1056 that are newly introduced.
1058 module: ietf-yang-push
1060 rpcs:
1061 +---x resync-subscription {on-change}?
1062 +---w input
1063 +---w id sn:subscription-id
1065 YANG-data: (for placement into rpc error responses)
1066 +-- resync-subscription-error
1067 | +--ro reason? identityref
1068 | +--ro period-hint? centiseconds
1069 | +--ro filter-failure-hint? string
1070 | +--ro object-count-estimate? uint32
1071 | +--ro object-count-limit? uint32
1072 | +--ro kilobytes-estimate? uint32
1073 | +--ro kilobytes-limit? uint32
1074 +-- establish-subscription-error-datastore
1075 | +--ro reason? identityref
1076 | +--ro period-hint? centiseconds
1077 | +--ro filter-failure-hint? string
1078 | +--ro object-count-estimate? uint32
1079 | +--ro object-count-limit? uint32
1080 | +--ro kilobytes-estimate? uint32
1081 | +--ro kilobytes-limit? uint32
1082 +-- modify-subscription-error-datastore
1083 +--ro reason? identityref
1084 +--ro period-hint? centiseconds
1085 +--ro filter-failure-hint? string
1086 +--ro object-count-estimate? uint32
1087 +--ro object-count-limit? uint32
1088 +--ro kilobytes-estimate? uint32
1089 +--ro kilobytes-limit? uint32
1091 notifications:
1092 +---n push-update
1093 | +--ro id? sn:subscription-id
1094 | +--ro datastore-contents?
1095 | +--ro incomplete-update? empty
1096 +---n push-change-update {on-change}?
1097 +--ro id? sn:subscription-id
1098 +--ro datastore-changes
1099 | +--ro yang-patch
1100 | +--ro patch-id string
1101 | +--ro comment? string
1102 | +--ro edit* [edit-id]
1103 | +--ro edit-id string
1104 | +--ro operation enumeration
1105 | +--ro target target-resource-offset
1106 | +--ro point? target-resource-offset
1107 | +--ro where? enumeration
1108 | +--ro value?
1109 +--ro incomplete-update? empty
1111 Figure 9: Model structure (non-augmentation portions
1113 Selected components of the model are summarized below.
1115 4.2. Subscription Configuration
1117 Both configured and dynamic subscriptions are represented within the
1118 list "subscription". New parameters extending the basic subscription
1119 data model in [I-D.draft-ietf-netconf-subscribed-notifications]
1120 include:
1122 o The targeted datastore from which the selection is being made.
1123 The potential datastores include those from [RFC8341]. A platform
1124 may also choose to support a custom datastore.
1126 o A selection filter identifying YANG nodes of interest within a
1127 datastore. Filter contents are specified via a reference to an
1128 existing filter, or via an in-line definition for only that
1129 subscription. Referenced filters allows an implementation to
1130 avoid evaluating filter acceptability during a dynamic
1131 subscription request. The case statement differentiates the
1132 options.
1134 o For periodic subscriptions, triggered updates will occur at the
1135 boundaries of a specified time interval. These boundaries can be
1136 calculated from the periodic parameters:
1138 * a "period" which defines the duration between push updates.
1140 * an "anchor-time"; update intervals fall on the points in time
1141 that are a multiple of a "period" from an "anchor-time". If
1142 "anchor-time" is not provided, then the "anchor-time" MUST be
1143 set with the creation time of the initial update record.
1145 o For on-change subscriptions, assuming any dampening period has
1146 completed, triggering occurs whenever a change in the subscribed
1147 information is detected. On-change subscriptions have more
1148 complex semantics that is guided by its own set of parameters:
1150 * a "dampening-period" specifies the interval that must pass
1151 before a successive update for the subscription is sent. If no
1152 dampening period is in effect, the update is sent immediately.
1153 If a subsequent change is detected, another update is only sent
1154 once the dampening period has passed for this subscription.
1156 * an "excluded-change" parameter which allows restriction of the
1157 types of changes for which updates should be sent (e.g., only
1158 add to an update record on object creation).
1160 * a "sync-on-start" specifies whether a complete update with all
1161 the subscribed data is to be sent at the beginning of a
1162 subscription.
1164 4.3. YANG Notifications
1166 4.3.1. State Change Notifications
1168 Subscription state notifications and mechanism are reused from
1169 [I-D.draft-ietf-netconf-subscribed-notifications]. Notifications
1170 "subscription-started" and "subscription-modified" have been
1171 augmented to include the datastore specific objects.
1173 4.3.2. Notifications for Subscribed Content
1175 Along with the subscribed content, there are other objects which
1176 might be part of a "push-update" or "push-change-update"
1177 notification.
1179 An "id" (that identifies the subscription) MUST be transported along
1180 with the subscribed contents. This allows a receiver to
1181 differentiate which subscription resulted in a particular update
1182 record.
1184 A "time-of-update" which represents the time an update record
1185 snapshot was generated. A receiver MAY assume that at this point in
1186 time a publisher's objects have the values that were pushed.
1188 An "incomplete-update" leaf. This leaf indicates that not all
1189 changes which have occurred since the last update are actually
1190 included with this update. In other words, the publisher has failed
1191 to fulfill its full subscription obligations. (For example a
1192 datastore was unable to provide the full set of datastore nodes to a
1193 publisher process.) To facilitate re-synchronization of on-change
1194 subscriptions, a publisher MAY subsequently send a "push-update"
1195 containing a full selection snapshot of subscribed data.
1197 4.4. YANG RPCs
1199 YANG-Push subscriptions are established, modified, and deleted using
1200 RPCs augmented from
1201 [I-D.draft-ietf-netconf-subscribed-notifications].
1203 4.4.1. Establish-subscription RPC
1205 The subscriber sends an establish-subscription RPC with the
1206 parameters in section 3.1. An example might look like:
1208
1210
1213
1215 ds:operational
1216
1217
1219 /ex:foo
1220
1221
1222 500
1223
1224
1225
1227 Figure 10: Establish-subscription RPC
1229 A positive response includes the "id" of the accepted subscription.
1230 In that case a publisher may respond:
1232
1234
1236 52
1237
1238
1240 Figure 11: Establish-subscription positive RPC response
1242 A subscription can be rejected for multiple reasons, including the
1243 lack of authorization to establish a subscription, no capacity to
1244 serve the subscription at the publisher, or the inability of the
1245 publisher to select datastore content at the requested cadence.
1247 If a request is rejected because the publisher is not able to serve
1248 it, the publisher SHOULD include in the returned error hints which
1249 help a subscriber understand subscription parameters might have been
1250 accepted for the request. These hints would be included within the
1251 YANG-data structure "establish-subscription-error-datastore".
1252 However even with these hints, there are no guarantee that subsequent
1253 requests will in fact be accepted.
1255 The specific parameters to be returned as part of the RPC error
1256 response depend on the specific transport that is used to manage the
1257 subscription. For NETCONF, those parameters are defined in
1258 [I-D.draft-ietf-netconf-netconf-event-notifications]. For example,
1259 for the following NETCONF request:
1261
1263
1267
1269 ds:operational
1270
1271
1273 /ex:foo
1274
1275
1276 100
1277
1278
1279
1281 Figure 12: Establish-subscription request example 2
1283 a publisher that cannot serve on-change updates but periodic updates
1284 might return the following NETCONF response:
1286
1289
1290 application
1291 operation-failed
1292 error
1293 /yp:periodic/yp:period
1294
1295
1296 yp:on-change-unsupported
1297
1298
1299
1300
1302 Figure 13: Establish-subscription error response example 2
1304 4.4.2. Modify-subscription RPC
1306 The subscriber MAY invoke the "modify-subscription" RPC for a
1307 subscription it previously established. The subscriber will include
1308 newly desired values in the "modify-subscription" RPC. Parameters
1309 not included MUST remain unmodified. Below is an example where a
1310 subscriber attempts to modify the period and datastore XPath filter
1311 of a subscription using NETCONF.
1313
1315
1319 1011
1320
1322 ds:operational
1323
1324
1326 /ex:bar
1327
1328
1329 250
1330
1331
1332
1334 Figure 14: Modify subscription request
1336 The publisher MUST respond to the subscription modification request.
1337 If the request is rejected, the existing subscription is left
1338 unchanged, and the publisher MUST send an RPC error response. This
1339 response might have hints encapsulated within the YANG-data structure
1340 "modify-subscription-error-datastore". A subscription MAY be
1341 modified multiple times.
1343 The specific parameters to be returned in as part of the RPC error
1344 response depend on the specific transport that is used to manage the
1345 subscription. For NETCONF, those parameters are specified in
1346 [I-D.draft-ietf-netconf-netconf-event-notifications].
1348 A configured subscription cannot be modified using "modify-
1349 subscription" RPC. Instead, the configuration needs to be edited as
1350 needed.
1352 4.4.3. Delete-subscription RPC
1354 To stop receiving updates from a subscription and effectively delete
1355 a subscription that had previously been established using an
1356 "establish-subscription" RPC, a subscriber can send a "delete-
1357 subscription" RPC, which takes as only input the subscription's "id".
1358 This RPC is unmodified from
1359 [I-D.draft-ietf-netconf-subscribed-notifications].
1361 4.4.4. Resync-subscription RPC
1363 This RPC is supported only for on-change subscriptions previously
1364 established using an "establish-subscription" RPC. For example:
1366
1368 1011
1371
1372
1374 Figure 15: Resync subscription
1376 On receipt, a publisher must either accept the request and quickly
1377 follow with a "push-update", or send an appropriate error within an
1378 rpc error response. Within an error response, the publisher MAY
1379 include supplemental information about the reasons within the YANG-
1380 data structure "resync-subscription-error".
1382 4.4.5. YANG Module Synchronization
1384 To make subscription requests, the subscriber needs to know the YANG
1385 datastore schemas used by the publisher, which are available via the
1386 YANG Library module, ietf-yang-library.yang from [RFC8525]. The
1387 receiver is expected to know the YANG library information before
1388 starting a subscription.
1390 The set of modules, revisions, features, and deviations can change at
1391 run-time (if supported by the publisher implementation). For this
1392 purpose, the YANG library provides a simple "yang-library-change"
1393 notification that informs the subscriber that the library has
1394 changed. In this case, a subscription may need to be updated to take
1395 the updates into account. The receiver may also need to be informed
1396 of module changes in order to process updates regarding datastore
1397 nodes from changed modules correctly.
1399 5. YANG Module
1401 This YANG module imports typedefs from [RFC6991], identities from
1402 [RFC8342], the YANG-data extension from [RFC8040], and the yang-patch
1403 grouping from [RFC8072]. In addition, it imports and augments many
1404 definitions from [I-D.draft-ietf-netconf-subscribed-notifications].
1406 file "ietf-yang-push@2019-04-30.yang"
1407 module ietf-yang-push {
1408 yang-version 1.1;
1409 namespace "urn:ietf:params:xml:ns:yang:ietf-yang-push";
1410 prefix yp;
1412 import ietf-yang-types {
1413 prefix yang;
1414 reference
1415 "RFC 6991: Common YANG Data Types";
1416 }
1417 import ietf-subscribed-notifications {
1418 prefix sn;
1419 reference
1420 "draft-ietf-netconf-subscribed-notifications:
1421 Customized Subscriptions to a Publisher's Event Streams
1422 NOTE TO RFC Editor: Please replace above reference to
1423 draft-ietf-netconf-subscribed-notifications with RFC number
1424 when published (i.e. RFC xxxx).";
1425 }
1426 import ietf-datastores {
1427 prefix ds;
1428 reference
1429 "RFC 8342: Network Management Datastore Architecture (NMDA)";
1430 }
1431 import ietf-restconf {
1432 prefix rc;
1433 reference
1434 "RFC 8040: RESTCONF Protocol";
1435 }
1436 import ietf-yang-patch {
1437 prefix ypatch;
1438 reference
1439 "RFC 8072: YANG Patch Media Type";
1440 }
1442 organization
1443 "IETF NETCONF Working Group";
1444 contact
1445 "WG Web:
1446 WG List:
1448 Editor: Alexander Clemm
1449
1450 Editor: Eric Voit
1451
1452 Editor: Alberto Gonzalez Prieto
1453
1454 Editor: Ambika Prasad Tripathy
1455
1456 Editor: Einar Nilsen-Nygaard
1457
1458 Editor: Andy Bierman
1459
1460 Editor: Balazs Lengyel
1461 ";
1462 description
1463 "This module contains YANG specifications for YANG push.
1465 The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
1466 NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED',
1467 'MAY', and 'OPTIONAL' in this document are to be interpreted as
1468 described in BCP 14 (RFC 2119) (RFC 8174) when, and only when,
1469 they appear in all capitals, as shown here.
1471 Copyright (c) 2019 IETF Trust and the persons identified as
1472 authors of the code. All rights reserved.
1474 Redistribution and use in source and binary forms, with or
1475 without modification, is permitted pursuant to, and subject to
1476 the license terms contained in, the Simplified BSD License set
1477 forth in Section 4.c of the IETF Trust's Legal Provisions
1478 Relating to IETF Documents
1479 (https://trustee.ietf.org/license-info).
1481 This version of this YANG module is part of RFC XXXX;
1482 see the RFC itself for full legal notices.";
1484 // RFC Ed.: replace XXXX with actual RFC number and remove this
1485 // note.
1487 revision 2019-04-30 {
1488 description
1489 "Initial revision.
1490 NOTE TO RFC EDITOR:
1491 (1)Please replace the above revision date to
1492 the date of RFC publication when published.
1493 (2) Please replace the date in the file name
1494 (ietf-yang-push@2019-04-30.yang) to the date of RFC
1495 publication.
1496 (3) Please replace the following reference to
1497 draft-ietf-netconf-yang-push-23 with RFC number when
1498 published (i.e. RFC xxxx).";
1499 reference
1500 "draft-ietf-netconf-yang-push-23";
1501 }
1503 /*
1504 * FEATURES
1505 */
1507 feature on-change {
1508 description
1509 "This feature indicates that on-change triggered subscriptions
1510 are supported.";
1511 }
1513 /*
1514 * IDENTITIES
1515 */
1517 /* Error type identities for datastore subscription */
1519 identity resync-subscription-error {
1520 description
1521 "Problem found while attempting to fulfill an
1522 'resync-subscription' RPC request.";
1523 }
1525 identity cant-exclude {
1526 base sn:establish-subscription-error;
1527 description
1528 "Unable to remove the set of 'excluded-changes'. This means
1529 the publisher is unable to restrict 'push-change-update's to
1530 just the change types requested for this subscription.";
1531 }
1533 identity datastore-not-subscribable {
1534 base sn:establish-subscription-error;
1535 base sn:subscription-terminated-reason;
1536 description
1537 "This is not a subscribable datastore.";
1538 }
1540 identity no-such-subscription-resync {
1541 base resync-subscription-error;
1542 description
1543 "Referenced subscription doesn't exist. This may be as a result
1544 of a non-existent subscription ID, an ID which belongs to
1545 another subscriber, or an ID for configured subscription.";
1546 }
1548 identity on-change-unsupported {
1549 base sn:establish-subscription-error;
1550 description
1551 "On-change is not supported for any objects which are
1552 selectable by this filter.";
1553 }
1555 identity on-change-sync-unsupported {
1556 base sn:establish-subscription-error;
1557 description
1558 "Neither sync on start nor resynchronization are supported for
1559 this subscription. This error will be used for two
1560 reasons. First if an 'establish-subscription' RPC includes
1561 'sync-on-start', yet the publisher can't support sending a
1562 'push-update' for this subscription for reasons other than
1563 'on-change-unsupported' or 'sync-too-big'. And second, if the
1564 'resync-subscription' RPC is invoked either for an existing
1565 periodic subscription, or for an on-change subscription which
1566 can't support resynchronization.";
1567 }
1569 identity period-unsupported {
1570 base sn:establish-subscription-error;
1571 base sn:modify-subscription-error;
1572 base sn:subscription-suspended-reason;
1573 description
1574 "Requested time period or dampening-period is too short. This
1575 can be for both periodic and on-change subscriptions (with or
1576 without dampening.) Hints suggesting alternative periods may
1577 be returned as supplemental information.";
1578 }
1580 identity update-too-big {
1581 base sn:establish-subscription-error;
1582 base sn:modify-subscription-error;
1583 base sn:subscription-suspended-reason;
1584 description
1585 "Periodic or on-change push update datatrees exceed a maximum
1586 size limit. Hints on estimated size of what was too big may
1587 be returned as supplemental information.";
1588 }
1589 identity sync-too-big {
1590 base sn:establish-subscription-error;
1591 base sn:modify-subscription-error;
1592 base resync-subscription-error;
1593 base sn:subscription-suspended-reason;
1594 description
1595 "Sync-on-start or resynchronization datatree exceeds a maximum
1596 size limit. Hints on estimated size of what was too big may
1597 be returned as supplemental information.";
1598 }
1600 identity unchanging-selection {
1601 base sn:establish-subscription-error;
1602 base sn:modify-subscription-error;
1603 base sn:subscription-terminated-reason;
1604 description
1605 "Selection filter is unlikely to ever select datatree nodes.
1606 This means that based on the subscriber's current access
1607 rights, the publisher recognizes that the selection filter is
1608 unlikely to ever select datatree nodes which change. Examples
1609 for this might be that node or subtree doesn't exist, read
1610 access is not permitted for a receiver, or static objects that
1611 only change at reboot have been chosen.";
1612 }
1614 /*
1615 * TYPE DEFINITIONS
1616 */
1618 typedef change-type {
1619 type enumeration {
1620 enum create {
1621 description
1622 "A change that refers to the creation of a new datastore
1623 node.";
1624 }
1625 enum delete {
1626 description
1627 "A change that refers to the deletion of a datastore
1628 node.";
1629 }
1630 enum insert {
1631 description
1632 "A change that refers to the insertion of a new
1633 user-ordered datastore node.";
1634 }
1635 enum move {
1636 description
1637 "A change that refers to a reordering of the target
1638 datastore node.";
1639 }
1640 enum replace {
1641 description
1642 "A change that refers to a replacement of the target
1643 datastore node's value.";
1644 }
1645 }
1646 description
1647 "Specifies different types of datastore changes.
1649 This type is based on the edit operations defined for YANG
1650 Patch, with the difference that it is valid for a receiver to
1651 process an update record which performs a create operation on
1652 a datastore node the receiver believes exists, or to process a
1653 delete on a datastore node the receiver believes is missing.";
1654 reference
1655 "RFC 8072: YANG Patch Media Type, section 2.5";
1656 }
1658 typedef selection-filter-ref {
1659 type leafref {
1660 path "/sn:filters/yp:selection-filter/yp:filter-id";
1661 }
1662 description
1663 "This type is used to reference a selection filter.";
1664 }
1666 typedef centiseconds {
1667 type uint32;
1668 description
1669 "A period of time, measured in units of 0.01 seconds.";
1670 }
1672 /*
1673 * GROUP DEFINITIONS
1674 */
1676 grouping datastore-criteria {
1677 description
1678 "A grouping to define criteria for which selected objects
1679 from a targeted datastore should be included in push
1680 updates.";
1681 leaf datastore {
1682 type identityref {
1683 base ds:datastore;
1685 }
1686 mandatory true;
1687 description
1688 "Datastore from which to retrieve data.";
1689 }
1690 uses selection-filter-objects;
1691 }
1693 grouping selection-filter-types {
1694 description
1695 "This grouping defines the types of selectors for objects
1696 from a datastore.";
1697 choice filter-spec {
1698 description
1699 "The content filter specification for this request.";
1700 anydata datastore-subtree-filter {
1701 if-feature "sn:subtree";
1702 description
1703 "This parameter identifies the portions of the
1704 target datastore to retrieve.";
1705 reference
1706 "RFC 6241: Network Configuration Protocol, Section 6.";
1707 }
1708 leaf datastore-xpath-filter {
1709 if-feature "sn:xpath";
1710 type yang:xpath1.0;
1711 description
1712 "This parameter contains an XPath expression identifying
1713 the portions of the target datastore to retrieve.
1715 If the expression returns a node-set, all nodes in the
1716 node-set are selected by the filter. Otherwise, if the
1717 expression does not return a node-set, the filter
1718 doesn't select any nodes.
1720 The expression is evaluated in the following XPath
1721 context:
1723 o The set of namespace declarations is the set of prefix
1724 and namespace pairs for all YANG modules implemented
1725 by the server, where the prefix is the YANG module
1726 name and the namespace is as defined by the
1727 'namespace' statement in the YANG module.
1729 If the leaf is encoded in XML, all namespace
1730 declarations in scope on the 'stream-xpath-filter'
1731 leaf element are added to the set of namespace
1732 declarations. If a prefix found in the XML is
1733 already present in the set of namespace declarations,
1734 the namespace in the XML is used.
1736 o The set of variable bindings is empty.
1738 o The function library is the core function library, and
1739 the XPath functions defined in section 10 in RFC 7950.
1741 o The context node is the root node of the target
1742 datastore.";
1743 }
1744 }
1745 }
1747 grouping selection-filter-objects {
1748 description
1749 "This grouping defines a selector for objects from a
1750 datastore.";
1751 choice selection-filter {
1752 description
1753 "The source of the selection filter applied to the
1754 subscription. This will come either referenced from a global
1755 list, or be provided within the subscription itself.";
1756 case by-reference {
1757 description
1758 "Incorporate a filter that has been configured
1759 separately.";
1760 leaf selection-filter-ref {
1761 type selection-filter-ref;
1762 mandatory true;
1763 description
1764 "References an existing selection filter which is to be
1765 applied to the subscription.";
1766 }
1767 }
1768 case within-subscription {
1769 description
1770 "Local definition allows a filter to have the same
1771 lifecycle as the subscription.";
1772 uses selection-filter-types;
1773 }
1774 }
1775 }
1777 grouping update-policy-modifiable {
1778 description
1779 "This grouping describes the datastore specific subscription
1780 conditions that can be changed during the lifetime of the
1781 subscription.";
1782 choice update-trigger {
1783 description
1784 "Defines necessary conditions for sending an event record to
1785 the subscriber.";
1786 case periodic {
1787 container periodic {
1788 presence "indicates a periodic subscription";
1789 description
1790 "The publisher is requested to notify periodically the
1791 current values of the datastore as defined by the
1792 selection filter.";
1793 leaf period {
1794 type centiseconds;
1795 mandatory true;
1796 description
1797 "Duration of time which should occur between periodic
1798 push updates, in one hundredths of a second.";
1799 }
1800 leaf anchor-time {
1801 type yang:date-and-time;
1802 description
1803 "Designates a timestamp before or after which a series
1804 of periodic push updates are determined. The next
1805 update will take place at a whole multiple interval
1806 from the anchor time. For example, for an anchor time
1807 is set for the top of a particular minute and a period
1808 interval of a minute, updates will be sent at the top
1809 of every minute this subscription is active.";
1810 }
1811 }
1812 }
1813 case on-change {
1814 if-feature "on-change";
1815 container on-change {
1816 presence "indicates an on-change subscription";
1817 description
1818 "The publisher is requested to notify changes in values
1819 in the datastore subset as defined by a selection
1820 filter.";
1821 leaf dampening-period {
1822 type centiseconds;
1823 default "0";
1824 description
1825 "Specifies the minimum interval between the assembly of
1826 successive update records for a single receiver of a
1827 subscription. Whenever subscribed objects change, and
1828 a dampening period interval (which may be zero) has
1829 elapsed since the previous update record creation for
1830 a receiver, then any subscribed objects and properties
1831 which have changed since the previous update record
1832 will have their current values marshalled and placed
1833 into a new update record.";
1834 }
1835 }
1836 }
1837 }
1838 }
1840 grouping update-policy {
1841 description
1842 "This grouping describes the datastore-specific subscription
1843 conditions of a subscription.";
1844 uses update-policy-modifiable {
1845 augment "update-trigger/on-change/on-change" {
1846 description
1847 "Includes objects not modifiable once subscription is
1848 established.";
1849 leaf sync-on-start {
1850 type boolean;
1851 default "true";
1852 description
1853 "When this object is set to false, it restricts an
1854 on-change subscription from sending push-update
1855 notifications. When false, pushing a full selection per
1856 the terms of the selection filter MUST NOT be done for
1857 this subscription. Only updates about changes,
1858 i.e. only push-change-update notifications are sent.
1859 When true (default behavior), in order to facilitate a
1860 receiver's synchronization, a full update is sent when
1861 the subscription starts using a push-update
1862 notification. After that, push-change-update
1863 notifications are exclusively sent unless the publisher
1864 chooses to resync the subscription via a new push-update
1865 notification.";
1866 }
1867 leaf-list excluded-change {
1868 type change-type;
1869 description
1870 "Use to restrict which changes trigger an update. For
1871 example, if modify is excluded, only creation and
1872 deletion of objects is reported.";
1873 }
1874 }
1875 }
1876 }
1877 grouping hints {
1878 description
1879 "Parameters associated with some error for a subscription
1880 made upon a datastore.";
1881 leaf period-hint {
1882 type centiseconds;
1883 description
1884 "Returned when the requested time period is too short. This
1885 hint can assert a viable period for either a periodic push
1886 cadence or an on-change dampening interval.";
1887 }
1888 leaf filter-failure-hint {
1889 type string;
1890 description
1891 "Information describing where and/or why a provided filter
1892 was unsupportable for a subscription.";
1893 }
1894 leaf object-count-estimate {
1895 type uint32;
1896 description
1897 "If there are too many objects which could potentially be
1898 returned by the selection filter, this identifies the
1899 estimate of the number of objects which the filter would
1900 potentially pass.";
1901 }
1902 leaf object-count-limit {
1903 type uint32;
1904 description
1905 "If there are too many objects which could be returned by
1906 the selection filter, this identifies the upper limit of
1907 the publisher's ability to service for this subscription.";
1908 }
1909 leaf kilobytes-estimate {
1910 type uint32;
1911 description
1912 "If the returned information could be beyond the capacity
1913 of the publisher, this would identify the data size which
1914 could result from this selection filter.";
1915 }
1916 leaf kilobytes-limit {
1917 type uint32;
1918 description
1919 "If the returned information would be beyond the capacity
1920 of the publisher, this identifies the upper limit of the
1921 publisher's ability to service for this subscription.";
1922 }
1923 }
1924 /*
1925 * RPCs
1926 */
1928 rpc resync-subscription {
1929 if-feature "on-change";
1930 description
1931 "This RPC allows a subscriber of an active on-change
1932 subscription to request a full push of objects.
1934 A successful invocation results in a push-update of all
1935 datastore nodes that the subscriber is permitted to access.
1936 This RPC can only be invoked on the same session on which the
1937 subscription is currently active. In case of an error, a
1938 resync-subscription-error is sent as part of an error
1939 response.";
1940 input {
1941 leaf id {
1942 type sn:subscription-id;
1943 mandatory true;
1944 description
1945 "Identifier of the subscription that is to be resynced.";
1946 }
1947 }
1948 }
1950 rc:yang-data resync-subscription-error {
1951 container resync-subscription-error {
1952 description
1953 "If a 'resync-subscription' RPC fails, the subscription is
1954 not resynced and the RPC error response MUST indicate the
1955 reason for this failure. This YANG-data MAY be inserted as
1956 structured data within a subscription's RPC error response
1957 to indicate the failure reason.";
1958 leaf reason {
1959 type identityref {
1960 base resync-subscription-error;
1961 }
1962 mandatory true;
1963 description
1964 "Indicates the reason why the publisher has declined a
1965 request for subscription resynchronization.";
1966 }
1967 uses hints;
1968 }
1969 }
1971 augment "/sn:establish-subscription/sn:input" {
1972 description
1973 "This augmentation adds additional subscription parameters
1974 that apply specifically to datastore updates to RPC input.";
1975 uses update-policy;
1976 }
1978 augment "/sn:establish-subscription/sn:input/sn:target" {
1979 description
1980 "This augmentation adds the datastore as a valid target
1981 for the subscription to RPC input.";
1982 case datastore {
1983 description
1984 "Information specifying the parameters of an request for a
1985 datastore subscription.";
1986 uses datastore-criteria;
1987 }
1988 }
1990 rc:yang-data establish-subscription-datastore-error-info {
1991 container establish-subscription-datastore-error-info {
1992 description
1993 "If any 'establish-subscription' RPC parameters are
1994 unsupportable against the datastore, a subscription is not
1995 created and the RPC error response MUST indicate the reason
1996 why the subscription failed to be created. This YANG-data
1997 MAY be inserted as structured data within a subscription's
1998 RPC error response to indicate the failure reason. This
1999 YANG-data MUST be inserted if hints are to be provided back
2000 to the subscriber.";
2001 leaf reason {
2002 type identityref {
2003 base sn:establish-subscription-error;
2004 }
2005 description
2006 "Indicates the reason why the subscription has failed to
2007 be created to a targeted datastore.";
2008 }
2009 uses hints;
2010 }
2011 }
2013 augment "/sn:modify-subscription/sn:input" {
2014 description
2015 "This augmentation adds additional subscription parameters
2016 specific to datastore updates.";
2017 uses update-policy-modifiable;
2018 }
2019 augment "/sn:modify-subscription/sn:input/sn:target" {
2020 description
2021 "This augmentation adds the datastore as a valid target
2022 for the subscription to RPC input.";
2023 case datastore {
2024 description
2025 "Information specifying the parameters of an request for a
2026 datastore subscription.";
2027 uses datastore-criteria;
2028 }
2029 }
2031 rc:yang-data modify-subscription-datastore-error-info {
2032 container modify-subscription-datastore-error-info {
2033 description
2034 "This YANG-data MAY be provided as part of a subscription's
2035 RPC error response when there is a failure of a
2036 'modify-subscription' RPC which has been made against a
2037 datastore. This YANG-data MUST be used if hints are to be
2038 provides back to the subscriber.";
2039 leaf reason {
2040 type identityref {
2041 base sn:modify-subscription-error;
2042 }
2043 description
2044 "Indicates the reason why the subscription has failed to
2045 be modified.";
2046 }
2047 uses hints;
2048 }
2049 }
2051 /*
2052 * NOTIFICATIONS
2053 */
2055 notification push-update {
2056 description
2057 "This notification contains a push update, containing data
2058 subscribed to via a subscription. This notification is sent
2059 for periodic updates, for a periodic subscription. It can
2060 also be used for synchronization updates of an on-change
2061 subscription. This notification shall only be sent to
2062 receivers of a subscription. It does not constitute a
2063 general-purpose notification that would be subscribable as
2064 part of the NETCONF event stream by any receiver.";
2065 leaf id {
2066 type sn:subscription-id;
2067 description
2068 "This references the subscription which drove the
2069 notification to be sent.";
2070 }
2071 anydata datastore-contents {
2072 description
2073 "This contains the updated data. It constitutes a snapshot
2074 at the time-of-update of the set of data that has been
2075 subscribed to. The snapshot corresponds to the same
2076 snapshot that would be returned in a corresponding get
2077 operation with the same selection filter parameters
2078 applied.";
2079 }
2080 leaf incomplete-update {
2081 type empty;
2082 description
2083 "This is a flag which indicates that not all datastore
2084 nodes subscribed to are included with this update. In
2085 other words, the publisher has failed to fulfill its full
2086 subscription obligations, and despite its best efforts is
2087 providing an incomplete set of objects.";
2088 }
2089 }
2091 notification push-change-update {
2092 if-feature "on-change";
2093 description
2094 "This notification contains an on-change push update. This
2095 notification shall only be sent to the receivers of a
2096 subscription; it does not constitute a general-purpose
2097 notification.";
2098 leaf id {
2099 type sn:subscription-id;
2100 description
2101 "This references the subscription which drove the
2102 notification to be sent.";
2103 }
2104 container datastore-changes {
2105 description
2106 "This contains the set of datastore changes of the target
2107 datastore starting at the time of the previous update, per
2108 the terms of the subscription.";
2109 uses ypatch:yang-patch;
2110 }
2111 leaf incomplete-update {
2112 type empty;
2113 description
2114 "The presence of this object indicates not all changes which
2115 have occurred since the last update are included with this
2116 update. In other words, the publisher has failed to
2117 fulfill its full subscription obligations, for example in
2118 cases where it was not able to keep up with a change
2119 burst.";
2120 }
2121 }
2123 augment "/sn:subscription-started" {
2124 description
2125 "This augmentation adds datastore-specific objects to
2126 the notification that a subscription has started.";
2127 uses update-policy;
2128 }
2130 augment "/sn:subscription-started/sn:target" {
2131 description
2132 "This augmentation allows the datastore to be included as
2133 part of the notification that a subscription has started.";
2134 case datastore {
2135 uses datastore-criteria {
2136 refine "selection-filter/within-subscription" {
2137 description
2138 "Specifies the selection filter and where it originated
2139 from. If the 'selection-filter-ref' is populated, the
2140 filter within the subscription came from the 'filters'
2141 container. Otherwise it is populated in-line as part of
2142 the subscription itself.";
2143 }
2144 }
2145 }
2146 }
2148 augment "/sn:subscription-modified" {
2149 description
2150 "This augmentation adds datastore-specific objects to
2151 the notification that a subscription has been modified.";
2152 uses update-policy;
2153 }
2155 augment "/sn:subscription-modified/sn:target" {
2156 description
2157 "This augmentation allows the datastore to be included as
2158 part of the notification that a subscription has been
2159 modified.";
2160 case datastore {
2161 uses datastore-criteria {
2162 refine "selection-filter/within-subscription" {
2163 description
2164 "Specifies where the selection filter, and where it came
2165 from within the subscription and then populated within
2166 this notification. If the 'selection-filter-ref' is
2167 populated, the filter within the subscription came from
2168 the 'filters' container. Otherwise it is populated
2169 in-line as part of the subscription itself.";
2170 }
2171 }
2172 }
2173 }
2175 /*
2176 * DATA NODES
2177 */
2179 augment "/sn:filters" {
2180 description
2181 "This augmentation allows the datastore to be included as part
2182 of the selection filtering criteria for a subscription.";
2183 list selection-filter {
2184 key "filter-id";
2185 description
2186 "A list of pre-configured filters that can be applied
2187 to datastore subscriptions.";
2188 leaf filter-id {
2189 type string;
2190 description
2191 "An identifier to differentiate between selection
2192 filters.";
2193 }
2194 uses selection-filter-types;
2195 }
2196 }
2198 augment "/sn:subscriptions/sn:subscription" {
2199 when 'yp:datastore';
2200 description
2201 "This augmentation adds many datastore specific objects to a
2202 subscription.";
2203 uses update-policy;
2204 }
2206 augment "/sn:subscriptions/sn:subscription/sn:target" {
2207 description
2208 "This augmentation allows the datastore to be included as
2209 part of the selection filtering criteria for a subscription.";
2210 case datastore {
2211 uses datastore-criteria;
2212 }
2213 }
2214 }
2216
2218 6. IANA Considerations
2220 This document registers the following namespace URI in the "IETF XML
2221 Registry" [RFC3688]:
2223 URI: urn:ietf:params:xml:ns:yang:ietf-yang-push
2224 Registrant Contact: The IESG.
2225 XML: N/A; the requested URI is an XML namespace.
2227 This document registers the following YANG module in the "YANG Module
2228 Names" registry [RFC6020]:
2230 Name: ietf-yang-push
2231 Namespace: urn:ietf:params:xml:ns:yang:ietf-yang-push
2232 Prefix: yp
2233 Reference: draft-ietf-netconf-yang-push-21.txt (RFC form)
2235 7. Security Considerations
2237 The YANG module specified in this document defines a schema for data
2238 that is designed to be accessed via network management protocols such
2239 as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer
2240 is the secure transport layer, and the mandatory-to-implement secure
2241 transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer
2242 is HTTPS, and the mandatory-to-implement secure transport is TLS
2243 [RFC8446].
2245 The Network Configuration Access Control Model (NACM) [RFC8341]
2246 provides the means to restrict access for particular NETCONF or
2247 RESTCONF users to a preconfigured subset of all available NETCONF or
2248 RESTCONF protocol operations and content.
2250 There are a number of data nodes defined in this YANG module that are
2251 writable/creatable/deletable (i.e., config true, which is the
2252 default). These data nodes may be considered sensitive or vulnerable
2253 in some network environments. Write operations (e.g., edit-config)
2254 to these data nodes without proper protection can have a negative
2255 effect on network operations. These are the subtrees and data nodes
2256 and their sensitivity/vulnerability. (It should be noted that the
2257 YANG module augments the YANG module from
2259 [I-D.draft-ietf-netconf-subscribed-notifications]. All security
2260 considerations that are listed there are relevant also for datastore
2261 subscriptions. In the following, we focus on the data nodes that are
2262 newly introduced here.)
2264 o Subtree "selection-filter" under container "filters": This subtree
2265 allows to specify which objects or subtrees to include in a
2266 datastore subscription. An attacker could attempt to modify the
2267 filter. For example, the filter might be modified to result in
2268 very few objects being filtered in order to attempt to overwhelm
2269 the receiver. Alternatively, the filter might be modified to
2270 result in certain objects to be excluded from updates, in order to
2271 have certain changes go unnoticed.
2273 o Subtree "datastore" in choice "target" in list "subscription":
2274 Analogous to "selection filter", an attacker might attempt to
2275 modify the objects being filtered in order to overwhelm a receiver
2276 with a larger volume of object updates than expected, or to have
2277 certain changes go unnoticed.
2279 o Choice "update-trigger" in list "subscription": By modifying the
2280 update trigger, an attacker might alter the updates that are being
2281 sent in order to confuse a receiver, to withhold certain updates
2282 to be sent to the receiver, and/or to overwhelm a receiver. For
2283 example, an attacker might modify the period with which updates
2284 are reported for a periodic subscription, or it might modify the
2285 dampening period for an on-change subscription, resulting in
2286 greater delay of successive updates (potentially affecting
2287 responsiveness of applications that depend on the updates) or in a
2288 high volume of updates (to exhaust receiver resources).
2290 o RPC "resync-subscription": This RPC allows a subscriber of an on-
2291 change subscription to request a full push of objects in the
2292 subscription's scope. This can result in a large volume of data.
2293 An attacker could attempt to use this RPC to exhaust resources on
2294 the server to generate the data, and attempt to overwhelm a
2295 receiver with the resulting data volume.
2297 NACM provides one means to mitigate these threats on the publisher
2298 side. In order to address those threats as a subscriber, a
2299 subscriber could monitor the subscription configuration for any
2300 unexpected changes. For this, it can subscribe to updates to the
2301 YANG datastore nodes that represent his datastore subscriptions. As
2302 this data volume is small, a paranoid subscriber could even revert to
2303 occasional polling to guard against a compromised subscription
2304 against subscription configuration updates itself.
2306 8. Acknowledgments
2308 For their valuable comments, discussions, and feedback, we wish to
2309 acknowledge Tim Jenkins, Martin Bjorklund, Kent Watsen, Susan Hares,
2310 Yang Geng, Peipei Guo, Michael Scharf, Guangying Zheng, Tom Petch,
2311 Henk Birkholz, Reshad Rahman, Qin Wu, Rohit Ranade, and Rob Wilton.
2313 9. References
2315 9.1. Normative References
2317 [I-D.draft-ietf-netconf-subscribed-notifications]
2318 Voit, E., Clemm, A., Gonzalez Prieto, A., Tripathy, A.,
2319 and E. Nilsen-Nygaard, "Subscription to YANG Event
2320 Notifications", draft-ietf-netconf-subscribed-
2321 notifications-24 (work in progress), April 2019.
2323 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
2324 Requirement Levels", BCP 14, RFC 2119,
2325 DOI 10.17487/RFC2119, March 1997,
2326 .
2328 [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
2329 DOI 10.17487/RFC3688, January 2004,
2330 .
2332 [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
2333 the Network Configuration Protocol (NETCONF)", RFC 6020,
2334 DOI 10.17487/RFC6020, October 2010,
2335 .
2337 [RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
2338 RFC 6991, DOI 10.17487/RFC6991, July 2013,
2339 .
2341 [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
2342 RFC 7950, DOI 10.17487/RFC7950, August 2016,
2343 .
2345 [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
2346 Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
2347 .
2349 [RFC8072] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Patch
2350 Media Type", RFC 8072, DOI 10.17487/RFC8072, February
2351 2017, .
2353 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2354 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
2355 May 2017, .
2357 [RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration
2358 Access Control Model", STD 91, RFC 8341,
2359 DOI 10.17487/RFC8341, March 2018,
2360 .
2362 [RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
2363 and R. Wilton, "Network Management Datastore Architecture
2364 (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
2365 .
2367 [RFC8525] Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K.,
2368 and R. Wilton, "YANG Library", RFC 8525,
2369 DOI 10.17487/RFC8525, March 2019,
2370 .
2372 9.2. Informative References
2374 [I-D.draft-ietf-netconf-netconf-event-notifications]
2375 Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
2376 E., and A. Tripathy, "Dynamic subscription to YANG Events
2377 and DAtastores over NETCONF", April 2019.
2379 [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
2380 and A. Bierman, Ed., "Network Configuration Protocol
2381 (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
2382 .
2384 [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
2385 Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
2386 .
2388 [RFC7923] Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements
2389 for Subscription to YANG Datastores", RFC 7923,
2390 DOI 10.17487/RFC7923, June 2016,
2391 .
2393 [RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
2394 BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
2395 .
2397 [RFC8343] Bjorklund, M., "A YANG Data Model for Interface
2398 Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
2399 .
2401 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
2402 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
2403 .
2405 Appendix A. Appendix A: Subscription Errors
2407 A.1. RPC Failures
2409 Rejection of an RPC for any reason is indicated by via RPC error
2410 response from the publisher. Valid RPC errors returned include both
2411 existing transport layer RPC error codes, such as those seen with
2412 NETCONF in [RFC6241], as well as subscription specific errors such as
2413 those defined within the YANG model. As a result, how subscription
2414 errors are encoded within an RPC error response is transport
2415 dependent.
2417 References to specific identities in the ietf-subscribed-
2418 notifications YANG model or the ietf-yang-push YANG model may be
2419 returned as part of the error responses resulting from failed
2420 attempts at datastore subscription. For errors defined as part of
2421 ietf-subscribed-notifications, please refer to
2422 [I-D.draft-ietf-netconf-subscribed-notifications]. The errors
2423 introduced in this document, grouped per RPC, are as follows:
2425 establish-subscription modify-subscription
2426 ---------------------- -------------------
2427 cant-exclude period-unsupported
2428 datastore-not-subscribable update-too-big
2429 on-change-unsupported sync-too-big
2430 on-change-sync-unsupported unchanging-selection
2431 period-unsupported
2432 update-too-big resync-subscription
2433 sync-too-big --------------------
2434 unchanging-selection no-such-subscription-resync
2435 sync-too-big
2437 There is one final set of transport independent RPC error elements
2438 included in the YANG model. These are the following four YANG-data
2439 structures for failed datastore subscriptions:
2441 1. YANG-data establish-subscription-error-datastore
2442 This MUST be returned if information identifying the reason for an
2443 RPC error has not been placed elsewhere within the transport
2444 portion of a failed "establish-subscription" RPC response. This
2445 MUST be sent if hints are included.
2447 2. YANG-data modify-subscription-error-datastore
2448 This MUST be returned if information identifying the reason for an
2449 RPC error has not been placed elsewhere within the transport
2450 portion of a failed "modifiy-subscription" RPC response. This
2451 MUST be sent if hints are included.
2453 3. YANG-data sn:delete-subscription-error
2454 This MUST be returned if information identifying the reason for an
2455 RPC error has not been placed elsewhere within the transport
2456 portion of a failed "delete-subscription" or "kill-subscription"
2457 RPC response.
2459 4. YANG-data resync-subscription-error
2460 This MUST be returned if information identifying the reason for an
2461 RPC error has not been placed elsewhere within the transport
2462 portion of a failed "resync-subscription" RPC response.
2464 A.2. Notifications of Failure
2466 A subscription may be unexpectedly terminated or suspended
2467 independent of any RPC or configuration operation. In such cases,
2468 indications of such a failure MUST be provided. To accomplish this,
2469 a number of errors can be returned as part of the corresponding
2470 subscription state change notification. For this purpose, the
2471 following error identities have been introduced in this document, in
2472 addition to those that were already defined in
2473 [I-D.draft-ietf-netconf-subscribed-notifications]:
2475 subscription-terminated subscription-suspended
2476 ----------------------- ----------------------
2477 datastore-not-subscribable period-unsupported
2478 unchanging-selection update-too-big
2479 synchronization-size
2481 Appendix B. Changes Between Revisions
2483 (To be removed by RFC editor prior to publication)
2485 v21 - v22
2486 o Minor updates per Martin Bjorklund's YANG doctor review.
2488 v20 - v21
2490 o Minor updates, simplifying RPC input conditions.
2492 v19 - v20
2494 o Minor updates per WGLC comments.
2496 v18 - v19
2498 o Minor updates per WGLC comments.
2500 v17 - v18
2502 o Minor updates per WGLC comments.
2504 v16 - v17
2506 o Minor updates to YANG module, incorporating comments from Tom
2507 Petch.
2509 o Updated references.
2511 v15 - v16
2513 o Updated security considerations.
2515 o Updated references.
2517 o Addressed comments from last call review, specifically comments
2518 received from Martin Bjorklund.
2520 v14 - v15
2522 o Minor text fixes. Includes a fix to on-change update calculation
2523 to cover churn when an object changes to and from a value during a
2524 dampening period.
2526 v13 - v14
2528 o Minor text fixes.
2530 v12 - v13
2532 o Hint negotiation models now show error examples.
2534 o yang-data structures for rpc errors.
2536 v11 - v12
2538 o Included Martin's review clarifications.
2540 o QoS moved to subscribed-notifications
2542 o time-of-update removed as it is redundant with RFC5277's
2543 eventTime, and other times from notification-messages.
2545 o Error model moved to match existing implementations
2547 o On-change notifiable removed, how to do this is implementation
2548 specific.
2550 o NMDA model supported. Non NMDA version at https://github.com/
2551 netconf-wg/yang-push/
2553 v10 - v11
2555 o Promise model reference added.
2557 o Error added for no-such-datastore
2559 o Inherited changes from subscribed notifications (such as optional
2560 feature definitions).
2562 o scrubbed the examples for proper encodings
2564 v09 - v10
2566 o Returned to the explicit filter subtyping of v00-v05
2568 o identityref to ds:datastore made explicit
2570 o Returned ability to modify a selection filter via RPC.
2572 v08 - v09
2574 o Minor tweaks cleaning up text, removing appendicies, and making
2575 reference to revised-datastores.
2577 o Subscription-id (now:id) optional in push updates, except when
2578 encoded in RFC5277, Section 4 one-way notification.
2580 o Finished adding the text descibing the resync subscription RPC.
2582 o Removed relationships to other drafts and future technology
2583 appendicies as this work is being explored elsewhere.
2585 o Deferred the multi-line card issue to new drafts
2587 o Simplified the NACM interactions.
2589 v07 - v08
2591 o Updated YANG models with minor tweaks to accommodate changes of
2592 ietf-subscribed-notifications.
2594 v06 - v07
2596 o Clarifying text tweaks.
2598 o Clarification that filters act as selectors for subscribed
2599 datastore nodes; support for value filters not included but
2600 possible as a future extension
2602 o Filters don't have to be matched to existing YANG objects
2604 v05 - v06
2606 o Security considerations updated.
2608 o Base YANG model in [subscribe] updated as part of move to
2609 identities, YANG augmentations in this doc matched up
2611 o Terms refined and text updates throughout
2613 o Appendix talking about relationship to other drafts added.
2615 o Datastore replaces stream
2617 o Definitions of filters improved
2619 v04 to v05
2621 o Referenced based subscription document changed to Subscribed
2622 Notifications from 5277bis.
2624 o Getting operational data from filters
2626 o Extension notifiable-on-change added
2628 o New appendix on potential futures. Moved text into there from
2629 several drafts.
2631 o Subscription configuration section now just includes changed
2632 parameters from Subscribed Notifications
2634 o Subscription monitoring moved into Subscribed Notifications
2636 o New error and hint mechanisms included in text and in the YANG
2637 model.
2639 o Updated examples based on the error definitions
2641 o Groupings updated for consistency
2643 o Text updates throughout
2645 v03 to v04
2647 o Updates-not-sent flag added
2649 o Not notifiable extension added
2651 o Dampening period is for whole subscription, not single objects
2653 o Moved start/stop into rfc5277bis
2655 o Client and Server changed to subscriber, publisher, and receiver
2657 o Anchor time for periodic
2659 o Message format for synchronization (i.e. sync-on-start)
2661 o Material moved into 5277bis
2663 o QoS parameters supported, by not allowed to be modified by RPC
2665 o Text updates throughout
2667 Authors' Addresses
2669 Alexander Clemm
2670 Huawei USA
2672 Email: ludwig@clemm.org
2674 Eric Voit
2675 Cisco Systems
2677 Email: evoit@cisco.com
2678 Alberto Gonzalez Prieto
2679 Microsoft
2681 Email: albgonz@microsoft.com
2683 Ambika Prasad Tripathy
2684 Cisco Systems
2686 Email: ambtripa@cisco.com
2688 Einar Nilsen-Nygaard
2689 Cisco Systems
2691 Email: einarnn@cisco.com
2693 Andy Bierman
2694 YumaWorks
2696 Email: andy@yumaworks.com
2698 Balazs Lengyel
2699 Ericsson
2701 Email: balazs.lengyel@ericsson.com