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(See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (May 21, 2019) is 1801 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-26) exists of draft-ietf-netconf-subscribed-notifications-24 Summary: 0 errors (**), 0 flaws (~~), 7 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 NETCONF A. Clemm 3 Internet-Draft Futurewei 4 Intended status: Standards Track E. Voit 5 Expires: November 22, 2019 Cisco Systems 6 May 21, 2019 8 Subscription to YANG Datastores 9 draft-ietf-netconf-yang-push-25 11 Abstract 13 This document describes a mechanism that allows subscriber 14 applications to request a continuous and customized stream of updates 15 from a YANG datastore. Providing such visibility into updates 16 enables new capabilities based on the remote mirroring and monitoring 17 of configuration and operational state. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at https://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on November 22, 2019. 36 Copyright Notice 38 Copyright (c) 2019 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (https://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 This document may contain material from IETF Documents or IETF 52 Contributions published or made publicly available before November 53 10, 2008. The person(s) controlling the copyright in some of this 54 material may not have granted the IETF Trust the right to allow 55 modifications of such material outside the IETF Standards Process. 56 Without obtaining an adequate license from the person(s) controlling 57 the copyright in such materials, this document may not be modified 58 outside the IETF Standards Process, and derivative works of it may 59 not be created outside the IETF Standards Process, except to format 60 it for publication as an RFC or to translate it into languages other 61 than English. 63 Table of Contents 65 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 66 2. Definitions and Acronyms . . . . . . . . . . . . . . . . . . 3 67 3. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 5 68 3.1. Subscription Model . . . . . . . . . . . . . . . . . . . 5 69 3.2. Negotiation of Subscription Policies . . . . . . . . . . 6 70 3.3. On-Change Considerations . . . . . . . . . . . . . . . . 7 71 3.4. Reliability Considerations . . . . . . . . . . . . . . . 8 72 3.5. Data Encodings . . . . . . . . . . . . . . . . . . . . . 9 73 3.6. Defining the Selection with a Datastore . . . . . . . . . 10 74 3.7. Streaming Updates . . . . . . . . . . . . . . . . . . . . 11 75 3.8. Subscription Management . . . . . . . . . . . . . . . . . 13 76 3.9. Receiver Authorization . . . . . . . . . . . . . . . . . 15 77 3.10. On-Change Notifiable Datastore Nodes . . . . . . . . . . 16 78 3.11. Other Considerations . . . . . . . . . . . . . . . . . . 17 79 4. A YANG Data Model for Management of Datastore Push 80 Subscriptions . . . . . . . . . . . . . . . . . . . . . . . . 18 81 4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 18 82 4.2. Subscription Configuration . . . . . . . . . . . . . . . 24 83 4.3. YANG Notifications . . . . . . . . . . . . . . . . . . . 25 84 4.4. YANG RPCs . . . . . . . . . . . . . . . . . . . . . . . . 26 85 5. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . . 31 86 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 48 87 7. Security Considerations . . . . . . . . . . . . . . . . . . . 48 88 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 50 89 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 50 90 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 50 91 10.1. Normative References . . . . . . . . . . . . . . . . . . 50 92 10.2. Informative References . . . . . . . . . . . . . . . . . 51 93 Appendix A. Appendix A: Subscription Errors . . . . . . . . . . 52 94 A.1. RPC Failures . . . . . . . . . . . . . . . . . . . . . . 52 95 A.2. Notifications of Failure . . . . . . . . . . . . . . . . 54 97 Appendix B. Changes Between Revisions . . . . . . . . . . . . . 54 98 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 58 100 1. Introduction 102 Traditional approaches to provide visibility into managed entities 103 from a remote system have been built on polling. With polling, data 104 is periodically requested and retrieved by a client from a server to 105 stay up-to-date. However, there are issues associated with polling- 106 based management: 108 o Polling incurs significant latency. This latency prohibits many 109 types of application. 111 o Polling cycles may be missed and requests may be delayed or get 112 lost, often when the network is under stress and the need for the 113 data is the greatest. 115 o Polling requests may undergo slight fluctuations, resulting in 116 intervals of different lengths. The resulting data is difficult 117 to calibrate and compare. 119 o For applications that monitor for changes, many remote polling 120 cycles place unwanted and ultimately wasteful load on the network, 121 devices, and applications, particularly when changes occur only 122 infrequently. 124 A more effective alternative to polling is for an application to 125 receive automatic and continuous updates from a targeted subset of a 126 datastore. Accordingly, there is a need for a service that allows 127 applications to subscribe to updates from a datastore and that 128 enables the server (also referred to as publisher) to push and in 129 effect stream those updates. The requirements for such a service 130 have been documented in [RFC7923]. 132 This document defines a corresponding solution that is built on top 133 of "Custom Subscription to Event Streams" 134 [I-D.draft-ietf-netconf-subscribed-notifications]. Supplementing 135 that work are YANG data model augmentations, extended RPCs, and new 136 datastore specific update notifications. Transport options for 137 [I-D.draft-ietf-netconf-subscribed-notifications] will work 138 seamlessly with this solution. 140 2. Definitions and Acronyms 142 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 143 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 144 "OPTIONAL" in this document are to be interpreted as described in BCP 145 14 [RFC2119] [RFC8174] when, and only when, they appear in all 146 capitals, as shown here. 148 This document uses the terminology defined in [RFC7950], [RFC8341], 149 [RFC8342], and [I-D.draft-ietf-netconf-subscribed-notifications]. In 150 addition, the following terms are introduced: 152 o Datastore node: A node in the instantiated YANG data tree 153 associated with a datastore. In this document, datastore nodes 154 are often also simply referred to as "objects" 156 o Datastore node update: A data item containing the current value of 157 a datastore node at the time the datastore node update was 158 created, as well as the path to the datastore node. 160 o Datastore subscription: A subscription to a stream of datastore 161 node updates. 163 o Datastore subtree: A datastore node and all its descendant 164 datastore nodes 166 o On-change subscription: A datastore subscription with updates that 167 are triggered when changes in subscribed datastore nodes are 168 detected. 170 o Periodic subscription: A datastore subscription with updates that 171 are triggered periodically according to some time interval. 173 o Selection filter: Evaluation and/or selection criteria, which may 174 be applied against a targeted set of objects. 176 o Update record: A representation of one or more datastore node 177 updates. In addition, an update record may contain which type of 178 update led to the datastore node update (e.g., whether the 179 datastore node was added, changed, deleted). Also included in the 180 update record may be other metadata, such as a subscription id of 181 the subscription as part of which the update record was generated. 182 In this document, update records are often also simply referred to 183 as "updates". 185 o Update trigger: A mechanism that determines when an update record 186 needs to be generated. 188 o YANG-Push: The subscription and push mechanism for datastore 189 updates that is specified in this document. 191 3. Solution Overview 193 This document specifies a solution that provides a subscription 194 service for updates from a datastore. This solution supports dynamic 195 as well as configured subscriptions to updates of datastore nodes. 196 Subscriptions specify when notification messages (also referred to as 197 "push updates") should be sent and what data to include in update 198 records. Datastore node updates are subsequently pushed from the 199 publisher to the receiver per the terms of the subscription. 201 3.1. Subscription Model 203 YANG-push subscriptions are defined using a YANG data model. This 204 model enhances the subscription model defined in 205 [I-D.draft-ietf-netconf-subscribed-notifications] with capabilities 206 that allow subscribers to subscribe to datastore node updates, 207 specifically to specify the update triggers defining when to generate 208 update records as well as what to include in an update record. Key 209 enhancements include: 211 o Specification of selection filters which identify targeted YANG 212 datastore nodes and/or datastore subtrees for which updates are to 213 be pushed. 215 o Specification of update policies contain conditions which trigger 216 the generation and pushing of new update records. There are two 217 types of subscriptions, distinguished by how updates are 218 triggered: periodic and on-change. 220 * For periodic subscriptions, the update trigger is specified by 221 two parameters that define when updates are to be pushed. 222 These parameters are the period interval with which to report 223 updates, and an "anchor time", i.e. a reference point in time 224 that can be used to calculate at which points in time periodic 225 updates need to be assembled and sent. 227 * For on-change subscriptions, an update trigger occurs whenever 228 a change in the subscribed information is detected. Included 229 are additional parameters that include: 231 + Dampening period: In an on-change subscription, detected 232 object changes should be sent as quickly as possible. 233 However it may be undesirable to send a rapid series of 234 object changes. Such behavior has the potential to exhaust 235 resources in the publisher or receiver. In order to protect 236 against that, a dampening period MAY be used to specify the 237 interval which has to pass before successive update records 238 for the same subscription are generated for a receiver. The 239 dampening period collectively applies to the set of all 240 datastore nodes selected by a single subscription. This 241 means that when there is a change to one or more subscribed 242 objects, an update record containing those objects is 243 created immediately (when no dampening period is in effect) 244 or at the end of a dampening period (when a dampening period 245 is in fact in effect). If multiple changes to a single 246 object occur during a dampening period, only the value that 247 is in effect at the time when the update record is created 248 is included. The dampening period goes into effect every 249 time an update record completes assembly. 251 + Change type: This parameter can be used to reduce the types 252 of datastore changes for which updates are sent (e.g., you 253 might only send an update when an object is created or 254 deleted, but not when an object value changes). 256 + Sync on start: defines whether or not a complete push-update 257 of all subscribed data will be sent at the beginning of a 258 subscription. Such early synchronization establishes the 259 frame of reference for subsequent updates. 261 o An encoding (using anydata) for the contents of periodic and on- 262 change push updates. 264 3.2. Negotiation of Subscription Policies 266 A dynamic subscription request SHOULD be declined if a publisher's 267 assessment is that it may be unable to provide update records meeting 268 the terms of an "establish-subscription" or "modify-subscription" RPC 269 request. In this case, a subscriber may quickly follow up with a new 270 RPC request using different parameters. 272 Random guessing of different parameters by a subscriber is to be 273 discouraged. Therefore, in order to minimize the number of 274 subscription iterations between subscriber and publisher, a dynamic 275 subscription supports a simple negotiation between subscribers and 276 publishers for subscription parameters. This negotiation is in the 277 form of supplemental information which should be inserted within 278 error responses to a failed RPC request. This returned error 279 response information, when considered, should increase the likelihood 280 of success for subsequent RPC requests. Such hints include suggested 281 periodic time intervals, acceptable dampening periods, and size 282 estimates for the number or objects which would be returned from a 283 proposed selection filter. However, there are no guarantees that 284 subsequent requests which consider these hints will be accepted. 286 3.3. On-Change Considerations 288 On-change subscriptions allow receivers to receive updates whenever 289 changes to targeted objects occur. As such, on-change subscriptions 290 are particularly effective for data that changes infrequently, yet 291 for which applications need to be quickly notified whenever a change 292 does occur with minimal delay. 294 On-change subscriptions tend to be more difficult to implement than 295 periodic subscriptions. Accordingly, on-change subscriptions may not 296 be supported by all implementations or for every object. 298 Whether or not to accept or reject on-change subscription requests 299 when the scope of the subscription contains objects for which on- 300 change is not supported is up to the publisher implementation. A 301 publisher MAY accept an on-change subscription even when the scope of 302 the subscription contains objects for which on-change is not 303 supported. In that case, updates are sent only for those objects 304 within the scope that do support on-change updates, whereas other 305 objects are excluded from update records, even if their values 306 change. In order for a subscriber to determine whether objects 307 support on-change subscriptions, objects are marked accordingly on a 308 publisher. Accordingly, when subscribing, it is the responsibility 309 of the subscriber to ensure it is aware of which objects support on- 310 change and which do not. For more on how objects are so marked, see 311 Section 3.10. 313 Alternatively, a publisher MAY decide to simply reject an on-change 314 subscription in case the scope of the subscription contains objects 315 for which on-change is not supported. In case of a configured 316 subscription, the publisher MAY suspend the subscription. 318 To avoid flooding receivers with repeated updates for subscriptions 319 containing fast-changing objects, or objects with oscillating values, 320 an on-change subscription allows for the definition of a dampening 321 period. Once an update record for a given object is generated, no 322 other updates for this particular subscription will be created until 323 the end of the dampening period. Values sent at the end of the 324 dampening period are the values that are current at the end of the 325 dampening period of all changed objects. Changed objects include 326 those which were deleted or newly created during that dampening 327 period. If an object has returned to its original value (or even has 328 been created and then deleted) during the dampening-period, that 329 value (and not the interim change) will still be sent. This will 330 indicate churn is occurring on that object. 332 On-change subscriptions can be refined to let users subscribe only to 333 certain types of changes. For example, a subscriber might only want 334 object creations and deletions, but not modifications of object 335 values. 337 Putting it all together, following is the conceptual process for 338 creating an update record as part of an on-change subscription: 340 1. Just before a change, or at the start of a dampening period, 341 evaluate any filtering and any access control rules to ensure 342 receiver is authorized to view all subscribed datastore nodes 343 (filtering out any nodes for which this is not the case). The 344 result is a set "A" of datastore nodes and subtrees. 346 2. Just after a change, or at the end of a dampening period, 347 evaluate any filtering and any (possibly new) access control 348 rules. The result is a set "B" of datastore nodes and subtrees. 350 3. Construct an update record, which takes the form of YANG patch 351 record [RFC8072] for going from A to B. 353 4. If there were any changes made between A and B which canceled 354 each other out, insert into the YANG patch record the last change 355 made, even if the new value is no different from the original 356 value (since changes that were made in the interim were canceled 357 out). In case the changes involve creating a new datastore node, 358 then deleting it, the YANG patch record will indicate deletion of 359 the datastore node. Similarly, in case the changes involve 360 deleting a new datastore node, then recreating it, the YANG patch 361 record will indicate creation of the datastore node. 363 5. If the resulting patch record is non-empty, send it to the 364 receiver. 366 Note: In cases where a subscriber wants to have separate dampening 367 periods for different objects, the subscriber has the option to 368 create multiple subscriptions with different selection filters. 370 3.4. Reliability Considerations 372 A subscription to updates from a datastore is intended to obviate the 373 need for polling. However, in order to do so, it is critical that 374 subscribers can rely on the subscription and have confidence that 375 they will indeed receive the subscribed updates without having to 376 worry about updates being silently dropped. In other words, a 377 subscription constitutes a promise on the side of the publisher to 378 provide the receivers with updates per the terms of the subscription. 380 Now, there are many reasons why a publisher may at some point no 381 longer be able to fulfill the terms of the subscription, even if the 382 subscription had been entered into with good faith. For example, the 383 volume of datastore nodes may be larger than anticipated, the 384 interval may prove too short to send full updates in rapid 385 succession, or an internal problem may prevent objects from being 386 collected. For this reason, the solution that is defined in this 387 document mandates that a publisher notifies receivers immediately and 388 reliably whenever it encounters a situation in which it is unable to 389 keep the terms of the subscription, and provides the publisher with 390 the option to suspend the subscription in such a case. This includes 391 indicating the fact that an update is incomplete as part of a push- 392 update or push-change-update notification, as well as emitting a 393 subscription-suspended notification as applicable. This is described 394 further in Section 3.11.1. 396 A publisher SHOULD reject a request for a subscription if it is 397 unlikely that the publisher will be able to fulfill the terms of that 398 subscription request. In such cases, it is preferable to have a 399 subscriber request a less resource intensive subscription than to 400 deal with frequently degraded behavior. 402 The solution builds on 403 [I-D.draft-ietf-netconf-subscribed-notifications]. As defined there, 404 any loss of underlying transport connection will be detected and 405 result in subscription termination (in case of dynamic subscriptions) 406 or suspension (in case of configured subscriptions), ensuring that 407 situations will not occur in which the loss of update notifications 408 would go unnoticed. 410 3.5. Data Encodings 412 3.5.1. Periodic Subscriptions 414 In a periodic subscription, the data included as part of an update 415 record corresponds to data that could have been read using a 416 retrieval operation. 418 3.5.2. On-Change Subscriptions 420 In an on-change subscription, update records need to indicate not 421 only values of changed datastore nodes but also the types of changes 422 that occurred since the last update. Therefore, encoding rules for 423 data in on-change updates will generally follow YANG-patch operation 424 as specified in [RFC8072]. The YANG-patch will describe what needs 425 to be applied to the earlier state reported by the preceding update, 426 to result in the now-current state. Note that contrary to [RFC8072], 427 objects encapsulated are not restricted to only configuration 428 objects. 430 A publisher indicates the type of change to a datastore node using 431 the different YANG patch operations: the "create" operation is used 432 for newly created objects (except entries in a user-ordered list), 433 the "delete" operation is used for deleted objects (including in 434 user-ordered lists), the "replace" operation is used when only the 435 object value changes, the "insert" operation is used when a new entry 436 is inserted in a list, and the "move" operation is used when an 437 existing entry in a user-ordered list is moved. 439 However, a patch must be able to do more than just describe the delta 440 from the previous state to the current state. As per Section 3.3, it 441 must also be able to identify whether transient changes have occurred 442 on an object during a dampening period. To support this, it is valid 443 to encode a YANG patch operation so that its application would result 444 in no change between the previous and current state. This indicates 445 that some churn has occurred on the object. An example of this would 446 be a patch that indicates a "create" operation for a datastore node 447 where the receiver believes one already exists, or a "replace" 448 operation which replaces a previous value with the same value. Note 449 that this means that the "create" and "delete" errors described in 450 [RFC8072] section 2.5 are not errors, and are valid operations with 451 YANG-Push. 453 3.6. Defining the Selection with a Datastore 455 A subscription must specify both the selection filters and the 456 datastore against which these selection filters will be applied. 457 This information is used to choose and subsequently push data from 458 the publisher's datastore to the receivers. 460 Only a single selection filter can be applied to a subscription at a 461 time. An RPC request proposing a new selection filter replaces any 462 existing filter. The following selection filter types are included 463 in the YANG-push data model, and may be applied against a datastore: 465 o subtree: A subtree selection filter identifies one or more 466 datastore subtrees. When specified, update records will only come 467 from the datastore nodes of selected datastore subtree(s). The 468 syntax and semantics correspond to that specified for [RFC6241] 469 section 6. 471 o xpath: An "xpath" selection filter is an XPath expression that 472 returns a node set. (XPath is a query language for selecting 473 nodes in an XML document.) When specified, updates will only come 474 from the selected datastore nodes. 476 These filters are intended to be used as selectors that define which 477 objects are within the scope of a subscription. A publisher MUST 478 support at least one type of selection filter. 480 XPath itself provides powerful filtering constructs and care must be 481 used in filter definition. Consider an XPath filter which only 482 passes a datastore node when an interface is up. It is up to the 483 receiver to understand implications of the presence or absence of 484 objects in each update. 486 When the set of selection filtering criteria is applied for a 487 periodic subscription, then they are applied whenever a periodic 488 update record is constructed, and only datastore nodes that pass the 489 filter and to which a receiver has access are provided to that 490 receiver. If the same filtering criteria is applied to an on-change 491 subscription, only the subset of those datastore nodes supporting on- 492 change is provided. A datastore node which doesn't support on-change 493 is never sent as part of an on-change subscription's "push-update" or 494 "push-change-update" (see Section 3.7). 496 3.7. Streaming Updates 498 Contrary to traditional data retrieval requests, datastore 499 subscription enables an unbounded series of update records to be 500 streamed over time. Two generic YANG notifications for update 501 records have been defined for this: "push-update" and "push-change- 502 update". 504 A "push-update" notification defines a complete, filtered update of 505 the datastore per the terms of a subscription. This type of YANG 506 notification is used for continuous updates of periodic 507 subscriptions. A "push-update" notification can also be used for the 508 on-change subscriptions in two cases. First, it MUST be used as the 509 initial "push-update" if there is a need to synchronize the receiver 510 at the start of a new subscription. It also MAY be sent if the 511 publisher later chooses to resync an on-change subscription. The 512 "push-update" update record contains an instantiated datastore 513 subtree with all of the subscribed contents. The content of the 514 update record is equivalent to the contents that would be obtained 515 had the same data been explicitly retrieved using a datastore 516 retrieval operation using the same transport with the same filters 517 applied. 519 A "push-change-update" notification is the most common type of update 520 for on-change subscriptions. The update record in this case contains 521 the set of changes that datastore nodes have undergone since the last 522 notification message. In other words, this indicates which datastore 523 nodes have been created, deleted, or have had changes to their 524 values. In cases where multiple changes have occurred over the 525 course of a dampening period and the object has not been deleted, the 526 object's most current value is reported. (In other words, for each 527 object, only one change is reported, not its entire history. Doing 528 so would defeat the purpose of the dampening period.) 530 "Push-update" and "push-change-update" are encoded and placed within 531 notification messages, and ultimately queued for egress over the 532 specified transport. 534 The following is an example of a notification message for a 535 subscription tracking the operational status of a single Ethernet 536 interface (per [RFC8343]). This notification message is encoded XML 537 over NETCONF as per 538 [I-D.draft-ietf-netconf-netconf-event-notifications]. 540 541 2017-10-25T08:00:11.22Z 542 543 1011 544 545 546 547 eth0 548 up 549 550 551 552 553 555 Figure 1: Push example 557 The following is an example of an on-change notification message for 558 the same subscription. 560 561 2017-10-25T08:22:33.44Z 562 564 89 565 566 567 0 568 569 edit1 570 replace 571 /ietf-interfaces:interfaces 572 573 575 576 eth0 577 down 578 579 580 581 582 583 584 585 587 Figure 2: Push example for on change 589 Of note in the above example is the 'patch-id' with a value of '0'. 590 Per [RFC8072], the 'patch-id' is an arbitrary string. With YANG 591 Push, the publisher SHOULD put into the 'patch-id' a counter starting 592 at '0' which increments with every 'push-change-update' generated for 593 a subscription. If used as a counter, this counter MUST be reset to 594 '0' anytime a resynchronization occurs (i.e., with the sending of a 595 'push-update'). Also if used as a counter, the counter MUST be reset 596 to '0' after passing a maximum value of '4294967295' (i.e. maximum 597 value that can be represented using uint32 data type). Such a 598 mechanism allows easy identification of lost or out-of-sequence 599 update records. 601 3.8. Subscription Management 603 The RPCs defined within 604 [I-D.draft-ietf-netconf-subscribed-notifications] have been enhanced 605 to support datastore subscription negotiation. Also, new error codes 606 have been added that are able to indicate why a datastore 607 subscription attempt has failed, along with new YANG-data that MAY be 608 used to include details on input parameters that might result in a 609 successful subsequent RPC invocation. 611 The establishment or modification of a datastore subscription can be 612 rejected for multiple reasons. This includes a too large subtree 613 request, or the inability of the publisher to push update records as 614 frequently as requested. In such cases, no subscription is 615 established. Instead, the subscription-result with the failure 616 reason is returned as part of the RPC response. As part of this 617 response, a set of alternative subscription parameters MAY be 618 returned that would likely have resulted in acceptance of the 619 subscription request. The subscriber may consider these as part of 620 future subscription attempts. 622 In the case of a rejected request for an establishment of a datastore 623 subscription, if there are hints, the hints SHOULD be transported 624 within a YANG-data "establish-subscription-datastore-error-info" 625 container inserted into the RPC error response, in lieu of the 626 "establish-subscription-stream-error-info" that is inserted in case 627 of a stream subscription. 629 Below is a tree diagram for "establish-subscription-datastore-error- 630 info". All tree diagrams used in this document follow the notation 631 defined in [RFC8340] 633 YANG-data establish-subscription-datastore-error-info 634 +--ro establish-subscription-datastore-error-info 635 +--ro reason? identityref 636 +--ro period-hint? centiseconds 637 +--ro filter-failure-hint? string 638 +--ro object-count-estimate? uint32 639 +--ro object-count-limit? uint32 640 +--ro kilobytes-estimate? uint32 641 +--ro kilobytes-limit? uint32 643 Figure 3: Tree diagram for establish-subscription-datastore-error- 644 info 646 Similarly, in the case of a rejected request for modification of a 647 datastore subscription, if there are hints, the hints SHOULD be 648 transported within a YANG-data "modify-subscription-datastore-error- 649 info" container inserted into the RPC error response, in lieu of the 650 "modify-subscription-stream-error-info" that is inserted in case of a 651 stream subscription. 653 Below is a tree diagram for "modify-subscription-datastore-error- 654 info". 656 YANG-data modify-subscription-datastore-error-info 657 +--ro modify-subscription-datasore-error-info 658 +--ro reason? identityref 659 +--ro period-hint? centiseconds 660 +--ro filter-failure-hint? string 661 +--ro object-count-estimate? uint32 662 +--ro object-count-limit? uint32 663 +--ro kilobytes-estimate? uint32 664 +--ro kilobytes-limit? uint32 666 Figure 4: Tree diagram for modify-subscription-datastore-error-info 668 3.9. Receiver Authorization 670 A receiver of subscription data MUST only be sent updates for which 671 it has proper authorization. A publisher MUST ensure that no non- 672 authorized data is included in push updates. To do so, it needs to 673 apply all corresponding checks applicable at the time of a specific 674 pushed update and if necessary silently remove any non-authorized 675 data from datastore subtrees. This enables YANG data pushed based on 676 subscriptions to be authorized equivalently to a regular data 677 retrieval (get) operation. 679 Each "push-update" and "push-change-update" MUST have access control 680 applied, as is depicted in the following diagram. This includes 681 validating that read access is permitted for any new objects selected 682 since the last notification message was sent to a particular 683 receiver. To accomplish this, implementations SHOULD support the 684 conceptual authorization model of [RFC8341], specifically section 685 3.2.4. 687 +-----------------+ +--------------------+ 688 push-update or --> | datastore node | yes | add datastore node | 689 push-change-update | access allowed? | ---> | to update record | 690 +-----------------+ +--------------------+ 692 Figure 5: Updated [RFC8341] access control for push updates 694 A publisher MUST allow for the possibility that a subscription's 695 selection filter references non-existent data or data that a receiver 696 is not allowed to access. Such support permits a receiver the 697 ability to monitor the entire lifecyle of some datastore tree without 698 needing to explicitly enumerate every individual datastore node. If, 699 after access control has been applied, there are no objects remaining 700 in an update record, then (in case of a periodic subscription) only a 701 single empty "push-update" notification MUST be sent. Empty "push- 702 change-update" messages (in case of an on-change subscription) MUST 703 NOT be sent. This is required to ensure that clients cannot 704 surreptitiously monitor objects that they do not have access to via 705 carefully crafted selection filters. By the same token, changes to 706 objects that are filtered MUST NOT affect any dampening intervals. 708 A publisher MAY choose to reject an establish-subscription request 709 which selects non-existent data or data that a receiver is not 710 allowed to access. As reason, the error identity "unchanging- 711 selection" SHOULD be returned. In addition, a publisher MAY choose 712 to terminate a dynamic subscription or suspend a configured receiver 713 when the authorization privileges of a receiver change, or the access 714 controls for subscribed objects change. In that case, the publisher 715 SHOULD include the error identity "unchanging-selection" as reason 716 when sending the "subscription-terminated" respectively 717 "subscription-suspended" notification. Such a capability enables the 718 publisher to avoid having to support continuous and total filtering 719 of a subscription's content for every update record. It also reduces 720 the possibility of leakage of access-controlled objects. 722 If read access into previously accessible nodes has been lost due to 723 a receiver permissions change, this SHOULD be reported as a patch 724 "delete" operation for on-change subscriptions. If not capable of 725 handling such receiver permission changes with such a "delete", 726 publisher implementations MUST force dynamic subscription re- 727 establishment or configured subscription re-initialization so that 728 appropriate filtering is installed. 730 3.10. On-Change Notifiable Datastore Nodes 732 In some cases, a publisher supporting on-change notifications may not 733 be able to push on-change updates for some object types. Reasons for 734 this might be that the value of the datastore node changes frequently 735 (e.g., [RFC8343]'s in-octets counter), that small object changes are 736 frequent and meaningless (e.g., a temperature gauge changing 0.1 737 degrees), or that the implementation is not capable of on-change 738 notification for a particular object. 740 In those cases, it will be important for client applications to have 741 a way to identify for which objects on-change notifications are 742 supported and for which ones they are not supported. Otherwise 743 client applications will have no way of knowing whether they can 744 indeed rely on their on-change subscription to provide them with the 745 change updates that they are interested in. In other words, if 746 implementations do not provide a solution and do not support 747 comprehensive on-change notifiability, clients of those 748 implementations will have no way of knowing what their on-change 749 subscription actually covers. 751 Implementations are therefore strongly advised to provide a solution 752 to this problem. One solution might involve making discoverable to 753 clients which objects are on-change notifiable, specified using 754 another YANG data model. Such a solution is specified in 755 [I-D.draft-ietf-netconf-notification-capabilities]. Until this 756 solution is standardized, implementations SHOULD provide their own 757 solution. 759 3.11. Other Considerations 761 3.11.1. Robustness and reliability 763 Particularly in the case of on-change updates, it is important that 764 these updates do not get lost. In case the loss of an update is 765 unavoidable, it is critical that the receiver is notified 766 accordingly. 768 Update records for a single subscription MUST NOT be resequenced 769 prior to transport. 771 It is conceivable that under certain circumstances, a publisher will 772 recognize that it is unable to include within an update record the 773 full set of objects desired per the terms of a subscription. In this 774 case, the publisher MUST act as follows. 776 o The publisher MUST set the "incomplete-update" flag on any update 777 record which is known to be missing information. 779 o The publisher MAY choose to suspend the subscription as per 780 [I-D.draft-ietf-netconf-subscribed-notifications]. If the 781 publisher does not create an update record at all, it MUST suspend 782 the subscription. 784 o When resuming an on-change subscription, the publisher SHOULD 785 generate a complete patch from the previous update record. If 786 this is not possible and the "sync-on-start" option is true for 787 the subscription, then the full datastore contents MAY be sent via 788 a "push-update" instead (effectively replacing the previous 789 contents). If neither of these are possible, then an "incomplete- 790 update" flag MUST be included on the next "push-change-update". 792 Note: It is perfectly acceptable to have a series of "push-change- 793 update" notifications (and even "push update" notifications) serially 794 queued at the transport layer awaiting transmission. It is not 795 required for the publisher to merge pending update records sent at 796 the same time. 798 On the receiver side, what action to take when a record with an 799 incomplete-update flag is received depends on the application. It 800 could simply choose to wait and do nothing. It could choose to 801 resynch, actively retrieving all subscribed information. It could 802 also choose to tear down the subscription and start a new one, 803 perhaps with a lesser scope that contains less objects. 805 3.11.2. Publisher capacity 807 It is far preferable to decline a subscription request than to accept 808 such a request when it cannot be met. 810 Whether or not a subscription can be supported will be determined by 811 a combination of several factors such as the subscription update 812 trigger (on-change or periodic), the period in which to report 813 changes (one second periods will consume more resources than one hour 814 periods), the amount of data in the datastore subtree that is being 815 subscribed to, and the number and combination of other subscriptions 816 that are concurrently being serviced. 818 4. A YANG Data Model for Management of Datastore Push Subscriptions 820 4.1. Overview 822 The YANG data model for datastore push subscriptions is depicted in 823 the following figures. The tree diagram that is used follows the 824 notation defined in [RFC8340]. New schema objects defined here 825 (i.e., beyond those from 826 [I-D.draft-ietf-netconf-subscribed-notifications]) are identified 827 with "yp". For the reader's convenience, in order to compact the 828 tree representation, some nodes that are defined in ietf-subscribed- 829 notifications and that are not essential to the understanding of the 830 data model defined here have been removed. This is indicated by 831 "..." in the diagram where applicable. 833 Because the tree diagram is quite large, its depiction is broken up 834 into several figures. The first figure depicts the augmentations 835 that are introduced in module ietf-yang-push to subscription 836 configuration specified in module ietf-subscribed-notifications. 838 module: ietf-subscribed-notifications 839 ... 840 +--rw filters 841 | ... 842 | +--rw yp:selection-filter* [filter-id] 843 | +--rw yp:filter-id string 844 | +--rw (yp:filter-spec)? 845 | +--:(yp:datastore-subtree-filter) 846 | | +--rw yp:datastore-subtree-filter? 847 | | {sn:subtree}? 848 | +--:(yp:datastore-xpath-filter) 849 | +--rw yp:datastore-xpath-filter? yang:xpath1.0 850 | {sn:xpath}? 851 +--rw subscriptions 852 +--rw subscription* [id] 853 | ... 854 +--rw (target) 855 | +--:(stream) 856 | | ... 857 | +--:(yp:datastore) 858 | +--rw yp:datastore identityref 859 | +--rw (yp:selection-filter)? 860 | +--:(yp:by-reference) 861 | | +--rw yp:selection-filter-ref 862 | | selection-filter-ref 863 | +--:(yp:within-subscription) 864 | +--rw (yp:filter-spec)? 865 | +--:(yp:datastore-subtree-filter) 866 | | +--rw yp:datastore-subtree-filter? 867 | | {sn:subtree}? 868 | +--:(yp:datastore-xpath-filter) 869 | +--rw yp:datastore-xpath-filter? 870 | yang:xpath1.0 {sn:xpath}? 871 | ... 872 +--rw (yp:update-trigger) 873 +--:(yp:periodic) 874 | +--rw yp:periodic! 875 | +--rw yp:period centiseconds 876 | +--rw yp:anchor-time? yang:date-and-time 877 +--:(yp:on-change) {on-change}? 878 +--rw yp:on-change! 879 +--rw yp:dampening-period? centiseconds 880 +--rw yp:sync-on-start? boolean 881 +--rw yp:excluded-change* change-type 883 Figure 6: Model structure: subscription configuration 885 The next figure depicts the augmentations of module ietf-yang-push 886 made to RPCs specified in module ietf-subscribed-notifications. 887 Specifically, these augmentations concern the establish-subscription 888 and modify-subscription RPCs, which are augmented with parameters 889 that are needed to specify datastore push subscriptions. 891 rpcs: 892 +---x establish-subscription 893 | +---w input 894 | | ... 895 | | +---w (target) 896 | | | +--:(stream) 897 | | | | ... 898 | | | +--:(yp:datastore) 899 | | | +---w yp:datastore identityref 900 | | | +---w (yp:selection-filter)? 901 | | | +--:(yp:by-reference) 902 | | | | +---w yp:selection-filter-ref 903 | | | | selection-filter-ref 904 | | | +--:(yp:within-subscription) 905 | | | +---w (yp:filter-spec)? 906 | | | +--:(yp:datastore-subtree-filter) 907 | | | | +---w yp:datastore-subtree-filter? 908 | | | | {sn:subtree}? 909 | | | +--:(yp:datastore-xpath-filter) 910 | | | +---w yp:datastore-xpath-filter? 911 | | | yang:xpath1.0 {sn:xpath}? 912 | | | ... 913 | | +---w (yp:update-trigger) 914 | | +--:(yp:periodic) 915 | | | +---w yp:periodic! 916 | | | +---w yp:period centiseconds 917 | | | +---w yp:anchor-time? yang:date-and-time 918 | | +--:(yp:on-change) {on-change}? 919 | | +---w yp:on-change! 920 | | +---w yp:dampening-period? centiseconds 921 | | +---w yp:sync-on-start? boolean 922 | | +---w yp:excluded-change* change-type 923 | +--ro output 924 | +--ro id subscription-id 925 | +--ro replay-start-time-revision? yang:date-and-time 926 | {replay}? 927 +---x modify-subscription 928 | +---w input 929 | ... 930 | +---w (target) 931 | | ... 933 | | +--:(yp:datastore) 934 | | +---w yp:datastore identityref 935 | | +---w (yp:selection-filter)? 936 | | +--:(yp:by-reference) 937 | | | +---w yp:selection-filter-ref 938 | | | selection-filter-ref 939 | | +--:(yp:within-subscription) 940 | | +---w (yp:filter-spec)? 941 | | +--:(yp:datastore-subtree-filter) 942 | | | +---w yp:datastore-subtree-filter? 943 | | | {sn:subtree}? 944 | | +--:(yp:datastore-xpath-filter) 945 | | +---w yp:datastore-xpath-filter? 946 | | yang:xpath1.0 {sn:xpath}? 947 | | ... 948 | +---w (yp:update-trigger) 949 | +--:(yp:periodic) 950 | | +---w yp:periodic! 951 | | +---w yp:period centiseconds 952 | | +---w yp:anchor-time? yang:date-and-time 953 | +--:(yp:on-change) {on-change}? 954 | +---w yp:on-change! 955 | +---w yp:dampening-period? centiseconds 956 +---x delete-subscription 957 | ... 958 +---x kill-subscription 959 ... 961 YANG-data (for placement into rpc error responses) 962 ... 964 Figure 7: Model structure: RPCs 966 The next figure depicts augmentations of module ietf-yang-push to the 967 notifications that are specified in module ietf-subscribed- 968 notifications. The augmentations allow the inclusion of subscription 969 configuration parameters that are specific to datastore push 970 subscriptions as part of subscription-started and subscription- 971 modified notifications. 973 notifications: 974 +---n replay-completed {replay}? 975 | ... 976 +---n subscription-completed 977 | ... 978 +---n subscription-started {configured}? 979 | | ... 980 | +--ro (target) 981 | | ... 982 | | +--:(yp:datastore) 983 | | +--ro yp:datastore identityref 984 | | +--ro (yp:selection-filter)? 985 | | +--:(yp:by-reference) 986 | | | +--ro yp:selection-filter-ref 987 | | | selection-filter-ref 988 | | +--:(yp:within-subscription) 989 | | +--ro (yp:filter-spec)? 990 | | +--:(yp:datastore-subtree-filter) 991 | | | +--ro yp:datastore-subtree-filter? 992 | | | {sn:subtree}? 993 | | +--:(yp:datastore-xpath-filter) 994 | | +--ro yp:datastore-xpath-filter? 995 | | yang:xpath1.0 {sn:xpath}? 996 | ... 997 | +--ro (yp:update-trigger) 998 | +--:(yp:periodic) 999 | | +--ro yp:periodic! 1000 | | +--ro yp:period centiseconds 1001 | | +--ro yp:anchor-time? yang:date-and-time 1002 | +--:(yp:on-change) {on-change}? 1003 | +--ro yp:on-change! 1004 | +--ro yp:dampening-period? centiseconds 1005 | +--ro yp:sync-on-start? boolean 1006 | +--ro yp:excluded-change* change-type 1007 +---n subscription-resumed 1008 | ... 1009 +---n subscription-modified 1010 | ... 1011 | +--ro (target) 1012 | | | ... 1013 | | +--:(yp:datastore) 1014 | | +--ro yp:datastore identityref 1015 | | +--ro (yp:selection-filter)? 1016 | | +--:(yp:by-reference) 1017 | | | +--ro yp:selection-filter-ref 1018 | | | selection-filter-ref 1019 | | +--:(yp:within-subscription) 1020 | | +--ro (yp:filter-spec)? 1021 | | +--:(yp:datastore-subtree-filter) 1022 | | | +--ro yp:datastore-subtree-filter? 1023 | | | {sn:subtree}? 1024 | | +--:(yp:datastore-xpath-filter) 1025 | | +--ro yp:datastore-xpath-filter? 1026 | | yang:xpath1.0 {sn:xpath}? 1027 | ... 1028 | +--ro (yp:update-trigger)? 1029 | +--:(yp:periodic) 1030 | | +--ro yp:periodic! 1031 | | +--ro yp:period centiseconds 1032 | | +--ro yp:anchor-time? yang:date-and-time 1033 | +--:(yp:on-change) {on-change}? 1034 | +--ro yp:on-change! 1035 | +--ro yp:dampening-period? centiseconds 1036 | +--ro yp:sync-on-start? boolean 1037 | +--ro yp:excluded-change* change-type 1038 +---n subscription-terminated 1039 | ... 1040 +---n subscription-suspended 1041 ... 1043 Figure 8: Model structure: Notifications 1045 The final figure in this section depicts the parts of module ietf- 1046 yang-push that are not simply augmentations to another module, but 1047 that are newly introduced. 1049 module: ietf-yang-push 1051 rpcs: 1052 +---x resync-subscription {on-change}? 1053 +---w input 1054 +---w id sn:subscription-id 1056 YANG-data: (for placement into rpc error responses) 1057 +-- resync-subscription-error 1058 | +--ro reason? identityref 1059 | +--ro period-hint? centiseconds 1060 | +--ro filter-failure-hint? string 1061 | +--ro object-count-estimate? uint32 1062 | +--ro object-count-limit? uint32 1063 | +--ro kilobytes-estimate? uint32 1064 | +--ro kilobytes-limit? uint32 1065 +-- establish-subscription-error-datastore 1066 | +--ro reason? identityref 1067 | +--ro period-hint? centiseconds 1068 | +--ro filter-failure-hint? string 1069 | +--ro object-count-estimate? uint32 1070 | +--ro object-count-limit? uint32 1071 | +--ro kilobytes-estimate? uint32 1072 | +--ro kilobytes-limit? uint32 1073 +-- modify-subscription-error-datastore 1074 +--ro reason? identityref 1075 +--ro period-hint? centiseconds 1076 +--ro filter-failure-hint? string 1077 +--ro object-count-estimate? uint32 1078 +--ro object-count-limit? uint32 1079 +--ro kilobytes-estimate? uint32 1080 +--ro kilobytes-limit? uint32 1082 notifications: 1083 +---n push-update 1084 | +--ro id? sn:subscription-id 1085 | +--ro datastore-contents? 1086 | +--ro incomplete-update? empty 1087 +---n push-change-update {on-change}? 1088 +--ro id? sn:subscription-id 1089 +--ro datastore-changes 1090 | +--ro yang-patch 1091 | +--ro patch-id string 1092 | +--ro comment? string 1093 | +--ro edit* [edit-id] 1094 | +--ro edit-id string 1095 | +--ro operation enumeration 1096 | +--ro target target-resource-offset 1097 | +--ro point? target-resource-offset 1098 | +--ro where? enumeration 1099 | +--ro value? 1100 +--ro incomplete-update? empty 1102 Figure 9: Model structure (non-augmentation portions 1104 Selected components of the model are summarized below. 1106 4.2. Subscription Configuration 1108 Both configured and dynamic subscriptions are represented within the 1109 list "subscription". New parameters extending the basic subscription 1110 data model in [I-D.draft-ietf-netconf-subscribed-notifications] 1111 include: 1113 o The targeted datastore from which the selection is being made. 1114 The potential datastores include those from [RFC8341]. A platform 1115 may also choose to support a custom datastore. 1117 o A selection filter identifying YANG nodes of interest within a 1118 datastore. Filter contents are specified via a reference to an 1119 existing filter, or via an in-line definition for only that 1120 subscription. Referenced filters allows an implementation to 1121 avoid evaluating filter acceptability during a dynamic 1122 subscription request. The case statement differentiates the 1123 options. 1125 o For periodic subscriptions, triggered updates will occur at the 1126 boundaries of a specified time interval. These boundaries can be 1127 calculated from the periodic parameters: 1129 * a "period" which defines the duration between push updates. 1131 * an "anchor-time"; update intervals fall on the points in time 1132 that are a multiple of a "period" from an "anchor-time". If 1133 "anchor-time" is not provided, then the "anchor-time" MUST be 1134 set with the creation time of the initial update record. 1136 o For on-change subscriptions, assuming any dampening period has 1137 completed, triggering occurs whenever a change in the subscribed 1138 information is detected. On-change subscriptions have more 1139 complex semantics that are guided by their own set of parameters: 1141 * a "dampening-period" specifies the interval that must pass 1142 before a successive update for the subscription is sent. If no 1143 dampening period is in effect, the update is sent immediately. 1144 If a subsequent change is detected, another update is only sent 1145 once the dampening period has passed for this subscription. 1147 * an "excluded-change" parameter which allows restriction of the 1148 types of changes for which updates should be sent (e.g., only 1149 add to an update record on object creation). 1151 * a "sync-on-start" specifies whether a complete update with all 1152 the subscribed data is to be sent at the beginning of a 1153 subscription. 1155 4.3. YANG Notifications 1157 4.3.1. State Change Notifications 1159 Subscription state notifications and mechanism are reused from 1160 [I-D.draft-ietf-netconf-subscribed-notifications]. Notifications 1161 "subscription-started" and "subscription-modified" have been 1162 augmented to include the datastore specific objects. 1164 4.3.2. Notifications for Subscribed Content 1166 Along with the subscribed content, there are other objects which 1167 might be part of a "push-update" or "push-change-update" 1168 notification. 1170 An "id" (that identifies the subscription) MUST be transported along 1171 with the subscribed contents. This allows a receiver to 1172 differentiate which subscription resulted in a particular update 1173 record. 1175 A "time-of-update" which represents the time an update record 1176 snapshot was generated. A receiver MAY assume that at this point in 1177 time a publisher's objects had the values that were pushed. 1179 An "incomplete-update" leaf. This leaf indicates that not all 1180 changes which have occurred since the last update are actually 1181 included with this update. In other words, the publisher has failed 1182 to fulfill its full subscription obligations. (For example a 1183 datastore was unable to provide the full set of datastore nodes to a 1184 publisher process.) To facilitate re-synchronization of on-change 1185 subscriptions, a publisher MAY subsequently send a "push-update" 1186 containing a full selection snapshot of subscribed data. 1188 4.4. YANG RPCs 1190 YANG-Push subscriptions are established, modified, and deleted using 1191 RPCs augmented from 1192 [I-D.draft-ietf-netconf-subscribed-notifications]. 1194 4.4.1. Establish-subscription RPC 1196 The subscriber sends an establish-subscription RPC with the 1197 parameters in section 3.1. An example might look like: 1199 1201 1204 1206 ds:operational 1207 1208 1210 /ex:foo 1211 1212 1213 500 1214 1215 1216 1218 Figure 10: Establish-subscription RPC 1220 A positive response includes the "id" of the accepted subscription. 1221 In that case a publisher may respond: 1223 1225 1227 52 1228 1229 1231 Figure 11: Establish-subscription positive RPC response 1233 A subscription can be rejected for multiple reasons, including the 1234 lack of authorization to establish a subscription, no capacity to 1235 serve the subscription at the publisher, or the inability of the 1236 publisher to select datastore content at the requested cadence. 1238 If a request is rejected because the publisher is not able to serve 1239 it, the publisher SHOULD include in the returned error hints which 1240 help a subscriber understand subscription parameters might have been 1241 accepted for the request. These hints would be included within the 1242 YANG-data structure "establish-subscription-error-datastore". 1243 However even with these hints, there are no guarantee that subsequent 1244 requests will in fact be accepted. 1246 The specific parameters to be returned as part of the RPC error 1247 response depend on the specific transport that is used to manage the 1248 subscription. For NETCONF, those parameters are defined in 1249 [I-D.draft-ietf-netconf-netconf-event-notifications]. For example, 1250 for the following NETCONF request: 1252 1254 1258 1260 ds:operational 1261 1262 1264 /ex:foo 1265 1266 1267 100 1268 1269 1270 1272 Figure 12: Establish-subscription request example 2 1274 a publisher that cannot serve on-change updates but that can serve 1275 periodic updates might return the following NETCONF response: 1277 1280 1281 application 1282 operation-failed 1283 error 1284 /yp:periodic/yp:period 1285 1286 1287 yp:on-change-unsupported 1288 1289 1290 1291 1293 Figure 13: Establish-subscription error response example 2 1295 4.4.2. Modify-subscription RPC 1297 The subscriber MAY invoke the "modify-subscription" RPC for a 1298 subscription it previously established. The subscriber will include 1299 newly desired values in the "modify-subscription" RPC. Parameters 1300 not included MUST remain unmodified. Below is an example where a 1301 subscriber attempts to modify the period and datastore XPath filter 1302 of a subscription using NETCONF. 1304 1306 1310 1011 1311 1313 ds:operational 1314 1315 1317 /ex:bar 1318 1319 1320 250 1321 1322 1323 1325 Figure 14: Modify subscription request 1327 The publisher MUST respond to the subscription modification request. 1328 If the request is rejected, the existing subscription is left 1329 unchanged, and the publisher MUST send an RPC error response. This 1330 response might have hints encapsulated within the YANG-data structure 1331 "modify-subscription-error-datastore". A subscription MAY be 1332 modified multiple times. 1334 The specific parameters to be returned as part of the RPC error 1335 response depend on the specific transport that is used to manage the 1336 subscription. For NETCONF, those parameters are specified in 1337 [I-D.draft-ietf-netconf-netconf-event-notifications]. 1339 A configured subscription cannot be modified using "modify- 1340 subscription" RPC. Instead, the configuration needs to be edited as 1341 needed. 1343 4.4.3. Delete-subscription RPC 1345 To stop receiving updates from a subscription and effectively delete 1346 a subscription that had previously been established using an 1347 "establish-subscription" RPC, a subscriber can send a "delete- 1348 subscription" RPC, which takes as only input the subscription's "id". 1349 This RPC is unmodified from 1350 [I-D.draft-ietf-netconf-subscribed-notifications]. 1352 4.4.4. Resync-subscription RPC 1354 This RPC is supported only for on-change subscriptions previously 1355 established using an "establish-subscription" RPC. For example: 1357 1359 1011 1362 1363 1365 Figure 15: Resync subscription 1367 On receipt, a publisher must either accept the request and quickly 1368 follow with a "push-update", or send an appropriate error within an 1369 rpc error response. Within an error response, the publisher MAY 1370 include supplemental information about the reasons within the YANG- 1371 data structure "resync-subscription-error". 1373 4.4.5. YANG Module Synchronization 1375 To make subscription requests, the subscriber needs to know the YANG 1376 datastore schemas used by the publisher, which are available via the 1377 YANG Library module, ietf-yang-library.yang from [RFC8525]. The 1378 receiver is expected to know the YANG library information before 1379 starting a subscription. 1381 The set of modules, revisions, features, and deviations can change at 1382 run-time (if supported by the publisher implementation). For this 1383 purpose, the YANG library provides a simple "yang-library-change" 1384 notification that informs the subscriber that the library has 1385 changed. In this case, a subscription may need to be updated to take 1386 the updates into account. The receiver may also need to be informed 1387 of module changes in order to process updates regarding datastore 1388 nodes from changed modules correctly. 1390 5. YANG Module 1392 This YANG module imports typedefs from [RFC6991], identities from 1393 [RFC8342], the YANG-data extension from [RFC8040], and the yang-patch 1394 grouping from [RFC8072]. In addition, it imports and augments many 1395 definitions from [I-D.draft-ietf-netconf-subscribed-notifications]. 1397 file "ietf-yang-push@2019-05-21.yang" 1398 module ietf-yang-push { 1399 yang-version 1.1; 1400 namespace "urn:ietf:params:xml:ns:yang:ietf-yang-push"; 1401 prefix yp; 1403 import ietf-yang-types { 1404 prefix yang; 1405 reference 1406 "RFC 6991: Common YANG Data Types"; 1407 } 1408 import ietf-subscribed-notifications { 1409 prefix sn; 1410 reference 1411 "draft-ietf-netconf-subscribed-notifications: 1412 Customized Subscriptions to a Publisher's Event Streams 1413 NOTE TO RFC Editor: Please replace above reference to 1414 draft-ietf-netconf-subscribed-notifications with RFC number 1415 when published (i.e. RFC xxxx)."; 1416 } 1417 import ietf-datastores { 1418 prefix ds; 1419 reference 1420 "RFC 8342: Network Management Datastore Architecture (NMDA)"; 1421 } 1422 import ietf-restconf { 1423 prefix rc; 1424 reference 1425 "RFC 8040: RESTCONF Protocol"; 1426 } 1427 import ietf-yang-patch { 1428 prefix ypatch; 1429 reference 1430 "RFC 8072: YANG Patch Media Type"; 1431 } 1433 organization 1434 "IETF NETCONF Working Group"; 1435 contact 1436 "WG Web: 1437 WG List: 1439 Editor: Alexander Clemm 1440 1441 Editor: Eric Voit 1442 1443 Editor: Alberto Gonzalez Prieto 1444 1445 Editor: Ambika Prasad Tripathy 1446 1447 Editor: Einar Nilsen-Nygaard 1448 1449 Editor: Andy Bierman 1450 1451 Editor: Balazs Lengyel 1452 "; 1453 description 1454 "This module contains YANG specifications for YANG push. 1456 The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL 1457 NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED', 1458 'MAY', and 'OPTIONAL' in this document are to be interpreted as 1459 described in BCP 14 (RFC 2119) (RFC 8174) when, and only when, 1460 they appear in all capitals, as shown here. 1462 Copyright (c) 2019 IETF Trust and the persons identified as 1463 authors of the code. All rights reserved. 1465 Redistribution and use in source and binary forms, with or 1466 without modification, is permitted pursuant to, and subject to 1467 the license terms contained in, the Simplified BSD License set 1468 forth in Section 4.c of the IETF Trust's Legal Provisions 1469 Relating to IETF Documents 1470 (https://trustee.ietf.org/license-info). 1472 This version of this YANG module is part of RFC XXXX; 1473 see the RFC itself for full legal notices."; 1475 // RFC Ed.: replace XXXX with actual RFC number and remove this 1476 // note. 1478 revision 2019-05-21 { 1479 description 1480 "Initial revision. 1481 NOTE TO RFC EDITOR: 1482 (1)Please replace the above revision date to 1483 the date of RFC publication when published. 1484 (2) Please replace the date in the file name 1485 (ietf-yang-push@2019-05-21.yang) to the date of RFC 1486 publication. 1487 (3) Please replace the following reference to 1488 draft-ietf-netconf-yang-push-25 with RFC number when 1489 published (i.e. RFC xxxx)."; 1490 reference 1491 "draft-ietf-netconf-yang-push-25"; 1492 } 1494 /* 1495 * FEATURES 1496 */ 1498 feature on-change { 1499 description 1500 "This feature indicates that on-change triggered subscriptions 1501 are supported."; 1502 } 1504 /* 1505 * IDENTITIES 1506 */ 1508 /* Error type identities for datastore subscription */ 1510 identity resync-subscription-error { 1511 description 1512 "Problem found while attempting to fulfill an 1513 'resync-subscription' RPC request."; 1514 } 1516 identity cant-exclude { 1517 base sn:establish-subscription-error; 1518 description 1519 "Unable to remove the set of 'excluded-changes'. This means 1520 the publisher is unable to restrict 'push-change-update's to 1521 just the change types requested for this subscription."; 1522 } 1524 identity datastore-not-subscribable { 1525 base sn:establish-subscription-error; 1526 base sn:subscription-terminated-reason; 1527 description 1528 "This is not a subscribable datastore."; 1529 } 1531 identity no-such-subscription-resync { 1532 base resync-subscription-error; 1533 description 1534 "Referenced subscription doesn't exist. This may be as a result 1535 of a non-existent subscription ID, an ID which belongs to 1536 another subscriber, or an ID for configured subscription."; 1537 } 1539 identity on-change-unsupported { 1540 base sn:establish-subscription-error; 1541 description 1542 "On-change is not supported for any objects which are 1543 selectable by this filter."; 1544 } 1546 identity on-change-sync-unsupported { 1547 base sn:establish-subscription-error; 1548 description 1549 "Neither sync on start nor resynchronization are supported for 1550 this subscription. This error will be used for two 1551 reasons. First if an 'establish-subscription' RPC includes 1552 'sync-on-start', yet the publisher can't support sending a 1553 'push-update' for this subscription for reasons other than 1554 'on-change-unsupported' or 'sync-too-big'. And second, if the 1555 'resync-subscription' RPC is invoked either for an existing 1556 periodic subscription, or for an on-change subscription which 1557 can't support resynchronization."; 1558 } 1560 identity period-unsupported { 1561 base sn:establish-subscription-error; 1562 base sn:modify-subscription-error; 1563 base sn:subscription-suspended-reason; 1564 description 1565 "Requested time period or dampening-period is too short. This 1566 can be for both periodic and on-change subscriptions (with or 1567 without dampening.) Hints suggesting alternative periods may 1568 be returned as supplemental information."; 1569 } 1571 identity update-too-big { 1572 base sn:establish-subscription-error; 1573 base sn:modify-subscription-error; 1574 base sn:subscription-suspended-reason; 1575 description 1576 "Periodic or on-change push update datatrees exceed a maximum 1577 size limit. Hints on estimated size of what was too big may 1578 be returned as supplemental information."; 1579 } 1580 identity sync-too-big { 1581 base sn:establish-subscription-error; 1582 base sn:modify-subscription-error; 1583 base resync-subscription-error; 1584 base sn:subscription-suspended-reason; 1585 description 1586 "Sync-on-start or resynchronization datatree exceeds a maximum 1587 size limit. Hints on estimated size of what was too big may 1588 be returned as supplemental information."; 1589 } 1591 identity unchanging-selection { 1592 base sn:establish-subscription-error; 1593 base sn:modify-subscription-error; 1594 base sn:subscription-terminated-reason; 1595 description 1596 "Selection filter is unlikely to ever select datatree nodes. 1597 This means that based on the subscriber's current access 1598 rights, the publisher recognizes that the selection filter is 1599 unlikely to ever select datatree nodes which change. Examples 1600 for this might be that node or subtree doesn't exist, read 1601 access is not permitted for a receiver, or static objects that 1602 only change at reboot have been chosen."; 1603 } 1605 /* 1606 * TYPE DEFINITIONS 1607 */ 1609 typedef change-type { 1610 type enumeration { 1611 enum create { 1612 description 1613 "A change that refers to the creation of a new datastore 1614 node."; 1615 } 1616 enum delete { 1617 description 1618 "A change that refers to the deletion of a datastore 1619 node."; 1620 } 1621 enum insert { 1622 description 1623 "A change that refers to the insertion of a new 1624 user-ordered datastore node."; 1625 } 1626 enum move { 1627 description 1628 "A change that refers to a reordering of the target 1629 datastore node."; 1630 } 1631 enum replace { 1632 description 1633 "A change that refers to a replacement of the target 1634 datastore node's value."; 1635 } 1636 } 1637 description 1638 "Specifies different types of datastore changes. 1640 This type is based on the edit operations defined for YANG 1641 Patch, with the difference that it is valid for a receiver to 1642 process an update record which performs a create operation on 1643 a datastore node the receiver believes exists, or to process a 1644 delete on a datastore node the receiver believes is missing."; 1645 reference 1646 "RFC 8072: YANG Patch Media Type, section 2.5"; 1647 } 1649 typedef selection-filter-ref { 1650 type leafref { 1651 path "/sn:filters/yp:selection-filter/yp:filter-id"; 1652 } 1653 description 1654 "This type is used to reference a selection filter."; 1655 } 1657 typedef centiseconds { 1658 type uint32; 1659 description 1660 "A period of time, measured in units of 0.01 seconds."; 1661 } 1663 /* 1664 * GROUP DEFINITIONS 1665 */ 1667 grouping datastore-criteria { 1668 description 1669 "A grouping to define criteria for which selected objects 1670 from a targeted datastore should be included in push 1671 updates."; 1672 leaf datastore { 1673 type identityref { 1674 base ds:datastore; 1676 } 1677 mandatory true; 1678 description 1679 "Datastore from which to retrieve data."; 1680 } 1681 uses selection-filter-objects; 1682 } 1684 grouping selection-filter-types { 1685 description 1686 "This grouping defines the types of selectors for objects 1687 from a datastore."; 1688 choice filter-spec { 1689 description 1690 "The content filter specification for this request."; 1691 anydata datastore-subtree-filter { 1692 if-feature "sn:subtree"; 1693 description 1694 "This parameter identifies the portions of the 1695 target datastore to retrieve."; 1696 reference 1697 "RFC 6241: Network Configuration Protocol, Section 6."; 1698 } 1699 leaf datastore-xpath-filter { 1700 if-feature "sn:xpath"; 1701 type yang:xpath1.0; 1702 description 1703 "This parameter contains an XPath expression identifying 1704 the portions of the target datastore to retrieve. 1706 If the expression returns a node-set, all nodes in the 1707 node-set are selected by the filter. Otherwise, if the 1708 expression does not return a node-set, the filter 1709 doesn't select any nodes. 1711 The expression is evaluated in the following XPath 1712 context: 1714 o The set of namespace declarations is the set of prefix 1715 and namespace pairs for all YANG modules implemented 1716 by the server, where the prefix is the YANG module 1717 name and the namespace is as defined by the 1718 'namespace' statement in the YANG module. 1720 If the leaf is encoded in XML, all namespace 1721 declarations in scope on the 'stream-xpath-filter' 1722 leaf element are added to the set of namespace 1723 declarations. If a prefix found in the XML is 1724 already present in the set of namespace declarations, 1725 the namespace in the XML is used. 1727 o The set of variable bindings is empty. 1729 o The function library is the core function library, and 1730 the XPath functions defined in section 10 in RFC 7950. 1732 o The context node is the root node of the target 1733 datastore."; 1734 } 1735 } 1736 } 1738 grouping selection-filter-objects { 1739 description 1740 "This grouping defines a selector for objects from a 1741 datastore."; 1742 choice selection-filter { 1743 description 1744 "The source of the selection filter applied to the 1745 subscription. This will come either referenced from a global 1746 list, or be provided within the subscription itself."; 1747 case by-reference { 1748 description 1749 "Incorporate a filter that has been configured 1750 separately."; 1751 leaf selection-filter-ref { 1752 type selection-filter-ref; 1753 mandatory true; 1754 description 1755 "References an existing selection filter which is to be 1756 applied to the subscription."; 1757 } 1758 } 1759 case within-subscription { 1760 description 1761 "Local definition allows a filter to have the same 1762 lifecycle as the subscription."; 1763 uses selection-filter-types; 1764 } 1765 } 1766 } 1768 grouping update-policy-modifiable { 1769 description 1770 "This grouping describes the datastore specific subscription 1771 conditions that can be changed during the lifetime of the 1772 subscription."; 1773 choice update-trigger { 1774 description 1775 "Defines necessary conditions for sending an event record to 1776 the subscriber."; 1777 case periodic { 1778 container periodic { 1779 presence "indicates a periodic subscription"; 1780 description 1781 "The publisher is requested to notify periodically the 1782 current values of the datastore as defined by the 1783 selection filter."; 1784 leaf period { 1785 type centiseconds; 1786 mandatory true; 1787 description 1788 "Duration of time which should occur between periodic 1789 push updates, in one hundredths of a second."; 1790 } 1791 leaf anchor-time { 1792 type yang:date-and-time; 1793 description 1794 "Designates a timestamp before or after which a series 1795 of periodic push updates are determined. The next 1796 update will take place at a whole multiple interval 1797 from the anchor time. For example, for an anchor time 1798 is set for the top of a particular minute and a period 1799 interval of a minute, updates will be sent at the top 1800 of every minute this subscription is active."; 1801 } 1802 } 1803 } 1804 case on-change { 1805 if-feature "on-change"; 1806 container on-change { 1807 presence "indicates an on-change subscription"; 1808 description 1809 "The publisher is requested to notify changes in values 1810 in the datastore subset as defined by a selection 1811 filter."; 1812 leaf dampening-period { 1813 type centiseconds; 1814 default "0"; 1815 description 1816 "Specifies the minimum interval between the assembly of 1817 successive update records for a single receiver of a 1818 subscription. Whenever subscribed objects change, and 1819 a dampening period interval (which may be zero) has 1820 elapsed since the previous update record creation for 1821 a receiver, then any subscribed objects and properties 1822 which have changed since the previous update record 1823 will have their current values marshalled and placed 1824 into a new update record."; 1825 } 1826 } 1827 } 1828 } 1829 } 1831 grouping update-policy { 1832 description 1833 "This grouping describes the datastore-specific subscription 1834 conditions of a subscription."; 1835 uses update-policy-modifiable { 1836 augment "update-trigger/on-change/on-change" { 1837 description 1838 "Includes objects not modifiable once subscription is 1839 established."; 1840 leaf sync-on-start { 1841 type boolean; 1842 default "true"; 1843 description 1844 "When this object is set to false, it restricts an 1845 on-change subscription from sending push-update 1846 notifications. When false, pushing a full selection per 1847 the terms of the selection filter MUST NOT be done for 1848 this subscription. Only updates about changes, 1849 i.e. only push-change-update notifications are sent. 1850 When true (default behavior), in order to facilitate a 1851 receiver's synchronization, a full update is sent when 1852 the subscription starts using a push-update 1853 notification. After that, push-change-update 1854 notifications are exclusively sent unless the publisher 1855 chooses to resync the subscription via a new push-update 1856 notification."; 1857 } 1858 leaf-list excluded-change { 1859 type change-type; 1860 description 1861 "Use to restrict which changes trigger an update. For 1862 example, if modify is excluded, only creation and 1863 deletion of objects is reported."; 1864 } 1865 } 1866 } 1867 } 1868 grouping hints { 1869 description 1870 "Parameters associated with some error for a subscription 1871 made upon a datastore."; 1872 leaf period-hint { 1873 type centiseconds; 1874 description 1875 "Returned when the requested time period is too short. This 1876 hint can assert a viable period for either a periodic push 1877 cadence or an on-change dampening interval."; 1878 } 1879 leaf filter-failure-hint { 1880 type string; 1881 description 1882 "Information describing where and/or why a provided filter 1883 was unsupportable for a subscription."; 1884 } 1885 leaf object-count-estimate { 1886 type uint32; 1887 description 1888 "If there are too many objects which could potentially be 1889 returned by the selection filter, this identifies the 1890 estimate of the number of objects which the filter would 1891 potentially pass."; 1892 } 1893 leaf object-count-limit { 1894 type uint32; 1895 description 1896 "If there are too many objects which could be returned by 1897 the selection filter, this identifies the upper limit of 1898 the publisher's ability to service for this subscription."; 1899 } 1900 leaf kilobytes-estimate { 1901 type uint32; 1902 description 1903 "If the returned information could be beyond the capacity 1904 of the publisher, this would identify the data size which 1905 could result from this selection filter."; 1906 } 1907 leaf kilobytes-limit { 1908 type uint32; 1909 description 1910 "If the returned information would be beyond the capacity 1911 of the publisher, this identifies the upper limit of the 1912 publisher's ability to service for this subscription."; 1913 } 1914 } 1915 /* 1916 * RPCs 1917 */ 1919 rpc resync-subscription { 1920 if-feature "on-change"; 1921 description 1922 "This RPC allows a subscriber of an active on-change 1923 subscription to request a full push of objects. 1925 A successful invocation results in a push-update of all 1926 datastore nodes that the subscriber is permitted to access. 1927 This RPC can only be invoked on the same session on which the 1928 subscription is currently active. In case of an error, a 1929 resync-subscription-error is sent as part of an error 1930 response."; 1931 input { 1932 leaf id { 1933 type sn:subscription-id; 1934 mandatory true; 1935 description 1936 "Identifier of the subscription that is to be resynced."; 1937 } 1938 } 1939 } 1941 rc:yang-data resync-subscription-error { 1942 container resync-subscription-error { 1943 description 1944 "If a 'resync-subscription' RPC fails, the subscription is 1945 not resynced and the RPC error response MUST indicate the 1946 reason for this failure. This YANG-data MAY be inserted as 1947 structured data within a subscription's RPC error response 1948 to indicate the failure reason."; 1949 leaf reason { 1950 type identityref { 1951 base resync-subscription-error; 1952 } 1953 mandatory true; 1954 description 1955 "Indicates the reason why the publisher has declined a 1956 request for subscription resynchronization."; 1957 } 1958 uses hints; 1959 } 1960 } 1962 augment "/sn:establish-subscription/sn:input" { 1963 description 1964 "This augmentation adds additional subscription parameters 1965 that apply specifically to datastore updates to RPC input."; 1966 uses update-policy; 1967 } 1969 augment "/sn:establish-subscription/sn:input/sn:target" { 1970 description 1971 "This augmentation adds the datastore as a valid target 1972 for the subscription to RPC input."; 1973 case datastore { 1974 description 1975 "Information specifying the parameters of an request for a 1976 datastore subscription."; 1977 uses datastore-criteria; 1978 } 1979 } 1981 rc:yang-data establish-subscription-datastore-error-info { 1982 container establish-subscription-datastore-error-info { 1983 description 1984 "If any 'establish-subscription' RPC parameters are 1985 unsupportable against the datastore, a subscription is not 1986 created and the RPC error response MUST indicate the reason 1987 why the subscription failed to be created. This YANG-data 1988 MAY be inserted as structured data within a subscription's 1989 RPC error response to indicate the failure reason. This 1990 YANG-data MUST be inserted if hints are to be provided back 1991 to the subscriber."; 1992 leaf reason { 1993 type identityref { 1994 base sn:establish-subscription-error; 1995 } 1996 description 1997 "Indicates the reason why the subscription has failed to 1998 be created to a targeted datastore."; 1999 } 2000 uses hints; 2001 } 2002 } 2004 augment "/sn:modify-subscription/sn:input" { 2005 description 2006 "This augmentation adds additional subscription parameters 2007 specific to datastore updates."; 2008 uses update-policy-modifiable; 2009 } 2010 augment "/sn:modify-subscription/sn:input/sn:target" { 2011 description 2012 "This augmentation adds the datastore as a valid target 2013 for the subscription to RPC input."; 2014 case datastore { 2015 description 2016 "Information specifying the parameters of an request for a 2017 datastore subscription."; 2018 uses datastore-criteria; 2019 } 2020 } 2022 rc:yang-data modify-subscription-datastore-error-info { 2023 container modify-subscription-datastore-error-info { 2024 description 2025 "This YANG-data MAY be provided as part of a subscription's 2026 RPC error response when there is a failure of a 2027 'modify-subscription' RPC which has been made against a 2028 datastore. This YANG-data MUST be used if hints are to be 2029 provides back to the subscriber."; 2030 leaf reason { 2031 type identityref { 2032 base sn:modify-subscription-error; 2033 } 2034 description 2035 "Indicates the reason why the subscription has failed to 2036 be modified."; 2037 } 2038 uses hints; 2039 } 2040 } 2042 /* 2043 * NOTIFICATIONS 2044 */ 2046 notification push-update { 2047 description 2048 "This notification contains a push update, containing data 2049 subscribed to via a subscription. This notification is sent 2050 for periodic updates, for a periodic subscription. It can 2051 also be used for synchronization updates of an on-change 2052 subscription. This notification shall only be sent to 2053 receivers of a subscription. It does not constitute a 2054 general-purpose notification that would be subscribable as 2055 part of the NETCONF event stream by any receiver."; 2056 leaf id { 2057 type sn:subscription-id; 2058 description 2059 "This references the subscription which drove the 2060 notification to be sent."; 2061 } 2062 anydata datastore-contents { 2063 description 2064 "This contains the updated data. It constitutes a snapshot 2065 at the time-of-update of the set of data that has been 2066 subscribed to. The snapshot corresponds to the same 2067 snapshot that would be returned in a corresponding get 2068 operation with the same selection filter parameters 2069 applied."; 2070 } 2071 leaf incomplete-update { 2072 type empty; 2073 description 2074 "This is a flag which indicates that not all datastore 2075 nodes subscribed to are included with this update. In 2076 other words, the publisher has failed to fulfill its full 2077 subscription obligations, and despite its best efforts is 2078 providing an incomplete set of objects."; 2079 } 2080 } 2082 notification push-change-update { 2083 if-feature "on-change"; 2084 description 2085 "This notification contains an on-change push update. This 2086 notification shall only be sent to the receivers of a 2087 subscription. It does not constitute ageneral-purpose 2088 notification that would be subscribable as part of the 2089 NETCONF event stream by any receiver."; 2090 leaf id { 2091 type sn:subscription-id; 2092 description 2093 "This references the subscription which drove the 2094 notification to be sent."; 2095 } 2096 container datastore-changes { 2097 description 2098 "This contains the set of datastore changes of the target 2099 datastore starting at the time of the previous update, per 2100 the terms of the subscription."; 2101 uses ypatch:yang-patch; 2102 } 2103 leaf incomplete-update { 2104 type empty; 2105 description 2106 "The presence of this object indicates not all changes which 2107 have occurred since the last update are included with this 2108 update. In other words, the publisher has failed to 2109 fulfill its full subscription obligations, for example in 2110 cases where it was not able to keep up with a change 2111 burst."; 2112 } 2113 } 2115 augment "/sn:subscription-started" { 2116 description 2117 "This augmentation adds datastore-specific objects to 2118 the notification that a subscription has started."; 2119 uses update-policy; 2120 } 2122 augment "/sn:subscription-started/sn:target" { 2123 description 2124 "This augmentation allows the datastore to be included as 2125 part of the notification that a subscription has started."; 2126 case datastore { 2127 uses datastore-criteria { 2128 refine "selection-filter/within-subscription" { 2129 description 2130 "Specifies the selection filter and where it originated 2131 from. If the 'selection-filter-ref' is populated, the 2132 filter within the subscription came from the 'filters' 2133 container. Otherwise it is populated in-line as part of 2134 the subscription itself."; 2135 } 2136 } 2137 } 2138 } 2140 augment "/sn:subscription-modified" { 2141 description 2142 "This augmentation adds datastore-specific objects to 2143 the notification that a subscription has been modified."; 2144 uses update-policy; 2145 } 2147 augment "/sn:subscription-modified/sn:target" { 2148 description 2149 "This augmentation allows the datastore to be included as 2150 part of the notification that a subscription has been 2151 modified."; 2152 case datastore { 2153 uses datastore-criteria { 2154 refine "selection-filter/within-subscription" { 2155 description 2156 "Specifies the selection filter and where it originated 2157 from. If the 'selection-filter-ref' is populated, the 2158 filter within the subscription came from the 'filters' 2159 container. Otherwise it is populated in-line as part of 2160 the subscription itself."; 2161 } 2162 } 2163 } 2164 } 2166 /* 2167 * DATA NODES 2168 */ 2170 augment "/sn:filters" { 2171 description 2172 "This augmentation allows the datastore to be included as part 2173 of the selection filtering criteria for a subscription."; 2174 list selection-filter { 2175 key "filter-id"; 2176 description 2177 "A list of pre-configured filters that can be applied 2178 to datastore subscriptions."; 2179 leaf filter-id { 2180 type string; 2181 description 2182 "An identifier to differentiate between selection 2183 filters."; 2184 } 2185 uses selection-filter-types; 2186 } 2187 } 2189 augment "/sn:subscriptions/sn:subscription" { 2190 when 'yp:datastore'; 2191 description 2192 "This augmentation adds many datastore specific objects to a 2193 subscription."; 2194 uses update-policy; 2195 } 2197 augment "/sn:subscriptions/sn:subscription/sn:target" { 2198 description 2199 "This augmentation allows the datastore to be included as 2200 part of the selection filtering criteria for a subscription."; 2201 case datastore { 2202 uses datastore-criteria; 2203 } 2204 } 2205 } 2207 2209 6. IANA Considerations 2211 This document registers the following namespace URI in the "IETF XML 2212 Registry" [RFC3688]: 2214 URI: urn:ietf:params:xml:ns:yang:ietf-yang-push 2215 Registrant Contact: The IESG. 2216 XML: N/A; the requested URI is an XML namespace. 2218 This document registers the following YANG module in the "YANG Module 2219 Names" registry [RFC6020]: 2221 Name: ietf-yang-push 2222 Namespace: urn:ietf:params:xml:ns:yang:ietf-yang-push 2223 Prefix: yp 2224 Reference: draft-ietf-netconf-yang-push-21.txt (RFC form) 2226 7. Security Considerations 2228 The YANG module specified in this document defines a schema for data 2229 that is designed to be accessed via network management protocols such 2230 as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer 2231 is the secure transport layer, and the mandatory-to-implement secure 2232 transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer 2233 is HTTPS, and the mandatory-to-implement secure transport is TLS 2234 [RFC8446]. 2236 The Network Configuration Access Control Model (NACM) [RFC8341] 2237 provides the means to restrict access for particular NETCONF or 2238 RESTCONF users to a preconfigured subset of all available NETCONF or 2239 RESTCONF protocol operations and content. 2241 There are a number of data nodes defined in this YANG module that are 2242 writable/creatable/deletable (i.e., config true, which is the 2243 default). These data nodes may be considered sensitive or vulnerable 2244 in some network environments. Write operations (e.g., edit-config) 2245 to these data nodes without proper protection can have a negative 2246 effect on network operations. These are the subtrees and data nodes 2247 and their sensitivity/vulnerability. (It should be noted that the 2248 YANG module augments the YANG module from 2250 [I-D.draft-ietf-netconf-subscribed-notifications]. All security 2251 considerations that are listed there are relevant also for datastore 2252 subscriptions. In the following, we focus on the data nodes that are 2253 newly introduced here.) 2255 o Subtree "selection-filter" under container "filters": This subtree 2256 allows to specify which objects or subtrees to include in a 2257 datastore subscription. An attacker could attempt to modify the 2258 filter. For example, the filter might be modified to result in 2259 very few objects being filtered in order to attempt to overwhelm 2260 the receiver. Alternatively, the filter might be modified to 2261 result in certain objects to be excluded from updates, in order to 2262 have certain changes go unnoticed. 2264 o Subtree "datastore" in choice "target" in list "subscription": 2265 Analogous to "selection filter", an attacker might attempt to 2266 modify the objects being filtered in order to overwhelm a receiver 2267 with a larger volume of object updates than expected, or to have 2268 certain changes go unnoticed. 2270 o Choice "update-trigger" in list "subscription": By modifying the 2271 update trigger, an attacker might alter the updates that are being 2272 sent in order to confuse a receiver, to withhold certain updates 2273 to be sent to the receiver, and/or to overwhelm a receiver. For 2274 example, an attacker might modify the period with which updates 2275 are reported for a periodic subscription, or it might modify the 2276 dampening period for an on-change subscription, resulting in 2277 greater delay of successive updates (potentially affecting 2278 responsiveness of applications that depend on the updates) or in a 2279 high volume of updates (to exhaust receiver resources). 2281 o RPC "resync-subscription": This RPC allows a subscriber of an on- 2282 change subscription to request a full push of objects in the 2283 subscription's scope. This can result in a large volume of data. 2284 An attacker could attempt to use this RPC to exhaust resources on 2285 the server to generate the data, and attempt to overwhelm a 2286 receiver with the resulting data volume. 2288 NACM provides one means to mitigate these threats on the publisher 2289 side. In order to address those threats as a subscriber, a 2290 subscriber could monitor the subscription configuration for any 2291 unexpected changes. For this, it can subscribe to updates to the 2292 YANG datastore nodes that represent his datastore subscriptions. As 2293 this data volume is small, a paranoid subscriber could even revert to 2294 occasional polling to guard against a compromised subscription 2295 against subscription configuration updates itself. 2297 8. Acknowledgments 2299 For their valuable comments, discussions, and feedback, we wish to 2300 acknowledge Tim Jenkins, Martin Bjorklund, Kent Watsen, Susan Hares, 2301 Yang Geng, Peipei Guo, Michael Scharf, Guangying Zheng, Tom Petch, 2302 Henk Birkholz, Reshad Rahman, Qin Wu, Rohit Ranade, and Rob Wilton. 2304 9. Contributors 2306 Alberto Gonzalez Prieto 2307 Microsoft 2308 albgonz@microsoft.com 2310 Ambika Prasad Tripathy 2311 Cisco Systems 2312 ambtripa@cisco.com 2314 Einar Nilsen-Nygaard 2315 Cisco Systems 2316 einarnn@cisco.com 2318 Andy Bierman 2319 YumaWorks 2320 andy@yumaworks.com 2322 Balazs Lengyel 2323 Ericsson 2324 balazs.lengyel@ericsson.com 2326 10. References 2328 10.1. Normative References 2330 [I-D.draft-ietf-netconf-subscribed-notifications] 2331 Voit, E., Clemm, A., Gonzalez Prieto, A., Tripathy, A., 2332 and E. Nilsen-Nygaard, "Subscription to YANG Event 2333 Notifications", draft-ietf-netconf-subscribed- 2334 notifications-24 (work in progress), April 2019. 2336 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2337 Requirement Levels", BCP 14, RFC 2119, 2338 DOI 10.17487/RFC2119, March 1997, 2339 . 2341 [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, 2342 DOI 10.17487/RFC3688, January 2004, 2343 . 2345 [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for 2346 the Network Configuration Protocol (NETCONF)", RFC 6020, 2347 DOI 10.17487/RFC6020, October 2010, 2348 . 2350 [RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types", 2351 RFC 6991, DOI 10.17487/RFC6991, July 2013, 2352 . 2354 [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", 2355 RFC 7950, DOI 10.17487/RFC7950, August 2016, 2356 . 2358 [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF 2359 Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, 2360 . 2362 [RFC8072] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Patch 2363 Media Type", RFC 8072, DOI 10.17487/RFC8072, February 2364 2017, . 2366 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2367 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2368 May 2017, . 2370 [RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration 2371 Access Control Model", STD 91, RFC 8341, 2372 DOI 10.17487/RFC8341, March 2018, 2373 . 2375 [RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K., 2376 and R. Wilton, "Network Management Datastore Architecture 2377 (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018, 2378 . 2380 [RFC8525] Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K., 2381 and R. Wilton, "YANG Library", RFC 8525, 2382 DOI 10.17487/RFC8525, March 2019, 2383 . 2385 10.2. Informative References 2387 [I-D.draft-ietf-netconf-netconf-event-notifications] 2388 Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard, 2389 E., and A. Tripathy, "Dynamic subscription to YANG Events 2390 and Datastores over NETCONF", April 2019. 2392 [I-D.draft-ietf-netconf-notification-capabilities] 2393 Lengyel, B. and A. Clemm, "YangPush Notification 2394 Capabilities", March 2019. 2396 [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., 2397 and A. Bierman, Ed., "Network Configuration Protocol 2398 (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, 2399 . 2401 [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure 2402 Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011, 2403 . 2405 [RFC7923] Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements 2406 for Subscription to YANG Datastores", RFC 7923, 2407 DOI 10.17487/RFC7923, June 2016, 2408 . 2410 [RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", 2411 BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, 2412 . 2414 [RFC8343] Bjorklund, M., "A YANG Data Model for Interface 2415 Management", RFC 8343, DOI 10.17487/RFC8343, March 2018, 2416 . 2418 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 2419 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 2420 . 2422 Appendix A. Appendix A: Subscription Errors 2424 A.1. RPC Failures 2426 Rejection of an RPC for any reason is indicated by via RPC error 2427 response from the publisher. Valid RPC errors returned include both 2428 existing transport layer RPC error codes, such as those seen with 2429 NETCONF in [RFC6241], as well as subscription specific errors such as 2430 those defined within the YANG model. As a result, how subscription 2431 errors are encoded within an RPC error response is transport 2432 dependent. 2434 References to specific identities in the ietf-subscribed- 2435 notifications YANG model or the ietf-yang-push YANG model may be 2436 returned as part of the error responses resulting from failed 2437 attempts at datastore subscription. For errors defined as part of 2438 ietf-subscribed-notifications, please refer to 2440 [I-D.draft-ietf-netconf-subscribed-notifications]. The errors 2441 introduced in this document, grouped per RPC, are as follows: 2443 establish-subscription modify-subscription 2444 ---------------------- ------------------- 2445 cant-exclude period-unsupported 2446 datastore-not-subscribable update-too-big 2447 on-change-unsupported sync-too-big 2448 on-change-sync-unsupported unchanging-selection 2449 period-unsupported 2450 update-too-big resync-subscription 2451 sync-too-big -------------------- 2452 unchanging-selection no-such-subscription-resync 2453 sync-too-big 2455 There is one final set of transport independent RPC error elements 2456 included in the YANG model. These are the following four YANG-data 2457 structures for failed datastore subscriptions: 2459 1. YANG-data establish-subscription-error-datastore 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 "establish-subscription" RPC response. This 2463 MUST be sent if hints are included. 2465 2. YANG-data modify-subscription-error-datastore 2466 This MUST be returned if information identifying the reason for an 2467 RPC error has not been placed elsewhere within the transport 2468 portion of a failed "modifiy-subscription" RPC response. This 2469 MUST be sent if hints are included. 2471 3. YANG-data sn:delete-subscription-error 2472 This MUST be returned if information identifying the reason for an 2473 RPC error has not been placed elsewhere within the transport 2474 portion of a failed "delete-subscription" or "kill-subscription" 2475 RPC response. 2477 4. YANG-data resync-subscription-error 2478 This MUST be returned if information identifying the reason for an 2479 RPC error has not been placed elsewhere within the transport 2480 portion of a failed "resync-subscription" RPC response. 2482 A.2. Notifications of Failure 2484 A subscription may be unexpectedly terminated or suspended 2485 independent of any RPC or configuration operation. In such cases, 2486 indications of such a failure MUST be provided. To accomplish this, 2487 a number of errors can be returned as part of the corresponding 2488 subscription state change notification. For this purpose, the 2489 following error identities have been introduced in this document, in 2490 addition to those that were already defined in 2491 [I-D.draft-ietf-netconf-subscribed-notifications]: 2493 subscription-terminated subscription-suspended 2494 ----------------------- ---------------------- 2495 datastore-not-subscribable period-unsupported 2496 unchanging-selection update-too-big 2497 synchronization-size 2499 Appendix B. Changes Between Revisions 2501 (To be removed by RFC editor prior to publication) 2503 v24 - v25 2505 o Minor updates to address IESG review comment regarding referencing 2506 the draft which addresses the notification capabilities problem. 2508 v23 - v24 2510 o Minor updates to address IESG review comments. Moving five of the 2511 coauthors to contributors as requested. 2513 v22 - v23 2515 o Minor updates to address IESG review comments. 2517 v21 - v22 2519 o Minor updates per Martin Bjorklund's YANG doctor review. 2521 v20 - v21 2523 o Minor updates, simplifying RPC input conditions. 2525 v19 - v20 2527 o Minor updates per WGLC comments. 2529 v18 - v19 2531 o Minor updates per WGLC comments. 2533 v17 - v18 2535 o Minor updates per WGLC comments. 2537 v16 - v17 2539 o Minor updates to YANG module, incorporating comments from Tom 2540 Petch. 2542 o Updated references. 2544 v15 - v16 2546 o Updated security considerations. 2548 o Updated references. 2550 o Addressed comments from last call review, specifically comments 2551 received from Martin Bjorklund. 2553 v14 - v15 2555 o Minor text fixes. Includes a fix to on-change update calculation 2556 to cover churn when an object changes to and from a value during a 2557 dampening period. 2559 v13 - v14 2561 o Minor text fixes. 2563 v12 - v13 2565 o Hint negotiation models now show error examples. 2567 o yang-data structures for rpc errors. 2569 v11 - v12 2571 o Included Martin's review clarifications. 2573 o QoS moved to subscribed-notifications 2575 o time-of-update removed as it is redundant with RFC5277's 2576 eventTime, and other times from notification-messages. 2578 o Error model moved to match existing implementations 2580 o On-change notifiable removed, how to do this is implementation 2581 specific. 2583 o NMDA model supported. Non NMDA version at https://github.com/ 2584 netconf-wg/yang-push/ 2586 v10 - v11 2588 o Promise model reference added. 2590 o Error added for no-such-datastore 2592 o Inherited changes from subscribed notifications (such as optional 2593 feature definitions). 2595 o scrubbed the examples for proper encodings 2597 v09 - v10 2599 o Returned to the explicit filter subtyping of v00-v05 2601 o identityref to ds:datastore made explicit 2603 o Returned ability to modify a selection filter via RPC. 2605 v08 - v09 2607 o Minor tweaks cleaning up text, removing appendicies, and making 2608 reference to revised-datastores. 2610 o Subscription-id (now:id) optional in push updates, except when 2611 encoded in RFC5277, Section 4 one-way notification. 2613 o Finished adding the text descibing the resync subscription RPC. 2615 o Removed relationships to other drafts and future technology 2616 appendicies as this work is being explored elsewhere. 2618 o Deferred the multi-line card issue to new drafts 2620 o Simplified the NACM interactions. 2622 v07 - v08 2624 o Updated YANG models with minor tweaks to accommodate changes of 2625 ietf-subscribed-notifications. 2627 v06 - v07 2629 o Clarifying text tweaks. 2631 o Clarification that filters act as selectors for subscribed 2632 datastore nodes; support for value filters not included but 2633 possible as a future extension 2635 o Filters don't have to be matched to existing YANG objects 2637 v05 - v06 2639 o Security considerations updated. 2641 o Base YANG model in [subscribe] updated as part of move to 2642 identities, YANG augmentations in this doc matched up 2644 o Terms refined and text updates throughout 2646 o Appendix talking about relationship to other drafts added. 2648 o Datastore replaces stream 2650 o Definitions of filters improved 2652 v04 to v05 2654 o Referenced based subscription document changed to Subscribed 2655 Notifications from 5277bis. 2657 o Getting operational data from filters 2659 o Extension notifiable-on-change added 2661 o New appendix on potential futures. Moved text into there from 2662 several drafts. 2664 o Subscription configuration section now just includes changed 2665 parameters from Subscribed Notifications 2667 o Subscription monitoring moved into Subscribed Notifications 2669 o New error and hint mechanisms included in text and in the YANG 2670 model. 2672 o Updated examples based on the error definitions 2674 o Groupings updated for consistency 2675 o Text updates throughout 2677 v03 to v04 2679 o Updates-not-sent flag added 2681 o Not notifiable extension added 2683 o Dampening period is for whole subscription, not single objects 2685 o Moved start/stop into rfc5277bis 2687 o Client and Server changed to subscriber, publisher, and receiver 2689 o Anchor time for periodic 2691 o Message format for synchronization (i.e. sync-on-start) 2693 o Material moved into 5277bis 2695 o QoS parameters supported, by not allowed to be modified by RPC 2697 o Text updates throughout 2699 Authors' Addresses 2701 Alexander Clemm 2702 Futurewei 2704 Email: ludwig@clemm.org 2706 Eric Voit 2707 Cisco Systems 2709 Email: evoit@cisco.com