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Bierman 8 YumaWorks 9 July 27, 2021 11 Comparison of NMDA datastores 12 draft-ietf-netmod-nmda-diff-11 14 Abstract 16 This document defines an RPC operation to compare management 17 datastores that comply with the NMDA architecture. 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 January 28, 2022. 36 Copyright Notice 38 Copyright (c) 2021 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 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 2. Key Words . . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 3. Definitions and Acronyms . . . . . . . . . . . . . . . . . . 3 56 4. Data Model Overview . . . . . . . . . . . . . . . . . . . . . 4 57 5. YANG Data Model . . . . . . . . . . . . . . . . . . . . . . . 6 58 6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 59 7. Performance Considerations . . . . . . . . . . . . . . . . . 14 60 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 61 8.1. Updates to the IETF XML Registry . . . . . . . . . . . . 15 62 8.2. Updates to the YANG Module Names Registry . . . . . . . . 15 63 9. Security Considerations . . . . . . . . . . . . . . . . . . . 15 64 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 65 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 66 11.1. Normative References . . . . . . . . . . . . . . . . . . 16 67 11.2. Informative References . . . . . . . . . . . . . . . . . 18 68 Appendix A. Possible Future Extensions . . . . . . . . . . . . . 18 69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 71 1. Introduction 73 The revised Network Management Datastore Architecture (NMDA) 74 [RFC8342] introduces a set of new datastores that each hold YANG- 75 defined data [RFC7950] and represent a different "viewpoint" on the 76 data that is maintained by a server. New YANG datastores that are 77 introduced include , which contains validated configuration 78 data that a client application intends to be in effect, and 79 , which contains operational state data (such as 80 statistics) as well as configuration data that is actually in effect. 82 NMDA introduces in effect a concept of "lifecycle" for management 83 data, distinguishing between data that is part of a configuration 84 that was supplied by a user, configuration data that has actually 85 been successfully applied and that is part of the operational state, 86 and overall operational state that includes both applied 87 configuration data as well as status and statistics. 89 As a result, data from the same management model can be reflected in 90 multiple datastores. Clients need to specify the target datastore to 91 be specific about which viewpoint of the data they want to access. 92 For example, a client application can differentiate whether they are 93 interested in the configuration supplied to a server and that is 94 supposed to be in effect, or the configuration that has been applied 95 and is actually in effect on the server. 97 Due to the fact that data can propagate from one datastore to 98 another, it is possible for differences between datastores to occur. 99 Some of this is entirely expected, as there may be a time lag between 100 when a configuration is given to the device and reflected in 101 , until when it actually takes effect and is reflected in 102 . However, there may be cases when a configuration item 103 that was to be applied may not actually take effect at all or needs 104 an unusually long time to do so. This can be the case due to certain 105 conditions not being met, certain parts of the configuration not 106 propagating because considered inactive, resource dependencies not 107 being resolved, or even implementation errors in corner conditions. 109 When configuration that is in effect is different from configuration 110 that was applied, many issues can result. It becomes more difficult 111 to operate the network properly due to limited visibility of actual 112 operational status which makes it more difficult to analyze and 113 understand what is going on in the network. Services may be 114 negatively affected (for example, degrading or breaking a customer 115 service) and network resources may be misallocated. 117 Applications can potentially analyze any differences between two 118 datastores by retrieving the contents from both datastores and 119 comparing them. However, in many cases this will be at the same time 120 costly and extremely wasteful. 122 This document introduces a YANG data model which defines RPCs, 123 intended to be used in conjunction with NETCONF [RFC6241] or RESTCONF 124 [RFC8040], that allow a client to request a server to compare two 125 NMDA datastores and report any differences. 127 2. Key Words 129 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 130 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 131 "OPTIONAL" in this document are to be interpreted as described in BCP 132 14 [RFC2119] [RFC8174] when, and only when, they appear in all 133 capitals, as shown here. 135 3. Definitions and Acronyms 137 NMDA: Network Management Datastore Architecture 139 RPC: Remote Procedure Call 141 4. Data Model Overview 143 The core of the solution is a new management operation, , 144 that compares the data tree contents of two datastores. The 145 operation checks whether there are any differences in values or in 146 data nodes that are contained in either datastore, and returns any 147 differences as output. The output is returned in the format 148 specified in YANG-Patch [RFC8072]. 150 The YANG data model defines the operation as a new RPC. 151 The operation takes the following input parameters: 153 o source: The source identifies the datastore that will serve as the 154 reference for the comparison, for example . 156 o target: The target identifies the datastore to compare against the 157 source, for example . 159 o filter-spec: This is a choice between different filter constructs 160 to identify the parts of the datastore to be retrieved. It acts 161 as a node selector that specifies which data nodes are within the 162 scope of the comparison and which nodes are outside the scope. 163 This allows a comparison operation to be applied only to a 164 specific part of the datastore that is of interest, such as a 165 particular subtree. Note, the filter does not allow expressions 166 that match against data node values, since this may incur 167 implementation difficulties and is not required for normal use 168 cases. 170 o all: When set, this parameter indicates that all differences 171 should be included, including differences pertaining to schema 172 nodes that exist in only one of the datastores. When this 173 parameter is not included, a prefiltering step is automatically 174 applied to exclude data from the comparison that does not pertain 175 to both datastores: if the same schema node is not present in both 176 datastores, then all instances of that schema node and all its 177 descendants are excluded from the comparison. This allows client 178 applications to focus on the differences that constitute true 179 mismatches of instance data without needing to specify more 180 complex filter constructs. 182 o report-origin: When set, this parameter indicates that origin 183 metadata should be included as part of RPC output. When this 184 parameter is omitted, origin metadata in comparisons that involve 185 is by default omitted. Note that origin metadata 186 only applies to it is therefore also omitted in 187 comparisons that do not involve regardless of 188 whether or not the parameter is set. 190 The operation provides the following output parameter: 192 o differences: This parameter contains the list of differences. 193 Those differences are encoded per YANG-Patch data model defined in 194 RFC8072. When a datastore node in the source of the comparison is 195 not present in the target of the comparison, this can be indicated 196 either as a "delete" or as a "remove" in the patch as there is no 197 differentiation between those operations for the purposes of the 198 comparison. The YANG-Patch data model is augmented to indicate 199 the value of source datastore nodes in addition to the patch 200 itself that would need to be applied to the source to produce the 201 target. When the target datastore is and the input 202 parameter "report-origin" is set, "origin" metadata is included as 203 part of the patch. Including origin metadata can help in some 204 cases explain the cause of a difference, for example when a data 205 node is part of but the origin of the same data node in 206 is reported as "system". 208 The data model is defined in the ietf-nmda-compare YANG module. Its 209 structure is shown in the following figure. The notation syntax 210 follows [RFC8340]. 212 module: ietf-nmda-compare 213 rpcs: 214 +---x compare 215 +---w input 216 | +---w source identityref 217 | +---w target identityref 218 | +---w all? empty 219 | +---w report-origin? empty 220 | +---w (filter-spec)? 221 | +--:(subtree-filter) 222 | | +---w subtree-filter? 223 | +--:(xpath-filter) 224 | +---w xpath-filter? yang:xpath1.0 {nc:xpath}? 225 +--ro output 226 +--ro (compare-response)? 227 +--:(no-matches) 228 | +--ro no-matches? empty 229 +--:(differences) 230 +--ro differences 231 +--ro yang-patch 232 +--ro patch-id string 233 +--ro comment? string 234 +--ro edit* [edit-id] 235 +--ro edit-id string 236 +--ro operation enumeration 237 +--ro target target-resource-offset 238 +--ro point? target-resource-offset 239 +--ro where? enumeration 240 +--ro value? 241 +--ro source-value? 243 Structure of ietf-nmda-compare 245 5. YANG Data Model 247 file "ietf-nmda-compare@2021-07-27.yang" 248 module ietf-nmda-compare { 250 yang-version 1.1; 251 namespace "urn:ietf:params:xml:ns:yang:ietf-nmda-compare"; 253 prefix cmp; 255 import ietf-yang-types { 256 prefix yang; 257 reference "RFC 6991: Common YANG Data Types"; 258 } 259 import ietf-datastores { 260 prefix ds; 261 reference "RFC 8342: Network Management Datastore 262 Architecture (NMDA)"; 263 } 264 import ietf-yang-patch { 265 prefix ypatch; 266 reference "RFC 8072: YANG Patch Media Type"; 267 } 268 import ietf-netconf { 269 prefix nc; 270 reference "RFC6241: Network Configuration Protocol (NETCONF)"; 271 } 273 organization "IETF"; 274 contact 275 "WG Web: 276 WG List: 278 Author: Alexander Clemm 279 281 Author: Yingzhen Qu 282 284 Author: Jeff Tantsura 285 287 Author: Andy Bierman 288 "; 290 description 291 "The YANG data model defines a new operation, , that 292 can be used to compare NMDA datastores. 294 Copyright (c) 2021 IETF Trust and the persons identified as 295 authors of the code. All rights reserved. 297 Redistribution and use in source and binary forms, with or 298 without modification, is permitted pursuant to, and subject to 299 the license terms contained in, the Simplified BSD License set 300 forth in Section 4.c of the IETF Trust's Legal Provisions 301 Relating to IETF Documents 302 (https://trustee.ietf.org/license-info). 304 This version of this YANG module is part of 305 draft-ietf-netmod-nmda-diff-11; see the RFC itself for full 306 legal notices. 308 NOTE TO RFC EDITOR: Please replace above reference to 309 draft-ietf-netmod-nmda-diff-11 with RFC number when published 310 (i.e. RFC xxxx)."; 312 revision 2021-07-27 { 313 description 314 "Initial revision. 315 NOTE TO RFC EDITOR: 316 (1)Please replace the above revision date to 317 the date of RFC publication when published. 318 (2) Please replace the date in the file name 319 (ietf-nmda-compare@2021-07-27.yang) to the date of RFC 320 publication. 321 (3) Please replace the following reference to 322 draft-ietf-netmod-nmda-diff-11 with RFC number when published 323 (i.e. RFC xxxx)."; 324 reference 325 "draft-ietf-netmod-nmda-diff-11: Comparison of NMDA 326 datastores"; 327 } 329 /* RPC */ 330 rpc compare { 331 description 332 "NMDA datastore compare operation."; 333 input { 334 leaf source { 335 type identityref { 336 base ds:datastore; 337 } 338 mandatory true; 339 description 340 "The source datastore to be compared."; 341 } 342 leaf target { 343 type identityref { 344 base ds:datastore; 345 } 346 mandatory true; 347 description 348 "The target datastore to be compared."; 349 } 350 leaf all { 351 type empty; 352 description 353 "When this leaf is provided, all data nodes are compared, 354 whether their schema node pertains to both datastores or 355 not. When this leaf is omitted, a prefiltering step is 356 automatically applied that excludes data nodes from the 357 comparison that can occur in only one datastore but not 358 the other. Specifically, if one of the datastores 359 (source or target) contains only configuration data and 360 the other datastore is , data nodes for 361 which config is false are excluded from the comparison."; 362 } 363 leaf report-origin { 364 type empty; 365 description 366 "When this leaf is provided, origin metadata is 367 included as part of RPC output. When this leaf is 368 omitted, origin metadata in comparisons that involve 369 is by default omitted."; 370 } 371 choice filter-spec { 372 description 373 "Identifies the portions of the datastores to be 374 compared."; 375 anydata subtree-filter { 376 description 377 "This parameter identifies the portions of the 378 target datastore to retrieve."; 379 reference "RFC 6241, Section 6."; 380 } 381 leaf xpath-filter { 382 if-feature nc:xpath; 383 type yang:xpath1.0; 384 description 385 "This parameter contains an XPath expression 386 identifying the portions of the target 387 datastore to retrieve."; 388 reference "RFC 6991: Common YANG Data Types"; 389 } 390 } 391 } 392 output { 393 choice compare-response { 394 description 395 "Comparison results."; 396 leaf no-matches { 397 type empty; 398 description 399 "This leaf indicates that the filter did not match 400 anything and nothing was compared."; 401 } 402 container differences { 403 description 404 "The list of differences, encoded per RFC8072 with an 405 augmentation to include source values where applicable. 406 When a datastore node in the source is not present in 407 the target, this can be indicated either as a 'delete' 408 or as a 'remove' as there is no difference between 409 them for the purposes of the comparison."; 410 uses ypatch:yang-patch { 411 augment "yang-patch/edit" { 412 description 413 "Provide the value of the source of the patch, 414 respectively of the comparison, in addition to 415 the target value, where applicable."; 416 anydata source-value { 417 when "../operation = 'delete'" 418 + "or ../operation = 'merge'" 419 + "or ../operation = 'move'" 420 + "or ../operation = 'replace'" 421 + "or ../operation = 'remove'"; 422 description 423 "The anydata 'value' is only used for 'delete', 424 'move', 'merge', 'replace', and 'remove' 425 operations."; 426 } 427 reference "RFC 8072: YANG Patch Media Type"; 428 } 429 } 430 } 431 } 432 } 433 } 434 } 435 437 6. Example 439 The following example compares the difference between 440 and for a subtree under "interfaces". The subtree 441 contains a subset of objects that are defined in a YANG data model 442 for the management of interfaces defined in [RFC8343]. The excerpt 443 of the data model whose instantiation is the basis of the comparison 444 is as follows: 446 container interfaces { 447 description 448 "Interface parameters."; 449 list interface { 450 key "name"; 451 leaf name { 452 type string; 453 description 454 "The name of the interface". 455 } 456 leaf description { 457 type string; 458 description 459 "A textual description of the interface."; 460 } 461 leaf enabled { 462 type boolean; 463 default "true"; 464 description 465 "This leaf contains the configured, desired state of the 466 interface.";" 467 } 468 } 469 } 471 The contents of and datastores: 473 //INTENDED 474 475 476 eth0 477 false 478 ip interface 479 480 482 //OPERATIONAL 483 486 487 eth0 488 true 489 490 491 does not contain an instance for leaf "description" 492 that is contained in . Another leaf, "enabled", has 493 different values in the two datastores, being "true" in 494 and "false" in . A third leaf, "name", is the same in both 495 cases. The origin of the leaf instances in is 496 "learned", which may help explain the discrepancies. 498 RPC request to compare (source of the comparison) with 499 (target of the comparison): 501 503 505 ds:operational 506 ds:intended 507 508 510 /if:interfaces 511 512 513 515 RPC reply, when a difference is detected: 517 520 523 524 interface status 525 526 diff between operational (source) and intended (target) 527 528 529 1 530 replace 531 /ietf-interfaces:interface=eth0/enabled 532 533 false 534 535 536 true 537 538 539 540 2 541 create 542 /ietf-interfaces:interface=eth0/description 543 544 ip interface 545 546 547 548 549 551 The same request in RESTCONF (using JSON format): 553 POST /restconf/operations/ietf-nmda-compare:compare HTTP/1.1 554 Host: example.com 555 Content-Type: application/yang-data+json 556 Accept: application/yang-data+json 557 { "ietf-nmda-compare:input" { 558 "source" : "ietf-datastores:operational", 559 "target" : "ietf-datastores:intended", 560 "report-origin" : null, 561 "xpath-filter" : "/ietf-interfaces:interfaces" 562 } 563 } 564 The same response in RESTCONF (using JSON format): 566 HTTP/1.1 200 OK 567 Date: Thu, 26 Jan 2019 20:56:30 GMT 568 Server: example-server 569 Content-Type: application/yang-data+json 570 { "ietf-nmda-compare:output" : { 571 "differences" : { 572 "ietf-yang-patch:yang-patch" : { 573 "patch-id" : "interface status", 574 "comment" : "diff between intended (source) and operational", 575 "edit" : [ 576 { 577 "edit-id" : "1", 578 "operation" : "replace", 579 "target" : "/ietf-interfaces:interface=eth0/enabled", 580 "value" : { 581 "ietf-interfaces:interface/enabled" : "false" 582 }, 583 "source-value" : { 584 "ietf-interfaces:interface/enabled" : "true", 585 "@ietf-interfaces:interface/enabled" : { 586 "ietf-origin:origin" : "ietf-origin:learned" 587 } 588 } 589 }, 590 { 591 "edit-id" : "2", 592 "operation" : "create", 593 "target" : "/ietf-interfaces:interface=eth0/description", 594 "value" : { 595 "ietf-interface:interface/description" : "ip interface" 596 } 597 } 598 ] 599 } 600 } 601 } 602 } 604 7. Performance Considerations 606 The compare operation can be computationally expensive. While 607 responsible client applications are expected to use the operation 608 responsibly and sparingly only when warranted, implementations need 609 to be aware of the fact that excessive invocation of this operation 610 will burden system resources and need to ensure that system 611 performance will not be adversely impacted. One possibility for an 612 implementation to mitigate against such a possibility is to limit the 613 number of requests that is served to a client, or to any number of 614 clients, in any one time interval, rejecting requests made at a 615 higher frequency than the implementation can reasonably sustain. 617 While useful, tools such as YANG Data Models that allow for the 618 monitoring of server resources, system performance, and 619 statisticsabout RPCs and RPC rates are outside the scope of this 620 document. When defined, any such model should be general in nature 621 and not limited to the RPC operation defined in this document. 623 8. IANA Considerations 625 8.1. Updates to the IETF XML Registry 627 This document registers one URI in the IETF XML registry [RFC3688]. 628 Following the format in [RFC3688], the following registration is 629 requested: 631 URI: urn:ietf:params:xml:ns:yang:ietf-nmda-compare 633 Registrant Contact: The IESG. 635 XML: N/A, the requested URI is an XML namespace. 637 8.2. Updates to the YANG Module Names Registry 639 This document registers a YANG module in the YANG Module Names 640 registry [RFC6020]. Following the format in [RFC6020], the following 641 registration is requested: 643 name: ietf-nmda-compare 645 namespace: urn:ietf:params:xml:ns:yang:ietf-nmda-compare 647 prefix: cmp 649 reference: draft-ietf-netmod-nmda-diff-11 (RFC form) 651 9. Security Considerations 653 The YANG module specified in this document defines a schema for data 654 that is designed to be accessed via network management protocols such 655 as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer 656 is the secure transport layer, and the mandatory-to-implement secure 657 transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer 658 is HTTPS, and the mandatory-to-implement secure transport is TLS 659 [RFC8446]. 661 The NETCONF access control model [RFC8341] provides the means to 662 restrict access for particular NETCONF or RESTCONF users to a 663 preconfigured subset of all available NETCONF or RESTCONF protocol 664 operations and content. 666 NACM specifies access for the server in its entirety and the same 667 access rules apply to all datastores. Any subtrees to which a 668 requestor does not have read access are silently skipped and not 669 included in the comparison. 671 The RPC operation defined in this YANG module, "compare", may be 672 considered sensitive or vulnerable in some network environments. It 673 is thus important to control access to this operation. This is the 674 sensitivity/vulnerability of RPC operation "compare": 676 Comparing datastores for differences requires a certain amount of 677 processing resources at the server. An attacker could attempt to 678 attack a server by making a high volume of comparison requests. 679 Server implementations can guard against such scenarios in several 680 ways. For one, they can implement the NETCONF access control model 681 in order to require proper authorization for requests to be made. 682 Second, server implementations can limit the number of requests that 683 they serve to a client in any one time interval, rejecting requests 684 made at a higher frequency than the implementation can reasonably 685 sustain. 687 10. Acknowledgments 689 We thank Rob Wilton, Martin Bjorklund, Mahesh Jethanandani, Lou 690 Berger, Kent Watsen, Phil Shafer, Ladislav Lhotka, Tim Carey, and 691 Reshad Rahman for valuable feedback and suggestions. 693 11. References 695 11.1. Normative References 697 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 698 Requirement Levels", BCP 14, RFC 2119, 699 DOI 10.17487/RFC2119, March 1997, 700 . 702 [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, 703 DOI 10.17487/RFC3688, January 2004, 704 . 706 [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for 707 the Network Configuration Protocol (NETCONF)", RFC 6020, 708 DOI 10.17487/RFC6020, October 2010, 709 . 711 [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., 712 and A. Bierman, Ed., "Network Configuration Protocol 713 (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, 714 . 716 [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure 717 Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011, 718 . 720 [RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types", 721 RFC 6991, DOI 10.17487/RFC6991, July 2013, 722 . 724 [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", 725 RFC 7950, DOI 10.17487/RFC7950, August 2016, 726 . 728 [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF 729 Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, 730 . 732 [RFC8072] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Patch 733 Media Type", RFC 8072, DOI 10.17487/RFC8072, February 734 2017, . 736 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 737 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 738 May 2017, . 740 [RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", 741 BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, 742 . 744 [RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration 745 Access Control Model", STD 91, RFC 8341, 746 DOI 10.17487/RFC8341, March 2018, 747 . 749 [RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K., 750 and R. Wilton, "Network Management Datastore Architecture 751 (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018, 752 . 754 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 755 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 756 . 758 11.2. Informative References 760 [RFC8343] Bjorklund, M., "A YANG Data Model for Interface 761 Management", RFC 8343, DOI 10.17487/RFC8343, March 2018, 762 . 764 Appendix A. Possible Future Extensions 766 It is conceivable to extend the compare operation with a number of 767 possible additional features in the future. 769 Specifically, it is possible to define an extension with an optional 770 feature for dampening. This will allow clients to specify a minimum 771 time period for which a difference must persist for it to be 772 reported. This will enable clients to distinguish between 773 differences that are only fleeting from ones that are not and that 774 may represent a real operational issue and inconsistency within the 775 device. 777 For this purpose, an additional input parameter can be added to 778 specify the dampening period. Only differences that pertain for at 779 least the dampening time are reported. A value of 0 or omission of 780 the parameter indicates no dampening. Reporting of differences MAY 781 correspondingly be delayed by the dampening period from the time the 782 request is received. 784 To implement this feature, a server implementation might run a 785 comparison when the RPC is first invoked and temporarily store the 786 result. Subsequently, it could wait until after the end of the 787 dampening period to check whether the same differences are still 788 observed. The differences that still persist are then returned. 790 Authors' Addresses 792 Alexander Clemm 793 Futurewei 794 2330 Central Expressway 795 Santa Clara, CA 95050 796 USA 798 Email: ludwig@clemm.org 799 Yingzhen Qu 800 Futurewei 801 2330 Central Expressway 802 Santa Clara, CA 95050 803 USA 805 Email: yqu@futurewei.com 807 Jeff Tantsura 808 Microsoft 810 Email: jefftant.ietf@gmail.com 812 Andy Bierman 813 YumaWorks 815 Email: andy@yumaworks.com