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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Unused Reference: 'RFC6991' is defined on line 706, but no explicit reference was found in the text Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group A. Clemm 3 Internet-Draft Y. Qu 4 Intended status: Standards Track Futurewei 5 Expires: December 19, 2021 J. Tantsura 6 Apstra 7 A. Bierman 8 YumaWorks 9 June 17, 2021 11 Comparison of NMDA datastores 12 draft-ietf-netmod-nmda-diff-09 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 December 19, 2021. 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 . . . . . . . . . . . . . . . . . 17 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. 187 The operation provides the following output parameter: 189 o differences: This parameter contains the list of differences. 190 Those differences are encoded per YANG-Patch data model defined in 191 RFC8072. When a datastore node in the source of the comparison is 192 not present in the target of the comparison, this can be indicated 193 either as a "delete" or as a "remove" in the patch as there is no 194 differentiation between those operations for the purposes of the 195 comparison. The YANG-Patch data model is augmented to indicate 196 the value of source datastore nodes in addition to the patch 197 itself that would need to be applied to the source to produce the 198 target. When the target datastore is and the input 199 parameter "report-origin" is set, "origin" metadata is included as 200 part of the patch. Including origin metadata can help in some 201 cases explain the cause of a difference, for example when a data 202 node is part of but the origin of the same data node in 203 is reported as "system". 205 The data model is defined in the ietf-nmda-compare YANG module. Its 206 structure is shown in the following figure. The notation syntax 207 follows [RFC8340]. 209 module: ietf-nmda-compare 210 rpcs: 211 +---x compare 212 +---w input 213 | +---w source identityref 214 | +---w target identityref 215 | +---w all? empty 216 | +---w report-origin? empty 217 | +---w (filter-spec)? 218 | +--:(subtree-filter) 219 | | +---w subtree-filter? 220 | +--:(xpath-filter) 221 | +---w xpath-filter? yang:xpath1.0 {nc:xpath}? 222 +--ro output 223 +--ro (compare-response)? 224 +--:(no-matches) 225 | +--ro no-matches? empty 226 +--:(differences) 227 +--ro differences 228 +--ro yang-patch 229 +--ro patch-id string 230 +--ro comment? string 231 +--ro edit* [edit-id] 232 +--ro edit-id string 233 +--ro operation enumeration 234 +--ro target target-resource-offset 235 +--ro point? target-resource-offset 236 +--ro where? enumeration 237 +--ro value? 238 +--ro source-value? 240 Structure of ietf-nmda-compare 242 5. YANG Data Model 244 file "ietf-nmda-compare@2021-06-17.yang" 245 module ietf-nmda-compare { 247 yang-version 1.1; 248 namespace "urn:ietf:params:xml:ns:yang:ietf-nmda-compare"; 250 prefix cmp; 252 import ietf-yang-types { 253 prefix yang; 254 reference "RFC 6991: Common YANG Data Types"; 255 } 256 import ietf-datastores { 257 prefix ds; 258 reference "RFC 8342: Network Management Datastore 259 Architecture (NMDA)"; 260 } 261 import ietf-yang-patch { 262 prefix ypatch; 263 reference "RFC 8072: YANG Patch Media Type"; 264 } 265 import ietf-netconf { 266 prefix nc; 267 reference "RFC6241: Network Configuration Protocol (NETCONF)"; 268 } 270 organization "IETF"; 271 contact 272 "WG Web: 273 WG List: 275 Author: Alexander Clemm 276 278 Author: Yingzhen Qu 279 281 Author: Jeff Tantsura 282 284 Author: Andy Bierman 285 "; 287 description 288 "The YANG data model defines a new operation, , that 289 can be used to compare NMDA datastores. 291 Copyright (c) 2021 IETF Trust and the persons identified as 292 authors of the code. All rights reserved. 294 Redistribution and use in source and binary forms, with or 295 without modification, is permitted pursuant to, and subject to 296 the license terms contained in, the Simplified BSD License set 297 forth in Section 4.c of the IETF Trust's Legal Provisions 298 Relating to IETF Documents 299 (https://trustee.ietf.org/license-info). 301 This version of this YANG module is part of 302 draft-ietf-netmod-nmda-diff-09; see the RFC itself for full 303 legal notices. 305 NOTE TO RFC EDITOR: Please replace above reference to 306 draft-ietf-netmod-nmda-diff-09 with RFC number when published 307 (i.e. RFC xxxx)."; 309 revision 2021-06-17 { 310 description 311 "Initial revision. 312 NOTE TO RFC EDITOR: 313 (1)Please replace the above revision date to 314 the date of RFC publication when published. 315 (2) Please replace the date in the file name 316 (ietf-nmda-compare@2021-06-17.yang) to the date of RFC 317 publication. 318 (3) Please replace the following reference to 319 draft-ietf-netmod-nmda-diff-09 with RFC number when published 320 (i.e. RFC xxxx)."; 321 reference 322 "draft-ietf-netmod-nmda-diff-09: Comparison of NMDA 323 datastores"; 324 } 326 /* RPC */ 327 rpc compare { 328 description 329 "NMDA datastore compare operation."; 330 input { 331 leaf source { 332 type identityref { 333 base ds:datastore; 334 } 335 mandatory true; 336 description 337 "The source datastore to be compared."; 338 } 339 leaf target { 340 type identityref { 341 base ds:datastore; 342 } 343 mandatory true; 344 description 345 "The target datastore to be compared."; 346 } 347 leaf all { 348 type empty; 349 description 350 "When this leaf is provided, all data nodes are compared, 351 whether their schema node pertains to both datastores or 352 not. When this leaf is omitted, a prefiltering step is 353 automatically applied that excludes data nodes from the 354 comparison that can occur in only one datastore but not 355 the other. Specifically, if one of the datastores 356 (source or target) contains only configuration data and 357 the other datastore is , data nodes for 358 which config is false are excluded from the comparison."; 359 } 360 leaf report-origin { 361 type empty; 362 description 363 "When this leaf is provided, origin metadata is 364 included as part of RPC output. When this leaf is 365 omitted, origin metadata in comparisons that involve 366 is by default omitted."; 367 } 368 choice filter-spec { 369 description 370 "Identifies the portions of the datastores to be 371 compared."; 372 anydata subtree-filter { 373 description 374 "This parameter identifies the portions of the 375 target datastore to retrieve."; 376 reference "RFC 6241, Section 6."; 377 } 378 leaf xpath-filter { 379 if-feature nc:xpath; 380 type yang:xpath1.0; 381 description 382 "This parameter contains an XPath expression 383 identifying the portions of the target 384 datastore to retrieve."; 385 reference "RFC 6991: Common YANG Data Types"; 386 } 387 } 388 } 389 output { 390 choice compare-response { 391 description 392 "Comparison results."; 393 leaf no-matches { 394 type empty; 395 description 396 "This leaf indicates that the filter did not match 397 anything and nothing was compared."; 398 } 399 container differences { 400 description 401 "The list of differences, encoded per RFC8072 with an 402 augmentation to include source values where applicable. 403 When a datastore node in the source is not present in 404 the target, this can be indicated either as a 'delete' 405 or as a 'remove' as there is no difference between 406 them for the purposes of the comparison."; 407 uses ypatch:yang-patch { 408 augment "yang-patch/edit" { 409 description 410 "Provide the value of the source of the patch, 411 respectively of the comparison, in addition to 412 the target value, where applicable."; 413 anydata source-value { 414 when "../operation = 'delete'" 415 + "or ../operation = 'merge'" 416 + "or ../operation = 'move'" 417 + "or ../operation = 'replace'" 418 + "or ../operation = 'remove'"; 419 description 420 "The anydata 'value' is only used for 'delete', 421 'move', 'merge', 'replace', and 'remove' 422 operations."; 423 } 424 reference "RFC 8072: YANG Patch Media Type"; 425 } 426 } 427 } 428 } 429 } 430 } 431 } 432 434 6. Example 436 The following example compares the difference between 437 and for a subtree under "interfaces". The subtree 438 contains a subset of objects that are defined in a YANG data model 439 for the management of interfaces defined in [RFC8343]. The excerpt 440 of the data model whose instantiation is the basis of the comparison 441 is as follows: 443 container interfaces { 444 description 445 "Interface parameters."; 446 list interface { 447 key "name"; 448 leaf name { 449 type string; 450 description 451 "The name of the interface". 452 } 453 leaf description { 454 type string; 455 description 456 "A textual description of the interface."; 457 } 458 leaf enabled { 459 type boolean; 460 default "true"; 461 description 462 "This leaf contains the configured, desired state of the 463 interface.";" 464 } 465 } 466 } 468 The contents of and datastores: 470 //INTENDED 471 472 473 eth0 474 false 475 ip interface 476 477 479 //OPERATIONAL 480 483 484 eth0 485 true 486 487 488 does not contain an instance for leaf "description" 489 that is contained in . Another leaf, "enabled", has 490 different values in the two datastores, being "true" in 491 and "false" in . A third leaf, "name", is the same in both 492 cases. The origin of the leaf instances in is 493 "learned", which may help explain the discrepancies. 495 RPC request to compare (source of the comparison) with 496 (target of the comparison): 498 500 502 ds:operational 503 ds:intended 504 505 507 /if:interfaces 508 509 510 512 RPC reply, when a difference is detected: 514 517 520 521 interface status 522 523 diff between operational (source) and intended (target) 524 525 526 1 527 replace 528 /ietf-interfaces:interface=eth0/enabled 529 530 false 531 532 533 true 534 535 536 537 2 538 create 539 /ietf-interfaces:interface=eth0/description 540 541 ip interface 542 543 544 545 546 548 The same request in RESTCONF (using JSON format): 550 POST /restconf/operations/ietf-nmda-compare:compare HTTP/1.1 551 Host: example.com 552 Content-Type: application/yang-data+json 553 Accept: application/yang-d 554 { "ietf-nmda-compare:input" { 555 "source" : "ietf-datastores:operational", 556 "target" : "ietf-datastores:intended", 557 "report-origin" : null, 558 "xpath-filter" : "/ietf-interfaces:interfaces" 559 } 560 } 561 The same response in RESTCONF (using JSON format): 563 HTTP/1.1 200 OK 564 Date: Thu, 26 Jan 2019 20:56:30 GMT 565 Server: example-server 566 Content-Type: application/yang-d 567 { "ietf-nmda-compare:output" : { 568 "differences" : { 569 "ietf-yang-patch:yang-patch" : { 570 "patch-id" : "interface status", 571 "comment" : "diff between intended (source) and operational", 572 "edit" : [ 573 { 574 "edit-id" : "1", 575 "operation" : "replace", 576 "target" : "/ietf-interfaces:interface=eth0/enabled", 577 "value" : { 578 "ietf-interfaces:interface/enabled" : "false" 579 }, 580 "source-value" : { 581 "ietf-interfaces:interface/enabled" : "true", 582 "@ietf-interfaces:interface/enabled" : { 583 "ietf-origin:origin" : "ietf-origin:learned" 584 } 585 } 586 }, 587 { 588 "edit-id" : "2", 589 "operation" : "create", 590 "target" : "/ietf-interfaces:interface=eth0/description", 591 "value" : { 592 "ietf-interface:interface/description" : "ip interface" 593 } 594 } 595 ] 596 } 597 } 598 } 599 } 601 7. Performance Considerations 603 The compare operation can be computationally expensive. While 604 responsible client applications are expected to use the operation 605 responsibly and sparingly only when warranted, implementations need 606 to be aware of the fact that excessive invocation of this operation 607 will burden system resources and need to ensure that system 608 performance will not be adversely impacted. One possibility for an 609 implementation to mitigate against such a possibility is to limit the 610 number of requests that is served to a client, or to any number of 611 clients, in any one time interval, rejecting requests made at a 612 higher frequency than the implementation can reasonably sustain. 614 8. IANA Considerations 616 8.1. Updates to the IETF XML Registry 618 This document registers one URI in the IETF XML registry [RFC3688]. 619 Following the format in [RFC3688], the following registration is 620 requested: 622 URI: urn:ietf:params:xml:ns:yang:ietf-nmda-compare 624 Registrant Contact: The IESG. 626 XML: N/A, the requested URI is an XML namespace. 628 8.2. Updates to the YANG Module Names Registry 630 This document registers a YANG module in the YANG Module Names 631 registry [RFC6020]. Following the format in [RFC6020], the following 632 registration is requested: 634 name: ietf-nmda-compare 636 namespace: urn:ietf:params:xml:ns:yang:ietf-nmda-compare 638 prefix: cmp 640 reference: draft-ietf-netmod-nmda-diff-09 (RFC form) 642 9. Security Considerations 644 The YANG module specified in this document defines a schema for data 645 that is designed to be accessed via network management protocols such 646 as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer 647 is the secure transport layer, and the mandatory-to-implement secure 648 transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer 649 is HTTPS, and the mandatory-to-implement secure transport is TLS 650 [RFC8446]. 652 The NETCONF access control model [RFC8341] provides the means to 653 restrict access for particular NETCONF or RESTCONF users to a 654 preconfigured subset of all available NETCONF or RESTCONF protocol 655 operations and content. 657 The RPC operation defined in this YANG module, "compare", may be 658 considered sensitive or vulnerable in some network environments. It 659 is thus important to control access to this operation. This is the 660 sensitivity/vulnerability of RPC operation "compare": 662 Comparing datastores for differences requires a certain amount of 663 processing resources at the server. An attacker could attempt to 664 attack a server by making a high volume of comparison requests. 665 Server implementations can guard against such scenarios in several 666 ways. For one, they can implement the NETCONF access control model 667 in order to require proper authorization for requests to be made. 668 Second, server implementations can limit the number of requests that 669 they serve to a client in any one time interval, rejecting requests 670 made at a higher frequency than the implementation can reasonably 671 sustain. 673 10. Acknowledgments 675 We thank Rob Wilton, Martin Bjorklund, Mahesh Jethanandani, Lou 676 Berger, Kent Watsen, Phil Shafer, Ladislav Lhotka, Tim Carey, and 677 Reshad Rahman for valuable feedback and suggestions. 679 11. References 681 11.1. Normative References 683 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 684 Requirement Levels", BCP 14, RFC 2119, 685 DOI 10.17487/RFC2119, March 1997, 686 . 688 [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, 689 DOI 10.17487/RFC3688, January 2004, 690 . 692 [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for 693 the Network Configuration Protocol (NETCONF)", RFC 6020, 694 DOI 10.17487/RFC6020, October 2010, 695 . 697 [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., 698 and A. Bierman, Ed., "Network Configuration Protocol 699 (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, 700 . 702 [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure 703 Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011, 704 . 706 [RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types", 707 RFC 6991, DOI 10.17487/RFC6991, July 2013, 708 . 710 [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", 711 RFC 7950, DOI 10.17487/RFC7950, August 2016, 712 . 714 [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF 715 Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, 716 . 718 [RFC8072] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Patch 719 Media Type", RFC 8072, DOI 10.17487/RFC8072, February 720 2017, . 722 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 723 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 724 May 2017, . 726 [RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", 727 BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, 728 . 730 [RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration 731 Access Control Model", STD 91, RFC 8341, 732 DOI 10.17487/RFC8341, March 2018, 733 . 735 [RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K., 736 and R. Wilton, "Network Management Datastore Architecture 737 (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018, 738 . 740 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 741 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 742 . 744 11.2. Informative References 746 [RFC8343] Bjorklund, M., "A YANG Data Model for Interface 747 Management", RFC 8343, DOI 10.17487/RFC8343, March 2018, 748 . 750 Appendix A. Possible Future Extensions 752 It is conceivable to extend the compare operation with a number of 753 possible additional features in the future. 755 Specifically, it is possible to define an extension with an optional 756 feature for dampening. This will allow clients to specify a minimum 757 time period for which a difference must persist for it to be 758 reported. This will enable clients to distinguish between 759 differences that are only fleeting from ones that are not and that 760 may represent a real operational issue and inconsistency within the 761 device. 763 For this purpose, an additional input parameter can be added to 764 specify the dampening period. Only differences that pertain for at 765 least the dampening time are reported. A value of 0 or omission of 766 the parameter indicates no dampening. Reporting of differences MAY 767 correspondingly be delayed by the dampening period from the time the 768 request is received. 770 To implement this feature, a server implementation might run a 771 comparison when the RPC is first invoked and temporarily store the 772 result. Subsequently, it could wait until after the end of the 773 dampening period to check whether the same differences are still 774 observed. The differences that still persist are then returned. 776 Authors' Addresses 778 Alexander Clemm 779 Futurewei 780 2330 Central Expressway 781 Santa Clara, CA 95050 782 USA 784 Email: ludwig@clemm.org 786 Yingzhen Qu 787 Futurewei 788 2330 Central Expressway 789 Santa Clara, CA 95050 790 USA 792 Email: yqu@futurewei.com 793 Jeff Tantsura 794 Apstra 796 Email: jefftant.ietf@gmail.com 798 Andy Bierman 799 YumaWorks 801 Email: andy@yumaworks.com