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Bierman 8 YumaWorks 9 August 6, 2021 11 Comparison of NMDA datastores 12 draft-ietf-netmod-nmda-diff-12 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 February 7, 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 applied configuration 87 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 they are considered inactive, resource 107 dependencies not being resolved, or even implementation errors in 108 corner conditions. 110 When configuration that is in effect is different from configuration 111 that was applied, many issues can result. It becomes more difficult 112 to operate the network properly due to limited visibility of actual 113 operational status which makes it more difficult to analyze and 114 understand what is going on in the network. Services may be 115 negatively affected (for example, degrading or breaking a customer 116 service) and network resources may be misallocated. 118 Applications can potentially analyze any differences between two 119 datastores by retrieving the contents from both datastores and 120 comparing them. However, in many cases this will be at the same time 121 costly and extremely wasteful. 123 This document introduces a YANG data model which defines RPCs, 124 intended to be used in conjunction with NETCONF [RFC6241] or RESTCONF 125 [RFC8040], that allow a client to request a server to compare two 126 NMDA datastores and report any differences. 128 2. Key Words 130 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 131 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 132 "OPTIONAL" in this document are to be interpreted as described in BCP 133 14 [RFC2119] [RFC8174] when, and only when, they appear in all 134 capitals, as shown here. 136 3. Definitions and Acronyms 138 NMDA: Network Management Datastore Architecture 140 RPC: Remote Procedure Call 142 4. Data Model Overview 144 The core of the solution is a new management operation, , 145 that compares the data tree contents of two datastores. The 146 operation checks whether there are any differences in values or in 147 data nodes that are contained in either datastore, and returns any 148 differences as output. The output is returned in the format 149 specified in YANG-Patch [RFC8072]. 151 The YANG data model defines the operation as a new RPC. 152 The operation takes the following input parameters: 154 o source: The source identifies the datastore that will serve as the 155 reference for the comparison, for example . 157 o target: The target identifies the datastore to compare against the 158 source, for example . 160 o filter-spec: This is a choice between different filter constructs 161 to identify the parts of the datastore to be retrieved. It acts 162 as a node selector that specifies which data nodes are within the 163 scope of the comparison and which nodes are outside the scope. 164 This allows a comparison operation to be applied only to a 165 specific part of the datastore that is of interest, such as a 166 particular subtree. Note, the filter does not allow expressions 167 that match against data node values, since this may incur 168 implementation difficulties and is not required for normal use 169 cases. 171 o all: When set, this parameter indicates that all differences 172 should be included, including differences pertaining to schema 173 nodes that exist in only one of the datastores. When this 174 parameter is not included, a prefiltering step is automatically 175 applied to exclude data from the comparison that does not pertain 176 to both datastores: if the same schema node is not present in both 177 datastores, then all instances of that schema node and all its 178 descendants are excluded from the comparison. This allows client 179 applications to focus on the differences that constitute true 180 mismatches of instance data without needing to specify more 181 complex filter constructs. 183 o report-origin: When set, this parameter indicates that origin 184 metadata should be included as part of RPC output. When this 185 parameter is omitted, origin metadata in comparisons that involve 186 is by default omitted. Note that origin metadata 187 only applies to it is therefore also omitted in 188 comparisons that do not involve regardless of 189 whether or not the parameter is set. 191 The operation provides the following output parameter: 193 o differences: This parameter contains the list of differences. 194 Those differences are encoded per the YANG-Patch data model 195 defined in RFC8072. When a datastore node in the source of the 196 comparison is not present in the target of the comparison, this 197 can be indicated either as a "delete" or as a "remove" in the 198 patch as there is no differentiation between those operations for 199 the purposes of the comparison. The YANG-Patch data model is 200 augmented to indicate the value of source datastore nodes in 201 addition to the patch itself that would need to be applied to the 202 source to produce the target. When the target datastore is 203 and the input parameter "report-origin" is set, 204 "origin" metadata is included as part of the patch. Including 205 origin metadata can help in some cases explain the cause of a 206 difference, for example when a data node is part of but 207 the origin of the same data node in is reported as 208 "system". 210 The data model is defined in the ietf-nmda-compare YANG module. Its 211 structure is shown in the following figure. The notation syntax 212 follows [RFC8340]. 214 module: ietf-nmda-compare 215 rpcs: 216 +---x compare 217 +---w input 218 | +---w source identityref 219 | +---w target identityref 220 | +---w all? empty 221 | +---w report-origin? empty 222 | +---w (filter-spec)? 223 | +--:(subtree-filter) 224 | | +---w subtree-filter? 225 | +--:(xpath-filter) 226 | +---w xpath-filter? yang:xpath1.0 {nc:xpath}? 227 +--ro output 228 +--ro (compare-response)? 229 +--:(no-matches) 230 | +--ro no-matches? empty 231 +--:(differences) 232 +--ro differences 233 +--ro yang-patch 234 +--ro patch-id string 235 +--ro comment? string 236 +--ro edit* [edit-id] 237 +--ro edit-id string 238 +--ro operation enumeration 239 +--ro target target-resource-offset 240 +--ro point? target-resource-offset 241 +--ro where? enumeration 242 +--ro value? 243 +--ro source-value? 245 Structure of ietf-nmda-compare 247 5. YANG Data Model 249 file "ietf-nmda-compare@2021-08-06.yang" 250 module ietf-nmda-compare { 252 yang-version 1.1; 253 namespace "urn:ietf:params:xml:ns:yang:ietf-nmda-compare"; 255 prefix cmp; 257 import ietf-yang-types { 258 prefix yang; 259 reference "RFC 6991: Common YANG Data Types"; 260 } 261 import ietf-datastores { 262 prefix ds; 263 reference "RFC 8342: Network Management Datastore 264 Architecture (NMDA)"; 265 } 266 import ietf-yang-patch { 267 prefix ypatch; 268 reference "RFC 8072: YANG Patch Media Type"; 269 } 270 import ietf-netconf { 271 prefix nc; 272 reference "RFC6241: Network Configuration Protocol (NETCONF)"; 273 } 275 organization "IETF"; 276 contact 277 "WG Web: 278 WG List: 280 Author: Alexander Clemm 281 283 Author: Yingzhen Qu 284 286 Author: Jeff Tantsura 287 289 Author: Andy Bierman 290 "; 292 description 293 "The YANG data model defines a new operation, , that 294 can be used to compare NMDA datastores. 296 Copyright (c) 2021 IETF Trust and the persons identified as 297 authors of the code. All rights reserved. 299 Redistribution and use in source and binary forms, with or 300 without modification, is permitted pursuant to, and subject to 301 the license terms contained in, the Simplified BSD License set 302 forth in Section 4.c of the IETF Trust's Legal Provisions 303 Relating to IETF Documents 304 (https://trustee.ietf.org/license-info). 306 This version of this YANG module is part of 307 draft-ietf-netmod-nmda-diff-12; see the RFC itself for full 308 legal notices. 310 NOTE TO RFC EDITOR: Please replace above reference to 311 draft-ietf-netmod-nmda-diff-12 with RFC number when published 312 (i.e. RFC xxxx)."; 314 revision 2021-08-06 { 315 description 316 "Initial revision. 317 NOTE TO RFC EDITOR: 318 (1)Please replace the above revision date to 319 the date of RFC publication when published. 320 (2) Please replace the date in the file name 321 (ietf-nmda-compare@2021-08-06.yang) to the date of RFC 322 publication. 323 (3) Please replace the following reference to 324 draft-ietf-netmod-nmda-diff-12 with RFC number when published 325 (i.e. RFC xxxx)."; 326 reference 327 "draft-ietf-netmod-nmda-diff-12: Comparison of NMDA 328 datastores"; 329 } 331 /* RPC */ 332 rpc compare { 333 description 334 "NMDA datastore compare operation."; 335 input { 336 leaf source { 337 type identityref { 338 base ds:datastore; 339 } 340 mandatory true; 341 description 342 "The source datastore to be compared."; 343 } 344 leaf target { 345 type identityref { 346 base ds:datastore; 347 } 348 mandatory true; 349 description 350 "The target datastore to be compared."; 351 } 352 leaf all { 353 type empty; 354 description 355 "When this leaf is provided, all data nodes are compared, 356 whether their schema node pertains to both datastores or 357 not. When this leaf is omitted, a prefiltering step is 358 automatically applied that excludes data nodes from the 359 comparison that can occur in only one datastore but not 360 the other. Specifically, if one of the datastores 361 (source or target) contains only configuration data and 362 the other datastore is , data nodes for 363 which config is false are excluded from the comparison."; 364 } 365 leaf report-origin { 366 type empty; 367 description 368 "When this leaf is provided, origin metadata is 369 included as part of RPC output. When this leaf is 370 omitted, origin metadata in comparisons that involve 371 is by default omitted."; 372 } 373 choice filter-spec { 374 description 375 "Identifies the portions of the datastores to be 376 compared."; 377 anydata subtree-filter { 378 description 379 "This parameter identifies the portions of the 380 target datastore to retrieve."; 381 reference "RFC 6241, Section 6."; 382 } 383 leaf xpath-filter { 384 if-feature nc:xpath; 385 type yang:xpath1.0; 386 description 387 "This parameter contains an XPath expression 388 identifying the portions of the target 389 datastore to retrieve."; 390 reference "RFC 6991: Common YANG Data Types"; 391 } 392 } 393 } 394 output { 395 choice compare-response { 396 description 397 "Comparison results."; 398 leaf no-matches { 399 type empty; 400 description 401 "This leaf indicates that the filter did not match 402 anything and nothing was compared."; 403 } 404 container differences { 405 description 406 "The list of differences, encoded per RFC8072 with an 407 augmentation to include source values where applicable. 408 When a datastore node in the source is not present in 409 the target, this can be indicated either as a 'delete' 410 or as a 'remove' as there is no difference between 411 them for the purposes of the comparison."; 412 uses ypatch:yang-patch { 413 augment "yang-patch/edit" { 414 description 415 "Provide the value of the source of the patch, 416 respectively of the comparison, in addition to 417 the target value, where applicable."; 418 anydata source-value { 419 when "../operation = 'delete'" 420 + "or ../operation = 'merge'" 421 + "or ../operation = 'move'" 422 + "or ../operation = 'replace'" 423 + "or ../operation = 'remove'"; 424 description 425 "The anydata 'value' is only used for 'delete', 426 'move', 'merge', 'replace', and 'remove' 427 operations."; 428 } 429 reference "RFC 8072: YANG Patch Media Type"; 430 } 431 } 432 } 433 } 434 } 435 } 436 } 437 439 6. Example 441 The following example compares the difference between 442 and for a subtree under "interfaces". The subtree 443 contains a subset of objects that are defined in a YANG data model 444 for the management of interfaces defined in [RFC8343]. For the 445 purposes of understanding the subsequent example, the following 446 excerpt of the data model whose instantiation is the basis of the 447 comparison is provided: 449 container interfaces { 450 description 451 "Interface parameters."; 452 list interface { 453 key "name"; 454 leaf name { 455 type string; 456 description 457 "The name of the interface". 458 } 459 leaf description { 460 type string; 461 description 462 "A textual description of the interface."; 463 } 464 leaf enabled { 465 type boolean; 466 default "true"; 467 description 468 "This leaf contains the configured, desired state of the 469 interface.";" 470 } 471 } 472 } 474 The contents of and datastores: 476 //INTENDED 477 478 479 eth0 480 false 481 ip interface 482 483 485 //OPERATIONAL 486 489 490 eth0 491 true 492 493 494 does not contain an instance for leaf "description" 495 that is contained in . Another leaf, "enabled", has 496 different values in the two datastores, being "true" in 497 and "false" in . A third leaf, "name", is the same in both 498 cases. The origin of the leaf instances in is 499 "learned", which may help explain the discrepancies. 501 RPC request to compare (source of the comparison) with 502 (target of the comparison): 504 506 508 ds:operational 509 ds:intended 510 511 513 /if:interfaces 514 515 516 518 RPC reply, when a difference is detected: 520 523 526 527 interface status 528 529 diff between operational (source) and intended (target) 530 531 532 1 533 replace 534 /ietf-interfaces:interface=eth0/enabled 535 536 false 537 538 539 true 540 541 542 543 2 544 create 545 /ietf-interfaces:interface=eth0/description 546 547 ip interface 548 549 550 551 552 554 The same request in RESTCONF (using JSON format): 556 POST /restconf/operations/ietf-nmda-compare:compare HTTP/1.1 557 Host: example.com 558 Content-Type: application/yang-data+json 559 Accept: application/yang-data+json 561 { "ietf-nmda-compare:input" : { 562 "source" : "ietf-datastores:operational", 563 "target" : "ietf-datastores:intended", 564 "report-origin" : null, 565 "xpath-filter" : "/ietf-interfaces:interfaces" 566 } 567 } 568 The same response in RESTCONF (using JSON format): 570 HTTP/1.1 200 OK 571 Date: Thu, 24 Jan 2019 20:56:30 GMT 572 Server: example-server 573 Content-Type: application/yang-data+json 575 { "ietf-nmda-compare:output" : { 576 "differences" : { 577 "ietf-yang-patch:yang-patch" : { 578 "patch-id" : "interface status", 579 "comment" : "diff between intended (source) and operational", 580 "edit" : [ 581 { 582 "edit-id" : "1", 583 "operation" : "replace", 584 "target" : "/ietf-interfaces:interface=eth0/enabled", 585 "value" : { 586 "ietf-interfaces:interface/enabled" : "false" 587 }, 588 "source-value" : { 589 "ietf-interfaces:interface/enabled" : "true", 590 "@ietf-interfaces:interface/enabled" : { 591 "ietf-origin:origin" : "ietf-origin:learned" 592 } 593 } 594 }, 595 { 596 "edit-id" : "2", 597 "operation" : "create", 598 "target" : "/ietf-interfaces:interface=eth0/description", 599 "value" : { 600 "ietf-interface:interface/description" : "ip interface" 601 } 602 } 603 ] 604 } 605 } 606 } 607 } 609 7. Performance Considerations 611 The compare operation can be computationally expensive. While 612 responsible client applications are expected to use the operation 613 responsibly and sparingly only when warranted, implementations need 614 to be aware of the fact that excessive invocation of this operation 615 will burden system resources and need to ensure that system 616 performance will not be adversely impacted. One possibility for an 617 implementation to mitigate against this is to limit the number of 618 requests that are served to a client, or to any number of clients, in 619 any one time interval, by rejecting requests made at a higher 620 frequency than the implementation can reasonably sustain. 622 While useful, tools such as YANG Data Models that allow for the 623 monitoring of server resources, system performance, and statistics 624 about RPCs and RPC rates are outside the scope of this document. 625 When defined, any such model should be general in nature and not 626 limited to the RPC operation defined in this document. 628 8. IANA Considerations 630 8.1. Updates to the IETF XML Registry 632 This document registers one URI in the IETF XML registry [RFC3688]. 633 Following the format in [RFC3688], the following registration is 634 requested: 636 URI: urn:ietf:params:xml:ns:yang:ietf-nmda-compare 638 Registrant Contact: The IESG. 640 XML: N/A, the requested URI is an XML namespace. 642 8.2. Updates to the YANG Module Names Registry 644 This document registers a YANG module in the YANG Module Names 645 registry [RFC6020]. Following the format in [RFC6020], the following 646 registration is requested: 648 name: ietf-nmda-compare 650 namespace: urn:ietf:params:xml:ns:yang:ietf-nmda-compare 652 prefix: cmp 654 reference: draft-ietf-netmod-nmda-diff-12 (RFC form) 656 9. Security Considerations 658 The YANG module specified in this document defines a schema for data 659 that is designed to be accessed via network management protocols such 660 as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer 661 is the secure transport layer, and the mandatory-to-implement secure 662 transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer 663 is HTTPS, and the mandatory-to-implement secure transport is TLS 664 [RFC8446]. 666 The NETCONF access control model [RFC8341] provides the means to 667 restrict access for particular NETCONF or RESTCONF users to a 668 preconfigured subset of all available NETCONF or RESTCONF protocol 669 operations and content. 671 NACM specifies access for the server in its entirety and the same 672 access rules apply to all datastores. Any subtrees to which a 673 requestor does not have read access are silently skipped and not 674 included in the comparison. 676 The RPC operation defined in this YANG module, "compare", may be 677 considered sensitive or vulnerable in some network environments. It 678 is thus important to control access to this operation. This is the 679 sensitivity/vulnerability of RPC operation "compare": 681 Comparing datastores for differences requires a certain amount of 682 processing resources at the server. An attacker could attempt to 683 attack a server by making a high volume of comparison requests. 684 Server implementations can guard against such scenarios in several 685 ways. For one, they can implement the NETCONF access control model 686 in order to require proper authorization for requests to be made. 687 Second, server implementations can limit the number of requests that 688 they serve to a client in any one time interval, rejecting requests 689 made at a higher frequency than the implementation can reasonably 690 sustain. 692 10. Acknowledgments 694 We thank Rob Wilton, Martin Bjorklund, Mahesh Jethanandani, Lou 695 Berger, Kent Watsen, Phil Shafer, Ladislav Lhotka, Tim Carey, and 696 Reshad Rahman for valuable feedback and suggestions. 698 11. References 700 11.1. Normative References 702 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 703 Requirement Levels", BCP 14, RFC 2119, 704 DOI 10.17487/RFC2119, March 1997, 705 . 707 [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, 708 DOI 10.17487/RFC3688, January 2004, 709 . 711 [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for 712 the Network Configuration Protocol (NETCONF)", RFC 6020, 713 DOI 10.17487/RFC6020, October 2010, 714 . 716 [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., 717 and A. Bierman, Ed., "Network Configuration Protocol 718 (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, 719 . 721 [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure 722 Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011, 723 . 725 [RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types", 726 RFC 6991, DOI 10.17487/RFC6991, July 2013, 727 . 729 [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", 730 RFC 7950, DOI 10.17487/RFC7950, August 2016, 731 . 733 [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF 734 Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, 735 . 737 [RFC8072] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Patch 738 Media Type", RFC 8072, DOI 10.17487/RFC8072, February 739 2017, . 741 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 742 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 743 May 2017, . 745 [RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", 746 BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, 747 . 749 [RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration 750 Access Control Model", STD 91, RFC 8341, 751 DOI 10.17487/RFC8341, March 2018, 752 . 754 [RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K., 755 and R. Wilton, "Network Management Datastore Architecture 756 (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018, 757 . 759 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 760 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 761 . 763 11.2. Informative References 765 [RFC8343] Bjorklund, M., "A YANG Data Model for Interface 766 Management", RFC 8343, DOI 10.17487/RFC8343, March 2018, 767 . 769 Appendix A. Possible Future Extensions 771 It is conceivable to extend the compare operation with a number of 772 possible additional features in the future. 774 Specifically, it is possible to define an extension with an optional 775 feature for dampening. This will allow clients to specify a minimum 776 time period for which a difference must persist for it to be 777 reported. This will enable clients to distinguish between 778 differences that are only fleeting from ones that are not and that 779 may represent a real operational issue and inconsistency within the 780 device. 782 For this purpose, an additional input parameter can be added to 783 specify the dampening period. Only differences that pertain for at 784 least the dampening time are reported. A value of 0 or omission of 785 the parameter indicates no dampening. Reporting of differences MAY 786 correspondingly be delayed by the dampening period from the time the 787 request is received. 789 To implement this feature, a server implementation might run a 790 comparison when the RPC is first invoked and temporarily store the 791 result. Subsequently, it could wait until after the end of the 792 dampening period to check whether the same differences are still 793 observed. The differences that still persist are then returned. 795 Authors' Addresses 797 Alexander Clemm 798 Futurewei 799 2330 Central Expressway 800 Santa Clara, CA 95050 801 USA 803 Email: ludwig@clemm.org 804 Yingzhen Qu 805 Futurewei 806 2330 Central Expressway 807 Santa Clara, CA 95050 808 USA 810 Email: yqu@futurewei.com 812 Jeff Tantsura 813 Microsoft 815 Email: jefftant.ietf@gmail.com 817 Andy Bierman 818 YumaWorks 820 Email: andy@yumaworks.com