Network Working Group A. Clemm Internet-Draft Y. Qu Intended status: Standards Track Futurewei Expires: November 24, 2019 J. Tantsura Apstra A. Bierman YumaWorks May 23, 2019 Comparison of NMDA datastores draft-ietf-netmod-nmda-diff-01 Abstract This document defines an RPC operation to compare management datastores that comply with the NMDA architecture. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on November 24, 2019. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of Clemm, et al. Expires November 24, 2019 [Page 1] Internet-Draft May 2019 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Key Words . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Definitions and Acronyms . . . . . . . . . . . . . . . . . . 3 4. Data Model Overview . . . . . . . . . . . . . . . . . . . . . 4 5. YANG Data Model . . . . . . . . . . . . . . . . . . . . . . . 5 6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 11 8. Possible Future Extensions . . . . . . . . . . . . . . . . . 11 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 9.1. Updates to the IETF XML Registry . . . . . . . . . . . . 12 9.2. Updates to the YANG Module Names Registry . . . . . . . . 12 10. Security Considerations . . . . . . . . . . . . . . . . . . . 13 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 12.1. Normative References . . . . . . . . . . . . . . . . . . 13 12.2. Informative References . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 1. Introduction The revised Network Management Datastore Architecture (NMDA) [RFC8342] introduces a set of new datastores that each hold YANG- defined data [RFC7950] and represent a different "viewpoint" on the data that is maintained by a server. New YANG datastores that are introduced include , which contains validated configuration data that a client application intends to be in effect, and , which contains at least conceptually operational state data (such as statistics) as well as configuration data that is actually in effect. NMDA introduces in effect a concept of "lifecycle" for management data, allowing to clearly distinguish between data that is part of a configuration that was supplied by a user, configuration data that has actually been successfully applied and that is part of the operational state, and overall operational state that includes both applied configuration data as well as status and statistics. As a result, data from the same management model can be reflected in multiple datastores. Clients need to specify the target datastore to be specific about which viewpoint of the data they want to access. This way, an application can differentiate whether they are (for example) interested in the configuration that has been applied and is Clemm, et al. Expires November 24, 2019 [Page 2] Internet-Draft May 2019 actually in effect, or in the configuration that was supplied by a client and that is supposed to be in effect. Due to the fact that data can propagate from one datastore to another, it is possibly for differences between datastores to occur. Some of this is entirely expected, as there may be a time lag between when a configuration is given to the device and reflected in , until when it actually takes effect and is reflected in . However, there may be cases when a configuration item that was to be applied may not actually take effect at all or needs an unusually long time to do so. This can be the case due to certain conditions not being met, resource dependencies not being resolved, or even implementation errors in corner conditions. When configuration that is in effect is different from configuration that was applied, many issues can result. It becomes more difficult to operate the network properly due to limited visibility of actual status which makes it more difficult to analyze and understand what is going on in the network. Services may be negatively affected (for example, breaking a service instance resulting in service is not properly delivered to a customer) and network resources be misallocated. Applications can potentially analyze any differences between two datastores by retrieving the contents from both datastores and comparing them. However, in many cases this will be at the same time costly and extremely wasteful. This document introduces a YANG data model which defines RPCs, intended to be used in conjunction with NETCONF [RFC6241] or RESTCONF [RFC8040], that allow a client to request a server to compare two NMDA datastores and report any differences. 2. Key Words The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 3. Definitions and Acronyms NMDA: Network Management Datastore Architecture RPC: Remote Procedure Call Clemm, et al. Expires November 24, 2019 [Page 3] Internet-Draft May 2019 4. Data Model Overview At the core of the solution is a new management operation, , that allows to compare two datastores for the same data. The operation checks whether there are any differences in values or in data nodes that are contained in either datastore, and returns any differences as output. The output is returned in the format specified in YANG-Patch [RFC8072]. The YANG data model defines the operation as a new RPC. The operation takes the following input parameters: o source: The source identifies the datastore that will serve as reference for the comparison, for example . o target: The target identifies the datastore to compare against the source. o filter-spec: This is a choice between different filter constructs to identify the portions of the datastore to be retrieved. It acts as a node selector that specifies which data nodes are within the scope of the comparison and which nodes are outside the scope. This allows a comparison operation to be applied only to a specific portion of the datastore that is of interest, such as a particular subtree. (The filter dow not contain expressions that would match values data nodes, as this is not required by most use cases and would complicate the scheme, from implementation to dealing with race conditions.) o all: When set, this parameter indicates that all differences should be included, including differences pertaining to schema nodes that exist in only one of the datastores. When this parameter is not included, a prefiltering step is automatically applied to exclude data from the comparison that does not pertain to both datastores: if the same schema node is not present in both datastores, then all instances of that schema node and all its descendants are excluded from the comparison. This allows client applications to focus on the differences that constitute true mismatches of instance data without needing to specify more complex filter constructs. The operation provides the following output parameter: o differences: This parameter contains the list of differences. Those differences are encoded per YANG-Patch data model defined in RFC8072. The YANG-Patch data model is augmented to indicate the value of source datastore nodes in addition to the patch itself that would need to be applied to the source to produce the target. Clemm, et al. Expires November 24, 2019 [Page 4] Internet-Draft May 2019 When the target datastore is , "origin" metadata is included as part of the patch. Including origin metadata can help explain the cause of a difference, for example when a data node is part of but the origin of the same data node in is reported as "system". The data model is defined in the ietf-nmda-compare YANG module. Its structure is shown in the following figure. The notation syntax follows [RFC8340]. module: ietf-nmda-compare rpcs: +---x compare +---w input | +---w source identityref | +---w target identityref | +---w all? empty | +---w (filter-spec)? | +--:(subtree-filter) | | +---w subtree-filter? | +--:(xpath-filter) | +---w xpath-filter? yang:xpath1.0 {nc:xpath}? +--ro output +--ro (compare-response)? +--:(no-matches) | +--ro no-matches? empty +--:(differences) +--ro differences +--ro yang-patch +--ro patch-id string +--ro comment? string +--ro edit* [edit-id] +--ro edit-id string +--ro operation enumeration +--ro target target-resource-offset +--ro point? target-resource-offset +--ro where? enumeration +--ro value? +--ro source-value? Structure of ietf-nmda-compare 5. YANG Data Model file "ietf-nmda-compare@2019-05-23.yang" module ietf-nmda-compare { yang-version 1.1; Clemm, et al. Expires November 24, 2019 [Page 5] Internet-Draft May 2019 namespace "urn:ietf:params:xml:ns:yang:ietf-nmda-compare"; prefix cp; import ietf-yang-types { prefix yang; } import ietf-datastores { prefix ds; } import ietf-yang-patch { prefix ypatch; } import ietf-netconf { prefix nc; } organization "IETF"; contact "WG Web: WG List: Author: Alexander Clemm Author: Yingzhen Qu Author: Jeff Tantsura Author: Andy Bierman "; description "The YANG data model defines a new operation, , that can be used to compare NMDA datastores."; revision 2019-05-23 { description "Initial revision"; reference "RFC XXXX: Comparison of NMDA datastores"; } /* RPC */ rpc compare { description Clemm, et al. Expires November 24, 2019 [Page 6] Internet-Draft May 2019 "NMDA compare operation."; input { leaf source { type identityref { base ds:datastore; } mandatory true; description "The source datastore to be compared."; } leaf target { type identityref { base ds:datastore; } mandatory true; description "The target datastore to be compared."; } leaf all { type empty; description "When this leaf is provided, all data nodes are compared, whether their schema node pertains to both datastores or not. When this leaf is omitted, a prefiltering step is automatically applied that excludes data nodes from the comparison that can occur in only one datastore but not the other. Specifically, if one of the datastores (source or target) contains only configuration data and the other datastore is , data nodes for which config is false are excluded from the comparison."; } choice filter-spec { description "Identifies the portions of the datastores to be compared."; anydata subtree-filter { description "This parameter identifies the portions of the target datastore to retrieve."; reference "RFC 6241, Section 6."; } leaf xpath-filter { if-feature nc:xpath; type yang:xpath1.0; description "This parameter contains an XPath expression identifying the portions of the target datastore to retrieve."; Clemm, et al. Expires November 24, 2019 [Page 7] Internet-Draft May 2019 } } } output { choice compare-response { description "Comparison results."; leaf no-matches { type empty; description "This leaf indicates that the filter did not match anything and nothing was compared."; } container differences { description "The list of differences, encoded per RFC8072 with an augmentation to include source values where applicable."; uses ypatch:yang-patch { augment "yang-patch/edit" { description "Provide the value of the source of the patch, respectively of the comparison, in addition to the target value, where applicable."; anydata source-value { when "../operation = 'delete'" + "or ../operation = 'merge'" + "or ../operation = 'move'" + "or ../operation = 'replace'" + "or ../operation = 'remove'"; description "The anydata 'value' is only used for 'delete', 'move', 'merge', 'replace', and 'remove' operations."; } } } } } } } } Clemm, et al. Expires November 24, 2019 [Page 8] Internet-Draft May 2019 6. Example The following example compares the difference between and for object "explicit-router-id", as defined in data module [I-D.ietf-ospf-yang]. RPC request: ds:operational ds:intended \ /rt:routing/rt:control-plane-protocols\ /rt:control-plane-protocol/ospf:ospf\ RPC reply, when a difference is detected: ospf router-id diff between operational and intended 1 replace /ietf-ospf:explicit-router-id 1.1.1.1 Clemm, et al. Expires November 24, 2019 [Page 9] Internet-Draft May 2019 RPC reply when no difference is detected: The same request in RESTCONF (using JSON format): POST /restconf/operations/ietf-nmda-compare:compare HTTP/1.1 Host: example.com Content-Type: application/yang-data+json Accept: application/yang-data+json { "ietf-nmda-compare:input" { "source" : "ietf-datastores:operational", "target" : "ietf-datastores:intended". "xpath-filter" : \ "/ietf-routing:routing/control-plane-protocols\ /control-plane-protocol/ietf-ospf:ospf" } } The same response in RESTCONF (using JSON format): Clemm, et al. Expires November 24, 2019 [Page 10] Internet-Draft May 2019 HTTP/1.1 200 OK Date: Thu, 26 Jan 2017 20:56:30 GMT Server: example-server Content-Type: application/yang-data+json { "ietf-nmda-compare:output" : { "differences" : { "ietf-yang-patch:yang-patch" : { "patch-id" : "ospf router-id", "comment" : "diff between operational and intended", "edit" : [ { "edit-id" : "1", "operation" : "replace", "target" : "/ietf-ospf:explicit-router-id", "value" : { "ietf-ospf:explicit-router-id" : "1.1.1.1" "@ietf-ospf:explicit-router-id" : { "ietf-origin:origin" : "ietf-origin:system" } } } ] } } } } 7. Open Issues Currently, origin metadata is included in RPC output per default in comparisons that involve . It is conceivable to introduce an input parameter that controls whether origin metadata should in fact be included. Currently the comparison filter is defined using subtree and XPath as in NETCONF[RFC6241]. It is not clear whether there is a requirement to allow for the definition of filters that relate instead to target resources per RESTCONF [RFC7950]. 8. Possible Future Extensions It is conceivable to extend the compare operation with a number of possible additional features in the future. Specifically, it is possible to define an extension with an optional feature for dampening. This will allow clients to specify a minimum time period for which a difference must persist for it to be Clemm, et al. Expires November 24, 2019 [Page 11] Internet-Draft May 2019 reported. This will enable clients to distinguish between differences that are only fleeting from ones that are not and that may represent a real operational issue and inconsistency within the device. For this purpose, an additional input parameter can be added to specify the dampening period. Only differences that pertain for at least the dampening time are reported. A value of 0 or omission of the parameter indicates no dampening. Reporting of differences MAY correspondingly be delayed by the dampening period from the time the request is received. To implement this feature, a server implementation might run a comparison when the RPC is first invoked and temporarily store the result. Subsequently, it could wait until after the end of the dampening period to check whether the same differences are still observed. The differences that still persist are then returned. 9. IANA Considerations 9.1. Updates to the IETF XML Registry This document registers one URI in the IETF XML registry [RFC3688]. Following the format in [RFC3688], the following registration is requested: URI: urn:ietf:params:xml:ns:yang:ietf-nmda-compare Registrant Contact: The IESG. XML: N/A, the requested URI is an XML namespace. 9.2. Updates to the YANG Module Names Registry This document registers a YANG module in the YANG Module Names registry [RFC7950]. Following the format in [RFC7950], the following registration is requested: name: ietf-nmda-compare namespace: urn:ietf:params:xml:ns:yang:ietf-nmda-compare prefix: cp reference: RFC XXXX Clemm, et al. Expires November 24, 2019 [Page 12] Internet-Draft May 2019 10. Security Considerations Comparing discrepancies between datastores requires a certain amount of processing resources at the server. An attacker could attempt to attack a server by making a high volume of comparison requests. Server implementations can guard against such scenarios in several ways. For one, they can implement NACM in order to require proper authorization for requests to be made. Second, server implementations can limit the number of requests that they serve in any one time interval, potentially rejecting requests made at a higher frequency than the implementation can reasonably sustain. 11. Acknowledgments We thank Rob Wilton, Martin Bjorklund, Mahesh Jethanandani, Lou Berger, Kent Watsen, Phil Shafer, Ladislav Lhotka for valuable feedback and suggestions. 12. References 12.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, . [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, . [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, . [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, . [RFC8072] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Patch Media Type", RFC 8072, DOI 10.17487/RFC8072, February 2017, . Clemm, et al. Expires November 24, 2019 [Page 13] Internet-Draft May 2019 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, . [RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K., and R. Wilton, "Network Management Datastore Architecture (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018, . 12.2. Informative References [I-D.ietf-ospf-yang] Yeung, D., Qu, Y., Zhang, Z., Chen, I., and A. Lindem, "YANG Data Model for OSPF Protocol", draft-ietf-ospf- yang-21 (work in progress), January 2019. Authors' Addresses Alexander Clemm Futurewei 2330 Central Expressway Santa Clara, CA 95050 USA Email: ludwig@clemm.org Yingzhen Qu Futurewei 2330 Central Expressway Santa Clara, CA 95050 USA Email: yqu@futurewei.com Jeff Tantsura Apstra Email: jefftant.ietf@gmail.com Clemm, et al. Expires November 24, 2019 [Page 14] Internet-Draft May 2019 Andy Bierman YumaWorks Email: andy@yumaworks.com Clemm, et al. Expires November 24, 2019 [Page 15]