Network Working Group A. Clemm Internet-Draft Y. Qu Intended status: Standards Track Huawei Expires: August 27, 2018 J. Tantsura Nuage Networks February 23, 2018 Discrepancy detection between NMDA datastores draft-clemm-netconf-nmda-diff-02 Abstract This document defines a capability that allows to report discrepancies between management datastores in Netconf or Restconf servers that comply with the NMDA architecture. The capability is based on a set of RPCs that are defined as part of a YANG data model and that are intended to be used in conjunction with Netconf and Restconf. 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 August 27, 2018. Copyright Notice Copyright (c) 2018 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 Clemm, et al. Expires August 27, 2018 [Page 1] Internet-Draft February 2018 include Simplified BSD License text as described in Section 4.e of 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 7.1. Updates to the IETF XML Registry . . . . . . . . . . . . 9 7.2. Updates to the YANG Module Names Registry . . . . . . . . 9 8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 10. Normative References . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 1. Introduction The revised Network Management Datastore Architecture (NMDA) [NMDA] 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 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 discrepancies to occur. Some of this is Clemm, et al. Expires August 27, 2018 [Page 2] Internet-Draft February 2018 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 discrepancies 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. It will also not be an effective approach to discover changes that are only "fleeting", or for that matter to distinguish between changes that are only fleeting from ones that are not and that may represent a real operational issue and inconsistency within the device. 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 discepancies. It also features a dampening option that allows to exclude discrepancies that are only fleeting from the report. 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 August 27, 2018 [Page 3] Internet-Draft February 2018 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 discrepancies in values or in objects that are contained in either datastore, and returns any discrepancies 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 dampening: Identifies the minimum time period for which a discrepancy must persist for it to be reported. The reporting of the output MAY correspondingly delayed by the dampening period. Implementations MAY thus run a comparison when the RPC is first invoked, then wait until after the dampening period to check whether any differences still persist. This parameter is conditional of a dampening being supported as a feature. The operation provides the following output parameter: o differences: This parameter contains the list of differences, encoded per RFC8072, i.e. specifying which patches would need to be applied to the source to produce the target. Values for patch- id and edit-id are generated by the server. As part of the differences, it will be useful to include "origin" metadata where applicable, specifically when the target datastore is . This can help explain the cause of a discrepancy, for example when a data item is part of but the origin in Clemm, et al. Expires August 27, 2018 [Page 4] Internet-Draft February 2018 is reported as "system". How to best report "origin" metadata is an item for further study, specifically whether it should be automatically returned per default or whether its reporting should be controlled using another RPC parameter. The data model is defined in the ietf-nmda-compare YANG module. Its structure is shown in the following figure. The notation syntax follows [I-D.draft-ietf-netmod-yang-tree-diagrams]. module: ietf-nmda-compare rpcs: +---x compare +---w input | +---w source identityref | +---w target identityref | +---w (filter-spec)? | | +--:(subtree-filter) | | | +---w subtree-filter? | | +--:(xpath-filter) | | +---w xpath-filter? yang:xpath1.0 {nc:xpath}? | +---w dampening? yang:timeticks {cmp-dampening}? +--ro output +--ro differences Structure of ietf-nmda-compare 5. YANG Data Model file "ietf-nmda-compare@2018-02-23.yang" module ietf-nmda-compare { yang-version 1.1; 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 { Clemm, et al. Expires August 27, 2018 [Page 5] Internet-Draft February 2018 prefix nc; } organization "IETF"; contact "WG Web: WG List: Author: Alexander Clemm Author: Yingzhen Qu Author: Jeff Tantsura "; description "The YANG data model defines a new operation, , that can be used to compare NMDA datastores."; revision 2018-02-23 { description "Initial revision"; reference "RFC XXXX: Discrepancy detection between NMDA datastores"; } feature cmp-dampening { description "This feature indicates that the ability to only report differences that pertain for a certain amount of time, as indicated through a dampening period, is supported."; } /* RPC */ rpc compare { description "NMDA compare operation."; input { leaf source { type identityref { base ds:datastore; } mandatory true; description "The source datastore to be compared."; } Clemm, et al. Expires August 27, 2018 [Page 6] Internet-Draft February 2018 leaf target { type identityref { base ds:datastore; } mandatory true; description "The target datastore to be compared."; } 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."; } } leaf dampening { if-feature cmp-dampening; type yang:timeticks; default "0"; description "The dampening period, in hundredths of a second, for the reporting of differences. Only differences that pertain for at least the dampening time are reported. Reporting of differences may be deferred by the dampening time. A value of 0 or omission of the leaf indicates no dampening."; } } output { container differences { uses ypatch:yang-patch; description "The list of differences, encoded per RFC8072, with a value for patch-id and values for edit-id generated by the server. If there are no differences, an Clemm, et al. Expires August 27, 2018 [Page 7] Internet-Draft February 2018 empty container is returned."; } } } } 6. Example The following example compares the difference between and in any elements of list "instance" contained under "ospf", as defined in data module [I-D.draft-ietf-ospf-yang]. RPC request: operational intended /ospf:ospf/ospf:instance/ 500 RPC reply when a difference is detected: Clemm, et al. Expires August 27, 2018 [Page 8] Internet-Draft February 2018 p101 1 replace /ospf:ospf/ospf:instance[ospf:af='1']/ospf:areas/ ospf:area[ospf:area-id='1']/ospf:default-cost 128 RPC reply when no difference is detected: 7. IANA Considerations 7.1. 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. 7.2. Updates to the YANG Module Names Registry This document registers a YANG module in the YANG Module Names registry [RFC6020]. Following the format in [RFC6020], the following registration is requested: Clemm, et al. Expires August 27, 2018 [Page 9] Internet-Draft February 2018 name: ietf-nmda-compare namespace: urn:ietf:params:xml:ns:yang:ietf-nmda-compare prefix: cp reference: RFC XXXX 8. 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 discrepancy detection 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. 9. Acknowledgments We thank Rob Wilton for valuable feedback and suggestions on an earlier revision of this document. 10. Normative References [I-D.draft-ietf-netmod-yang-tree-diagrams] Bjorklund, M. and L. Berger, "YANG Tree Diagrams", I-D draft-ietf-netmod-yang-tree-diagrams, February 2018. [I-D.draft-ietf-ospf-yang] Yeung, D., Qu, Y., Zhang, J., Chen, I., and A. Lindem, "Yang Data Model for OSPF Protocol", I-D draft-ietf-ospf- yang, October 2017. [NMDA] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K., and R. Wilton, "Network Management Datastore Architecture", January 2018, . [notif-sub] Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard, E., and A. Tripathy, "Custom subscription to event notifications", January 2018, . Clemm, et al. Expires August 27, 2018 [Page 10] Internet-Draft February 2018 [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, . [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, . [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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [yang-push] Clemm, A., Voit, E., Gonzalez Prieto, A., Tripathy, A., Nilsen-Nygaard, E., Bierman, A., and B. Lengyel, "Subscribing to YANG datastore push updates", February 2018, . Authors' Addresses Clemm, et al. Expires August 27, 2018 [Page 11] Internet-Draft February 2018 Alexander Clemm Huawei 2330 Central Expressway Santa Clara, CA 95050 USA Email: ludwig@clemm.org Yingzhen Qu Huawei 2330 Central Expressway Santa Clara, CA 95050 USA Email: yingzhen.qu@huawei.com Jeff Tantsura Nuage Networks Email: jefftant.ietf@gmail.com Clemm, et al. Expires August 27, 2018 [Page 12]