Network Working Group                                           A. Clemm
Internet-Draft                                                     Y. Qu
Intended status: Standards Track                               Futurewei
Expires: January 14, 2021                                    J. Tantsura
                                                              A. Bierman
                                                           July 13, 2020

                     Comparison of NMDA datastores


   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
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   This Internet-Draft will expire on January 14, 2021.

Copyright Notice

   Copyright (c) 2020 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
   ( 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

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   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 . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Performance Considerations  . . . . . . . . . . . . . . . . .  13
   8.  Possible Future Extensions  . . . . . . . . . . . . . . . . .  14
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
     9.1.  Updates to the IETF XML Registry  . . . . . . . . . . . .  14
     9.2.  Updates to the YANG Module Names Registry . . . . . . . .  15
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  15
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  16
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     12.2.  Informative References . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

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 <intended>, which contains validated configuration
   data that a client application intends to be in effect, and
   <operational>, 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

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   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
   <intended>, until when it actually takes effect and is reflected in
   <operational>.  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

   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",
   "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

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4.  Data Model Overview

   At the core of the solution is a new management operation, <compare>,
   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 <compare> 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 <intended>.

   o  target: The target identifies the datastore to compare against the

   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.

   o  exclude-origin: When set, this parameter indicates that origin
      metadata should not not be included as part of RPC output.  When
      this parameter is omitted, origin metadata in comparisons that
      involve <operational> is by default included.

   The operation provides the following output parameter:

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   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.
      When the target datastore is <operational>, "origin" metadata is
      included as part of the patch.  Including origin metadata can help
      in some cases explain the cause of a difference, for example when
      a data node is part of <intended> but the origin of the same data
      node in <operational> 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
      +---x compare
         +---w input
         |  +---w source            identityref
         |  +---w target            identityref
         |  +---w all?              empty
         |  +---w exclude-origin?   empty
         |  +---w (filter-spec)?
         |     +--:(subtree-filter)
         |     |  +---w subtree-filter?
         |     +--:(xpath-filter)
         |        +---w xpath-filter?     yang:xpath1.0 {nc:xpath}?
         +--ro output
            +--ro (compare-response)?
               |  +--ro no-matches?    empty
                  +--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

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5.  YANG Data Model

   <CODE BEGINS> file "ietf-nmda-compare@2019-11-04.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 {
       prefix nc;

     organization "IETF";
       "WG Web:   <>
        WG List:  <>

        Author: Alexander Clemm

        Author: Yingzhen Qu

        Author: Jeff Tantsura

        Author: Andy Bierman

       "The YANG data model defines a new operation, <compare>, that
        can be used to compare NMDA datastores.

        The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
        'MAY', and 'OPTIONAL' in this document are to be interpreted as
        described in BCP 14 (RFC 2119) (RFC 8174) when, and only when,

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        they appear in all capitals, as shown here.

        Copyright (c) 2019 IETF Trust and the persons identified as
        authors of the code.  All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject to
        the license terms contained in, the Simplified BSD License set
        forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents

        This version of this YANG module is part of RFC XXXX; see the
        RFC itself for full legal notices.";

     revision 2019-11-04 {
         "Initial revision";
         "RFC XXXX: Comparison of NMDA datastores";

     /* RPC */
     rpc compare {
         "NMDA compare operation.";
       input {
         leaf source {
           type identityref {
             base ds:datastore;
           mandatory true;
             "The source datastore to be compared.";
         leaf target {
           type identityref {
             base ds:datastore;
           mandatory true;
             "The target datastore to be compared.";
         leaf all {
           type empty;
             "When this leaf is provided, all data nodes are compared,
              whether their schema node pertains to both datastores or

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              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 <operational>, data nodes for
              which config is false are excluded from the comparison.";
         leaf exclude-origin {
           type empty;
             "When this leaf is provided, origin metadata is not
              included as part of RPC output. When this leaf is
              omitted, origin metadata in comparisons that involve
              <operational> is by default included.";
         choice filter-spec {
             "Identifies the portions of the datastores to be
           anydata subtree-filter {
               "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;
               "This parameter contains an XPath expression
                identifying the portions of the target
                datastore to retrieve.";
       output {
         choice compare-response {
             "Comparison results.";
           leaf no-matches {
             type empty;
               "This leaf indicates that the filter did not match
                anything and nothing was compared.";
           container differences {

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               "The list of differences, encoded per RFC8072 with an
                augmentation to include source values where
             uses ypatch:yang-patch {
               augment "yang-patch/edit" {
                   "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'";
                     "The anydata 'value' is only used for 'delete',
                      'move', 'merge', 'replace', and 'remove'

6.  Example

   The following example compares the difference between <operational>
   and <intended> for a subtree under "interfaces".  The subtree
   contains objects that are defined in a YANG data model for the
   management of interfaces defined in [RFC8343].  The excerpt of the
   data model whose instantiation is basis of the comparison is as

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   container interfaces {
       "Interface parameters.";
     list interface {
       key "name";
       leaf name {
         type string;
           "The name of the interface".
       leaf description {
         type string;
           "A textual description of the interface.";
       leaf enabled {
         type boolean;
         default "true";
           "This leaf contains the configured, desired state of the

   The contents of <intended> and <operational> datastores:

   <interfaces xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
       <description>ip interface</description>
   <interfaces xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"

   <operational> contains one object that was not contained in
   <intended>, "preference".  Another object, "explicit-router-id", has
   differences in values.  A third object, "enable", is the same in both

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   RPC request to compare <operational< (source of the comparison) with
   <intended>(target of the comparison):

   <rpc message-id="101"
     <compare xmlns="urn:ietf:params:xml:ns:yang:ietf-nmda-compare"

   RPC reply, when a difference is detected:

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         <patch-id>interface status</patch-id>
         <comment>diff between operational and intended</comment>
               or:origin="or:system">ip interface<description>

   The same request in RESTCONF (using JSON format):

   POST /restconf/operations/ietf-nmda-compare:compare HTTP/1.1
   Content-Type: application/yang-data+json
   Accept: application/yang-d
   { "ietf-nmda-compare:input" {
      "source" : "ietf-datastores:operational",
      "target" : "ietf-datastores:intended".
      "xpath-filter" : \

   The same response in RESTCONF (using JSON format):

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  HTTP/1.1 200 OK
  Date: Thu, 26 Jan 2019 20:56:30 GMT
  Server: example-server
  Content-Type: application/yang-d
  { "ietf-nmda-compare:output" : {
      "differences" : {
        "ietf-yang-patch:yang-patch" : {
          "patch-id" : "interface status",
          "comment" : "diff between operational and intended",
          "edit" : [
              "edit-id" : "1",
              "operation" : "replace",
              "target" : "/ietf-interfaces:interface=eth0/enabled",
              "value" : {
                 "ietf-interfaces:interface/enabled" : "true"
                 "@ietf-interfaces:interface/enabled" : {
                 "ietf-origin:origin" : "ietf-origin:system"
              "source-value" : {
                 "ietf-interfaces:interface/enabled" : "false"
                 "@ietf-interfaces:interface/enabled" : {
                 "ietf-origin:origin" : "ietf-origin:intended"
              "edit-id" : "2",
              "operation" : "create",
              "target" : "/ietf-interfaces:interface=eth0/description",
              "value" : {
                 "ietf-interface:interface/description" : "ip interface"
                 "@ietf-interface:interfaces/description" : {
                 "ietf-origin:origin" : "ietf-origin:intended"

7.  Performance Considerations

   The compare operation can be computationally expensive.  While
   responsible client applications are expected to use the operation
   responsibly and sparingly only when warranted, implementations need
   to be aware of the fact that excessive invocation of this operation
   will burden system resources and need to ensure that system
   performance will not be adversely impacted.  One possibility for an
   implementation to mitigate against such a possibility is to limit the

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   number of requests that is served to a client in any one time
   interval, rejecting requests made at a higher frequency than the
   implementation can reasonably sustain.

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
   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

   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

      URI: urn:ietf:params:xml:ns:yang:ietf-nmda-compare

      Registrant Contact: The IESG.

      XML: N/A, the requested URI is an XML namespace.

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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

10.  Security Considerations

   The YANG module specified in this document defines a schema for data
   that is designed to be accessed via network management protocols such
   as NETCONF [RFC6241] or RESTCONF [RFC8040].  The lowest NETCONF layer
   is the secure transport layer, and the mandatory-to-implement secure
   transport is Secure Shell (SSH) [RFC6242].  The lowest RESTCONF layer
   is HTTPS, and the mandatory-to-implement secure transport is TLS

   The NETCONF access control model [RFC8341] provides the means to
   restrict access for particular NETCONF or RESTCONF users to a
   preconfigured subset of all available NETCONF or RESTCONF protocol
   operations and content.

   The RPC operation defined in this YANG module, "compare", may be
   considered sensitive or vulnerable in some network environments.  It
   is thus important to control access to this operation.  This is the
   sensitivity/vulnerability of RPC operation "compare":

   Comparing datastores for differences 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 the NETCONF access control model
   in order to require proper authorization for requests to be made.
   Second, server implementations can limit the number of requests that
   they serve to a client in any one time interval, rejecting requests
   made at a higher frequency than the implementation can reasonably

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11.  Acknowledgments

   We thank Rob Wilton, Martin Bjorklund, Mahesh Jethanandani, Lou
   Berger, Kent Watsen, Phil Shafer, Ladislav Lhotka, and Tim Carey 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,

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, 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, <>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,

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   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, 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,

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,

12.2.  Informative References

   [RFC8343]  Bjorklund, M., "A YANG Data Model for Interface
              Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,

Authors' Addresses

   Alexander Clemm
   2330 Central Expressway
   Santa Clara,  CA 95050


   Yingzhen Qu
   2330 Central Expressway
   Santa Clara,  CA 95050


   Jeff Tantsura


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   Andy Bierman


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