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Versions: (draft-lengyel-netmod-yang-instance-data) 00 01 02 03 04 05 06 07 08 09 10 11

Netmod                                                        B. Lengyel
Internet-Draft                                                  Ericsson
Intended status: Standards Track                               B. Claise
Expires: October 10, 2020                            Cisco Systems, Inc.
                                                           April 8, 2020


                     YANG Instance Data File Format
             draft-ietf-netmod-yang-instance-file-format-11

Abstract

   There is a need to document data defined in YANG models when a live
   server is unavailable.  Data is often needed at design or
   implementation time or needed when a live running server is
   unavailable.  This document specifies a standard file format for YANG
   instance data, which follows the syntax and semantics of existing
   YANG models, and annotates it with metadata.

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 October 10, 2020.

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
   (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



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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
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Principles  . . . . . . . . . . . . . . . . . . . . . . .   4
     1.3.  Delivery of Instance Data . . . . . . . . . . . . . . . .   4
     1.4.  Data Life cycle . . . . . . . . . . . . . . . . . . . . .   5
   2.  Instance Data File Format . . . . . . . . . . . . . . . . . .   5
     2.1.  Specifying the Content Schema . . . . . . . . . . . . . .   7
       2.1.1.  Inline Method . . . . . . . . . . . . . . . . . . . .   7
       2.1.2.  Simplified-Inline Method  . . . . . . . . . . . . . .   8
       2.1.3.  URI Method  . . . . . . . . . . . . . . . . . . . . .   8
     2.2.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   8
       2.2.1.  UC1, Documenting Server Capabilities  . . . . . . . .   8
       2.2.2.  UC2, Preloading Default Configuration . . . . . . . .  10
       2.2.3.  UC5, Storing diagnostics data . . . . . . . . . . . .  11
   3.  YANG Instance Data Model  . . . . . . . . . . . . . . . . . .  12
     3.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .  12
     3.2.  YANG Model  . . . . . . . . . . . . . . . . . . . . . . .  13
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
     5.1.  URI Registration  . . . . . . . . . . . . . . . . . . . .  20
     5.2.  YANG Module Name Registration . . . . . . . . . . . . . .  20
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  20
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  20
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  21
   Appendix A.  Changes between revisions  . . . . . . . . . . . . .  22
   Appendix B.  Backwards Compatibility  . . . . . . . . . . . . . .  25
   Appendix C.  Detailed Use Cases . . . . . . . . . . . . . . . . .  25
     C.1.  Use Case 1: Early Documentation of Server Capabilities  .  25
     C.2.  Use Case 2: Preloading Data . . . . . . . . . . . . . . .  26
     C.3.  Use Case 3: Documenting Factory Default Settings  . . . .  27
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27

1.  Introduction

   There is a need to document data defined in YANG models when a live
   server is unavailable.  Data is often needed at design or
   implementation time or needed when a live running server is
   unavailable.  To facilitate this offline delivery of data, this
   document specifies a standard format for YANG instance data sets and
   YANG instance data files.  The format of the instance data set is
   defined by the "ietf-yang-instance-data" YANG module, see Section 3.




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   The YANG data model in this document conforms to the Network
   Management Datastore Architecture (NMDA) defined in [RFC8342]

   The following is a list of already implemented and potential use
   cases.

   UC1  Documentation of server capabilities

   UC2  Preloading default configuration data

   UC3  Documenting Factory Default Settings

   UC4  Storing the configuration of a device, e.g., for backup, archive
        or audit purposes

   UC5  Storing diagnostics data

   UC6  Allowing YANG instance data to potentially be carried within
        other IPC message formats

   UC7  Default instance data used as part of a templating solution

   UC8  Providing data examples in RFCs or internet drafts

   In Appendix C describes the first three use cases in detail.

   There are many and varied use cases where YANG instance data could be
   used.  This document does not limit future uses of instance data
   sets, so specifying how and when to use YANG instance data is out of
   scope for this document.  It is anticipated that other documents will
   define specific use cases.  Use cases are listed only as examples.

1.1.  Terminology

   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.

   Instance Data: A collection of instantiated data nodes.

   Instance Data Set: A named set of data items annotated with metadata
   that can be used as instance data in a YANG data tree.

   Instance Data File: A file containing an instance data set formatted
   according to the rules described in this document.




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   Content-schema: A set of YANG modules with their revision, supported
   features, and deviations for which the instance data set contains
   instance data.

   Content defining YANG module: an individual YANG module that is part
   of the content-schema.

   The term "server" is used as defined in [RFC8342].

1.2.  Principles

   The following is a list of the basic principles of the instance data
   format:

   P1  Two standard formats shall be defined based on the XML and JSON
       encodings.

   P2  Instance data shall reuse existing encoding rules for YANG
       defined data.

   P3  Metadata about the instance data set (Section 2, Paragraph 9)
       shall be defined.

   P4  A YANG instance data set shall be allowed to contain data for
       multiple YANG modules.

   P5  Instance data shall be allowed to contain configuration data,
       state data, or a mix of the two.

   P6  Partial data sets shall be allowed.

   P7  The YANG instance data format shall be usable for any data for
       which YANG module(s) are defined and available to the reader,
       independent of whether the module is implemented by a server.

   P8  It shall be possible to report the identity of the datastore with
       which the instance data set is associated.

1.3.  Delivery of Instance Data

   Instance data sets that are produced as a result of some sort of
   specification or design effort may be available without the need for
   a live server e.g., via download from the vendor's website, or in any
   other way that product documentation is distributed.

   Other instance data sets may be read from or produced by the YANG
   server itself e.g., UC5 documenting diagnostic data.




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1.4.  Data Life cycle

   A YANG instance data set is created at a specific point of time.  If
   the data changes afterwards, this is not represented in the instance
   data set anymore.  The current values may be retrieved at run-time
   via NETCONF/RESTCONF or received e.g., in YANG-Push notifications.

   Whether the instance data changes and if so, when and how, should be
   described either in the instance data set's description statement or
   in some other implementation specific manner.

2.  Instance Data File Format

   A YANG instance data file MUST contain a single instance data set and
   no additional data.

   The format of the instance data set is defined by the "ietf-yang-
   instance-data" YANG module.  It is made up of a header part and
   content-data.  The header part carries metadata for the instance data
   set.  The content-data, defined as an anydata data node, carries the
   instance data that the user wants to document/provide.  The syntax
   and semantics of content-data is defined by the content-schema.

   Two formats are specified based on the XML and JSON YANG encodings.
   Later as other YANG encodings (e.g., CBOR) are defined, further
   instance data formats may be specified.

   The content-data part MUST conform to the content-schema, while
   allowing for the exceptions listed below.  The content-data part
   SHALL follow the encoding rules defined in [RFC7950] for XML and
   [RFC7951] for JSON and MUST use UTF-8 character encoding.  Content-
   data MAY include:

   o  metadata as defined by [RFC7952].

   o  a default attribute as defined in [RFC6243] section 6. and in
      [RFC8040] section 4.8.9.

   o  origin metadata as specified in [RFC8526] and [RFC8527]

   o  implementation specific metadata relevant to individual data
      nodes.  Unknown metadata MUST be ignored by users of instance
      data, allowing it to be used later for other purposes.

   An instance data set MAY contain data for any number of YANG modules;
   if needed it MAY carry the complete configuration and state data for
   a server.  Default values SHOULD NOT be included.




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   Configuration ("config true") and operational state data ("config
   false") MAY be mixed in the instance data file.

   Instance data files MAY contain partial data sets.  This means
   "mandatory", "min-elements", "require-instance true", "must" and
   "when" constrains MAY be violated.

   The name of the instance data file SHOULD take one of the following
   two forms:

      If "revision" information is present inside the data set:

         instance-data-set-name ['@' revision-date] '.filetype'

         E.g., acme-router-modules@2018-01-25.xml

      If the leaf "name" is present in the instance data header, its
      value SHOULD be used for the "instance-data-set-name".  If the
      "revision-date" is present in both the filename and in the
      instance data header, the revision date in the file name MUST be
      set to the latest revision date inside the instance data set.

      If timestamp information inside the data set is present

         instance-data-set-name ['@' timestamp] '.filetype'

         E.g., acme-router-modules@2018-01-25T15_06_34_3+01_00.json

      If the leaf "name" is present in the instance data header, its
      value SHOULD be used for the "instance-data-set-name".  If the
      "timestamp" is present both in the filename and in the instance
      data header, the timestamp in the file name SHOULD be set to the
      timestamp inside the instance data set; the semicolons and the
      decimal point, if present, shall be replaced by underscores.

   The revision date or timestamp is optional. ".filetype" SHOULD be
   ".json" or ".xml" according to the format used.

   Metadata, information about the data set itself SHOULD be included in
   the instance data set.  Some metadata items are defined in the YANG
   module "ietf-yang-instance-data", but other items MAY be used.

   Metadata MUST include:

   o  Version of the YANG Instance Data format

   Metadata SHOULD include:




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   o  Name of the data set

   o  Content schema specification (i.e., the "content-schema" node)

   o  Description of the instance data set.  The description SHOULD
      contain information whether and how the data can change during the
      lifetime of the server.

2.1.  Specifying the Content Schema

   To properly understand and use an instance data set, the user needs
   to know the content-schema.  One of the following methods SHOULD be
   used:

      Inline method: Include the needed information as part of the
      instance data set.

      Simplified-Inline method: Include the needed information as part
      of the instance data set; short specification.

      URI method: Include a URI that references another YANG instance
      data file.  This instance data file will use the same content-
      schema as the referenced YANG instance data file.  (if you don't
      want to repeat the info again and again)

      External Method: Do not include the "content-schema" node; the
      user needs to obtain the information through external documents.

   Additional methods e.g., a YANG-package based solution may be added
   later.

   Note, the specified content-schema only indicates the set of modules
   that were used to define this YANG instance data set.  Sometimes
   instance data may be used for a server supporting a different YANG
   module set. (e.g., for "UC2 Preloading Data" the instance data set
   may not be updated every time the YANG modules on the server are
   updated) Whether an instance data set originally defined using a
   specific content-schema is usable with a different other schema
   depends on many factors including the amount of differences and the
   compatibility between the original and the other schema, considering
   modules, revisions, features, deviations, the scope of the instance
   data, etc.

2.1.1.  Inline Method

   One or more inline-module elements define YANG module(s) used to
   specify the content defining YANG modules.




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      E.g., ietf-yang-library@2016-06-21

   The anydata inline-schema carries instance data (conforming to the
   inline-modules) that actually specifies the content defining YANG
   modules including revision, supported features, deviations and any
   relevant additional data (e.g., revision labels which can be used as
   alternative to the revision
   date[I-D.verdt-netmod-yang-module-versioning]).  See Section 2.2.

2.1.2.  Simplified-Inline Method

   The instance data set contains a list of content defining YANG
   modules including the revision date for each.  Usage of this method
   implies that the modules are used without any deviations and with all
   features supported.

2.1.3.  URI Method

   The "same-schema-as-file" leaf SHALL contain a URI that references
   another YANG instance data file.  The current instance data file will
   use the same content schema as the referenced file.

   The referenced instance data file MAY have no content-data if it is
   used solely for specifying the content-schema.

   If a referenced instance data file is unavailable, content-schema is
   unknown.

   The URI method is advantageous when the user wants to avoid the
   overhead of specifying the content-schema in each instance data file:
   E.g., In UC6, when the system creates a diagnostic file every minute
   to document the state of the server.

2.2.  Examples

2.2.1.  UC1, Documenting Server Capabilities

   The example illustrates UC1 Section 1.  It provides a list of
   supported YANG modules and NETCONF capabilities for a server.  It
   uses the "inline" method to specify the content-schema.

   The example uses artwork folding[I-D.ietf-netmod-artwork-folding].

  ========== NOTE: '\' line wrapping per BCP XXX (RFC XXXX) ===========

  <?xml version="1.0" encoding="UTF-8"?>
  <instance-data-set xmlns=\
      "urn:ietf:params:xml:ns:yang:ietf-yang-instance-data">



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    <name>acme-router-modules</name>
    <content-schema>
      <inline-module>ietf-yang-library@2016-06-21</inline-module>
      <inline-schema>
        <modules-state \
          xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
          <module>
            <name>ietf-yang-library</name>
            <revision>2016-06-21</revision>
          </module>
          <module>
            <name>ietf-netconf-monitoring</name>
            <revision>2010-10-04</revision>
          </module>
        </modules-state>
      </inline-schema>
    </content-schema>
    <revision>
      <date>1956-10-23</date>
      <description>Initial version</description>
    </revision>
    <description>Defines the minimal set of modules that any \
        acme-router will contain.</description>
    <contact>info@acme.com</contact>
    <content-data>
      <modules-state \
          xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
        <module>
          <name>ietf-yang-library</name>
          <revision>2016-06-21</revision>
          <namespace>\
            urn:ietf:params:xml:ns:yang:ietf-yang-library\
          </namespace>
          <conformance-type>implement</conformance-type>
        </module>
        <module>
          <name>ietf-system</name>
          <revision>2014-08-06</revision>
          <namespace>urn:ietf:params:xml:ns:yang:ietf-system</namespace>
          <feature>sys:authentication</feature>
          <feature>sys:local-users</feature>
          <deviation>
            <name>acme-system-ext</name>
            <revision>2018-08-06</revision>
          </deviation>
          <conformance-type>implement</conformance-type>
        </module>
        <module>



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          <name>ietf-netconf-monitoring</name>
          <revision>2010-10-04</revision>
          <namespace>\
            urn:ietf:params:xml:ns:yang:ietf-netconf-monitoring\
          </namespace>
          <conformance-type>implement</conformance-type>
        </module>
        <module>
          <name>ietf-yang-types</name>
          <revision>2013-07-15</revision>
          <namespace>urn:ietf:params:xml:ns:yang:ietf-yang-types\
            </namespace>
          <conformance-type>import</conformance-type>
        </module>
        <module>
          <name>acme-system-ext</name>
          <revision>2018-08-06</revision>
          <namespace>urn:rdns:acme.com:oammodel:acme-system-ext\
            </namespace>
          <conformance-type>implement</conformance-type>
        </module>
      </modules-state>
      <netconf-state \
          xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-monitoring">
        <capabilities>
          <capability>\
            urn:ietf:params:netconf:capability:validate:1.1\
          </capability>
        </capabilities>
      </netconf-state>
    </content-data>
  </instance-data-set>

                 Figure 1: Documenting server capabilities

2.2.2.  UC2, Preloading Default Configuration

   The example illustrates UC2 Section 1.  It provides a default rule
   set for a read-only operator role.  It uses the "simplified-inline"
   method for specifying the content-schema.











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 <?xml version="1.0" encoding="UTF-8"?>
 <instance-data-set
     xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-instance-data">
   <name>read-only-acm-rules</name>
   <content-schema>
     <module>ietf-netconf-acm@2018-02-14</module>
   </content-schema>
   <revision>
     <date>1776-07-04</date>
     <description>Initial version</description>
   </revision>
   <description>Access control rules for a read-only role.</description>
   <content-data>
     <nacm xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
       <enable-nacm>true</enable-nacm>
       <read-default>deny</read-default>
       <exec-default>deny</exec-default>
       <rule-list>
         <name>read-only-role</name>
         <group>read-only-group</group>
         <rule>
           <name>read-all</name>
           <module-name>*</module-name>
           <access-operation>read</access-operation>
           <action>permit</action>
         </rule>
       </rule-list>
     </nacm>
   </content-data>
 </instance-data-set>

                 Figure 2: Preloading access control data

2.2.3.  UC5, Storing diagnostics data

   The example illustrates UC5 Section 1.  An instance data set is
   produced by the server every 15 minutes that contains statistics
   about the NETCONF server.  As a new set is produced periodically many
   times a day a revision-date would be useless; instead a timestamp is
   included.











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   {
     "ietf-yang-instance-data:instance-data-set": {
       "name": "acme-router-netconf-diagnostics",
       "content-schema": {
         "same-schema-as-file": "file:///acme-diagnostics-schema.json"
       },
       "timestamp": "2018-01-25T17:00:38Z",
       "description":  ["NETCONF statistics"],
       "content-data": {
         "ietf-netconf-monitoring:netconf-state": {
           "statistics": {
             "netconf-start-time ": "2018-12-05T17:45:00Z",
             "in-bad-hellos ": "32",
             "in-sessions ": "397",
             "dropped-sessions ": "87",
             "in-rpcs ": "8711",
             "in-bad-rpcs ": "408",
             "out-rpc-errors ": "408",
             "out-notifications": "39007"
           }
         }
       }
     }
   }

                    Figure 3: Storing diagnostics data

3.  YANG Instance Data Model

3.1.  Tree Diagram

   The following tree diagram [RFC8340] provides an overview of the data
   model.


















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   module: ietf-yang-instance-data
     structure instance-data-set:
        +-- name?             string
        +-- format-version?   string
        +-- content-schema
        |  +-- (content-schema-spec)?
        |     +--:(simplified-inline)
        |     |  +-- module*                string
        |     +--:(inline) {inline-content-schema}?
        |     |  +-- inline-module*         string
        |     |  +-- inline-schema          <anydata>
        |     +--:(uri)
        |        +-- same-schema-as-file?   inet:uri
        +-- description*      string
        +-- contact?          string
        +-- organization?     string
        +-- datastore?        ds:datastore-ref
        +-- revision* [date]
        |  +-- date           string
        |  +-- description?   string
        +-- timestamp?        yang:date-and-time
        +-- content-data?     <anydata>

3.2.  YANG Model

   This YANG module imports typedefs from [RFC6991], identities from
   [RFC8342] and the "structure" extension from
   [I-D.ietf-netmod-yang-data-ext].

   <CODE BEGINS> file "ietf-yang-instance-data@2020-04-02.yang"
   module ietf-yang-instance-data {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-yang-instance-data";
     prefix yid;

     import ietf-yang-structure-ext {
       prefix sx;
       reference
         "YANG Data Structure Extensions:
          draft-ietf-netmod-yang-data-ext-05";
     }
     import ietf-datastores {
       prefix ds;
       reference
         "RFC 8342: Network Management Datastore Architecture (NMDA)";
     }
     import ietf-inet-types {
       prefix inet;



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       reference
         "RFC 6991: Common YANG Data Types";
     }
     import ietf-yang-types {
       prefix yang;
       reference
         "RFC 6991: Common YANG Data Types";
     }

     organization
       "IETF NETMOD Working Group";
     contact
       "WG Web:   <https://datatracker.ietf.org/wg/netmodf/>
        WG List:  <mailto:netmod@ietf.org>

        Author:  Balazs Lengyel
           <mailto:balazs.lengyel@ericsson.com>";
     description
       "The module defines the structure and content of YANG
        instance data sets.

        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 (RFC 2119)
        (RFC 8174) when, and only when, they appear in all
        capitals, as shown here.

        Copyright (c) 2020 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
        (http://trustee.ietf.org/license-info).

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

     revision 2020-04-02 {
       description
         "Initial revision.";
       reference
         "RFC XXXX: YANG Instance Data Format";
     }




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     feature inline-content-schema {
       description
         "This feature indicates that inline content-schema
             option is supported.";
     }

     typedef module-with-revision-date {
       type string {
         pattern '[a-zA-Z_][a-zA-Z0-9\-_.]*' +
           '(@\d{4}-(1[0-2]|0[1-9])-(0[1-9]|[1|2][0-9]|3[0-1]))?';
         pattern '.|..|[^xX].*|.[^mM].*|..[^lL].*';
       }
       description
         "A type definining a module name and an optional revision
          date, e.g. ietf-yang-library@2016-06-21";
     }

     sx:structure "instance-data-set" {
       description
         "A data structure to define a format for
          YANG instance data sets. Consists of meta-data about
          the instance data set and the real content-data.";
       leaf name {
         type string;
         description
           "An arbitrary name for the YANG instance data set.  This
            value is primarily used for descriptive purposes.  However,
            when the instance data set is saved to a file, then the
            filename MUST encode the name's value, per Section 3
            of RFC XXXX.";
       }
       leaf format-version {
         type string {
           pattern '\d{4}-(1[0-2]|0[1-9])-(0[1-9]|[1|2][0-9]|3[0-1])';
         }
         default "2020-04-02";
         description
           "The 'revision' of the 'ietf-yang-instance-data' module
            used to encode this 'instance-data-set'.";
       }
       container content-schema {
         description
           "The content schema used to create the instance data set.
            If not present the user needs to obtain the information
            through external documents.";
         choice content-schema-spec {
           description
             "Specification of the content-schema.";



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           case simplified-inline {
             leaf-list module {
               type module-with-revision-date;
               description
                 "The list of content defining YANG modules.

                  The value SHALL start with the module name.
                  If the module contains a revision statement the
                  revision date SHALL be included in the leaf-list
                  entry. If other methods (e.g., revision-label) are
                  defined to identify individual module revisions
                  those MAY be used instead of using a revision date.

                  E.g., ietf-yang-library@2016-06-21

                  Usage of this leaf-list implies the modules are
                  used without any deviations and with all features
                  supported. Multiple revisions of the same module
                  MUST NOT be specified.";
             }
           }
           case inline {
             if-feature "inline-content-schema";
             leaf-list inline-module {
               type module-with-revision-date;
               min-elements 1;
               description
                 "Indicates that content defining YANG modules
                  are specified inline.

                  The value SHALL start with the module name.
                  If the module contains a revision statement the
                  revision date SHALL be included in the leaf-list
                  entry. If other methods (e.g., revision-label) are
                  defined to identify individual module revisions
                  those MAY be used instead of using a revision date.

                  E.g., ietf-yang-library@2016-06-21

                  The first item is either ietf-yang-library or some
                  other YANG module that contains a list of YANG modules
                  with their name, revision-date, supported-features,
                  and deviations. The usage of revision '2019-01-04'
                  of the 'ietf-yang-library' module MUST be supported.
                  Using other modules, module versions MAY also be
                  supported.

                  Some versions of ietf-yang-library MAY contain



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                  different module-sets for different datastores. In
                  this case the instance data set MUST contain the
                  'datastore' leaf and instance data for the
                  ietf-yang-library MUST also contain information
                  specifying the module-set for the relevant datastore.

                  Subsequent items MAY specify YANG modules augmenting
                  the first module with useful data
                  (e.g., revision label).";
               reference
                 "RFC 8525";
             }
             anydata inline-schema {
               mandatory true;
               description
                 "Instance data corresponding to the YANG modules
                  specified in the inline-module nodes defining the set
                  of content defining YANG modules for this
                  instance-data-set.";
             }
           }
           case uri {
             leaf same-schema-as-file {
               type inet:uri;
               description
                 "A reference to another YANG instance data file.
                  This instance data file uses the same
                  content schema as the referenced file.";
             }
           }
         }
       }
       leaf-list description {
         type string;
         description
           "Description of the instance data set.";
       }
       leaf contact {
         type string;
         description
           "Contact information for the person or
            organization to whom queries concerning this
            instance data set should be sent.";
       }
       leaf organization {
         type string;
         description
           "Organization responsible for the instance



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            data set.";
       }
       leaf datastore {
         type ds:datastore-ref;
         description
           "The identity of the datastore with which the
            instance data set is associated, e.g., the datastore from
            where the data was read or the datastore into which the data
            may be loaded or the datastore which is being documented.
            If a single specific datastore cannot be specified, the
            leaf MUST be absent.

            If this leaf is absent, then the datastore to which the
            instance data belongs is undefined.";
       }
       list revision {
         key "date";
         description
           "Instance data sets that are produced as
            a result of some sort of specification or design effort
            SHOULD have at least one revision entry.  For every
            published editorial change, a new one SHOULD be added
            in front of the revisions sequence so that all
            revisions are in reverse chronological order.

            Instance data sets that are read from
            or produced by a server or otherwise
            subject to frequent updates or changes: revision
            SHOULD NOT be present";
         leaf date {
           type string {
             pattern '\d{4}-(1[0-2]|0[1-9])-(0[1-9]|[1|2][0-9]|3[0-1])';
           }
           description
             "Specifies the date the instance data set
              was last modified. Formatted as YYYY-MM-DD";
         }
         leaf description {
           type string;
           description
             "Description of this revision of the instance data set.";
         }
       }
       leaf timestamp {
         type yang:date-and-time;
         description
           "The date and time when the instance data set
            was last modified.



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            Instance data sets that are read from or produced
            by a server or otherwise subject to frequent
            updates or changes: timestamp SHOULD be present";
       }
       anydata content-data {
         description
           "Contains the real instance data.
            The data MUST conform to the relevant YANG modules specified
            either in the content-schema or in some other
            implementation specific manner.";
       }
     }
   }
   <CODE ENDS>

4.  Security Considerations

   The YANG module defined in this document only defines a wrapper
   structure specifying a format and a metadata header for YANG instance
   data defined by the content-schema, so it does not follow the
   security considerations template for YANG models.  The instance data
   is designed to be accessed as a stored file or over any file access
   method or protocol.

   The document does not specify any method to influence the behavior of
   a server.

   Instance data files may contain sensitive data.

   The header part is not security sensitive.

   The security sensitivity of the instance data in the content part is
   completely dependent on the content schema.  Depending on the nature
   of the instance data, instance data files MAY need to be handled in a
   secure way.  The same kind of handling should be applied, that would
   be needed for the result of a read operation returning the same data.

   Instance data files should be protected against modification or
   unauthorized access using normal file handling mechanisms.  Care
   should be taken, when copying the original files or providing file
   access for additional users, not to reveal information
   unintentionally.

5.  IANA Considerations

   This document registers one URI and one YANG module.





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5.1.  URI Registration

   This document registers one URI in the IETF XML registry [RFC3688].
   Following the format in RFC 3688, the following registration is
   requested to be made:

   URI: urn:ietf:params:xml:ns:yang:ietf-yang-instance-data
   Registrant Contact: The IESG.
   XML: N/A, the requested URI is an XML namespace.

5.2.  YANG Module Name Registration

   This document registers one YANG module in the YANG Module Names
   registry [RFC6020].

   name: ietf-yang-instance-data
   namespace: urn:ietf:params:xml:ns:yang:ietf-yang-instance-data
   prefix: yid
   reference: RFC XXXX

6.  Acknowledgments

   For their valuable comments, discussions, and feedback, we wish to
   acknowledge Andy Bierman, Juergen Schoenwaelder, Rob Wilton, Joe
   Clarke, Kent Watsen Martin Bjorklund, Ladislav Lhotka, Qin Wu and
   other members of the Netmod WG.

7.  References

7.1.  Normative References

   [I-D.ietf-netmod-yang-data-ext]
              Bierman, A., Bjorklund, M., and K. Watsen, "YANG Data
              Structure Extensions", draft-ietf-netmod-yang-data-ext-05
              (work in progress), December 2019.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC6243]  Bierman, A. and B. Lengyel, "With-defaults Capability for
              NETCONF", RFC 6243, DOI 10.17487/RFC6243, June 2011,
              <https://www.rfc-editor.org/info/rfc6243>.

   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
              RFC 6991, DOI 10.17487/RFC6991, July 2013,
              <https://www.rfc-editor.org/info/rfc6991>.



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   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              RFC 7951, DOI 10.17487/RFC7951, August 2016,
              <https://www.rfc-editor.org/info/rfc7951>.

   [RFC7952]  Lhotka, L., "Defining and Using Metadata with YANG",
              RFC 7952, DOI 10.17487/RFC7952, August 2016,
              <https://www.rfc-editor.org/info/rfc7952>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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,
              <https://www.rfc-editor.org/info/rfc8342>.

   [RFC8525]  Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K.,
              and R. Wilton, "YANG Library", RFC 8525,
              DOI 10.17487/RFC8525, March 2019,
              <https://www.rfc-editor.org/info/rfc8525>.

   [RFC8526]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "NETCONF Extensions to Support the Network
              Management Datastore Architecture", RFC 8526,
              DOI 10.17487/RFC8526, March 2019,
              <https://www.rfc-editor.org/info/rfc8526>.

   [RFC8527]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "RESTCONF Extensions to Support the Network
              Management Datastore Architecture", RFC 8527,
              DOI 10.17487/RFC8527, March 2019,
              <https://www.rfc-editor.org/info/rfc8527>.

7.2.  Informative References








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   [I-D.ietf-netmod-artwork-folding]
              Watsen, K., Auerswald, E., Farrel, A., and Q. WU,
              "Handling Long Lines in Inclusions in Internet-Drafts and
              RFCs", draft-ietf-netmod-artwork-folding-12 (work in
              progress), January 2020.

   [I-D.ietf-netmod-factory-default]
              WU, Q., Lengyel, B., and Y. Niu, "A YANG Data Model for
              Factory Default Settings", draft-ietf-netmod-factory-
              default-14 (work in progress), February 2020.

   [I-D.verdt-netmod-yang-module-versioning]
              Claise, B., Clarke, J., Rahman, R., Wilton, R., Lengyel,
              B., Sterne, J., and K. D'Souza, "Updated YANG Module
              Revision Handling", draft-verdt-netmod-yang-module-
              versioning-01 (work in progress), October 2019.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [RFC8632]  Vallin, S. and M. Bjorklund, "A YANG Data Model for Alarm
              Management", RFC 8632, DOI 10.17487/RFC8632, September
              2019, <https://www.rfc-editor.org/info/rfc8632>.

   [RFC8641]  Clemm, A. and E. Voit, "Subscription to YANG Notifications
              for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641,
              September 2019, <https://www.rfc-editor.org/info/rfc8641>.

Appendix A.  Changes between revisions

   Note to RFC Editor (To be removed by RFC Editor)

   v09 - v10

   o  Editorial updates

   v08 - v09




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   o  Removed reference to similar to get reply

   o  Introduced artwork folding in the examples

   v07 - v08

   o  Moved compatibility into appendix

   o  Renamed yid-version to format-version.  Changed format to date of
      the YANG module

   o  Made support of ietf-yang-library mandatory if inline-content-
      schema is supported

   o  Many small changes based on WGLC

   v06 - v07

   o  Updated terminology, use-cases

   o  Many small changes based on WGLC

   v05 - v06

   o  Modified module name format, removed .yin or .yang extension

   o  Removed pattern for module and inline-module.  The usage of
      revision-label should also be allowed.

   v04 - v05

   o  Updated according to YANG-Doctor review

   o  Updated security considerations

   o  Added a wrapping container for the schema, and renamed the data
      nodes in the inline and uri cases.

   o  Allowed .yin for simplified-inline schema naming.  Made date
      optional if it is unavailable in the YANG module.

   o  Added a mandatory yid-version to the header metadata to allow
      later updates of the module.

   v03 - v04

   o  removed entity-tag and last-modified timestamp




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   o  Added simplified-inline method of content-schema specification

   v02 - v03

   o  target renamed to "content-schema" and "content defining YANG
      module(s)"

   o  Made name of instance data set optional

   o  Updated according to draft-ietf-netmod-yang-data-ext-03

   o  Clarified that entity-tag and last-modified timestamp are encoded
      as metadata.  While they contain useful data, the HTTP-header
      based encoding from Restconf is not suitable.

   v01 - v02

   o  Removed design time from terminology

   o  Defined the format of the content-data part by referencing various
      RFCs and drafts instead of the result of the get-data and get
      operations.

   o  Changed target-ptr to a choice

   o  Inline target-ptr may include augmenting modules and alternatives
      to ietf-yang-library

   o  Moved list of target modules into a separate <target-modules>
      element.

   o  Added backwards compatibility considerations

   v00 - v01

   o  Added the target-ptr metadata with 3 methods

   o  Added timestamp metadata

   o  Removed usage of dedicated .yid file extension

   o  Added list of use cases

   o  Added list of principles

   o  Updated examples

   o  Moved detailed use case descriptions to appendix



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Appendix B.  Backwards Compatibility

   The concept of backwards compatibility and what changes are backwards
   compatible are not defined for instance data sets as it is highly
   dependent on the specific use case and the content-schema.

   For instance data that is the result of a design or specification
   activity, some changes that may be good to avoid are listed below.

   YANG uses the concept of managed entities identified by key values;
   if the connection between the represented entity and the key value is
   not preserved during an update, this may lead to the following
   problems.

   o  If the key value of a list entry that represents the same managed
      entity as before is changed, the user may mistakenly identify the
      list entry as new.

   o  If the meaning of a list entry is changed, but the key values are
      not (e.g., redefining an alarm-type but not changing its alarm-
      type-id) the change may not be noticed.

   o  If the key value of a previously removed list entry is reused for
      a different entity, the change may be misinterpreted as
      reintroducing the previous entity.

Appendix C.  Detailed Use Cases

   This section is non-normative.

C.1.  Use Case 1: Early Documentation of Server Capabilities

   A server has a number of server-capabilities that are defined in YANG
   modules and can be retrieved from the server using protocols like
   NETCONF or RESTCONF.  Server capabilities include:

   o  data defined in "ietf-yang-library": YANG modules, submodules,
      features, deviations, schema-mounts, and datastores supported
      ([RFC8525])

   o  alarms supported ([RFC8632])

   o  data nodes and subtrees that support or do not support on-change
      notifications ([RFC8641])

   o  netconf-capabilities in ietf-netconf-monitoring





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   While it is good practice to allow a client to query these
   capabilities from the live server, that is often not possible.

   Often when a network node is released, an associated NMS (network
   management system) is also released with it.  The NMS depends on the
   capabilities of the server.  During NMS implementation, information
   about server capabilities is needed.  If the information is
   unavailable early in some offline document, but only as instance data
   from the live network node, the NMS implementation will be delayed,
   because it has to wait until the network node is ready.  Also
   assuming that all NMS implementors will have a correctly configured
   network nodes from which data can be retrieved, is a very expensive
   proposition.  (An NMS may handle dozens of node types.)

   Network operators often build their own home-grown NMS systems that
   need to be integrated with a vendor's network node.  The operator
   needs to know the network node's server capabilities in order to do
   this.  Moreover, the network operator's decision to buy a vendor's
   product may even be influenced by the network node's OAM feature set
   documented as the server's capabilities.

   Beside NMS implementors, system integrators and many others also need
   the same information early.  Examples could be model driven testing,
   generating documentation, etc.

   Most server-capabilities are relatively stable and change only during
   upgrade or due to licensing or the addition or removal of hardware.
   They are usually defined by a vendor at design time, before the
   product is released.  It is feasible and advantageous to define/
   document them early e.g., in a YANG instance data File.

   It is anticipated that a separate IETF document will define in detail
   how and which set of server capabilities should be documented.

C.2.  Use Case 2: Preloading Data

   There are parts of the configuration that must be fully configurable
   by the operator.  However, often a simple default configuration will
   be sufficient.

   One example is access control groups/roles and related rules.  While
   a sophisticated operator may define dozens of different groups, often
   a basic (read-only operator, read-write system administrator,
   security-administrator) triplet will be enough.  Vendors will often
   provide such default configuration data to make device configuration
   easier for an operator.





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   Defining access control data is a complex task.  To help, the device
   vendor predefines a set of default groups (/nacm:nacm/groups) and
   rules for these groups to access specific parts of common models
   (/nacm:nacm/rule-list/rule).

   YANG instance data files are used to document and/or preload the
   default configuration.

C.3.  Use Case 3: Documenting Factory Default Settings

   Nearly every server has a factory default configuration.  If the
   system is really badly misconfigured or if the current configuration
   is to be abandoned, the system can be reset the default factory
   configuration.

   In NETCONF, the <delete-config> operation can already be used to
   reset the startup datastore.  There are ongoing efforts to introduce
   a new, more generic factory-reset operation for the same purpose
   [I-D.ietf-netmod-factory-default]

   The operator currently has no way to know what the default
   configuration actually contains.  YANG instance data can also be used
   to document the factory default configuration.

Authors' Addresses

   Balazs Lengyel
   Ericsson
   Magyar Tudosok korutja 11
   1117 Budapest
   Hungary

   Phone: +36-70-330-7909
   Email: balazs.lengyel@ericsson.com


   Benoit Claise
   Cisco Systems, Inc.
   De Kleetlaan 6a b1
   1831 Diegem
   Belgium

   Phone: +32 2 704 5622
   Email: bclaise@cisco.com







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