Status of This Memo

This is an Internet Standards Track document.¶

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.¶

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9195.¶

Copyright Notice

Copyright (c) 2022 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶

Table of Contents

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 time, implementation time, or even later 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. 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 inter-process communication (IPC) message formats¶

UC7

Default instance data used as part of a templating solution¶

UC8

Providing data examples in RFCs or internet drafts¶

Appendix B 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.¶

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 and/or provide. The syntax and semantics of content-data are defined by the content-schema.¶

Two formats are specified based on the XML and JSON YANG encodings. The file formats are achieved by applying the respective XML and JSON encoding rules for the YANG structure included in this document. 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:¶

• metadata, as defined by [RFC7952].¶
• origin metadata, as specified in [RFC8526] and [RFC8527].¶
• 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 be excluded where they do not provide additional useful data.¶

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" constraints MAY be violated.¶

The name of the instance data file SHOULD be of the following form (using ABNF notation [RFC5234]):¶

   instance-data-set-name ["@" ( revision-date / timestamp ) ]
                  ( ".xml" / ".json" )

Examples include:¶

      acme-router-modules.xml
      acme-router-modules@2018-01-25.xml
      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" in the filename. If the "revision-date" is present in the filename, it MUST conform to the format of the revision-date leaf in the YANG model. If the "revision-date" is present in both the filename and the instance data header, the revision date in the filename MUST be set to the latest revision date inside the instance data set. If the "timestamp" is present in the filename, it MUST conform to the format of the timestamp leaf in the YANG model except for replacing colons as described below. If the "timestamp" is present in both the filename and the instance data header, the timestamp in the filename SHOULD be set to the timestamp inside the instance data set; any colons, if present, shall be replaced by underscores.¶

Metadata MUST include:¶

• • Version of the YANG instance data format (if not explicitly present, the default value is used).¶

Metadata SHOULD include:¶

• • Name of the data set.¶
  • Content-schema specification (i.e., the "content-schema" node).¶
  • Description of the instance data set. The description SHOULD contain information on whether and how the data can change during the lifetime of the server.¶
  • An indication of whether default values are included. The default handling uses the concepts defined in [RFC6243]; however, as only concepts are re-used, users of instance data sets do not need to support [RFC6243].¶

========== NOTE: '\' line wrapping per RFC 8792 ===========

<?xml version="1.0" encoding="UTF-8"?>
<instance-data-set xmlns=\
    "urn:ietf:params:xml:ns:yang:ietf-yang-instance-data">
  <name>acme-router-modules</name>
  <content-schema>
    <inline-yang-library>
      <modules-state \
        xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
        <module>
          <name>ietf-yang-library</name>
          <revision>2019-01-04</revision>
        </module>
        <module>
          <name>ietf-netconf-monitoring</name>
          <revision>2010-10-04</revision>
        </module>
      </modules-state>
    </inline-yang-library>
  </content-schema>
  <revision>
    <date>2020-10-23</date>
    <description>Initial version</description>
  </revision>
  <description>Defines the minimal set of modules that any \
      acme-router will contain. This minimal set will \
      only change when a new software release is \
      introduced.</description>
  <contact>info@acme.example.com</contact>
  <content-data>
    <modules-state \
        xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
      <module>
        <name>ietf-yang-library</name>
        <revision>2019-01-04</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>
        <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.example.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>

========== NOTE: '\' line wrapping per RFC 8792 ===========

<?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>2018-07-04</date>
    <description>Initial version</description>
  </revision>
  <description>Default access control rules for a read-only \
      role. This set of rules will only change when a new  \
      software release is introduced.</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>

========== NOTE: '\' line wrapping per RFC 8792 ===========

{
  "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, \
        The data may change at any time."],
    "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"
        }
      }
    }
  }
}

3. YANG Instance Data Model

module: ietf-yang-instance-data
  structure instance-data-set:
    +--name?                string
    +--format-version?      string
    +--includes-defaults?   enumeration
    +--content-schema
    |  +--(content-schema-spec)?
    |     +--:(simplified-inline)
    |     |  +--module*                module-with-revision-date
    |     +--:(inline)
    |     |  +--inline-yang-library    <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>

<CODE BEGINS> file "ietf-yang-instance-data@2022-02-17.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
      "RFC 8791: YANG Data Structure Extensions";
  }
  import ietf-datastores {
    prefix ds;
    reference
      "RFC 8342: Network Management Datastore Architecture (NMDA)";
  }
  import ietf-inet-types {
    prefix inet;
    reference
      "RFC 6991: Common YANG Data Types";
  }
  import ietf-yang-types {
    prefix yang;
    reference
      "RFC 6991: Common YANG Data Types";
  }
  import ietf-netconf-with-defaults {
    prefix ncwd;
    reference
      "RFC 6243: With-defaults Capability for NETCONF";
  }

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

     Author:  Balazs Lengyel
        <mailto:balazs.lengyel@ericsson.com>

     Author:  Benoit Claise
        <mailto:benoit.claise@huawei.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) 2022 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 Revised BSD License
     set forth in Section 4.c of the IETF Trust's
     Legal Provisions Relating to IETF Documents
     (https://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC 9195
     (https://www.rfc-editor.org/info/rfc9195); see the RFC itself
     for full legal notices.";

  revision 2022-02-17 {
    description
      "Initial revision.";
    reference
      "RFC 9195: YANG Instance Data File Format";
  }

  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 defining a module name and an optional revision
       date, e.g., ietf-yang-library@2019-01-04.";
  }

  sx:structure instance-data-set {
    description
      "A data structure to define a format for YANG instance
       data.  The majority of the YANG nodes provides metadata
       about the instance data; the instance data itself is
       contained only in the 'content-data' node.";
    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 2
         of RFC 9195.";
    }
    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 "2022-01-20";
      description
        "The 'revision' of the 'ietf-yang-instance-data' module
         used to encode this 'instance-data-set'.";
    }
    leaf includes-defaults {
      type ncwd:with-defaults-mode;
      default "report-all";
      description
        "Indicates how data nodes with default values are
         represented for all data nodes contained in the
         instance-data-set.

         It uses the same definitions as per Section 3 of RFC 6243
         but applied in the context of an instance data file rather
         than a NETCONF request using the <with-defaults>
         parameter.

         For JSON files, the encoding of the 'report-all-tagged'
         option is as defined in Section 4.8.9 of RFC 8040.";
      reference
        "RFC 6243: With-defaults Capability for NETCONF";
    }
    container content-schema {
      description
        "The content schema (i.e., YANG modules) 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.";
        case simplified-inline {
          leaf-list module {
            type module-with-revision-date;
            min-elements 1;
            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, e.g., ietf-yang-library@2019-01-04.

               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 {
          anydata inline-yang-library {
            mandatory true;
            description
              "Instance data corresponding to the
               ietf-yang-library@2019-01-04 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.

               Referenced files using the 'inline' or the
               'simplified-inline' methods MUST be supported.
               Referenced files using the 'URI method' MAY be
               supported.

               The URL schemes 'file://' and 'https://' MUST
               be supported; other schemes MAY also be
               supported.";
          }
        }
      }
    }
    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
         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, the datastore into which the data
         may be loaded, or the datastore that 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 unspecified.";
    }
    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 unique revision SHOULD
         be added in front of the revisions sequence so that all
         revisions are in reverse chronological order.

         In cases of 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.

         In cases of instance data sets that are read from or
         produced by a server or otherwise subject to frequent
         updates or changes, the timestamp SHOULD be present.

         If both a revision list entry and timestamp are present,
         the timestamp SHOULD contain the same date as the
         latest revision statement.";
    }
    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. Because of this, the security considerations template for YANG models in Section 3.7.1 of [RFC8407] is not followed. 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.¶

The header part is usually not security sensitive; however, sensitive information may be included, in which case it needs to be handled securely, as mentioned below. Information to consider includes:¶

• If the URI method is used for specification of the content-schema and the URI includes a userinfo subcomponent¶
• Any description text¶

The content part may contain sensitive data. The security sensitivity of this data is completely dependent on the content-schema. Depending on the nature of the instance data, instance data files MAY need to be handled securely. The same kind of handling should be applied to this file at rest and in transit that would be needed for the result of a read operation returning the same data. These in-transit protection mechanisms will also mitigate integrity issues when transporting the file.¶

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

If the URI method is used for specification of the content-schema, there is a risk that the config schema section in the referenced YANG instance data file may be altered maliciously or even as part of its normal handling. In this case, the content-schema might differ from the one expected. Protecting the integrity and stability of the referenced file should be ensured.¶

5. IANA Considerations

This document registers one URI and one YANG module.¶

Appendix B. Detailed Use Cases

This section is non-normative.¶

Authors' Addresses