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IETF RFC 9195
Last modified on Thursday, February 17th, 2022
 Permanent link to RFC 9195
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Internet Engineering Task Force (IETF) B. Lengyel
Request for Comments: 9195 Ericsson
Category: Standards Track B. Claise
ISSN: 2070-1721 Huawei
February 2022
A File Format for YANG Instance Data
 Abstract
There is a need to document data defined in YANG models at design
time, implementation time, or when a live 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 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/RFC 9195.
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
1.1. Terminology
1.2. Principles
1.3. Delivery of Instance Data
1.4. Data Life Cycle
2. Instance Data File Format
2.1. Specifying the Content Schema
2.1.1. Inline Method
2.1.2. Simplified-Inline Method
2.1.3. URI Method
2.2. Examples
2.2.1. Documentation of Server Capabilities
2.2.2. Preloading Default Configuration Data
2.2.3. Storing Diagnostics Data
3. YANG Instance Data Model
3.1. Tree Diagram
3.2. YANG Model
4. Security Considerations
5. IANA Considerations
5.1. URI Registration
5.2. YANG Module Name Registration
6. References
6.1. Normative References
6.2. Informative References
Appendix A. Backwards Compatibility
Appendix B. Detailed Use Cases
B.1. Use Case 1: Early Documentation of Server Capabilities
B.2. Use Case 2: Preloading Data
B.3. Use Case 3: Documenting Factory Default Settings
Acknowledgments
Authors' Addresses
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 [RFC 8342].
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.
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 [RFC 2119] [RFC 8174] 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.
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 [RFC 8342].
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 14)
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.
1.4. Data Life Cycle
A YANG instance data set is created at a specific point of time. If
the data changes afterwards, the instance data set will no longer
represent the current data unless it is updated. The current values
may be retrieved at runtime 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 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 [RFC 7950] for XML and
[RFC 7951] for JSON and MUST use UTF-8 character encoding. Content-
data MAY include:
* metadata, as defined by [RFC 7952].
* origin metadata, as specified in [RFC 8526] and [RFC 8527].
* 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 [RFC 5234]):
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, information about the data set itself, MUST be included.
Some metadata items are defined in the YANG module "ietf-yang-
instance-data", but other items MAY be used.
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 [RFC 6243];
however, as only concepts are re-used, users of instance data
sets do not need to support [RFC 6243].
2.1. Specifying the Content Schema
To properly understand and use an instance data set, the user needs
to know the content-schema. The content-schema can be specified
either in external documents or within the instance data set. In the
latter case, one of the following methods MUST 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; only the modules' name and revision-date
are used.
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).
Additional methods, e.g., a YANG-package-based solution may be added
later.
Note that 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 the "Preloading default
configuration data" use case, UC2 in Section 1, 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 another schema depends on many
factors, including the number of differences and the compatibility
between the original and the other schema when considering modules,
revisions, features, deviations, the scope of the instance data, etc.
2.1.1. Inline Method
The "inline-yang-library" anydata data node carries instance data
(conforming to "ietf-yang-library@2019-01-04") [RFC 8525] that
specifies the content-defining YANG modules, including revision,
supported features, deviations, and any additional relevant data. An
example of the inline method is provided in Section 2.2.1.
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. YANG modules that are only required to satisfy
import-only dependencies MAY be excluded from the leaf-list. If they
are excluded, then the consumer of the instance data set has to apply
the YANG language rules to resolve the imports. An example of the
simplified-inline method is provided in Section 2.2.2.
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, the 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
-- for example, in UC6, when the system creates a diagnostic file
every minute to document the state of the server.
An example of the URI method is provided in Section 2.2.3.
2.2. Examples
2.2.1. Documentation of Server Capabilities
The example file acme-router-modules@2022-01-20.xml reflects UC1 in
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 [RFC 8792].
========== 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>
Figure 1
2.2.2. Preloading Default Configuration Data
The example file read-only-acm-rules@2022-01-20.xml reflects UC2 in
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.
========== 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>
Figure 2
2.2.3. Storing Diagnostics Data
The example file acme-router-netconf-
diagnostics@2018-01-25T17_00_38Z.json reflects UC5 in Section 1. An
instance data set that contains statistics about the NETCONF server
is produced by the server every 15 minutes. As a new set is produced
periodically many times a day, a revision-date would be useless;
instead, a timestamp is included.
========== 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"
}
}
}
}
}
Figure 3
3. YANG Instance Data Model
3.1. Tree Diagram
The following tree diagram [RFC 8340] provides an overview of the 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>
3.2. YANG Model
This YANG module imports typedefs from [RFC 6991], [RFC 6243],
identities from [RFC 8342], and the "structure" extension from
[RFC 8791]. It also references [RFC 8525].
<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/RFC 9195); 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 [RFC 8407]
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.
5.1. URI Registration
This document registers the following URI in the "IETF XML Registry"
[RFC 3688]:
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 the following YANG module in the "YANG Module
Names" registry [RFC 6020]:
Name: ietf-yang-instance-data
Namespace: urn:ietf:params:xml:ns:yang:ietf-yang-instance-data
Prefix: yid
Reference: RFC 9195
6. References
6.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC 2119, March 1997,
<https://www.rfc-editor.org/info/RFC 2119>.
[RFC 5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC 5234, January 2008,
<https://www.rfc-editor.org/info/RFC 5234>.
[RFC 6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC 6020, October 2010,
<https://www.rfc-editor.org/info/RFC 6020>.
[RFC 6243] Bierman, A. and B. Lengyel, "With-defaults Capability for
NETCONF", RFC 6243, DOI 10.17487/RFC 6243, June 2011,
<https://www.rfc-editor.org/info/RFC 6243>.
[RFC 6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6991, DOI 10.17487/RFC 6991, July 2013,
<https://www.rfc-editor.org/info/RFC 6991>.
[RFC 7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC 7950, August 2016,
<https://www.rfc-editor.org/info/RFC 7950>.
[RFC 7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG",
RFC 7951, DOI 10.17487/RFC 7951, August 2016,
<https://www.rfc-editor.org/info/RFC 7951>.
[RFC 7952] Lhotka, L., "Defining and Using Metadata with YANG",
RFC 7952, DOI 10.17487/RFC 7952, August 2016,
<https://www.rfc-editor.org/info/RFC 7952>.
[RFC 8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC 8174,
May 2017, <https://www.rfc-editor.org/info/RFC 8174>.
[RFC 8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "Network Management Datastore Architecture
(NMDA)", RFC 8342, DOI 10.17487/RFC 8342, March 2018,
<https://www.rfc-editor.org/info/RFC 8342>.
[RFC 8525] Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K.,
and R. Wilton, "YANG Library", RFC 8525,
DOI 10.17487/RFC 8525, March 2019,
<https://www.rfc-editor.org/info/RFC 8525>.
[RFC 8526] 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/RFC 8526, March 2019,
<https://www.rfc-editor.org/info/RFC 8526>.
[RFC 8527] 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/RFC 8527, March 2019,
<https://www.rfc-editor.org/info/RFC 8527>.
[RFC 8791] Bierman, A., Björklund, M., and K. Watsen, "YANG Data
Structure Extensions", RFC 8791, DOI 10.17487/RFC 8791,
June 2020, <https://www.rfc-editor.org/info/RFC 8791>.
6.2. Informative References
[RFC 3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC 3688, January 2004,
<https://www.rfc-editor.org/info/RFC 3688>.
[RFC 8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
BCP 215, RFC 8340, DOI 10.17487/RFC 8340, March 2018,
<https://www.rfc-editor.org/info/RFC 8340>.
[RFC 8407] Bierman, A., "Guidelines for Authors and Reviewers of
Documents Containing YANG Data Models", BCP 216, RFC 8407,
DOI 10.17487/RFC 8407, October 2018,
<https://www.rfc-editor.org/info/RFC 8407>.
[RFC 8632] Vallin, S. and M. Bjorklund, "A YANG Data Model for Alarm
Management", RFC 8632, DOI 10.17487/RFC 8632, September
2019, <https://www.rfc-editor.org/info/RFC 8632>.
[RFC 8641] Clemm, A. and E. Voit, "Subscription to YANG Notifications
for Datastore Updates", RFC 8641, DOI 10.17487/RFC 8641,
September 2019, <https://www.rfc-editor.org/info/RFC 8641>.
[RFC 8792] Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
"Handling Long Lines in Content of Internet-Drafts and
RFCs", RFC 8792, DOI 10.17487/RFC 8792, June 2020,
<https://www.rfc-editor.org/info/RFC 8792>.
[RFC 8808] Wu, Q., Lengyel, B., and Y. Niu, "A YANG Data Model for
Factory Default Settings", RFC 8808, DOI 10.17487/RFC 8808,
August 2020, <https://www.rfc-editor.org/info/RFC 8808>.
Appendix A. Backwards Compatibility
The concept of "backwards compatibility" and what changes are
backwards compatible are not defined for instance data sets as they
are highly dependent on the specific use case and the content-schema.
In case of "instance data sets" that are the result of 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.
* 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.
* 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.
* 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 B. Detailed Use Cases
This section is non-normative.
B.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:
* data defined in "ietf-yang-library": YANG modules, submodules,
features, deviations, schema-mounts, and datastores supported
([RFC 8525]).
* alarms supported ([RFC 8632]).
* data nodes and subtrees that support or do not support on-change
notifications ([RFC 8641]).
* netconf-capabilities in ietf-netconf-monitoring.
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 Network
Management System (NMS) 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 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 homegrown 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 Operations,
Administration, and Maintenance (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 and
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.
B.2. Use Case 2: Preloading Data
There are parts of the configuration that must be fully configurable
by the operator. However, a simple default configuration often 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.
The device vendor may define a set of default groups (/nacm:nacm/
groups) and rules for these groups to access specific parts of the
common models (/nacm:nacm/rule-list/rule).
YANG instance data files can be used to document and/or preload the
default configuration.
B.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 to the default factory
configuration.
YANG instance data can be used to document the factory default
configuration. See [RFC 8808].
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 Working Group.
Authors' Addresses
Balazs Lengyel
Ericsson
Budapest
Magyar Tudosok korutja 11
1117
Hungary
Email: balazs.lengyel@ericsson.com
Benoit Claise
Huawei
Email: benoit.claise@huawei.com
RFC TOTAL SIZE: 45684 bytes
PUBLICATION DATE: Thursday, February 17th, 2022
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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