A File Format for YANG Instance DataEricssonMagyar Tudosok korutja 11BudapestHungary1117balazs.lengyel@ericsson.comHuaweibenoit.claise@huawei.com
OPS
Netmod
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
.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Provisions Relating to IETF Documents
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Table of Contents
. Introduction
. Terminology
. Principles
. Delivery of Instance Data
. Data Life Cycle
. Instance Data File Format
. Specifying the Content Schema
. Inline Method
. Simplified-Inline Method
. URI Method
. Examples
. Documentation of Server Capabilities
. Preloading Default Configuration Data
. Storing Diagnostics Data
. YANG Instance Data Model
. Tree Diagram
. YANG Model
. Security Considerations
. IANA Considerations
. URI Registration
. YANG Module Name Registration
. References
. Normative References
. Informative References
. Backwards Compatibility
. Detailed Use Cases
. Use Case 1: Early Documentation of Server Capabilities
. Use Case 2: Preloading Data
. Use Case 3: Documenting Factory Default Settings
Acknowledgments
Authors' Addresses
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 .
The YANG data model in this document conforms to the Network
Management Datastore Architecture (NMDA) defined in .
The following is a list of already-implemented and potential use cases.
Documentation of server capabilities
Preloading default configuration data
Documenting factory default settings
Storing the configuration of a device, e.g., for backup, archive, or
audit purposes
Storing diagnostics data
Allowing YANG instance data to potentially be carried within other inter-process communication (IPC) message formats
Default instance data used as part of a templating solution
Providing data examples in RFCs or internet drafts
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.
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
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 .PrinciplesThe following is a list of the basic principles of the instance data format:
Two standard formats shall be defined based on the XML and
JSON encodings.
Instance data shall reuse existing encoding rules for
YANG-defined data.
Metadata about the instance data set
() shall be defined.
A YANG instance data set shall be allowed to contain data
for multiple YANG modules.
Instance data shall be allowed to contain configuration data,
state data, or a mix of the two.
Partial data sets shall be allowed.
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.
It shall be possible to report the identity of the datastore with which the
instance data set is associated.
Delivery of Instance DataInstance 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.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.
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 for XML and
for JSON and MUST use UTF-8 character encoding.
Content-data MAY include:
metadata, as defined by .
origin metadata, as specified in
and .
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 ):
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 ;
however, as only concepts are re-used, users of instance data sets
do not need to support .
Specifying the Content SchemaTo 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 , 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.
Inline MethodThe "inline-yang-library" anydata data node carries instance data (conforming to
"ietf-yang-library@2019-01-04") 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 .
Simplified-Inline MethodThe 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 .
URI MethodThe "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 .ExamplesDocumentation of Server CapabilitiesThe example file acme-router-modules@2022-01-20.xml reflects UC1 in .
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 .
========== 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>
Preloading Default Configuration DataThe example file read-only-acm-rules@2022-01-20.xml reflects UC2 in .
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>
Storing Diagnostics DataThe example file acme-router-netconf-diagnostics@2018-01-25T17_00_38Z.json
reflects UC5 in .
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"
}
}
}
}
}
YANG Instance Data ModelTree Diagram
The following tree diagram
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>
YANG Model
This YANG module imports typedefs from ,
,
identities from , and
the "structure" extension from .
It also references .
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.";
}
}
}
Security ConsiderationsThe 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
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.
IANA ConsiderationsThis document registers one URI and one YANG module.URI RegistrationThis document registers the following URI in the
"IETF XML Registry":
ReferencesNormative ReferencesKey words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.Augmented BNF for Syntax Specifications: ABNFInternet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK]YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)YANG is a data modeling language used to model configuration and state data manipulated by the Network Configuration Protocol (NETCONF), NETCONF remote procedure calls, and NETCONF notifications. [STANDARDS-TRACK]With-defaults Capability for NETCONFThe Network Configuration Protocol (NETCONF) defines ways to read and edit configuration data from a NETCONF server. In some cases, part of this data may not be set by the NETCONF client, but rather a default value known to the server is used instead. In many situations the NETCONF client has a priori knowledge about default data, so the NETCONF server does not need to save it in a NETCONF configuration datastore or send it to the client in a retrieval operation reply. In other situations the NETCONF client will need this data from the server. Not all server implementations treat this default data the same way. This document defines a capability-based extension to the NETCONF protocol that allows the NETCONF client to identify how defaults are processed by the server, and also defines new mechanisms for client control of server processing of default data. [STANDARDS-TRACK]Common YANG Data TypesThis document introduces a collection of common data types to be used with the YANG data modeling language. This document obsoletes RFC 6021.The YANG 1.1 Data Modeling LanguageYANG is a data modeling language used to model configuration data, state data, Remote Procedure Calls, and notifications for network management protocols. This document describes the syntax and semantics of version 1.1 of the YANG language. YANG version 1.1 is a maintenance release of the YANG language, addressing ambiguities and defects in the original specification. There are a small number of backward incompatibilities from YANG version 1. This document also specifies the YANG mappings to the Network Configuration Protocol (NETCONF).JSON Encoding of Data Modeled with YANGThis document defines encoding rules for representing configuration data, state data, parameters of Remote Procedure Call (RPC) operations or actions, and notifications defined using YANG as JavaScript Object Notation (JSON) text.Defining and Using Metadata with YANGThis document defines a YANG extension that allows for defining metadata annotations in YANG modules. The document also specifies XML and JSON encoding of annotations and other rules for annotating instances of YANG data nodes.Ambiguity of Uppercase vs Lowercase in RFC 2119 Key WordsRFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.Network Management Datastore Architecture (NMDA)Datastores are a fundamental concept binding the data models written in the YANG data modeling language to network management protocols such as the Network Configuration Protocol (NETCONF) and RESTCONF. This document defines an architectural framework for datastores based on the experience gained with the initial simpler model, addressing requirements that were not well supported in the initial model. This document updates RFC 7950.YANG LibraryThis document describes a YANG library that provides information about the YANG modules, datastores, and datastore schemas used by a network management server. Simple caching mechanisms are provided to allow clients to minimize retrieval of this information. This version of the YANG library supports the Network Management Datastore Architecture (NMDA) by listing all datastores supported by a network management server and the schema that is used by each of these datastores.NETCONF Extensions to Support the Network Management Datastore ArchitectureThis document extends the Network Configuration Protocol (NETCONF) defined in RFC 6241 in order to support the Network Management Datastore Architecture (NMDA) defined in RFC 8342.This document updates RFCs 6241 and 7950. The update to RFC 6241 adds new <get-data> and <edit-data> operations and augments existing <lock>, <unlock>, and <validate> operations. The update to RFC 7950 requires the usage of the YANG library (described in RFC 8525) by NETCONF servers implementing the NMDA.RESTCONF Extensions to Support the Network Management Datastore ArchitectureThis document extends the RESTCONF protocol defined in RFC 8040 in order to support the Network Management Datastore Architecture (NMDA) defined in RFC 8342.This document updates RFC 8040 by introducing new datastore resources, adding a new query parameter, and requiring the usage of the YANG library (described in RFC 8525) by RESTCONF servers implementing the NMDA.YANG Data Structure ExtensionsThis document describes YANG mechanisms for defining abstract data structures with YANG.Informative ReferencesThe IETF XML RegistryThis document describes an IANA maintained registry for IETF standards which use Extensible Markup Language (XML) related items such as Namespaces, Document Type Declarations (DTDs), Schemas, and Resource Description Framework (RDF) Schemas.YANG Tree DiagramsThis document captures the current syntax used in YANG module tree diagrams. The purpose of this document is to provide a single location for this definition. This syntax may be updated from time to time based on the evolution of the YANG language.Guidelines for Authors and Reviewers of Documents Containing YANG Data ModelsThis memo provides guidelines for authors and reviewers of specifications containing YANG modules. Recommendations and procedures are defined, which are intended to increase interoperability and usability of Network Configuration Protocol (NETCONF) and RESTCONF protocol implementations that utilize YANG modules. This document obsoletes RFC 6087.A YANG Data Model for Alarm ManagementThis document defines a YANG module for alarm management. It includes functions for alarm-list management, alarm shelving, and notifications to inform management systems. There are also operations to manage the operator state of an alarm and administrative alarm procedures. The module carefully maps to relevant alarm standards.Subscription to YANG Notifications for Datastore UpdatesThis document describes a mechanism that allows subscriber applications to request a continuous and customized stream of updates from a YANG datastore. Providing such visibility into updates enables new capabilities based on the remote mirroring and monitoring of configuration and operational state.Handling Long Lines in Content of Internet-Drafts and RFCsThis document defines two strategies for handling long lines in width-bounded text content. One strategy, called the "single backslash" strategy, is based on the historical use of a single backslash ('\') character to indicate where line-folding has occurred, with the continuation occurring with the first character that is not a space character (' ') on the next line. The second strategy, called the "double backslash" strategy, extends the first strategy by adding a second backslash character to identify where the continuation begins and is thereby able to handle cases not supported by the first strategy. Both strategies use a self-describing header enabling automated reconstitution of the original content.A YANG Data Model for Factory Default SettingsThis document defines a YANG data model with the "factory-reset" RPC to allow clients to reset a server back to its factory default condition. It also defines an optional "factory-default" datastore to allow clients to read the factory default configuration for the device.The YANG data model in this document conforms to the Network Management Datastore Architecture (NMDA) defined in RFC 8342.Backwards CompatibilityThe 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.
Detailed Use CasesThis section is non-normative.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 ().
alarms supported ().
data nodes and subtrees that support or do not support on-change
notifications ().
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.
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.
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 .
AcknowledgmentsFor their valuable comments, discussions, and feedback, we wish to
acknowledge , , , , , , , , and other members of the Netmod Working Group.Authors' AddressesEricssonMagyar Tudosok korutja 11BudapestHungary1117balazs.lengyel@ericsson.comHuaweibenoit.claise@huawei.com