YANG Instance Data File Format Ericsson balazs.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.
There is a need to document data defined in YANG models when a live server is unavailable.
Data is often needed at design, implementation time or
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 capabilitiesPreloading default configuration dataDocumenting Factory Default SettingsStoring the configuration of a device, e.g., for backup, archive or
audit purposesStoring diagnostics dataAllowing YANG instance data to potentially be carried within other IPC message formatsDefault instance data used as part of a templating solutionProviding data examples in RFCs or internet draftsIn 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.
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 .The 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.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.
A YANG instance data set is created at a specific
point of time. If the data changes afterwards, this is not
represented in the instance data set anymore. The current values may be
retrieved at run-time via NETCONF/RESTCONF or
received e.g., in YANG-Push notifications.
Whether the instance data changes and if so, when and how,
should be described either in the instance data set's description
statement or in some other implementation specific manner.
A YANG instance data file MUST contain a single instance data set and no
additional data.
The format of the instance data set is defined by the
"ietf-yang-instance-data" YANG module.
It is made up of a header part and content-data.
The header part carries metadata for the instance data set.
The content-data, defined as an anydata data node, carries
the instance data that the user wants to document/provide.
The syntax and semantics of content-data is defined by the content-schema.
Two formats are specified based on the XML and JSON YANG encodings.
Later, as other YANG encodings (e.g., CBOR) are defined, further
instance data formats may be specified.
The content-data part MUST conform to the content-schema, while allowing for the
exceptions listed below. The content-data part SHALL follow the
encoding rules defined in 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" constrains MAY be violated.
The name of the instance data file SHOULD be of the form:
If the leaf "name" is present in the instance data header,
its value SHOULD be used for the "instance-data-set-name".
If the "revision-date" is present in 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 in the
instance data header, the revision date in the file name MUST be
set to the latest revision date inside the instance data set.
If 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 both in the filename and in the
instance data header, the timestamp in the file name SHOULD be
set to the timestamp inside the instance data set; any colons,
if present, shall be replaced by underscores.
Metadata, information about the data set itself
SHOULD be included in the instance data set. Some metadata items are
defined in the YANG module "ietf-yang-instance-data", but other items MAY
be used.
Metadata MUST include:
Version of the YANG Instance Data format
Metadata SHOULD include:
Name of the data setContent schema specification (i.e., the "content-schema” node)Description of the instance data set. The description SHOULD
contain information whether and how the data can change during
the lifetime of the server
An indication 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 RFC 6243.
To properly understand and use an instance data set, the user needs to
know the content-schema. One of the following methods SHOULD be used:
Simplified-Inline method: Include the needed information as part of
the instance data set; short specification.Inline method: Include the needed information as part of the
instance data set.URI method: Include a URI that references another YANG instance
data file. This instance data file will use the same content-schema
as the referenced YANG instance data file.
(if you don't want to repeat the info again and again)External Method: Do not include the "content-schema" node; the
user needs to obtain the information through external documents.
Additional methods e.g., a YANG-package based solution may be added later.
Note, the specified content-schema only indicates the set of
modules that were used to define this YANG instance data set.
Sometimes instance data may be used for a server supporting a
different YANG module set (e.g., for 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 a different other schema
depends on many factors including the amount of differences and the
compatibility between the original and the
other schema, considering modules, revisions, features,
deviations, the scope of the instance data, etc.
The 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 relevant additional data.
An example of the "inline" method is provided in .
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 .
The "same-schema-as-file" leaf SHALL contain a URI that references another YANG
instance data file. The current instance data file will use the same
content schema as the referenced file.
The referenced instance data file MAY have no content-data if it is
used solely for specifying the content-schema.
If a referenced instance data file is unavailable, content-schema
is unknown.
The URI method is advantageous when the user wants to avoid the
overhead of specifying the content-schema in each instance data
file: E.g., In UC6, when the system creates a diagnostic file
every minute to document the state of the server.
An example of the "URI" method is provided in .The example file acme-router-modules@2021-07-07.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 .acme-router-modulesietf-yang-library2019-01-04ietf-netconf-monitoring2010-10-041956-10-23Initial versionDefines the minimal set of modules that any \
acme-router will contain.info@acme.comietf-yang-library2019-01-04\
urn:ietf:params:xml:ns:yang:ietf-yang-library\
implementietf-system2014-08-06urn:ietf:params:xml:ns:yang:ietf-systemsys:authenticationsys:local-usersacme-system-ext2018-08-06implementietf-netconf-monitoring2010-10-04\
urn:ietf:params:xml:ns:yang:ietf-netconf-monitoring\
implementietf-yang-types2013-07-15urn:ietf:params:xml:ns:yang:ietf-yang-types\
importacme-system-ext2018-08-06urn:rdns:acme.com:oammodel:acme-system-ext\
implement\
urn:ietf:params:netconf:capability:validate:1.1\
]]>The example file read-only-acm-rules@2021-07-07.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.read-only-acm-rulesietf-netconf-acm@2018-02-141776-07-04Initial versionAccess control rules for a read-only role.truedenydenyread-only-roleread-only-groupread-all*readpermit
]]>The example file acme-router-netconf-diagnostics@2018-01-25T17_00_38Z.json
reflects UC5 in .
An instance data set is produced by the server every 15 minutes that contains
statistics about the NETCONF server. As a new set is produced periodically many times a day a revision-date
would be useless; instead a timestamp is included.
The following tree diagram
provides an overview of the data model.
| +--:(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?
]]>
This YANG module imports typedefs from ,
identities from and
the "structure" extension from .
It also references and .
file "ietf-yang-instance-data@2021-07-07.yang"
// RFC Ed.: replace the date above if the module gets changed in
//anyway during reviews or RFC editor process and remove this note
module ietf-yang-instance-data {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-yang-instance-data";
prefix yid;
import ietf-yang-structure-ext {
prefix sx;
reference
"YANG Data Structure Extensions:
draft-ietf-netmod-yang-data-ext-05";
}
import ietf-datastores {
prefix ds;
reference
"RFC 8342: Network Management Datastore Architecture (NMDA)";
}
import ietf-inet-types {
prefix inet;
reference
"RFC 6991: Common YANG Data Types";
}
import ietf-yang-types {
prefix yang;
reference
"RFC 6991: Common YANG Data Types";
}
organization
"IETF NETMOD Working Group";
contact
"WG Web:
WG List:
Author: Balazs Lengyel
Author: Benoit Claise
";
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) 2021 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.";
// RFC Ed.: replace XXXX with RFC number and remove this note
revision 2021-07-07 {
// RFC Ed.: replace the date above if the module gets changed in
// anyway during reviews or RFC editor process and remove
//this note
description
"Initial revision.";
reference
"RFC XXXX: YANG Instance Data Format";
// RFC Ed.: replace XXXX with RFC number and remove this note
}
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 provide meta-data
about the instance data; the instance data itself is
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 3
of RFC XXXX.";
// RFC Ed.: replace XXXX with RFC number and remove this note
}
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 "2021-07-07";
// RFC Ed.: replace the date above if the module gets changed
// in anyway during reviews or RFC editor process and remove
// this note
description
"The 'revision' of the 'ietf-yang-instance-data' module
used to encode this 'instance-data-set'.";
}
leaf includes-defaults {
type enumeration {
enum report-all {
value 1;
description
"All data nodes SHOULD be included independent of
any default values.";
}
enum trim {
value 2;
description
"Data nodes that have a default defined and where
the actual value is the default value SHOULD
NOT be included.";
}
enum explicit {
value 3;
description
"Data nodes that have a default defined and where
the actual value is the default value SHOULD NOT be
included. However, if the actual value was set by
a NETCONF client or other management application
by the way of an explicit management operation the
data node SHOULD be included.";
}
}
default trim;
description
"As instance-data-sets MAY contain incomplete data sets,
thus any data node MAY be absent.
Providing the instance-data-set intends to contain a
full data set, this leaf specifies whether the data set
includes data nodes that have a default defined and
where the actual value is the same as the default value.
Data nodes that have no default values should always
be included.
Data nodes that have a default value, but the actual
value is not equal to the schema defined default
should always be included.";
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 or the datastore into which the data
may be loaded or the datastore which is being documented.
If a single specific datastore cannot be specified, the
leaf MUST be absent.
If this leaf is absent, then the datastore to which the
instance data belongs is 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 case 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 case of instance data sets that are read from or
produced by a server or otherwise subject to frequent
updates or changes, 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.";
}
}
}
]]>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 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.Instance data files may contain sensitive data.
The header part is not security sensitive with one possible exception.
If the URI method is used for specification of the content schema and
the URI includes a username and/or a password, the instance data file
needs to be handled in a secure way as mentioned below.
The security sensitivity of the instance data in the content
part is completely dependent on the content schema.
Depending on the nature of the instance data, instance data
files MAY need to be handled securely. The same kind of
handling should be applied, that would be needed for the result
of a read operation returning the same data.
Instance data files should be protected against modification or
unauthorized access using normal file handling mechanisms.
Care should be taken, when copying the original files or
providing file access for additional users, not to reveal
information unintentionally.
This document registers one URI and one YANG module.This document registers one URI in the
IETF XML registry . Following the format in RFC 3688, the
following registration is requested to be made:
URI: urn:ietf:params:xml:ns:yang:ietf-yang-instance-data
Registrant Contact: The IESG.
XML: N/A, the requested URI is an XML namespace.
This document registers one YANG module in the YANG Module Names
registry . Following the format in [RFC6020],
the following registrations are requested:
name: ietf-yang-instance-data
namespace: urn:ietf:params:xml:ns:yang:ietf-yang-instance-data
prefix: yid
reference: RFC XXXX
// RFC Ed.: replace XXXX with RFC number and remove this note
For their valuable comments, discussions, and feedback, we wish to
acknowledge Andy Bierman, Juergen Schoenwaelder, Rob Wilton, Joe Clarke, Kent Watsen
Martin Bjorklund, Ladislav Lhotka, Qin Wu and other members of the Netmod WG.RFC Ed.: Remove section "Changes between revisions"v15 - v16
Editorial changesv14 - v15
Removed reference to revision-labelFor the inline method made the usage of
ietf-yang-library@2019-01-04 mandatory.
Simplified the case "inline" in the YANG module.Removed the "inline-module" leaf as it does not carry
useful information anymore.Removed YANG featurev13 - v14
Added leaf includes-defaultsMany small changes based on AD reviewv09 - v13
Editorial updatesv08 - v09
Removed reference to similar to get replyIntroduced artwork folding in the examplesv07 - v08
Moved compatibility into appendixRenamed yid-version to format-version.
Changed format to date of the YANG moduleMade support of ietf-yang-library mandatory if
inline-content-schema is supportedMany small changes based on WGLCv06 - v07
Updated terminology, use-casesMany small changes based on WGLCv05 - v06
Modified module name format, removed .yin or .yang extensionRemoved pattern for module and inline-module. The
usage of revision-label should also be allowed.
v04 - v05
Updated according to YANG-Doctor reviewUpdated security considerationsAdded a wrapping container for the schema, and renamed the data
nodes in the inline and uri cases.
Allowed .yin for simplified-inline schema naming.
Made date optional if it is unavailable in the YANG module.Added a mandatory yid-version to the header metadata to allow
later updates of the module.v03 - v04
removed entity-tag and last-modified timestampAdded simplified-inline method of content-schema specificationv02 - v03
target renamed to "content-schema" and "content defining YANG
module(s)"Made name of instance data set optionalUpdated according to draft-ietf-netmod-yang-data-ext-03Clarified that entity-tag and last-modified timestamp are encoded
as metadata. While they contain useful data, the HTTP-header based
encoding from Restconf is not suitable.v01 - v02
Removed design time from terminologyDefined the format of the content-data part by referencing various
RFCs and drafts instead of the result of the get-data and get operations.Changed target-ptr to a choiceInline target-ptr may include augmenting modules and alternatives to ietf-yang-libraryMoved list of target modules into a separate <target-modules> element.Added backwards compatibility considerationsv00 - v01
Added the target-ptr metadata with 3 methodsAdded timestamp metadataRemoved usage of dedicated .yid file extensionAdded list of use casesAdded list of principlesUpdated examplesMoved detailed use case descriptions to appendixThe concept of backwards compatibility and what changes are backwards
compatible are not defined for "instance data sets" as it is highly
dependent on the specific use case and the content-schema.
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.This section is non-normative. 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 NMS
(network management system) is also released with it. The NMS depends on the capabilities of the server.
During NMS implementation, information about server capabilities is needed.
If the information is unavailable early in some offline
document, but only as instance data from the live network node, the NMS implementation will be
delayed, because it has to wait until the network node is ready. Also assuming
that all NMS implementors will have a correctly configured network nodes
from which data can be retrieved, is a very expensive proposition. (An NMS may handle dozens
of node types.)
Network operators often build their own home-grown NMS systems that
need to be integrated with a vendor's network node. The operator
needs to know the network node's server capabilities in order to do
this. Moreover, the network operator's decision to buy a vendor's
product may even be influenced by the network node's OAM feature set
documented as the server's capabilities.
Beside NMS implementors, system integrators and many others also need the same
information early. Examples could be model driven testing, generating documentation, etc.
Most server-capabilities are relatively stable and change only during
upgrade or due to licensing or the addition or removal of hardware. They are
usually defined by a vendor at design time, before the product is released.
It is feasible and advantageous to define/document them early
e.g., in a YANG instance data File.
It is anticipated that a separate IETF document will define in
detail how and which set of server capabilities should be documented.
There are parts of the configuration that must be fully configurable
by the operator. However, often a simple default configuration will
be sufficient.
One example is access control groups/roles and related rules.
While a sophisticated operator may define dozens of different groups,
often a basic (read-only operator, read-write system administrator,
security-administrator) triplet will be enough.
Vendors will often provide such default configuration data to make
device configuration easier for an operator.
Defining access control data is a complex task. To help, the device
vendor predefines a set of default groups (/nacm:nacm/groups) and rules
for these groups to access specific parts of common models (/nacm:nacm/rule-list/rule).
YANG instance data files are used to document and/or preload the
default configuration.
Nearly every server has a factory default configuration. If the
system is really badly misconfigured or if the current configuration
is to be abandoned, the system can be reset the default factory
configuration.
The operator currently needs to know what the
default configuration actually contains.
YANG instance data can be used to document the factory default
configuration. See .