| Netmod | B. Lengyel |
| Internet-Draft | Ericsson |
| Intended status: Standards Track | B. Claise |
| Expires: October 16, 2020 | Cisco Systems, Inc. |
| April 14, 2020 |
YANG Instance Data File Format
draft-ietf-netmod-yang-instance-file-format-12
There is a need to document data defined in YANG models when a live server is unavailable. Data is often needed at design or implementation time or needed when a live running server is unavailable. This document specifies a standard file format for YANG instance data, which follows the syntax and semantics of existing YANG models, and annotates it with metadata.
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Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 16, 2020.
Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
There is a need to document data defined in YANG models when a live server is unavailable. Data is often needed at design or implementation time or needed when a live running server is unavailable. To facilitate this offline delivery of data, this document specifies a standard format for YANG instance data sets and YANG instance data files. The format of the instance data set is defined by the "ietf-yang-instance-data" YANG module, see Section 3. The YANG data model in this document conforms to the Network Management Datastore Architecture (NMDA) defined in [RFC8342]
The following is a list of already implemented and potential use cases.
In Appendix C describes the first three use cases in detail.
There are many and varied use cases where YANG instance data could be used. This document does not limit future uses of instance data sets, so specifying how and when to use YANG instance data is out of scope for this document. It is anticipated that other documents will define specific use cases. Use cases are listed only as examples.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
Instance Data: A collection of instantiated data nodes.
Instance Data Set: A named set of data items annotated with metadata that can be used as instance data in a YANG data tree.
Instance Data File: A file containing an instance data set formatted according to the rules described in this document.
Content-schema: A set of YANG modules with their revision, supported features, and deviations for which the instance data set contains instance data.
Content defining YANG module: an individual YANG module that is part of the content-schema.
The term "server" is used as defined in [RFC8342].
The following is a list of the basic principles of the instance data format:
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 [RFC7950] for XML and [RFC7951] for JSON and MUST use UTF-8 character encoding. Content-data MAY include:
An instance data set MAY contain data for any number of YANG modules; if needed it MAY carry the complete configuration and state data for a server. Default values SHOULD NOT be included.
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.
instance-data-set-name ['@' ( revision-date / timestamp ) ]
( '.xml' / '.json' )
E.g., acme-router-modules@2018-01-25.xml
E.g., acme-router-modules@2018-01-25T15_06_34_3+01_00.json
The name of the instance data file SHOULD be of the form:
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:
Metadata SHOULD include:
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:
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 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 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.
One or more inline-module elements define YANG module(s) used to specify the content defining YANG modules. [I-D.ietf-netmod-yang-module-versioning]) as alternative to the revision date). An example of the "inline" method is provided in Figure 2.
The anydata inline-schema carries instance data (conforming to the inline-modules) that actually specifies the content defining YANG modules including revision, supported features, deviations and any relevant additional data (e.g., revision labels, described by
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. An example of the "simplified-inline" method is provided in Figure 3.
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 Figure 4.
The example 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 [I-D.ietf-netmod-artwork-folding].
========== NOTE: '\' line wrapping per BCP XXX (RFC XXXX) ===========
<?xml version="1.0" encoding="UTF-8"?>
<instance-data-set xmlns=\
"urn:ietf:params:xml:ns:yang:ietf-yang-instance-data">
<name>acme-router-modules</name>
<content-schema>
<inline-module>ietf-yang-library@2016-06-21</inline-module>
<inline-schema>
<modules-state \
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
<module>
<name>ietf-yang-library</name>
<revision>2016-06-21</revision>
</module>
<module>
<name>ietf-netconf-monitoring</name>
<revision>2010-10-04</revision>
</module>
</modules-state>
</inline-schema>
</content-schema>
<revision>
<date>1956-10-23</date>
<description>Initial version</description>
</revision>
<description>Defines the minimal set of modules that any \
acme-router will contain.</description>
<contact>info@acme.com</contact>
<content-data>
<modules-state \
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
<module>
<name>ietf-yang-library</name>
<revision>2016-06-21</revision>
<namespace>\
urn:ietf:params:xml:ns:yang:ietf-yang-library\
</namespace>
<conformance-type>implement</conformance-type>
</module>
<module>
<name>ietf-system</name>
<revision>2014-08-06</revision>
<namespace>urn:ietf:params:xml:ns:yang:ietf-system</namespace>
<feature>sys:authentication</feature>
<feature>sys:local-users</feature>
<deviation>
<name>acme-system-ext</name>
<revision>2018-08-06</revision>
</deviation>
<conformance-type>implement</conformance-type>
</module>
<module>
<name>ietf-netconf-monitoring</name>
<revision>2010-10-04</revision>
<namespace>\
urn:ietf:params:xml:ns:yang:ietf-netconf-monitoring\
</namespace>
<conformance-type>implement</conformance-type>
</module>
<module>
<name>ietf-yang-types</name>
<revision>2013-07-15</revision>
<namespace>urn:ietf:params:xml:ns:yang:ietf-yang-types\
</namespace>
<conformance-type>import</conformance-type>
</module>
<module>
<name>acme-system-ext</name>
<revision>2018-08-06</revision>
<namespace>urn:rdns:acme.com:oammodel:acme-system-ext\
</namespace>
<conformance-type>implement</conformance-type>
</module>
</modules-state>
<netconf-state \
xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-monitoring">
<capabilities>
<capability>\
urn:ietf:params:netconf:capability:validate:1.1\
</capability>
</capabilities>
</netconf-state>
</content-data>
</instance-data-set>
Figure 2
The example 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.
<?xml version="1.0" encoding="UTF-8"?>
<instance-data-set
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-instance-data">
<name>read-only-acm-rules</name>
<content-schema>
<module>ietf-netconf-acm@2018-02-14</module>
</content-schema>
<revision>
<date>1776-07-04</date>
<description>Initial version</description>
</revision>
<description>Access control rules for a read-only role.</description>
<content-data>
<nacm xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
<enable-nacm>true</enable-nacm>
<read-default>deny</read-default>
<exec-default>deny</exec-default>
<rule-list>
<name>read-only-role</name>
<group>read-only-group</group>
<rule>
<name>read-all</name>
<module-name>*</module-name>
<access-operation>read</access-operation>
<action>permit</action>
</rule>
</rule-list>
</nacm>
</content-data>
</instance-data-set>
Figure 3
The example reflects UC5 in Section 1. An instance data set is produced by the server every 15 minutes that contains statistics about the NETCONF server. As a new set is produced periodically many times a day a revision-date would be useless; instead a timestamp is included.
{
"ietf-yang-instance-data:instance-data-set": {
"name": "acme-router-netconf-diagnostics",
"content-schema": {
"same-schema-as-file": "file:///acme-diagnostics-schema.json"
},
"timestamp": "2018-01-25T17:00:38Z",
"description": ["NETCONF statistics"],
"content-data": {
"ietf-netconf-monitoring:netconf-state": {
"statistics": {
"netconf-start-time ": "2018-12-05T17:45:00Z",
"in-bad-hellos ": "32",
"in-sessions ": "397",
"dropped-sessions ": "87",
"in-rpcs ": "8711",
"in-bad-rpcs ": "408",
"out-rpc-errors ": "408",
"out-notifications": "39007"
}
}
}
}
}
Figure 4
The following tree diagram [RFC8340] provides an overview of the data model.
module: ietf-yang-instance-data
structure instance-data-set:
+-- name? string
+-- format-version? string
+-- content-schema
| +-- (content-schema-spec)?
| +--:(simplified-inline)
| | +-- module* string
| +--:(inline) {inline-content-schema}?
| | +-- inline-module* string
| | +-- inline-schema <anydata>
| +--:(uri)
| +-- same-schema-as-file? inet:uri
+-- description* string
+-- contact? string
+-- organization? string
+-- datastore? ds:datastore-ref
+-- revision* [date]
| +-- date string
| +-- description? string
+-- timestamp? yang:date-and-time
+-- content-data? <anydata>
This YANG module imports typedefs from [RFC6991], identities from [RFC8342] and the "structure" extension from [I-D.ietf-netmod-yang-data-ext]. It also references [RFC8525].
<CODE BEGINS> file "ietf-yang-instance-data@2020-04-02.yang"
module ietf-yang-instance-data {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-yang-instance-data";
prefix yid;
import ietf-yang-structure-ext {
prefix sx;
reference
"YANG Data Structure Extensions:
draft-ietf-netmod-yang-data-ext-05";
}
import ietf-datastores {
prefix ds;
reference
"RFC 8342: Network Management Datastore Architecture (NMDA)";
}
import ietf-inet-types {
prefix inet;
reference
"RFC 6991: Common YANG Data Types";
}
import ietf-yang-types {
prefix yang;
reference
"RFC 6991: Common YANG Data Types";
}
organization
"IETF NETMOD Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/netmodf/>
WG List: <mailto:netmod@ietf.org>
Author: Balazs Lengyel
<mailto:balazs.lengyel@ericsson.com>";
description
"The module defines the structure and content of YANG
instance data sets.
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
are to be interpreted as described in BCP 14 (RFC 2119)
(RFC 8174) when, and only when, they appear in all
capitals, as shown here.
Copyright (c) 2020 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.";
revision 2020-04-02 {
description
"Initial revision.";
reference
"RFC XXXX: YANG Instance Data Format";
}
feature inline-content-schema {
description
"This feature indicates that inline content-schema
option is supported. Support for this feature might
be documented only via out-of-band documentation.";
}
typedef module-with-revision-date {
type string {
pattern '[a-zA-Z_][a-zA-Z0-9\-_.]*' +
'(@\d{4}-(1[0-2]|0[1-9])-(0[1-9]|[1|2][0-9]|3[0-1]))?';
pattern '.|..|[^xX].*|.[^mM].*|..[^lL].*';
}
description
"A type definining a module name and an optional revision
date, e.g. ietf-yang-library@2016-06-21";
}
sx:structure "instance-data-set" {
description
"A data structure to define a format for YANG instance
data. 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.";
}
leaf format-version {
type string {
pattern '\d{4}-(1[0-2]|0[1-9])-(0[1-9]|[1|2][0-9]|3[0-1])';
}
default "2020-04-02";
description
"The 'revision' of the 'ietf-yang-instance-data' module
used to encode this 'instance-data-set'.";
}
container content-schema {
description
"The content schema used to create the instance data set.
If not present the user needs to obtain the information
through external documents.";
choice content-schema-spec {
description
"Specification of the content-schema.";
case simplified-inline {
leaf-list module {
min-elements 1;
type module-with-revision-date;
description
"The list of content defining YANG modules.
The value SHALL start with the module name.
If the module contains a revision statement the
revision date SHALL be included in the leaf-list
entry. If other methods (e.g., revision-label) are
defined to identify individual module revisions
those MAY be used instead of using a revision date.
E.g., ietf-yang-library@2016-06-21
Usage of this leaf-list implies the modules are
used without any deviations and with all features
supported. Multiple revisions of the same module
MUST NOT be specified.";
}
}
case inline {
if-feature "inline-content-schema";
leaf-list inline-module {
type module-with-revision-date;
min-elements 1;
description
"Indicates that content defining YANG modules
are specified inline.
The value SHALL start with the module name.
If the module contains a revision statement the
revision date SHALL be included in the leaf-list
entry. If other methods (e.g., revision-label) are
defined to identify individual module revisions
those MAY be used instead of using a revision date.
E.g., ietf-yang-library@2016-06-21
The first item is either ietf-yang-library or some
other YANG module that contains a list of YANG modules
with their name, revision-date, supported-features,
and deviations. The usage of revision '2019-01-04'
of the 'ietf-yang-library' module MUST be supported.
Using other modules, module versions MAY also be
supported.
Some versions of ietf-yang-library MAY contain
different module-sets for different datastores. In
this case the instance data set MUST contain the
'datastore' leaf and instance data for the
ietf-yang-library MUST also contain information
specifying the module-set for the relevant datastore.
Subsequent items MAY specify YANG modules augmenting
the first module with useful data
(e.g., revision label).";
reference
"RFC 8525: YANG Library";
}
anydata inline-schema {
mandatory true;
description
"Instance data corresponding to the YANG modules
specified in the inline-module nodes defining the set
of content defining YANG modules for this
instance-data-set.";
}
}
case uri {
leaf same-schema-as-file {
type inet:uri;
description
"A reference to another YANG instance data file.
This instance data file uses the same
content schema as the referenced file.";
}
}
}
}
leaf-list description {
type string;
description
"Description of the instance data set.";
}
leaf contact {
type string;
description
"Contact information for the person or
organization to whom queries concerning this
instance data set should be sent.";
}
leaf organization {
type string;
description
"Organization responsible for the instance
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 one SHOULD be added
in front of the revisions sequence so that all
revisions are in reverse chronological order.
Instance data sets that are read from
or produced by a server or otherwise
subject to frequent updates or changes: revision
SHOULD NOT be present";
leaf date {
type string {
pattern '\d{4}-(1[0-2]|0[1-9])-(0[1-9]|[1|2][0-9]|3[0-1])';
}
description
"Specifies the date the instance data set
was last modified. Formatted as YYYY-MM-DD";
}
leaf description {
type string;
description
"Description of this revision of the instance data set.";
}
}
leaf timestamp {
type yang:date-and-time;
description
"The date and time when the instance data set
was last modified.
Instance data sets that are read from or produced
by a server or otherwise subject to frequent
updates or changes: timestamp SHOULD be present";
}
anydata content-data {
description
"Contains the real instance data.
The data MUST conform to the relevant YANG modules specified
either in the content-schema or in some other
implementation specific manner.";
}
}
}
<CODE ENDS>
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 the security considerations template for YANG models in section 3.7.1 in [RFC8407] is not followed. The instance data is designed to be accessed as a stored file or over any file access method or protocol.
The document does not specify any method to influence the behavior of a server.
Instance data files may contain sensitive data.
The header part is not security sensitive.
The security sensitivity of the instance data in the content part is completely dependent on the content schema. Depending on the nature of the instance data, instance data files MAY need to be handled in a secure way. The same kind of handling should be applied, that would be needed for the result of a read operation returning the same data.
Instance data files should be protected against modification or unauthorized access using normal file handling mechanisms. Care should be taken, when copying the original files or providing file access for additional users, not to reveal information unintentionally.
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 [RFC6020].
name: ietf-yang-instance-data
namespace: urn:ietf:params:xml:ns:yang:ietf-yang-instance-data
prefix: yid
reference: RFC XXXX
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.
| [I-D.ietf-netmod-artwork-folding] | Watsen, K., Auerswald, E., Farrel, A. and Q. WU, "Handling Long Lines in Inclusions in Internet-Drafts and RFCs", Internet-Draft draft-ietf-netmod-artwork-folding-12, January 2020. |
| [I-D.ietf-netmod-factory-default] | WU, Q., Lengyel, B. and Y. Niu, "A YANG Data Model for Factory Default Settings", Internet-Draft draft-ietf-netmod-factory-default-14, February 2020. |
| [I-D.ietf-netmod-yang-module-versioning] | Claise, B., Clarke, J., Rahman, R., Wilton, R., Lengyel, B., Sterne, J. and K. D'Souza, "Updated YANG Module Revision Handling", Internet-Draft draft-ietf-netmod-yang-module-versioning-00, March 2020. |
| [RFC3688] | Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004. |
| [RFC6020] | Bjorklund, M., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010. |
| [RFC8340] | Bjorklund, M. and L. Berger, "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018. |
| [RFC8407] | Bierman, A., "Guidelines for Authors and Reviewers of Documents Containing YANG Data Models", BCP 216, RFC 8407, DOI 10.17487/RFC8407, October 2018. |
| [RFC8632] | Vallin, S. and M. Bjorklund, "A YANG Data Model for Alarm Management", RFC 8632, DOI 10.17487/RFC8632, September 2019. |
| [RFC8641] | Clemm, A. and E. Voit, "Subscription to YANG Notifications for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641, September 2019. |
Note to RFC Editor (To be removed by RFC Editor)
v09 - v12
v08 - v09
v07 - v08
v06 - v07
v05 - v06
v04 - v05
v03 - v04
v02 - v03
v01 - v02
v00 - v01
The concept of backwards compatibility and what changes are backwards compatible are not defined for instance data sets as it is highly dependent on the specific use case and the content-schema.
For "instance data 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.
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:
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.
In NETCONF, the <delete-config> operation can already be used to reset the startup datastore. There are ongoing efforts to introduce a new, more generic factory-reset operation for the same purpose [I-D.ietf-netmod-factory-default]
The operator currently has no way to know what the default configuration actually contains. YANG instance data can also be used to document the factory default configuration.