RFC 9195
A File Format for YANG Instance Data
RFC 9195: A File Format for YANG Instance Data 💖
okay bestie, the title block tea ☕: this is RFC 9195, A File Format for YANG Instance Data, from the Internet Engineering Task Force (IETF). It's by B. Lengyel (Ericsson) and B. Claise (Huawei), it's on the Standards Track 🔥, the ISSN is 2070-1721, and it came out in February 2022. The title block doesn't list anything it obsoletes or updates 🫶.
Abstract ✨
so the problem is that we need to document YANG-defined data at design time, at implementation time, or when a live server is just not around 😭. This doc gives us a standard file format for YANG instance data. It follows the syntax and semantics of existing YANG models and then adds metadata on top 🎀.
Status of This Memo 📜
This is an Internet Standards Track document.
It's a product of the IETF 🌈 and represents the consensus of the IETF community. It got public review and was approved for publication by the Internet Engineering Steering Group (IESG). If you want more on Internet Standards, check Section 2 of RFC 7841. For the current status, any errata, and how to give feedback, go to https://www.rfc-editor.org/info/rfc9195.
Copyright Notice ©
Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved. 💜
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) as in effect on the date of publication. Please read those carefully, because they spell out your rights and restrictions for this document 📖. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions, and they come without warranty as described in the Revised BSD License 💀.
Table of Contents 🗂️
1. Introduction
1.1. Terminology
1.2. Principles
1.3. Delivery of Instance Data
1.4. Data Life Cycle
2. Instance Data File Format
2.1. Specifying the Content Schema
2.1.1. Inline Method
2.1.2. Simplified-Inline Method
2.1.3. URI Method
2.2. Examples
2.2.1. Documentation of Server Capabilities
2.2.2. Preloading Default Configuration Data
2.2.3. Storing Diagnostics Data
3. YANG Instance Data Model
3.1. Tree Diagram
3.2. YANG Model
4. Security Considerations
5. IANA Considerations
5.1. URI Registration
5.2. YANG Module Name Registration
6. References
6.1. Normative References
6.2. Informative References
Appendix A. Backwards Compatibility
Appendix B. Detailed Use Cases
B.1. Use Case 1: Early Documentation of Server Capabilities
B.2. Use Case 2: Preloading Data
B.3. Use Case 3: Documenting Factory Default Settings
Acknowledgments
Authors' Addresses1. Introduction 🌸
there's a need to document YANG-defined data when a live server is unavailable 😩. Data is often needed at design time, at implementation time, or even later on when a live running server isn't around. So to make this offline delivery work, 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].
here's the list of already-implemented and potential use cases 🍓:
- UC1 Documentation of server capabilities
- UC2 Preloading default configuration data
- UC3 Documenting factory default settings
- UC4 Storing the configuration of a device, e.g., for backup, archive, or audit purposes
- UC5 Storing diagnostics data
- UC6 Allowing YANG instance data to potentially be carried within other inter-process communication (IPC) message formats
- UC7 Default instance data used as part of a templating solution
- UC8 Providing data examples in RFCs or internet drafts
Appendix B describes the first three use cases in detail 🧚.
there are many and varied use cases where YANG instance data could be used 🌈. This document doesn't limit future uses of instance data sets, so specifying how and when to use YANG instance data is out of scope here. Other documents will probably define specific use cases, and the ones listed are only examples.
1.1. Terminology 💅
the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. (so they only count when they're in all caps, just like I wrote them 💖)
here are the terms you need:
- 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.
and the term "server" is used as defined in [RFC8342] ✨.
1.2. Principles 👑
here's the basic principles of the instance data format, no cap 🔥:
- P1 Two standard formats shall be defined based on the XML and JSON encodings.
- P2 Instance data shall reuse existing encoding rules for YANG-defined data.
- P3 Metadata about the instance data set (Section 2, Paragraph 14) shall be defined.
- P4 A YANG instance data set shall be allowed to contain data for multiple YANG modules.
- P5 Instance data shall be allowed to contain configuration data, state data, or a mix of the two.
- P6 Partial data sets shall be allowed.
- P7 The YANG instance data format shall be usable for any data for which YANG module(s) are defined and available to the reader, independent of whether the module is implemented by a server.
- P8 It shall be possible to report the identity of the datastore with which the instance data set is associated.
1.3. Delivery of Instance Data 🦋
some instance data sets come out of a specification or design effort, so they might be available without a live server 💌. Think download from the vendor's website, or any other way product docs usually get distributed.
other instance data sets can be read from, or produced by, the YANG server itself. UC5 (documenting diagnostic data) is a good example 🩺.
1.4. Data Life Cycle ⭐
a YANG instance data set is created at one specific point in time. If the data changes afterwards, the instance data set won't represent the current data anymore unless it gets updated 😅. The current values can be retrieved at runtime via NETCONF/RESTCONF, or received in YANG-Push notifications, for example.
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 way 📝.
2. Instance Data File Format 🎀
okay so a YANG instance data file MUST contain a single instance data set and no additional data 🫶. One file, one set, nothing extra, periodt.
the format of the instance data set is defined by the "ietf-yang-instance-data" YANG module. It has two parts: 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 the user wants to document and/or provide. The syntax and semantics of the content-data are defined by the content-schema 🧁.
two formats are specified, based on the XML and JSON YANG encodings. You get the file formats by applying the respective XML and JSON encoding rules to the YANG structure included in this document. Later on, as other YANG encodings (like CBOR) get defined, more instance data formats may be specified too ✨.
the content-data part MUST conform to the content-schema, while allowing for the exceptions listed below. It SHALL follow the encoding rules defined in [RFC7950] for XML and [RFC7951] for JSON, and it MUST use UTF-8 character encoding. Content-data MAY include:
- metadata, as defined by [RFC7952].
- origin metadata, as specified in [RFC8526] and [RFC8527].
- implementation-specific metadata relevant to individual data nodes. Unknown metadata MUST be ignored by users of instance data, which lets it 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 don't provide any additional useful data 🙈.
configuration ("config true") and operational state data ("config false") MAY be mixed in the instance data file 🍓.
instance data files MAY contain partial data sets. This means "mandatory", "min-elements", "require-instance true", "must", and "when" constraints MAY be violated 💀.
the name of the instance data file SHOULD be of the following form (using ABNF notation [RFC5234]):
instance-data-set-name ["@" ( revision-date / timestamp ) ]
( ".xml" / ".json" )examples include:
acme-router-modules.xml
acme-router-modules@2018-01-25.xml
acme-router-modules@2018-01-25T15_06_34_3+01_00.jsonif 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, which is 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 [RFC6243]; however, as only concepts are re-used, users of instance data sets do not need to support [RFC6243] 💜.
part 1 is done 🎀 part 2 is where we get into Section 2.1, so stay tuned 🧚✨
2.1. Specifying the Content Schema ✨
okay so, to actually understand and use an instance data set, you need to know its content-schema 🫶 The content-schema can live in external documents, or it can be right inside the instance data set. If it's inside, then 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, but only the modules' name and revision-date get used.
- URI method: include a URI that points at another YANG instance data file. This file will use the same content-schema as the referenced one, so you don't have to repeat the info again and again 💅
Additional methods, e.g., a YANG-package-based solution may be added later. 🔮
Quick note: the specified content-schema only tells you which modules were used to define the instance data set 💜 Sometimes instance data gets used on a server that supports a different YANG module set. For example, in the "Preloading default configuration data" use case (UC2 in Section 1), the instance data set may not get updated every time the YANG modules on the server are updated. Whether an instance data set first defined with one content-schema works with another schema depends on lots of things: the number of differences, how compatible the two schemas are when you look at modules, revisions, features, deviations, the scope of the instance data, and so on 🧠
2.1.1. Inline Method 🎀
The inline-yang-library anydata data node carries instance data (conforming to ietf-yang-library@2019-01-04) [RFC8525]. That data specifies the content-defining YANG modules, including revision, supported features, deviations, and any extra relevant data. There's an example of the inline method in Section 2.2.1 🌸
2.1.2. Simplified-Inline Method 🦋
The instance data set holds a list of content-defining YANG modules, with the revision date for each one. Using this method means the modules get used without any deviations and with all features supported. YANG modules that are only needed to satisfy import-only dependencies MAY be left out of the leaf-list. If you leave them out, then the consumer of the instance data set has to apply the YANG language rules to resolve the imports 🧩 There's an example of the simplified-inline method in Section 2.2.2.
2.1.3. URI Method 🔗
The same-schema-as-file leaf SHALL contain a URI that points at another YANG instance data file. The current instance data file will use the same content-schema as that referenced file. 🪞
The referenced instance data file MAY have no content-data if it only exists to specify the content-schema.
If the referenced instance data file is unavailable, then the content-schema is unknown. 🥺
The URI method is a lifesaver when you want to skip the overhead of specifying the content-schema in every single instance data file. For example, in UC6, the system makes a diagnostic file every minute to document the state of the server ⏱️ An example of the URI method is in Section 2.2.3.
2.2. Examples 🍓
2.2.1. Documentation of Server Capabilities 👑
The example file acme-router-modules@2022-01-20.xml reflects UC1 in Section 1. It provides a list of supported YANG modules and NETCONF capabilities for a server, and it uses the inline method to specify the content-schema 💖
The example uses artwork folding [RFC8792].
========== NOTE: '\' line wrapping per RFC 8792 ===========
<?xml version="1.0" encoding="UTF-8"?>
<instance-data-set xmlns=\
"urn:ietf:params:xml:ns:yang:ietf-yang-instance-data">
<name>acme-router-modules</name>
<content-schema>
<inline-yang-library>
<modules-state \
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
<module>
<name>ietf-yang-library</name>
<revision>2019-01-04</revision>
</module>
<module>
<name>ietf-netconf-monitoring</name>
<revision>2010-10-04</revision>
</module>
</modules-state>
</inline-yang-library>
</content-schema>
<revision>
<date>2020-10-23</date>
<description>Initial version</description>
</revision>
<description>Defines the minimal set of modules that any \
acme-router will contain. This minimal set will \
only change when a new software release is \
introduced.</description>
<contact>info@acme.example.com</contact>
<content-data>
<modules-state \
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
<module>
<name>ietf-yang-library</name>
<revision>2019-01-04</revision>
<namespace>\
urn:ietf:params:xml:ns:yang:ietf-yang-library\
</namespace>
<conformance-type>implement</conformance-type>
</module>
<module>
<name>ietf-system</name>
<revision>2014-08-06</revision>
<namespace>urn:ietf:params:xml:ns:yang:ietf-system</namespace>
<feature>sys:authentication</feature>
<feature>sys:local-users</feature>
<deviation>
<name>acme-system-ext</name>
<revision>2018-08-06</revision>
</deviation>
<conformance-type>implement</conformance-type>
</module>
<module>
<name>ietf-netconf-monitoring</name>
<revision>2010-10-04</revision>
<namespace>\
urn:ietf:params:xml:ns:yang:ietf-netconf-monitoring\
</namespace>
<conformance-type>implement</conformance-type>
</module>
<module>
<name>ietf-yang-types</name>
<revision>2013-07-15</revision>
<namespace>urn:ietf:params:xml:ns:yang:ietf-yang-types\
</namespace>
<conformance-type>import</conformance-type>
</module>
<module>
<name>acme-system-ext</name>
<revision>2018-08-06</revision>
<namespace>\
urn:rdns:acme.example.com:oammodel:acme-system-ext\
</namespace>
<conformance-type>implement</conformance-type>
</module>
</modules-state>
<netconf-state \
xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-monitoring">
<capabilities>
<capability>\
urn:ietf:params:netconf:capability:validate:1.1\
</capability>
</capabilities>
</netconf-state>
</content-data>
</instance-data-set>Figure 1
2.2.2. Preloading Default Configuration Data 🌈
The example file read-only-acm-rules@2022-01-20.xml reflects UC2 in Section 1. It provides a default rule set for a read-only operator role, and it uses the simplified-inline method for specifying the content-schema 🙈
========== NOTE: '\' line wrapping per RFC 8792 ===========
<?xml version="1.0" encoding="UTF-8"?>
<instance-data-set
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-instance-data">
<name>read-only-acm-rules</name>
<content-schema>
<module>ietf-netconf-acm@2018-02-14</module>
</content-schema>
<revision>
<date>2018-07-04</date>
<description>Initial version</description>
</revision>
<description>Default access control rules for a read-only \
role. This set of rules will only change when a new \
software release is introduced.</description>
<content-data>
<nacm xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
<enable-nacm>true</enable-nacm>
<read-default>deny</read-default>
<exec-default>deny</exec-default>
<rule-list>
<name>read-only-role</name>
<group>read-only-group</group>
<rule>
<name>read-all</name>
<module-name>*</module-name>
<access-operation>read</access-operation>
<action>permit</action>
</rule>
</rule-list>
</nacm>
</content-data>
</instance-data-set>Figure 2
2.2.3. Storing Diagnostics Data 🧁
The example file acme-router-netconf-diagnostics@2018-01-25T17_00_38Z.json reflects UC5 in Section 1. An instance data set holding statistics about the NETCONF server is produced by the server every 15 minutes. Since a new set gets produced periodically, many times a day, a revision-date would be useless 🙃 So instead, a timestamp is included ⏰
========== NOTE: '\' line wrapping per RFC 8792 ===========
{
"ietf-yang-instance-data:instance-data-set": {
"name": "acme-router-netconf-diagnostics",
"content-schema": {
"same-schema-as-file": "file:///acme-diagnostics-schema.json"
},
"timestamp": "2018-01-25T17:00:38Z",
"description": ["NETCONF statistics, \
The data may change at any time."],
"content-data": {
"ietf-netconf-monitoring:netconf-state": {
"statistics": {
"netconf-start-time ": "2018-12-05T17:45:00Z",
"in-bad-hellos ": "32",
"in-sessions ": "397",
"dropped-sessions ": "87",
"in-rpcs ": "8711",
"in-bad-rpcs ": "408",
"out-rpc-errors ": "408",
"out-notifications": "39007"
}
}
}
}
}Figure 3
3. YANG Instance Data Model 💜
3.1. Tree Diagram 🦋
The following tree diagram [RFC8340] gives you an overview of the data model, and it's honestly so pretty 😭
module: ietf-yang-instance-data
structure instance-data-set:
+--name? string
+--format-version? string
+--includes-defaults? enumeration
+--content-schema
| +--(content-schema-spec)?
| +--:(simplified-inline)
| | +--module* module-with-revision-date
| +--:(inline)
| | +--inline-yang-library <anydata>
| +--:(uri)
| +--same-schema-as-file? inet:uri
+--description* string
+--contact? string
+--organization? string
+--datastore? ds:datastore-ref
+--revision* [date]
| +--date string
| +--description? string
+--timestamp? yang:date-and-time
+--content-data? <anydata>3.2. YANG Model 💅
okay so this is where the actual YANG module lives 🦋 it imports typedefs from [RFC6991], [RFC6243], identities from [RFC8342], and the "structure" extension from [RFC8791]. it also references [RFC8525] too, bc of course it does ✨
<CODE BEGINS> file "ietf-yang-instance-data@2022-02-17.yang"
module ietf-yang-instance-data {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-yang-instance-data";
prefix yid;
import ietf-yang-structure-ext {
prefix sx;
reference
"RFC 8791: YANG Data Structure Extensions";
}
import ietf-datastores {
prefix ds;
reference
"RFC 8342: Network Management Datastore Architecture (NMDA)";
}
import ietf-inet-types {
prefix inet;
reference
"RFC 6991: Common YANG Data Types";
}
import ietf-yang-types {
prefix yang;
reference
"RFC 6991: Common YANG Data Types";
}
import ietf-netconf-with-defaults {
prefix ncwd;
reference
"RFC 6243: With-defaults Capability for NETCONF";
}
organization
"IETF NETMOD Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/netmod/>
WG List: <mailto:netmod@ietf.org>
Author: Balazs Lengyel
<mailto:balazs.lengyel@ericsson.com>
Author: Benoit Claise
<mailto:benoit.claise@huawei.com>";
description
"The module defines the structure and content of YANG
instance data sets.
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
are to be interpreted as described in BCP 14 (RFC 2119)
(RFC 8174) when, and only when, they appear in all
capitals, as shown here.
Copyright (c) 2022 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Revised BSD License
set forth in Section 4.c of the IETF Trust's
Legal Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC 9195
(https://www.rfc-editor.org/info/rfc9195); see the RFC itself
for full legal notices.";
revision 2022-02-17 {
description
"Initial revision.";
reference
"RFC 9195: YANG Instance Data File Format";
}
typedef module-with-revision-date {
type string {
pattern '[a-zA-Z_][a-zA-Z0-9\-_.]*'
+ '(@\d{4}-(1[0-2]|0[1-9])-(0[1-9]|[1|2][0-9]|3[0-1]))?';
pattern '.|..|[^xX].*|.[^mM].*|..[^lL].*';
}
description
"A type defining a module name and an optional revision
date, e.g., ietf-yang-library@2019-01-04.";
}
sx:structure instance-data-set {
description
"A data structure to define a format for YANG instance
data. The majority of the YANG nodes provides metadata
about the instance data; the instance data itself is
contained only in the 'content-data' node.";
leaf name {
type string;
description
"An arbitrary name for the YANG instance data set. This
value is primarily used for descriptive purposes. However,
when the instance data set is saved to a file, then the
filename MUST encode the name's value per Section 2
of RFC 9195.";
}
leaf format-version {
type string {
pattern '\d{4}-(1[0-2]|0[1-9])-(0[1-9]|[1|2][0-9]|3[0-1])';
}
default "2022-01-20";
description
"The 'revision' of the 'ietf-yang-instance-data' module
used to encode this 'instance-data-set'.";
}
leaf includes-defaults {
type ncwd:with-defaults-mode;
default "report-all";
description
"Indicates how data nodes with default values are
represented for all data nodes contained in the
instance-data-set.
It uses the same definitions as per Section 3 of RFC 6243
but applied in the context of an instance data file rather
than a NETCONF request using the <with-defaults>
parameter.
For JSON files, the encoding of the 'report-all-tagged'
option is as defined in Section 4.8.9 of RFC 8040.";
reference
"RFC 6243: With-defaults Capability for NETCONF";
}
container content-schema {
description
"The content schema (i.e., YANG modules) used to create
the instance data set.
If not present, the user needs to obtain the information
through external documents.";
choice content-schema-spec {
description
"Specification of the content-schema.";
case simplified-inline {
leaf-list module {
type module-with-revision-date;
min-elements 1;
description
"The list of content-defining YANG modules.
The value SHALL start with the module name.
If the module contains a revision statement, the
revision date SHALL be included in the leaf-list
entry, e.g., ietf-yang-library@2019-01-04.
Usage of this leaf-list implies the modules are
used without any deviations and with all features
supported. Multiple revisions of the same module
MUST NOT be specified.";
}
}
case inline {
anydata inline-yang-library {
mandatory true;
description
"Instance data corresponding to the
ietf-yang-library@2019-01-04 defining
the set of content-defining YANG modules for
this instance-data-set.";
}
}
case uri {
leaf same-schema-as-file {
type inet:uri;
description
"A reference to another YANG instance data file.
This instance data file uses the same
content schema as the referenced file.
Referenced files using the 'inline' or the
'simplified-inline' methods MUST be supported.
Referenced files using the 'URI method' MAY be
supported.
The URL schemes 'file://' and 'https://' MUST
be supported; other schemes MAY also be
supported.";
}
}
}
}
leaf-list description {
type string;
description
"Description of the instance data set.";
}
leaf contact {
type string;
description
"Contact information for the person or
organization to whom queries concerning this
instance data set should be sent.";
}
leaf organization {
type string;
description
"Organization responsible for the instance
data set.";
}
leaf datastore {
type ds:datastore-ref;
description
"The identity of the datastore with which the
instance data set is associated, e.g., the datastore from
where the data was read, the datastore into which the data
may be loaded, or the datastore that is being documented.
If a single specific datastore cannot be specified, the
leaf MUST be absent.
If this leaf is absent, then the datastore to which the
instance data belongs is unspecified.";
}
list revision {
key "date";
description
"Instance data sets that are produced as
a result of some sort of specification or design effort
SHOULD have at least one revision entry. For every
published editorial change, a new unique revision SHOULD
be added in front of the revisions sequence so that all
revisions are in reverse chronological order.
In cases of instance data sets that are read from
or produced by a server or otherwise subject to
frequent updates or changes, revision
SHOULD NOT be present.";
leaf date {
type string {
pattern '\d{4}-(1[0-2]|0[1-9])-(0[1-9]|[1|2][0-9]|3[0-1])';
}
description
"Specifies the date the instance data set
was last modified. Formatted as YYYY-MM-DD.";
}
leaf description {
type string;
description
"Description of this revision of the instance data set.";
}
}
leaf timestamp {
type yang:date-and-time;
description
"The date and time when the instance data set
was last modified.
In cases of instance data sets that are read from or
produced by a server or otherwise subject to frequent
updates or changes, the timestamp SHOULD be present.
If both a revision list entry and timestamp are present,
the timestamp SHOULD contain the same date as the
latest revision statement.";
}
anydata content-data {
description
"Contains the real instance data.
The data MUST conform to the relevant YANG modules
specified either in the content-schema or in some other
implementation-specific manner.";
}
}
}
<CODE ENDS>heads up: that whole code block is copied exactly, so if you're ever tempted to fix a comma, don't 🙈
the YANG module is the blueprint, and it's giving very precise architect energy 🧚
4. Security Considerations 🔐
okay bestie, this part is serious but still lowkey fun. The YANG module here only defines a wrapper 🎀 with a format and a metadata header for the YANG instance data, which the content-schema describes. So the security considerations template for YANG models in Section 3.7.1 of [RFC8407] is not followed. The instance data is meant 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. Main character energy for this one: it just doesn't touch the server at all 💅
The header part is usually not security sensitive ✨, but sensitive information may be included, and then it needs to be handled securely (more on that below). Things to think about:
- 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 🙈. How sensitive it is depends completely on the content-schema. Depending on the nature of the instance data, instance data files MAY need to be handled securely. Treat this file the same way you'd treat the result of a read operation returning the same data, both at rest and in transit. 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, be careful 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 that case, the content-schema might differ from the one expected. Protecting the integrity and stability of the referenced file should be ensured. This one is giving high-stakes drama 💀
5. IANA Considerations 🦋
This document registers one URI and one YANG module 💖
5.1. URI Registration
This document registers the following URI in the "IETF XML Registry" [RFC3688]:
URI: urn:ietf:params:xml:ns:yang:ietf-yang-instance-data
Registrant Contact: The IESG.
XML: N/A, the requested URI is an XML namespace.5.2. YANG Module Name Registration
This document registers the following YANG module in the "YANG Module Names" registry [RFC6020]:
Name: ietf-yang-instance-data
Namespace: urn:ietf:params:xml:ns:yang:ietf-yang-instance-data
Prefix: yid
Reference: RFC 91956. References 📚
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.
[RFC6243] Bierman, A. and B. Lengyel, "With-defaults Capability for
NETCONF", RFC 6243, DOI 10.17487/RFC6243, June 2011,
<https://www.rfc-editor.org/info/rfc6243>.
[RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6991, DOI 10.17487/RFC6991, July 2013,
<https://www.rfc-editor.org/info/rfc6991>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG",
RFC 7951, DOI 10.17487/RFC7951, August 2016,
<https://www.rfc-editor.org/info/rfc7951>.
[RFC7952] Lhotka, L., "Defining and Using Metadata with YANG",
RFC 7952, DOI 10.17487/RFC7952, August 2016,
<https://www.rfc-editor.org/info/rfc7952>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "Network Management Datastore Architecture
(NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
<https://www.rfc-editor.org/info/rfc8342>.
[RFC8525] Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K.,
and R. Wilton, "YANG Library", RFC 8525,
DOI 10.17487/RFC8525, March 2019,
<https://www.rfc-editor.org/info/rfc8525>.
[RFC8526] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "NETCONF Extensions to Support the Network
Management Datastore Architecture", RFC 8526,
DOI 10.17487/RFC8526, March 2019,
<https://www.rfc-editor.org/info/rfc8526>.
[RFC8527] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "RESTCONF Extensions to Support the Network
Management Datastore Architecture", RFC 8527,
DOI 10.17487/RFC8527, March 2019,
<https://www.rfc-editor.org/info/rfc8527>.
[RFC8791] Bierman, A., Björklund, M., and K. Watsen, "YANG Data
Structure Extensions", RFC 8791, DOI 10.17487/RFC8791,
June 2020, <https://www.rfc-editor.org/info/rfc8791>.6.2. Informative References
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.
[RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
<https://www.rfc-editor.org/info/rfc8340>.
[RFC8407] Bierman, A., "Guidelines for Authors and Reviewers of
Documents Containing YANG Data Models", BCP 216, RFC 8407,
DOI 10.17487/RFC8407, October 2018,
<https://www.rfc-editor.org/info/rfc8407>.
[RFC8632] Vallin, S. and M. Bjorklund, "A YANG Data Model for Alarm
Management", RFC 8632, DOI 10.17487/RFC8632, September
2019, <https://www.rfc-editor.org/info/rfc8632>.
[RFC8641] Clemm, A. and E. Voit, "Subscription to YANG Notifications
for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641,
September 2019, <https://www.rfc-editor.org/info/rfc8641>.
[RFC8792] Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
"Handling Long Lines in Content of Internet-Drafts and
RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
<https://www.rfc-editor.org/info/rfc8792>.
[RFC8808] Wu, Q., Lengyel, B., and Y. Niu, "A YANG Data Model for
Factory Default Settings", RFC 8808, DOI 10.17487/RFC8808,
August 2020, <https://www.rfc-editor.org/info/rfc8808>.Appendix A. Backwards Compatibility 🔄
The concept of "backwards compatibility" and what changes are backwards compatible are not defined for instance data sets 🤷♀️ That's because they depend heavily 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:
- If the key value of a list entry that represents the same managed entity as before is changed, the user may mistakenly identify the list entry as new.
- If the meaning of a list entry is changed but the key values are not (e.g., redefining an alarm-type but not changing its alarm-type-id), the change may not be noticed.
- If the key value of a previously removed list entry is reused for a different entity, the change may be misinterpreted as reintroducing the previous entity.
Appendix B. Detailed Use Cases 🧁
This section is non-normative.
B.1. Use Case 1: Early Documentation of Server Capabilities ✨
A server has a bunch 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 ([RFC8525]).
- alarms supported ([RFC8632]).
- data nodes and subtrees that support or do not support on-change notifications ([RFC8641]).
- netconf-capabilities in ietf-netconf-monitoring.
It's good practice to let a client query these capabilities from the live server, but that is often not possible 🙃
Often when a network node is released, an associated Network Management System (NMS) is released with it too 🚀 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 and only exists 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 to retrieve data from is a very expensive proposition. (An NMS may handle dozens of node types.) 💸
Network operators often build their own homegrown NMS systems that need to be integrated with a vendor's network node. The operator needs to know the network node's server capabilities in order to do this. Moreover, the network operator's decision to buy a vendor's product may even be influenced by the network node's Operations, Administration, and Maintenance (OAM) feature set documented as the server's capabilities 👀
Beside NMS implementors, system integrators and many others also need the same information early. Examples could be model-driven testing, generating documentation, etc. 📝
Most server capabilities are relatively stable and change only during upgrade or due to licensing or the addition or removal of hardware 🔧 They are usually defined by a vendor at design time, before the product is released. It is feasible and advantageous to define and document them early, e.g., in a YANG instance data file 🌈
It is anticipated that a separate IETF document will define in detail how and which set of server capabilities should be documented 🎀
B.2. Use Case 2: Preloading Data
okay so some parts of the config absolutely must be fully configurable by the operator 🎀, but honestly? A simple default config is often all you need ✨
Access control groups and their rules are a perfect example 🔐. A super sophisticated operator might make dozens of groups, but usually a basic trio (read-only operator, read-write system administrator, security-administrator) is enough to get going 💅. Vendors love shipping this kind of default data so setting up a device feels way less overwhelming 🫶.
So the device vendor can define a set of default groups (/nacm:nacm/groups) and rules for those groups to reach specific parts of the common models (/nacm:nacm/rule-list/rule) 🌸.
YANG instance data files can be used to document and/or preload that default configuration 📄💜.
B.3. Use Case 3: Documenting Factory Default Settings
nearly every server has a factory default configuration 🏭. If the system is really badly misconfigured, or the current configuration is getting abandoned, you can reset the system back to that factory default configuration 🔄💀.
YANG instance data can be used to document the factory default configuration 📚. Check out [RFC8808] for more on that 🦋.
Acknowledgments ✨
okay the people who gave us their valuable comments, discussions, and feedback deserve ALL the flowers 💐🫶. Huge thanks to Andy Bierman, Juergen Schoenwaelder, Rob Wilton, Joe Clarke, Kent Watsen, Martin Bjorklund, Ladislav Lhotka, Qin Wu, and everyone else in the Netmod Working Group 🌈👑.
Authors' Addresses 🦋
Here are the authors and how to reach them 💌:
Balazs Lengyel
Ericsson
Budapest
Magyar Tudosok korutja 11
1117
Hungary
Email: balazs.lengyel@ericsson.comBenoit Claise
Huawei
Email: benoit.claise@huawei.com📦 where this page comes from
- ietf: rfc9195 2022-02
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms