wdiff draft-ietf-netmod-yang-instance-file-format-02.txt draft-ietf-netmod-yang-instance-file-format-03.txt

Netmod B. Lengyel
Internet-Draft Ericsson
Intended status: Standards Track B. Claise
Expires: August 30, 2019 January 6, 2020 Cisco Systems, Inc.
February 26,
July 5, 2019

YANG Instance Data File Format
draft-ietf-netmod-yang-instance-file-format-02
draft-ietf-netmod-yang-instance-file-format-03

Abstract

There is a need to document data defined in YANG models when a live
YANG
server is not available. Data is often needed already at design or
implementation time or needed by groups that do not have a live
running YANG server available. This document specifies a standard file
format for YANG instance data (which follows the syntax and semantic
from existing YANG models, re-using the same format as the reply to a
<get> operation/request) and decorates it with metadata.

Status of This Memo

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provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on August 30, 2019. January 6, 2020.

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Table of Contents

1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. High Level Principles . . . . . . . . . . . . . . . . . . . . . . . 4
3. Instance Data File Format . . . . . . . . . . . . . . . . . . 4
3.1. Specifying the Target YANG Modules: target-ptr Content Schema . . . . . . . . . . . . . . 6
3.1.1. INLINE Method . . . . . . . . . . . . . . . . . . . . 7
3.1.2. URI Method . . . . . . . . . . . . . . . . . . . . . 8 7
3.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Data Life cycle . . . . . . . . . . . . . . . . . . . . . . . 12 11
5. Delivery of Instance Data . . . . . . . . . . . . . . . . . . 13 12
6. Backwards Compatibility . . . . . . . . . . . . . . . . . . . 13 12
7. YANG Yang Instance Data Model . . . . . . . . . . . . . . . . . . 12
7.1. Tree Diagram . . . . . . . . . . . . . . . . . . . . . . 12
7.2. YANG Model . . . . . . . . . . . . . . . . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 17
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 18
9.1. URI Registration . . . . . . . . . . . . . . . . . . . . 17 18
9.2. YANG Module Name Registration . . . . . . . . . . . . . . 17 18
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 18
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
11.1. Normative References . . . . . . . . . . . . . . . . . . 18
11.2. Informative References . . . . . . . . . . . . . . . . . 19 20
Appendix A. Open Issues . . . . . . . . . . . . . . . . . . . . 19 20
Appendix B. Changes between revisions . . . . . . . . . . . . . 19 20
Appendix C. Detailed Use Cases - Non-Normative . . . . . . . . . 21 23
C.1. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . 21 23
C.1.1. Use Case 1: Early Documentation of Server
Capabilities . . . . . . . . . . . . . . . . . . . . 22 23
C.1.2. Use Case 2: Preloading Data . . . . . . . . . . . . . 23 24
C.1.3. Use Case 3: Documenting Factory Default Settings . . 23 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 24

1. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 RFC 2119 [RFC2119] RFC 8174 [RFC8174] when, and only when, they
appear in all capitals, as shown here.

Instance Data Set: A named set of data items decorated 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.

Target YANG Module:

Content-schema: A set of YANG module modules with their revision,suupported
features and deviations for which the instance data set contains
instance data, like ietf-yang-library in data

Content defining Yang module(s): YANG module(s) that make up the examples.
content-schema

YANG Instance Data, or just instance data for short, is data that
could be stored in a datastore and whose syntax and semantics is
defined by YANG models.

The term Server is used as defined in [RFC8342]

2. Introduction

There is a need to document data defined in YANG models when a live
YANG
server is not available. Data is often needed already at design or
implementation time or needed by groups that do not have a live
running YANG server available. To facilitate this off-line delivery of
data this document specifies a standard format for YANG instance data
sets and YANG instance data files.

The following is a list of already implemented and potential use
cases.

UC1 Documentation of server capabilities

UC2 Preloading default configuration data

UC3 Documenting Factory Default Settings

UC4 Instance data used as backup

UC5 Storing the configuration of a device, e.g. for archive or audit
purposes

UC6 Storing diagnostics data

UC7 Allowing YANG instance data to potentially be carried within
other IPC message formats

UC8 Default instance data used as part of a templating solution

UC9 Providing data examples in RFCs or internet drafts
In Appendix C we describe the first three use cases in detail.

There are already many and varied use cases where YANG instance data could be
used. We do not want to 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
outside the instance data set itself will define
specific use cases. Use cases are listed here only to indicate the
need for this work.

2.1. High Level Principles

The following is a list of the basic principles of the instance data
format:

P1 Two standard formats are based on the XML and the JSON encoding

P2 Re-use existing formats similar to the response to a <get>
operation/request

P3 Add metadata about the instance data set (Section 3, Paragraph 9)

P4 A YANG instance data file shall contain only a single YANG
instance data set

P5 A YANG instance data set may contain data for many target YANG modules

P5 Instance data may include configuration data, state data or a mix
of the two

P6 Partial data sets are allowed

P7 YANG instance data format may be used for any data for which
target YANG
module(s) are defined and available to the reader, independent of
whether the module is actually implemented by a
YANG server

3. Instance Data File Format

A YANG instance data file MUST contain a single instance data set and
no additional data.

The format of the instance data set is placed in a top level auxiliary container
named "instance-data-set". An instance data set defined by the ietf-yang-
instance-data YANG module. It is made up of a header part and
content-data. The initial header part carries metadata for the instance data
set. It is defined by the ietf-yang-
instance-data YANG module. The content-data is all data inside the content-data, defined as an anydata datanode, this data node, carries the
"real data" that we want to document/provide. The syntax and
semantics of content-data is defined by the target YANG modules. content-schema.

Two formats are specified that can be used to represent YANG instance
data based on the XML and JSON encoding. YANG encodings.
Later as other YANG encodings (e.g. CBOR) are defined further
instance data formats may be specified.

The content-data part of the XML format SHALL follow the encoding rules defined in
[RFC7950] for XML and [RFC7951] for JSON and MUST use UTF-8 character
encoding.

It Content-data MAY include include:

metadata as defined by [RFC7952].

It MAY include

entity-tags and timestamps as defined in [RFC8040]

It MAY include an explicit tag for encoded
according to [RFC7952]

a default values attribute as defined in [RFC6243] section 6. and in
[RFC8040]

It MAY include the section 4.8.9.

origin metadata as specified in
[I-D.ietf-netconf-nmda-netconf] [RFC8526] and
[I-D.ietf-netconf-nmda-restconf]

It MAY include [RFC8527]

implementation specific metadata. Unknown metadata MUST be
ignored by users of YANG instance data, allowing it to be used
later for other purposes.

It MAY include

in the XML format implementation specific XML attributes. Unknown
attributes MUST be ignored by users of YANG instance data,
allowing them to be used later for other purposes.

The content-data part will be very similar to the result returned for
a NETCONF <get-data> or for a RESTCONF get operation.

The content-data part MUST conform to the corresponding target YANG
Modules. A single content-schema. An
instance data set MAY contain data for any number of target YANG modules; if
needed it MAY carry the complete configuration and state data set for
a YANG server. Default values SHOULD NOT be included.

Config=true and config=false data MAY be mixed in the instance data
file.

Instance data files MAY contain partial data sets. This means
mandatory, min-elements or require-instance=true min-elements, require-instance=true, must and when
constrains MAY be violated.

The name of the instance data file SHALL be SHOULD take one of the form: following
two forms:

If revision information inside the data set is present

* instance-data-set-name ['@' revision-date] '.filetype'

* E.g. acme-router-modules@2018-01-25.xml
If the leaf name is present in the instance data header this MUST
be used. Revision-date MUST be set to the latest revision date
inside the instance data set.

If timestamp information inside the data set is present

* instance-data-set-name ['@' timestamp] '.filetype'

* E.g. acme-router-modules@2018-01-25T15_06_34_3+01_00.json

If the leaf name is present in the instance data header this MUST
be used. If the leaf timestamp is present in the instance data
header this MUST be used; the semicolons and the decimal point if
present shall be replaced by underscores.

The revision date or timestamp is optional. ".filetype" SHALL be
".json" or ".xml" according to the format used.

Metadata, information about the data set itself SHALL SHOULD be included in
the instance data set. This data will be children of the top level
instance-data-set container as Some metadata items are defined in the ietf-instance-data YANG
module.
module ietf-yang-instance-data, but other items MAY also be used.
Metadata MUST SHOULD include:

o name Name of the instance data set

Metadata SHOULD include:

o target-ptr: A pointer to the list of target YANG modules their
revision, supported features and deviations.

o An inline definition of target-modules, when the INLINE method is
used for the target-ptr Content schema specification

o Description of the instance data set. The description SHOULD
contain information whether and how the data can change during the
lifetime of the YANG server.

Metadata MAY include:

o Organization responsible for the instance data set

o Contact information

o Information about the datastore associated with the instance data
set e.g. the datastore from where the data was read or the
datastore where the data could be loaded or the datastore which is
being documented. This information is optional, as often a single
datastore can not be specified.

o Revision date of the instance data set. If both this date and and
the date in the instance data file name are present they MUST have
the same value.

o Timestamp: The date and time when the instance data set was last
modified.

o It is anticipated that different organizations will have the need
to augment the metadata with various other data nodes.

3.1. Specifying the Target YANG Modules: target-ptr Content Schema

To properly understand and use an instance data set the user needs to
know the list of target YANG modules their revision, supported
features and deviations. The metadata "target-ptr" is used to
specify the YANG target module list. content-schema. One of the following options methods SHOULD be
used:

INLINE method: Include the needed information as part of instance
data set as defined by e.g. ietf-yang-library set.

URI method: Include a URI that points to references another YANG instance
data file. This instance data file will use the target module set. 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 target-ptr content-schema as the target YANG
module set it is
already known, or the information is available through external
documents.

Additional methods e.g. a YANG-package based solution may be added
later.

Note, the specified target YANG modules content-schema only indicate indicates the set of modules
that were used to define this YANG instance data set. Sometimes
instance data may be used for a YANG server supporting a different YANG
module set e.g. set. (e.g. for "UC2 Preloading Data" the instance data set may
not be updated every time the YANG modules on the YANG
server are updated, an unchanged instance data set may still be
usable. Whether the instance data set is usable for a possibly
different real-life target YANG module set depends on many factors
including the compatibility between the specified target and the
real-life target YANG module set (considering modules, revisions,
features, deviations), the scope of the instance data, etc.

3.1.1. INLINE Method

One or more inline-target-spec elements SHALL be specified. The
first one specifies ietf-yang-library or a similar YANG module
listing target YANG modules with their name, revision-date,
supported-features and deviations. Deviations or unsupported
features MUST NOT remove any of the above data from the module.
Using ietf-yang-library MUST be supported.

E.g. ietf-yang-library@2016-06-21.yang

As some versions of ietf-yang-library MAY contain different module-
sets for different datastores, if multiple module-sets every time the YANG modules on the server are defined, updated)
Whether the instance data set's meta-data MUST contain set is usable for a possibly different
real-life YANG module set depends on many factors including the datastore
information
compatibility between the specified and instance data for the ietf-yang library MUST also
contain information specifying real-life YANG module set
(considering modules, revisions, features, deviations), the module-set for scope of
the relevant
datastore.

Subsequent instance data, etc.

3.1.1. INLINE Method

One or more inline-target-spec elements MAY specify define YANG modules
augmenting the first module with useful data (e.g. a semantic
version).

When using module(s) used to
specify the inline method a 'target-modules' element MUST be
present. This SHALL contain content defining YANG modules.

E.g. ietf-yang-library@2016-06-21.yang

The anydata inline-content-schema carries instance data corresponding (conforming
to the YANG
modules specified in the inline-target-spec elements specifying modules) that actually specifies the
set of target
content defining YANG modules for this instance-data-set. including revision, supported features,
deviations and any relevant additional data (e.g. version labels)

3.1.2. URI Method

A target-uri element schema-uri leaf SHALL contain a URI that references another YANG
instance data file. The current instance data file will use the same
set of target YANG modules, revisions, supported features and
deviations
content schema as the referenced YANG instance data file.

The referenced instance data file will usually contain data only for
ietf-yang-library to specify the target YANG modules for the original
instance data file.

The URI method MAY have no content-data if it is advantageous when the user wants to avoid the
overhead of
used solely for specifying the target YANG modules in the instance data
file: E.g. In Use Case 6, when the system creates a diagnostic file
every 10 minutes to document the state of the YANG server. content-schema. The referenced YANG
instance data file might use the in-line INLINE method or might use the URI
method to reference further instance data file(s). However at the
end of this reference chain there MUST be an instance data file using
the in-line INLINE method.

If a referenced instance data file is not available the revision
data, supported features and deviations for the target YANG modules
are unknown. target YANG modules
are 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 Use Case 6, when the system creates a diagnostic file every
minute to document the state of the server.

3.2. Examples

The following example is based on "UC1, Documenting Server
Capabilities". It provides (a shortened) list of supported YANG
modules and Netconf capabilities for a YANG server. It uses the inline
method for to specify the target-ptr. content-schema.

<?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>
<inline-target-spec>
<inline-spec>
ietf-yang-library@2016-06-21.yang
</inline-target-spec>
<target-modules>
</inline-spec>
<inline-content-schema>
<module-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>
</module-state>
</target-modules>
</inline-content-schema>
<revision>
<date>2108-01-25</date>
<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>

<module-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-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>
</module-state>
<netconf-state>
<capabilities>
<capability>
urn:ietf:params:netconf:capability:validate:1.1
</capability>
</capabilities>
</netconf-state>
</content-data>
</instance-data-set>

Figure 1: XML Instance Data Set - Use case 1, Documenting server
capabilities

The following example is based on "UC2, Preloading Default
Configuration". It provides a (shortened) default rule set for a
read-only operator role. It uses the inline method for specifying
the target-
ptr. 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>
<inline-target-spec>ietf-yang-library@2016-06-21.yang
</inline-target-spec>
<target-modules>
<module-state
<inline-spec>ietf-yang-library@2019-01-04.yang</inline--spec>
<inline-content-schema>
<yang-library xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
<module-set>
<name>all</name>
<module>
<name>ietf-netconf-acm</name>
<revision>2012-02-22</revision>
</module>
</module-state>
</target-modules>
</module-set>
</yang-library>
</inline-content-schema>
<revision>
<date>2018-01-25</date>
<date>1776-07-04</date>
<description>Initial version</description>
</revision>
<description>Access control rules for a read-only role.</description>
<contact>info@acme.com</contact>
<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: XML Instance Data Set - Use case 2, Preloading access
control data

The following example is based on UC6 Storing diagnostics data. An
instance data set is produced by the YANG server every 15 minutes that
contains statistics about NETCONF. As a new set is produced
periodically multiple 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",
"target-uri":
"schema-uri": "file:///acme-netconf-diagnostics-yanglib.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 3: JSON Instance Data File example - UC6 Storing diagnostics
data

4. Data Life cycle

Data defined or documented in YANG instance data sets may be used for
preloading a YANG server with this data, but the server may populate
the data without using the actual file in which case

In UC2 "Preloading default configuration data" the instance
data file is only used as documentation.

While such data will usually not change, data documented by instance loaded data sets MAY may be
changed by the YANG server itself or later e.g. by management operations. It is out of scope for this document to specify a method
to prevent this. Whether such data changes and if so, when and how,
SHOULD be described either in In UC6 "Storing
Diagnostics data" the instance data set's description
statement or in some other implementation specific manner. diagnostics values may change on device every
second.

YANG instance data is a snap-shot of information at a specific point
of time. If the data changes afterwards this is not represented in
the instance data set anymore, the anymore. The valid values can be retrieved in
run-time via NETCONF/RESTCONF.

Notifications about NETCONF/RESTCONF or received e.g. in Yang-Push
notifications.

Whether the change of data documented by instance data
sets may changes and if so, when and how, SHOULD be supplied by e.g.
described either in the Yang-Push mechanism, but it is out
of scope for this document. instance data set's description statement or
in some other implementation specific manner.

5. Delivery of Instance Data

Instance data sets that are produced as a result of some sort of
specification or design effort SHOULD be available without the need
for a live YANG server e.g. via download from the vendor's website, or in
any other way product documentation is distributed.

Other instance data sets may be read from or produced by the YANG
server itself e.g. UC6 documenting diagnostic data.

6. Backwards Compatibility

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 target YANG model.
However as content-schema.

For instance data does use that is the result of a design or specification
activity some changes that may be good to avoid are listed. YANG
uses the concept of managed entities identified by key values values; if the following guidelines are provided:

o For list entries representing
connection between the same managed represented entity as
previously and the key values SHOULD NOT be changed. value is not
preserved during an update this may lead to problems.

o The meaning If the key value of a list entries, representing entry that represents the same managed
entity as previously, SHOULD NOT be changed e.g. before is changed, the user may mistakenly identify the
list entry as new.

o 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 should alarm-
type-id) the change may not be avoided. noticed.

o Keys for If the key value of a previously removed list entries SHOULD NOT be entry is reused if
they represent for
a different meaning. entity, the change may be mis-interpreted as
reintroducing the previous entity.

7. Yang Instance Data Model

7.1. Tree Diagram

The following tree diagram [RFC8340] provides an overview of the data
model.

module: ietf-yang-instance-data
structure instance-data-set:
+--rw name? string
+--rw (content-schema-spec)?
| +--:(inline)
| | +--rw inline-spec* string
| | +--rw inline-content-schema <anydata>
| +--:(uri)
| +--rw schema-uri? inet:uri
+--rw description? string
+--rw contact? string
+--rw organization? string
+--rw datastore? ds:datastore-ref
+--rw revision* [date]
| +--rw date string
| +--rw description? string
+--rw timestamp? yang:date-and-time
+--rw content-data? <anydata>

7.2. YANG Model

<CODE BEGINS> file "ietf-yang-instance-data.yang" "ietf-yang-instance-data@2019-07-04.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-data-ext ietf-yang-structure-ext { prefix yd; sx; }
import ietf-datastores { prefix ds; }
import ietf-inet-types { prefix inet; }
import ietf-yang-types { prefix yang; }
import ietf-yang-metadata { prefix "md"; }

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."; 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.

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 2019-02-20 2019-07-04 {
description "Initial revision.";
reference "RFC XXXX: YANG Instance Data Format";
}

yd:yang-data instance-data-format

md:annotation entity-tag {
type string;
description "Used to encode the entity-tag defined in
RFC8040 for the annotated instance.";
reference "RESTCONF Protocol RFC8040";
}

md:annotation last-modified {
container
type yang:date-and-time;
description "Contains the date and time when the annotated
instance was last modified (or created).";
reference "RESTCONF Protocol RFC8040";
}

sx:structure instance-data-set {
description "Auxiliary container "A data structure to carry meta-data define a format for a
YANG instance data set.Consists of meta-data about
the complete instance data set."; set and the real content-data.";

leaf name {
type string;
mandatory true;
description "Name of the YANG instance data set.";
}

choice target-ptr content-schema-spec {
description "A pointer to the list "Specification of target YANG modules
their revisions, supported features and deviations."; the content-schema";

case inline {
leaf-list inline-target-spec inline-spec {
type string {
pattern '.+@\d{4}-\d{2}-\d{2}\.yang';
}
min-elements 1;
ordered-by user;
description
"Indicates that target content defining Yang modules
are specified inline.
Each value MUST be a YANG Module name including the
revision-date as defined for YANG file names in RFC7950.

E.g. ietf-yang-library@2016-06-21.yang

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.
As some versions of ietf-yang-library MAY contain
different module-sets for different datastores, if
multiple module-sets are defined, included, the instance data set's
meta-data MUST contain the datastore information 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. a semantic version)."; version label).";
}
anydata target-modules inline-content-schema {
mandatory true;
description "Instance data corresponding to the YANG modules
specified in the inline-target-spec inline-spec nodes defining the set
of target content defining Yang YANG modules for this
instance-data-set.";
}
}

case uri {
leaf target-uri schema-uri {
type inet:uri;
description
"A reference to another YANG instance data file.
This instance data file will use the same set of target
YANG modules, revisions, supported features and deviations
as the referenced YANG instance data file.";
}
}
}

leaf

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. associated e.g. the datastore from
where the data was read or the datastore where the data
could be loaded or the datastore which is being documented.
If a single specific datastore can not be specified, the
leaf MUST be absent.

If this leaf is absent, then the datastore to which the
instance data belongs is undefined.";
}

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.

For instance data sets that are read from
or produced by the YANG a server or otherwise
subject to frequent updates or changes, revision
SHOULD NOT be present";

leaf date {
type string {
pattern '\d{4}-\d{2}-\d{2}';
}
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.

For instance data sets that are read from or produced
by the YANG a server or otherwise subject to frequent
updates or changes, timestamp SHOULD be present";
}

anydata content-data {
mandatory true;
description "Contains the real instance data.
The data MUST conform to the relevant YANG Modules.";
} Modules specified
either in the content-schema-spec or in some other
implementation specific manner.";
}
}
}
<CODE ENDS>

8. Security Considerations

Depending on the nature of the instance data, instance data files MAY
need to be handled in a secure way. The same type of handling should
be applied, that would be needed for the result of a <get> operation
returning the same data.

9. IANA Considerations

This document registers one URI and one YANG module.

9.1. URI Registration

This document registers one URI in the IETF XML registry [RFC3688].
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.

9.2. YANG Module Name Registration

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

10. Acknowledgments

For their valuable comments, discussions, and feedback, we wish to
acknowledge Andy Bierman, Juergen Schoenwaelder, Rob Wilton, Joe
Clark,
Clarke, Kent Watsen Martin Bjorklund, Ladislav Lhotka, Qin Wu and
other members of the Netmod WG.

11. References

11.1. Normative References

[I-D.ietf-netconf-nmda-netconf]
Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "NETCONF Extensions to Support the Network
Management Datastore Architecture", draft-ietf-netconf-
nmda-netconf-08 (work in progress), October 2018.

[I-D.ietf-netconf-nmda-restconf]
Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "RESTCONF Extensions to Support the Network
Management Datastore Architecture", draft-ietf-netconf-
nmda-restconf-05 (work in progress), October 2018.

[I-D.ietf-netmod-yang-data-ext]
Bierman, A., Bjorklund, M., and K. Watsen, "YANG Data
Structure Extensions", draft-ietf-netmod-yang-data-ext-01 draft-ietf-netmod-yang-data-ext-03
(work in progress), March 2018. April 2019.

[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.

[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>.

[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>.

[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.

[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>.

[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>.

[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>.

11.2. Informative References

[I-D.ietf-ccamp-alarm-module]
Vallin, S. and M. Bjorklund, "YANG Alarm Module", draft-
ietf-ccamp-alarm-module-07
ietf-ccamp-alarm-module-09 (work in progress), January April 2019.

[I-D.ietf-netconf-rfc7895bis]
Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K.,
and R. Wilton, "YANG Library", draft-ietf-netconf-
rfc7895bis-07 (work in progress), October 2018.

[I-D.ietf-netconf-yang-push]
Clemm, A., Voit, E., Prieto, A., Tripathy, A., Nilsen-
Nygaard, E., Bierman, A., A. and B. Lengyel, E. Voit, "Subscription to YANG Datastores", draft-ietf-netconf-yang-push-22
draft-ietf-netconf-yang-push-25 (work in progress), February May
2019.

[I-D.wu-netconf-restconf-factory-restore]
Wu, Q., Lengyel, B., and Y. Niu, "Factory default
Setting", draft-wu-netconf-restconf-factory-restore-03
(work in progress), October 2018.

[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>.

[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>.

Appendix A. Open Issues

o Augmenting metadata must be possible. As of now it looks like
yang-data-ext will solve that. If not, define instance data as
regular YANG instead of yd:yang-data. -

Appendix B. Changes between revisions

v02 - v03

o target renamed to "content-schema" and "content defining Yang
module(s)"

o Made name of instance data set optional

o Updated according to draft-ietf-netmod-tang-data-ext-02

o Clarified that entity-tag and last-modified timestamp are encoded
as metadata. While htey contain useful data, the HTTP-header
based encoding from Restconf is not suitable.

v01 - v02

o Removed design time from terminology

o Defined the format of the content-data part by referencing various
RFCs and drafts instead of the result of the get-data and get
operations.

o Changed target-ptr to a choice

o Inline target-ptr may include augmenting modules and alternatives
to ietf-yang-library

o Moved list of target modules into a separate <target-modules>
element.

o Added backwards compatibility considerations

v00 - v01

o Added the target-ptr metadata with 3 methods

o Added timestamp metadata

o Removed usage of dedicated .yid file extension

o Added list of use cases

o Added list of principles

o Updated examples

o Moved detailed use case descriptions to appendix

v05 - v00-netmod

o New name for the draft following Netmod workgroup adoption. No
other changes

v04 - v05

o Changed title and introduction to clarify that this draft is only
about the file format and documenting server capabilities is just
a use case.

o Added reference to draft-wu-netconf-restconf-factory-restore
o Added new open issues.

v03 - v04

o Updated changelog for v02-v03

v02 - v03

o Updated the document according to comments received at IETF102

o Added parameter to specify datastore

o Rearranged chapters

o Added new use case: Documenting Factory Default Settings

o Added "Target YANG Module" to terminology

o Clarified that instance data is a snapshot valid at the time of
creation, so it does not contain any later changes.

o Removed topics from Open Issues according to comments received at
IETF102

v01 - v02

o The recommendation to document server capabilities was changed to
be just the primary use-case. (Merged chapter 4 into the use case
chapter.)

o Stated that RFC7950/7951 encoding must be followed which also
defines (dis)allowed whitespace rules.

o Added UTF-8 encoding as it is not specified in t950 for instance
data

o added XML declaration

v00 - v01

o Redefined using yang-data-ext

o Moved metadata into ordinary leafs/leaf-lists

Appendix C. Detailed Use Cases - Non-Normative

C.1. Use Cases

We present a number of use cases were YANG instance data is needed.

C.1.1. Use Case 1: Early Documentation of Server Capabilities

A YANG 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. YANG server capabilities include

o data defined in ietf-yang-library: YANG modules, submodules,
features, deviations, schema-mounts, datastores supported
([I-D.ietf-netconf-rfc7895bis])

o alarms supported ([I-D.ietf-ccamp-alarm-module])

o data nodes, subtrees that support or do not support on-change
notifications ([I-D.ietf-netconf-yang-push])

o netconf-capabilities in ietf-netconf-monitoring

While it is good practice to allow a client to query these
capabilities from the live YANG 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 YANG server. During NMS implementation information
about server capabilities is needed. If the information is not
available early in some off-line document, but only as instance data
from the live network node, the NMS implementation will be delayed,
because it has to wait for the network node to be ready. Also
assuming that all NMS implementors will have a correctly configured
network node available to retrieve data from, is a very expensive
proposition. (An NMS may handle dozens of node types.)

Network operators often build their own home-grown NMS systems that
needs 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 Yang server's 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 addition or removal of HW. They are
usually defined by a vendor at design time, before the product is
released. It 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.

C.1.2. Use Case 2: Preloading Data

There are parts of the configuration that must be fully configurable
by the operator, however for which 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 pre-defines 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.

C.1.3. Use Case 3: Documenting Factory Default Settings

Nearly every YANG server has a factory default configuration. If the
system is really badly misconfigured or if the current configuration
is to be abandoned the system can be reset to this default.

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 reset-datastore operation for the same purpose
[I-D.wu-netconf-restconf-factory-restore]

The operator currently has no way to know what the default
configuration actually contains. YANG instance data can be used to
document the factory default configuration.

Authors' Addresses
Balazs Lengyel
Ericsson
Magyar Tudosok korutja 11
1117 Budapest
Hungary

Phone: +36-70-330-7909
Email: balazs.lengyel@ericsson.com

Benoit Claise
Cisco Systems, Inc.
De Kleetlaan 6a b1
1831 Diegem
Belgium

Phone: +32 2 704 5622
Email: bclaise@cisco.com