| Netmod | B. Lengyel |
| Internet-Draft | Ericsson |
| Intended status: Standards Track | B. Claise |
| Expires: August 30, 2019 | Cisco Systems, Inc. |
| February 26, 2019 |
YANG Instance Data File Format
draft-ietf-netmod-yang-instance-file-format-02
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.
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Copyright (c) 2019 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.
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.
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: A YANG module for which the instance data set contains instance data, like ietf-yang-library in the examples.
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.
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.
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.
The following is a list of the basic principles of the instance data format:
A YANG instance data file MUST contain a single instance data set and no additional data.
The instance data set is placed in a top level auxiliary container named "instance-data-set". An instance data set 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 anydata datanode, this carries the "real data" that we want to document/provide. The syntax and semantics of content-data is defined by the target YANG modules.
Two formats are specified that can be used to represent YANG instance data based on the XML and JSON encoding. 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.
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 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 constrains MAY be violated.
The name of the file SHALL be of the form:
The revision date is optional. ".filetype" SHALL be ".json" or ".xml" according to the format used.
Metadata, information about the data set itself SHALL be included in the instance data set. This data will be children of the top level instance-data-set container as defined in the ietf-instance-data YANG module. Metadata MUST include:
Metadata SHOULD include:
Metadata MAY include:
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. One of the following options SHOULD be used:
Additional methods e.g. a YANG-package based solution may be added later.
Note, the specified target YANG modules only indicate 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. 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.
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.
As some versions of ietf-yang-library MAY contain different module-sets for different datastores, if multiple module-sets are defined, 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 inline-target-spec elements MAY specify YANG modules augmenting the first module with useful data (e.g. a semantic version).
When using the inline method a 'target-modules' element MUST be present. This SHALL contain instance data corresponding to the YANG modules specified in the inline-target-spec elements specifying the set of target YANG modules for this instance-data-set.
A target-uri element 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 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 is advantageous when the user wants to avoid the overhead of 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.
The referenced YANG instance data file might use the in-line 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 method.
If a referenced instance data file is not available the revision data, supported features and deviations for the target YANG modules are unknown.
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 the target-ptr.
<?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>
ietf-yang-library@2016-06-21.yang
</inline-target-spec>
<target-modules>
<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>
<revision>
<date>2108-01-25</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>
<!-- The example lists only 4 modules, but it could list the
full set of supported modules for a YANG server, potentially many
dozens of modules -->
<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 the target-ptr.
<?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 xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
<module>
<name>ietf-netconf-acm</name>
<revision>2012-02-22</revision>
</module>
</module-state>
</target-modules>
<revision>
<date>2018-01-25</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 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": "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
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 the instance data file is only used as documentation.
While such data will usually not change, data documented by instance data sets MAY be changed by the YANG server itself or 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 the instance data set's description statement or in some other implementation specific manner.
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 valid values can be retrieved in run-time via NETCONF/RESTCONF.
Notifications about the change of data documented by instance data sets may be supplied by e.g. the Yang-Push mechanism, but it is out of scope for this document.
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.
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 instance data does use the concept of managed entities identified by key values the following guidelines are provided:
<CODE BEGINS> file "ietf-yang-instance-data.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 { prefix yd; }
import ietf-datastores { prefix ds; }
import ietf-inet-types { prefix inet; }
import ietf-yang-types { prefix yang; }
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.";
revision 2019-02-20 {
description "Initial revision.";
reference "RFC XXXX: YANG Instance Data Format";
}
yd:yang-data instance-data-format {
container instance-data-set {
description "Auxiliary container to carry meta-data for
the complete instance data set.";
leaf name {
type string;
mandatory true;
description "Name of the YANG instance data set.";
}
choice target-ptr {
description "A pointer to the list of target YANG modules
their revisions, supported features and deviations.";
case inline {
leaf-list inline-target-spec {
type string {
pattern '.+@\d{4}-\d{2}-\d{2}\.yang';
}
min-elements 1;
ordered-by user;
description
"Indicates that target 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, 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).";
}
anydata target-modules {
mandatory true;
description "Instance data corresponding to the YANG modules
specified in the inline-target-spec nodes defining the set
of target YANG modules for this instance-data-set.";
}
}
case uri {
leaf target-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 description { type string; }
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. 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 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; }
}
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 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.";
}
}
}
}
<CODE ENDS>
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.
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 Clark, Martin Bjorklund, Ladislav Lhotka, Qin Wu and other members of the Netmod WG.
| [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", Internet-Draft draft-ietf-netconf-nmda-netconf-08, 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", Internet-Draft draft-ietf-netconf-nmda-restconf-05, October 2018. |
| [I-D.ietf-netmod-yang-data-ext] | Bierman, A., Bjorklund, M. and K. Watsen, "YANG Data Extensions", Internet-Draft draft-ietf-netmod-yang-data-ext-01, March 2018. |
| [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. |
| [RFC6243] | Bierman, A. and B. Lengyel, "With-defaults Capability for NETCONF", RFC 6243, DOI 10.17487/RFC6243, June 2011. |
| [RFC7950] | Bjorklund, M., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016. |
| [RFC7951] | Lhotka, L., "JSON Encoding of Data Modeled with YANG", RFC 7951, DOI 10.17487/RFC7951, August 2016. |
| [RFC7952] | Lhotka, L., "Defining and Using Metadata with YANG", RFC 7952, DOI 10.17487/RFC7952, August 2016. |
| [RFC8040] | Bierman, A., Bjorklund, M. and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017. |
| [I-D.ietf-ccamp-alarm-module] | Vallin, S. and M. Bjorklund, "YANG Alarm Module", Internet-Draft draft-ietf-ccamp-alarm-module-07, January 2019. |
| [I-D.ietf-netconf-rfc7895bis] | Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K. and R. Wilton, "YANG Library", Internet-Draft draft-ietf-netconf-rfc7895bis-07, October 2018. |
| [I-D.ietf-netconf-yang-push] | Clemm, A., Voit, E., Prieto, A., Tripathy, A., Nilsen-Nygaard, E., Bierman, A. and B. Lengyel, "Subscription to YANG Datastores", Internet-Draft draft-ietf-netconf-yang-push-22, February 2019. |
| [I-D.wu-netconf-restconf-factory-restore] | Wu, Q., Lengyel, B. and Y. Niu, "Factory default Setting", Internet-Draft draft-wu-netconf-restconf-factory-restore-03, 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. |
| [RFC8174] | Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017. |
v01 - v02
v00 - v01
v05 - v00-netmod
v04 - v05
v03 - v04
v02 - v03
v01 - v02
v00 - v01
We present a number of use cases were YANG instance data is needed.
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
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 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.
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.
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.