| Netmod | B. Lengyel |
| Internet-Draft | Ericsson |
| Intended status: Standards Track | B. Claise |
| Expires: June 9, 2019 | Cisco Systems, Inc. |
| December 6, 2018 |
YANG Instance Data File Format
draft-ietf-netmod-yang-instance-file-format-01
There is a need to document data defined in YANG models when a live YANG server is not available. Data is often needed already in design 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 existing formats from <get> operation/request and decorates them with metadata.
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Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved.
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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.
Design time: A time during which a YANG model and the implementation behind it is created. Sometimes in other documents this period is divided into design and implementation time.
Instance Data Set: A named set of data items 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 in design 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 format returned for a NETCONF GET operation. The <content-data> anydata node SHALL contain all elements that would be inside the <data> wrapper element of a reply to the <get> operation. Some XML attributes (e.g. metadata like origin) MAY be absent. SW handling YANG instance data MUST ignore XML attributes unknown to it, allowing them to be used later for other purposes.
The content-data part of the JSON format SHALL follow the format of the payload of the reply returned for a RESTCONF GET request directed at the datastore resource: {+restconf}/data or {+restconf}/ds/<datastore>.
Instance data MUST conform to the corresponding target YANG Modules and follow the XML/JSON encoding rules as defined in [RFC7950] and [RFC7951] and MUST use UTF-8 character encoding. 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 3 options SHALL be used:
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 the compatibility between the specified target and the real-life target YANG module set (considering modules, revisions, features, deviations).
Target-ptr MUST bet set to:
The revision date in the inline target-ptr is mandatory, it specifies the revision of the ietf-yang-library used. The first group of data inside the "anydata data" element MUST be instance data targeted at the ietf-yang-library. This data SHALL specify the target YANG modules, revisions, supported features and deviations for this and all the other target YANG modules.
Target-ptr MUST bet set to 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 other 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 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>
<target-ptr>inline:ietf-yang-library@2016-06-21.yang</target-ptr>
<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>
<feature>sys:ntp</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>
</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>
<target-ptr>inline:ietf-yang-library@2016-06-21.yang</target-ptr>
<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>
<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-acm</name>
<revision>2012-02-22</revision>
</module>
</module-state>
<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 automatically a revision-date would be useless; instead a timestamp is included.
{
"ietf-yang-instance-data:instance-data-set": {
"name": "acme-router-netconf-diagnostics",
"target-ptr": "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 file 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.
<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 2018-11-30 {
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.";
}
leaf target-ptr {
type union {
type string {
pattern 'inline:ietf-yang-library@\d{4}-\d{2}-\d{2}\.yang';
}
type inet:uri;
}
description "A pointer to the list of target YANG modules
their revisions, supported features and deviations.
target-ptr SHALL use one of the following formats:
IN-LINE format: target-ptr should bet set to:
'inline:ietf-yang-library@' revision-date '.yang'
E.g. inline:ietf-yang-library@2016-06-21.yang
The revision date is mandatory. When using the in-line
format the first group of data inside the content-data
node MUST be instance data targeted at the
ietf-yang-library. This data SHALL specify the target YANG
modules, revisions, supported features and deviations for
this and all the other target YANG modules of the set.
URI format. target-ptr MUST be a URI that references
another YANG instance data file.
This instance data file will use the same set of target
YANG modules, revisions, supported features and deviations
as this other 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-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. |
| [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. |
| [I-D.ietf-ccamp-alarm-module] | Vallin, S. and M. Bjorklund, "YANG Alarm Module", Internet-Draft draft-ietf-ccamp-alarm-module-06, November 2018. |
| [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-20, October 2018. |
| [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. |
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 in 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.