New YANG Module Update Procedure
draft-clacla-netmod-yang-model-update-03
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
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|---|---|---|---|
| Authors | Benoît Claise , Joe Clarke , Balázs Lengyel , Kevin D'Souza | ||
| Last updated | 2017-12-15 (Latest revision 2017-11-11) | ||
| Replaced by | draft-verdt-netmod-yang-semver, draft-verdt-netmod-yang-semver | ||
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draft-clacla-netmod-yang-model-update-03
Network Working Group B. Claise
Internet-Draft J. Clarke
Updates: 7950 (if approved) Cisco Systems, Inc.
Intended status: Standards Track B. Lengyel
Expires: June 18, 2018 Ericsson
K. D'Souza
AT&T
December 15, 2017
New YANG Module Update Procedure
draft-clacla-netmod-yang-model-update-03
Abstract
This document specifies a new YANG module update procedure in case of
backward-incompatible changes, as an alternative proposal to the YANG
1.1 specifications. This document updates RFC 7950.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 18, 2018.
Copyright Notice
Copyright (c) 2017 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
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. The Problems . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Slow Standardization . . . . . . . . . . . . . . . . . . 3
2.2. Some YANG Modules are Not Backward Compatible . . . . . . 3
2.3. Non-Backward Compatible Errors . . . . . . . . . . . . . 4
2.4. A Zoo of YANG Modules . . . . . . . . . . . . . . . . . . 4
2.5. YANG Modules Obsolete Relationship . . . . . . . . . . . 5
2.6. YANG Module Transition Strategy . . . . . . . . . . . . . 6
2.7. Need to Allow Non-Backward Compatible changes . . . . . . 6
2.8. Problematic Handling of Status Statement . . . . . . . . 7
2.9. No way to easily decide whether a change is Backward
Compatible . . . . . . . . . . . . . . . . . . . . . . . 7
2.10. Early Warning about Removal . . . . . . . . . . . . . . . 8
3. The Solution . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. SEMVER Semantic Versioning . . . . . . . . . . . . . . . 9
3.2. Updates to YANG 1.1 status statement . . . . . . . . . . 11
3.3. Updating the YANG 1.1 Module Update rules . . . . . . . . 11
3.4. The Derived Semantic Version . . . . . . . . . . . . . . 11
3.5. Import by Semantic Version . . . . . . . . . . . . . . . 12
4. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 13
5. Semantic Version Extension YANG Module . . . . . . . . . . . 14
6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
The YANG data modeling language [RFC7950] specifies strict rules for
updating YANG modules (see section 11 "Updating a Module"). Citing a
few of the relevant rules:
1. "As experience is gained with a module, it may be desirable to
revise that module. However, changes to published modules are
not allowed if they have any potential to cause interoperability
problems between a client using an original specification and a
server using an updated specification."
2. "Note that definitions contained in a module are available to be
imported by any other module and are referenced in "import"
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statements via the module name. Thus, a module name MUST NOT be
changed. Furthermore, the "namespace" statement MUST NOT be
changed, since all XML elements are qualified by the namespace."
3. "Otherwise, if the semantics of any previous definition are
changed (i.e., if a non-editorial change is made to any
definition other than those specifically allowed above), then
this MUST be achieved by a new definition with a new identifier."
4. "deprecated indicates an obsolete definition, but it permits new/
continued implementation in order to foster interoperability with
older/existing implementations."
What are the consequences?
1. Ideally, the YANG module names should not be changed due the
importance of not changing the automation code in case of import
statements or service composition at the orchestration layer.
2. When the same YANG module name is kept, its new revision must be
updated in a backward-compatible way.
3. While most of the non-backward compatible changes are prohibited,
a client still does not know if a changed module is backward
compatible, as a server may remove parts of a module after
marking it deprecated or obsolete.
2. The Problems
This section lists a series of problems, hopefully listed in a
logical order, which leads to the solution in the next section.
2.1. Slow Standardization
The conclusions drawn in the introduction lead to the logical
conclusion that the standardized YANG modules have to be perfect on
day one (at least the structure), which in turn might explain why all
the IETF YANG modules take so long to standardize. Shooting for
perfection (at least in structure) is obviously a noble goal, but if
the perfect standard comes too late, it doesn't help the industry.
2.2. Some YANG Modules are Not Backward Compatible
As we learn from our mistakes, we're going to face more and more
backward-incompatible YANG modules. An example is the YANG data
model for L3VPN service delivery [RFC8049], which, based on
implementation experience, must be updated in a backward-incompatible
way with draft-wu-l3sm-rfc8049bis [I-D.wu-l3sm-rfc8049bis].
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While Standards Development Organization (SDO) YANG modules are
obviously better for the industry, we must recognize that many YANG
modules are actually generated YANG modules (for example, from
internal databases), also known as native YANG modules, or vendor
modules [RFC8199]. From time to time, the new YANG modules are not
backward-compatible.
In such cases, it would be better to indicate how backward-compatible
a given YANG module actually is.
2.3. Non-Backward Compatible Errors
Sometimes small errors force us to make non-backward compatible
updates. As an example imagine that we have a string with a complex
pattern (e.g., an IP address). Let's assume the initial pattern
incorrectly allows IP addresses to start with 355. In the next
version this is corrected to disallow addresses starting with 355.
Formally this is an non-backward compatible change as the value space
of the string is decreased. In reality an IP address and the
implementation behind it was never capable of handling an address
starting with 355. So practically this is a backward compatible
change, just like a correction of the description statement. Still
current YANG rules would force a module name change.
2.4. A Zoo of YANG Modules
Even if we focus on the IETF, we have to observe that many SDOs,
opensource fora, and vendors develop YANG modules. This should be
considered a success for an IETF developed technology. However, the
operators are faced with this problem: how to select the YANG modules
to take into account for their service developments.
The site <https://www.yangcatalog.org> (and the YANG catalog that it
provides: YANG module for yangcatalog.org,
[I-D.clacla-netmod-model-catalog]) is an attempt to become a
reference for all YANG modules available in the industry, for both
YANG developers to search on what exists already) and for operators
(to discover the more mature YANG models to automate services). This
YANG catalog should not only contain pointers to the YANG modules
themselves, but also contain metadata related to those YANG modules:
What is the module type (service model or not?); what is the maturity
level? (e.g., for the IETF: is this an RFC, a working group document
or an individual draft?); is this module implemented?; who is the
contact?; is there open-source code available? And we expect many
more in the future. The industry has begun to understand that the
metadata related to YANG models become equally important as the YANG
models themselves.
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The yangcatalog.org instantiation of the catalog provides a means for
module authors and vendors implementing modules to upload their
metadata, which is then searchable via an API, as well as using a
variety of web-based tools. The instructions for contributing and
searching for metadata can be found at <https://www.yangcatalog.org/
contribute.php>.
The issue is actually the number of YANG modules the operators are
offered. At the time of writing this document, the number of unique
YANG modules in the catalog is exactly 2596 (and that number keeps
growing), while the IETF has standardized or is busy standardizing a
small subset of those. Therefore, it's important to distinguish the
relevant YANG modules with the pack and to understand the
relationship between the YANG modules.
2.5. YANG Modules Obsolete Relationship
So the operators use the yangcatalog.org to discover which YANG
modules they can use NOW. They base their selection not only on the
YANG module content, but also on the related metadata. When faced
with the zoo of the YANG modules, it's difficult to understand the
relationship between YANG modules. As an example: how could an
operator discover that YANG-MODULE-B obsoletes YANG-MODULE-A?
Indeed, both have different YANG module names. The only available
information is an "obsolete" tag in the published RFC containing
YANG-MODULE-B: this tag would point to YANG-MODULE-A. In the world
of automation, going through a published RFC as a level of
indirection to understand the YANG module obsolete relationship is a
non-starter. Food for thought: the IETF should stop thinking that
the metric for success is an RFC number, as opposed to the contained
YANG module(s).
We need an automatic way to discover that a YANG-MODULE-B obsoletes
YANG-MODULE-A, so that YANG-MODULE-A should not be given any
attention.
The following example is not an automatic way.
description
"This YANG module defines a generic service configuration
model for Layer 3 VPNs. This model is common across all
vendor implementations. This obsoletes the RFC8049 YANG
module, ietf-l3vpn-svc@2017-01-2";
revision 2017-09-14 {
description
"First revision of RFC8049.";
reference
"RFC xxxx: YANG Data Model for L3VPN Service Delivery";
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Along the same lines, while going through an out-of-band tool such as
the yangcatalog.org in order to discover the obsolete relationship is
a possible automatic way, it is not ideal.
2.6. YANG Module Transition Strategy
Let's assume for a moment that we change the YANG module, with the
specific example of ietf-routing, which some propose to update to
ietf-routing-2.
Here are all the ietf-routing dependent YANG modules (those modules
that depend on ietf-routing) <https://www.yangcatalog.org/yang-
search/impact_analysis.php?modules[]=ietf-
routing&recurse=0&rfcs=1&show_subm=1&show_dir=dependents>. So many
YANG modules.
Let's look at the difference for ietf-routing-2:
<https://www.yangcatalog.org/yang-search/
impact_analysis.php?modules[]=ietf-routing-
2&recurse=0&rfcs=1&show_subm=1&show_dir=dependents>.
Changing the module name from ietf-routing to ietf-routing-2 implies
that the we have to warn all draft authors of ietf-routing YANG
dependent modules. First, to make sure they are aware of ietf-
routing-2 (publishing a RFC8022bis mentioning in the module
description that this module is not compatible with the NMDA
architecture, and providing a pointer to ietf-routing-2 ... is not an
automatic way... so barely useful). And second, to ask them to
change their import (or service composition) to ietf-routing-2.
Hopefully, in the ietf-routing case, most dependent YANG modules are
part of the IETF, so the communication is a manageable. For the
already existing dependent vendor modules the problem is worse.
Changing the ietf-interfaces YANG module name would be a different
challenge, as it's used throughout the industry:
<https://www.yangcatalog.org/yang-search/
impact_analysis.php?modules[]=ietf-
interfaces&recurse=0&rfcs=1&show_subm=1&show_dir=dependents>
2.7. Need to Allow Non-Backward Compatible changes
As described in the previous sections, there is a need to allow non-
backward compatible changes without changing a module's name. This
would avoid many of the above problems. In most cases even after
non-backward compatible updates a module should keep its name.
However, for really major changes renaming the module is still the
proper way to go:
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when splitting a module into two separate modules
when removing 80% of a module's schema
when a standard module is moved from one organization to another
(e.g., from ietf to ieee)
when a company's name is changed and new versions of the module
are renamed to reflect that
Allowing non-backward compatible changes to happen without a module
name change will decrease the number of separate modules to handle
and will make it a trivial task to track these non-backward
compatible changes.
2.8. Problematic Handling of Status Statement
The current definition of deprecated and obsolete in [RFC7950] (as
quoted below) is problematic and should be corrected.
o "deprecated" indicates an obsolete definition, but it permits new/
continued implementation in order to foster interoperability with
older/existing implementations.
o "obsolete" means that the definition is obsolete and SHOULD NOT be
implemented and/or can be removed from implementations.
YANG is considered an interface contract between the server and the
client. The current definitions of deprecated and obsolete mean that
a schema node that is either deprecated or obsolete may or may not be
implemented. The client has no way to find out which is the case
except for by trying to write or read data at the leaf in question.
This probing would need to be done for each separate data-node, which
not a trivial thing to do. This "may or may not" is unacceptable in
a contract. In effect, this works as if there would be an if-feature
statement on each deprecated schema node where the server does not
advertise whether the feature is supported or not. Why is it not
advertised?
2.9. No way to easily decide whether a change is Backward Compatible
A management system, SDN controller or any other user of a module
should be capable of easily determining the compatibility between two
module versions. Higher level logic for a network function,
something that can not be implemented in a purely model driven way,
is always dependent on a specific version of the module. If the
client finds that the module has been updated on the network node, it
has to decide if it tries to handle it as it handled the previous
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version of the model or if it just stops, to avoid problems. To make
this decision the client needs to know if the module was updated in a
backward compatible way or not.
This is not possible to decide today because of the following:
o It is possible to change the semantic behavior of a data node,
action or rpc while the YANG definition does not change (with the
possible exception of the description statement). In such a case
it is impossible to determine whether the change is backward
compatible just by looking at the YANG statements. Its only the
human model designer that can decide.
o Problems with the status statement, Section 2.8
o Modelers might decide to violate YANG 1.1 update rules for some of
the reasons above
Finding status changes or violations of update rules need a line by
line comparision of the old and new modules, no easy task.
2.10. Early Warning about Removal
If a schema part is considered old/bad we need to be able to give
advance warning that it will be removed. As this is an advance
warning the part shall still be present and usable in the current
revision; however, it will be removed in one of the next revisions.
We need the advance warning to allow users of the module time enough
to plan/execute migration away from the deprecated functionality.
Often deprecation will be accompanied by information whether the
functionality will just disappear or that there is an alternative,
possibly more advanced solution that should be used.
Vendors use such warnings often, but the NMDA related redesign of
IETF modules is also an example where it would be useful. (As
another example see the usage of deprecated in the Java programing
language.) The current definition of the deprecated status does not
serve this purpose as described in Section 2.8. The definition of
"deprecated" in the status statement shall be changed to address this
issue.
3. The Solution
The solution is composed of four parts, a semantic versioning YANG
extension, updates to the YANG 1.1. status statement and module
update rules and the import by version statement. An optional
additional check, validating the semantic versioning from a syntactic
point of view, can either assist in determining the correct semantic
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versioning values, or can help in determining the values for YANG
modules that don't support this extension.
3.1. SEMVER Semantic Versioning
The semantic versioning solution proposed here has already been
proposed in [I-D.openconfig-netmod-model-catalog] (included here with
the authors permission)which itself is based on [openconfigsemver].
The goal is to indicate the YANG module backwards (in)compatibility,
following semver.org semantic versioning [semver]:
"The SEMVER version number for the module is introduced. This is
expressed as a semantic version number of the form: x.y.z
o x is the MAJOR version. It is incremented when the new version of
the specification is incompatible with previous versions.
o y is the MINOR version. It is incremented when new functionality
is added in a manner that is backward-compatible with previous
versions.
o z is the PATCH level. It is incremented when bug fixes are made
in a backward-compatible manner.
Along these lines, we propose the following YANG 1.1 extension for a
more generic semantic version. The formal definition is found at the
end of this document.
extension module-version {
argument "semver" {
yin-element false;
}
}
The extension would typically be used this way:
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module yang-module-name {
namespace "name-space";
prefix "prefix-name";
import ietf-semver { prefix "semver"; }
description
"to be completed";
revision 2017-10-30 {
description
"Change the module structure";
semver:module-version "2.0.0";
}
revision 2017-07-30 {
description
"Added new feature XXX";
semver:module-version "1.2.0";";
}
revision 2017-04-03 {
description
"Update copyright notice.";
semver:module-version "1.0.1";;
}
revision 2017-04-03 {
description
"First release version.";
semver:module-version "1.0.0";;
}
revision 2017-01-26 {
description
"Initial module for inet types";
semver:module-version "0.1.0";;
}
//YANG module definition starts here
See also "Semantic Versioning and Structure for IETF Specifications"
[I-D.claise-semver] for a mechanism to combine the semantic
versioning, the github tools, and a potential change to the IETF
process.
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3.2. Updates to YANG 1.1 status statement
RFC 7950 section 11, must be updated to change the definition of
deprecated and obsolete. In both cases the client must be able to
determine whether the relevant parts are implemented or not without
probing. The following definition is proposed:
o Deprecated schema nodes MUST still work as defined. The
deprecated status serves only as a a warning that the schema node
will be removed or obsoleted in the future.
o Obsolete schema nodes MUST be removed from the implementation.
Requests concerning these schema nodes MUST be rejected with:
* error-tag: operation-failed
* error-app-tag: obsolete element
If there is a need to allow the server to decide whether a
deprecated/obsolete schema part is implemented YANG already has a
facility for that: the feature statement. Use it!
3.3. Updating the YANG 1.1 Module Update rules
RFC 7950 section 11, must be updated to express:
"As experience is gained with a module, it may be desirable to revise
that module. Changes to published modules are allowed, even if they
have some potential to cause interoperability problems, if the
module-version YANG extension is used in the revision statement to
clearly indicate the nature of the change."
3.4. The Derived Semantic Version
The YANG catalog contains not only the most up-to-date YANG module
revision of a given module, but keeps all previous revisions as well.
With APIs in mind, it's important to understand whether different
YANG module revisions are backward compatible (this is specifically
imported for native YANG modules, i.e. the ones where generated-from
= native), even for the YANG modules that don't support the YANG
extension specified in this document.
Two distinct leaves in the YANG module
[I-D.clacla-netmod-model-catalog] contain this semver notation:
o the semantic-version leaf contains the value embedded within a
YANG module (if it is available).
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o the derived-semantic-version leaf is established by examining the
the YANG module themselves. As such derived-semantic-version only
takes syntax into account as opposed to the meaning of various
elements when it computes the semantic version.
o The algorithm used to produce the derived-semantic-version is as
follows:
1. Order all modules of the same name by revision from oldest to
newest. Include module revisions that are not available, but
which are defined in the revision statements in one of the
available module versions.
2. If module A, revision N+1 has failed compilation, bump its
derived semantic MAJOR version. For unavailable module
versions assume non-backward compatible changes were done.,
thus bump its derived semantic MAJOR version.
3. Else, run "pyang --check-update-from" on module A, revision N
and revision N+1 to see if backward-incompatible changes
exist.
4. If backward-incompatible changes exist, bump module A,
revision N+1's derived MAJOR semantic version.
5. If no backward-incompatible changes exist, compare the pyang
trees of module A, revision N and revision N+1.
6. If there are structural differences (e.g., new nodes), bump
module A, revision N+1's derived MINOR semantic version.
7. If no structural differences exist, bump module A, revision
N+1's derived PATCH semantic version.
Note that the absolute numbers in the semantic-version and derived-
semantic-version are actually meaningless by themselves. That is,
one must compare two different semver values for a given module to
understand the compatibility between them.
3.5. Import by Semantic Version
If a module is imported by another one, it is usually not specified
which version of the imported module should be used. However not all
versions may be acceptable. Today YANG 1.1 allows us to specify the
revision date of the imported module, but that is too specific, as
even a small spelling correction of the imported module results in a
change to its revision date, thus making the module revision
ineligible for import.
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Using semantic versioning to indicate the acceptable imported module
versions is much more flexible.
o We might indicate that any compatible module-version after e.g.
3.1.0 is acceptable
o We might indicate that any compatible module-version of the 3.1.0,
4.0.0 or 5.0.0 major versions is acceptable. Later depending on
updates in the 6.0.0 series we might allow those revisions also to
be imported. As an non-backward compatible change in the 6.0.0
line might just change a small part of the imported module, the
non-backward compatible changes may or may not affect the
importer.
The module-version statement SHOULD be a substatement of the import
statement. An import statement MUST NOT contain both a module-
version and a revision substatement. The use of the revision
substatement of import should be discouraged/deprecated.
4. Open Issues
There are a number of open issues to be disccused. These include the
following:
o Do we need include-by-Semver?
o Should IETF/IANA officially generate derived semantic versions for
their own modules? As they are the owner of the modules it should
be their responsibility, but how to document it?
o There are cases where the module's name should be changed but we
still want to formally document the connection between the old and
the new module names. For these cases shall we introduce a new
YANG extension statement
o "replaces-module ietf-vlan;" ?
o We could consider a new naming convention for module files.
Today, module files are named using a module@revision.yang
notation. We could consider a module%semver.yang variant. Re-
using the '@' for version is not ideal, so another separator
character should be used. In this manner, both version and
revision could be used.
o Taking another page from Openconfig, the notion of a module bundle
could be considered. That is, there may need to be a way to
enumerate modules that are part of a bundle and are known to
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interoperate. This may not be as critical if a rich import-by-
version is defined.
While the issue is interesting, it will be not be handled in this
document.
o Similarly, the concept of a feature bundle should be considered.
Typically, operators combine and test YANG modules to build value-
add services. These bundles form releases for specific features
or services, and it is critical to ensure as the modules evolve,
the bundles can coherently evolve with them.
While the issue is interesting, it will be not be handled in this
document.
o When we'll start using this new procedure for a new YANG module
revision, will we have to update all the dependent YANG modules to
start using this new procedure, along with the new import
statement? Is this a moot point, as a new YANG module name would
suffer from the same symptoms?
We see no need for updating other dependent modules. It is a good
idea to update them, as they will benefit from using SEMVER,
however there is no specific need to update them.
5. Semantic Version Extension YANG Module
The extension described in this module is defined in the YANG module
below.
<CODE BEGINS> file "ietf-semver@2017-12-15.yang"
module ietf-semver {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-semver";
prefix semver;
organization
"IETF NETMOD (Network Modeling) Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/netmod/>
WG List: <mailto:netmod@ietf.org>
Author: Benoit Claise
<mailto:bclaise@cisco.com>
Author: Joe Clarke
<mailto:jclarke@cisco.com>
Author: Kevin D'Souza
<mailto:kd6913@att.com>
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Author: Balazs Lengyel
<mailto:balazs.lengyel@ericsson.com>";
description
"This module contains a definition for a YANG 1.1 extension to
express the semantic version of YANG modules.";
revision 2017-12-15 {
description
"Initial revision.";
reference "draft-clacla-netmod-yang-model-update:
New YANG Module Update Procedure";
semver:module-semver 0.1.1;
}
extension module-version {
argument semver;
description
"The version number for the module revision it is used in.
This is expressed as a semantic version string in the form:
x.y.z
where:
* x corresponds to the major version,
* y corresponds to a minor version,
* z corresponds to a patch version.
A major version number of 0 indicates that this model is still
in development, and is potentially subject to change.
Following a release of major version 1, all modules will
increment major revision number where backwards incompatible
changes to the model are made.
The minor version is changed when features are added to the
model that do not impact current clients use of the model.
When major version is stepped, the minor version is reset to 0.
The patch-level version is incremented when non-feature changes
(such as bugfixes or clarifications to human-readable
descriptions that do not impact model functionality) are made
that maintain backwards compatibility.
When major or minor version is stepped, the patch-level is
reset to 0.
The version number is stored in the module meta-data.
By comparing the module-version between two revisions of a
given module, one can know if revision N+1 is backwards
compatible or not relative to revision N, as well as
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whether or not new features have been added to revision N+1.
If a module contains this extension it indicates that for this
module the updated status and update rules as this described in
RFC XXXX are used.
The statement MUST only be a substatement of the revision,
import or include statements.
Zero or One module-version statement is allowed per parent
statement. NO substatements are allowed.
";
reference "http://semver.org/ : Semantic Versioning 2.0.0";
}
augment /yanglib:modules-state/yanglib:module {
leaf module-version {
type string {
pattern "[0-9]+.[0-9]+.[0-9]+";
}
}
}
augment /yanglib:modules-state/yanglib:module/yanglib:submodule {
leaf submodule-version {
type string {
pattern "[0-9]+.[0-9]+.[0-9]+";
}
}
}
}
<CODE ENDS>
6. Contributors
o Anees Shaikh, Google
o Rob Shakir, Google
7. Security Considerations
The document does not define any new protocol or data model. There
are no security impacts.
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8. IANA Considerations
No IANA action is requested.
9. References
9.1. Normative References
[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>.
9.2. Informative References
[I-D.clacla-netmod-model-catalog]
Clarke, J. and B. Claise, "YANG module for
yangcatalog.org", draft-clacla-netmod-model-catalog-02
(work in progress), October 2017.
[I-D.claise-semver]
Claise, B., Barnes, R., and J. Clarke, "Semantic
Versioning and Structure for IETF Specifications", draft-
claise-semver-01 (work in progress), July 2017.
[I-D.openconfig-netmod-model-catalog]
Shaikh, A., Shakir, R., and K. D'Souza, "Catalog and
registry for YANG models", draft-openconfig-netmod-model-
catalog-02 (work in progress), March 2017.
[I-D.wu-l3sm-rfc8049bis]
Wu, Q., Litkowski, S., Tomotaki, L., and K. Ogaki, "YANG
Data Model for L3VPN Service Delivery", draft-wu-l3sm-
rfc8049bis-11 (work in progress), December 2017.
[openconfigsemver]
"Semantic Versioning for Openconfig Models",
<http://www.openconfig.net/docs/semver/>.
[RFC8049] Litkowski, S., Tomotaki, L., and K. Ogaki, "YANG Data
Model for L3VPN Service Delivery", RFC 8049,
DOI 10.17487/RFC8049, February 2017, <https://www.rfc-
editor.org/info/rfc8049>.
[RFC8199] Bogdanovic, D., Claise, B., and C. Moberg, "YANG Module
Classification", RFC 8199, DOI 10.17487/RFC8199, July
2017, <https://www.rfc-editor.org/info/rfc8199>.
[semver] "Semantic Versioning 2.0.0", <https://www.semver.org>.
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Authors' Addresses
Benoit Claise
Cisco Systems, Inc.
De Kleetlaan 6a b1
1831 Diegem
Belgium
Phone: +32 2 704 5622
Email: bclaise@cisco.com
Joe Clarke
Cisco Systems, Inc.
7200-12 Kit Creek Rd
Research Triangle Park, North Carolina
United States of America
Phone: +1-919-392-2867
Email: jclarke@cisco.com
Balazs Lengyel
Ericsson
Magyar Tudosok Korutja
1117 Budapest
Hungary
Phone: +36-70-330-7909
Email: balazs.lengyel@ericsson.com
Kevin D'Souza
AT&T
200 S. Laurel Ave
Middletown, NJ
United States of America
Email: kd6913@att.com
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