Network Working Group R. Wilton, Ed.
Internet-Draft R. Rahman, Ed.
Updates: 7950,8407,8525 (if approved) Cisco Systems, Inc.
Intended status: Standards Track B. Lengyel, Ed.
Expires: January 11, 2021 Ericsson
J. Clarke
Cisco Systems, Inc.
J. Sterne
Nokia
B. Claise
Cisco Systems, Inc.
K. D'Souza
AT&T
July 10, 2020
Updated YANG Module Revision Handling
draft-ietf-netmod-yang-module-versioning-01
Abstract
This document specifies a new YANG module update procedure that can
document when non-backwards-compatible changes have occurred during
the evolution of a YANG module. It extends the YANG import statement
with an earliest revision filter to better represent inter-module
dependencies. It provides help and guidelines for managing the
lifecycle of YANG modules and individual schema nodes. It provides a
mechanism, via the revision-label YANG extension, to specify a
revision identifier for YANG modules. This document updates RFC
7950, RFC 8407 and RFC 8525.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 11, 2021.
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Copyright Notice
Copyright (c) 2020 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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Updates to YANG RFCs . . . . . . . . . . . . . . . . . . 4
2. Terminology and Conventions . . . . . . . . . . . . . . . . . 4
3. Refinements to YANG revision handling . . . . . . . . . . . . 5
3.1. Updating a YANG module with a new revision . . . . . . . 5
3.1.1. Backwards-compatible changes . . . . . . . . . . . . 6
3.1.2. Non-backwards-compatible changes . . . . . . . . . . 6
3.2. nbc-changes revision extension statement . . . . . . . . 7
3.3. Revision label . . . . . . . . . . . . . . . . . . . . . 7
3.3.1. Revision label scheme extension statement . . . . . . 8
3.4. Examples for updating the YANG module revision history . 8
4. Import by derived revision . . . . . . . . . . . . . . . . . 11
4.1. Module import examples . . . . . . . . . . . . . . . . . 12
5. Updates to ietf-yang-library . . . . . . . . . . . . . . . . 14
5.1. Resolving ambiguous module imports . . . . . . . . . . . 14
5.2. YANG library versioning augmentations . . . . . . . . . . 15
5.2.1. Advertising revision-label . . . . . . . . . . . . . 15
5.2.2. Reporting how deprecated and obsolete nodes are
handled . . . . . . . . . . . . . . . . . . . . . . . 15
6. Versioning of YANG instance data . . . . . . . . . . . . . . 16
7. Guidelines for using the YANG module update rules . . . . . . 16
7.1. Guidelines for YANG module authors . . . . . . . . . . . 16
7.1.1. Making non-backwards-compatible changes to a YANG
module . . . . . . . . . . . . . . . . . . . . . . . 17
7.2. Versioning Considerations for Clients . . . . . . . . . . 18
8. Module Versioning Extension YANG Modules . . . . . . . . . . 18
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 26
10. Security Considerations . . . . . . . . . . . . . . . . . . . 27
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
11.1. YANG Module Registrations . . . . . . . . . . . . . . . 27
11.2. Instructions . . . . . . . . . . . . . . . . . . . . . . 28
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12. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
12.1. Normative References . . . . . . . . . . . . . . . . . . 28
12.2. Informative References . . . . . . . . . . . . . . . . . 29
Appendix A. Examples of changes that are NBC . . . . . . . . . . 29
Appendix B. Examples of applying the NBC change guidelines . . . 30
B.1. Removing a data node . . . . . . . . . . . . . . . . . . 30
B.2. Changing the type of a leaf node . . . . . . . . . . . . 31
B.3. Reducing the range of a leaf node . . . . . . . . . . . . 32
B.4. Changing the key of a list . . . . . . . . . . . . . . . 32
B.5. Renaming a node . . . . . . . . . . . . . . . . . . . . . 33
B.6. Changing a default value . . . . . . . . . . . . . . . . 34
Appendix C. Changes between revisions . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
1. Introduction
This document defines a solution to the YANG module lifecycle
problems described in [I-D.ietf-netmod-yang-versioning-reqs].
Complementary documents provide a complete solution to the YANG
versioning requirements, with the overall relationship of the
solution drafts described in [I-D.ietf-netmod-yang-solutions].
Specifically, this document recognises a need (within standards
organizations, vendors, and the industry) to sometimes allow YANG
modules to evolve with non-backwards-compatible changes, which could
cause breakage to clients and importing YANG modules. Accepting that
non-backwards-compatible changes do sometimes occur, it is important
to have mechanisms to report where these changes occur, and to manage
their effect on clients and the broader YANG ecosystem.
The document comprises five parts:
Refinements to the YANG 1.1 module revision update procedure,
supported by new extension statements to indicate when a revision
contains non-backwards-compatible changes, and an optional
revision label.
A YANG extension statement allowing YANG module imports to specify
an earliest module revision that may satisfy the import
dependency.
Updates and augmentations to ietf-yang-library to include the
revision label in the module descriptions, to report how
"deprecated" and "obsolete" nodes are handled by a server, and to
clarify how module imports are resolved when multiple revisions
could otherwise be chosen.
Considerations of how versioning applies to YANG instance data.
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Guidelines for how the YANG module update rules defined in this
document should be used, along with examples.
Note to RFC Editor (To be removed by RFC Editor)
Open issues are tracked at <https://github.com/netmod-wg/yang-ver-dt/
issues>.
1.1. Updates to YANG RFCs
This document updates [RFC7950] section 11. Section 3 describes
modifications to YANG revision handling and update rules, and
Section 4 describes a YANG extension statement to do import by
derived revision.
This document updates [RFC7950] section 5.6.5. Section 5.1 defines
how a client of a YANG library datastore schema resolves ambiguous
imports for modules which are not "import-only".
This document updates [RFC8407] section 4.7. Section 7 provides
guidelines on managing the lifecycle of YANG modules that may contain
non-backwards-compatible changes and a branched revision history.
This document updates [RFC7950] section 5.2. Section 3.3 describes
the use of a revision label in the name of a file containing a YANG
module or submodule.
2. Terminology and Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
In addition, this document uses the terminology:
o YANG module revision: An instance of a YANG module, uniquely
identified with a revision date, with no implied ordering or
backwards compatibility between different revisions of the same
module.
o Backwards-compatible (BC) change: A backwards-compatible change
between two YANG module revisions, as defined in Section 3.1.1
o Non-backwards-compatible (NBC) change: A non-backwards-compatible
change between two YANG module revisions, as defined in
Section 3.1.2
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3. Refinements to YANG revision handling
[RFC7950] assumes, but does not explicitly state, that the revision
history for a YANG module is strictly linear, i.e., it is prohibited
to have two independent revisions of a YANG module that are both
directly derived from the same parent revision.
This document clarifies [RFC7950] to explicitly allow non linear
development of YANG module revisions, so modules MAY have multiple
revisions that directly derive from the same parent revision. As per
[RFC7950], YANG module revisions continue to be uniquely identified
by the module's revision date, and hence all revisions of a module
MUST have unique revision dates.
A corollary to the above is that the relationship between two module
revisions cannot be determined by comparing the module revision date
alone, and the revision history, or revision label, must also be
taken into consideration.
A module's name and revision date identifies a specific immutable
definition of that module within its revision history. Hence, if a
module includes submodules then to ensure that the module's content
is uniquely defined, the module's "include" statements SHOULD use
"revision-date" substatements to specify the exact revision date of
each included submodule. When a module does not include its
submodules by revision-date, the revision of submodules used cannot
be derived from the including module. Mechanisms such as YANG
packages [I-D.ietf-netmod-yang-packages], and YANG library [[RFC7895]
[RFC8525], MAY be used to specify the exact submodule revisions used
when the submodule revision date is not constrained by the "include"
statement.
[RFC7950] section 11 requires that all updates to a YANG module are
BC to the previous revision of the module. This document allows for
more flexible evolution of YANG modules: NBC changes between module
revisions are allowed and are documented using a new "nbc-changes"
YANG extension statement in the module revision history.
Two revisions of a module MAY have identical content except for the
revision history. This could occur, for example, if a module has a
branched history and identical changes are applied in multiple
branches.
3.1. Updating a YANG module with a new revision
This section updates [RFC7950] section 11 to refine the rules for
permissible changes when a new YANG module revision is created.
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Where pragmatic, updates to YANG modules SHOULD be backwards-
compatible, following the definition in Section 3.1.1.
A new module revision MAY contain NBC changes, i.e., the semantics of
an existing definition MAY be changed in an NBC way without requiring
a new definition with a new identifier. A new module revision with
NBC changes MUST include the "rev:nbc-changes" extension substatement
to signal the potential for incompatibility to existing module users
and readers.
3.1.1. Backwards-compatible changes
A change between two module revisions is defined as being "backwards-
compatible" if the change conforms to the module update rules
specified in [RFC7950] section 11, updated by the following rules:
o A "status" "deprecated" statement MAY be added, or changed from
"current" to "deprecated", but adding or changing "status" to
"obsolete" is not a backwards-compatible change.
o Obsolete definitions MAY be removed from published modules, and
are classified as backwards-compatible changes. In some
circumstances it may be helpful to retain the obsolete definitions
to ensure that their identifiers are not reused with a different
meaning.
o In statements that have any data definition statements as
substatements, those data definition substatements MAY be
reordered, as long as they do not change the ordering of any
"input" or "output" data definition substatements of "rpc" or
"action" statements. If new data definition statements are added,
they can be added anywhere in the sequence of existing
substatements.
o Any changes (including whitespace or formatting changes) that do
not change the semantic meaning of the module are backwards
compatible.
3.1.2. Non-backwards-compatible changes
Any changes to YANG modules that are not defined by Section 3.1.1 as
being backwards-compatible are classified as "non-backwards-
compatible" changes.
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3.2. nbc-changes revision extension statement
The "rev:nbc-changes" extension statement is used to indicate YANG
module revisions that contain NBC changes.
If a revision of a YANG module contains changes, relative to the
preceding revision in the revision history, that do not conform to
the module update rules defined in Section 3.1.1, then a "rev:nbc-
changes" extension statement MUST be added as a substatement to the
"revision" statement.
Conversely, if a revision does not contain an "rev:nbc-changes"
extension substatement then all changes, relative to the preceding
revision in the revision history, MUST be backwards-compatible.
3.3. Revision label
This section updates [RFC7950] section 5.2, it explains how a
revision label can be used in the name of a file containing a YANG
module or submodule.
Each revision entry in a module or submodule MAY have a revision
label associated with it, providing an alternative alias to identify
a particular revision of a module or submodule. The revision label
could be used to provide an additional versioning identifier
associated with the revision.
YANG Semver [I-D.ietf-netmod-yang-semver] defines a versioning scheme
based on Semver 2.0.0 [semver] that can be used as a revision label.
Submodules MAY use a revision label scheme. When they use a revision
label scheme, submodules MAY use a revision label scheme that is
different from the one used in the including module.
The revision label space of submodules is separate from the revision
label space of the including module. A change in one submodule MUST
result in a new revision label of that submodule and the including
module, but the actual values of the revision labels in the module
and submodule could be completely different. A change in one
submodule does not result in a new revision label in another
submodule. A change in a module revision label does not necessarily
mean a change to the revision label in all included submodules.
If a revision has an associated revision label, then it may be used
instead of the revision date in an "rev:revision-or-derived"
extension statement argument.
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If a revision has an associated revision label, then it may be used
instead of the revision date in the filename of a YANG module, where
it takes the form:
module-or-submodule-name [['@' revision-date]|['#' revision-label]]
( '.yang' / '.yin' )
E.g., acme-router-modules@2018-01-25.yang
E.g., acme-router-modules#2.0.3.yang
Two file names, one with the revision date and another with the
revision label, MAY exist for the same module (or submodule)
revision.
A specific revision-label identifies a specific revision (variant) of
the module. If two YANG modules contain the same module name and the
same revision-label (and hence also the same revision-date) in their
latest revision statement, then the contents of the two modules MUST
be identical.
3.3.1. Revision label scheme extension statement
The "rev:revision-label-scheme" extension statement is used to
indicate which revision-label scheme a module or submodule uses. The
mandatory argument to this extension statement:
o Specifies the revision-label scheme used by the module or
submodule
o Is defined in the document which specifies the revision-label
scheme
o MUST be an identity derived from "revision-label-scheme-base"
The revision-label scheme used by a module or submodule SHOULD NOT
change during the lifetime of the module or submodule. If the
revision-label scheme used by a module or submodule is changed to a
new scheme, then all revision-label statements that do not conform to
the new scheme MUST be replaced or removed.
3.4. Examples for updating the YANG module revision history
The following diagram, explanation, and module history illustrates
how the branched revision history, "nbc-changes" extension statement,
and "revision-label" extension statement could be used:
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Example YANG module with branched revision history.
Module revision date Revision label
2019-01-01 <- 1.0.0
|
2019-02-01 <- 2.0.0
| \
2019-03-01 \ <- 3.0.0
| \
| 2019-04-01 <- 2.1.0
| |
| 2019-05-01 <- 2.2.0
|
2019-06-01 <- 3.1.0
The tree diagram above illustrates how an example module's revision
history might evolve, over time. For example, the tree might
represent the following changes, listed in chronological order from
oldest revision to newest:
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Example module, revision 2019-06-01:
module example-module {
namespace "urn:example:module";
prefix "prefix-name";
import ietf-yang-revisions { prefix "rev"; }
description
"to be completed";
revision 2019-06-01 {
rev:revision-label 3.1.0;
description "Add new functionality.";
}
revision 2019-04-01 {
rev:revision-label 3.0.0;
rev:nbc-changes;
description
"Add new functionality. Remove some deprecated nodes.";
}
revision 2019-02-01 {
rev:revision-label 2.0.0;
rev:nbc-changes;
description "Apply bugfix to pattern statement";
}
revision 2019-01-01 {
rev:revision-label 1.0.0;
description "Initial revision";
}
//YANG module definition starts here
}
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Example module, revision 2019-05-01:
module example-module {
namespace "urn:example:module";
prefix "prefix-name";
import ietf-yang-revisions { prefix "rev"; }
description
"to be completed";
revision 2019-05-01 {
rev:revision-label 2.2.0;
description "Backwards-compatible bugfix to enhancement.";
}
revision 2019-03-01 {
rev:revision-label 2.1.0;
description "Apply enhancement to older release train.";
}
revision 2019-02-01 {
rev:revision-label 2.0.0;
rev:nbc-changes;
description "Apply bugfix to pattern statement";
}
revision 2019-01-01 {
rev:revision-label 1.0.0;
description "Initial revision";
}
//YANG module definition starts here
}
4. Import by derived revision
RFC 7950 allows YANG module "import" statements to optionally require
the imported module to have a particular revision date. In practice,
importing a module with an exact revision date is often too
restrictive because it requires the importing module to be updated
whenever any change to the imported module occurs. The alternative
choice of using an import statement without any revision date
statement is also not ideal because the importing module may not work
with all possible revisions of the imported module.
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Instead, it is desirable for a importing module to specify a "minimum
required revision" of a module that it is compatible with, based on
the assumption that later revisions derived from that "minimum
required revision" are also likely to be compatible. Many possible
changes to a YANG module do not break importing modules, even if the
changes themselves are not strictly backwards-compatible. E.g.,
fixing an incorrect pattern statement or description for a leaf would
not break an import, changing the name of a leaf could break an
import but frequently would not, but removing a container would break
imports if that container is augmented by another module.
The ietf-revisions module defines the "revision-or-derived" extension
statement, a substatement to the YANG "import" statement, to allow
for a "minimum required revision" to be specified during import:
The argument to the "revision-or-derived" extension statement is a
revision date or a revision label.
A particular revision of an imported module satisfies an import's
"revision-or-derived" extension statement if the imported module's
revision history contains a revision statement with a matching
revision date or revision label.
An "import" statement MUST NOT contain both a "revision-or-
derived" extension statement and a "revision-date" statement.
The "revision-or-derived" extension statement MAY be specified
multiple times, allowing the import to use any module revision
that satisfies at least one of the "revision-or-derived" extension
statements.
The "revision-or-derived" extension statement does not guarantee
that all module revisions that satisfy an import statement are
necessarily compatible, it only gives an indication that the
revisions are more likely to be compatible. Hence, NBC changes to
an imported module may also require new revisions of any importing
modules, updated to accommodation those changes, along with
updated import "revision-or-derived" extension statements to
depend on the updated imported module revision.
4.1. Module import examples
Consider the example module "example-module" from Section 3.4 that is
hypothetically available in the following revision/label pairings:
2019-01-01/1.0.0, 2019-02-01/2.0.0, 2019-03-01/3.0.0,
2019-04-01/2.1.0, 2019-05-01/2.2.0 and 2019-06-01/3.1.0. The
relationship between the revisions is as before:
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Module revision date Revision label
2019-01-01 <- 1.0.0
|
2019-02-01 <- 2.0.0
| \
2019-03-01 \ <- 3.0.0
| \
| 2019-04-01 <- 2.1.0
| |
| 2019-05-01 <- 2.2.0
|
2019-06-01 <- 3.1.0
4.1.1. Example 1
This example selects module revisions that match, or are derived from
the revision 2019-02-01. E.g., this dependency might be used if
there was a new container added in revision 2019-02-01 that is
augmented by the importing module.It includes revisions/labels:
2019-02-01/2.0.0, 2019-03-01/3.0.0, 2019-04-01/2.1.0,
2019-05-01/2.2.0 and 2019-06-01/3.1.0.
import example-module {
rev:revision-or-derived 2019-02-01;
}
Alternatively, the first example could have used the revision label
"2.0.0" instead, which selects the same set of revisions/labels.
import example-module {
rev:revision-or-derived 2.0.0;
}
4.1.2. Example 2
This example selects module revisions that are derived from
2019-04-01 by using the revision label 2.1.0. It includes revisions/
labels: 2019-04-01/2.1.0 and 2019-05-01/2.2.0. Even though
2019-06-01/3.1.0 has a higher revision label number than
2019-04-01/2.1.0 it is not a derived revision, and hence it is not a
valid revision for import.
import example-module {
rev:revision-or-derived 2.1.0;
}
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4.1.3. Example 3
This example selects revisions derived from either 2019-04-01 or
2019-06-01. It includes revisions/labels: 2019-04-01/2.1.0,
2019-05-01/2.2.0, and 2019-06-01/3.1.0.
import example-module {
rev:revision-or-derived 2019-04-01;
rev:revision-or-derived 2019-06-01;
}
5. Updates to ietf-yang-library
This document updates YANG library [RFC7950] to clarify how ambiguous
module imports are resolved. It also defines the YANG module, ietf-
yang-library-revisions that augments YANG library [RFC8525] with new
revision-label related meta-data.
5.1. Resolving ambiguous module imports
A YANG datastore schema, defined in [RFC8525], can specify multiple
revisions of a YANG module in the schema using the "import-only"
list, with the requirement from [RFC7950] that only a single revision
of a YANG module may be implemented.
If a YANG module import statement does not specify a specific
revision within the datastore schema then it could be ambiguous as to
which module revision the import statement should resolve to. Hence,
a datastore schema constructed by a client using the information
contained in YANG library may not exactly match the datastore schema
actually used by the server.
The following two rules remove the ambiguity:
If a module import statement could resolve to more than one module
revision defined in the datastore schema, and one of those revisions
is implemented (i.e., not an "import-only" module), then the import
statement MUST resolve to the revision of the module that is defined
as being implemented by the datastore schema.
If a module import statement could resolve to more than one module
revision defined in the datastore schema, and none of those revisions
are implemented, then the import MUST resolve to the module revision
with the latest revision date.
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5.2. YANG library versioning augmentations
The "ietf-yang-library-revisions" YANG module has the following
structure (using the notation defined in [RFC8340]):
module: ietf-yang-library-revisions
augment /yanglib:yang-library/yanglib:module-set/yanglib:module:
+--ro revision-label? rev:revision-label
augment /yanglib:yang-library/yanglib:schema:
+--ro deprecated-nodes-implemented? boolean
+--ro obsolete-nodes-absent? boolean
5.2.1. Advertising revision-label
The ietf-yang-library-revisions YANG module augments the "module"
list in ietf-yang-library with a "revision-label" leaf to optionally
declare the revision label associated wth the particular revision of
each module.
5.2.2. Reporting how deprecated and obsolete nodes are handled
The ietf-yang-library-revisions YANG module augments YANG library
with two leaves to allow a server to report how it handles status
"deprecated" and status "obsolete" nodes. The leaves are:
deprecated-nodes-implemented: If set to "true", this leaf indicates
that all schema nodes with a status "deprecated" child statement
are implemented equivalently as if they had status "current", or
otherwise deviations MUST be used to explicitly remove
"deprecated" nodes from the schema. If this leaf is set to
"false" or absent, then the behavior is unspecified.
obsolete-nodes-absent: If set to "true", this leaf indicates that
the server does not implement any status "obsolete" nodes. If
this leaf is set to "false" or absent, then the behaviour is
unspecified.
Servers SHOULD set both the "deprecated-nodes-implemented" and
"obsolete-nodes-absent" leaves to "true".
If a server does not set the "deprecated-nodes-implemented" leaf to
"true", then clients MUST NOT rely solely on the "rev:nbc-changes"
statements to determine whether two module revisions are backwards-
compatible, and MUST also consider whether the status of any nodes
has changed to "deprecated" and whether those nodes are implemented
by the server.
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6. Versioning of YANG instance data
Instance data sets [I-D.ietf-netmod-yang-instance-file-format] do not
directly make use of the updated revision handling rules described in
this document, as compatibility for instance data is undefined.
However, instance data specifies the content-schema of the data-set.
This schema SHOULD make use of versioning using revision dates and/or
revision labels for the individual YANG modules that comprise the
schema or potentially for the entire schema itself (e.g.,
[I-D.ietf-netmod-yang-packages] ).
In this way, the versioning of a content-schema associated with an
instance data set may help a client to determine whether the instance
data could also be used in conjunction with other revisions of the
YANG schema, or other revisions of the modules that define the
schema.
7. Guidelines for using the YANG module update rules
The following text updates section 4.7 of [RFC8407] to revise the
guidelines for updating YANG modules.
7.1. Guidelines for YANG module authors
All IETF YANG modules MUST include revision-label statements for all
newly published YANG modules, and all newly published revisions of
existing YANG modules. The revision-label MUST take the form of a
YANG semantic version number [I-D.ietf-netmod-yang-semver].
NBC changes to YANG modules may cause problems to clients, who are
consumers of YANG models, and hence YANG module authors are
RECOMMENDED to minimize NBC changes and keep changes BC whenever
possible.
When NBC changes are introduced, consideration should be given to the
impact on clients and YANG module authors SHOULD try to mitigate that
impact.
A "rev:nbc-changes" statement MUST be added if there are NBC changes
relative to the previous revision.
Removing old revision statements from a module's revision history
could break import by revision, and hence it is RECOMMENDED to retain
them. If all depencencies have been updated to not import specific
revisions of a module, then the corresponding revision statements can
be removed from that module. An alternative solution, if the
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revision section is too long, would be remove, or curtail, the older
description statements associated with the previous revisions.
The "rev:revision-or-derived" extension should be used in YANG module
imports to indicate revision dependencies between modules in
preference to the "revision-date" statement, which causes overly
strict import dependencies and SHOULD NOT be used.
A module that includes submodules SHOULD use the "revision-date"
statement to include specific submodule revisions. The revision of
the including module MUST be updated when any included submodule has
changed. The revision-label substatement used in the new module
revision MUST indicate the nature of the change, i.e. NBC or BC, to
the module's schema tree.
7.1.1. Making non-backwards-compatible changes to a YANG module
There are various valid situations where a YANG module has to be
modified in an NBC way. Here are the different ways in which this
can be done:
o NBC changes can be sometimes be done incrementally using the
"deprecated" status to provide clients time to adapt to NBC
changes.
o NBC changes are done at once, i.e. without using "status"
statements. Depending on the change, this may have a big impact
on clients.
o If the server can support multiple revisions of the YANG module or
of YANG packages(as specified in [I-D.ietf-netmod-yang-packages]),
and allows the client to select the revision (as per
[I-D.ietf-netmod-yang-ver-selection]), then NBC changes MAY be
done without using "status" statements. Clients would be required
to select the revision which they support and the NBC change would
have no impact on them
Here are some guidelines on how non-backwards-compatible changes can
be made incrementally, with the assumption that deprecated nodes are
implemented by the server, and obsolete nodes are not:
1. The changes should be made gradually, e.g. a data node's status
SHOULD NOT be changed directly from "current" to "obsolete" (see
Section 4.7 of [RFC8407]), instead the status SHOULD first be
marked "deprecated" and then when support is removed its status
MUST be changed to "obsolete". Instead of using the "obsolete"
status, the data node MAY be removed from the model but this has
the risk of breaking modules which import the modified module.
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2. For deprecated data nodes the "description" statement SHOULD also
indicate until when support for the node is guaranteed (if
known). If there is a replacement data node, rpc, action or
notification for the deprecated node, this SHOULD be stated in
the "description". The reason for deprecating the node can also
be included in the "description" if it is deemed to be of
potential interest to the user.
3. For obsolete data nodes, it is RECOMMENDED to keep the above
information, from when the node had status "deprecated", which is
still relevant.
4. When obsoleting or deprecating data nodes, the "deprecated" or
"obsolete" status SHOULD be applied at the highest possible level
in the data tree. For clarity, the "status" statement SHOULD
also be applied to all descendent data nodes, but the additional
status related information does not need to be repeated if it
does not introduce any additional information.
See Appendix B for examples on how NBC changes can be made.
7.2. Versioning Considerations for Clients
Guidelines for clients of modules using the new module revision
update procedure:
o Clients SHOULD be liberal when processing data received from a
server. For example, the server may have increased the range of
an operational node causing the client to receive a value which is
outside the range of the YANG model revision it was coded against.
o Clients SHOULD monitor changes to published YANG modules through
their revision history, and use appropriate tooling to understand
the specific changes between module revision. In particular,
clients SHOULD NOT migrate to NBC revisions of a module without
understanding any potential impact of the specific NBC changes.
o Clients SHOULD plan to make changes to match published status
changes. When a node's status changes from "current" to
"deprecated", clients SHOULD plan to stop using that node in a
timely fashion. When a node's status changes to "obsolete",
clients MUST stop using that node.
8. Module Versioning Extension YANG Modules
YANG module with extension statements for annotating NBC changes,
revision label, revision label scheme, and importing by revision.
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<CODE BEGINS> file "ietf-yang-revisions@2020-07-06.yang"
module ietf-yang-revisions {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-yang-revisions";
prefix rev;
import ietf-yang-types {
prefix yang;
reference
"XXXX [ietf-netmod-rfc6991-bis]: Common YANG Data Types";
}
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: Reshad Rahman
<mailto:rrahman@cisco.com>
Author: Robert Wilton
<mailto:rwilton@cisco.com>
Author: Kevin D'Souza
<mailto:kd6913@att.com>
Author: Balazs Lengyel
<mailto:balazs.lengyel@ericsson.com>
Author: Jason Sterne
<mailto:jason.sterne@nokia.com>";
description
"This YANG 1.1 module contains definitions and extensions to
support updated YANG revision handling.
Copyright (c) 2019 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
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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.
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.";
// RFC Ed.: update the date below with the date of RFC publication
// and remove this note.
// RFC Ed.: replace XXXX (inc above) with actual RFC number and
// remove this note.
revision 2020-07-06 {
description
"Initial version.";
reference
"XXXX: Updated YANG Module Revision Handling";
}
typedef revision-label {
type string {
length "1..255";
pattern '[^\s@]+';
pattern '\d{4}-\d{2}-\d{2}' {
modifier invert-match;
}
}
description
"A label associated with a YANG revision.
Excludes spaces and '@'. MUST NOT match revision-date.";
reference
"XXXX: Updated YANG Module Revision Handling;
Section 3.3, Revision label";
}
typedef revision-date-or-label {
type union {
type yang:revision-identifier;
type revision-label;
}
description
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"Represents either a YANG revision date or a revision label";
}
extension nbc-changes {
description
"This statement is used to indicate YANG module revisions that
contain non-backwards-compatible changes.
The statement MUST only be a substatement of the 'revision'
statement.
Zero or one 'nbc-changes' statement per parent statement is
allowed.
The statement MUST NOT have any substatements.
If a revision of a YANG module contains changes, relative to
the preceding revision in the revision history, that do not
conform to the module update rules defined in RFC-XXX, then
the 'nbc-changes' statement MUST be added as a substatement to
the revision statement.
Conversely, if a revision of a YANG module only contains
changes, relative to the preceding revision in the revision
history, that are classified as 'backwards-compatible' then
the revision statement MUST NOT contain any 'nbc-changes'
substatement.";
reference
"XXXX: Updated YANG Module Revision Handling;
Section 3.2, nbc-changes revision extension statement";
}
extension revision-label {
argument revision-label;
description
"The revision label can be used to provide an additional
versioning identifier associated with the revision. E.g., one
option for a versioning scheme that could be used is [TODO -
Reference semver draft].
The format of the revision-label argument MUST conform to the
pattern defined for the revision-label typedef.
The statement MUST only be a substatement of the revision
statement.
Zero or one revision-label statement per parent statement
is allowed.
The statement MUST NOT have any substatements.
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Revision labels MUST be unique amongst all revisions of a
module.";
reference
"XXXX: Updated YANG Module Revision Handling;
Section 3.3, Revision label";
}
extension revision-label-scheme {
argument revision-label-scheme-identity;
description
"The revision label scheme specifies which revision-label scheme
the module or submodule uses.
The mandatory revision-label-scheme-identity argument MUST be an
identity derived from revision-label-scheme-base.
This extension is only valid as a top-level statement, i.e.,
given as as a substatement to 'module' or 'submodule'.
This extension MUST be used if there is a revision-label
statement in the module or submodule.
The statement MUST NOT have any substatements.";
reference
"XXXX: Updated YANG Module Revision Handling;
Section 3.3.1, Revision label scheme extension statement";
}
extension revision-or-derived {
argument revision-date-or-label;
description
"Restricts the revision of the module that may be imported to
one that matches or is derived from the specified
revision-date or revision-label.
The argument value MUST conform to the
'revision-date-or-label' defined type.
The statement MUST only be a substatement of the import
statement.
Zero, one or more 'revision-or-derived' statement per parent
statement is allowed.
The statement MUST NOT have any substatements.
If specified multiple
times, then any module revision that satisfies at least one of
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the 'revision-or-derived' statements is an acceptable revision
for import.
An 'import' statement MUST NOT contain both a
'revision-or-derived' extension statement and a
'revision-date' statement.
A particular revision of an imported module satisfies an
import's 'revision-or-derived' extension statement if the
imported module's revision history contains a revision
statement with a matching revision date or revision label.
The 'revision-or-derived' extension statement does not
guarantee that all module revisions that satisfy an import
statement are necessarily compatible, it only gives an
indication that the revisions are more likely to be
compatible.";
reference
"XXXX: Updated YANG Module Revision Handling;
Section 4, Import by derived revision";
}
identity revision-label-scheme-base {
description
"Base identity from which all revision label schemes are
derived.";
reference
"XXXX: Updated YANG Module Revision Handling;
Section 3.3.1, Revision label scheme extension statement";
}
}
<CODE ENDS>
YANG module with augmentations to YANG Library to revision labels
<CODE BEGINS> file "ietf-yang-library-revisions@2020-07-06.yang"
module ietf-yang-library-revisions {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-yang-library-revisions";
prefix yl-rev;
import ietf-yang-revisions {
prefix rev;
reference
"XXXX: Updated YANG Module Revision Handling";
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}
import ietf-yang-library {
prefix yanglib;
reference "RFC 8525: YANG Library";
}
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: Reshad Rahman
<mailto:rrahman@cisco.com>
Author: Robert Wilton
<mailto:rwilton@cisco.com>
Author: Kevin D'Souza
<mailto:kd6913@att.com>
Author: Balazs Lengyel
<mailto:balazs.lengyel@ericsson.com>
Author: Jason Sterne
<mailto:jason.sterne@nokia.com>";
description
"This module contains augmentations to YANG Library to add module
level revision label and to provide an indication of how
deprecated and obsolete nodes are handled by the server.
Copyright (c) 2019 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the 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).
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This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.
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.";
// RFC Ed.: update the date below with the date of RFC publication
// and remove this note.
// RFC Ed.: replace XXXX (including in the imports above) with
// actual RFC number and remove this note.
// RFC Ed.: please replace revision-label version with 1.0.0 and
// remove this note.
revision 2020-07-06 {
rev:revision-label 0.1.0;
description
"Initial revision";
reference
"XXXX: Updated YANG Module Revision Handling";
}
augment "/yanglib:yang-library/yanglib:module-set/yanglib:module" {
description
"Augmentation modules with a revision label";
leaf revision-label {
type rev:revision-label;
description
"The revision label associated with this module revision.
The label MUST match the rev:label value in the specific
revision of the module loaded in this module-set.";
reference
"XXXX: Updated YANG Module Revision Handling;
Section 5.2.1, Advertising revision-label";
}
}
augment "/yanglib:yang-library/yanglib:schema" {
description
"Augmentations to the ietf-yang-library module to indicate how
deprecated and obsoleted nodes are handled for each datastore
schema supported by the server.";
leaf deprecated-nodes-implemented {
type boolean;
description
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"If set to true, this leaf indicates that all schema nodes with
a status 'deprecated' child statement are implemented
equivalently as if they had status 'current', or otherwise
deviations MUST be used to explicitly remove 'deprecated'
nodes from the schema. If this leaf is set to false or absent,
then the behavior is unspecified.";
reference
"XXXX: Updated YANG Module Revision Handling;
Section 5.2.2, Reporting how deprecated and obsolete nodes
are handled";
}
leaf obsolete-nodes-absent {
type boolean;
description
"If set to true, this leaf indicates that the server does not
implement any status 'obsolete' nodes. If this leaf is
set to false or absent, then the behaviour is unspecified.";
reference
"XXXX: Updated YANG Module Revision Handling;
Section 5.2.2, Reporting how deprecated and obsolete nodes
are handled";
}
}
}
<CODE ENDS>
9. Contributors
This document grew out of the YANG module versioning design team that
started after IETF 101. The following individuals are (or have been)
members of the design team and have worked on the YANG versioning
project:
o Balazs Lengyel
o Benoit Claise
o Ebben Aries
o Jason Sterne
o Joe Clarke
o Juergen Schoenwaelder
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o Mahesh Jethanandani
o Michael (Wangzitao)
o Qin Wu
o Reshad Rahman
o Rob Wilton
o Bo Wu
The initial revision of this document was refactored and built upon
[I-D.clacla-netmod-yang-model-update].
Discussons on the use of Semver for YANG versioning has been held
with authors of the OpenConfig YANG models. We would like thank both
Anees Shaikh and Rob Shakir for their input into this problem space.
We would also like to thank Martin Bjorklund, Jan Lindblad and Italo
Busi for their contributions.
10. Security Considerations
The document does not define any new protocol or data model. There
are no security considerations beyond those specified in [RFC7950].
11. IANA Considerations
11.1. YANG Module Registrations
The following YANG module is requested to be registred in the "IANA
Module Names" registry:
The ietf-yang-revisions module:
Name: ietf-yang-revisions
XML Namespace: urn:ietf:params:xml:ns:yang:ietf-yang-revisions
Prefix: rev
Reference: [RFCXXXX]
The ietf-yang-library-revisions module:
Name: ietf-yang-library-revisions
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XML Namespace: urn:ietf:params:xml:ns:yang:ietf-yang-library-
revisions
Prefix: yl-rev
Reference: [RFCXXXX]
11.2. Instructions
We may need to give new instructions to IANA e.g. how to review
revision-label statements to make sure they are accurate? TBD
12. References
12.1. Normative References
[I-D.ietf-netmod-rfc6991-bis]
Schoenwaelder, J., "Common YANG Data Types", draft-ietf-
netmod-rfc6991-bis-04 (work in progress), July 2020.
[I-D.ietf-netmod-yang-semver]
Claise, B., Clarke, J., Rahman, R., Wilton, R., Lengyel,
B., Sterne, J., and K. D'Souza, "YANG Semantic
Versioning", draft-ietf-netmod-yang-semver-00 (work in
progress), March 2020.
[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>.
[RFC7895] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Module
Library", RFC 7895, DOI 10.17487/RFC7895, June 2016,
<https://www.rfc-editor.org/info/rfc7895>.
[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>.
[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>.
[RFC8407] Bierman, A., "Guidelines for Authors and Reviewers of
Documents Containing YANG Data Models", BCP 216, RFC 8407,
DOI 10.17487/RFC8407, October 2018,
<https://www.rfc-editor.org/info/rfc8407>.
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[RFC8525] Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K.,
and R. Wilton, "YANG Library", RFC 8525,
DOI 10.17487/RFC8525, March 2019,
<https://www.rfc-editor.org/info/rfc8525>.
12.2. Informative References
[I-D.clacla-netmod-yang-model-update]
Claise, B., Clarke, J., Lengyel, B., and K. D'Souza, "New
YANG Module Update Procedure", draft-clacla-netmod-yang-
model-update-06 (work in progress), July 2018.
[I-D.ietf-netmod-yang-instance-file-format]
Lengyel, B. and B. Claise, "YANG Instance Data File
Format", draft-ietf-netmod-yang-instance-file-format-12
(work in progress), April 2020.
[I-D.ietf-netmod-yang-packages]
Wilton, R., Rahman, R., Clarke, J., Sterne, J., and W. Bo,
"YANG Packages", draft-ietf-netmod-yang-packages-00 (work
in progress), March 2020.
[I-D.ietf-netmod-yang-solutions]
Wilton, R., "YANG Versioning Solution Overview", draft-
ietf-netmod-yang-solutions-00 (work in progress), March
2020.
[I-D.ietf-netmod-yang-ver-selection]
Wilton, R., Rahman, R., Clarke, J., Sterne, J., and W. Bo,
"YANG Schema Selection", draft-ietf-netmod-yang-ver-
selection-00 (work in progress), March 2020.
[I-D.ietf-netmod-yang-versioning-reqs]
Clarke, J., "YANG Module Versioning Requirements", draft-
ietf-netmod-yang-versioning-reqs-03 (work in progress),
June 2020.
[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>.
[semver] "Semantic Versioning 2.0.0", <https://www.semver.org>.
Appendix A. Examples of changes that are NBC
Examples of NBC changes include:
o Deleting a data node, or changing it to status obsolete.
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o Changing the name, type, or units of a data node.
o Modifying the description in a way that changes the semantic
meaning of the data node.
o Any changes that change or reduce the allowed value set of the
data node, either through changes in the type definition, or the
addition or changes to "must" statements, or changes in the
description.
o Adding or modifying "when" statements that reduce when the data
node is available in the schema.
o Making the statement conditional on if-feature.
Appendix B. Examples of applying the NBC change guidelines
The following sections give guidance for how some of these NBC
changes could be made to a YANG module. The examples are all for
"config true" nodes.
B.1. Removing a data node
Removing a leaf or container from the data tree, e.g. because support
for the corresponding feature is being removed:
1. The node's status is changed to "deprecated" and it is supported
for at least one year. This is a BC change.
2. When the node is not available anymore, its status is changed to
"obsolete" and the "description" updated, this is an NBC change.
If the server can support NBC revisions of the YANG module
simultaneously using version selection
[I-D.ietf-netmod-yang-ver-selection], then the changes can be done
immediately:
1. The new revision of the YANG module has the node's status changed
to "obsolete" and the "description" updated, this is an NBC
change.
2. Clients which require the data node select the YANG package
containing the schema version they use
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B.2. Changing the type of a leaf node
Changing the type of a leaf-node. e.g. consider a "vpn-id" node of
type integer being changed to a string:
1. The status of node "vpn-id" is changed to "deprecated" and the
node should be available for at least one year. This is a BC
change.
2. A new node, e.g. "vpn-name", of type string is added to the same
location as the existing node "vpn-id". This new node has status
"current" and its description explains that it is replacing node
"vpn-id".
3. During the period of time where both nodes are available, how the
server behaves when either node is set is outside the scope of
this document and will vary on a case by case basis. Here are
some options:
1. A server may prevent the new node from being set if the old
node is already set (and vice-versa). The new node may have
a when statement to achieve this. The old node must not have
a when statement since this would be an NBC change, but the
server could reject the old node from being set if the new
node is already set.
2. If the new node is set and a client does a get or get-config
operation on the old node, the server could map the value.
For example, if the new node "vpn-name" has value "123" then
the server could return integer value 123 for the old node
"vpn-id". However, if the value can not be mapped then the
configuration would be incomplete, this is outside the scope
of this document.
4. When node "vpn-id" is not available anymore, its status is
changed to "obsolete" and the "description" is updated. This is
an NBC change.
If the server can support NBC revisions of the YANG module
simultaneously using version selection
[I-D.ietf-netmod-yang-ver-selection], then the changes can be done
immediately:
1. In the new revision of the YANG module, the status of node "vpn-
id" is changed to "obsolete". This is an NBC change.
2. New node "vpn-name" is added to the same location as described
above.
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3. Clients which require the data node select the YANG package
containing the schema version they use
4. A server should not map between the nodes "vpn-id" and "vpn-
name", i.e. if a client creates a data instance with "vpn-name"
then that data instance should not be visible to a client using a
module revision which has "vpn-id" (and vice-versa).
B.3. Reducing the range of a leaf node
Reducing the range of values of a leaf-node. e.g. consider a "vpn-id"
node of type integer being changed from type uint32 to type uint16:
1. If all values which are being removed were never supported, e.g.
if a vpn-id of 65536 or higher was never accepted, this is a BC
change for the functionality (no functionality change). Even if
it is an NBC change for the YANG model, there should be no impact
for clients using that YANG model.
2. If one or more values being removed was previously supported,
e.g. if a vpn-id of 65536 was accepted previously, this is an NBC
change for the YANG model. Clients using the old YANG model will
be impacted, so a change of this nature should be done carefully,
e.g. by using the steps described in Appendix B.2
B.4. Changing the key of a list
Changing the key of a list has a big impact to the client. For
example, consider a "sessions" list which has a key "interface" and
there is a need to change the key to "dest-address", such a change
can be done in steps:
1. The status of list "sessions" is changed to "deprecated" and the
list should be available for at least one year. This is a BC
change.
2. A new list is created in the same location with the same data but
with "dest-address" as key. Finding an appropriate name for the
new list can be tricky especially if the name of the existing
list was perfect. In this case the new list is called "sessions-
address", has status "current" and its description should explain
that it is replacing list "session".
3. During the period of time where both lists are available, how the
server behaves when either list is set is outside the scope of
this document and will vary on a case by case basis. Here are
some options:
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1. A server could prevent the new list from being set if the old
list already has entries (and vice-versa).
2. If the new list is set and a client does a get or get-config
operation on the old list, the server could map the entries.
However if the new list has entries which would lead to
duplicate keys in the old list, the mapping can not be done.
4. When list "sessions" is not available anymore, its status is
changed to "obsolete" and the "description" is updated. This is
an NBC change.
If the server can support NBC revisions of the YANG module
simultaneously using version selection
[I-D.ietf-netmod-yang-ver-selection], then the changes can be done
immediately:
1. The new revision of the YANG module has the list "sessions"
modified to have "dest-address" as key, this is an NBC change.
2. Clients which require the previous functionality select the older
module revision
B.5. Renaming a node
A leaf-node or a container may be renamed, either due to a spelling
error in the previous name or because of a better name. For example
a node "ip-adress" could be renamed to "ip-address":
1. The status of the existing node "ip-adress" is changed to
"deprecated" and the node should be available for at least one
year. This is a BC change.
2. The new node "ip-address" is added to the same location as the
existing node "ip-adress". This new node has status "current"
and its description should explain that it is replacing node "ip-
adress".
3. During the period of time where both nodes are available, how the
server behaves when either node is set is outside the scope of
this document and will vary on a case by case basis. Here are
some options:
1. A server could prevent the new node from being set if the old
node is already set (and vice-versa). The new node could
have a when statement to achieve this. The old node must not
have a when statement since this would be an NBC change, but
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the server could reject the old node from being set if the
new node is already set.
2. If the new node is set and a client does a get or get-config
operation on the old node, the server could use the value of
the new node. For example, if the new node "ip-address" has
value X then the server may return value X for the old node
"ip-adress".
4. When node "ip-adress" is not available anymore, its status is
changed to "obsolete" and the "description" is updated. This is
an NBC change.
If the server can support NBC revisions of the YANG module
simultaneously using version selection
[I-D.ietf-netmod-yang-ver-selection], then the changes can be done
immediately:
1. The new revision of the YANG module has the node with the new
name replacing the node with the old name, this is an NBC change.
2. Clients which require the previous node name select the older
module revision
B.6. Changing a default value
Appendix C. Changes between revisions
Note to RFC Editor (To be removed by RFC Editor)
v00 - v01
o Removed status-description
o Allowed both revision-date and revision-label in the filename.
o New extension revision-label-scheme
o To include submodules, inclusion by revision-date changed from
MUST to SHOULD
o Submodules can use revision label scheme and it can be same or
different as the including module's scheme
o Addressed various comments provided at WG adoption on rev-00
Authors' Addresses
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Robert Wilton (editor)
Cisco Systems, Inc.
Email: rwilton@cisco.com
Reshad Rahman (editor)
Cisco Systems, Inc.
Email: rrahman@cisco.com
Balazs Lengyel (editor)
Ericsson
Email: balazs.lengyel@ericsson.com
Joe Clarke
Cisco Systems, Inc.
Email: jclarke@cisco.com
Jason Sterne
Nokia
Email: jason.sterne@nokia.com
Benoit Claise
Cisco Systems, Inc.
Email: bclaise@cisco.com
Kevin D'Souza
AT&T
Email: kd6913@att.com
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