| 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
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.
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.
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.
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:
Note to RFC Editor (To be removed by RFC Editor)
Open issues are tracked at <https://github.com/netmod-wg/yang-ver-dt/issues>.
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.
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:
[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.
This section updates [RFC7950] section 11 to refine the rules for permissible changes when a new YANG module revision is created.
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.
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:
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.
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.
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.
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
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:
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.
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:
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.
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:
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:
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
}
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
}
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.
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:
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:
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
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;
}
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;
}
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;
}
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.
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.
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
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.
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:
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.
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.
The following text updates section 4.7 of [RFC8407] to revise the guidelines for updating YANG modules.
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 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.
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:
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:
See Appendix B for examples on how NBC changes can be made.
Guidelines for clients of modules using the new module revision update procedure:
YANG module with extension statements for annotating NBC changes, revision label, revision label scheme, and importing by revision.
<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
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
"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.
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
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";
}
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).
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
"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>
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:
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.
The document does not define any new protocol or data model. There are no security considerations beyond those specified in [RFC7950].
The following YANG module is requested to be registred in the "IANA Module Names" registry:
The ietf-yang-revisions module:
The ietf-yang-library-revisions module:
We may need to give new instructions to IANA e.g. how to review revision-label statements to make sure they are accurate? TBD
| [I-D.ietf-netmod-rfc6991-bis] | Schoenwaelder, J., "Common YANG Data Types", Internet-Draft draft-ietf-netmod-rfc6991-bis-04, 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", Internet-Draft draft-ietf-netmod-yang-semver-00, 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. |
| [RFC7895] | Bierman, A., Bjorklund, M. and K. Watsen, "YANG Module Library", RFC 7895, DOI 10.17487/RFC7895, June 2016. |
| [RFC7950] | Bjorklund, M., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016. |
| [RFC8174] | Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017. |
| [RFC8407] | Bierman, A., "Guidelines for Authors and Reviewers of Documents Containing YANG Data Models", BCP 216, RFC 8407, DOI 10.17487/RFC8407, October 2018. |
| [RFC8525] | Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K. and R. Wilton, "YANG Library", RFC 8525, DOI 10.17487/RFC8525, March 2019. |
| [I-D.clacla-netmod-yang-model-update] | Claise, B., Clarke, J., Lengyel, B. and K. D'Souza, "New YANG Module Update Procedure", Internet-Draft draft-clacla-netmod-yang-model-update-06, July 2018. |
| [I-D.ietf-netmod-yang-instance-file-format] | Lengyel, B. and B. Claise, "YANG Instance Data File Format", Internet-Draft draft-ietf-netmod-yang-instance-file-format-12, April 2020. |
| [I-D.ietf-netmod-yang-packages] | Wilton, R., Rahman, R., Clarke, J., Sterne, J. and W. Bo, "YANG Packages", Internet-Draft draft-ietf-netmod-yang-packages-00, March 2020. |
| [I-D.ietf-netmod-yang-solutions] | Wilton, R., "YANG Versioning Solution Overview", Internet-Draft draft-ietf-netmod-yang-solutions-00, March 2020. |
| [I-D.ietf-netmod-yang-ver-selection] | Wilton, R., Rahman, R., Clarke, J., Sterne, J. and W. Bo, "YANG Schema Selection", Internet-Draft draft-ietf-netmod-yang-ver-selection-00, March 2020. |
| [I-D.ietf-netmod-yang-versioning-reqs] | Clarke, J., "YANG Module Versioning Requirements", Internet-Draft draft-ietf-netmod-yang-versioning-reqs-03, June 2020. |
| [RFC8340] | Bjorklund, M. and L. Berger, "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018. |
| [semver] | "Semantic Versioning 2.0.0" |
Examples of NBC changes include:
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.
Removing a leaf or container from the data tree, e.g. because support for the corresponding feature is being removed:
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:
Changing the type of a leaf-node. e.g. consider a "vpn-id" node of type integer being changed to a string:
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:
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:
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:
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:
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":
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:
Note to RFC Editor (To be removed by RFC Editor)
v00 - v01