Internet Engineering Task Force A. Bierman
Internet-Draft InterWorking Labs
Intended status: Informational June 22, 2010
Expires: December 24, 2010
Guidelines for YANG Documents
draft-ietf-netmod-yang-usage-06
Abstract
This memo provides guidelines for authors and reviewers of standards
track specifications containing YANG data model modules. Applicable
portions may be used as a basis for reviews of other YANG data model
documents. Recommendations and procedures are defined, which are
intended to increase interoperability and usability of NETCONF
implementations which utilize YANG data model modules.
Status of this Memo
This Internet-Draft is submitted to IETF 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 http://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 December 24, 2010.
Copyright Notice
Copyright (c) 2010 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
(http://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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Requirements Notation . . . . . . . . . . . . . . . . . . 5
2.2. NETCONF Terms . . . . . . . . . . . . . . . . . . . . . . 5
2.3. YANG Terms . . . . . . . . . . . . . . . . . . . . . . . . 5
2.4. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. General Documentation Guidelines . . . . . . . . . . . . . . . 7
3.1. Module Copyright . . . . . . . . . . . . . . . . . . . . . 7
3.2. Narrative Sections . . . . . . . . . . . . . . . . . . . . 7
3.3. Definitions Section . . . . . . . . . . . . . . . . . . . 8
3.4. Security Considerations Section . . . . . . . . . . . . . 8
3.5. IANA Considerations Section . . . . . . . . . . . . . . . 8
3.5.1. Documents that Create a New Name Space . . . . . . . . 9
3.5.2. Documents that Extend an Existing Name Space . . . . . 9
3.6. Reference Sections . . . . . . . . . . . . . . . . . . . . 9
3.7. Intellectual Property Section . . . . . . . . . . . . . . 9
4. YANG Usage Guidelines . . . . . . . . . . . . . . . . . . . . 10
4.1. Module Naming Conventions . . . . . . . . . . . . . . . . 10
4.2. Identifiers . . . . . . . . . . . . . . . . . . . . . . . 10
4.3. Defaults . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.4. Conditional Statements . . . . . . . . . . . . . . . . . . 11
4.5. XPath Usage . . . . . . . . . . . . . . . . . . . . . . . 11
4.6. Lifecycle Management . . . . . . . . . . . . . . . . . . . 12
4.7. Module Header, Meta, and Revision Statements . . . . . . . 13
4.8. Namespace Assignments . . . . . . . . . . . . . . . . . . 14
4.9. Top Level Data Definitions . . . . . . . . . . . . . . . . 15
4.10. Data Types . . . . . . . . . . . . . . . . . . . . . . . . 15
4.11. Reusable Type Definitions . . . . . . . . . . . . . . . . 16
4.12. Data Definitions . . . . . . . . . . . . . . . . . . . . . 16
4.13. Operation Definitions . . . . . . . . . . . . . . . . . . 17
4.14. Notification Definitions . . . . . . . . . . . . . . . . . 18
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
6. Security Considerations . . . . . . . . . . . . . . . . . . . 20
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
8.1. Normative References . . . . . . . . . . . . . . . . . . . 22
8.2. Informative References . . . . . . . . . . . . . . . . . . 22
Appendix A. Module Review Checklist . . . . . . . . . . . . . . . 23
Appendix B. YANG Module Template . . . . . . . . . . . . . . . . 25
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 28
C.1. Changes from 05 to 06 . . . . . . . . . . . . . . . . . . 28
C.2. Changes from 04 to 05 . . . . . . . . . . . . . . . . . . 28
C.3. Changes from 03 to 04 . . . . . . . . . . . . . . . . . . 28
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C.4. Changes from 02 to 03 . . . . . . . . . . . . . . . . . . 29
C.5. Changes from 01 to 02 . . . . . . . . . . . . . . . . . . 29
C.6. Changes from 00 to 01 . . . . . . . . . . . . . . . . . . 30
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 31
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1. Introduction
The standardization of network configuration interfaces for use with
the NETCONF [RFC4741] protocol requires a modular set of data models,
which can be reused and extended over time.
This document defines a set of usage guidelines for standards track
documents containing YANG [I-D.ietf-netmod-yang] data models. It is
similar to the SMIv2 usage guidelines specification [RFC4181] in
intent and structure. However, since that document was written a
decade after SMIv2 modules had been in use, it was published as a
'best current practice' (BCP). This document is not a BCP, but
rather an informational reference, intended to promote consistency in
documents containing YANG modules.
Many YANG constructs are defined as optional to use, such as the
description statement. However, in order to maximize
interoperability of NETCONF implementations utilizing YANG data
models, it is desirable to define a set of usage guidelines which may
require a higher level of compliance than the minimum level defined
in the YANG specification.
In addition, YANG allows constructs such as infinite length
identifiers and string values, or top-level mandatory nodes, that a
compliant server is not required to support. Only constructs which
all servers are required to support can be used in IETF YANG modules.
This document defines usage guidelines related to the NETCONF
operations layer, and NETCONF content layer, as defined in [RFC4741].
These guidelines are intended to be used by authors and reviewers to
improve the readability and interoperability of published YANG data
models.
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2. Terminology
2.1. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
RFC 2119 language is used here to express the views of the NETMOD
working group regarding content for YANG modules. YANG modules
complying with this document will treat the RFC 2119 terminology as
if it were describing best current practices.
2.2. NETCONF Terms
The following terms are defined in [RFC4741] and are not redefined
here:
o capabilities
o client
o operation
o server
2.3. YANG Terms
The following terms are defined in [I-D.ietf-netmod-yang] and are not
redefined here:
o data node
o module
o namespace
o submodule
o version
Note that the term 'module' may be used as a generic term for a YANG
module or submodule. When describing properties which are specific
to submodules, the term 'submodule' is used instead.
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2.4. Terms
The following terms are used throughout this document:
published: A stable release of a module or submodule, usually
contained in an RFC.
unpublished: An unstable release of a module or submodule, usually
contained in an Internet-Draft.
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3. General Documentation Guidelines
YANG data model modules under review are likely to be contained in
Internet-Drafts. All guidelines for Internet-Draft authors MUST be
followed. These guidelines are available online at:
http://www.rfc-editor.org/rfc-editor/instructions2authors.txt
The following sections MUST be present in an Internet-Draft
containing a module:
o Narrative sections
o Definitions section
o Security Considerations section
o IANA Considerations section
o References section
3.1. Module Copyright
The module description statement MUST contain a reference to the
latest approved IETF Trust Copyright statement, which is available
on-line at:
http://trustee.ietf.org/license-info/
Each YANG module or submodule contained within an Internet-Draft or
RFC is considered to be a code component. The strings '<CODE
BEGINS>' and '<CODE ENDS>' MUST be used to identify each code
component.
The '<CODE BEGINS>' tag SHOULD be followed by a string identifying
the file name specified in section 5.2 of [I-D.ietf-netmod-yang].
For example, if the latest revision date of the 'ietf-foo' module is
'2010-01-18', then the following '<CODE BEGINS>' line would be used:
<CODE BEGINS> file "ietf-foo@2010-01-18.yang"
3.2. Narrative Sections
The narrative part MUST include an overview section that describes
the scope and field of application of the module(s) defined by the
specification and that specifies the relationship (if any) of these
modules to other standards, particularly to standards containing
other YANG modules. The narrative part SHOULD include one or more
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sections to briefly describe the structure of the modules defined in
the specification.
If the module(s) defined by the specification import definitions from
other modules (except for those defined in the YANG
[I-D.ietf-netmod-yang] or YANG Types [I-D.ietf-netmod-yang-types]
documents), or are always implemented in conjunction with other
modules, then those facts MUST be noted in the overview section, as
MUST be noted any special interpretations of definitions in other
modules.
3.3. Definitions Section
This section contains the module(s) defined by the specification.
These modules MUST be written using the YANG syntax defined in
[I-D.ietf-netmod-yang]. A YIN syntax version of the module MAY also
be present in the document.
See Section 4 for guidelines on YANG usage.
3.4. Security Considerations Section
Each specification that defines one or more modules MUST contain a
section that discusses security considerations relevant to those
modules. This section MUST be patterned after the latest approved
template (available at
http://www.ops.ietf.org/yang-security-considerations.txt).
In particular, writable data nodes that could be especially
disruptive if abused MUST be explicitly listed by name and the
associated security risks MUST be spelled out; similarly, readable
data nodes that contain especially sensitive information or that
raise significant privacy concerns MUST be explicitly listed by name
and the reasons for the sensitivity/privacy concerns MUST be
explained.
3.5. IANA Considerations Section
In order to comply with IESG policy as set forth in
http://www.ietf.org/ID-Checklist.html, every Internet-Draft that is
submitted to the IESG for publication which has action items for IANA
MUST contain an IANA Considerations section. The requirements for
this section vary depending what actions are required of the IANA.
If there are no IANA considerations applicable to the document, then
the IANA Considerations section is not required. Refer to the
guidelines in [RFC5226] for more details.
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3.5.1. Documents that Create a New Name Space
If an Internet-Draft defines a new name space that is to be
administered by the IANA, then the document MUST include an IANA
Considerations section, that specifies how the name space is to be
administered.
Specifically, if any YANG module namespace statement value contained
in the document is not already registered with IANA, then a new YANG
Namespace registry entry MUST be requested from the IANA. The YANG
specification includes the procedure for this purpose in its IANA
Considerations section.
3.5.2. Documents that Extend an Existing Name Space
It is possible to extend an existing namespace using a YANG submodule
which belongs to an existing module already administered by IANA. In
this case, the document containing the main module MUST be updated to
use the latest revision of the submodule.
3.6. Reference Sections
For every import or include statement which appears in a module
contained in the specification, which identifies a module in a
separate document, a corresponding normative reference to that
document MUST appear in the Normative References section. The
reference MUST correspond to the specific module version actually
used within the specification.
For every normative reference statement which appears in a module
contained in the specification, which identifies a separate document,
a corresponding normative reference to that document SHOULD appear in
the Normative References section. The reference SHOULD correspond to
the specific document version actually used within the specification.
If the reference statement identifies an informative reference, which
identifies a separate document, a corresponding informative reference
to that document MAY appear in the Informative References section.
3.7. Intellectual Property Section
The proper IPR statements MUST be present in the document, according
to the most current Internet-Draft boilerplate. Refer to the IETF
Trust Legal Provision for the exact legal text that needs to be
included.
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4. YANG Usage Guidelines
In general, modules in IETF standards-track specifications MUST
comply with all syntactic and semantic requirements of YANG.
[I-D.ietf-netmod-yang]. The guidelines in this section are intended
to supplement the YANG specification, which is intended to define a
minimum set of conformance requirements.
In order to promote interoperability and establish a set of practices
based on previous experience, the following sections establish usage
guidelines for specific YANG constructs.
Only guidelines which clarify or restrict the minimum conformance
requirements are included here.
4.1. Module Naming Conventions
Modules contained in standards track documents SHOULD be named
according to the guidelines in the IANA considerations section of
[I-D.ietf-netmod-yang].
A distinctive word or acronym (e.g., protocol name or working group
acronym) SHOULD be used in the module name. If new definitions are
being defined to extend one or more existing modules, then the same
word or acronym should be reused, instead of creating a new one.
All published module names MUST be unique.
Once a module name is published, it MUST NOT be reused, even if the
RFC containing the module is reclassified to 'Historic' status.
4.2. Identifiers
Identifiers for all YANG identifiers in published modules MUST be
between 1 and 64 characters in length. These include any construct
specified as an 'identifier-arg-str' token in the ABNF in section 12
of [I-D.ietf-netmod-yang].
4.3. Defaults
In general, it is suggested that sub-statements containing very
common default values SHOULD NOT be present. The following sub-
statements are commonly used with the default value, which would make
the module difficult to read if used everywhere they are allowed.
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+---------------+---------------+
| Statement | Default Value |
+---------------+---------------+
| config | true |
| | |
| mandatory | false |
| | |
| max-elements | unbounded |
| | |
| min-elements | 0 |
| | |
| ordered-by | system |
| | |
| status | current |
| | |
| yin-element | false |
+---------------+---------------+
4.4. Conditional Statements
A module may be conceptually partitioned in several ways, using the
'if-feature' and/or 'when' statements.
Data model designers need to carefully consider all modularity
aspects, including the use of YANG conditional statements.
If a data definition is optional, depending on server support for a
NETCONF protocol capability, then a YANG 'feature' statement SHOULD
be defined to indicate the NETCONF capability is supported within the
data model.
4.5. XPath Usage
This section describes guidelines for using the XML Path Language
[W3C.REC-xpath-19991116] (XPath) within YANG modules.
The 'attribute' and 'namespace' axes are not supported in YANG, and
MAY be empty in a NETCONF server implementation.
The 'position' and 'last' functions MAY be used with caution. A
server is not required to maintain any particular XML document order
for system-ordered data nodes. A server is only required to maintain
the relative XML document order of all instances of a particular
user-ordered list or leaf-list.
The 'preceding', and 'following' axes SHOULD NOT be used. These
constructs rely on XML document order within a NETCONF server
configuration database, which may not be supported consistently or
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produce reliable results across implementations. Predicate
expressions based on static node properties (e.g., name, value,
ancestors, descendants) SHOULD be used instead.
The 'preceding-sibling' and 'following-sibling' axes MAY be used,
with caution. A server is not required to maintain a persistent or
deterministic XML document order, which will affect use of these
axes.
Implicit 'position' function calls within predicates MAY be used with
caution. (e.g., //chapter[42]). Note that a NETCONF server is only
required to maintain relative document order for related instances of
a user-ordered list or leaf-list data definition (i.e., 'ordered-by'
statement set to 'user').
Data nodes which use the 'int64' and 'uint64' built-in type MAY be
used with caution, within relational expressions. There are boundary
conditions in which the translation from the YANG 64-bit type to an
XPath number can cause incorrect results. Specifically, an XPath
double precision floating point number cannot represent very large
positive or negative 64-bit numbers because it only provides a total
precision of 53 bits.
Data modelers need to be careful not to confuse the YANG value space
and the XPath value space. The data types are not the same in both,
and conversion between YANG and XPath data types SHOULD be considered
carefully.
Explicit XPath data type conversions MAY be used (e.g., 'string',
'boolean', or 'number' functions), instead of implicit XPath data
type conversions.
4.6. Lifecycle Management
The status statement MUST be present if its value is 'deprecated' or
'obsolete'.
The module or submodule name MUST NOT be changed, once the document
containing the module or submodule is published.
The module namespace URI value MUST NOT be changed, once the document
containing the module is published.
The revision-date sub-statement within the imports statement SHOULD
be present if any groupings are used from the external module.
The revision-date sub-statement within the include statement SHOULD
be present if any groupings are used from the external sub-module.
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If submodules are used, then the document containing the main module
MUST be updated so that the main module revision date is equal or
more recent than the revision date of any submodule which is
(directly or indirectly) included by the main module.
4.7. Module Header, Meta, and Revision Statements
For published modules, the namespace MUST be a globally unique URI,
as defined in [RFC3986]. This value is usually assigned by the IANA.
The organization statement MUST be present. If the module is
contained in a documented intended for standards-track status, then
the organization SHOULD be the IETF working group chartered to write
the document.
The contact statement MUST be present. If the module is contained in
a document intended for standards-track status, then the working
group WEB and mailing information MUST be present, and the main
document author or editor contact information SHOULD be present. If
additional authors or editors exist, their contact information MAY be
present. In addition, the Area Director and other contact
information MAY be present.
The description statement MUST be present. The appropriate IETF
Trust Copyright text MUST be present, as described in Section 3.1.
If the module relies on information contained in other documents,
which are not the same documents implied by the import statements
present in the module, then these documents MUST be identified in the
reference statement.
A revision statement MUST be present for each published version of
the module. The revision statement MUST have a reference
substatement. It MUST identify the published document which contains
the module. Modules are often extracted from their original
documents and it is useful for developers and operators to know how
to find the original source document in a consistent manner. The
revision statement MAY have a description substatement.
Each new revision MUST include a revision date which is higher than
any other revision date in the module.
It is acceptable to reuse the same revision statement within
unpublished versions (i.e., Internet-Drafts), but the revision date
MUST be updated to a higher value each time the Internet-Draft is re-
published.
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4.8. Namespace Assignments
It is RECOMMENDED that only valid YANG modules are included in
documents, whether they are published yet or not. This allows:
o the module to compile correctly instead of generating disruptive
fatal errors.
o early implementors to use the modules without picking a random
value for the XML namespace.
o early interoperability testing since independent implementations
will use the same XML namespace value.
Until a URI is assigned by the IANA, a proposed namespace URI MUST be
provided for the namespace statement in a YANG module. A value
SHOULD be selected which is not likely to collide with other YANG
namespaces. Standard module names, prefixes, and URI strings already
listed in the YANG Module Registry MUST NOT be used.
A standard namespace statement value SHOULD have the following form:
<URN prefix string>:<module-name>
The following URN prefix string SHOULD be used for published and
unpublished YANG modules:
urn:ietf:params:xml:ns:yang:
The following example URNs would be valid temporary namespace
statement values for standards-track modules:
urn:ietf:params:xml:ns:yang:ietf-netconf-partial-lock
urn:ietf:params:xml:ns:yang:ietf-netconf-state
urn:ietf:params:xml:ns:yang:ietf-netconf
Note that a different URN prefix string SHOULD be used for non-
standards track modules. The string SHOULD be selected according to
the guidelines in [I-D.ietf-netmod-yang].
The following examples of non-standards track modules are only
suggestions. There are no guidelines for this type of URN in this
document:
http://example.com/ns/example-interfaces
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http://example.com/ns/example-system
4.9. Top Level Data Definitions
There SHOULD only be one top-level data node defined in each YANG
module, if any data nodes are defined at all.
The top-level data organization SHOULD be considered carefully, in
advance. Data model designers need to consider how the functionality
for a given protocol or protocol family will grow over time.
The names and data organization SHOULD reflect persistent
information, such as the name of a protocol. The name of the working
group SHOULD NOT be used because this may change over time.
A mandatory database data definition is defined as a node that a
client must provide for the database to be valid. The server is not
required to provide a value.
Top-level database data definitions MUST NOT be mandatory. If a
mandatory node appears at the top-level, it will immediately cause
the database to be invalid. This can occur when the server boots or
when a module is loaded dynamically at runtime.
4.10. Data Types
Selection of an appropriate data type (i.e., built-in type, existing
derived type, or new derived type) is very subjective and therefore
few requirements can be specified on that subject.
Data model designers SHOULD use the most appropriate built-in data
type for the particular application.
If extensibility of enumerated values is required, then the
identityref data type SHOULD be used instead of an enumeration or
other built-in type.
For string data types, if a machine-readable pattern can be defined
for the desired semantics, then one or more pattern statements SHOULD
be present.
For string data types, if the length of the string is required to
bounded in all implementations, then a length statement MUST be
present.
For string data types, data definition semantics SHOULD NOT rely on
preservation of leading and trailing whitespace characters.
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For numeric data types, if the values allowed by the intended
semantics are different than those allowed by the unbounded intrinsic
data type (e.g., int32), then a range statement SHOULD be present.
The signed numeric data types (i.e., 'int8', 'int16', 'int32', and
'int64') SHOULD NOT be used unless negative values are allowed for
the desired semantics.
For enumeration or bits data types, the semantics for each enum or
bit SHOULD be documented. A separate description statement (within
each enum or bit statement) SHOULD be present.
4.11. Reusable Type Definitions
If an appropriate derived type exists in any standard module, such as
[I-D.ietf-netmod-yang-types], then it SHOULD be used instead of
defining a new derived type.
If an appropriate units identifier can be associated with the desired
semantics, then a units statement SHOULD be present.
If an appropriate default value can be associated with the desired
semantics, then a default statement SHOULD be present.
If a significant number of derived types are defined, and it is
anticipated that these data types will be reused by multiple modules,
then these derived types SHOULD be contained in a separate module or
submodule, to allow easier reuse without unnecessary coupling.
The description statement MUST be present.
If the type definition semantics are defined in an external document
(other than another YANG module indicated by an import statement),
then the reference statement MUST be present.
4.12. Data Definitions
The description statement MUST be present in the following YANG
statements:
o anyxml
o augment
o choice
o container
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o extension
o feature
o grouping
o identity
o leaf
o leaf-list
o list
o notification
o rpc
o typedef
If the data definition semantics are defined in an external document,
(other than another YANG module indicated by an import statement),
then a reference statement MUST be present.
The 'anyxml' construct MAY be used with caution within configuration
data. This may be useful to represent an HTML banner containing
markup elements, such as <b> and </b>. However, this construct
SHOULD NOT be used if other YANG data node types can be used instead
to represent the desired syntax and semantics.
If there are referential integrity constraints associated with the
desired semantics that can be represented with XPath, then one or
more must statements SHOULD be present.
For list and leaf-list data definitions, if the number of possible
instances is required to be bounded for all implementations, then the
max-elements statements SHOULD be present.
If any must or when statements are used within the data definition,
then the data definition description statement SHOULD describe the
purpose of each one.
4.13. Operation Definitions
If the operation semantics are defined in an external document (other
than another YANG module indicated by an import statement), then a
reference statement MUST be present.
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If the operation impacts system behavior in some way, it SHOULD be
mentioned in the description statement.
If the operation is potentially harmful to system behavior in some
way, it MUST be mentioned in the Security Considerations section of
the document.
4.14. Notification Definitions
The description statement MUST be present.
If the notification semantics are defined in an external document
(other than another YANG module indicated by an import statement),
then a reference statement MUST be present.
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5. IANA Considerations
This document registers one URI in the IETF XML registry [RFC3688].
The following registration is requested:
URI: urn:ietf:params:xml:ns:yang:ietf-template
Registrant Contact: The NETMOD WG of the IETF.
XML: N/A, the requested URI is an XML namespace.
This document requests the following assignment in the YANG Module
Names Registry for the YANG module template in Appendix B.
+---------------+-------------------------------------------+
| Field | Value |
+---------------+-------------------------------------------+
| name | ietf-template |
| | |
| namespace | urn:ietf:params:xml:ns:yang:ietf-template |
| | |
| prefix | temp |
| | |
| reference | RFCXXXX |
+---------------+-------------------------------------------+
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6. Security Considerations
This document defines documentation guidelines for NETCONF content
defined with the YANG data modeling language. The guidelines for how
to write a Security Considerations section for a YANG module are
defined in the online document
http://www.ops.ietf.org/yang-security-considerations.txt
This document does not introduce any new or increased security risks
into the management system.
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7. Acknowledgments
The structure and contents of this document are adapted from
Guidelines for MIB Documents [RFC4181], by C. M. Heard.
The working group thanks Martin Bjorklund and Juergen Schoenwaelder
for their extensive reviews and contributions to this document.
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8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC4741] Enns, R., "NETCONF Configuration Protocol", RFC 4741,
December 2006.
[RFC5378] Bradner, S. and J. Contreras, "Rights Contributors Provide
to the IETF Trust", BCP 78, RFC 5378, November 2008.
[W3C.REC-xpath-19991116]
DeRose, S. and J. Clark, "XML Path Language (XPath)
Version 1.0", World Wide Web Consortium
Recommendation REC-xpath-19991116, November 1999,
<http://www.w3.org/TR/1999/REC-xpath-19991116>.
[I-D.ietf-netmod-yang]
Bjorklund, M., "YANG - A data modeling language for the
Network Configuration Protocol (NETCONF)",
draft-ietf-netmod-yang-13 (work in progress), June 2010.
[I-D.ietf-netmod-yang-types]
Schoenwaelder, J., "Common YANG Data Types",
draft-ietf-netmod-yang-types-09 (work in progress),
April 2010.
8.2. Informative References
[RFC4181] Heard, C., "Guidelines for Authors and Reviewers of MIB
Documents", BCP 111, RFC 4181, September 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
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Appendix A. Module Review Checklist
This section is adapted from RFC 4181.
The purpose of a YANG module review is to review the YANG module both
for technical correctness and for adherence to IETF documentation
requirements. The following checklist may be helpful when reviewing
a draft document:
1. I-D Boilerplate -- verify that the draft contains the required
Internet-Draft boilerplate (see
http://www.ietf.org/ietf/1id-guidelines.txt), including the
appropriate statement to permit publication as an RFC, and that
I-D boilerplate does not contain references or section numbers.
2. Abstract -- verify that the abstract does not contain references,
that it does not have a section number, and that its content
follows the guidelines in
http://www.ietf.org/ietf/1id-guidelines.txt.
3. IETF Trust Copyright -- verify that the draft has the appropriate
text regarding the rights that document contributers provide to
the IETF Trust [RFC5378]. Some guidelines related to this
requirement are described in Section 3.1. The IETF Trust license
policy (TLP) can be found at:
http://trustee.ietf.org/docs/IETF-Trust-License-Policy.pdf
4. Security Considerations Section -- verify that the draft uses the
latest approved template from the OPS area web site
(http://www.ops.ietf.org/yang-security-considerations.txt) and
that the guidelines therein have been followed.
5. IANA Considerations Section -- this section must always be
present. For each module within the document, ensure that the
IANA Considerations section contains entries for the following
IANA registries:
XML Namespace Registry: Register the YANG module namespace.
YANG Module Registry: Register the YANG module name, prefix,
namespace, and RFC number, according to the rules specified in
[I-D.ietf-netmod-yang].
6. References -- verify that the references are properly divided
between normative and informative references, that RFC 2119 is
included as a normative reference if the terminology defined
therein is used in the document, that all references required by
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the boilerplate are present, that all YANG modules containing
imported items are cited as normative references, and that all
citations point to the most current RFCs unless there is a valid
reason to do otherwise (for example, it is OK to include an
informative reference to a previous version of a specification to
help explain a feature included for backward compatibility).
7. Copyright Notices -- verify that the draft contains an
abbreviated IETF Trust copyright notice in the description
statement of each YANG module or sub-module, and that it contains
the full IETF Trust copyright notice at the end of the document.
Make sure that the correct year is used in all copyright dates.
Use the approved text from the latest Trust Legal Provisions
(TLP) document, which can be found at:
http://trustee.ietf.org/license-info/
8. Other Issues -- check for any issues mentioned in
http://www.ietf.org/ID-Checklist.html that are not covered
elsewhere.
9. Technical Content -- review the actual technical content for
compliance with the guidelines in this document. The use of a
YANG module compiler is RECOMMENDED when checking for syntax
errors. A list of freely available tools and other information
can be found at:
http://trac.tools.ietf.org/wg/netconf/trac/wiki
Checking for correct syntax, however, is only part of the job.
It is just as important to actually read the YANG module document
from the point of view of a potential implementor. It is
particularly important to check that description statements are
sufficiently clear and unambiguous to allow interoperable
implementations to be created.
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Appendix B. YANG Module Template
<CODE BEGINS> file "ietf-template@2010-05-18.yang"
module ietf-template {
// replace this string with a unique namespace URN value
namespace
"urn:ietf:params:xml:ns:yang:ietf-template";
// replace this string, and try to pick a unique prefix
prefix "temp";
// import statements here: e.g.,
// import ietf-yang-types { prefix yang; }
// import ietf-inet-types { prefix inet; }
// identify the IETF working group if applicable
organization
"IETF NETMOD (NETCONF Data Modeling Language) Working Group";
// update this contact statement with your info
contact
"WG Web: <http://tools.ietf.org/wg/your-wg-name/>
WG List: <mailto:your-wg-name@ietf.org>
WG Chair: your-WG-chair
<mailto:your-WG-chair@example.com>
Editor: your-name
<mailto:your-email@example.com>";
// replace the first sentence in this description statement.
// replace the copyright notice with the most recent
// version, if it has been updated since the publication
// of this document
description
"This module defines a template for other YANG modules.
Copyright (c) 2010 IETF Trust and the persons identified as
the document authors. All rights reserved.
Redistribution and use in source and binary forms, with or
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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.";
// RFC Ed.: replace XXXX with actual RFC number and remove this note
reference "RFC XXXX";
// RFC Ed.: remove this note
// Note: extracted from draft-ietf-netmod-yang-usage-04.txt
// replace '2010-05-18' with the module publication date
// The format is (year-month-day)
revision "2010-05-18" {
description
"Initial version";
}
// extension statements
// feature statements
// identity statements
// typedef statements
// grouping statements
// data definition statements
// augment statements
// rpc statements
// notification statements
// DO NOT put deviation statements in a published module
}
<CODE ENDS>
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Figure 1
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Appendix C. Change Log
C.1. Changes from 05 to 06
o Several clarifications and corrections, based on the AD review by
Dan Romascanu.
C.2. Changes from 04 to 05
o Changed 'object' terminology to 'data definition'.
o Put XPath guidelines in separate section.
o Clarified XPath usage for XML document order dependencies.
o Updated <CODE BEGINS> guidelines to current conventions.
o Added informative reference for IANA considerations guidelines and
XML registry.
o Updated IANA Considerations section to reserve the ietf-template
module in the YANG Module Name Registry so it cannot be reused
accidently.
o Many other clarifications and fixed typos found in WGLC reviews.
C.3. Changes from 03 to 04
o Removed figure 1 to reduce duplication, just refer to 4741bis
draft.
o Fixed bugs and typos found in WGLC reviews.
o Removed some guidelines and referring to YANG draft instead of
duplicating YANG rules here.
o Changed security guidelines so they refer to the IETF Trust TLP
instead of MIB-specific references.
o Change temporary namespace guidelines so the DRAFT-XX and RFC-nnnn
suffix strings are not used.
o Changed some MIB boilerplate so it refers to YANG boilerplate
instead.
o Introduced dangling URL reference to online YANG security
guidelines
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http://www.ops.ietf.org/yang-security.html
[ed.: Text from Bert Wijnen will be completed soon and posted
online, and then this URL will be finalized.]
o Moved reference for identifying the source document inside the
each revision statement.
o Removed guideline about valid XPath since YANG already requires
valid XPath.
o Added guideline that strings should not rely on preservation of
leading and trailing whitespace characters.
o Relaxed some XPath and anyxml guidelines from SHOULD NOT or MUST
NOT to MAY use with caution.
o Updated the TLP text within the example module again.
o Reversed order of change log so most recent entries are first.
C.4. Changes from 02 to 03
o Updated figure 1 to align with 4741bis draft.
o Updated guidelines for import-by-revision and include-by-revision.
o Added file name to code begins convention in ietf-template module.
C.5. Changes from 01 to 02
o Updated figure 1 per mailing list comments.
o Updated suggested organization to include the working group name.
o Updated ietf-template.yang to use new organization statement
value.
o Updated Code Component requirements as per new TLP.
o Updated ietf-template.yang to use new Code Component begin and end
markers.
o Updated references to the TLP in a couple sections.
o Change manager/agent terminology to client/server.
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C.6. Changes from 00 to 01
o Added transport 'TLS' to figure 1.
o Added note about RFC 2119 terminology.
o Corrected URL for instructions to authors.
o Updated namespace procedures section.
o Updated guidelines on module contact, reference, and organization
statements.
o Added note on use of preceding-sibling and following-sibling axes
in XPath expressions.
o Added section on temporary namespace statement values.
o Added section on top level database objects.
o Added ietf-template.yang appendix.
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Author's Address
Andy Bierman
InterWorking Labs
Email: andyb@iwl.com
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