Internet Engineering Task Force (IETF) A. Bierman
Request for Comments: 6087 Brocade
Category: Informational January 2011
ISSN: 2070-1721
Guidelines for Authors and Reviewers of YANG Data Model Documents
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 Network
Configuration Protocol (NETCONF) implementations that utilize YANG
data model modules.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6087.
Copyright Notice
Copyright (c) 2011 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
described in the Simplified BSD License.
Bierman Informational [Page 1]
RFC 6087 Guidelines for YANG Documents January 2011
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Notation . . . . . . . . . . . . . . . . . . 3
2.2. NETCONF Terms . . . . . . . . . . . . . . . . . . . . . . 4
2.3. YANG Terms . . . . . . . . . . . . . . . . . . . . . . . . 4
2.4. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. General Documentation Guidelines . . . . . . . . . . . . . . . 5
3.1. Module Copyright . . . . . . . . . . . . . . . . . . . . . 5
3.2. Narrative Sections . . . . . . . . . . . . . . . . . . . . 6
3.3. Definitions Section . . . . . . . . . . . . . . . . . . . 6
3.4. Security Considerations Section . . . . . . . . . . . . . 6
3.5. IANA Considerations Section . . . . . . . . . . . . . . . 7
3.5.1. Documents that Create a New Namespace . . . . . . . . 7
3.5.2. Documents that Extend an Existing Namespace . . . . . 8
3.6. Reference Sections . . . . . . . . . . . . . . . . . . . . 8
4. YANG Usage Guidelines . . . . . . . . . . . . . . . . . . . . 8
4.1. Module Naming Conventions . . . . . . . . . . . . . . . . 8
4.2. Identifiers . . . . . . . . . . . . . . . . . . . . . . . 9
4.3. Defaults . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.4. Conditional Statements . . . . . . . . . . . . . . . . . . 10
4.5. XPath Usage . . . . . . . . . . . . . . . . . . . . . . . 10
4.6. Lifecycle Management . . . . . . . . . . . . . . . . . . . 11
4.7. Module Header, Meta, and Revision Statements . . . . . . . 12
4.8. Namespace Assignments . . . . . . . . . . . . . . . . . . 13
4.9. Top-Level Data Definitions . . . . . . . . . . . . . . . . 14
4.10. Data Types . . . . . . . . . . . . . . . . . . . . . . . . 14
4.11. Reusable Type Definitions . . . . . . . . . . . . . . . . 15
4.12. Data Definitions . . . . . . . . . . . . . . . . . . . . . 15
4.13. Operation Definitions . . . . . . . . . . . . . . . . . . 17
4.14. Notification Definitions . . . . . . . . . . . . . . . . . 17
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
6. Security Considerations . . . . . . . . . . . . . . . . . . . 18
6.1. Security Considerations Section Template . . . . . . . . . 19
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
8.1. Normative References . . . . . . . . . . . . . . . . . . . 20
8.2. Informative References . . . . . . . . . . . . . . . . . . 21
Appendix A. Module Review Checklist . . . . . . . . . . . . . . . 22
Appendix B. YANG Module Template . . . . . . . . . . . . . . . . 24
Bierman Informational [Page 2]RFC 6087 Guidelines for YANG Documents January 2011
1. Introduction
The standardization of network configuration interfaces for use with
the Network Configuration Protocol (NETCONF) [RFC4741] 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 [RFC6020] data models. YANG is used to
define the data structures, protocol operations, and notification
content used within a NETCONF server. A server that supports a
particular YANG module will support client NETCONF operation
requests, as indicated by the specific content defined in the YANG
module.
This document is similar to the Structure of Management Information
version 2 (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 that 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 that
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.
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].
Bierman Informational [Page 3]
RFC 6087 Guidelines for YANG Documents January 2011
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 [RFC6020] and are not redefined
here:
o data node
o module
o namespace
o submodule
o version
o YANG
o YIN
Note that the term 'module' may be used as a generic term for a YANG
module or submodule. When describing properties that are specific to
submodules, the term 'submodule' is used instead.
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.
Bierman Informational [Page 4]RFC 6087 Guidelines for YANG Documents January 2011
unpublished: An unstable release of a module or submodule, usually
contained in an Internet-Draft.
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. The RFC Editor provides guidelines for authors of RFCs,
which are first published as Internet-Drafts. These guidelines
should be followed and are defined in [RFC2223] and updated in
[RFC5741] and "RFC Document Style" [RFC-STYLE].
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
online 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 [RFC6020]. The following
example is for the '2010-01-18' revision of the 'ietf-foo' module:
Bierman Informational [Page 5]RFC 6087 Guidelines for YANG Documents January 2011
<CODE BEGINS> file "ietf-foo@2010-01-18.yang"
module ietf-foo {
// ...
revision 2010-01-18 {
description "Latest revision";
reference "RFC XXXX";
}
// ...
}
<CODE ENDS>
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
sections to briefly describe the structure of the modules defined in
the specification.
If the module(s) defined by the specification imports definitions
from other modules (except for those defined in the YANG [RFC6020] or
YANG Types [RFC6021] 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
[RFC6020]. A YIN syntax version of the module MAY also be present in
the document. There MAY also be other types of modules present in
the document, such as SMIv2, which are not affected by these
guidelines.
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/netconf/yang-security-considerations.txt).
Bierman Informational [Page 6]RFC 6087 Guidelines for YANG Documents January 2011
Section 6.1 contains the security considerations template dated
2010-06-16. Authors MUST check the webpage at the URL listed above
in case there is a more recent version available.
In particular:
o Writable data nodes that could be especially disruptive if abused
MUST be explicitly listed by name and the associated security
risks MUST be explained.
o 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.
o Operations (i.e., YANG 'rpc' statements) that are potentially
harmful to system behavior 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-info/checklist.html, every Internet-Draft that
is submitted to the IESG for publication MUST contain an IANA
Considerations section. The requirements for this section vary
depending on what actions are required of the IANA. If there are no
IANA considerations applicable to the document, then the IANA
Considerations section stating that there are no actions is removed
by the RFC Editor before publication. Refer to the guidelines in
[RFC5226] for more details.
3.5.1. Documents that Create a New Namespace
If an Internet-Draft defines a new namespace that is to be
administered by the IANA, then the document MUST include an IANA
Considerations section that specifies how the namespace 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
[RFC6020] specification includes the procedure for this purpose in
its IANA Considerations section.
Bierman Informational [Page 7]RFC 6087 Guidelines for YANG Documents January 2011
3.5.2. Documents that Extend an Existing Namespace
It is possible to extend an existing namespace using a YANG submodule
that 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 that 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 that 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.
4. YANG Usage Guidelines
In general, modules in IETF Standards Track specifications MUST
comply with all syntactic and semantic requirements of YANG
[RFC6020]. 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 that 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
[RFC6020].
Bierman Informational [Page 8]
RFC 6087 Guidelines for YANG Documents January 2011
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. For a YANG module
published in an RFC, this uniqueness is guaranteed by IANA. For
unpublished modules, the authors need to check that no other work in
progress is using the same module name.
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 [RFC6020].
4.3. Defaults
In general, it is suggested that substatements containing very common
default values SHOULD NOT be present. The following substatements
are commonly used with the default value, which would make the module
difficult to read if used everywhere they are allowed.
+---------------+---------------+
| Statement | Default Value |
+---------------+---------------+
| config | true |
| | |
| mandatory | false |
| | |
| max-elements | unbounded |
| | |
| min-elements | 0 |
| | |
| ordered-by | system |
| | |
| status | current |
| | |
| yin-element | false |
+---------------+---------------+
Bierman Informational [Page 9]RFC 6087 Guidelines for YANG Documents January 2011
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 that the NETCONF capability is supported
within the data model.
If any notification data, or any data definition, for a non-
configuration data node is not mandatory, then the server may or may
not be required to return an instance of this data node. If any
conditional requirements exist for returning the data node in a
notification payload or retrieval request, they MUST be documented
somewhere. For example, a 'when' or 'if-feature' statement could
apply to the data node, or the conditional requirements could be
explained in a 'description' statement within the data node or one of
its ancestors (if any).
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 SHOULD NOT be used. This applies
to implicit use of the 'position' function as well (e.g.,
'//chapter[42]'). 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 'position' and 'last' functions MAY be used if
they are evaluated in a context where the context node is a 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
produce reliable results across implementations. Predicate
expressions based on static node properties (e.g., element name or
value, 'ancestor' or 'descendant' axes) SHOULD be used instead. The
'preceding' and 'following' axes MAY be used if document order is not
relevant to the outcome of the expression (e.g., check for global
uniqueness of a parameter value).
Bierman Informational [Page 10]
RFC 6087 Guidelines for YANG Documents January 2011
The 'preceding-sibling' and 'following-sibling' axes SHOULD NOT used.
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-sibling' and 'following-sibling' axes MAY be used if they
are evaluated in a context where the context node is a user-ordered
'list' or 'leaf-list'.
Data nodes that use the 'int64' and 'uint64' built-in type SHOULD NOT
be used within numeric 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. The 'int64' and 'uint64' data types MAY be used in
numeric expressions if the value can be represented with no more than
53 bits of precision.
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 substatement within the imports statement SHOULD be
present if any groupings are used from the external module.
The revision-date substatement within the include statement SHOULD be
present if any groupings are used from the external submodule.
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 that is (directly
or indirectly) included by the main module.
Bierman Informational [Page 11]
RFC 6087 Guidelines for YANG Documents January 2011
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 document 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 that 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 that is higher than
any other revision date in the module. The revision date does not
need to be updated if the module contents do not change in the new
document revision.
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-
posted.
Bierman Informational [Page 12]
RFC 6087 Guidelines for YANG Documents January 2011
4.8. Namespace Assignments
It is RECOMMENDED that only valid YANG modules be included in
documents, whether or not they are published yet. 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 that 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 [RFC6020].
The following examples of non-Standards-Track modules are only
suggestions. There are no guidelines for this type of URN in this
document:
Bierman Informational [Page 13]RFC 6087 Guidelines for YANG Documents January 2011
http://example.com/ns/example-interfaces
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 be
bounded in all implementations, then a length statement MUST be
present.
Bierman Informational [Page 14]RFC 6087 Guidelines for YANG Documents January 2011
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
[RFC6021], 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
Bierman Informational [Page 15]
RFC 6087 Guidelines for YANG Documents January 2011
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 useful to represent an HTML banner
containing markup elements, such as '<b>' and '</b>', and MAY be used
in such cases. 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.
Bierman Informational [Page 16]
RFC 6087 Guidelines for YANG Documents January 2011
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.
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.
5. IANA Considerations
This document registers one URI in the IETF XML registry [RFC3688].
The following registration has been made:
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.
Per this document, the following assignment has been made 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 | RFC 6087 |
+---------------+-------------------------------------------+
Bierman Informational [Page 17]RFC 6087 Guidelines for YANG Documents January 2011
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/netconf/yang-security-considerations.txt
This document does not introduce any new or increased security risks
into the management system.
The following section contains the security considerations template
dated 2010-06-16. Be sure to check the webpage at the URL listed
above in case there is a more recent version available.
Each specification that defines one or more YANG 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/netconf/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.
Further, if new RPC operations have been defined, then the security
considerations of each new RPC operation MUST be explained.
Bierman Informational [Page 18]
RFC 6087 Guidelines for YANG Documents January 2011
6.1. Security Considerations Section Template
X. Security Considerations
The YANG module defined in this memo is designed to be accessed
via the NETCONF protocol [RFC4741]. The lowest NETCONF layer is
the secure transport layer and the mandatory-to-implement secure
transport is SSH [RFC4742].
-- if you have any writable data nodes (those are all the
-- "config true" nodes, and remember, that is the default)
-- describe their specific sensitivity or vulnerability.
There are a number of data nodes defined in this YANG module
which are writable/creatable/deletable (i.e., config true, which
is the default). These data nodes may be considered sensitive
or vulnerable in some network environments. Write operations
(e.g., edit-config) to these data nodes without proper protection
can have a negative effect on network operations. These are
the subtrees and data nodes and their sensitivity/vulnerability:
<list subtrees and data nodes and state why they are sensitive>
-- for all YANG modules you must evaluate whether any readable data
-- nodes (those are all the "config false" nodes, but also all other
-- nodes, because they can also be read via operations like get or
-- get-config) are sensitive or vulnerable (for instance, if they
-- might reveal customer information or violate personal privacy
-- laws such as those of the European Union if exposed to
-- unauthorized parties)
Some of the readable data nodes in this YANG module may be
considered sensitive or vulnerable in some network environments.
It is thus important to control read access (e.g., via get,
get-config, or notification) to these data nodes. These are the
subtrees and data nodes and their sensitivity/vulnerability:
<list subtrees and data nodes and state why they are sensitive>
-- if your YANG module has defined any rpc operations
-- describe their specific sensitivity or vulnerability.
Some of the RPC operations in this YANG module may be considered
sensitive or vulnerable in some network environments. It is thus
important to control access to these operations. These are the
operations and their sensitivity/vulnerability:
<list RPC operations and state why they are sensitive>
Bierman Informational [Page 19]RFC 6087 Guidelines for YANG Documents January 2011
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.
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.
[RFC2223] Postel, J. and J. Reynolds, "Instructions to RFC Authors",
RFC 2223, October 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.
[RFC5741] Daigle, L., Kolkman, O., and IAB, "RFC Streams, Headers,
and Boilerplates", RFC 5741, December 2009.
[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>.
[RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the
Network Configuration Protocol (NETCONF)", RFC 6020,
October 2010.
[RFC6021] Schoenwaelder, J., "Common YANG Data Types", RFC 6021,
October 2010.
Bierman Informational [Page 20]RFC 6087 Guidelines for YANG Documents January 2011
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.
[RFC-STYLE]
Braden, R., Ginoza, S., and A. Hagens, "RFC Document
Style", September 2009,
<http://www.rfc-editor.org/rfc-style-guide/rfc-style>.
Bierman Informational [Page 21]RFC 6087 Guidelines for YANG Documents January 2011
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
an Internet-Draft:
1. I-D Boilerplate -- verify that the draft contains the required
Internet-Draft boilerplate (see
http://www.ietf.org/id-info/guidelines.html), 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/id-info/guidelines.html.
3. Copyright Notice -- verify that the draft has the appropriate
text regarding the rights that document contributers provide to
the IETF Trust [RFC5378]. Verify that it contains the full IETF
Trust copyright notice at the beginning of the document. The
IETF Trust Legal Provisions (TLP) can be found at:
http://trustee.ietf.org/license-info/
4. Security Considerations section -- verify that the draft uses the
latest approved template from the OPS area website (http://
www.ops.ietf.org/netconf/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
[RFC6020].
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
Bierman Informational [Page 22]RFC 6087 Guidelines for YANG Documents January 2011
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). Be
sure citations for all imported modules are present somewhere in
the document text (outside the YANG module).
7. License -- verify that the draft contains the Simplified BSD
License in each YANG module or submodule. Some guidelines
related to this requirement are described in Section 3.1. 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-info/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.
Bierman Informational [Page 23]RFC 6087 Guidelines for YANG Documents January 2011
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) <insert year> 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
Bierman Informational [Page 24]RFC 6087 Guidelines for YANG Documents January 2011
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 RFC 6087
// 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>
Bierman Informational [Page 25]RFC 6087 Guidelines for YANG Documents January 2011
Author's Address
Andy Bierman
Brocade
EMail: andy.bierman@brocade.com
Bierman Informational [Page 26]
