draft-ietf-netmod-yang-usage-05.txt   draft-ietf-netmod-yang-usage-06.txt 
Internet Engineering Task Force A. Bierman Internet Engineering Task Force A. Bierman
Internet-Draft InterWorking Labs Internet-Draft InterWorking Labs
Intended status: Informational May 18, 2010 Intended status: Informational June 22, 2010
Expires: November 19, 2010 Expires: December 24, 2010
Guidelines for Authors and Reviewers of YANG Data Model Documents Guidelines for YANG Documents
draft-ietf-netmod-yang-usage-05 draft-ietf-netmod-yang-usage-06
Abstract Abstract
This memo provides guidelines for authors and reviewers of standards This memo provides guidelines for authors and reviewers of standards
track specifications containing YANG data model modules. Applicable track specifications containing YANG data model modules. Applicable
portions may be used as a basis for reviews of other YANG data model portions may be used as a basis for reviews of other YANG data model
documents. Recommendations and procedures are defined, which are documents. Recommendations and procedures are defined, which are
intended to increase interoperability and usability of NETCONF intended to increase interoperability and usability of NETCONF
implementations which utilize YANG data model modules. implementations which utilize YANG data model modules.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 19, 2010. This Internet-Draft will expire on December 24, 2010.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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2.1. Requirements Notation . . . . . . . . . . . . . . . . . . 5 2.1. Requirements Notation . . . . . . . . . . . . . . . . . . 5
2.2. NETCONF Terms . . . . . . . . . . . . . . . . . . . . . . 5 2.2. NETCONF Terms . . . . . . . . . . . . . . . . . . . . . . 5
2.3. YANG Terms . . . . . . . . . . . . . . . . . . . . . . . . 5 2.3. YANG Terms . . . . . . . . . . . . . . . . . . . . . . . . 5
2.4. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.4. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. General Documentation Guidelines . . . . . . . . . . . . . . . 7 3. General Documentation Guidelines . . . . . . . . . . . . . . . 7
3.1. Module Copyright . . . . . . . . . . . . . . . . . . . . . 7 3.1. Module Copyright . . . . . . . . . . . . . . . . . . . . . 7
3.2. Narrative Sections . . . . . . . . . . . . . . . . . . . . 7 3.2. Narrative Sections . . . . . . . . . . . . . . . . . . . . 7
3.3. Definitions Section . . . . . . . . . . . . . . . . . . . 8 3.3. Definitions Section . . . . . . . . . . . . . . . . . . . 8
3.4. Security Considerations Section . . . . . . . . . . . . . 8 3.4. Security Considerations Section . . . . . . . . . . . . . 8
3.5. IANA Considerations Section . . . . . . . . . . . . . . . 8 3.5. IANA Considerations Section . . . . . . . . . . . . . . . 8
3.5.1. Documents that Create a New Name Space . . . . . . . . 8 3.5.1. Documents that Create a New Name Space . . . . . . . . 9
3.5.2. Documents that Extend an Existing Name Space . . . . . 9 3.5.2. Documents that Extend an Existing Name Space . . . . . 9
3.6. Reference Sections . . . . . . . . . . . . . . . . . . . . 9 3.6. Reference Sections . . . . . . . . . . . . . . . . . . . . 9
3.7. Intellectual Property Section . . . . . . . . . . . . . . 9 3.7. Intellectual Property Section . . . . . . . . . . . . . . 9
4. YANG Usage Guidelines . . . . . . . . . . . . . . . . . . . . 10 4. YANG Usage Guidelines . . . . . . . . . . . . . . . . . . . . 10
4.1. Module Naming Conventions . . . . . . . . . . . . . . . . 10 4.1. Module Naming Conventions . . . . . . . . . . . . . . . . 10
4.2. Identifiers . . . . . . . . . . . . . . . . . . . . . . . 10 4.2. Identifiers . . . . . . . . . . . . . . . . . . . . . . . 10
4.3. Defaults . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.3. Defaults . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.4. Conditional Statements . . . . . . . . . . . . . . . . . . 11 4.4. Conditional Statements . . . . . . . . . . . . . . . . . . 11
4.5. XPath Usage . . . . . . . . . . . . . . . . . . . . . . . 11 4.5. XPath Usage . . . . . . . . . . . . . . . . . . . . . . . 11
4.6. Lifecycle Management . . . . . . . . . . . . . . . . . . . 12 4.6. Lifecycle Management . . . . . . . . . . . . . . . . . . . 12
4.7. Module Header, Meta, and Revision Statements . . . . . . . 13 4.7. Module Header, Meta, and Revision Statements . . . . . . . 13
4.8. Namespace Assignments . . . . . . . . . . . . . . . . . . 13 4.8. Namespace Assignments . . . . . . . . . . . . . . . . . . 14
4.9. Top Level Data Definitions . . . . . . . . . . . . . . . . 15 4.9. Top Level Data Definitions . . . . . . . . . . . . . . . . 15
4.10. Data Types . . . . . . . . . . . . . . . . . . . . . . . . 15 4.10. Data Types . . . . . . . . . . . . . . . . . . . . . . . . 15
4.11. Reusable Type Definitions . . . . . . . . . . . . . . . . 16 4.11. Reusable Type Definitions . . . . . . . . . . . . . . . . 16
4.12. Data Definitions . . . . . . . . . . . . . . . . . . . . . 16 4.12. Data Definitions . . . . . . . . . . . . . . . . . . . . . 16
4.13. Operation Definitions . . . . . . . . . . . . . . . . . . 17 4.13. Operation Definitions . . . . . . . . . . . . . . . . . . 17
4.14. Notification Definitions . . . . . . . . . . . . . . . . . 18 4.14. Notification Definitions . . . . . . . . . . . . . . . . . 18
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
6. Security Considerations . . . . . . . . . . . . . . . . . . . 20 6. Security Considerations . . . . . . . . . . . . . . . . . . . 20
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
8.1. Normative References . . . . . . . . . . . . . . . . . . . 22 8.1. Normative References . . . . . . . . . . . . . . . . . . . 22
8.2. Informative References . . . . . . . . . . . . . . . . . . 22 8.2. Informative References . . . . . . . . . . . . . . . . . . 22
Appendix A. Module Review Checklist . . . . . . . . . . . . . . . 23 Appendix A. Module Review Checklist . . . . . . . . . . . . . . . 23
Appendix B. YANG Module Template . . . . . . . . . . . . . . . . 25 Appendix B. YANG Module Template . . . . . . . . . . . . . . . . 25
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 28 Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 28
C.1. Changes from 04 to 05 . . . . . . . . . . . . . . . . . . 28 C.1. Changes from 05 to 06 . . . . . . . . . . . . . . . . . . 28
C.2. Changes from 03 to 04 . . . . . . . . . . . . . . . . . . 28 C.2. Changes from 04 to 05 . . . . . . . . . . . . . . . . . . 28
C.3. Changes from 02 to 03 . . . . . . . . . . . . . . . . . . 29 C.3. Changes from 03 to 04 . . . . . . . . . . . . . . . . . . 28
C.4. Changes from 01 to 02 . . . . . . . . . . . . . . . . . . 29 C.4. Changes from 02 to 03 . . . . . . . . . . . . . . . . . . 29
C.5. Changes from 00 to 01 . . . . . . . . . . . . . . . . . . 29 C.5. Changes from 01 to 02 . . . . . . . . . . . . . . . . . . 29
C.6. Changes from 00 to 01 . . . . . . . . . . . . . . . . . . 30
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 31 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction 1. Introduction
The standardization of network configuration interfaces for use with The standardization of network configuration interfaces for use with
the NETCONF [RFC4741] protocol requires a modular set of data models, the NETCONF [RFC4741] protocol requires a modular set of data models,
which can be reused and extended over time. which can be reused and extended over time.
This document defines a set of usage guidelines for standards track This document defines a set of usage guidelines for standards track
documents containing YANG [I-D.ietf-netmod-yang] data models. It is documents containing YANG [I-D.ietf-netmod-yang] data models. It is
similar to the SMIv2 usage guidelines specification [RFC4181] in similar to the SMIv2 usage guidelines specification [RFC4181] in
intent and structure. 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 Many YANG constructs are defined as optional to use, such as the
description statement. However, in order to maximize description statement. However, in order to maximize
interoperability of NETCONF implementations utilizing YANG data interoperability of NETCONF implementations utilizing YANG data
models, it is desirable to define a set of usage guidelines which may models, it is desirable to define a set of usage guidelines which may
require a higher level of compliance than the minimum level defined require a higher level of compliance than the minimum level defined
in the YANG specification. 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 This document defines usage guidelines related to the NETCONF
operations layer, and NETCONF content layer, as defined in [RFC4741]. 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. Terminology
2.1. Requirements Notation 2.1. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
RFC 2119 language is used here to express the views of the NETMOD RFC 2119 language is used here to express the views of the NETMOD
working group regarding YANG module content. YANG modules complying working group regarding content for YANG modules. YANG modules
with this document will treat the RFC 2119 terminology as if it were complying with this document will treat the RFC 2119 terminology as
describing best current practices. if it were describing best current practices.
2.2. NETCONF Terms 2.2. NETCONF Terms
The following terms are defined in [RFC4741] and are not redefined The following terms are defined in [RFC4741] and are not redefined
here: here:
o capabilities o capabilities
o client o client
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to submodules, the term 'submodule' is used instead. to submodules, the term 'submodule' is used instead.
2.4. Terms 2.4. Terms
The following terms are used throughout this document: The following terms are used throughout this document:
published: A stable release of a module or submodule, usually published: A stable release of a module or submodule, usually
contained in an RFC. contained in an RFC.
unpublished: An unstable release of a module or submodule, usually unpublished: An unstable release of a module or submodule, usually
contained in an Internet Draft. contained in an Internet-Draft.
3. General Documentation Guidelines 3. General Documentation Guidelines
YANG data model modules under review are likely to be contained in YANG data model modules under review are likely to be contained in
Internet Drafts. All guidelines for Internet Draft authors MUST be Internet-Drafts. All guidelines for Internet-Draft authors MUST be
followed. These guidelines are available online at: followed. These guidelines are available online at:
http://www.rfc-editor.org/rfc-editor/instructions2authors.txt http://www.rfc-editor.org/rfc-editor/instructions2authors.txt
The following sections MUST be present in an Internet Draft The following sections MUST be present in an Internet-Draft
containing a module: containing a module:
o Narrative sections o Narrative sections
o Definitions section o Definitions section
o Security Considerations section o Security Considerations section
o IANA Considerations section o IANA Considerations section
o References section o References section
3.1. Module Copyright 3.1. Module Copyright
The module description statement MUST contain a reference to the The module description statement MUST contain a reference to the
latest approved IETF Trust Copyright statement, which is available latest approved IETF Trust Copyright statement, which is available
on-line at: on-line at:
http://trustee.ietf.org/license-info/ http://trustee.ietf.org/license-info/
Each YANG module or submodule contained within an Internet Draft or Each YANG module or submodule contained within an Internet-Draft or
RFC is considered to be a code component. The strings '<CODE RFC is considered to be a code component. The strings '<CODE
BEGINS>' and '<CODE ENDS>' SHOULD be used to identify each code BEGINS>' and '<CODE ENDS>' MUST be used to identify each code
component. component.
The '<CODE BEGINS>' tag SHOULD be followed by a string identifying 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]. 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 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: '2010-01-18', then the following '<CODE BEGINS>' line would be used:
<CODE BEGINS> file "ietf-foo@2010-01-18.yang" <CODE BEGINS> file "ietf-foo@2010-01-18.yang"
3.2. Narrative Sections 3.2. Narrative Sections
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the scope and field of application of the module(s) defined by the the scope and field of application of the module(s) defined by the
specification and that specifies the relationship (if any) of these specification and that specifies the relationship (if any) of these
modules to other standards, particularly to standards containing modules to other standards, particularly to standards containing
other YANG modules. The narrative part SHOULD include one or more other YANG modules. The narrative part SHOULD include one or more
sections to briefly describe the structure of the modules defined in sections to briefly describe the structure of the modules defined in
the specification. the specification.
If the module(s) defined by the specification import definitions from If the module(s) defined by the specification import definitions from
other modules (except for those defined in the YANG other modules (except for those defined in the YANG
[I-D.ietf-netmod-yang] or YANG Types [I-D.ietf-netmod-yang-types] [I-D.ietf-netmod-yang] or YANG Types [I-D.ietf-netmod-yang-types]
documents) or are always implemented in conjunction with other documents), or are always implemented in conjunction with other
modules, then those facts MUST be noted in the overview section, as modules, then those facts MUST be noted in the overview section, as
MUST any special interpretations of definitions in other modules. MUST be noted any special interpretations of definitions in other
modules.
3.3. Definitions Section 3.3. Definitions Section
This section contains the module(s) defined by the specification. This section contains the module(s) defined by the specification.
These modules MUST be written in YANG [I-D.ietf-netmod-yang]. 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. See Section 4 for guidelines on YANG usage.
3.4. Security Considerations Section 3.4. Security Considerations Section
Each specification that defines one or more modules MUST contain a Each specification that defines one or more modules MUST contain a
section that discusses security considerations relevant to those section that discusses security considerations relevant to those
modules. This section MUST be patterned after the latest approved modules. This section MUST be patterned after the latest approved
template (available at http://www.ops.ietf.org/yang-security.html). template (available at
[ed.: this online document does not exist yet.] http://www.ops.ietf.org/yang-security-considerations.txt).
In particular, writable data nodes that could be especially In particular, writable data nodes that could be especially
disruptive if abused MUST be explicitly listed by name and the disruptive if abused MUST be explicitly listed by name and the
associated security risks MUST be spelled out; similarly, readable associated security risks MUST be spelled out; similarly, readable
data nodes that contain especially sensitive information or that data nodes that contain especially sensitive information or that
raise significant privacy concerns MUST be explicitly listed by name raise significant privacy concerns MUST be explicitly listed by name
and the reasons for the sensitivity/privacy concerns MUST be and the reasons for the sensitivity/privacy concerns MUST be
explained. explained.
3.5. IANA Considerations Section 3.5. IANA Considerations Section
In order to comply with IESG policy as set forth in In order to comply with IESG policy as set forth in
http://www.ietf.org/ID-Checklist.html, every Internet-Draft that is http://www.ietf.org/ID-Checklist.html, every Internet-Draft that is
submitted to the IESG for publication MUST contain an IANA submitted to the IESG for publication which has action items for IANA
Considerations section. The requirements for this section vary MUST contain an IANA Considerations section. The requirements for
depending what actions are required of the IANA. Refer to the 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. guidelines in [RFC5226] for more details.
3.5.1. Documents that Create a New Name Space 3.5.1. Documents that Create a New Name Space
If an Internet-Draft defines a new name space that is to be If an Internet-Draft defines a new name space that is to be
administered by the IANA, then the document MUST include an IANA administered by the IANA, then the document MUST include an IANA
Considerations section, that specifies how the name space is to be Considerations section, that specifies how the name space is to be
administered. administered.
Specifically, if any YANG module namespace statement value contained Specifically, if any YANG module namespace statement value contained
in the document is not already registered with IANA, then a new YANG in the document is not already registered with IANA, then a new YANG
Namespace registry entry must be requested from the IANA. The YANG Namespace registry entry MUST be requested from the IANA. The YANG
specification includes the procedure for this purpose in its IANA specification includes the procedure for this purpose in its IANA
Considerations section. Considerations section.
3.5.2. Documents that Extend an Existing Name Space 3.5.2. Documents that Extend an Existing Name Space
It is possible to extend an existing namespace using a YANG submodule It is possible to extend an existing namespace using a YANG submodule
which belongs to an existing module already administered by IANA. In which belongs to an existing module already administered by IANA. In
this case, the document containing the main module MUST be updated to this case, the document containing the main module MUST be updated to
use the latest revision of the submodule. use the latest revision of the submodule.
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a corresponding normative reference to that document SHOULD appear in a corresponding normative reference to that document SHOULD appear in
the Normative References section. The reference SHOULD correspond to the Normative References section. The reference SHOULD correspond to
the specific document version actually used within the specification. the specific document version actually used within the specification.
If the reference statement identifies an informative reference, which If the reference statement identifies an informative reference, which
identifies a separate document, a corresponding informative reference identifies a separate document, a corresponding informative reference
to that document MAY appear in the Informative References section. to that document MAY appear in the Informative References section.
3.7. Intellectual Property Section 3.7. Intellectual Property Section
The proper IPR statements MUST be present in the document, according The proper IPR statements MUST be present in the document, according
to the most current Internet Draft boilerplate. Refer to the IETF to the most current Internet-Draft boilerplate. Refer to the IETF
Trust Legal Provision for the exact legal text that needs to be Trust Legal Provision for the exact legal text that needs to be
included. included.
4. YANG Usage Guidelines 4. YANG Usage Guidelines
In general, modules in IETF standards-track specifications MUST In general, modules in IETF standards-track specifications MUST
comply with all syntactic and semantic requirements of YANG. comply with all syntactic and semantic requirements of YANG.
[I-D.ietf-netmod-yang]. The guidelines in this section are intended [I-D.ietf-netmod-yang]. The guidelines in this section are intended
to supplement the YANG specification, which is intended to define a to supplement the YANG specification, which is intended to define a
minimum set of conformance requirements. minimum set of conformance requirements.
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according to the guidelines in the IANA considerations section of according to the guidelines in the IANA considerations section of
[I-D.ietf-netmod-yang]. [I-D.ietf-netmod-yang].
A distinctive word or acronym (e.g., protocol name or working group A distinctive word or acronym (e.g., protocol name or working group
acronym) SHOULD be used in the module name. If new definitions are acronym) SHOULD be used in the module name. If new definitions are
being defined to extend one or more existing modules, then the same being defined to extend one or more existing modules, then the same
word or acronym should be reused, instead of creating a new one. word or acronym should be reused, instead of creating a new one.
All published module names MUST be unique. All published module names MUST be unique.
Once a module name is published, it MUST not be reused, even if the Once a module name is published, it MUST NOT be reused, even if the
RFC containing the module is reclassified to 'Historic' status. RFC containing the module is reclassified to 'Historic' status.
4.2. Identifiers 4.2. Identifiers
Identifiers for all YANG identifiers in published modules MUST be Identifiers for all YANG identifiers in published modules MUST be
between 1 and 64 characters in length. These includes any construct between 1 and 64 characters in length. These include any construct
specified as an 'identifier-arg-str' token in the ABNF in section 12 specified as an 'identifier-arg-str' token in the ABNF in section 12
of [I-D.ietf-netmod-yang]. of [I-D.ietf-netmod-yang].
4.3. Defaults 4.3. Defaults
In general, it is suggested that sub-statements containing very In general, it is suggested that sub-statements containing very
common default values SHOULD NOT be present. The following sub- common default values SHOULD NOT be present. The following sub-
statements are commonly used with the default value, which would make statements are commonly used with the default value, which would make
the module difficult to read if used everywhere they are allowed. the module difficult to read if used everywhere they are allowed.
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Data model designers need to carefully consider all modularity Data model designers need to carefully consider all modularity
aspects, including the use of YANG conditional statements. aspects, including the use of YANG conditional statements.
If a data definition is optional, depending on server support for a If a data definition is optional, depending on server support for a
NETCONF protocol capability, then a YANG 'feature' statement SHOULD NETCONF protocol capability, then a YANG 'feature' statement SHOULD
be defined to indicate the NETCONF capability is supported within the be defined to indicate the NETCONF capability is supported within the
data model. data model.
4.5. XPath Usage 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 The 'attribute' and 'namespace' axes are not supported in YANG, and
MAY be empty in a NETCONF server implementation. MAY be empty in a NETCONF server implementation.
The 'position' and 'last' functions MAY be used with caution. A The 'position' and 'last' functions MAY be used with caution. A
server is not required to maintain any particular XML document order server is not required to maintain any particular XML document order
for system-ordered data nodes. A server is only required to maintain for system-ordered data nodes. A server is only required to maintain
the relative XML document order of all instances of a particular the relative XML document order of all instances of a particular
user-ordered list or leaf-list. user-ordered list or leaf-list.
The 'preceding', and 'following' axes SHOULD NOT be used. These The 'preceding', and 'following' axes SHOULD NOT be used. These
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For published modules, the namespace MUST be a globally unique URI, For published modules, the namespace MUST be a globally unique URI,
as defined in [RFC3986]. This value is usually assigned by the IANA. as defined in [RFC3986]. This value is usually assigned by the IANA.
The organization statement MUST be present. If the module is The organization statement MUST be present. If the module is
contained in a documented intended for standards-track status, then contained in a documented intended for standards-track status, then
the organization SHOULD be the IETF working group chartered to write the organization SHOULD be the IETF working group chartered to write
the document. the document.
The contact statement MUST be present. If the module is contained in The contact statement MUST be present. If the module is contained in
a document intended for standards-track status, then the working a document intended for standards-track status, then the working
group WEB and mailing information MUST be present, and the document group WEB and mailing information MUST be present, and the main
author contact information SHOULD be present. In addition, the Area document author or editor contact information SHOULD be present. If
Director and other contact information MAY be present. 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 The description statement MUST be present. The appropriate IETF
Trust Copyright text MUST be present, as described in Section 3.1. Trust Copyright text MUST be present, as described in Section 3.1.
If the module relies on information contained in other documents, If the module relies on information contained in other documents,
which are not the same documents implied by the import statements which are not the same documents implied by the import statements
present in the module, then these documents MUST be identified in the present in the module, then these documents MUST be identified in the
reference statement. reference statement.
A revision statement MUST be present for each published version of A revision statement MUST be present for each published version of
skipping to change at page 13, line 42 skipping to change at page 13, line 48
substatement. It MUST identify the published document which contains substatement. It MUST identify the published document which contains
the module. Modules are often extracted from their original the module. Modules are often extracted from their original
documents and it is useful for developers and operators to know how documents and it is useful for developers and operators to know how
to find the original source document in a consistent manner. The to find the original source document in a consistent manner. The
revision statement MAY have a description substatement. revision statement MAY have a description substatement.
Each new revision MUST include a revision date which is higher than Each new revision MUST include a revision date which is higher than
any other revision date in the module. any other revision date in the module.
It is acceptable to reuse the same revision statement within It is acceptable to reuse the same revision statement within
unpublished versions (i.e., Internet Drafts), but the revision date unpublished versions (i.e., Internet-Drafts), but the revision date
MUST be updated to a higher value each time the Internet Draft is re- MUST be updated to a higher value each time the Internet-Draft is re-
published. published.
4.8. Namespace Assignments 4.8. Namespace Assignments
It is desirable to include only valid YANG modules in documents, It is RECOMMENDED that only valid YANG modules are included in
whether they are published yet or not. This allows: documents, whether they are published yet or not. This allows:
o the module to compile correctly instead of generating disruptive o the module to compile correctly instead of generating disruptive
fatal errors. fatal errors.
o early implementors to use the modules without picking a random o early implementors to use the modules without picking a random
value for the XML namespace. value for the XML namespace.
o early interoperability testing since independent implementations o early interoperability testing since independent implementations
will use the same XML namespace value. will use the same XML namespace value.
skipping to change at page 14, line 47 skipping to change at page 15, line 4
Note that a different URN prefix string SHOULD be used for non- Note that a different URN prefix string SHOULD be used for non-
standards track modules. The string SHOULD be selected according to standards track modules. The string SHOULD be selected according to
the guidelines in [I-D.ietf-netmod-yang]. the guidelines in [I-D.ietf-netmod-yang].
The following examples of non-standards track modules are only The following examples of non-standards track modules are only
suggestions. There are no guidelines for this type of URN in this suggestions. There are no guidelines for this type of URN in this
document: document:
http://example.com/ns/example-interfaces http://example.com/ns/example-interfaces
http://example.com/ns/example-system http://example.com/ns/example-system
4.9. Top Level Data Definitions 4.9. Top Level Data Definitions
There SHOULD only be one top-level data node defined in each YANG There SHOULD only be one top-level data node defined in each YANG
module. However, there MAY be more than one if needed. module, if any data nodes are defined at all.
The top-level data organization SHOULD be considered carefully, in The top-level data organization SHOULD be considered carefully, in
advance. Data model designers need to consider how the functionality advance. Data model designers need to consider how the functionality
for a given protocol or protocol family will grow over time. for a given protocol or protocol family will grow over time.
The names and data organization SHOULD reflect persistent The names and data organization SHOULD reflect persistent
information, such as the name of a protocol. The name of the working information, such as the name of a protocol. The name of the working
group SHOULD NOT be used because this may change over time. group SHOULD NOT be used because this may change over time.
A mandatory database data definition is defined as a node that a A mandatory database data definition is defined as a node that a
skipping to change at page 15, line 45 skipping to change at page 15, line 46
If extensibility of enumerated values is required, then the If extensibility of enumerated values is required, then the
identityref data type SHOULD be used instead of an enumeration or identityref data type SHOULD be used instead of an enumeration or
other built-in type. other built-in type.
For string data types, if a machine-readable pattern can be defined For string data types, if a machine-readable pattern can be defined
for the desired semantics, then one or more pattern statements SHOULD for the desired semantics, then one or more pattern statements SHOULD
be present. be present.
For string data types, if the length of the string is required to For string data types, if the length of the string is required to
bounded in all implementations, then a length statement SHOULD be bounded in all implementations, then a length statement MUST be
present. present.
For string data types, data definition semantics SHOULD NOT rely on For string data types, data definition semantics SHOULD NOT rely on
preservation of leading and trailing whitespace characters. preservation of leading and trailing whitespace characters.
For numeric data types, if the values allowed by the intended For numeric data types, if the values allowed by the intended
semantics are different than those allowed by the unbounded intrinsic semantics are different than those allowed by the unbounded intrinsic
data type (e.g., int32), then a range statement SHOULD be present. data type (e.g., int32), then a range statement SHOULD be present.
The signed numeric data types (i.e., 'int8', 'int16', 'int32', and The signed numeric data types (i.e., 'int8', 'int16', 'int32', and
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If an appropriate default value can be associated with the desired If an appropriate default value can be associated with the desired
semantics, then a default statement SHOULD be present. semantics, then a default statement SHOULD be present.
If a significant number of derived types are defined, and it is If a significant number of derived types are defined, and it is
anticipated that these data types will be reused by multiple modules, anticipated that these data types will be reused by multiple modules,
then these derived types SHOULD be contained in a separate module or then these derived types SHOULD be contained in a separate module or
submodule, to allow easier reuse without unnecessary coupling. submodule, to allow easier reuse without unnecessary coupling.
The description statement MUST be present. The description statement MUST be present.
If the type definition semantics are defined in an external document, If the type definition semantics are defined in an external document
then the reference statement SHOULD be present. (other than another YANG module indicated by an import statement),
then the reference statement MUST be present.
4.12. Data Definitions 4.12. Data Definitions
The description statement MUST be present in the following YANG The description statement MUST be present in the following YANG
statements: statements:
o anyxml o anyxml
o augment o augment
skipping to change at page 17, line 23 skipping to change at page 17, line 25
o list o list
o notification o notification
o rpc o rpc
o typedef o typedef
If the data definition semantics are defined in an external document, If the data definition semantics are defined in an external document,
then a reference statement SHOULD be present. (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 The 'anyxml' construct MAY be used with caution within configuration
data. This may be useful to represent an HTML banner containing data. This may be useful to represent an HTML banner containing
markup elements, such as <b> and </b>. However, this construct markup elements, such as <b> and </b>. However, this construct
SHOULD NOT be used if other YANG data node types can be used instead SHOULD NOT be used if other YANG data node types can be used instead
to represent the desired syntax and semantics. to represent the desired syntax and semantics.
If there are referential integrity constraints associated with the If there are referential integrity constraints associated with the
desired semantics that can be represented with XPath, then one or desired semantics that can be represented with XPath, then one or
more must statements SHOULD be present. more must statements SHOULD be present.
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For list and leaf-list data definitions, if the number of possible For list and leaf-list data definitions, if the number of possible
instances is required to be bounded for all implementations, then the instances is required to be bounded for all implementations, then the
max-elements statements SHOULD be present. max-elements statements SHOULD be present.
If any must or when statements are used within the data definition, If any must or when statements are used within the data definition,
then the data definition description statement SHOULD describe the then the data definition description statement SHOULD describe the
purpose of each one. purpose of each one.
4.13. Operation Definitions 4.13. Operation Definitions
If the operation semantics are defined in an external document, then If the operation semantics are defined in an external document (other
a reference statement SHOULD be present. 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 If the operation impacts system behavior in some way, it SHOULD be
mentioned in the description statement. mentioned in the description statement.
If the operation is potentially harmful to system behavior in some If the operation is potentially harmful to system behavior in some
way, it MUST be mentioned in the Security Considerations section of way, it MUST be mentioned in the Security Considerations section of
the document. the document.
4.14. Notification Definitions 4.14. Notification Definitions
The description statement MUST be present. The description statement MUST be present.
If the notification semantics are defined in an external document, If the notification semantics are defined in an external document
then a reference statement SHOULD be present. (other than another YANG module indicated by an import statement),
then a reference statement MUST be present.
5. IANA Considerations 5. IANA Considerations
This document registers one URI in the IETF XML registry [RFC3688]. This document registers one URI in the IETF XML registry [RFC3688].
The following registration is requested: The following registration is requested:
URI: urn:ietf:params:xml:ns:yang:ietf-template URI: urn:ietf:params:xml:ns:yang:ietf-template
Registrant Contact: The NETMOD WG of the IETF. Registrant Contact: The NETMOD WG of the IETF.
skipping to change at page 20, line 12 skipping to change at page 20, line 12
| reference | RFCXXXX | | reference | RFCXXXX |
+---------------+-------------------------------------------+ +---------------+-------------------------------------------+
6. Security Considerations 6. Security Considerations
This document defines documentation guidelines for NETCONF content This document defines documentation guidelines for NETCONF content
defined with the YANG data modeling language. The guidelines for how defined with the YANG data modeling language. The guidelines for how
to write a Security Considerations section for a YANG module are to write a Security Considerations section for a YANG module are
defined in the online document defined in the online document
http://www.ops.ietf.org/yang-security.html [ed.: this online document http://www.ops.ietf.org/yang-security-considerations.txt
does not exist yet.]
This document does not introduce any new or increased security risks This document does not introduce any new or increased security risks
into the management system. into the management system.
7. Acknowledgments 7. Acknowledgments
The structure and contents of this document are adapted from The structure and contents of this document are adapted from
Guidelines for MIB Documents [RFC4181], by C. M. Heard. Guidelines for MIB Documents [RFC4181], by C. M. Heard.
The working group thanks Martin Bjorklund and Juergen Schoenwaelder The working group thanks Martin Bjorklund and Juergen Schoenwaelder
skipping to change at page 22, line 22 skipping to change at page 22, line 22
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004. January 2004.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005. RFC 3986, January 2005.
[RFC4741] Enns, R., "NETCONF Configuration Protocol", RFC 4741, [RFC4741] Enns, R., "NETCONF Configuration Protocol", RFC 4741,
December 2006. 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] [I-D.ietf-netmod-yang]
Bjorklund, M., "YANG - A data modeling language for Bjorklund, M., "YANG - A data modeling language for the
NETCONF", draft-ietf-netmod-yang-12 (work in progress), Network Configuration Protocol (NETCONF)",
April 2010. draft-ietf-netmod-yang-13 (work in progress), June 2010.
[I-D.ietf-netmod-yang-types] [I-D.ietf-netmod-yang-types]
Schoenwaelder, J., "Common YANG Data Types", Schoenwaelder, J., "Common YANG Data Types",
draft-ietf-netmod-yang-types-09 (work in progress), draft-ietf-netmod-yang-types-09 (work in progress),
April 2010. April 2010.
8.2. Informative References 8.2. Informative References
[RFC4181] Heard, C., "Guidelines for Authors and Reviewers of MIB [RFC4181] Heard, C., "Guidelines for Authors and Reviewers of MIB
Documents", BCP 111, RFC 4181, September 2005. Documents", BCP 111, RFC 4181, September 2005.
skipping to change at page 23, line 25 skipping to change at page 23, line 25
Internet-Draft boilerplate (see Internet-Draft boilerplate (see
http://www.ietf.org/ietf/1id-guidelines.txt), including the http://www.ietf.org/ietf/1id-guidelines.txt), including the
appropriate statement to permit publication as an RFC, and that appropriate statement to permit publication as an RFC, and that
I-D boilerplate does not contain references or section numbers. I-D boilerplate does not contain references or section numbers.
2. Abstract -- verify that the abstract does not contain references, 2. Abstract -- verify that the abstract does not contain references,
that it does not have a section number, and that its content that it does not have a section number, and that its content
follows the guidelines in follows the guidelines in
http://www.ietf.org/ietf/1id-guidelines.txt. http://www.ietf.org/ietf/1id-guidelines.txt.
3. IETF Trust Copyright -- verify that the draft contains the latest 3. IETF Trust Copyright -- verify that the draft has the appropriate
approved TLP boilerplate as described in Section 3.1. 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 4. Security Considerations Section -- verify that the draft uses the
latest approved template from the OPS area web site latest approved template from the OPS area web site
(http://www.ops.ietf.org/yang-security.html) and that the (http://www.ops.ietf.org/yang-security-considerations.txt) and
guidelines therein have been followed. that the guidelines therein have been followed.
5. IANA Considerations Section -- this section must always be 5. IANA Considerations Section -- this section must always be
present. For each module within the document, ensure that the present. For each module within the document, ensure that the
IANA Considerations section contains entries for the following IANA Considerations section contains entries for the following
IANA registries: IANA registries:
XML Namespace Registry: Register the YANG module namespace. XML Namespace Registry: Register the YANG module namespace.
YANG Module Registry: Register the YANG module name, prefix, YANG Module Registry: Register the YANG module name, prefix,
namespace, and RFC number, according to the rules specified in namespace, and RFC number, according to the rules specified in
skipping to change at page 24, line 22 skipping to change at page 24, line 27
(TLP) document, which can be found at: (TLP) document, which can be found at:
http://trustee.ietf.org/license-info/ http://trustee.ietf.org/license-info/
8. Other Issues -- check for any issues mentioned in 8. Other Issues -- check for any issues mentioned in
http://www.ietf.org/ID-Checklist.html that are not covered http://www.ietf.org/ID-Checklist.html that are not covered
elsewhere. elsewhere.
9. Technical Content -- review the actual technical content for 9. Technical Content -- review the actual technical content for
compliance with the guidelines in this document. The use of a compliance with the guidelines in this document. The use of a
YANG module compiler is recommended when checking for syntax YANG module compiler is RECOMMENDED when checking for syntax
errors, [ed.: online YANG validation tool URL TBD]. Checking for errors. A list of freely available tools and other information
correct syntax, however, is only part of the job. It is just as can be found at:
important to actually read the YANG module document from the
point of view of a potential implementor. It is particularly http://trac.tools.ietf.org/wg/netconf/trac/wiki
important to check that description statements are sufficiently
clear and unambiguous to allow interoperable implementations to Checking for correct syntax, however, is only part of the job.
be created. 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.
Appendix B. YANG Module Template Appendix B. YANG Module Template
<CODE BEGINS> file "ietf-template@2010-05-18.yang" <CODE BEGINS> file "ietf-template@2010-05-18.yang"
module ietf-template { module ietf-template {
// replace this string with a unique namespace URN value // replace this string with a unique namespace URN value
namespace namespace
"urn:ietf:params:xml:ns:yang:ietf-template"; "urn:ietf:params:xml:ns:yang:ietf-template";
skipping to change at page 28, line 7 skipping to change at page 28, line 7
// DO NOT put deviation statements in a published module // DO NOT put deviation statements in a published module
} }
<CODE ENDS> <CODE ENDS>
Figure 1 Figure 1
Appendix C. Change Log Appendix C. Change Log
C.1. Changes from 04 to 05 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 Changed 'object' terminology to 'data definition'.
o Put XPath guidelines in separate section. o Put XPath guidelines in separate section.
o Clarified XPath usage for XML document order dependencies. o Clarified XPath usage for XML document order dependencies.
o Updated <CODE BEGINS> guidelines to current conventions. o Updated <CODE BEGINS> guidelines to current conventions.
o Added informative reference for IANA considerations guidelines and o Added informative reference for IANA considerations guidelines and
XML registry. XML registry.
o Updated IANA Considerations section to reserve the ietf-template o Updated IANA Considerations section to reserve the ietf-template
module in the YANG Module Name Registry so it cannot be reused module in the YANG Module Name Registry so it cannot be reused
accidently. accidently.
o Many other clarifications and fixed typos found in WGLC reviews. o Many other clarifications and fixed typos found in WGLC reviews.
C.2. Changes from 03 to 04 C.3. Changes from 03 to 04
o Removed figure 1 to reduce duplication, just refer to 4741bis o Removed figure 1 to reduce duplication, just refer to 4741bis
draft. draft.
o Fixed bugs and typos found in WGLC reviews. o Fixed bugs and typos found in WGLC reviews.
o Removed some guidelines and referring to YANG draft instead of o Removed some guidelines and referring to YANG draft instead of
duplicating YANG rules here. duplicating YANG rules here.
o Changed security guidelines so they refer to the IETF Trust TLP o Changed security guidelines so they refer to the IETF Trust TLP
skipping to change at page 29, line 21 skipping to change at page 29, line 25
o Added guideline that strings should not rely on preservation of o Added guideline that strings should not rely on preservation of
leading and trailing whitespace characters. leading and trailing whitespace characters.
o Relaxed some XPath and anyxml guidelines from SHOULD NOT or MUST o Relaxed some XPath and anyxml guidelines from SHOULD NOT or MUST
NOT to MAY use with caution. NOT to MAY use with caution.
o Updated the TLP text within the example module again. o Updated the TLP text within the example module again.
o Reversed order of change log so most recent entries are first. o Reversed order of change log so most recent entries are first.
C.3. Changes from 02 to 03 C.4. Changes from 02 to 03
o Updated figure 1 to align with 4741bis draft. o Updated figure 1 to align with 4741bis draft.
o Updated guidelines for import-by-revision and include-by-revision. o Updated guidelines for import-by-revision and include-by-revision.
o Added file name to code begins convention in ietf-template module. o Added file name to code begins convention in ietf-template module.
C.4. Changes from 01 to 02 C.5. Changes from 01 to 02
o Updated figure 1 per mailing list comments. o Updated figure 1 per mailing list comments.
o Updated suggested organization to include the working group name. o Updated suggested organization to include the working group name.
o Updated ietf-template.yang to use new organization statement o Updated ietf-template.yang to use new organization statement
value. value.
o Updated Code Component requirements as per new TLP. o Updated Code Component requirements as per new TLP.
o Updated ietf-template.yang to use new Code Component begin and end o Updated ietf-template.yang to use new Code Component begin and end
markers. markers.
o Updated references to the TLP in a couple sections. o Updated references to the TLP in a couple sections.
o Change manager/agent terminology to client/server. o Change manager/agent terminology to client/server.
C.5. Changes from 00 to 01 C.6. Changes from 00 to 01
o Added transport 'TLS' to figure 1. o Added transport 'TLS' to figure 1.
o Added note about RFC 2119 terminology. o Added note about RFC 2119 terminology.
o Corrected URL for instructions to authors. o Corrected URL for instructions to authors.
o Updated namespace procedures section. o Updated namespace procedures section.
o Updated guidelines on module contact, reference, and organization o Updated guidelines on module contact, reference, and organization
 End of changes. 46 change blocks. 
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