draft-ietf-netmod-yang-usage-00.txt   draft-ietf-netmod-yang-usage-01.txt 
Internet Engineering Task Force A. Bierman Internet Engineering Task Force A. Bierman
Internet-Draft Netconf Central Internet-Draft Netconf Central
Intended status: Informational May 18, 2009 Intended status: Informational August 12, 2009
Expires: November 19, 2009 Expires: February 13, 2010
Guidelines for Authors and Reviewers of YANG Data Model Documents Guidelines for Authors and Reviewers of YANG Data Model Documents
draft-ietf-netmod-yang-usage-00 draft-ietf-netmod-yang-usage-01
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
skipping to change at page 1, line 32 skipping to change at page 1, line 32
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."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on November 19, 2009. This Internet-Draft will expire on February 13, 2010.
Copyright Notice Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the Copyright (c) 2009 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 in effect on the date of Provisions Relating to IETF Documents in effect on the date of
publication of this document (http://trustee.ietf.org/license-info). publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights Please review these documents carefully, as they describe your rights
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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.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
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 . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.4. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. General Documentation Guidelines . . . . . . . . . . . . . . . 7 3. General Documentation Guidelines . . . . . . . . . . . . . . . 7
3.1. YANG Data Model Boilerplate Section . . . . . . . . . . . 7 3.1. YANG Data Model Boilerplate Section . . . . . . . . . . . 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 . . . . . . . . 8
3.5.2. Documents that Extend an Existing Name Space . . . . . 8 3.5.2. Documents that Extend an Existing Name Space . . . . . 8
3.6. Reference Sections . . . . . . . . . . . . . . . . . . . . 9 3.6. Reference Sections . . . . . . . . . . . . . . . . . . . . 9
3.7. Copyright Notices . . . . . . . . . . . . . . . . . . . . 9 3.7. Copyright Notices . . . . . . . . . . . . . . . . . . . . 9
3.8. Intellectual Property Section . . . . . . . . . . . . . . 9 3.8. 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. Module Life-cycle Management . . . . . . . . . . . . . . . 12 4.5. Lifecycle Management . . . . . . . . . . . . . . . . . . . 12
4.6. Header Contents . . . . . . . . . . . . . . . . . . . . . 12 4.6. Header Contents . . . . . . . . . . . . . . . . . . . . . 12
4.7. Data Types . . . . . . . . . . . . . . . . . . . . . . . . 13 4.7. Temporary Namespace Assignments . . . . . . . . . . . . . 13
4.8. Reusable Type Definitions . . . . . . . . . . . . . . . . 13 4.8. Top Level Database Objects . . . . . . . . . . . . . . . . 14
4.9. Object Definitions . . . . . . . . . . . . . . . . . . . . 14 4.9. Data Types . . . . . . . . . . . . . . . . . . . . . . . . 15
4.10. RPC Definitions . . . . . . . . . . . . . . . . . . . . . 15 4.10. Reusable Type Definitions . . . . . . . . . . . . . . . . 15
4.11. Notification Definitions . . . . . . . . . . . . . . . . . 15 4.11. Object Definitions . . . . . . . . . . . . . . . . . . . . 16
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 4.12. RPC Definitions . . . . . . . . . . . . . . . . . . . . . 17
6. Security Considerations . . . . . . . . . . . . . . . . . . . 17 4.13. Notification Definitions . . . . . . . . . . . . . . . . . 17
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 6. Security Considerations . . . . . . . . . . . . . . . . . . . 19
8.1. Normative References . . . . . . . . . . . . . . . . . . . 19 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
8.2. Informative References . . . . . . . . . . . . . . . . . . 19 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Appendix A. Module Review Checklist . . . . . . . . . . . . . . . 20 8.1. Normative References . . . . . . . . . . . . . . . . . . . 21
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 22 8.2. Informative References . . . . . . . . . . . . . . . . . . 21
Appendix A. Module Review Checklist . . . . . . . . . . . . . . . 22
Appendix B. YANG Module Template . . . . . . . . . . . . . . . . 24
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 27
C.1. Changes from 00 to 01 . . . . . . . . . . . . . . . . . . 27
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 28
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 MIB usage guidelines specification [RFC4181] in intent similar to the MIB usage guidelines specification [RFC4181] in intent
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+-------------+ +--------------------+ +-------------------+ +-------------+ +--------------------+ +-------------------+
| | | | | |
+-------------+ +-----------------+ +---------------+ +-------------+ +-----------------+ +---------------+
(3) | Operations | | <edit-config> | | <eventType> | (3) | Operations | | <edit-config> | | <eventType> |
+-------------+ +-----------------+ +---------------+ +-------------+ +-----------------+ +---------------+
| | | | | |
+-------------+ +--------------------+ +----------------+ +-------------+ +--------------------+ +----------------+
(2) | RPC | | <rpc>, <rpc-reply> | | <notification> | (2) | RPC | | <rpc>, <rpc-reply> | | <notification> |
+-------------+ +--------------------+ +----------------+ +-------------+ +--------------------+ +----------------+
| | | | | |
+-------------+ +-----------------------------+ +-------------+ +--------------------------------+
(1) | Transport | | BEEP, SSH, SSL, console | (1) | Transport | | BEEP, SSH, SSL, TLS, console |
| Protocol | | | | Protocol | | |
+-------------+ +-----------------------------+ +-------------+ +--------------------------------+
Figure 1 Figure 1
This document defines usage guidelines related to the NETCONF This document defines usage guidelines related to the NETCONF
operations layer (3), and NETCONF content layer (4). operations layer (3), and NETCONF content layer (4).
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
working group regarding YANG module content. Yang modules complying
with this document will treat the RFC 2119 terminology as 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 agent o agent
o application o application
o capabilities o capabilities
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o Unpublished Document: An unstable release of a module, usually o Unpublished Document: An unstable release of a module, 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.isi.edu/in-notes/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 YANG data model boilerplate section o YANG data model boilerplate section
o Narrative sections o Narrative sections
o Definitions section o Definitions section
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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 MUST contain an IANA
Considerations section. The requirements for this section vary Considerations section. The requirements for this section vary
depending what actions are required of the IANA. depending what actions are required of the IANA.
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, 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 [ed: Namespace registry entry must be requested from the IANA. The YANG
procedure TBD]. specification includes the procedure for this purpose in its IANA
Considerations section.
3.5.2. Documents that Extend an Existing Name Space 3.5.2. Documents that Extend an Existing Name Space
If an Internet-Draft defines any extensions to a YANG Namespace If an Internet-Draft defines any extensions to a YANG Namespace
already administered by the IANA, then the document MUST include an already administered by the IANA, then the document MUST include an
IANA Considerations section, specifies how the name space extension IANA Considerations section, specifies how the name space extension
is to be administered. is to be administered.
Specifically, if any YANG submodule belongs-to value contained in the Specifically, if any YANG submodule belongs-to value contained in the
document is associated with a module that contains a namespace document is associated with a module that contains a namespace
statement value equal to a YANG Namespace already administered by the statement value equal to a YANG Namespace already administered by the
IANA, then a new YANG Module registry entry and YANG Namespace Update IANA, then the existing YANG Namespace must be updated to include the
Procedure must be requested from the IANA [ed: procedure TBD]. new submodule.
3.6. Reference Sections 3.6. Reference Sections
[ed: 2223bis text TBD] [ed: 2223bis text TBD]
For every import or include statement which appears in a module For every import or include statement which appears in a module
contained in the specification, which identifies a module in a contained in the specification, which identifies a module in a
separate document, a corresponding normative reference to that separate document, a corresponding normative reference to that
document MUST appear in the Normative References section. The document MUST appear in the Normative References section. The
reference MUST correspond to the specific module version actually reference MUST correspond to the specific module version actually
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to specify optional behavior. Instead, a 'feature' statement SHOULD to specify optional behavior. Instead, a 'feature' statement SHOULD
be defined to represent the NETCONF capability, and the 'if-feature' be defined to represent the NETCONF capability, and the 'if-feature'
statement SHOULD be used within the object definition. statement SHOULD be used within the object definition.
If the condition associated with the desired semantics is not If the condition associated with the desired semantics is not
dependent on any particular instance value within the database, then dependent on any particular instance value within the database, then
an 'if-feature' statement SHOULD be used instead of a 'when' an 'if-feature' statement SHOULD be used instead of a 'when'
statement. statement.
All 'must' and 'when' statements MUST contain valid XPath. If any All 'must' and 'when' statements MUST contain valid XPath. If any
name tests are present, they MUST contain valid module prefixes name tests are present, they MUST contain valid module prefixes and
and/or data node names. data node names. References to non-existent nodes are considered
invalid in YANG, even though they are permitted in XPath.
The 'attribute' and 'namespace' axis SHOULD NOT be used because the The 'attribute' and 'namespace' axis SHOULD NOT be used because the
associated XML node types are not supported in YANG, and may not be associated XML node types are not supported in YANG, and may not be
supported consistently across NETCONF agent implementations. supported consistently across NETCONF agent implementations.
The 'position' and 'last' functions SHOULD NOT be used. Also, the The 'position' and 'last' functions SHOULD NOT be used. Also, the
'preceding', 'preceding-sibling', 'following', and 'following- 'preceding', and 'following' axes SHOULD NOT be used. These
sibling' axis SHOULD NOT be used. These constructs rely on XML constructs rely on XML document order within a NETCONF agent
document order within a NETCONF agent configuration database, which configuration database, which may not be supported consistently or
may not be supported consistently or produce reliable results across produce reliable results across implementations. Predicate
implementations. Predicate expressions based on static node expressions based on static node properties (e.g., name, value,
properties (e.g., name, value, ancestors, descendants) SHOULD be used ancestors, descendants) SHOULD be used instead.
instead.
The 'preceding-sibling' and 'following-sibling' axes MAY be used,
with caution. An agent is not required to maintain a persistent or
deterministic XML document order, which will affect use of these
axes.
Implicit 'position' function calls within predicates SHOULD NOT be Implicit 'position' function calls within predicates SHOULD NOT be
used. (e.g., //chapter[42]). used. (e.g., //chapter[42]).
Data nodes which use the 'int64' and 'uint64' built-in type SHOULD Data nodes which use the 'int64' and 'uint64' built-in type SHOULD
NOT be used within relational expressions. There are boundary NOT be used within relational expressions. There are boundary
conditions in which the translation from the YANG 64-bit type to an conditions in which the translation from the YANG 64-bit type to an
XPath number can cause incorrect results. XPath number can cause incorrect results.
Data modelers need to be careful not to confuse the YANG value space 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 the XPath value space. The data types are not the same in both,
and conversion between YANG and XPath data types SHOULD be considered and conversion between YANG and XPath data types SHOULD be considered
carefully. carefully.
Explicit XPath data type conversions MAY be used (e.g., 'string', Explicit XPath data type conversions MAY be used (e.g., 'string',
'boolean', or 'number' functions), instead of implicit XPath data 'boolean', or 'number' functions), instead of implicit XPath data
type conversions. type conversions.
4.5. Module Life-cycle Management 4.5. Lifecycle Management
The status statement SHOULD NOT be present if its value is 'current'. The status statement SHOULD NOT be present if its value is 'current'.
It MUST be present if its value is 'deprecated' or 'obsolete'. It MUST be present if its value is 'deprecated' or 'obsolete'.
The module or submodule name MUST NOT be changed, once the document The module or submodule name MUST NOT be changed, once the document
containing the module or submodule is published. containing the module or submodule is published.
The module namespace URI value SHOULD NOT be changed, once the The module namespace URI value SHOULD NOT be changed, once the
document containing the module is published. document containing the module is published.
The revision-date sub-statement (within the imports statement) SHOULD The revision-date sub-statement (within the imports statement) SHOULD
be present. It MUST be present (in all published modules) if any be present. It MUST be present (in all published modules) if any
groupings are used from the external module. groupings are used from the external module.
The revision-date sub-statement (within the include statement) MAY be The revision-date sub-statement (within the include statement) MAY be
present. It SHOULD be present (in all published modules) if any present. It SHOULD be present (in all published modules) if any
groupings are used from the external sub-module. groupings are used from the external sub-module.
4.6. Header Contents 4.6. Header Contents
o The namespace MUST be a globally unique URI, as defined in For published modules, the namespace MUST be a globally unique URI,
[RFC3986]. This value is usually assigned by the IANA. as defined in [RFC3986]. This value is usually assigned by the IANA.
o Until a URI is assigned by the IANA, a temporary namespace URI MAY The organization statement MUST be present. If the module is
be selected which is not likely to collide with other YANG contained in a documented intended for standards-track status, then
namespaces, such as the filename of the Internet Draft containing the organization SHOULD be the IETF.
the module. This value MUST be a valid URI (e.g.,
'file:///draft-ietf-foo-bar-00').
o The organization statement MUST be present. The contact statement MUST be present. If the module is contained in
a documented intended for standards-track status, then the working
group WEB and mailing information MUST be present, and the document
author contact information SHOULD be present. In addition, the Area
Director and other contact information MAY be present.
o The contact statement MUST be present. The description statement MUST be present. If the module is
contained in an unpublished document, then the file name of this
document SHOULD be identified in the description statement. This
text MUST be removed when the document is published.
o The description statement MUST be present. 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.
o If the module represents a model defined in one or more external The reference statement MUST be present. It MUST identify the
documents, then a reference statement MUST be present. published document which contains the module.
o A revision statement MUST be present for each published version of 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 module.
o Each new revision MUST include a revision date which is higher Each new revision MUST include a revision date which is higher than
than any other revision date in the module. any other revision date in the module.
o 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 unpublished versions (i.e., Internet Drafts), but the revision date
date MUST be updated to a higher value each time the Internet MUST be updated to a higher value each time the Internet Draft is re-
Draft is re-published. published.
4.7. Data Types 4.7. Temporary Namespace Assignments
o Selection of an appropriate data type (i.e., built-in type, It is desirable to include only valid YANG modules in documents,
existing derived type, or new derived type) is very subjective and whether they are published yet or not.
therefore few requirements can be specified on that subject.
o Data model designers SHOULD use the most appropriate built-in data o allows the module to compile correctly instead of generating
disruptive fatal errors.
o allows early implementors to use the modules without picking a
random value for this field.
o allows early interoperability testing since independent
implementations will use the same namespace value.
Until a URI is assigned by the IANA, a temporary namespace URI MUST
be provided for the namespace statement in a YANG module. A value
SHOULD be selected which is not likely to collide with other YANG
namespaces.
An unpublished module namespace statement value SHOULD include the
field 'DRAFT-nn', where 'nn' is replaced by the current Internet
Draft number.
If the YANG module has been previously published, then the RPC being
updated needs to be identified. In this case, an unpublished module
namespace statement value SHOULD include the field
'DRAFT-XXXXBIS-nn', where 'XXXX' is replaced by the RFC number being
updated, and 'nn' is replaced by the current Internet Draft number.
A temporary namespace statement value SHOULD have the following form:
<URN prefix string>:<module-name>:<draft-field>
The suggested URN prefix string that SHOULD be used is shown below.
This value will be defined by the IANA. urn:ietf:params:xml:ns:yang:
The following example URNs would be valid temporary namespace
statement values:
urn:ietf:params:xml:ns:yang:ietf-netconf-partial-lock:DRAFT-09
urn:ietf:params:xml:ns:yang:ietf-netconf-state:DRAFT-07
urn:ietf:params:xml:ns:yang:ietf-netconf:DRAFT-4741BIS-01
4.8. Top Level Database Objects
There SHOULD only be one top-level data node defined in each YANG
module. However, there MAY be more than one if needed.
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 object is defined as a node that a manager must
provide for the database to be valid. The agent will not provide a
value under any conditions.
Top-level database objects 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 agent
boots or when a module is loaded dynamically at runtime.
Top level objects are declared in YANG as mandatory with the
mandatory statement or the min-elements statement. All nested non-
presence containers are transparent, so a mandatory node nested
within one or more non-presence containers causes the top-level
container to be considered mandatory.
4.9. 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. type for the particular application.
o 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.
o For string data types, if a machine-readable pattern can be For string data types, if a machine-readable pattern can be defined
defined for the desired semantics, then one or more pattern for the desired semantics, then one or more pattern statements SHOULD
statements SHOULD be present. be present.
o For string data types, if the length of the string is not required For string data types, if the length of the string is not required to
to be unbounded in all implementations, then a length statement be unbounded in all implementations, then a length statement SHOULD
SHOULD be present. [ed: should the 'resource-denied' error be be present. [ed: should the 'resource-denied' error be mentioned
mentioned here?] here?]
o 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 semantics are different than those allowed by the unbounded intrinsic
intrinsic data type (e.g., int32), then a range statement SHOULD data type (e.g., int32), then a range statement SHOULD be present.
be present.
o The signed numeric data types (i.e., 'int8', 'int16', 'int32', and The signed numeric data types (i.e., 'int8', 'int16', 'int32', and
'int64') SHOULD NOT be used unless negative values are allowed for 'int64') SHOULD NOT be used unless negative values are allowed for
the desired semantics. the desired semantics.
o For enumeration or bits data types, the semantics for each enum or For enumeration or bits data types, the semantics for each enum or
bit SHOULD be documented. A separate description statement bit SHOULD be documented. A separate description statement (within
(within each enum or bit statement) SHOULD be present. each enum or bit statement) SHOULD be present.
4.8. Reusable Type Definitions 4.10. Reusable Type Definitions
o If an appropriate derived type exists in any standard module, such If an appropriate derived type exists in any standard module, such as
as [I-D.ietf-netmod-yang-types], then it SHOULD be used instead of [I-D.ietf-netmod-yang-types], then it SHOULD be used instead of
defining a new derived type. defining a new derived type.
o If an appropriate units identifier can be associated with the If an appropriate units identifier can be associated with the desired
desired semantics, then a units statement SHOULD be present. semantics, then a units statement SHOULD be present.
o 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.
o 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 anticipated that these data types will be reused by multiple modules,
modules, then these derived types SHOULD be contained in a then these derived types SHOULD be contained in a separate module or
separate module or submodule, to allow easier reuse without submodule, to allow easier reuse without unnecessary coupling.
unnecessary coupling.
o The description statement MUST be present. The description statement MUST be present.
o If the type definition semantics are defined in an external If the type definition semantics are defined in an external document,
document, then the reference statement SHOULD be present. then the reference statement SHOULD be present.
4.9. Object Definitions 4.11. Object Definitions
o The description statement MUST be present in the following body The description statement MUST be present in the following body
statements: statements:
* extension o extension
* feature o feature
* identity o identity
* typedef o typedef
* grouping o grouping
* augment o augment
* rpc o rpc
* notification o notification
o The description statement MUST be present in the following data The description statement MUST be present in the following data
definition constructs: definition constructs:
* container o container
* leaf o leaf
* leaf-list o leaf-list
* list o list
* choice o choice
* anyxml
o If the object semantics are defined in an external document, then o anyxml
a reference statement SHOULD be present.
o The 'anyxml' construct MUST NOT be used within configuration data. If the object semantics are defined in an external document, then a
reference statement SHOULD be present.
o If there are referential integrity constraints associated with the The 'anyxml' construct MUST NOT be used within configuration data.
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.
o For list and leaf-list objects, if the number of possible For list and leaf-list objects, if the number of possible instances
instances is not required to be unbounded for all implementations, is not required to be unbounded for all implementations, then the
then the max-elements statement SHOULD be present. max-elements statement SHOULD be present.
o If any must or when statements are used within the object If any must or when statements are used within the object definition,
definition, then the object description statement SHOULD describe then the object description statement SHOULD describe the purpose of
the purpose of each one. each one.
4.10. RPC Definitions 4.12. RPC Definitions
o The description statement MUST be present. The description statement MUST be present.
o If the RPC method semantics are defined in an external document, If the RPC method semantics are defined in an external document, then
then a reference statement SHOULD be present. a reference statement SHOULD be present.
o If the RPC method impacts system behavior in some way, it SHOULD If the RPC method impacts system behavior in some way, it SHOULD be
be mentioned in the description statement. mentioned in the description statement.
o If the RPC method is potentially harmful to system behavior in If the RPC method is potentially harmful to system behavior in some
some way, it MUST be mentioned in the Security Considerations way, it MUST be mentioned in the Security Considerations section of
section of the document. the document.
4.11. Notification Definitions 4.13. Notification Definitions
o The description statement MUST be present. The description statement MUST be present.
o 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. then a reference statement SHOULD be present.
5. IANA Considerations 5. IANA Considerations
There are no actions requested of IANA at this time. There are no actions requested of IANA at this time.
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. It does not introduce defined with the YANG data modeling language. It does not introduce
skipping to change at page 19, line 21 skipping to change at page 21, line 21
[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.
[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
NETCONF", draft-ietf-netmod-yang-05 (work in progress), NETCONF", draft-ietf-netmod-yang-07 (work in progress),
April 2009. July 2009.
[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-03 (work in progress), draft-ietf-netmod-yang-types-03 (work in progress),
May 2009. May 2009.
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 22, line 5 skipping to change at page 24, line 5
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; see [YANG tool URL TBD] for more information. Checking errors; see [YANG tool URL TBD] for more information. Checking
for correct syntax, however, is only part of the job. It is for correct syntax, however, is only part of the job. It is
just as important to actually read the YANG module document from just as important to actually read the YANG module document from
the point of view of a potential implementor. It is the point of view of a potential implementor. It is
particularly important to check that description statements are particularly important to check that description statements are
sufficiently clear and unambiguous to allow interoperable sufficiently clear and unambiguous to allow interoperable
implementations to be created. implementations to be created.
Appendix B. YANG Module Template
== begin "ietf-template.yang"
module ietf-template {
// replace this string with a unique namespace URN value
namespace
"urn:ietf:params:xml:ns:yang:ietf-template:DRAFT-01";
// 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; }
organization
"Internet Engineering Task Force";
// 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) 2009 IETF Trust and the persons identified as
the document authors. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, are permitted provided that the
following conditions are met:
- Redistributions of source code must retain the above
copyright notice, this list of conditions and the
following disclaimer.
- Redistributions in binary form must reproduce the above
copyright notice, this list of conditions and the
following disclaimer in the documentation and/or other
materials provided with the distribution.
- Neither the name of Internet Society, IETF or IETF
Trust, nor the names of specific contributors, may be
used to endorse or promote products derived from this
software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
CONTRIBUTORS 'AS IS' AND ANY EXPRESS OR IMPLIED
WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.";
// RFC Ed.: replace XXXX with actual RFC number and remove this note
reference "RFC XXXX";
// RFC Ed.: remove this note
// Note: extracted from draft-ietf-netmod-yang-usage-01.txt
// replace YYYY-MM-DD with a real date (year-month-day)
// here is an example revision date: 2009-08-12
revision YYYY-MM-DD {
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
}
== end "ietf-template.yang"
Figure 2
Appendix C. Change Log
C.1. Changes from 00 to 01
o Added transport 'TLS' to figure 1.
o Added note about RFC 2119 terminology.
o Corrected URL for instructions to authors.
o Updated namespace procedures section.
o Updated guidelines on module contact, reference, and organization
statements.
o Added note on use of preceding-sibling and following-sibling axes
in XPath expressions.
o Added section on temporary namespace statement values.
o Added section on top level database objects.
o Added ietf-template.yang appendix.
Author's Address Author's Address
Andy Bierman Andy Bierman
Netconf Central Netconf Central
Simi Valley, CA Simi Valley, CA
USA USA
Email: andy@netconfcentral.com Email: andy@netconfcentral.com
 End of changes. 72 change blocks. 
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