Internet DRAFT - draft-bierman-netmod-yang-usage

draft-bierman-netmod-yang-usage






Internet Engineering Task Force                               A. Bierman
Internet-Draft                                           Netconf Central
Intended status: BCP                                    January 23, 2009
Expires: July 27, 2009


   Guidelines for Authors and Reviewers of YANG Data Model Documents
                   draft-bierman-netmod-yang-usage-00

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
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   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on July 27, 2009.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.








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Abstract

   This memo provides guidelines for authors and reviewers of standards
   track specifications containing YANG data model modules.  Applicable
   portions may be used as a basis for reviews of other YANG data model
   documents.  Recommendations and procedures are defined, which are
   intended to increase interoperability and usability of NETCONF
   implementations which utilize YANG data model modules.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  Requirements Notation  . . . . . . . . . . . . . . . . . .  5
     2.2.  NETCONF Terms  . . . . . . . . . . . . . . . . . . . . . .  5
     2.3.  YANG Terms . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.4.  Terms  . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  General Documentation Guidelines . . . . . . . . . . . . . . .  7
     3.1.  YANG Data Model Boilerplate Section  . . . . . . . . . . .  7
     3.2.  Narrative Sections . . . . . . . . . . . . . . . . . . . .  7
     3.3.  Definitions Section  . . . . . . . . . . . . . . . . . . .  8
     3.4.  Security Considerations Section  . . . . . . . . . . . . .  8
     3.5.  IANA Considerations Section  . . . . . . . . . . . . . . .  8
       3.5.1.  Documents that Create a New Name Space . . . . . . . .  8
       3.5.2.  Documents that Extend an Existing Name Space . . . . .  9
     3.6.  Reference Sections . . . . . . . . . . . . . . . . . . . .  9
     3.7.  Copyright Notices  . . . . . . . . . . . . . . . . . . . .  9
     3.8.  Intellectual Property Section  . . . . . . . . . . . . . .  9
   4.  YANG Usage Guidelines  . . . . . . . . . . . . . . . . . . . . 10
     4.1.  Identifiers  . . . . . . . . . . . . . . . . . . . . . . . 10
     4.2.  Defaults . . . . . . . . . . . . . . . . . . . . . . . . . 10
     4.3.  Conditional Statements . . . . . . . . . . . . . . . . . . 10
     4.4.  Header Contents  . . . . . . . . . . . . . . . . . . . . . 11
     4.5.  Data Types . . . . . . . . . . . . . . . . . . . . . . . . 12
     4.6.  Object Definitions . . . . . . . . . . . . . . . . . . . . 13
     4.7.  RPC Definitions  . . . . . . . . . . . . . . . . . . . . . 13
     4.8.  Notification Definitions . . . . . . . . . . . . . . . . . 14
   5.  YANG Module Registry . . . . . . . . . . . . . . . . . . . . . 15
     5.1.  YANG Registry Data Model . . . . . . . . . . . . . . . . . 16
     5.2.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . 18
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 21
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 22
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 23
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 24
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 24
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 25



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1.  Introduction

   The standardization of network configuration interfaces for use with
   the NETCONF [RFC4741] protocol requires a modular set of data models,
   which can be reused and extended over time.

   This document defines a set of usage guidelines for standards track
   documents containing YANG [I-D.ietf-netmod-yang] data models.  It is
   similar to the MIB usage guidelines specification [RFC4181] in intent
   and structure.

   Many YANG constructs are defined as optional to use, such as the
   description clause.  However, in order to maximize interoperability
   of NETCONF implementations utilizing YANG data models, it is
   desirable to define a set of usage guidelines which may require a
   higher level of compliance than the minimum level defined in the YANG
   specification.

   A new IANA registry is needed to support YANG.  This registry will
   allow YANG module namespace and other definitions to be centrally
   located, minimizing name collisions, and providing an authoritative
   status of each YANG module.

   The YANG Module Registry will support YANG modules, as well as YANG
   submodules which utilize a 'virtual' module definition.  A virtual
   module contains only the module header, submodule include statements,
   and meta statements.  The Submodule Registration procedure [ed: IANA
   procedure TBD] is used to publish specifications containing YANG
   submodules which extend a virtual module.  This procedure allows the
   main module revision statement and include statement to be updated,
   without requiring publication or a separate RFC to contain the main
   module.  Refer to Section 5 for more details.



















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    The NETCONF stack can be conceptually partitioned into four layers.

          Layer                Example
         +-------------+   +--------------------+ +-------------------+
     (4) |   Content   |   | Configuration data | | Notification data |
         +-------------+   +--------------------+ +-------------------+
                |                    |                   |
         +-------------+   +-----------------+     +---------------+
     (3) | Operations  |   |  <edit-config>  |     |  <eventType>  |
         +-------------+   +-----------------+     +---------------+
                |                    |                   |
         +-------------+   +--------------------+  +----------------+
     (2) |     RPC     |   | <rpc>, <rpc-reply> |  | <notification> |
         +-------------+   +--------------------+  +----------------+
                |                    |                   |
         +-------------+       +-----------------------------+
     (1) |  Transport  |       |   BEEP, SSH, SSL, console   |
         |   Protocol  |       |                             |
         +-------------+       +-----------------------------+



                                 Figure 1

   This document defines usage guidelines related to the NETCONF
   operations layer (3), and NETCONF content layer (4).

   It also contains a definition for a registry for YANG Modules, which
   can be used to locate documents which contain standards-track modules
   or submodules.





















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2.  Terminology

2.1.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.2.  NETCONF Terms

   The following terms are defined in [RFC4741] and are not redefined
   here:

   o  agent

   o  application

   o  capabilities

   o  manager

   o  operation

   o  RPC

2.3.  YANG Terms

   The following terms are defined in [I-D.ietf-netmod-yang] and are not
   redefined here:

   o  data node

   o  module

   o  submodule

   o  namespace

   o  version

2.4.  Terms

   The following terms are used throughout this document:

   o  YAM: Shorthand term for a YANG data model module or submodule,
      used for properties which apply to both modules and submodules.
      When describing properties which are specific to modules, the term
      'YANG module', or simply 'module', is used instead.  When



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      describing properties which are specific to submodules, the term
      'YANG submodule', or simply 'module' is used instead.

   o  Published Document: A stable release of a YAM, usually contained
      in an RFC.

   o  Unpublished Document: An unstable release of a YAM, usually
      contained in an Internet Draft.

   o  Virtual Module: A YANG module which does not contain any body
      statements, and is maintained in a registry.  The body statements
      are defined in submodules, in one or more documents, and
      'included' in the main module via a registry entry for the main
      module.





































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3.  General Documentation Guidelines

   YANG data model modules (YAMs) under review are likely to be
   contained in Internet Drafts.  All guidelines for Internet Draft
   authors MUST be followed.  These guidelines are available online at:

   http://www.isi.edu/in-notes/rfc-editor/instructions2authors.txt

   The following sections MUST be present in an Internet Draft
   containing a YAM:

   o  YANG data model boilerplate section

   o  Narrative sections

   o  Definitions section

   o  Security Considerations section

   o  IANA Considerations section

   o  References section

3.1.  YANG Data Model Boilerplate Section

   This section MUST contain a verbatim copy of the latest approved
   Internet-Standard Management Framework boilerplate, which is
   available on-line at [ed: URL TBD].

3.2.  Narrative Sections

   The narrative part MUST include an overview section that describes
   the scope and field of application of the YAM(s) defined by the
   specification and that specifies the relationship (if any) of these
   YAMs to other standards, particularly to standards containing other
   YAM modules.  The narrative part SHOULD include one or more sections
   to briefly describe the structure of the YAMs defined in the
   specification.

   If the YAM(s) defined by the specification import definitions from
   other YAMs (except for those defined in the YANG
   [I-D.ietf-netmod-yang] or YANG Types [I-D.ietf-netmod-yang-types]
   documents) or are always implemented in conjunction with other YAMs,
   then those facts MUST be noted in the overview section, as MUST any
   special interpretations of objects in other YAMs.






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3.3.  Definitions Section

   This section contains the YAM(s) defined by the specification.  These
   modules MUST be written in YANG [I-D.ietf-netmod-yang].

   See Section 4 for guidelines on YANG usage.

3.4.  Security Considerations Section

   Each specification that defines one or more YAMs MUST contain a
   section that discusses security considerations relevant to those
   modules.  This section MUST be patterned after the latest approved
   template (available at [ed: URL TBD]).

   In particular, writable YAM objects that could be especially
   disruptive if abused MUST be explicitly listed by name and the
   associated security risks MUST be spelled out; similarly, readable
   YAM objects that contain especially sensitive information or that
   raise significant privacy concerns MUST be explicitly listed by name
   and the reasons for the sensitivity/privacy concerns MUST be
   explained.

3.5.  IANA Considerations Section

   In order to comply with IESG policy as set forth in
   http://www.ietf.org/ID-Checklist.html, every Internet-Draft that is
   submitted to the IESG for publication MUST contain an IANA
   Considerations section.  The requirements for this section vary
   depending what actions are required of the IANA.

   Refer to [TBD] for details on the structure of the YANG registries
   maintained by the IANA.

3.5.1.  Documents that Create a New Name Space

   If an Internet-Draft defines a new name space that is to be
   administered by the IANA, then the document MUST include an IANA
   Considerations section, specifies how the name space is to be
   administered.

   Specifically, if any YANG module namespace statement value contained
   in the document is not already registered with IANA, then a new YANG
   Namespace registry entry must be requested from the IANA [ed:
   procedure TBD].







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3.5.2.  Documents that Extend an Existing Name Space

   If an Internet-Draft defines any extensions to a YANG Namespace
   already administered by the IANA, then the document MUST include an
   IANA Considerations section, specifies how the name space extension
   is to be administered.

   Specifically, if any YANG submodule belongs-to value contained in the
   document is associated with a module that contains a namespace
   statement value equal to a YANG Namespace already administered by the
   IANA, then a new YANG Module registry entry and YANG Namespace Update
   Procedure must be requested from the IANA [ed: procedure TBD].

3.6.  Reference Sections

   [ed: 2223bis text TBD]

   For every import or include statement which appears in a YAM
   contained in the specification, which identifies a YAM in a separate
   document, a corresponding normative reference to that document MUST
   appear in the Normative References section.  The reference MUST
   correspond to the specific YAM version actually used within the
   specification.

   If any YANG submodule contained in the specification contains a
   'belongs-to' statement value which identifies a 'virtual' YANG module
   maintained in the IANA YANG Module Registry, then a corresponding
   normative reference to the registry identifier MUST appear in the
   Normative References section.  The registry entry MUST be properly
   updated, using the appropriate procedures [ed: IANA procedures TBD].

3.7.  Copyright Notices

   The proper copyright notices MUST be present in the module
   description statement. [ed.: See RFC 4181, 3.7.  Exact text for
   insertion is TBD.]

3.8.  Intellectual Property Section

   The proper IPR statements MUST be present in the document, according
   to the most current Internet Draft boilerplate. [ed.: actual IETF IPR
   text reference TBD]









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4.  YANG Usage Guidelines

   In general, YAMs in IETF standards-track specifications MUST comply
   with all syntactic and semantic requirements of YANG.
   [I-D.ietf-netmod-yang].  The guidelines in this section are intended
   to supplement the YANG specification, which is intended to define a
   minimum set of conformance requirements.

   In order to promote interoperability and establish a set of practices
   based on previous experience, the following sections establish usage
   guidelines for specific YANG constructs.

   Only guidelines which clarify or restrict the minimum conformance
   requirements are included here.

4.1.  Identifiers

   Identifiers for modules, submodules, typedefs, groupings, data
   objects, rpcs, and notifications MUST be between 1 and 63 characters
   in length.

4.2.  Defaults

   In general, it is suggested that sub-statements containing default
   values SHOULD NOT be present.  For example, 'status current;',
   'config true;', 'mandatory false;', and 'max-elements unbounded;' are
   common defaults which would make the YAM difficult to read if used
   everywhere they are allowed.

   Instead, it is suggested that common statements SHOULD only be used
   when being set to a value other than the default value.

4.3.  Conditional Statements

   A YAM may be conceptually partitioned in several ways, using the 'if-
   feature' and/or 'when' statements.  In addition, NETCONF capabilities
   are designed to identify optional functionality.

   Data model designers need to carefully consider all modularity
   aspects, including the use of YANG conditional statements.

   Objects SHOULD NOT directly reference NETCONF capabilities, in order
   to specify optional behavior.  Instead, a 'feature' statement SHOULD
   be defined to represent the NETCONF capability, and the 'if-feature'
   statement SHOULD be used within the object definition.

   If the condition associated with the desired semantics is not
   dependent on any particular instance value within the database, then



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   an 'if-feature' statement SHOULD be used instead of a 'when'
   statement.

   All 'must' and 'when' statements MUST contain valid XPath.  If any
   name tests are present, they MUST contain valid module prefixes
   and/or data node names.

   The 'attribute', 'namespace', 'preceding', 'preceding-sibling',
   'following', and 'following-sibling' axis SHOULD NOT be used.

   The 'position' and 'last' functions SHOULD NOT be used.

   Implicit 'position' function calls within predicates SHOULD NOT be
   used. (e.g., //chapter[42]).

   Data nodes which use the 'int64' and 'uint64' built-in type SHOULD
   NOT be used within relational expressions.

   Data modelers need to be careful not to confuse the YANG value space
   and the XPath value space.  The data types are not the same in both,
   and conversion between YANG and XPath data types SHOULD be considered
   carefully.

   Explicit XPath data type conversions SHOULD be used (e.g., 'string',
   'boolean', or 'number' functions), instead of implicit XPath data
   type conversions.

4.4.  Header Contents

   o  The namespace MUST be a globally unique URI, usually assigned by
      the IANA.

   o  Until a URI is assigned by the IANA, a temporary namespace string
      SHOULD be selected which is not likely to collide with other YANG
      namespaces, such as the filename of the Internet Draft containing
      the YAM.

   o  The organization statement MUST be present.

   o  The contact statement MUST be present.

   o  The description statement MUST be present.

   o  If the YAM represents a model defined in one or more external
      documents, then a reference statement SHOULD be present.

   o  A revision statement MUST be present for each published version of
      the YAM.



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   o  Each new revision MUST include a revision date which is higher
      than any other revision date in the YAM.

   o  It is acceptable to reuse the same revision statement within
      unpublished versions (i.e., Internet Drafts), but the revision
      date MUST be updated to a higher value each time the Internet
      Draft is re-published.

4.5.  Data Types

   o  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.

   o  Data model designers SHOULD use the most appropriate built-in data
      type for the particular application.

   o  If extensibility of enumerated values is required, then the
      identityref data type SHOULD be used instead of an enumeration or
      other built-in type.

   o  If an appropriate derived type exists in any standard YAM, such as
      [I-D.ietf-netmod-yang-types], then it SHOULD be used instead of
      defining a new derived type.

   o  The description statement MUST be present.

   o  If the type semantics are defined in an external document, then a
      reference statement SHOULD be present.

   o  For string data types, if a machine-readable pattern can be
      defined for the desired semantics, then one or more pattern
      statements SHOULD be present.

   o  For string data types, if the length of the string is not
      unbounded in all implementations, then a length statement SHOULD
      be present.

   o  For numeric data types, if the values allowed by the intended
      semantics are different than those allowed by the unbounded
      intrinsic data type (e.g., int32), then a range statement SHOULD
      be present.

   o  The signed numeric data types (i.e., 'int8', 'int16', 'int32', and
      'int64') SHOULD NOT be used unless negative values are allowed for
      the desired semantics.





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   o  The 'float32' and 'float64' data types SHOULD only be used if the
      other numeric data types do not fully represent the desired
      semantics.

   o  For enumeration or bits data types, the semantics for each enum or
      bit SHOULD be documented.  A separate description statement
      (within each enum or bit statement) SHOULD be used, instead of the
      description statement for the type itself.

   o  If an appropriate units identifier can be associated with the
      desired semantics, then a units statement SHOULD be present.

   o  If an appropriate default value can be associated with the desired
      semantics, then a default statement SHOULD be present.

   o  If a significant number of derived types are defined, and it is
      anticipated that these data types will be reused by multiple YAMs,
      then these derived types SHOULD be contained in a separate module
      or submodule, to allow easier reuse without unnecessary coupling.

4.6.  Object Definitions

   o  The description statement MUST be present.

   o  If the object semantics are defined in an external document, then
      a reference statement SHOULD be present.

   o  The 'anyxml' construct MUST NOT be used within configuration data.

   o  If there are referential integrity constraints associated with the
      desired semantics that can be represented with XPath, then one or
      more must statements SHOULD be present.

   o  For list and leaf-list objects, if the number of possible
      instances for all implementations is not unbounded, then the min-
      elements and/or max-elements statements SHOULD be present.

4.7.  RPC Definitions

   o  The description statement MUST be present.

   o  If the RPC method semantics are defined in an external document,
      then a reference statement SHOULD be present.

   o  If the RPC method impacts system behavior in some way, it SHOULD
      be mentioned in the description statement.





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   o  If the RPC method is potentially harmful to system behavior in
      some way, it MUST be mentioned in the Security Considerations
      section of the document.

4.8.  Notification Definitions

   o  The description statement MUST be present.

   o  If the notification semantics are defined in an external document,
      then a reference statement SHOULD be present.









































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5.  YANG Module Registry

   This section contains a YANG module registry specification, which can
   be used to document each release of a module.  It can also be used to
   maintain virtual modules, in which all the body statements are
   contained in submodules specified in the registry, not in a YANG
   module within a published RFC or Internet Draft.

   In order for YANG submodules to be used effectively within standards
   track documents, it is desirable to avoid re-publishing an RFC
   containing the 'main' module, each time a submodule is added or
   changed.

   The use of submodules can effectively reduce the number of XML
   namespaces used within NETCONF PDUs, but their primary use is to
   allow flexible partitioning of a single XML namespace into multiple,
   independent documents, which can be easily extended over time.

   The YANG Module Registry is an XML instance document which contains
   minimal information about the modules represented in the registry.

   Each registry has a unique ID, called the 'registry-id'.  There are
   also zero or more 'module' entries.

   Each 'module' entry contains the module name, XML namespace, and
   optional 'url' field to identify its location.  If this is a virtual
   module, then the 'virtual' field will be present.

   Within each module entry, there are one or more 'release' entries.

   Each 'release' entry contains the publication date of the release.
   It also contains zero or more 'submodule' entries.

   For each submodule included by the main module represented by each
   'module' entry, a 'submodule' entry SHOULD be present.  Each entry
   provides the name, release date and an optional 'url' if the
   submodule is available online.

   It is expected that the IANA will maintain the official YANG Module
   Registry for YAMs contained in published standards-track documents.

   It is also expected that procedures for adding a new YANG module, and
   adding a new release of an existing module, will also be specified.

   [ed: A YANG data model and example XML instance document are provided
   below to demonstrate how such a registry might work.  This work is
   very preliminary and subject to change.]




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5.1.  YANG Registry Data Model

   This section contains a YANG module definition which represents the
   information stored in the IANA YANG Module Registry.  It is provided
   for informational purposes only.  The actual definition is [TBD].




     module yang-registry {

         namespace "yang-registry-TBD";

         prefix "yr";

         // for the uri data type
         import yang-types { prefix "yang"; }

         organization "IETF";

         contact
           "Send comments to <andy@netconfcentral.com>.";

         description
            "YANG Module Registry Data Structure";

         revision "2009-01-22" {
             description
               "Initial version.";
         }

         container registry {

             leaf registry-id {
                 description
                    "Contains the identity of this registry.";
                 type yang:uri;
                 mandatory true;
             }

             list module {
                 key "name";

                 unique "namespace";

                 leaf name {
                    description "YANG module name.";
                    // TBD: imported name string type



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                    type string { length "1..63"; }
                 }

                 leaf namespace {
                     description "YANG module namespace.";
                     type yang:uri;
                     mandatory true;
                 }

                 leaf url {
                     description
                        "URL for this YANG module, if one
                         is available.";
                     type yang:uri;
                 }

                 leaf virtual {
                     description
                       "If present, then this registry entry
                        represents a virtual YANG module,
                        which is a YANG module which does not
                        contain any body statements.  Instead,
                        submodules are used to contain all
                        body statements.

                        Each release entry within this entry
                        is expected to contain all
                        the submodule content information for
                        this virtual module.";
                     type empty;
                 }

                 list release {
                     description
                       "Describes the contents of a specific
                        release of a YANG module.  At least
                        one entry MUST exist for the most
                        current version of the module.";

                     min-elements 1;

                     key version;

                     leaf version {
                        description "YANG module release date.";
                        // TBD: imported date string type
                        // YYYY-MM-DD
                        type string { length "10"; }



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                     }

                     list submodule {
                         key "name";

                         leaf name {
                             description "YANG submodule name.";
                             // TBD: imported name string type
                             type string { length "1..63"; }
                         }

                         leaf version {
                             description "YANG module revision date.";
                             // TBD: imported date string type
                             // YYYY-MM-DD
                            type string { length "10"; }
                            mandatory true;
                         }

                         leaf url {
                             description
                               "URL for this YANG submodule, if one
                                is available.";
                             type yang:uri;
                         }
                     }  // list submodule
                 }  // list release
             } // list module
         }  // container registry
     } // module yang-registry



                                 Figure 2

5.2.  Examples

   This section contains some example registry entries, demonstrating
   the basic use cases.




     <?xml version="1.0" encoding="UTF-8"?>
     <registry xmlns="yang-registry-TBD">
       <registry-id>
         http://example.com/yang-registry
       </registry-id>



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       <module>
         <name>notification</name>
         <namespace>
           urn:ietf:params:xml:ns:netconf:notification:1.0
         </namespace>
         <url>
           ftp://ftp.rfc-editor.org/in-notes/rfc5277.txt
         </url>
         <release>
           <version>2008-07-01</version>
         </release>
       </module>
       <module>
         <name>notification-content</name>
         <namespace>
           urn:ietf:params:xml:ns:netmod:notification
         </namespace>
         <url>
           ftp://ftp.rfc-editor.org/in-notes/rfc5277.txt
         </url>
         <release>
           <version>2008-07-01</version>
         </release>
       </module>
       <module>
         <name>services</name>
         <namespace>
           http://example.com/yang/services
         </namespace>
         <url>
           http://example.com/yang/monitor-tools.yang
         </url>
         <virtual/>
         <release>
           <version>2009-01-23</version>
           <submodule>
             <name>common-types</name>
             <version>2008-11-14</version>
             <url>
               http://example.com/yang/common-types.yang
             </url>
           </submodule>
           <submodule>
             <name>ping</name>
             <version>2008-11-14</version>
             <url>
               http://example.com/yang/ping.yang
             </url>



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           </submodule>
           <submodule>
             <name>traceroute</name>
             <version>2009-01-23</version>
             <url>
               http://example.com/yang/traceroute.yang
             </url>
           </submodule>
         </release>
         <release>
           <version>2008-11-14</version>
           <submodule>
             <name>common-types</name>
             <version>2008-11-14</version>
             <url>
               http://example.com/yang/common-types.yang
             </url>
           </submodule>
           <submodule>
             <name>ping</name>
             <version>2008-11-14</version>
             <url>
               http://example.com/yang/ping.yang
             </url>
           </submodule>
         </release>
       </module>
     </registry>



                                 Figure 3



















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6.  IANA Considerations

   There are no actions requested of IANA at this time. [ed.: If the
   YANG Registry approach is pursued, then details for those procedures
   will need to be defined.]














































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7.  Security Considerations

   This document defines documentation guidelines for NETCONF content
   defined with the YANG data modeling language.  It does not introduce
   any new or increased security risks into the management system. [ed:
   RFC 4181 style security section TBD]













































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8.  Acknowledgments

   The structure and contents of this document are adapted from
   Guidelines for MIB Documents [RFC4181], by C. M. Heard.















































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9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4741]  Enns, R., "NETCONF Configuration Protocol", RFC 4741,
              December 2006.

   [I-D.ietf-netmod-yang]
              Bjorklund, M., "YANG - A data modeling language for
              NETCONF", draft-ietf-netmod-yang-03 (work in progress),
              January 2009.

   [I-D.ietf-netmod-yang-types]
              Schoenwaelder, J., "Common YANG Data Types",
              draft-ietf-netmod-yang-types-01 (work in progress),
              November 2008.

9.2.  Informative References

   [RFC4181]  Heard, C., "Guidelines for Authors and Reviewers of MIB
              Documents", BCP 111, RFC 4181, September 2005.



























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Author's Address

   Andy Bierman
   Netconf Central
   Simi Valley, CA
   USA

   Email: andy@netconfcentral.com











































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