--- 1/draft-ietf-netmod-yang-usage-04.txt 2010-05-18 23:12:07.000000000 +0200 +++ 2/draft-ietf-netmod-yang-usage-05.txt 2010-05-18 23:12:07.000000000 +0200 @@ -1,18 +1,18 @@ Internet Engineering Task Force A. Bierman Internet-Draft InterWorking Labs -Intended status: Informational April 20, 2010 -Expires: October 22, 2010 +Intended status: Informational May 18, 2010 +Expires: November 19, 2010 Guidelines for Authors and Reviewers of YANG Data Model Documents - draft-ietf-netmod-yang-usage-04 + draft-ietf-netmod-yang-usage-05 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. @@ -24,21 +24,21 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on October 22, 2010. + This Internet-Draft will expire on November 19, 2010. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -58,82 +58,83 @@ 2.4. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. General Documentation Guidelines . . . . . . . . . . . . . . . 7 3.1. Module Copyright . . . . . . . . . . . . . . . . . . . . . 7 3.2. Narrative Sections . . . . . . . . . . . . . . . . . . . . 7 3.3. Definitions Section . . . . . . . . . . . . . . . . . . . 8 3.4. Security Considerations Section . . . . . . . . . . . . . 8 3.5. IANA Considerations Section . . . . . . . . . . . . . . . 8 3.5.1. Documents that Create a New Name Space . . . . . . . . 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 + 3.7. Intellectual Property Section . . . . . . . . . . . . . . 9 4. YANG Usage Guidelines . . . . . . . . . . . . . . . . . . . . 10 4.1. Module Naming Conventions . . . . . . . . . . . . . . . . 10 4.2. Identifiers . . . . . . . . . . . . . . . . . . . . . . . 10 4.3. Defaults . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.4. Conditional Statements . . . . . . . . . . . . . . . . . . 11 - 4.5. Lifecycle Management . . . . . . . . . . . . . . . . . . . 12 - 4.6. Header Contents . . . . . . . . . . . . . . . . . . . . . 12 - 4.7. Temporary Namespace Assignments . . . . . . . . . . . . . 13 - 4.8. Top Level Database Objects . . . . . . . . . . . . . . . . 14 - 4.9. Data Types . . . . . . . . . . . . . . . . . . . . . . . . 15 - 4.10. Reusable Type Definitions . . . . . . . . . . . . . . . . 15 - 4.11. Object Definitions . . . . . . . . . . . . . . . . . . . . 16 - 4.12. Operation Definitions . . . . . . . . . . . . . . . . . . 17 - 4.13. Notification Definitions . . . . . . . . . . . . . . . . . 17 - 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 - 6. Security Considerations . . . . . . . . . . . . . . . . . . . 19 - 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20 - 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21 - 8.1. Normative References . . . . . . . . . . . . . . . . . . . 21 - 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 03 to 04 . . . . . . . . . . . . . . . . . . 27 - C.2. Changes from 02 to 03 . . . . . . . . . . . . . . . . . . 28 - C.3. Changes from 01 to 02 . . . . . . . . . . . . . . . . . . 28 - C.4. Changes from 00 to 01 . . . . . . . . . . . . . . . . . . 28 - Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 29 + 4.5. XPath Usage . . . . . . . . . . . . . . . . . . . . . . . 11 + 4.6. Lifecycle Management . . . . . . . . . . . . . . . . . . . 12 + 4.7. Module Header, Meta, and Revision Statements . . . . . . . 13 + 4.8. Namespace Assignments . . . . . . . . . . . . . . . . . . 13 + 4.9. Top Level Data Definitions . . . . . . . . . . . . . . . . 15 + 4.10. Data Types . . . . . . . . . . . . . . . . . . . . . . . . 15 + 4.11. Reusable Type Definitions . . . . . . . . . . . . . . . . 16 + 4.12. Data Definitions . . . . . . . . . . . . . . . . . . . . . 16 + 4.13. Operation Definitions . . . . . . . . . . . . . . . . . . 17 + 4.14. Notification Definitions . . . . . . . . . . . . . . . . . 18 + 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 + 6. Security Considerations . . . . . . . . . . . . . . . . . . . 20 + 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21 + 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22 + 8.1. Normative References . . . . . . . . . . . . . . . . . . . 22 + 8.2. Informative References . . . . . . . . . . . . . . . . . . 22 + Appendix A. Module Review Checklist . . . . . . . . . . . . . . . 23 + Appendix B. YANG Module Template . . . . . . . . . . . . . . . . 25 + Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 28 + C.1. Changes from 04 to 05 . . . . . . . . . . . . . . . . . . 28 + C.2. Changes from 03 to 04 . . . . . . . . . . . . . . . . . . 28 + C.3. Changes from 02 to 03 . . . . . . . . . . . . . . . . . . 29 + C.4. Changes from 01 to 02 . . . . . . . . . . . . . . . . . . 29 + C.5. Changes from 00 to 01 . . . . . . . . . . . . . . . . . . 29 + Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 31 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. + similar to the SMIv2 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. + description statement. However, in order to maximize + interoperability of NETCONF implementations utilizing YANG data + models, it is desirable to define a set of usage guidelines which may + require a higher level of compliance than the minimum level defined + in the YANG specification. This document defines usage guidelines related to the NETCONF operations layer, and NETCONF content layer, as defined in [RFC4741]. 2. Terminology 2.1. Requirements Notation The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. RFC 2119 language is used here to express the views of the NETMOD - working group regarding YANG module content. Yang modules complying + 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 The following terms are defined in [RFC4741] and are not redefined here: o capabilities @@ -176,92 +177,98 @@ YANG data model modules under review are likely to be contained in Internet Drafts. All guidelines for Internet Draft authors MUST be followed. These guidelines are available online at: http://www.rfc-editor.org/rfc-editor/instructions2authors.txt The following sections MUST be present in an Internet Draft containing a module: - o YANG data model boilerplate section - o Narrative sections o Definitions section o Security Considerations section o IANA Considerations section o References section 3.1. Module Copyright - The module description statement MUST contain the latest approved - IETF Trust Copyright statement, which is available on-line, in - section 4 of the Trust Legal Provisions (TLP) document, at: + The module description statement MUST contain a reference to the + latest approved IETF Trust Copyright statement, which is available + on-line at: http://trustee.ietf.org/license-info/ Each YANG module or submodule contained within an Internet Draft or - RFC MUST be identified as a 'Code Component'. The strings '' and '' SHOULD be used to identify each Code - Component. + RFC is considered to be a code component. The strings '' and '' SHOULD be used to identify each code + component. + + The '' tag SHOULD be followed by a string identifying + the file name specified in section 5.2 of [I-D.ietf-netmod-yang]. + For example, if the latest revision date of the 'ietf-foo' module is + '2010-01-18', then the following '' line would be used: + + file "ietf-foo@2010-01-18.yang" 3.2. Narrative Sections The narrative part MUST include an overview section that describes the scope and field of application of the module(s) defined by the specification and that specifies the relationship (if any) of these modules to other standards, particularly to standards containing - other module 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 the specification. If the module(s) defined by the specification import definitions from other modules (except for those defined in the YANG - [I-D.ietf-netmod-yang] or YANG Types [I-D.ietf-netmod-yang-types] documents) or are always implemented in conjunction with other modules, then those facts MUST be noted in the overview section, as - MUST any special interpretations of objects in other modules. + MUST any special interpretations of definitions in other modules. 3.3. Definitions Section This section contains the module(s) defined by the specification. These modules MUST be written 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 modules MUST contain a section that discusses security considerations relevant to those modules. This section MUST be patterned after the latest approved template (available at http://www.ops.ietf.org/yang-security.html). + [ed.: this online document does not exist yet.] - In particular, writable module objects that could be especially + In particular, writable data nodes that could be especially disruptive if abused MUST be explicitly listed by name and the associated security risks MUST be spelled out; similarly, readable - module objects 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 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. + depending what actions are required of the IANA. Refer to the + guidelines in [RFC5226] for more details. 3.5.1. Documents that Create a New Name Space If an Internet-Draft defines a new name space that is to be administered by the IANA, then the document MUST include an IANA Considerations section, that specifies how the name space is to be administered. Specifically, if any YANG module namespace statement value contained in the document is not already registered with IANA, then a new YANG @@ -278,33 +285,30 @@ 3.6. Reference Sections For every import or include statement which appears in a module contained in the specification, which identifies a module in a separate document, a corresponding normative reference to that document MUST appear in the Normative References section. The reference MUST correspond to the specific module version actually used within the specification. - For every reference statement which appears in a module contained in - the specification, which identifies a separate document, a - corresponding normative reference to that document SHOULD appear in + For every normative reference statement which appears in a module + contained in the specification, which identifies a separate document, + a corresponding normative reference to that document SHOULD appear in the Normative References section. The reference SHOULD correspond to the specific document version actually used within the specification. + If the reference statement identifies an informative reference, which + identifies a separate document, a corresponding informative reference + to that document MAY appear in the Informative References section. -3.7. Copyright Notices - - The proper copyright notices MUST be present in the module - description statement. Refer to the IETF Trust Legal Provision for - the exact legal text that needs to be included. - -3.8. Intellectual Property Section +3.7. Intellectual Property Section The proper IPR statements MUST be present in the document, according to the most current Internet Draft boilerplate. Refer to the IETF Trust Legal Provision for the exact legal text that needs to be included. 4. YANG Usage Guidelines In general, modules in IETF standards-track specifications MUST comply with all syntactic and semantic requirements of YANG. @@ -330,183 +334,197 @@ being defined to extend one or more existing modules, then the same word or acronym should be reused, instead of creating a new one. All published module names MUST be unique. Once a module name is published, it MUST not be reused, even if the RFC containing the module is reclassified to 'Historic' status. 4.2. Identifiers - Identifiers for all published modules, submodules, typedefs, - groupings, data objects, operations, and notifications MUST be - between 1 and 64 characters in length. + Identifiers for all YANG identifiers in published modules MUST be + between 1 and 64 characters in length. These includes any construct + specified as an 'identifier-arg-str' token in the ABNF in section 12 + of [I-D.ietf-netmod-yang]. 4.3. Defaults - In general, it is suggested that sub-statements containing 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 module difficult to read if used - everywhere they are allowed. + In general, it is suggested that sub-statements containing very + common default values SHOULD NOT be present. The following sub- + statements are commonly used with the default value, which would make + the module difficult to read if used everywhere they are allowed. - Instead, it is suggested that common statements SHOULD only be used - when being set to a value other than the default value. + +---------------+---------------+ + | Statement | Default Value | + +---------------+---------------+ + | config | true | + | | | + | mandatory | false | + | | | + | max-elements | unbounded | + | | | + | min-elements | 0 | + | | | + | ordered-by | system | + | | | + | status | current | + | | | + | yin-element | false | + +---------------+---------------+ 4.4. Conditional Statements A module may be conceptually partitioned in several ways, using the 'if-feature' and/or 'when' statements. Data model designers need to carefully consider all modularity aspects, including the use of YANG conditional statements. - Objects SHOULD NOT directly reference NETCONF capabilities, in order - to specify optional behavior. Instead, a 'feature' statement SHOULD - be defined instead of a NETCONF capability, and the 'if-feature' - statement SHOULD be used within the optional object definition. + If a data definition is optional, depending on server support for a + NETCONF protocol capability, then a YANG 'feature' statement SHOULD + be defined to indicate the NETCONF capability is supported within the + data model. - If the condition associated with the desired semantics is not - dependent on any particular instance value within the database, then - an 'if-feature' statement SHOULD be used instead of a 'when' - statement. +4.5. XPath Usage - The 'attribute' and 'namespace' axis SHOULD NOT be used because the - associated XML node types are not supported in YANG, and may not be - supported consistently across NETCONF server implementations. + The 'attribute' and 'namespace' axes are not supported in YANG, and + MAY be empty in a NETCONF server implementation. - The 'position' and 'last' functions MAY be used with caution, within - a single server implementation. These functions may be useful in - some cases when processing user-ordered lists. A server is only - required to maintain the XML order of a user-ordered list or leaf- - list. + The 'position' and 'last' functions MAY be used with caution. A + server is not required to maintain any particular XML document order + for system-ordered data nodes. A server is only required to maintain + the relative XML document order of all instances of a particular + user-ordered list or leaf-list. The 'preceding', and 'following' axes SHOULD NOT be used. These constructs rely on XML document order within a NETCONF server configuration database, which may not be supported consistently or produce reliable results across implementations. Predicate expressions based on static node properties (e.g., name, value, ancestors, descendants) SHOULD be used instead. The 'preceding-sibling' and 'following-sibling' axes MAY be used, with caution. A server is not required to maintain a persistent or deterministic XML document order, which will affect use of these axes. - Implicit 'position' function calls within predicates SHOULD NOT be - used. (e.g., //chapter[42]). + Implicit 'position' function calls within predicates MAY be used with + caution. (e.g., //chapter[42]). Note that a NETCONF server is only + required to maintain relative document order for related instances of + a user-ordered list or leaf-list data definition (i.e., 'ordered-by' + statement set to 'user'). Data nodes which use the 'int64' and 'uint64' built-in type MAY be used with caution, within relational expressions. There are boundary conditions in which the translation from the YANG 64-bit type to an XPath number can cause incorrect results. Specifically, an XPath double precision floating point number cannot represent very large positive or negative 64-bit numbers because it only provides a total precision of 53 bits. Data modelers need to be careful not to confuse the YANG value space and the XPath value space. The data types are not the same in both, and conversion between YANG and XPath data types SHOULD be considered carefully. Explicit XPath data type conversions MAY be used (e.g., 'string', 'boolean', or 'number' functions), instead of implicit XPath data type conversions. -4.5. Lifecycle Management +4.6. Lifecycle Management - The status statement SHOULD NOT be present if its value is 'current'. - It MUST be present if its value is 'deprecated' or 'obsolete'. + The status statement MUST be present if its value is 'deprecated' or + 'obsolete'. The module or submodule name MUST NOT be changed, once the document containing the module or submodule is published. The module namespace URI value MUST NOT be changed, once the document containing the module is published. - The revision-date sub-statement (within the imports statement) SHOULD + The revision-date sub-statement within the imports statement SHOULD be present if any groupings are used from the external module. - The revision-date sub-statement (within the include statement) SHOULD + The revision-date sub-statement within the include statement SHOULD be present if any groupings are used from the external sub-module. If submodules are used, then the document containing the main module MUST be updated so that the main module revision date is equal or more recent than the revision date of any submodule which is (directly or indirectly) included by the main module. -4.6. Header Contents +4.7. Module Header, Meta, and Revision Statements For published modules, the namespace MUST be a globally unique URI, as defined in [RFC3986]. This value is usually assigned by the IANA. The organization statement MUST be present. If the module is contained in a documented intended for standards-track status, then the organization SHOULD be the IETF working group chartered to write the document. The contact statement MUST be present. If the module is contained in a document intended for standards-track status, then the working group WEB and mailing information MUST be present, and the document author contact information SHOULD be present. In addition, the Area Director and other contact information MAY be present. The description statement MUST be present. The appropriate IETF Trust Copyright text MUST be present, as described in Section 3.1. - 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. - If the module relies on information contained in other documents, which are not the same documents implied by the import statements present in the module, then these documents MUST be identified in the reference statement. A revision statement MUST be present for each published version of the module. The revision statement MUST have a reference substatement. It MUST identify the published document which contains - the module. + the module. Modules are often extracted from their original + documents and it is useful for developers and operators to know how + to find the original source document in a consistent manner. The + revision statement MAY have a description substatement. Each new revision MUST include a revision date which is higher than any other revision date in the module. It is acceptable to reuse the same revision statement within unpublished versions (i.e., Internet Drafts), but the revision date MUST be updated to a higher value each time the Internet Draft is re- published. -4.7. Temporary Namespace Assignments +4.8. Namespace Assignments It is desirable to include only valid YANG modules in documents, whether they are published yet or not. This allows: o the module to compile correctly instead of generating disruptive fatal errors. o early implementors to use the modules without picking a random value for the XML namespace. o early interoperability testing since independent implementations will use the same XML namespace value. - Until a URI is assigned by the IANA, a temporary namespace URI MUST - be provided for the namespace statement in a YANG module. A value + Until a URI is assigned by the IANA, a proposed namespace URI MUST be + provided for the namespace statement in a YANG module. A value SHOULD be selected which is not likely to collide with other YANG - namespaces. + namespaces. Standard module names, prefixes, and URI strings already + listed in the YANG Module Registry MUST NOT be used. A standard namespace statement value SHOULD have the following form: : The following URN prefix string SHOULD be used for published and - unpublished YANG modules + unpublished YANG modules: urn:ietf:params:xml:ns:yang: The following example URNs would be valid temporary namespace statement values for standards-track modules: urn:ietf:params:xml:ns:yang:ietf-netconf-partial-lock urn:ietf:params:xml:ns:yang:ietf-netconf-state @@ -517,79 +535,79 @@ the guidelines in [I-D.ietf-netmod-yang]. The following examples of non-standards track modules are only suggestions. There are no guidelines for this type of URN in this document: http://example.com/ns/example-interfaces http://example.com/ns/example-system -4.8. Top Level Database Objects +4.9. Top Level Data Definitions 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 client must - provide for the database to be valid. The server will not provide a - value under any conditions. + A mandatory database data definition is defined as a node that a + client must provide for the database to be valid. The server is not + required to provide a value. - Top-level database 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 server boots or when a module - is loaded dynamically at runtime. + Top-level database data definitions MUST NOT be mandatory. If a + mandatory node appears at the top-level, it will immediately cause + the database to be invalid. This can occur when the server boots or + when a module is loaded dynamically at runtime. -4.9. Data Types +4.10. Data Types Selection of an appropriate data type (i.e., built-in type, existing derived type, or new derived type) is very subjective and therefore few requirements can be specified on that subject. Data model designers SHOULD use the most appropriate built-in data type for the particular application. If extensibility of enumerated values is required, then the identityref data type SHOULD be used instead of an enumeration or other built-in type. For string data types, if a machine-readable pattern can be defined for the desired semantics, then one or more pattern statements SHOULD be present. For string data types, if the length of the string is required to bounded in all implementations, then a length statement SHOULD be present. - For string data types, object semantics SHOULD NOT rely on + For string data types, data definition semantics SHOULD NOT rely on preservation of leading and trailing whitespace characters. For numeric data types, if the values allowed by the intended semantics are different than those allowed by the unbounded intrinsic data type (e.g., int32), then a range statement SHOULD be present. The signed numeric data types (i.e., 'int8', 'int16', 'int32', and 'int64') SHOULD NOT be used unless negative values are allowed for the desired semantics. For enumeration or bits data types, the semantics for each enum or bit SHOULD be documented. A separate description statement (within each enum or bit statement) SHOULD be present. -4.10. Reusable Type Definitions +4.11. Reusable Type Definitions If an appropriate derived type exists in any standard module, such as [I-D.ietf-netmod-yang-types], then it SHOULD be used instead of defining a new derived type. If an appropriate units identifier can be associated with the desired semantics, then a units statement SHOULD be present. If an appropriate default value can be associated with the desired semantics, then a default statement SHOULD be present. @@ -597,142 +615,175 @@ If a significant number of derived types are defined, and it is anticipated that these data types will be reused by multiple modules, then these derived types SHOULD be contained in a separate module or submodule, to allow easier reuse without unnecessary coupling. The description statement MUST be present. If the type definition semantics are defined in an external document, then the reference statement SHOULD be present. -4.11. Object Definitions +4.12. Data Definitions - The description statement MUST be present in the following body + The description statement MUST be present in the following YANG statements: - o extension - - o feature - - o identity - - o typedef - - o grouping + o anyxml o augment - o rpc + o choice - o notification + o container - The description statement MUST be present in the following data - definition constructs: + o extension + o feature - o container + o grouping + + o identity o leaf o leaf-list o list - o choice + o notification - o anyxml - If the object semantics are defined in an external document, then a - reference statement SHOULD be present. + o rpc + + o typedef + + If the data definition semantics are defined in an external document, + then a reference statement SHOULD be present. The 'anyxml' construct MAY be used with caution within configuration - data. This may be useful to represent an HTML banner for example. - However, this construct SHOULD NOT be used if other YANG data node - types can be used instead to represent the desired syntax and - semantics. + data. This may be useful to represent an HTML banner containing + markup elements, such as and . However, this construct + SHOULD NOT be used if other YANG data node types can be used instead + to represent the desired syntax and semantics. If there are referential integrity constraints associated with the desired semantics that can be represented with XPath, then one or more must statements SHOULD be present. - For list and leaf-list objects, if the number of possible instances - is required to be bounded for all implementations, then the max- - elements statements SHOULD be present. - - If any must or when statements are used within the object definition, - then the object description statement SHOULD describe the purpose of - each one. + For list and leaf-list data definitions, if the number of possible + instances is required to be bounded for all implementations, then the + max-elements statements SHOULD be present. -4.12. Operation Definitions + If any must or when statements are used within the data definition, + then the data definition description statement SHOULD describe the + purpose of each one. - The description statement MUST be present in 'rpc' statements - defining new operations. +4.13. Operation Definitions If the operation semantics are defined in an external document, then a reference statement SHOULD be present. If the operation impacts system behavior in some way, it SHOULD be mentioned in the description statement. If the operation is potentially harmful to system behavior in some way, it MUST be mentioned in the Security Considerations section of the document. -4.13. Notification Definitions +4.14. Notification Definitions The description statement MUST be present. If the notification semantics are defined in an external document, then a reference statement SHOULD be present. 5. IANA Considerations - There are no actions requested of IANA at this time. + This document registers one URI in the IETF XML registry [RFC3688]. + The following registration is requested: + + URI: urn:ietf:params:xml:ns:yang:ietf-template + + Registrant Contact: The NETMOD WG of the IETF. + + XML: N/A, the requested URI is an XML namespace. + + This document requests the following assignment in the YANG Module + Names Registry for the YANG module template in Appendix B. + + +---------------+-------------------------------------------+ + | Field | Value | + +---------------+-------------------------------------------+ + | name | ietf-template | + | | | + | namespace | urn:ietf:params:xml:ns:yang:ietf-template | + | | | + | prefix | temp | + | | | + | reference | RFCXXXX | + +---------------+-------------------------------------------+ 6. 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. + defined with the YANG data modeling language. The guidelines for how + to write a Security Considerations section for a YANG module are + defined in the online document + + http://www.ops.ietf.org/yang-security.html [ed.: this online document + does not exist yet.] + + This document does not introduce any new or increased security risks + into the management system. 7. Acknowledgments The structure and contents of this document are adapted from Guidelines for MIB Documents [RFC4181], by C. M. Heard. + The working group thanks Martin Bjorklund and Juergen Schoenwaelder + for their extensive reviews and contributions to this document. + 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. + [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, + January 2004. + [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. [RFC4741] Enns, R., "NETCONF Configuration Protocol", RFC 4741, December 2006. [I-D.ietf-netmod-yang] Bjorklund, M., "YANG - A data modeling language for NETCONF", draft-ietf-netmod-yang-12 (work in progress), April 2010. [I-D.ietf-netmod-yang-types] Schoenwaelder, J., "Common YANG Data Types", - draft-ietf-netmod-yang-types-08 (work in progress), + draft-ietf-netmod-yang-types-09 (work in progress), April 2010. 8.2. Informative References [RFC4181] Heard, C., "Guidelines for Authors and Reviewers of MIB Documents", BCP 111, RFC 4181, September 2005. + [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an + IANA Considerations Section in RFCs", BCP 26, RFC 5226, + May 2008. + Appendix A. Module Review Checklist This section is adapted from RFC 4181. The purpose of a YANG module review is to review the YANG module both for technical correctness and for adherence to IETF documentation requirements. The following checklist may be helpful when reviewing a draft document: 1. I-D Boilerplate -- verify that the draft contains the required @@ -786,37 +837,37 @@ http://trustee.ietf.org/license-info/ 8. Other Issues -- check for any issues mentioned in http://www.ietf.org/ID-Checklist.html that are not covered elsewhere. 9. Technical Content -- review the actual technical content for compliance with the guidelines in this document. The use of a YANG module compiler is recommended when checking for syntax - errors; see [YANG tool URL TBD] for more information. Checking - for correct syntax, however, is only part of the job. It is just - as important to actually read the YANG module document from the + errors, [ed.: online YANG validation tool URL TBD]. Checking for + correct syntax, however, is only part of the job. It is just as + important to actually read the YANG module document from the point of view of a potential implementor. It is particularly important to check that description statements are sufficiently clear and unambiguous to allow interoperable implementations to be created. Appendix B. YANG Module Template - file "ietf-template.yang" + file "ietf-template@2010-05-18.yang" module ietf-template { // replace this string with a unique namespace URN value namespace - "urn:ietf:params:xml:ns:yang:ietf-template:DRAFT-02"; + "urn:ietf:params:xml:ns:yang:ietf-template"; // replace this string, and try to pick a unique prefix prefix "temp"; // import statements here: e.g., // import ietf-yang-types { prefix yang; } // import ietf-inet-types { prefix inet; } // identify the IETF working group if applicable organization @@ -853,23 +904,23 @@ This version of this YANG module is part of RFC XXXX; see the RFC itself for full legal notices."; // RFC Ed.: replace XXXX with actual RFC number and remove this note reference "RFC XXXX"; // RFC Ed.: remove this note // Note: extracted from draft-ietf-netmod-yang-usage-04.txt - // replace YYYY-MM-DD with a real date (year-month-day) - // here is an example revision date: 2009-08-12 - revision YYYY-MM-DD { + // replace '2010-05-18' with the module publication date + // The format is (year-month-day) + revision "2010-05-18" { description "Initial version"; } // extension statements // feature statements // identity statements @@ -887,21 +938,40 @@ // DO NOT put deviation statements in a published module } Figure 1 Appendix C. Change Log -C.1. Changes from 03 to 04 +C.1. Changes from 04 to 05 + + o Changed 'object' terminology to 'data definition'. + + o Put XPath guidelines in separate section. + + o Clarified XPath usage for XML document order dependencies. + + o Updated guidelines to current conventions. + + o Added informative reference for IANA considerations guidelines and + XML registry. + + o Updated IANA Considerations section to reserve the ietf-template + module in the YANG Module Name Registry so it cannot be reused + accidently. + + o Many other clarifications and fixed typos found in WGLC reviews. + +C.2. Changes from 03 to 04 o Removed figure 1 to reduce duplication, just refer to 4741bis draft. o Fixed bugs and typos found in WGLC reviews. o Removed some guidelines and referring to YANG draft instead of duplicating YANG rules here. o Changed security guidelines so they refer to the IETF Trust TLP @@ -911,66 +981,66 @@ suffix strings are not used. o Changed some MIB boilerplate so it refers to YANG boilerplate instead. o Introduced dangling URL reference to online YANG security guidelines http://www.ops.ietf.org/yang-security.html - Text from Bert Wijnen will be completed soon and posted online, - and then this URL will be finalized. + [ed.: Text from Bert Wijnen will be completed soon and posted + online, and then this URL will be finalized.] o Moved reference for identifying the source document inside the each revision statement. o Removed guideline about valid XPath since YANG already requires valid XPath. o Added guideline that strings should not rely on preservation of leading and trailing whitespace characters. o Relaxed some XPath and anyxml guidelines from SHOULD NOT or MUST NOT to MAY use with caution. o Updated the TLP text within the example module again. o Reversed order of change log so most recent entries are first. -C.2. Changes from 02 to 03 +C.3. Changes from 02 to 03 o Updated figure 1 to align with 4741bis draft. o Updated guidelines for import-by-revision and include-by-revision. o Added file name to code begins convention in ietf-template module. -C.3. Changes from 01 to 02 +C.4. Changes from 01 to 02 o Updated figure 1 per mailing list comments. o Updated suggested organization to include the working group name. o Updated ietf-template.yang to use new organization statement value. o Updated Code Component requirements as per new TLP. o Updated ietf-template.yang to use new Code Component begin and end markers. o Updated references to the TLP in a couple sections. o Change manager/agent terminology to client/server. -C.4. Changes from 00 to 01 +C.5. 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