RFC 6087

Guidelines for Authors and Reviewers of YANG Data Model Documents

📅 published January 2011, from ietf

Guidelines for Authors and Reviewers of YANG Data Model Documents 💖

Okay bestie, here's the header tea 🫶 This is RFC 6087, written by A. Bierman from Brocade ✨. It's an Informational doc, so it's not Standards Track, just really good guidance 🧚. It's dated January 2011 and has ISSN 2070-1721. The header doesn't list anything it obsoletes or updates, so no drama there 💅.

Abstract 🦋

Okay so this memo gives guidelines for authors and reviewers of Standards Track specs that contain YANG data model modules 💜. Parts of it can be used as a base for reviewing other YANG data model docs too. It defines recommendations and procedures meant to boost the interoperability and usability of NETCONF implementations that use YANG data model modules 🔥.

Status of This Memo ⭐

This doc is not an Internet Standards Track spec. It's published for info purposes only 🌸.

It's a product of the Internet Engineering Task Force (IETF), so it reflects consensus from the IETF community. It got public review and was approved for publication by the Internet Engineering Steering Group (IESG). Not every IESG-approved doc is a candidate for any level of Internet Standard, so check out Section 2 of RFC 5741 for the details 👀.

For the latest status, errata, and how to send feedback, go to http://www.rfc-editor.org/info/rfc6087 🎀.

Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved.

This doc is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) as they stand on the publication date. Please read these carefully, because they spell out your rights and restrictions for this doc. Code components pulled out of this doc must include Simplified BSD License text, as described in Section 4.e of the Trust Legal Provisions. They come without warranty, as described in the Simplified BSD License 🧾.

Table of Contents 🗺️

1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
  2.1.  Requirements Notation  . . . . . . . . . . . . . . . . . .  3
  2.2.  NETCONF Terms  . . . . . . . . . . . . . . . . . . . . . .  4
  2.3.  YANG Terms . . . . . . . . . . . . . . . . . . . . . . . .  4
  2.4.  Terms  . . . . . . . . . . . . . . . . . . . . . . . . . .  4
3.  General Documentation Guidelines . . . . . . . . . . . . . . .  5
  3.1.  Module Copyright . . . . . . . . . . . . . . . . . . . . .  5
  3.2.  Narrative Sections . . . . . . . . . . . . . . . . . . . .  6
  3.3.  Definitions Section  . . . . . . . . . . . . . . . . . . .  6
  3.4.  Security Considerations Section  . . . . . . . . . . . . .  6
  3.5.  IANA Considerations Section  . . . . . . . . . . . . . . .  7
    3.5.1.  Documents that Create a New Namespace  . . . . . . . .  7
    3.5.2.  Documents that Extend an Existing Namespace  . . . . .  8
  3.6.  Reference Sections . . . . . . . . . . . . . . . . . . . .  8
4.  YANG Usage Guidelines  . . . . . . . . . . . . . . . . . . . .  8
  4.1.  Module Naming Conventions  . . . . . . . . . . . . . . . .  8
  4.2.  Identifiers  . . . . . . . . . . . . . . . . . . . . . . .  9
  4.3.  Defaults . . . . . . . . . . . . . . . . . . . . . . . . .  9
  4.4.  Conditional Statements . . . . . . . . . . . . . . . . . . 10
  4.5.  XPath Usage  . . . . . . . . . . . . . . . . . . . . . . . 10
  4.6.  Lifecycle Management . . . . . . . . . . . . . . . . . . . 11
  4.7.  Module Header, Meta, and Revision Statements . . . . . . . 12
  4.8.  Namespace Assignments  . . . . . . . . . . . . . . . . . . 13
  4.9.  Top-Level Data Definitions . . . . . . . . . . . . . . . . 14
  4.10. Data Types . . . . . . . . . . . . . . . . . . . . . . . . 14
  4.11. Reusable Type Definitions  . . . . . . . . . . . . . . . . 15
  4.12. Data Definitions . . . . . . . . . . . . . . . . . . . . . 15
  4.13. Operation Definitions  . . . . . . . . . . . . . . . . . . 17
  4.14. Notification Definitions . . . . . . . . . . . . . . . . . 17
5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
  6.1.  Security Considerations Section Template . . . . . . . . . 19
7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 20
8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
  8.1.  Normative References . . . . . . . . . . . . . . . . . . . 20
  8.2.  Informative References . . . . . . . . . . . . . . . . . . 21
Appendix A.  Module Review Checklist . . . . . . . . . . . . . . . 22
Appendix B.  YANG Module Template  . . . . . . . . . . . . . . . . 24

1. Introduction 🌸

Okay so standardizing network configuration interfaces for the Network Configuration Protocol (NETCONF) [RFC4741] needs a modular set of data models. They should be reusable and extendable over time 🧩.

This doc defines usage guidelines for Standards Track docs that contain YANG [RFC6020] data models. YANG defines the data structures, protocol operations, and notification content used inside a NETCONF server. A server that supports a particular YANG module will support client NETCONF operation requests, as shown by the specific content the YANG module defines 🦋.

This doc is similar in intent and structure to the Structure of Management Information version 2 (SMIv2) usage guidelines spec [RFC4181]. But that doc was written a decade after SMIv2 modules were already in use, so it got published as a 'Best Current Practice' (BCP). This doc is not a BCP. It's an informational reference that's meant to promote consistency in docs that contain YANG modules 📚.

A lot of YANG constructs are optional to use, like the description statement. Still, to get the most interoperability out of NETCONF implementations that use YANG data models, it's desirable to set usage guidelines that may ask for a higher level of compliance than the minimum YANG spec defines 💅.

YANG also allows things like infinite length identifiers and string values, or top-level mandatory nodes, that a compliant server isn't required to support. So only constructs that all servers are required to support can be used in IETF YANG modules 🙈.

This doc defines usage guidelines for the NETCONF operations layer and the NETCONF content layer, as defined in [RFC4741]. Authors and reviewers should use these guidelines to improve the readability and interoperability of published YANG data models ✨.

2. Terminology 🎀

2.1. Requirements Notation

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

RFC 2119 language is used here to express the views of the NETMOD working group about content for YANG modules. YANG modules that comply with this doc will treat the RFC 2119 terminology as if it were describing best current practices 🧠.

2.2. NETCONF Terms

These terms are defined in [RFC4741] and aren't redefined here:

  • capabilities
  • client
  • operation
  • server

2.3. YANG Terms

These terms are defined in [RFC6020] and aren't redefined here:

  • data node
  • module
  • namespace
  • submodule
  • version
  • YANG
  • YIN

Note that the term 'module' can be used as a generic term for a YANG module or submodule. When describing properties that are specific to submodules, the term 'submodule' is used instead 🫶.

2.4. Terms

These terms are used throughout this doc:

  • published: A stable release of a module or submodule, usually contained in an RFC.
  • unpublished: An unstable release of a module or submodule, usually contained in an Internet-Draft.

3. General Documentation Guidelines 🧚

YANG data model modules under review are likely to be in Internet-Drafts. All guidelines for Internet-Draft authors MUST be followed. The RFC Editor provides guidelines for RFC authors, since RFCs are first published as Internet-Drafts. These guidelines should be followed too, and they're defined in [RFC2223], updated in [RFC5741], and in "RFC Document Style" [RFC-STYLE] 📝.

The following sections MUST be present in an Internet-Draft that contains a module:

  • Narrative sections
  • Definitions section
  • Security Considerations section
  • IANA Considerations section
  • References section

The module description statement MUST contain a reference to the latest approved IETF Trust Copyright statement, which is available online at:

http://trustee.ietf.org/license-info/

Each YANG module or submodule in an Internet-Draft or RFC counts as a code component. The strings <CODE BEGINS> and <CODE ENDS> MUST be used to identify each code component 🔖.

The <CODE BEGINS> tag SHOULD be followed by a string that identifies the file name specified in Section 5.2 of [RFC6020]. Here's an example for the '2010-01-18' revision of the 'ietf-foo' module:

   <CODE BEGINS> file "ietf-foo@2010-01-18.yang"
   module ietf-foo {
       // ...
      revision 2010-01-18 {
         description "Latest revision";
         reference "RFC XXXX";
      }
      // ...
   }
   <CODE ENDS>

3.2. Narrative Sections 🌈

The narrative part MUST include an overview section that describes the scope and field of application of the module(s) defined by the specification. It also has to say how these modules relate (if at all) to other standards, especially standards that contain other YANG modules. The narrative part SHOULD include one or more sections that 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 [RFC6020] or YANG Types [RFC6021] docs), or are always implemented together with other modules, then those facts MUST be noted in the overview section. Any special interpretations of definitions in other modules MUST be noted there too 👀.

3.3. Definitions Section 💜

This section contains the module(s) defined by the specification. These modules MUST be written using the YANG syntax defined in [RFC6020]. A YIN syntax version of the module MAY also be present in the document. There MAY also be other types of modules in the document, such as SMIv2, and those aren't affected by these guidelines 🫧.

See Section 4 for guidelines on YANG usage 🔥.

3.4. Security Considerations Section 🔐✨

okay bestie, every spec that defines one or more modules MUST contain a section that talks about the security stuff relevant to those modules. no skipping it, this is serious 💀

This section MUST be patterned after the latest approved template (you can find it at http://www.ops.ietf.org/netconf/yang-security-considerations.txt).

Section 6.1 has the security considerations template dated 2010-06-16. Authors MUST check the webpage at the URL listed above in case there is a more recent version available. 🧐

In particular:

  • Writable data nodes that could be especially disruptive if abused MUST be explicitly listed by name and the associated security risks MUST be explained. 💥
  • Readable data nodes that contain especially sensitive information or that raise significant privacy concerns MUST be explicitly listed by name and the reasons for the sensitivity/privacy concerns MUST be explained. 🙈
  • Operations (i.e., YANG 'rpc' statements) that are potentially harmful to system behavior or that raise significant privacy concerns MUST be explicitly listed by name and the reasons for the sensitivity/privacy concerns MUST be explained. 🚨

3.5. IANA Considerations Section 🦋

okay so, to follow IESG policy (see http://www.ietf.org/id-info/checklist.html), every Internet-Draft that is submitted to the IESG for publication MUST contain an IANA Considerations section. 📝 What goes in it depends on what the IANA actually has to do. If there are no IANA considerations for the document, the section saying there are no actions gets removed by the RFC Editor before publication. For more details, check the guidelines in [RFC5226] 🌸

3.5.1. Documents that Create a New Namespace ✨

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

Specifically, if any YANG module namespace statement value contained in the document is not already registered with IANA, then a new YANG Namespace registry entry MUST be requested from the IANA. The YANG [RFC6020] specification includes the procedure for this purpose in its IANA Considerations section. 🎀

3.5.2. Documents that Extend an Existing Namespace 🌈

It is possible to extend an existing namespace using a YANG submodule that belongs to an existing module already administered by IANA. In this case, the document containing the main module MUST be updated to use the latest revision of the submodule. 🫶

3.6. Reference Sections 📚

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

For every normative reference statement that appears in a module contained in the specification, which identifies a separate document, a corresponding normative reference to that document SHOULD appear in the Normative References section. The reference SHOULD correspond to the specific document version actually used within the specification. If the reference statement identifies an informative reference, which identifies a separate document, a corresponding informative reference to that document MAY appear in the Informative References section. 🧚

4. YANG Usage Guidelines 👑

okay this part is the YANG playbook 📖. In general, modules in IETF Standards Track specifications MUST comply with all syntactic and semantic requirements of YANG [RFC6020]. The guidelines in this section are there to supplement the YANG specification, which defines a minimum set of conformance requirements. 💅

To promote interoperability and set up practices based on past experience, the following sections lay out usage guidelines for specific YANG constructs. 🍓

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

4.1. Module Naming Conventions 🏷️

Modules contained in Standards Track documents SHOULD be named according to the guidelines in the IANA Considerations section of [RFC6020]. 🦋

A distinctive word or acronym (e.g., protocol name or working group acronym) SHOULD be used in the module name. If new definitions are being defined to extend one or more existing modules, then the same word or acronym should be reused, instead of creating a new one. Reuse is the move here, bestie 🌸

All published module names MUST be unique. For a YANG module published in an RFC, this uniqueness is guaranteed by IANA. For unpublished modules, the authors need to check that no other work in progress is using the same module name. 🔍

Once a module name is published, it MUST NOT be reused, even if the RFC containing the module is reclassified to 'Historic' status. 🪦

4.2. Identifiers 🪪

Identifiers for all YANG identifiers in published modules MUST be between 1 and 64 characters in length. These include any construct specified as an 'identifier-arg-str' token in the ABNF in Section 12 of [RFC6020]. 📏

4.3. Defaults 🎀

In general, it is suggested that substatements containing very common default values SHOULD NOT be present. The following substatements are commonly used with the default value, which would make the module difficult to read if used everywhere they are allowed. 🙃

+---------------+---------------+
| Statement     | Default Value |
+---------------+---------------+
| config        | true          |
|               |               |
| mandatory     | false         |
|               |               |
| max-elements  | unbounded     |
|               |               |
| min-elements  | 0             |
|               |               |
| ordered-by    | system        |
|               |               |
| status        | current       |
|               |               |
| yin-element   | false         |
+---------------+---------------+

4.4. Conditional Statements 🌀

A module may be conceptually partitioned in several ways, using the 'if-feature' and/or 'when' statements. 🧩

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

If a data definition is optional, depending on server support for a NETCONF protocol capability, then a YANG 'feature' statement SHOULD be defined to indicate that the NETCONF capability is supported within the data model. 🔧

If any notification data, or any data definition, for a non-configuration data node is not mandatory, then the server may or may not be required to return an instance of this data node. If any conditional requirements exist for returning the data node in a notification payload or retrieval request, they MUST be documented somewhere. For example, a 'when' or 'if-feature' statement could apply to the data node, or the conditional requirements could be explained in a 'description' statement within the data node or one of its ancestors (if any). 📣

4.5. XPath Usage 🛤️

This section describes guidelines for using the XML Path Language [W3C.REC-xpath-19991116] (XPath) within YANG modules. 🌷

The 'attribute' and 'namespace' axes are not supported in YANG, and MAY be empty in a NETCONF server implementation. 🫥

The 'position' and 'last' functions SHOULD NOT be used. This applies to implicit use of the 'position' function as well (e.g., '//chapter[42]'). A server is only required to maintain the relative XML document order of all instances of a particular user-ordered list or leaf-list. The 'position' and 'last' functions MAY be used if they are evaluated in a context where the context node is a user-ordered 'list' or 'leaf-list'. 🙋‍♀️

The 'preceding', and 'following' axes SHOULD NOT be used. These constructs rely on XML document order within a NETCONF server configuration database, which may not be supported consistently or produce reliable results across implementations. Predicate expressions based on static node properties (e.g., element name or value, 'ancestor' or 'descendant' axes) SHOULD be used instead. The 'preceding' and 'following' axes MAY be used if document order is not relevant to the outcome of the expression (e.g., check for global uniqueness of a parameter value). 🕰️

The 'preceding-sibling' and 'following-sibling' axes SHOULD NOT used. A server is only required to maintain the relative XML document order of all instances of a particular user-ordered list or leaf-list. The 'preceding-sibling' and 'following-sibling' axes MAY be used if they are evaluated in a context where the context node is a user-ordered 'list' or 'leaf-list'. 👯

Data nodes that use the 'int64' and 'uint64' built-in type SHOULD NOT be used within numeric expressions. There are boundary conditions in which the translation from the YANG 64-bit type to an XPath number can cause incorrect results. Specifically, an XPath 'double' precision floating point number cannot represent very large positive or negative 64-bit numbers because it only provides a total precision of 53 bits. The 'int64' and 'uint64' data types MAY be used in numeric expressions if the value can be represented with no more than 53 bits of precision. 🔢⚠️

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

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

4.6. Lifecycle Management ♻️

The status statement MUST be present if its value is 'deprecated' or 'obsolete'. 🪄

The module or submodule name MUST NOT be changed, once the document containing the module or submodule is published. 🔒

The module namespace URI value MUST NOT be changed, once the document containing the module is published. 🔒✨

The revision-date substatement within the imports statement SHOULD be present if any groupings are used from the external module. 📅

The revision-date substatement within the include statement SHOULD be present if any groupings are used from the external submodule. 📆

If submodules are used, then the document containing the main module MUST be updated so that the main module revision date is equal or more recent than the revision date of any submodule that is (directly or indirectly) included by the main module. 🌟

4.7. Module Header, Meta, and Revision Statements ✨

okay so 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 lives in a document meant for Standards Track status, the organization SHOULD be the IETF working group chartered to write that document 🫶.

The contact statement MUST be present 📇. If the module is in a Standards Track document, the working group web and mailing information MUST be present, and the main document author or editor contact information SHOULD be present. If there are extra authors or editors, their contact information MAY be present. In addition, the Area Director and other contact information MAY be present 🌸.

The description statement MUST be present 📝. The appropriate IETF Trust Copyright text MUST be present, as described in Section 3.1 🦋.

If the module relies on information from other documents that aren't the same documents implied by the import statements in the module, then those documents MUST be identified in the reference statement 🧚.

A revision statement MUST be present for each published version of the module 🎀. The revision statement MUST have a reference substatement. It MUST identify the published document that contains the module. Modules get pulled out of their original documents all the time, so it's super useful for developers and operators to know how to find the original source document in a consistent way 🔍. The revision statement MAY have a description substatement.

Each new revision MUST include a revision date that is higher than any other revision date in the module 📅. The revision date doesn't need to be updated if the module contents don't change in the new document revision 💀.

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

4.8. Namespace Assignments 🧚

It is RECOMMENDED that only valid YANG modules be included in documents, whether or not they are published yet. This allows:

  • the module to compile correctly instead of generating disruptive fatal errors.
  • early implementors to use the modules without picking a random value for the XML namespace.
  • early interoperability testing, since independent implementations will use the same XML namespace value.

Until a URI is assigned by the IANA, a proposed namespace URI MUST be provided for the namespace statement in a YANG module 🌈. A value SHOULD be selected that is not likely to collide with other YANG namespaces. Standard module names, prefixes, and URI strings already listed in the YANG Module Registry MUST NOT be used 🙈.

A standard namespace statement value SHOULD have the following form:

<URN prefix string>:<module-name>

The following URN prefix string SHOULD be used for published and unpublished YANG modules:

urn:ietf:params:xml:ns:yang:

The following example URNs would be valid temporary namespace statement values for Standards Track modules:

urn:ietf:params:xml:ns:yang:ietf-netconf-partial-lock

urn:ietf:params:xml:ns:yang:ietf-netconf-state

urn:ietf:params:xml:ns:yang:ietf-netconf

Note that a different URN prefix string SHOULD be used for non-Standards-Track modules 👀. That string SHOULD be selected according to the guidelines in [RFC6020].

The following examples of non-Standards-Track modules are only suggestions. There are no guidelines for this type of URN in this document 🤷‍♀️:

http://example.com/ns/example-interfaces

http://example.com/ns/example-system

4.9. Top-Level Data Definitions 🌈

There SHOULD only be one top-level data node defined in each YANG module, if any data nodes are defined at all 🎯.

The top-level data organization SHOULD be considered carefully, in advance. Data model designers need to think about 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 it may change over time 🙅‍♀️.

A mandatory database data definition is defined as a node that a client must provide for the database to be valid. The server is not required to provide a value 🫠.

Top-level database data definitions MUST NOT be mandatory 🚫. If a mandatory node appears at the top level, it will immediately cause the database to be invalid. This can happen when the server boots or when a module is loaded dynamically at runtime 💥.

4.10. Data Types 💅

Selecting an appropriate data type (i.e., built-in type, existing derived type, or new derived type) is very subjective, so few requirements can be specified on that subject 🤌.

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

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

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

For string data types, if the length of the string is required to be bounded in all implementations, then a length statement MUST be present 📏.

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

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

For 'enumeration' or 'bits' data types, the semantics for each 'enum' or 'bit' SHOULD be documented. A separate description statement (within each 'enum' or 'bit' statement) SHOULD be present 📖.

4.11. Reusable Type Definitions ♻️

If an appropriate derived type exists in any standard module, such as [RFC6021], then it SHOULD be used instead of defining a new derived type 🙌.

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

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

If a significant number of derived types are defined, and it's anticipated that these data types will be reused by multiple modules, then these derived types SHOULD be contained in a separate module or submodule. That makes reuse easier without unnecessary coupling 🧩.

The description statement MUST be present 📝.

If the type definition semantics are defined in an external document (other than another YANG module indicated by an import statement), then the reference statement MUST be present 🔖.

4.12. Data Definitions 🎀

The description statement MUST be present in the following YANG statements 💁‍♀️:

  • anyxml
  • augment
  • choice
  • container
  • extension
  • feature
  • grouping
  • identity
  • leaf
  • leaf-list
  • list
  • notification
  • rpc
  • typedef

If the data definition semantics are defined in an external document (other than another YANG module indicated by an import statement), then a reference statement MUST be present 📚.

The anyxml construct may be useful to represent an HTML banner containing markup elements, such as <b> and </b>, and MAY be used in such cases 🍬. However, this construct SHOULD NOT be used if other YANG data node types can be used instead to represent the desired syntax and semantics 🙅‍♀️.

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

For list and leaf-list data definitions, if the number of possible instances is required to be bounded for all implementations, then the max-elements statements SHOULD be present 🔢.

If any 'must' or 'when' statements are used within the data definition, then the data definition description statement SHOULD describe the purpose of each one 🗒️.

4.13. Operation Definitions ⚡

If the operation semantics are defined in an external document (other than another YANG module indicated by an import statement), then a reference statement MUST be present 📖.

If the operation impacts system behavior in some way, it SHOULD be mentioned in the description statement 🫧.

If the operation is potentially harmful to system behavior in some way, it MUST be mentioned in the Security Considerations section of the document 😭🚨.

4.14. Notification Definitions 🔔

The description statement MUST be present 📝.

If the notification semantics are defined in an external document (other than another YANG module indicated by an import statement), then a reference statement MUST be present 🔖.

5. IANA Considerations 🦋

This document registers one URI in the IETF XML registry [RFC3688]. The following registration has been made 💌:

URI: urn:ietf:params:xml:ns:yang:ietf-template

Registrant Contact: The NETMOD WG of the IETF.

XML: N/A, the requested URI is an XML namespace.

Per this document, the following assignment has been made in the YANG Module Names Registry for the YANG module template in Appendix B 🧁:

    +---------------+-------------------------------------------+
    | Field         | Value                                     |
    +---------------+-------------------------------------------+
    | Name          | ietf-template                             |
    |               |                                           |
    | Namespace     | urn:ietf:params:xml:ns:yang:ietf-template |
    |               |                                           |
    | Prefix        | temp                                      |
    |               |                                           |
    | Reference     | RFC 6087                                  |
    +---------------+-------------------------------------------+

6. Security Considerations 🔒

okay bestie, this section is SERIOUS but also kind of iconic 💅 The YANG data modeling guidelines for security considerations live in an online document (http://www.ops.ietf.org/netconf/yang-security-considerations.txt), and the template in this RFC is dated 2010-06-16. Check that webpage in case there's a newer version, because it might have changed 👀

Good news first: this document doesn't introduce any new or increased security risks into the management system ✨

Now the rules. Every specification that defines one or more YANG modules MUST contain a section about the security considerations for those modules. That section MUST follow the latest approved template, which is also on that webpage. Writable data nodes that could be especially disruptive if abused MUST be listed by name, and the security risks MUST be spelled out 🚨 Readable data nodes with especially sensitive information, or with significant privacy concerns, MUST be listed by name too, and the reasons for the sensitivity or privacy concerns MUST be explained 🙈 And if you've defined new RPC operations, the security considerations of each new RPC operation MUST be explained. No skipping, no shortcuts, periodt 💀

6.1. Security Considerations Section Template 📝

Here's the template you copy-paste into your own spec. Keep it exact:

X.  Security Considerations

   The YANG module defined in this memo is designed to be accessed
   via the NETCONF protocol [RFC4741].  The lowest NETCONF layer is
   the secure transport layer and the mandatory-to-implement secure
   transport is SSH [RFC4742].

   -- if you have any writable data nodes (those are all the
   -- "config true" nodes, and remember, that is the default)
   -- describe their specific sensitivity or vulnerability.

   There are a number of data nodes defined in this YANG module
   which are writable/creatable/deletable (i.e., config true, which
   is the default).  These data nodes may be considered sensitive
   or vulnerable in some network environments.  Write operations
   (e.g., edit-config) to these data nodes without proper protection
   can have a negative effect on network operations.  These are
   the subtrees and data nodes and their sensitivity/vulnerability:

    <list subtrees and data nodes and state why they are sensitive>

   -- for all YANG modules you must evaluate whether any readable data
   -- nodes (those are all the "config false" nodes, but also all other
   -- nodes, because they can also be read via operations like get or
   -- get-config) are sensitive or vulnerable (for instance, if they
   -- might reveal customer information or violate personal privacy
   -- laws such as those of the European Union if exposed to
   -- unauthorized parties)

   Some of the readable data nodes in this YANG module may be
   considered sensitive or vulnerable in some network environments.
   It is thus important to control read access (e.g., via get,
   get-config, or notification) to these data nodes.  These are the
   subtrees and data nodes and their sensitivity/vulnerability:

    <list subtrees and data nodes and state why they are sensitive>

   -- if your YANG module has defined any rpc operations
   -- describe their specific sensitivity or vulnerability.

   Some of the RPC operations in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control access to these operations.  These are the
   operations and their sensitivity/vulnerability:

    <list RPC operations and state why they are sensitive>

7. Acknowledgments 🙏

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

The working group also thanks Martin Bjorklund and Juergen Schoenwaelder for their extensive reviews and contributions to this document. They were basically the MVPs 🏆

8. References 📚

8.1. Normative References

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

[RFC2223]  Postel, J. and J. Reynolds, "Instructions to RFC Authors",
           RFC 2223, October 1997.

[RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
           January 2004.

[RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
           Resource Identifier (URI): Generic Syntax", STD 66,
           RFC 3986, January 2005.

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

[RFC5378]  Bradner, S. and J. Contreras, "Rights Contributors Provide
           to the IETF Trust", BCP 78, RFC 5378, November 2008.

[RFC5741]  Daigle, L., Kolkman, O., and IAB, "RFC Streams, Headers,
           and Boilerplates", RFC 5741, December 2009.

[W3C.REC-xpath-19991116]
           DeRose, S. and J. Clark, "XML Path Language (XPath)
           Version 1.0", World Wide Web Consortium
           Recommendation REC-xpath-19991116, November 1999,
           <http://www.w3.org/TR/1999/REC-xpath-19991116>.

[RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
           Network Configuration Protocol (NETCONF)", RFC 6020,
           October 2010.

[RFC6021]  Schoenwaelder, J., "Common YANG Data Types", RFC 6021,
           October 2010.

8.2. Informative References

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

[RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
           IANA Considerations Section in RFCs", BCP 26, RFC 5226,
           May 2008.

[RFC-STYLE]
           Braden, R., Ginoza, S., and A. Hagens, "RFC Document
           Style", September 2009,
           <http://www.rfc-editor.org/rfc-style-guide/rfc-style>.

Appendix A. Module Review Checklist ✅

This section is adapted from RFC 4181 💖

The whole point of a YANG module review is to check the module for technical correctness and for following the IETF documentation requirements. Here's the checklist you can use when reviewing an Internet-Draft:

  1. I-D Boilerplate -- verify that the draft contains the required Internet-Draft boilerplate (see http://www.ietf.org/id-info/guidelines.html), including the appropriate statement to permit publication as an RFC, and that I-D boilerplate does not contain references or section numbers.
  2. Abstract -- verify that the abstract does not contain references, that it does not have a section number, and that its content follows the guidelines in http://www.ietf.org/id-info/guidelines.html.
  3. Copyright Notice -- verify that the draft has the appropriate text regarding the rights that document contributers provide to the IETF Trust [RFC5378]. Verify that it contains the full IETF Trust copyright notice at the beginning of the document. The IETF Trust Legal Provisions (TLP) can be found at http://trustee.ietf.org/license-info/.
  4. Security Considerations section -- verify that the draft uses the latest approved template from the OPS area website (http://www.ops.ietf.org/netconf/yang-security-considerations.txt) and that the guidelines therein have been followed.
  5. IANA Considerations section -- this section must always be present. For each module within the document, ensure that the IANA Considerations section contains entries for the following IANA registries:
    • XML Namespace Registry: Register the YANG module namespace.
    • YANG Module Registry: Register the YANG module name, prefix, namespace, and RFC number, according to the rules specified in [RFC6020].
  6. References -- verify that the references are properly divided between normative and informative references, that RFC 2119 is included as a normative reference if the terminology defined therein is used in the document, that all references required by the boilerplate are present, that all YANG modules containing imported items are cited as normative references, and that all citations point to the most current RFCs unless there is a valid reason to do otherwise (for example, it is OK to include an informative reference to a previous version of a specification to help explain a feature included for backward compatibility). Be sure citations for all imported modules are present somewhere in the document text (outside the YANG module).
  7. License -- verify that the draft contains the Simplified BSD License in each YANG module or submodule. Some guidelines related to this requirement are described in Section 3.1. Make sure that the correct year is used in all copyright dates. Use the approved text from the latest Trust Legal Provisions (TLP) document, which can be found at http://trustee.ietf.org/license-info/.
  8. Other Issues -- check for any issues mentioned in http://www.ietf.org/id-info/checklist.html that are not covered elsewhere.
  9. Technical Content -- review the actual technical content for compliance with the guidelines in this document. The use of a YANG module compiler is recommended when checking for syntax errors. A list of freely available tools and other information can be found at http://trac.tools.ietf.org/wg/netconf/trac/wiki.

Checking for correct syntax, however, is only part of the job. It is just as important to actually read the YANG module document from the point of view of a potential implementor. It is particularly important to check that description statements are sufficiently clear and unambiguous to allow interoperable implementations to be created. 🧐

Appendix B. YANG Module Template 🧩

<CODE BEGINS> file "ietf-template@2010-05-18.yang"

Okay bestie, this is the template itself, the exact file you copy when you start a new module 🎀 Here's the whole thing, every line of it:

module ietf-template {

    // replace this string with a unique namespace URN value
    namespace
      "urn:ietf:params:xml:ns:yang:ietf-template";

    // replace this string, and try to pick a unique prefix
    prefix "temp";


    // import statements here: e.g.,
    // import ietf-yang-types { prefix yang; }
    // import ietf-inet-types { prefix inet; }

    // identify the IETF working group if applicable
    organization
       "IETF NETMOD (NETCONF Data Modeling Language) Working Group";

    // update this contact statement with your info
    contact
       "WG Web:   <http://tools.ietf.org/wg/your-wg-name/>
        WG List:  <mailto:your-wg-name@ietf.org>

        WG Chair: your-WG-chair
                  <mailto:your-WG-chair@example.com>

        Editor:   your-name
                  <mailto:your-email@example.com>";


    // replace the first sentence in this description statement.
    // replace the copyright notice with the most recent
    // version, if it has been updated since the publication
    // of this document
    description
     "This module defines a template for other YANG modules.

      Copyright (c) <insert year> IETF Trust and the persons
      identified as authors of the code.  All rights reserved.

      Redistribution and use in source and binary forms, with or
      without modification, is permitted pursuant to, and subject
      to the license terms contained in, the Simplified BSD License
      set forth in Section 4.c of the IETF Trust's Legal Provisions
      Relating to IETF Documents
      (http://trustee.ietf.org/license-info).

      This version of this YANG module is part of RFC XXXX; see
      the RFC itself for full legal notices.";

    // RFC Ed.: replace XXXX with actual RFC number and remove this note

    reference "RFC XXXX";

    // RFC Ed.: remove this note
    // Note: extracted from RFC 6087


    // replace '2010-05-18' with the module publication date
    // The format is (year-month-day)
    revision "2010-05-18" {
      description
        "Initial version";
    }

    // extension statements

    // feature statements

    // identity statements

    // typedef statements

    // grouping statements

    // data definition statements

    // augment statements

    // rpc statements

    // notification statements

    // DO NOT put deviation statements in a published module

}

<CODE ENDS> 🧚 That's the end of the template module, and it's giving tidy and ready to fill in.

Author's Address 💌

Andy Bierman
Brocade

EMail: andy.bierman@brocade.com
📦 where this page comes from