Internet Engineering Task Force (IETF)                     D. Bogdanovic
Request for Comments: 8199                          Volta Networks, Inc.
Category: Informational                                        B. Claise
ISSN: 2070-1721                                                C. Moberg
                                                     Cisco Systems, Inc.
                                                               July 2017

YANG Module Classification




The YANG data modeling language is currently being considered for a wide variety of applications throughout the networking industry at large. Many standards development organizations (SDOs), open-source software projects, vendors, and users are using YANG to develop and publish YANG modules for a wide variety of applications. At the same time, there is currently no well-known terminology to categorize various types of YANG modules.


A consistent terminology would help with the categorization of YANG modules, assist in the analysis of the YANG data modeling efforts in the IETF and other organizations, and bring clarity to the YANG-related discussions between the different groups.


This document describes a set of concepts and associated terms to support consistent classification of YANG modules.


Status of This Memo


This document is not an Internet Standards Track specification; it is published for informational purposes.

このドキュメントはInternet Standards Trackの仕様ではありません。情報提供を目的として公開されています。

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 7841.

このドキュメントは、IETF(Internet Engineering Task Force)の製品です。これは、IETFコミュニティのコンセンサスを表しています。公開レビューを受け、インターネットエンジニアリングステアリンググループ(IESG)による公開が承認されました。 IESGによって承認されたすべてのドキュメントが、あらゆるレベルのインターネット標準の候補になるわけではありません。 RFC 7841のセクション2をご覧ください。

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at


Copyright Notice


Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.

Copyright(c)2017 IETF Trustおよびドキュメントの作成者として識別された人物。全著作権所有。

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents ( 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. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

この文書は、BCP 78およびこの文書の発行日に有効なIETF文書に関するIETFトラストの法的規定(の対象となります。これらのドキュメントは、このドキュメントに関するあなたの権利と制限を説明しているため、注意深く確認してください。このドキュメントから抽出されたコードコンポーネントには、Trust Legal Provisionsのセクション4.eに記載されているSimplified BSD Licenseのテキストが含まれている必要があり、Simplified BSD Licenseに記載されているように保証なしで提供されます。

Table of Contents


   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  First Dimension: YANG Module Abstraction Layers . . . . . . .   4
     2.1.  Network Service YANG Modules  . . . . . . . . . . . . . .   6
     2.2.  Network Element YANG Modules  . . . . . . . . . . . . . .   7
   3.  Second Dimension: YANG Module Origin Types  . . . . . . . . .   7
     3.1.  Standard YANG Modules . . . . . . . . . . . . . . . . . .   8
     3.2.  Vendor-Specific YANG Modules and Extensions . . . . . . .   8
     3.3.  User-Specific YANG Modules and Extensions . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11
1. Introduction
1. はじめに

The Internet Engineering Steering Group (IESG) has been actively encouraging IETF working groups to use the YANG data modeling language [RFC7950] and the Network Configuration Protocol (NETCONF) [RFC6241] for configuration management purposes, especially in new working group charters [IESG-Statement].


YANG is also gaining wide acceptance as the de facto standard data modeling language in the broader industry. This extends beyond the IETF to include many SDOs, industry consortia, ad hoc groups, open-source projects, vendors, and end users.


There are currently no clear guidelines on how to classify the layering of YANG modules according to abstraction or how to classify modules along the continuum spanning formal standards publications, vendor-specific modules, and modules provided by end users.


This document presents a set of concepts and terms to form a useful taxonomy for consistent classification of YANG modules in two dimensions:


o The layering of modules based on their abstraction levels

o 抽象化レベルに基づくモジュールの階層化

o The module origin type based on the nature and intent of the content

o コンテンツの性質と意図に基づくモジュールの起点タイプ

The intent of this document is to provide a taxonomy to simplify human communication around YANG modules. While the classification boundaries are at times blurry, this document should provide a robust starting point as the YANG community gains further experience with designing and deploying modules. To be more explicit, it is expected that the classification criteria will change over time.


A number of modules, for example, modules concerned with topologies, created substantial discussion during the development of this document. Topology modules are useful both on the network element level (e.g., link-state database content) and on the network service level (e.g., network-wide, configured topologies). In the end, it is the module developer that classifies the module according to the initial intent of the module content.


This document should provide benefits to multiple audiences:


o First, a common taxonomy helps with discussions among SDOs and industry consortia; the goals of such discussions are determined by the respective areas of work.

o まず、一般的な分類法は、SDOと業界コンソーシアムの間の議論に役立ちます。そのような議論の目的は、それぞれの作業分野によって決まります。

o Second, operators might look at the YANG module abstraction layers to understand which Network Service YANG Modules and Network Element YANG Modules are available for their service composition. It is difficult to determine the module type without inspecting the YANG module itself. The YANG module name might provide some useful information but is not a definite answer. For example, a Layer 2 Virtual Private Network (L2VPN) YANG module might be a Network Service YANG Module, ready to be used as a service model by a network operator. Alternatively, it might be a Network Element YANG Module that contains the L2VPN data definitions required to be configured on a single device.

o 次に、オペレーターはYANGモジュールの抽象化レイヤーを見て、サービス構成に使用できるネットワークサービスYANGモジュールとネットワークエレメントYANGモジュールを理解します。 YANGモジュール自体を検査せずにモジュールのタイプを判別することは困難です。 YANGモジュール名は、いくつかの有用な情報を提供する可能性がありますが、明確な答えではありません。たとえば、レイヤ2バーチャルプライベートネットワーク(L2VPN)YANGモジュールは、ネットワークオペレーターがサービスモデルとして使用する準備ができているネットワークサービスYANGモジュールである場合があります。または、単一のデバイスで構成する必要のあるL2VPNデータ定義を含むネットワークエレメントYANGモジュールである可能性があります。

o Third, this taxonomy will help equipment vendors (whether physical or virtual), controller vendors, and orchestrator vendors to explain to their customers the relationship between the different YANG modules they support in their products.

o 3番目に、この分類は、機器ベンダー(物理または仮想)、コントローラーベンダー、オーケストレーターベンダーが、製品でサポートするさまざまなYANGモジュール間の関係を顧客に説明するのに役立ちます。

1.1. Terminology
1.1. 用語

[RFC7950] specifies:


o data model: A data model describes how data is represented and accessed.

o データモデル:データモデルは、データの表現方法とアクセス方法を記述します。

o module: A YANG module defines hierarchies of schema nodes. With its definitions and the definitions it imports or includes from elsewhere, a module is self-contained and "compilable".

o module:YANGモジュールは、スキーマノードの階層を定義します。モジュールの定義とインポートまたは他の場所からの定義により、モジュールは自己完結型で「コンパイル可能」です。

2. First Dimension: YANG Module Abstraction Layers
2. 最初の次元:YANGモジュールの抽象化レイヤー

Module developers have taken two approaches to developing YANG modules: top-down and bottom-up. The top-down approach starts with high-level abstractions modeling business or customer requirements and maps them to specific networking technologies. The bottom-up approach starts with fundamental networking technologies and maps them into more abstract constructs.


There are currently no specific requirements or well-defined best practices for the development of YANG modules. This document considers both bottom-up and top-down approaches as they are both used and they each provide benefits that appeal to different groups.


For layering purposes, this document suggests the classification of YANG modules into two distinct abstraction layers:


o Network Element YANG Modules describe the configuration, state data, operations, and notifications of specific device-centric technologies or features.

o ネットワーク要素YANGモジュールは、特定のデバイス中心のテクノロジーまたは機能の構成、状態データ、操作、および通知を記述します。

o Network Service YANG Modules describe the configuration, state data, operations, and notifications of abstract representations of services implemented on one or multiple network elements.

o ネットワークサービスYANGモジュールは、1つまたは複数のネットワーク要素に実装されたサービスの抽象的な表現の構成、状態データ、操作、および通知を記述します。

                        |  Operations and Business |
                        |      Support Systems     |
                        |      (OSSs and BSSs)     |
        - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
        Network Service YANG Modules
             +------------+      +-------------+      +-------------+
             |            |      |             |      |             |
             |  - L2VPN   |      |   - L2VPN   |      |    L3VPN    |
             |  - VPWS    |      |   - VPLS    |      |             |
             |            |      |             |      |             |
             +------------+      +-------------+      +-------------+
        - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
        Network Element YANG Modules
        +------------+  +------------+  +-------------+  +------------+
        |            |  |            |  |             |  |            |
        |    MPLS    |  |    BGP     |  | IPv4 / IPv6 |  |  Ethernet  |
        |            |  |            |  |             |  |            |
        +------------+  +------------+  +-------------+  +------------+

L2VPN: Layer 2 Virtual Private Network L3VPN: Layer 3 Virtual Private Network VPWS: Virtual Private Wire Service VPLS: Virtual Private LAN Service


Figure 1: YANG Module Abstraction Layers


Figure 1 illustrates the application of YANG modules at different layers of abstraction. Layering of modules allows for reusability of existing lower-layer modules by higher-level modules while limiting duplication of features across layers.


For module developers, per-layer modeling allows for separation of concern across editing teams focusing on specific areas.


As an example, experience from the IETF shows that creating useful Network Element YANG Modules (e.g., for routing or switching protocols) requires teams that include developers with experience implementing those protocols.


On the other hand, Network Service YANG Modules are best developed by network operators experienced in defining network services for consumption by programmers, e.g., those developing flow-through provisioning systems or self-service portals.


2.1. Network Service YANG Modules
2.1. ネットワークサービスYANGモジュール

Network Service YANG Modules describe the characteristics of a service, as agreed upon with consumers of that service. That is, a service module does not expose the detailed configuration parameters of all participating network elements and features but describes an abstract model that allows instances of the service to be decomposed into instance data according to the Network Element YANG Modules of the participating network elements. The service-to-element decomposition is a separate process; the details depend on how the network operator chooses to realize the service. For the purpose of this document, the term "orchestrator" is used to describe a system implementing such a process.


External systems can be provisioning systems, service orchestrators, Operations Support Systems, Business Support Systems, and applications exposed to network service consumers (either internal network operations people or external customers). These modules are commonly designed, developed, and deployed by network infrastructure teams.


YANG allows for different design patterns to describe network services, ranging from monolithic to component-based approaches.


The monolithic approach captures the entire service in a single module and does not put focus on reusability of internal data definitions and groupings. The monolithic approach has the advantages of single-purpose development, including development speed at the expense of reusability.


The component-based approach captures device-centric features (e.g., VPN Routing and Forwarding (VRF), routing protocols, or packet filtering) in a vendor-independent manner. The components are designed for reuse across many service modules. The set of components required for a specific service is then composed into the higher-level service. The component-based approach has the advantages of modular development, including a higher degree of reusability at the expense of initial development speed.


As an example, an L2VPN service can be built on many different types of transport network technologies, including, e.g., MPLS or Carrier Ethernet. A component-based approach would allow for reuse of User-Network Interface (UNI) definitions, such as the MEF UNI interface or MPLS interface, independent of the underlying transport network. The monolithic approach would assume a specific set of transport technologies and interface definitions.

例として、L2VPNサービスは、MPLSやキャリアイーサネットなど、さまざまなタイプのトランスポートネットワークテクノロジー上に構築できます。コンポーネントベースのアプローチでは、基になるトランスポートネットワークとは関係なく、MEF UNIインターフェイスやMPLSインターフェイスなどのユーザーネットワークインターフェイス(UNI)定義を再利用できます。モノリシックアプローチでは、特定のトランスポートテクノロジーとインターフェース定義を想定します。

An example of a Network Service YANG Module is in [RFC8049]. It provides an abstract model for Layer 3 IP VPN service configuration. This module includes the concept of a 'site-network-access' to represent bearer and connection parameters. An orchestrator receives operations on service instances according to the service module and decomposes the data into configuration data according to specific Network Element YANG Modules to configure the participating network elements to the service. In the case of the L3VPN module, this would include translating the 'site-network-access' parameters to the appropriate parameters in the Network Element YANG Module implemented on the constituent elements.

Network Service YANGモジュールの例は[RFC8049]にあります。レイヤ3 IP VPNサービス構成の抽象的なモデルを提供します。このモジュールには、ベアラと接続パラメータを表す「サイトネットワークアクセス」の概念が含まれています。オーケストレーターは、サービスモジュールに従ってサービスインスタンスの操作を受け取り、特定のネットワーク要素YANGモジュールに従ってデータを構成データに分解して、サービスに参加するネットワーク要素を構成します。 L3VPNモジュールの場合、これには、「site-network-access」パラメーターを構成要素に実装されているネットワーク要素YANGモジュールの適切なパラメーターに変換することが含まれます。

2.2. Network Element YANG Modules
2.2. ネットワーク要素YANGモジュール

Network Element YANG Modules describe the characteristics of a network device as defined by the vendor of that device. The modules are commonly structured around features of the device, e.g., interface configuration [RFC7223], OSPF configuration [OSPF-YANG], and access control list (ACL) configuration [ACL-YANG].


The Network Element YANG Module provides a coherent data model representation of the software environment consisting of the operating system and applications running on the device. The decomposition, ordering, and execution of changes to the operating system and application configuration is the task of the agent that implements the module.

Network Element YANGモジュールは、デバイスで実行されているオペレーティングシステムとアプリケーションで構成されるソフトウェア環境の一貫したデータモデル表現を提供します。オペレーティングシステムとアプリケーション構成への変更の分解、順序付け、および実行は、モジュールを実装するエージェントのタスクです。

3. Second Dimension: YANG Module Origin Types
3. 2次元:YANGモジュールの原点タイプ

This document suggests classifying YANG module origin types as Standard YANG Modules, Vendor-Specific YANG Modules and Extensions, or User-Specific YANG Modules and Extensions.


The suggested classification applies to both Network Element YANG Modules and Network Service YANG Modules.

推奨される分類は、Network Element YANGモジュールとNetwork Service YANGモジュールの両方に適用されます。

It is to be expected that real-world implementations of both Network Service YANG Modules and Network Element YANG Modules will include a mix of all three module origin types.

Network Service YANGモジュールとNetwork Element YANGモジュールの両方の実際の実装には、3つすべてのモジュールオリジンタイプの組み合わせが含まれることが予想されます。

Figure 2 illustrates the relationship between the three types of modules.


  |     User     |
  |   Extensions |
  +------+-------+  +--------------+  +--------------+
  |   Vendor     |  |     User     |  |     User     |
  |  Extensions  |  |  Extensions  |  |  Extensions  |
  +------+-------+  +------+-------+  +------+-------+
      Augments          Augments          Augments
  +------+-----------------+-------+  +------+-------+  +--------------+
  |            Standard            |  |    Vendor    |  |    User      |
  |            Modules             |  |    Modules   |  |   Modules    |
  +--------------------------------+  +--------------+  +--------------+

Figure 2: YANG Module Origin Types


3.1. Standard YANG Modules
3.1. 標準のYANGモジュール

Standard YANG Modules are published by SDOs. Most SDOs create specifications according to a formal process in order to produce a standard that is useful for their constituencies.


The lifecycles of these modules are driven by the editing cycles of the specifications and not tied to a specific implementation.


Examples of SDOs in the networking industry are the IETF and the IEEE.


3.2. Vendor-Specific YANG Modules and Extensions
3.2. ベンダー固有のYANGモジュールと拡張機能

Vendor-Specific YANG Modules are developed by organizations with the intent to support a specific set of implementations under control of that organization, for example, vendors of virtual or physical equipment, industry consortia, and open-source projects. The intent of these modules ranges from providing openly published YANG modules that may eventually be contributed back to or adopted by an SDO to strictly internal YANG modules not intended for external consumption.


The lifecycles of these modules are generally aligned with the release cycles of the product or open-source software project deliverables.


It is worth noting that there is an increasing amount of interaction between open-source projects and SDOs in the networking industry. This includes open-source projects implementing published standards as well as open-source projects contributing content to SDO processes.


Vendors also develop vendor-specific extensions to standard modules using YANG constructs for extending data definitions of previously published modules. This is done using the 'augment' statement that allows locally defined data trees to be added into locations in externally defined data trees.

ベンダーはまた、以前に公開されたモジュールのデータ定義を拡張するためのYANG構造を使用して、標準モジュールへのベンダー固有の拡張を開発します。これは、ローカルで定義されたデータツリーを外部で定義されたデータツリーの場所に追加できるようにする 'augment'ステートメントを使用して行われます。

Vendors use this to extend standard modules to cover the full scope of features in implementations, which commonly is broader than that covered by the standard module.


3.3. User-Specific YANG Modules and Extensions
3.3. ユーザー固有のYANGモジュールと拡張機能

User-Specific YANG Modules are developed by organizations that operate YANG-based infrastructure including devices and orchestrators, for example, network administrators in enterprises or at service providers. The intent of these modules is to express the specific needs for a certain implementation, above and beyond what is provided by vendors.


This module type obviously requires the infrastructure to support the introduction of user-provided modules and extensions. This would include the ability to describe the service-to-network decomposition in orchestrators and the module-to-configuration decomposition in devices.


The lifecycles of these modules are generally aligned with the change cadence of the infrastructure.


4. Security Considerations
4. セキュリティに関する考慮事項

This document doesn't have any Security Considerations.


5. IANA Considerations
5. IANAに関する考慮事項

This document does not require any IANA actions.


6. References
6. 参考文献
6.1. Normative References
6.1. 引用文献

[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, <>.

[RFC6241] Enns、R。、編、Bjorklund、M。、編、Schoenwaelder、J。、編、およびA. Bierman、編、「Network Configuration Protocol(NETCONF)」、RFC 6241、DOI 10.17487 / RFC6241、2011年6月、<>。

[RFC7223] Bjorklund, M., "A YANG Data Model for Interface Management", RFC 7223, DOI 10.17487/RFC7223, May 2014, <>.

[RFC7223] Bjorklund、M。、「A YANG Data Model for Interface Management」、RFC 7223、DOI 10.17487 / RFC7223、2014年5月、<>。

[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, <>.

[RFC7950] Bjorklund、M。、編、「The YANG 1.1 Data Modeling Language」、RFC 7950、DOI 10.17487 / RFC7950、2016年8月、<>。

[RFC8049] Litkowski, S., Tomotaki, L., and K. Ogaki, "YANG Data Model for L3VPN Service Delivery", RFC 8049, DOI 10.17487/RFC8049, February 2017, <>.

[RFC8049] Litkowski、S.、Tomotaki、L。、およびK. Ogaki、「Y3 Data Model for L3VPN Service Delivery」、RFC 8049、DOI 10.17487 / RFC8049、2017年2月、<http://www.rfc-editor。 org / info / rfc8049>。

6.2. Informative References
6.2. 参考引用

[ACL-YANG] Bogdanovic, D., Jethanandani, M., Huang, L., Agarwal, S., and D. Blair, "Network Access Control List (ACL) YANG Data Model", Work in Progress, draft-ietf-netmod-acl-model-11, June 2017.

[ACL-YANG] Bogdanovic、D.、Jethanandani、M.、Huang、L.、Agarwal、S。、およびD. Blair、「Network Access Control List(ACL)YANG Data Model」、Work in Progress、draft-ietf -netmod-acl-model-11、2017年6月。

[IESG-Statement] "Writable MIB Module IESG Statement", < writable-mib-module.html>.

[IESG-Statement]「書き込み可能なMIBモジュールのIESGステートメント」、< writable-mib-module.html>。

[OSPF-YANG] Yeung, D., Qu, Y., Zhang, Z., Chen, I., and A. Lindem, "Yang Data Model for OSPF Protocol", Work in Progress, draft-ietf-ospf-yang-08, July 2017.

[OSPF-YANG] Yeung、D.、Qu、Y.、Zhang、Z.、Chen、I。、およびA. Lindem、「OSPFプロトコルのヤンデータモデル」、作業中、draft-ietf-ospf-yang -2017年7月8日。



Thanks to David Ball and Jonathan Hansford for feedback and suggestions.

フィードバックと提案をしてくれたDavid BallとJonathan Hansfordに感謝します。

Authors' Addresses


Dean Bogdanovic Volta Networks, Inc.

Dean Bogdanovic Volta Networks、Inc.


Benoit Claise Cisco Systems, Inc. De Kleetlaan 6a b1 1831 Diegem Belgium

Benoit Claise Cisco Systems、Inc. De Kleetlaan 6a b1 1831 Diegem Belgium

   Phone: +32 2 704 5622

Carl Moberg Cisco Systems, Inc.

Carl Moberg Cisco Systems、Inc.