RFC 8199
YANG Module Classification
RFC 8199: YANG Module Classification 🎀
Bestie, this is the RFC that gives YANG modules a shared vocabulary so everyone stops talking past each other 💅 Part 1 of 2 below.
Request for Comments: 8199 ✨ Category: Informational 🌸 Authors: D. Bogdanovic (Volta Networks, Inc.), B. Claise and C. Moberg (Cisco Systems, Inc.) 🫶 Date: July 2017 📅 ISSN: 2070-1721 Obsoletes / Updates: none listed in the title block 🦋 Published by: Internet Engineering Task Force (IETF) 🌈
Abstract ✨
YANG is being considered for a wide variety of applications across the whole networking industry 🌐 Tons of standards development organizations (SDOs), open-source projects, vendors, and users are using YANG to build and publish YANG modules for all kinds of uses 🔥 But here's the tea: there's no well-known terminology for sorting these modules into types 😭
A consistent vocabulary would help classify YANG modules, make it easier to analyze YANG modeling work in the IETF and beyond, and bring clarity to YANG discussions between different groups 💜
This document describes a set of concepts and associated terms that 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 💅
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 🙈
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc8199 🦋
Copyright Notice 🌈
Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved ✨
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document 📜 Please review these documents carefully, as they describe your rights and restrictions with respect to this document 👀 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 💖
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 . . . . . . . . . . . . . . . . . . . . . . . 111. Introduction 💖
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 🔥 That goes way beyond the IETF and includes 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:
- The layering of modules based on their abstraction levels 🪜
- The module origin type based on the nature and intent of the content 🧚
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:
- 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 🤝
- 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 🔧
- Third, this taxonomy will help equipment vendors (whether physical or virtual), controller vendors, and orchestrator vendors explain to their customers the relationship between the different YANG modules they support in their products 🎁
1.1. Terminology 📚
[RFC7950] specifies:
- data model: A data model describes how data is represented and accessed. 🗃️
- 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". 🧩
2. First Dimension: YANG Module Abstraction Layers 🪜✨
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, since both are used and each provides benefits that appeal to different groups 💖
For layering purposes, this document suggests the classification of YANG modules into two distinct abstraction layers:
- Network Element YANG Modules describe the configuration, state data, operations, and notifications of specific device-centric technologies or features 🖥️
- Network Service YANG Modules describe the configuration, state data, operations, and notifications of abstract representations of services implemented on one or multiple network elements ☁️
+--------------------------+
| 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 LayersFigure 1 illustrates the application of YANG modules at different layers of abstraction 🖼️ Layering modules allows reusing existing lower-layer modules in 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 🎀
okay so Network Service YANG Modules are all about describing what a service is, as agreed on with the people who consume it 💅 A service module does NOT dump every detailed config parameter from every participating network element and feature on you. Instead it gives you an abstract model, so an instance of the service can get broken down into instance data according to the Network Element YANG Modules of the elements involved. 🧩 That service-to-element decomposition is its own separate process, and how it works depends on how the operator chooses to realize the service. For this doc, "orchestrator" is the name for a system that runs that process ✨
External systems can be provisioning systems, service orchestrators, Operations Support Systems, Business Support Systems, and applications exposed to network service consumers (whether that's internal network ops people or external customers). These modules are usually designed, developed, and deployed by network infrastructure teams 🛠️
YANG lets you pick different design patterns for network services, anywhere from monolithic to component-based. 🌈
The monolithic approach packs the entire service into one single module and doesn't really focus on reusing internal data definitions and groupings. The big upside is single-purpose development, including faster development speed, but you pay for it with reusability 🙈
The component-based approach captures device-centric features (like VPN Routing and Forwarding (VRF), routing protocols, or packet filtering) in a vendor-independent way 🦋 The components are designed to be reused across lots of service modules, and the set of components a specific service needs gets composed into the higher-level service. The upside here is modular development and a much higher degree of reusability, but it costs you some initial development speed. Totally worth it, honestly 👑
Here's an example: an L2VPN service can be built on many different transport network technologies, including, e.g., MPLS or Carrier Ethernet 🌸 A component-based approach lets you reuse User-Network Interface (UNI) definitions, like the MEF UNI interface or the MPLS interface, no matter what the underlying transport network is. The monolithic approach would just assume one specific set of transport technologies and interface definitions. Lowkey rigid 😬
Now for the real-world example. [RFC8049] is an example of a Network Service YANG Module 💜 It gives you an abstract model for Layer 3 IP VPN service configuration, and it 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, then decomposes that data into configuration data according to specific Network Element YANG Modules so the participating network elements get configured to the service. In the case of the L3VPN module, that means translating the 'site-network-access' parameters into the right parameters in the Network Element YANG Module implemented on the constituent elements. The way that translation happens is literally the whole plot 🎬
2.2. Network Element YANG Modules 🧚
Network Element YANG Modules describe the characteristics of a network device, as defined by the vendor who made it 🍓 These modules are usually structured around the device's features, e.g., interface configuration [RFC7223], OSPF configuration [OSPF-YANG], and access control list (ACL) configuration [ACL-YANG].
A Network Element YANG Module gives you a coherent data model of the software environment on the device, which is the operating system plus the applications running on it ✨ The decomposition, ordering, and execution of changes to the operating system and application configuration is the job of the agent that implements the module. So the agent is doing the heavy lifting here, bestie 💪
3. Second Dimension: YANG Module Origin Types 🌈
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 💖 That suggested classification applies to BOTH Network Element YANG Modules and Network Service YANG Modules, so it's not just one side of the house 👯
It's totally 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 🫶 Figure 2 shows you how the three types of modules relate to each other:
+--------------+
| User |
| Extensions |
+------+-------+
Augments
+------+-------+ +--------------+ +--------------+
| Vendor | | User | | User |
| Extensions | | Extensions | | Extensions |
+------+-------+ +------+-------+ +------+-------+
Augments Augments Augments
+------+-----------------+-------+ +------+-------+ +--------------+
| Standard | | Vendor | | User |
| Modules | | Modules | | Modules |
+--------------------------------+ +--------------+ +--------------+
Figure 2: YANG Module Origin Types3.1. Standard YANG Modules 📘
Standard YANG Modules are published by SDOs (standards development organizations) 🏛️ Most SDOs make their specs through a formal process, so the end result is a standard that's actually useful for their constituencies.
The lifecycles of these modules are driven by the editing cycles of the specifications, and they aren't 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 🏭
Vendor-Specific YANG Modules are developed by organizations that want to support a specific set of implementations under their own control. Think vendors of virtual or physical equipment, industry consortia, and open-source projects 🌻 The intent of these modules ranges all the way from openly published YANG modules that may eventually be contributed back to or adopted by an SDO, to strictly internal YANG modules that are NOT meant 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's worth noting there's an increasing amount of interaction between open-source projects and SDOs in the networking industry 🤝 That includes open-source projects implementing published standards, as well as open-source projects contributing content to SDO processes. Main character crossover energy 🎭
Vendors also develop vendor-specific extensions to standard modules, using YANG constructs for extending the data definitions of previously published modules. They do this with the 'augment' statement, which lets locally defined data trees get added into locations in externally defined data trees 🧵 Vendors use this to extend standard modules so they cover the full scope of features in their implementations, which is commonly broader than what the standard module covers. It's giving "we're doing more than the standard, obviously" 💅
3.3. User-Specific YANG Modules and Extensions 🦄
User-Specific YANG Modules are developed by organizations that operate YANG-based infrastructure, including devices and orchestrators. Examples are network administrators in enterprises or at service providers 🏢 The intent of these modules is to express the specific needs of a certain implementation, above and beyond what vendors provide ✨
This module type obviously needs the infrastructure to support the introduction of user-provided modules and extensions 🧰 That includes 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 🔒
This document doesn't have any Security Considerations. Nothing to see here, bestie 🙈
5. IANA Considerations 🧾
This document does not require any IANA actions. 💅
6. References 📚
6.1. Normative References
[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,
<http://www.rfc-editor.org/info/rfc6241>.
[RFC7223] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 7223, DOI 10.17487/RFC7223, May 2014,
<http://www.rfc-editor.org/info/rfc7223>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<http://www.rfc-editor.org/info/rfc7950>.
[RFC8049] Litkowski, S., Tomotaki, L., and K. Ogaki, "YANG Data
Model for L3VPN Service Delivery", RFC 8049,
DOI 10.17487/RFC8049, February 2017,
<http://www.rfc-editor.org/info/rfc8049>.6.2. Informative References
[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.
[IESG-Statement]
"Writable MIB Module IESG Statement",
<https://www.ietf.org/iesg/statement/
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.Acknowledgements 🫶
Huge thanks to David Ball and Jonathan Hansford for the feedback and suggestions 💖
Authors' Addresses 💌
Dean Bogdanovic
Volta Networks, Inc.
Email: dean@voltanet.io
Benoit Claise
Cisco Systems, Inc.
De Kleetlaan 6a b1
1831 Diegem
Belgium
Phone: +32 2 704 5622
Email: bclaise@cisco.com
Carl Moberg
Cisco Systems, Inc.
Email: camoberg@cisco.com📦 where this page comes from
- ietf: rfc8199 2017-07
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms