--- 1/draft-ietf-netmod-yang-model-classification-00.txt 2016-04-04 05:19:01.468981924 -0700 +++ 2/draft-ietf-netmod-yang-model-classification-01.txt 2016-04-04 05:19:02.341003585 -0700 @@ -1,30 +1,31 @@ NETMOD D. Bogdanovic Internet-Draft Intended status: Informational B. Claise -Expires: June 9, 2016 C. Moberg +Expires: October 6, 2016 C. Moberg Cisco Systems, Inc. - December 7, 2015 + April 4, 2016 YANG Model Classification - draft-ietf-netmod-yang-model-classification-00 + draft-ietf-netmod-yang-model-classification-01 Abstract The YANG [RFC6020] data modeling language is currently being considered for a wide variety of applications throughout the - networking industry at large. Many standards defining organizations, - open source software projects, and vendors are using YANG to develop - and publish models of configuration, state data and operations for a - wide variety of applications. At the same time, there is currently - no well-known terminology to categorize various types of YANG models. + networking industry at large. Many standards-defining organizations + (SDOs), open source software projects, vendors and users are using + YANG to develop and publish models of configuration, state data and + operations for a wide variety of applications. At the same time, + there is currently no well-known terminology to categorize various + types of YANG models. A consistent terminology would help with the categorization of models, assist in the analysis 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 models. Status of This Memo @@ -35,119 +36,121 @@ 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 June 9, 2016. + This Internet-Draft will expire on October 6, 2016. Copyright Notice - Copyright (c) 2015 IETF Trust and the persons identified as the + Copyright (c) 2016 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 2. First Dimension: YANG Model Abstraction Layers . . . . . . . 3 2.1. Network Service YANG Data Models . . . . . . . . . . . . 4 2.2. Network Element YANG Data models . . . . . . . . . . . . 5 3. Second Dimension: Model Types . . . . . . . . . . . . . . . . 6 3.1. Standard YANG Models . . . . . . . . . . . . . . . . . . 6 - 3.2. Vendor-specific YANG Models . . . . . . . . . . . . . . . 6 - 3.3. Vendor-specific Extensions . . . . . . . . . . . . . . . 7 - 4. Security Considerations . . . . . . . . . . . . . . . . . . . 7 - 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 - 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 - 7. Change log [RFC Editor: Please remove] . . . . . . . . . . . 7 - 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 - 8.1. Normative References . . . . . . . . . . . . . . . . . . 8 - 8.2. Informative References . . . . . . . . . . . . . . . . . 8 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 + 3.2. Vendor-specific YANG Models and Extensions . . . . . . . 6 + 3.3. User-specific YANG Models and Extensions . . . . . . . . 7 + 3.4. Adding Models to Catalogs . . . . . . . . . . . . . . . . 7 + 3.5. Security Considerations . . . . . . . . . . . . . . . . . 8 + 3.6. IANA Considerations . . . . . . . . . . . . . . . . . . . 8 + 3.7. Acknowledgements . . . . . . . . . . . . . . . . . . . . 8 + 3.8. Change log [RFC Editor: Please remove] . . . . . . . . . 8 + 4. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 + 4.1. Normative References . . . . . . . . . . . . . . . . . . 8 + 4.2. Informative References . . . . . . . . . . . . . . . . . 8 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction The Internet Engineering Steering Group (IESG) has been actively encouraging IETF working groups to use the NETCONF [RFC6241] and YANG standards for configuration management purposes, especially in new working group charters [Writable-MIB-Module-IESG-Statement]. YANG is also gaining wide acceptance as the de-facto standard modeling language in the broader industry. This extends beyond the IETF, including many standards development organizations, industry - consortia, ad hoc groups, open source projects and vendors. + 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 models according to abstraction, or how to classify - models along the continuum spanning formal standards publications and - vendor-specific models. + models along the continuum spanning formal standards publications, + vendor-specific models and models provided by end-users. This document presents a set of concepts and terms to form a useful taxonomy for consistent classification of YANG models in two dimensions: o The layering of models based on their abstraction levels o The type of model based on the nature and intent of the content The two categories are covered in the next two sections. 2. First Dimension: YANG Model Abstraction Layers - Model developers have taken two approaches to developing YANG model: + Model developers have taken two approaches to developing YANG models: 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 on, or well-defined best practices around the development of models. For the purpose of this document we assume that both approaches (bottom-up and top-down) will - be used as they both provide benefits that appeals to different + be used as they both provide benefits that appeal to different groups. - For layering purposes, this documents suggests the classification of + For layering purposes, this document suggests the classification of data models into two distinct abstraction layers: o Network Element YANG Models describe the configuration, state data - and operations of a specific device-centric technology or feature. + and operations of specific device-centric technologies or features - o Network Service YANG Models describes the configuration, state - data and operations of an abstract representation of a service + o Network Service YANG Models describe the configuration, state data + and operations of an abstract representation of a service implemented on one or multiple network elements Figure 1 illustrates the application of YANG models at different - layers of abstraction. Layering of models allow for reusability of + layers of abstraction. Layering of models allows for reusability of existing lower layer models by higher level models while limiting duplication of features across layers. For model 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 models for e.g routing or switching protocols - requires teams that include developers with experience from + network element YANG models for e.g. routing or switching protocols + requires teams that include developers with experience of implementing those protocols. On the other hand, network service models are best developed by people experienced in defining network services for consumption by programmers developing e.g. flow-through provisioning systems or self-service portals. +--------------------------+ | Operations and Business | | Support Systems | @@ -190,21 +193,21 @@ system implementing such a process. As an example, the Network Service model included in [YANG-Data-Model-for-L3VPN-service-delivery] provides an abstracted model for Layer 3 IP VPN service configuration. An orchestrator receives operations on service instances according to the service model and decomposes the data into specific Network Element models to configure the participating network elements to perform the intent of the service. - Network Service YANG models defines services models to be consumed by + Network Service YANG models define services models to be consumed by external systems. These models 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 model and does not put focus on reusability of internal data definitions and groupings. The monolithic approach has the advantages of single- purpose development including speed at the expense of reusability. @@ -238,123 +241,147 @@ 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 management framework that implements the YANG model. 3. Second Dimension: Model Types This document suggests classifying YANG model types as either - standard YANG models, vendor-specific YANG models, or vendor-specific - extensions. + standard YANG models, vendor-specific YANG models and extensions, and + user-specific YANG models and extensions The suggested classification applies to both Network Element YANG - Data Models and to Network Service YANG Data Models. + Data Models and Network Service YANG Data Models. It is to be expected that real-world implementations of both Network Service and Network Element models will include a mix of all three types of models. 3.1. Standard YANG Models - Standard YANG models are published by standards defining + Standard YANG models are published by standards-defining organizations (SDOs). While there is no formal definition of what construes an SDO, a common feature is that they publish specifications along specific processes with content that reflects some sort of membership consensus. The specifications are developed for wide use among the membership or for audiences beyond that. - The lifecycle of these models are driven by the editing cycle of the + The lifecycle of these models is driven by the editing cycle of the specification and not tied to a specific implementation. Examples of SDOs in the networking industry are the IETF, the IEEE and the MEF. -3.2. Vendor-specific YANG Models +3.2. Vendor-specific YANG Models and Extensions Vendor-specific YANG models are developed by organizations with the intent to support a specific set of implementations under control of that organization. The intent of these models range from providing openly published YANG models that may eventually be contributed back to, or adopted by an SDO, to strictly internal YANG models not intended for external consumption. The lifecycle of these models are generally aligned with the release cycle 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. -3.3. Vendor-specific Extensions - - Vendors develop Vendor-specific Extensions to standard models using - YANG constructs for extending data definitions of previously + Vendors also develop Vendor-specific Extensions to standard models + using YANG constructs for extending data definitions of previously published models. This is done using the 'augment' statement that allows locally defined data trees to be augmented into locations in externally defined data trees. Vendors use this to extend standard data models to cover the full scope of features in implementations, which commonly is broader than what is covered by the standard model. -4. Security Considerations +3.3. User-specific YANG Models and Extensions + + User-specific YANG models are developed by organizations that operate + YANG-based infrastructure including devices and orchestrators. The + intent of these models is to express the specific needs for a certain + implementation, above and beyond what is provided by vendors. + + This model type obviously requires the infrastructure to support the + introduction of user-provided models and extensions. This would + include ability to describe the service-to-network decomposition in + orchestrators and the model to configuration decomposition in + devices. + + The lifecycle of these models are generally aligned with the change + cadence of the infrastructure. + +3.4. Adding Models to Catalogs + + The suggested classification in this document supports the creation + of catalogs, such as proposed in + [I-D.openconfig-netmod-model-catalog]. Such catalogs allows for easy + lookup and reusability of YANG models. SDO-classified models also + provide an educational resource providing architectural guidelines + for model development, based on a membership reviewn and consensus. + +3.5. Security Considerations At this stage, authors of the draft didn't look into security considerations. -5. IANA Considerations +3.6. IANA Considerations This document requests no action by IANA. -6. Acknowledgements - - Thanks to David Ball for his enlightenments on Metro Ethernet Forum - service aspects. +3.7. Acknowledgements -7. Change log [RFC Editor: Please remove] + Thanks to David Ball and David Hansford for feedback and suggestions. - version 1: restructure the document, add the two dimensions, add the - interaction with the different SDOs and opensource projects, add the - definitions. +3.8. Change log [RFC Editor: Please remove] - version 2: added definitions for config and service models clarified - second dimension of model classification. fixed typos + version 00: Renamed and small fixes based on WG feedback. - version 3: restructure and partial rewrite of section 2. + version 01: Language fixes, collapsing of vendor models and + extensions, and the introduction of user models and extensions. - version 4: Language fixes + version 02: Added two sections, Model Catalog and Benefits of model + classification. -8. References +4. References -8.1. Normative References +4.1. Normative References [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, . -8.2. Informative References +4.2. Informative References [I-D.ietf-netmod-acl-model] - Bogdanovic, D., Sreenivasa, K., Huang, L., and D. Blair, + Bogdanovic, D., Koushik, K., Huang, L., and D. Blair, "Network Access Control List (ACL) YANG Data Model", - draft-ietf-netmod-acl-model-05 (work in progress), October - 2015. + draft-ietf-netmod-acl-model-07 (work in progress), March + 2016. [I-D.ietf-ospf-yang] Yeung, D., Qu, Y., Zhang, J., Bogdanovic, D., and K. Koushik, "Yang Data Model for OSPF Protocol", draft-ietf- - ospf-yang-03 (work in progress), October 2015. + ospf-yang-04 (work in progress), March 2016. + + [I-D.openconfig-netmod-model-catalog] + D'Souza, K., Shaikh, A., and R. Shakir, "Catalog and + registry for YANG models", draft-openconfig-netmod-model- + catalog-00 (work in progress), October 2015. [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, . [RFC7223] Bjorklund, M., "A YANG Data Model for Interface Management", RFC 7223, DOI 10.17487/RFC7223, May 2014, .