--- 1/draft-ietf-netmod-yang-model-classification-01.txt 2016-06-22 06:15:52.571919566 -0700 +++ 2/draft-ietf-netmod-yang-model-classification-02.txt 2016-06-22 06:15:52.599920264 -0700 @@ -1,380 +1,492 @@ NETMOD D. Bogdanovic -Internet-Draft +Internet-Draft Volta Networks, Inc. Intended status: Informational B. Claise -Expires: October 6, 2016 C. Moberg +Expires: December 24, 2016 C. Moberg Cisco Systems, Inc. - April 4, 2016 + June 22, 2016 - YANG Model Classification - draft-ietf-netmod-yang-model-classification-01 + YANG Module Classification + draft-ietf-netmod-yang-model-classification-02 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 (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, + YANG to develop and publish YANG modules 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. + types of YANG modules. - A consistent terminology would help with the categorization of - models, assist in the analysis the YANG data modeling efforts in the + A consistent terminology would help with the categorization of YANG + modules, 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. + support consistent classification of YANG modules. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on October 6, 2016. + This Internet-Draft will expire on December 24, 2016. Copyright Notice 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 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 + 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 + 2. First Dimension: YANG Data Model Abstraction Layers . . . . . 4 + 2.1. Network Service YANG Modules . . . . . . . . . . . . . . 6 + 2.2. Network Element YANG Modules . . . . . . . . . . . . . . 7 + 3. Second Dimension: Module 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. Adding The Classification Type to YANG Module Catalogs . . . 9 + 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 + 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 + 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 + 8. Change log [RFC Editor: Please remove] . . . . . . . . . . . 10 + 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 + 9.1. Normative References . . . . . . . . . . . . . . . . . . 11 + 9.2. Informative References . . . . . . . . . . . . . . . . . 11 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 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]. + encouraging IETF working groups to use the YANG [RFC6020] + [I-D.ietf-netmod-rfc6020bis] and 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, 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, - vendor-specific models and models provided by end-users. + 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 models in two + taxonomy for consistent classification of YANG modules in two dimensions: - o The layering of models based on their abstraction levels + o The layering of modules based on their abstraction levels - o The type of model based on the nature and intent of the content + o The type of module based on the nature and intent of the content - The two categories are covered in the next two sections. + The intent of this document is to provide a taxonomy to simplify + human communication around YANG modules. The authors acknowledge + that the classification boundaries are at times blurry, but believe + that this document should provide a robust starting point as the YANG + community gain further experience with designing and deploying + modules. To be more explicit, the authors believe that the + classification criteria will change over time. -2. First Dimension: YANG Model Abstraction Layers + An example of a type of module that have created substantial + discussion during the development of this document is topologies. + Topology models are useful both on the Network Element level (e.g. + link-state database content) as well as in 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. - 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. + This document should provide benefits to multiple audiences: + + o First, a common taxonomy helps with the different standards + development organizations and industry consortia discussions, + whose goals are determined in their respective areas of work. + + o Second, operators might look at the YANG module classification + type 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, an + L2VPN YANG module might be a Network Service YANG module, ready to + be used by the operators. Alternatively, it might be a Network + Element YANG module that contains the L2VPN data definitions + required to be configured on a single device. + + o And thirdly, this taxonomy would help equipment vendors (whether + physical or virtual), controller vendors, orchestrator vendors to + explain to their customers the relationship between the different + YANG modules they propose in their products. See Figure 1. + +1.1. Terminology + + RFC6020bis [I-D.ietf-netmod-rfc6020bis] specifies: + + o data model: A data model describes how data is represented and + accessed. + + o module: A YANG module defines a hierarchy of nodes that can be + used for NETCONF-based operations. With its definitions and the + definitions it imports or includes from elsewhere, a module is + self-contained and "compilable". + +2. First Dimension: YANG Data Model Abstraction Layers + + Model 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 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 appeal to different + practices around the development of YANG modules 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 appeal to different groups. For layering purposes, this document suggests the classification of - data models into two distinct abstraction layers: + YANG modules into two distinct abstraction layers: - o Network Element YANG Models describe the configuration, state data - and operations of specific device-centric technologies or features + o Network Element YANG Modules describe the configuration, state + data and operations of specific device-centric technologies or + features - o Network Service YANG Models describe the configuration, state data - and operations of an abstract representation of a service + o Network Service YANG Modules 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 allows for reusability of - existing lower layer models by higher level models while limiting + 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 model developers, per-layer modeling allows for separation of + 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 models for e.g. routing or switching protocols + network element YANG modules 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. + On the other hand, network service YANG modules are best developed by + network operators 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 | | (OSS/BSS) | +--------------------------+ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Network Service YANG data models + Network Service YANG Modules +------------+ +-------------+ +-------------+ | | | | | | - | - VPWS | | - VPLS | | L3VPN | - | - L2VPN | | - L2VPN | | | + | - L2VPN | | - L2VPN | | L3VPN | + | - VPWS | | - VPLS | | | | | | | | | +------------+ +-------------+ +-------------+ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Network Element YANG data models + Network Element YANG Modules +------------+ +------------+ +-------------+ +------------+ | | | | | | | | - | MPLS | | BGP | | IPv4 & IPv6 | | Ethernet | + | MPLS | | BGP | | IPv4 / IPv6 | | Ethernet | | | | | | | | | +------------+ +------------+ +-------------+ +------------+ - Fig. 1 YANG Model Layers + L2VPN: Layer 2 Virtual Private Network + L3VPN: Layer 3 Virtual Private Network + VPWS: Virtual Private Wire Service + VPLS: Virtual Private LAN Service -2.1. Network Service YANG Data Models + Figure 1: YANG Module Layers - Network Service YANG Data Models describe the characteristics of a +2.1. Network Service YANG Modules + + Network Service YANG Modules describe the characteristics of a service, as agreed upon with consumers of that service. That is, a service model 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 data models of - the participating network elements. The service-to-element - decomposition is a separate process with details depending on how the - network operator chooses to realize the service. For the purpose of - this document we will use the term "orchestrator" to describe a - system implementing such a process. + into instance data according to the Network Element Modules of the + participating network elements. The service-to-element decomposition + is a separate process with details depending on how the network + operator chooses to realize the service. For the purpose of this + document we will use the term "orchestrator" to describe a 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. + As an example, the Network Service YANG Module included in + [YANG-Data-Model-for-L3VPN-service-delivery] provides an abstract + model for Layer 3 IP VPN service configuration. This model includes + e.g. the concept of a 'site-network-access' to represent bearer and + connection parameters. An orchestrator receives operations on + service instances according to the service model and decomposes the + data into specific Network Element Modules to configure the + participating network elements to perform the intent of 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 models define services models to be consumed by - external systems. These models are commonly designed, developed and + Network Service YANG Modules define services models to be consumed by + external systems. 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 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. + 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 speed at the + expense of reusability. The component-based approach captures device-centric features (e.g. the definition of a VRF, routing protocols, or packet filtering) in a vendor-independent manner. The components are designed for reuse - across many services. The set of components required for a specific - service is then composed into the higher-level service. The + 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 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 e.g. UNI-interface definitions independent of the underlying transport network (e.g. MEF UNI interface or MPLS interface). The monolithic approach would assume a specific set of transport technologies and interface definitions. -2.2. Network Element YANG Data models +2.2. Network Element YANG Modules - Network Element YANG Data Models describe the configuration, state - data and operations of a network device as defined by the vendor of - that device. The models are commonly structured around features of - the device, e.g. interface configuration [RFC7223], OSPF - configuration [I-D.ietf-ospf-yang], and firewall rules definitions - [I-D.ietf-netmod-acl-model]. The model provides a coherent data - model representation of what is commonly a very mixed software - environment consisting of the operating system and applications - running on the device. + Network Element YANG Modules describe the configuration, state data + and operations 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 + [I-D.ietf-ospf-yang], and firewall rules definitions + [I-D.ietf-netmod-acl-model]. - 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. + The module provides a coherent data model representation of what is + commonly a very mixed 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 management + framework that implements the YANG module. -3. Second Dimension: Model Types +3. Second Dimension: Module Types - This document suggests classifying YANG model types as either - standard YANG models, vendor-specific YANG models and extensions, and - user-specific YANG models and extensions + This document suggests classifying YANG module types as either + standard YANG modules, vendor-specific YANG modules and extensions, + and user-specific YANG modules and extensions The suggested classification applies to both Network Element YANG - Data Models and Network Service YANG Data Models. + Modules and Network Service YANG Modules. 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. + Service and Network Element YANG Modules will include a mix of all + three types of modules. -3.1. Standard YANG Models + Figure 2 illustrates the relationship between the three types of + modules. - Standard YANG models are published by standards-defining + +--------------+ + | User | + | Extensions | + +------+-------+ + Augments + +------+-------+ +--------------+ +--------------+ + | Vendor | | User | | User | + | Extensions | | Extensions | | Extensions | + +------+-------+ +------+-------+ +------+-------+ + Augments Augments Augments + +------+-----------------+-------+ +------+-------+ +--------------+ + | Standard | | Vendor | | User | + | Models | | Models | | Models | + +--------------------------------+ +--------------+ +--------------+ + + Figure 2: YANG Module Types + +3.1. Standard YANG Modules + + Standard YANG Modules 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 is driven by the editing cycle of the + The lifecycle of these modules 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. + (Institute of Electrical and Electronics Engineers) and the MEF. -3.2. Vendor-specific YANG Models and Extensions +3.2. Vendor-specific YANG Modules and Extensions - Vendor-specific YANG models are developed by organizations with the + Vendor-specific YANG modules 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. + that organization. For example vendors of virtual or physical + equipment, industry consortia, and opensource projects. The intent + of these modules range 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 lifecycle of these models are generally aligned with the release + The lifecycle of these modules 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. - Vendors also develop Vendor-specific Extensions to standard models + Vendors also develop Vendor-specific Extensions to standard modules using YANG constructs for extending data definitions of previously - published models. This is done using the 'augment' statement that + published modules. 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. + Vendors use this to extend standard modules to cover the full scope + of features in implementations, which commonly is broader than what + is covered by the standard module. -3.3. User-specific YANG Models and Extensions +3.3. User-specific YANG Modules 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. + User-specific YANG modules are developed by organizations that + operate YANG-based infrastructure including devices and + orchestrators. For example, network administrators in enterprises, + or operators 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 model type obviously requires the infrastructure to support the - introduction of user-provided models and extensions. This would + This module type obviously requires the infrastructure to support the + introduction of user-provided modules and extensions. This would include ability to describe the service-to-network decomposition in - orchestrators and the model to configuration decomposition in + orchestrators and the module to configuration decomposition in devices. - The lifecycle of these models are generally aligned with the change + The lifecycle of these modules are generally aligned with the change cadence of the infrastructure. -3.4. Adding Models to Catalogs +4. Adding The Classification Type to YANG Module 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. + The suggested classification in this document would be an useful + information in a catalog of YANG modules. Such catalog allows for + easy lookup and reusability of YANG modules. Practically, the YANG + module classification type would be an additional leaf to YANG module + specified in [I-D.openconfig-netmod-model-catalog]: -3.5. Security Considerations + leaf module-class{ + type enum { + service + device + notApplicable + } + description + "Categorization of the YANG module based on + draft-ietf-netmod-yang-model-classification."; + } - At this stage, authors of the draft didn't look into security - considerations. + Note: this leaf should actually be moved to + [I-D.openconfig-netmod-model-catalog]. Note2: since a YANG module + can belong to both service and device, the ENUM is not appropriate. + A extensible list of module type is more appropriate. -3.6. IANA Considerations + Indeed, without inspecting the YANG module itself, it's difficult to + determine whether its type is a network service or a network element. + The YANG module name might provide some useful information but is not + a definite answer. - This document requests no action by IANA. +5. Security Considerations -3.7. Acknowledgements + This document doesn't have any Security Considerations". + +6. IANA Considerations + + This document has no IANA actions. + +7. Acknowledgements Thanks to David Ball and David Hansford for feedback and suggestions. -3.8. Change log [RFC Editor: Please remove] +8. Change log [RFC Editor: Please remove] version 00: Renamed and small fixes based on WG feedback. - version 01: Language fixes, collapsing of vendor models and - extensions, and the introduction of user models and extensions. + version 01: Language fixes, collapsing of vendor data models and + extensions, and the introduction of user data models and extensions. - version 02: Added two sections, Model Catalog and Benefits of model - classification. + version 02: Updated the YANG Module Catalog section, terminology + alignment (YANG data model versus YANG module), epxlain better the + distinction between the Network Element and Service YANG data models + even if sometimes there are grey areas, editorial pass. Changed the + use of the term 'model' to 'module' to be better aligned with + RFC6020. -4. References +9. References -4.1. Normative References +9.1. 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, . -4.2. Informative References +9.2. Informative References [I-D.ietf-netmod-acl-model] Bogdanovic, D., Koushik, K., Huang, L., and D. Blair, "Network Access Control List (ACL) YANG Data Model", draft-ietf-netmod-acl-model-07 (work in progress), March 2016. + [I-D.ietf-netmod-rfc6020bis] + Bjorklund, M., "The YANG 1.1 Data Modeling Language", + draft-ietf-netmod-rfc6020bis-14 (work in progress), June + 2016. + [I-D.ietf-ospf-yang] - Yeung, D., Qu, Y., Zhang, J., Bogdanovic, D., and K. + Yeung, D., Qu, Y., Zhang, Z., Bogdanovic, D., and K. Koushik, "Yang Data Model for OSPF Protocol", draft-ietf- 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 @@ -390,22 +502,27 @@ . [YANG-Data-Model-for-L3VPN-service-delivery] "YANG Data Model for L3VPN service delivery", . Authors' Addresses Dean Bogdanovic + Volta Networks, Inc. - Email: ivandean@gmail.com + 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