--- 1/draft-ietf-netmod-yang-model-classification-07.txt 2017-06-13 10:13:12.039198430 -0700 +++ 2/draft-ietf-netmod-yang-model-classification-08.txt 2017-06-13 10:13:12.063198999 -0700 @@ -1,20 +1,20 @@ NETMOD D. Bogdanovic Internet-Draft Volta Networks, Inc. Intended status: Informational B. Claise -Expires: November 17, 2017 C. Moberg +Expires: December 15, 2017 C. Moberg Cisco Systems, Inc. - May 16, 2017 + June 13, 2017 YANG Module Classification - draft-ietf-netmod-yang-model-classification-07 + draft-ietf-netmod-yang-model-classification-08 Abstract 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. @@ -35,21 +35,21 @@ 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 November 17, 2017. + This Internet-Draft will expire on December 15, 2017. 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 @@ -59,21 +59,21 @@ 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: Module Types . . . . . . . . . . . . . . . 7 + 3. Second Dimension: 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. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 7. Change log [RFC Editor: Please remove] . . . . . . . . . . . 9 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 8.1. Normative References . . . . . . . . . . . . . . . . . . 10 8.2. Informative References . . . . . . . . . . . . . . . . . 10 @@ -97,58 +97,59 @@ 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 The type of module based on the nature and intent of the content + o 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 module types have created substantial discussion during - the development of this document including those concerned with + A number of modules have created substantial discussion during the + development of this document: for examples, modules concerned with topologies. Topology modules are useful both on the Network Element level (e.g. link-state database content) as well as 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 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 + 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, an 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 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 support in their products. See Figure 1. + YANG modules they support in their products. 1.1. Terminology [RFC7950] specifies: o data model: A data model describes how data is represented and accessed. o module: A YANG module defines hierarchies of schema nodes. With its definitions and the definitions it imports or includes from @@ -201,36 +202,36 @@ | | | | | | | | | 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 Layers + 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 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 YANG modules are best developed by + 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. 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 module does not expose the detailed configuration parameters of all participating network elements and features, but describes an @@ -253,39 +254,39 @@ 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. - the definition of a 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. + the definition of a 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 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. + User-Network Interface (UNI) 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. - An example of a network service module is in [RFC8049]. It provides - an abstract model for Layer 3 IP VPN service configuration. This - module includes e.g. the concept of a 'site-network-access' to + 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 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 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. 2.2. Network Element YANG Modules @@ -295,65 +296,65 @@ 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 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. -3. Second Dimension: Module Types +3. Second Dimension: Module Origin Types - This document suggests classifying YANG module types as standard YANG - modules, vendor-specific YANG modules and extensions, or user- - specific YANG modules and extensions + 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. 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 types of modules. + mix of all three module origin types. Figure 2 illustrates the relationship between the three types of modules. +--------------+ | User | | Extensions | +------+-------+ Augments +------+-------+ +--------------+ +--------------+ | Vendor | | User | | User | | Extensions | | Extensions | | Extensions | +------+-------+ +------+-------+ +------+-------+ Augments Augments Augments +------+-----------------+-------+ +------+-------+ +--------------+ | Standard | | Vendor | | User | | Modules | | Modules | | Modules | +--------------------------------+ +--------------+ +--------------+ - Figure 2: YANG Module Types + Figure 2: YANG Module Origin Types 3.1. Standard YANG Modules Standard YANG Modules are published by standards development organizations (SDOs). Most SDOs create specifications according to a formal process in order to produce a standard that is useful for their constituencies. 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. + 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 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 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.