draft-ietf-netmod-yang-model-classification-01.txt		draft-ietf-netmod-yang-model-classification-02.txt
	NETMOD D. Bogdanovic		NETMOD D. Bogdanovic
	Internet-Draft		Internet-Draft Volta Networks, Inc.
	Intended status: Informational B. Claise		Intended status: Informational B. Claise
	Expires: October 6, 2016 C. Moberg		Expires: December 24, 2016 C. Moberg
	Cisco Systems, Inc.		Cisco Systems, Inc.
	April 4, 2016		June 22, 2016
	YANG Model Classification		YANG Module Classification
	draft-ietf-netmod-yang-model-classification-01		draft-ietf-netmod-yang-model-classification-02
	Abstract		Abstract
	The YANG [RFC6020] data modeling language is currently being		The YANG [RFC6020] data modeling language is currently being
	considered for a wide variety of applications throughout the		considered for a wide variety of applications throughout the
	networking industry at large. Many standards-defining organizations		networking industry at large. Many standards-defining organizations
	(SDOs), open source software projects, vendors and users are using		(SDOs), open source software projects, vendors and users are using
	YANG to develop and publish models of configuration, state data and		YANG to develop and publish YANG modules of configuration, state data
	operations for a wide variety of applications. At the same time,		and operations for a wide variety of applications. At the same time,
	there is currently no well-known terminology to categorize various		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		A consistent terminology would help with the categorization of YANG
	models, assist in the analysis the YANG data modeling efforts in the		modules, assist in the analysis the YANG data modeling efforts in the
	IETF and other organizations, and bring clarity to the YANG-related		IETF and other organizations, and bring clarity to the YANG-related
	discussions between the different groups.		discussions between the different groups.
	This document describes a set of concepts and associated terms to		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		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		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 Notice
	Copyright (c) 2016 IETF Trust and the persons identified as the		Copyright (c) 2016 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. First Dimension: YANG Model Abstraction Layers . . . . . . . 3		1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
	2.1. Network Service YANG Data Models . . . . . . . . . . . . 4		2. First Dimension: YANG Data Model Abstraction Layers . . . . . 4
	2.2. Network Element YANG Data models . . . . . . . . . . . . 5		2.1. Network Service YANG Modules . . . . . . . . . . . . . . 6
	3. Second Dimension: Model Types . . . . . . . . . . . . . . . . 6		2.2. Network Element YANG Modules . . . . . . . . . . . . . . 7
	3.1. Standard YANG Models . . . . . . . . . . . . . . . . . . 6		3. Second Dimension: Module Types . . . . . . . . . . . . . . . 7
	3.2. Vendor-specific YANG Models and Extensions . . . . . . . 6		3.1. Standard YANG Modules . . . . . . . . . . . . . . . . . . 8
	3.3. User-specific YANG Models and Extensions . . . . . . . . 7		3.2. Vendor-specific YANG Modules and Extensions . . . . . . . 8
	3.4. Adding Models to Catalogs . . . . . . . . . . . . . . . . 7		3.3. User-specific YANG Modules and Extensions . . . . . . . . 9
	3.5. Security Considerations . . . . . . . . . . . . . . . . . 8		4. Adding The Classification Type to YANG Module Catalogs . . . 9
	3.6. IANA Considerations . . . . . . . . . . . . . . . . . . . 8		5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
	3.7. Acknowledgements . . . . . . . . . . . . . . . . . . . . 8		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
	3.8. Change log [RFC Editor: Please remove] . . . . . . . . . 8		7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
	4. References . . . . . . . . . . . . . . . . . . . . . . . . . 8		8. Change log [RFC Editor: Please remove] . . . . . . . . . . . 10
	4.1. Normative References . . . . . . . . . . . . . . . . . . 8		9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
	4.2. Informative References . . . . . . . . . . . . . . . . . 8		9.1. Normative References . . . . . . . . . . . . . . . . . . 11
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9		9.2. Informative References . . . . . . . . . . . . . . . . . 11
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
	1. Introduction		1. Introduction
	The Internet Engineering Steering Group (IESG) has been actively		The Internet Engineering Steering Group (IESG) has been actively
	encouraging IETF working groups to use the NETCONF [RFC6241] and YANG		encouraging IETF working groups to use the YANG [RFC6020]
	standards for configuration management purposes, especially in new		[I-D.ietf-netmod-rfc6020bis] and NETCONF [RFC6241] and YANG standards
	working group charters [Writable-MIB-Module-IESG-Statement].		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		YANG is also gaining wide acceptance as the de-facto standard
	modeling language in the broader industry. This extends beyond the		modeling language in the broader industry. This extends beyond the
	IETF, including many standards development organizations, industry		IETF, including many standards development organizations, industry
	consortia, ad hoc groups, open source projects, vendors, and end-		consortia, ad hoc groups, open source projects, vendors, and end-
	users.		users.
	There are currently no clear guidelines on how to classify the		There are currently no clear guidelines on how to classify the
	layering of YANG models according to abstraction, or how to classify		layering of YANG modules according to abstraction, or how to classify
	models along the continuum spanning formal standards publications,		modules along the continuum spanning formal standards publications,
	vendor-specific models and models provided by end-users.		vendor-specific modules and modules provided by end-users.
	This document presents a set of concepts and terms to form a useful		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:		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:		This document should provide benefits to multiple audiences:
	top-down and bottom-up. The top-down approach starts with high level
	abstractions modeling business or customer requirements and maps them		o First, a common taxonomy helps with the different standards
	to specific networking technologies. The bottom-up approach starts		development organizations and industry consortia discussions,
	with fundamental networking technologies and maps them into more		whose goals are determined in their respective areas of work.
	abstract constructs.
			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		There are currently no specific requirements on, or well-defined best
	practices around the development of models. For the purpose of this		practices around the development of YANG modules For the purpose of
	document we assume that both approaches (bottom-up and top-down) will		this document we assume that both approaches (bottom-up and top-down)
	be used as they both provide benefits that appeal to different		will be used as they both provide benefits that appeal to different
	groups.		groups.
	For layering purposes, this document suggests the classification of		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		o Network Element YANG Modules describe the configuration, state
	and operations of specific device-centric technologies or features		data and operations of specific device-centric technologies or
			features
	o Network Service YANG Models describe the configuration, state data		o Network Service YANG Modules describe the configuration, state
	and operations of an abstract representation of a service		data and operations of an abstract representation of a service
	implemented on one or multiple network elements		implemented on one or multiple network elements
	Figure 1 illustrates the application of YANG models at different		Figure 1 illustrates the application of YANG modules at different
	layers of abstraction. Layering of models allows for reusability of		layers of abstraction. Layering of modules allows for reusability of
	existing lower layer models by higher level models while limiting		existing lower layer modules by higher level modules while limiting
	duplication of features across layers.		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.		concern across editing teams focusing on specific areas.
	As an example, experience from the IETF shows that creating useful		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		requires teams that include developers with experience of
	implementing those protocols.		implementing those protocols.
	On the other hand, network service models are best developed by		On the other hand, network service YANG modules are best developed by
	people experienced in defining network services for consumption by		network operators experienced in defining network services for
	programmers developing e.g. flow-through provisioning systems or		consumption by programmers developing e.g. flow-through provisioning
	self-service portals.		systems or self-service portals.
	+--------------------------+		+--------------------------+
	| Operations and Business |		| Operations and Business |
	| Support Systems |		| Support Systems |
	| (OSS/BSS) |		| (OSS/BSS) |
	+--------------------------+		+--------------------------+
	- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -		- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
	Network Service YANG data models		Network Service YANG Modules
	+------------+ +-------------+ +-------------+		+------------+ +-------------+ +-------------+
	| | | | | |		| | | | | |
	| - VPWS | | - VPLS | | L3VPN |		| - L2VPN | | - L2VPN | | L3VPN |
	| - L2VPN | | - L2VPN | | |		| - 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, as agreed upon with consumers of that service. That is, a
	service model does not expose the detailed configuration parameters		service model does not expose the detailed configuration parameters
	of all participating network elements and features, but describes an		of all participating network elements and features, but describes an
	abstract model that allows instances of the service to be decomposed		abstract model that allows instances of the service to be decomposed
	into instance data according to the Network Element data models of		into instance data according to the Network Element Modules of the
	the participating network elements. The service-to-element		participating network elements. The service-to-element decomposition
	decomposition is a separate process with details depending on how the		is a separate process with details depending on how the network
	network operator chooses to realize the service. For the purpose of		operator chooses to realize the service. For the purpose of this
	this document we will use the term "orchestrator" to describe a		document we will use the term "orchestrator" to describe a system
	system implementing such a process.		implementing such a process.
	As an example, the Network Service model included in		As an example, the Network Service YANG Module included in
	[YANG-Data-Model-for-L3VPN-service-delivery] provides an abstracted		[YANG-Data-Model-for-L3VPN-service-delivery] provides an abstract
	model for Layer 3 IP VPN service configuration. An orchestrator		model for Layer 3 IP VPN service configuration. This model includes
	receives operations on service instances according to the service		e.g. the concept of a 'site-network-access' to represent bearer and
	model and decomposes the data into specific Network Element models to		connection parameters. An orchestrator receives operations on
	configure the participating network elements to perform the intent of		service instances according to the service model and decomposes the
	the service.		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		Network Service YANG Modules define services models to be consumed by
	external systems. These models are commonly designed, developed and		external systems. These modules are commonly designed, developed and
	deployed by network infrastructure teams.		deployed by network infrastructure teams.
	YANG allows for different design patterns to describe network		YANG allows for different design patterns to describe network
	services, ranging from monolithic to component-based approaches.		services, ranging from monolithic to component-based approaches.
	The monolithic approach captures the entire service in a single model		The monolithic approach captures the entire service in a single
	and does not put focus on reusability of internal data definitions		module and does not put focus on reusability of internal data
	and groupings. The monolithic approach has the advantages of single-		definitions and groupings. The monolithic approach has the
	purpose development including speed at the expense of reusability.		advantages of single-purpose development including speed at the
			expense of reusability.
	The component-based approach captures device-centric features (e.g.		The component-based approach captures device-centric features (e.g.
	the definition of a VRF, routing protocols, or packet filtering) in a		the definition of a VRF, routing protocols, or packet filtering) in a
	vendor-independent manner. The components are designed for reuse		vendor-independent manner. The components are designed for reuse
	across many services. The set of components required for a specific		across many service modules. The set of components required for a
	service is then composed into the higher-level service. The		specific service is then composed into the higher-level service. The
	component-based approach has the advantages of modular development		component-based approach has the advantages of modular development
	including a higher degree of reusability at the expense of initial		including a higher degree of reusability at the expense of initial
	speed.		speed.
	As an example, an L2VPN service can be built on many different types		As an example, an L2VPN service can be built on many different types
	of transport network technologies, including e.g. MPLS or carrier		of transport network technologies, including e.g. MPLS or carrier
	ethernet. A component-based approach would allow for reuse of e.g.		ethernet. A component-based approach would allow for reuse of e.g.
	UNI-interface definitions independent of the underlying transport		UNI-interface definitions independent of the underlying transport
	network (e.g. MEF UNI interface or MPLS interface). The monolithic		network (e.g. MEF UNI interface or MPLS interface). The monolithic
	approach would assume a specific set of transport technologies and		approach would assume a specific set of transport technologies and
	interface definitions.		interface definitions.
	2.2. Network Element YANG Data models		2.2. Network Element YANG Modules
	Network Element YANG Data Models describe the configuration, state		Network Element YANG Modules describe the configuration, state data
	data and operations of a network device as defined by the vendor of		and operations of a network device as defined by the vendor of that
	that device. The models are commonly structured around features of		device. The modules are commonly structured around features of the
	the device, e.g. interface configuration [RFC7223], OSPF		device, e.g. interface configuration [RFC7223], OSPF configuration
	configuration [I-D.ietf-ospf-yang], and firewall rules definitions		[I-D.ietf-ospf-yang], and firewall rules definitions
	[I-D.ietf-netmod-acl-model]. The model provides a coherent data		[I-D.ietf-netmod-acl-model].
	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		The module provides a coherent data model representation of what is
	operating system and application configuration is the task of the		commonly a very mixed software environment consisting of the
	management framework that implements the YANG model.		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		This document suggests classifying YANG module types as either
	standard YANG models, vendor-specific YANG models and extensions, and		standard YANG modules, vendor-specific YANG modules and extensions,
	user-specific YANG models and extensions		and user-specific YANG modules and extensions
	The suggested classification applies to both Network Element YANG		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		It is to be expected that real-world implementations of both Network
	Service and Network Element models will include a mix of all three		Service and Network Element YANG Modules will include a mix of all
	types of models.		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		organizations (SDOs). While there is no formal definition of what
	construes an SDO, a common feature is that they publish		construes an SDO, a common feature is that they publish
	specifications along specific processes with content that reflects		specifications along specific processes with content that reflects
	some sort of membership consensus. The specifications are developed		some sort of membership consensus. The specifications are developed
	for wide use among the membership or for audiences beyond that.		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.		specification and not tied to a specific implementation.
	Examples of SDOs in the networking industry are the IETF, the IEEE		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		intent to support a specific set of implementations under control of
	that organization. The intent of these models range from providing		that organization. For example vendors of virtual or physical
	openly published YANG models that may eventually be contributed back		equipment, industry consortia, and opensource projects. The intent
	to, or adopted by an SDO, to strictly internal YANG models not		of these modules range from providing openly published YANG modules
	intended for external consumption.		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.		cycle of the product or open source software project deliverables.
	It is worth noting that there is an increasing amount of interaction		It is worth noting that there is an increasing amount of interaction
	between open source projects and SDOs in the networking industry.		between open source projects and SDOs in the networking industry.
	This includes open source projects implementing published standards		This includes open source projects implementing published standards
	as well as open source projects contributing content to SDO		as well as open source projects contributing content to SDO
	processes.		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		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		allows locally defined data trees to be augmented into locations in
	externally defined data trees.		externally defined data trees.
	Vendors use this to extend standard data models to cover the full		Vendors use this to extend standard modules to cover the full scope
	scope of features in implementations, which commonly is broader than		of features in implementations, which commonly is broader than what
	what is covered by the standard model.		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		User-specific YANG modules are developed by organizations that
	YANG-based infrastructure including devices and orchestrators. The		operate YANG-based infrastructure including devices and
	intent of these models is to express the specific needs for a certain		orchestrators. For example, network administrators in enterprises,
	implementation, above and beyond what is provided by vendors.		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		This module type obviously requires the infrastructure to support the
	introduction of user-provided models and extensions. This would		introduction of user-provided modules and extensions. This would
	include ability to describe the service-to-network decomposition in		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.		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.		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		The suggested classification in this document would be an useful
	of catalogs, such as proposed in		information in a catalog of YANG modules. Such catalog allows for
	[I-D.openconfig-netmod-model-catalog]. Such catalogs allows for easy		easy lookup and reusability of YANG modules. Practically, the YANG
	lookup and reusability of YANG models. SDO-classified models also		module classification type would be an additional leaf to YANG module
	provide an educational resource providing architectural guidelines		specified in [I-D.openconfig-netmod-model-catalog]:
	for model development, based on a membership reviewn and consensus.
	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		Note: this leaf should actually be moved to
	considerations.		[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.		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 00: Renamed and small fixes based on WG feedback.
	version 01: Language fixes, collapsing of vendor models and		version 01: Language fixes, collapsing of vendor data models and
	extensions, and the introduction of user models and extensions.		extensions, and the introduction of user data models and extensions.
	version 02: Added two sections, Model Catalog and Benefits of model		version 02: Updated the YANG Module Catalog section, terminology
	classification.		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		[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
	the Network Configuration Protocol (NETCONF)", RFC 6020,		the Network Configuration Protocol (NETCONF)", RFC 6020,
	DOI 10.17487/RFC6020, October 2010,		DOI 10.17487/RFC6020, October 2010,
	<http://www.rfc-editor.org/info/rfc6020>.		<http://www.rfc-editor.org/info/rfc6020>.
	4.2. Informative References		9.2. Informative References
	[I-D.ietf-netmod-acl-model]		[I-D.ietf-netmod-acl-model]
	Bogdanovic, D., Koushik, K., Huang, L., and D. Blair,		Bogdanovic, D., Koushik, K., Huang, L., and D. Blair,
	"Network Access Control List (ACL) YANG Data Model",		"Network Access Control List (ACL) YANG Data Model",
	draft-ietf-netmod-acl-model-07 (work in progress), March		draft-ietf-netmod-acl-model-07 (work in progress), March
	2016.		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]		[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-		Koushik, "Yang Data Model for OSPF Protocol", draft-ietf-
	ospf-yang-04 (work in progress), March 2016.		ospf-yang-04 (work in progress), March 2016.
	[I-D.openconfig-netmod-model-catalog]		[I-D.openconfig-netmod-model-catalog]
	D'Souza, K., Shaikh, A., and R. Shakir, "Catalog and		D'Souza, K., Shaikh, A., and R. Shakir, "Catalog and
	registry for YANG models", draft-openconfig-netmod-model-		registry for YANG models", draft-openconfig-netmod-model-
	catalog-00 (work in progress), October 2015.		catalog-00 (work in progress), October 2015.
	[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,		[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
	and A. Bierman, Ed., "Network Configuration Protocol		and A. Bierman, Ed., "Network Configuration Protocol
	skipping to change at page 9, line 31 ¶		skipping to change at page 12, line 12 ¶
	<https://www.ietf.org/iesg/statement/writable-mib-		<https://www.ietf.org/iesg/statement/writable-mib-
	module.html>.		module.html>.
	[YANG-Data-Model-for-L3VPN-service-delivery]		[YANG-Data-Model-for-L3VPN-service-delivery]
	"YANG Data Model for L3VPN service delivery",		"YANG Data Model for L3VPN service delivery",
	<https://tools.ietf.org/id/draft-l3vpn-service-yang>.		<https://tools.ietf.org/id/draft-l3vpn-service-yang>.
	Authors' Addresses		Authors' Addresses
	Dean Bogdanovic		Dean Bogdanovic
			Volta Networks, Inc.
	Email: ivandean@gmail.com		Email: dean@voltanet.io
	Benoit Claise		Benoit Claise
	Cisco Systems, Inc.		Cisco Systems, Inc.
			De Kleetlaan 6a b1
			1831 Diegem
			Belgium
			Phone: +32 2 704 5622
	Email: bclaise@cisco.com		Email: bclaise@cisco.com
	Carl Moberg		Carl Moberg
	Cisco Systems, Inc.		Cisco Systems, Inc.
	Email: camoberg@cisco.com		Email: camoberg@cisco.com
End of changes. 80 change blocks.
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