draft-ietf-netmod-yang-model-classification-00.txt   draft-ietf-netmod-yang-model-classification-01.txt 
NETMOD D. Bogdanovic NETMOD D. Bogdanovic
Internet-Draft Internet-Draft
Intended status: Informational B. Claise Intended status: Informational B. Claise
Expires: June 9, 2016 C. Moberg Expires: October 6, 2016 C. Moberg
Cisco Systems, Inc. Cisco Systems, Inc.
December 7, 2015 April 4, 2016
YANG Model Classification YANG Model Classification
draft-ietf-netmod-yang-model-classification-00 draft-ietf-netmod-yang-model-classification-01
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
open source software projects, and vendors are using YANG to develop (SDOs), open source software projects, vendors and users are using
and publish models of configuration, state data and operations for a YANG to develop and publish models of configuration, state data and
wide variety of applications. At the same time, there is currently operations for a wide variety of applications. At the same time,
no well-known terminology to categorize various types of YANG models. there is currently no well-known terminology to categorize various
types of YANG models.
A consistent terminology would help with the categorization of A consistent terminology would help with the categorization of
models, assist in the analysis the YANG data modeling efforts in the models, 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 models.
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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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 June 9, 2016. This Internet-Draft will expire on October 6, 2016.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. First Dimension: YANG Model Abstraction Layers . . . . . . . 3 2. First Dimension: YANG Model Abstraction Layers . . . . . . . 3
2.1. Network Service YANG Data Models . . . . . . . . . . . . 4 2.1. Network Service YANG Data Models . . . . . . . . . . . . 4
2.2. Network Element YANG Data models . . . . . . . . . . . . 5 2.2. Network Element YANG Data models . . . . . . . . . . . . 5
3. Second Dimension: Model Types . . . . . . . . . . . . . . . . 6 3. Second Dimension: Model Types . . . . . . . . . . . . . . . . 6
3.1. Standard YANG Models . . . . . . . . . . . . . . . . . . 6 3.1. Standard YANG Models . . . . . . . . . . . . . . . . . . 6
3.2. Vendor-specific YANG Models . . . . . . . . . . . . . . . 6 3.2. Vendor-specific YANG Models and Extensions . . . . . . . 6
3.3. Vendor-specific Extensions . . . . . . . . . . . . . . . 7 3.3. User-specific YANG Models and Extensions . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7 3.4. Adding Models to Catalogs . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 3.5. Security Considerations . . . . . . . . . . . . . . . . . 8
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 3.6. IANA Considerations . . . . . . . . . . . . . . . . . . . 8
7. Change log [RFC Editor: Please remove] . . . . . . . . . . . 7 3.7. Acknowledgements . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.8. Change log [RFC Editor: Please remove] . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8 4. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 8 4.1. Normative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 4.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
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 NETCONF [RFC6241] and YANG
standards for configuration management purposes, especially in new standards for configuration management purposes, especially in new
working group charters [Writable-MIB-Module-IESG-Statement]. 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 and vendors. consortia, ad hoc groups, open source projects, vendors, and end-
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 models according to abstraction, or how to classify
models along the continuum spanning formal standards publications and models along the continuum spanning formal standards publications,
vendor-specific models. vendor-specific models and models 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 models in two
dimensions: dimensions:
o The layering of models based on their abstraction levels o The layering of models based on their abstraction levels
o The type of model based on the nature and intent of the content o The type of model based on the nature and intent of the content
The two categories are covered in the next two sections. The two categories are covered in the next two sections.
2. First Dimension: YANG Model Abstraction Layers 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 top-down and bottom-up. The top-down approach starts with high level
abstractions modeling business or customer requirements and maps them abstractions modeling business or customer requirements and maps them
to specific networking technologies. The bottom-up approach starts to specific networking technologies. The bottom-up approach starts
with fundamental networking technologies and maps them into more with fundamental networking technologies and maps them into more
abstract constructs. 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 models. For the purpose of this
document we assume that both approaches (bottom-up and top-down) will 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. 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: data models into two distinct abstraction layers:
o Network Element YANG Models describe the configuration, state data 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 o Network Service YANG Models describe the configuration, state data
data and operations of an abstract representation of a service 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 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 existing lower layer models by higher level models while limiting
duplication of features across layers. duplication of features across layers.
For model developers, per-layer modeling allows for separation of For model 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 models for e.g. routing or switching protocols
requires teams that include developers with experience from 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 models are best developed by
people experienced in defining network services for consumption by people experienced in defining network services for consumption by
programmers developing e.g. flow-through provisioning systems or programmers developing e.g. flow-through provisioning systems or
self-service portals. self-service portals.
+--------------------------+ +--------------------------+
| Operations and Business | | Operations and Business |
| Support Systems | | Support Systems |
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system implementing such a process. system implementing such a process.
As an example, the Network Service model included in As an example, the Network Service model included in
[YANG-Data-Model-for-L3VPN-service-delivery] provides an abstracted [YANG-Data-Model-for-L3VPN-service-delivery] provides an abstracted
model for Layer 3 IP VPN service configuration. An orchestrator model for Layer 3 IP VPN service configuration. An orchestrator
receives operations on service instances according to the service receives operations on service instances according to the service
model and decomposes the data into specific Network Element models to model and decomposes the data into specific Network Element models to
configure the participating network elements to perform the intent of configure the participating network elements to perform the intent of
the service. 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 external systems. These models 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 model
and does not put focus on reusability of internal data definitions and does not put focus on reusability of internal data definitions
and groupings. The monolithic approach has the advantages of single- and groupings. The monolithic approach has the advantages of single-
purpose development including speed at the expense of reusability. purpose development including speed at the expense of reusability.
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environment consisting of the operating system and applications environment consisting of the operating system and applications
running on the device. running on the device.
The decomposition, ordering, and execution of changes to the The decomposition, ordering, and execution of changes to the
operating system and application configuration is the task of the operating system and application configuration is the task of the
management framework that implements the YANG model. management framework that implements the YANG model.
3. Second Dimension: Model Types 3. Second Dimension: Model Types
This document suggests classifying YANG model types as either This document suggests classifying YANG model types as either
standard YANG models, vendor-specific YANG models, or vendor-specific standard YANG models, vendor-specific YANG models and extensions, and
extensions. user-specific YANG models and extensions
The suggested classification applies to both Network Element YANG 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 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 models will include a mix of all three
types of models. types of models.
3.1. Standard YANG 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 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 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. 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. 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 Vendor-specific YANG models 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. The intent of these models range from providing
openly published YANG models that may eventually be contributed back openly published YANG models that may eventually be contributed back
to, or adopted by an SDO, to strictly internal YANG models not to, or adopted by an SDO, to strictly internal YANG models not
intended for external consumption. intended for external consumption.
The lifecycle of these models are generally aligned with the release The lifecycle of these models 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.
3.3. Vendor-specific Extensions Vendors also develop Vendor-specific Extensions to standard models
using YANG constructs for extending data definitions of previously
Vendors 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 published models. 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 data models to cover the full
scope of features in implementations, which commonly is broader than scope of features in implementations, which commonly is broader than
what is covered by the standard model. 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 At this stage, authors of the draft didn't look into security
considerations. considerations.
5. IANA Considerations 3.6. IANA Considerations
This document requests no action by IANA. This document requests no action by IANA.
6. Acknowledgements 3.7. Acknowledgements
Thanks to David Ball for his enlightenments on Metro Ethernet Forum
service aspects.
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 3.8. Change log [RFC Editor: Please remove]
interaction with the different SDOs and opensource projects, add the
definitions.
version 2: added definitions for config and service models clarified version 00: Renamed and small fixes based on WG feedback.
second dimension of model classification. fixed typos
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 [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>.
8.2. Informative References 4.2. Informative References
[I-D.ietf-netmod-acl-model] [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", "Network Access Control List (ACL) YANG Data Model",
draft-ietf-netmod-acl-model-05 (work in progress), October draft-ietf-netmod-acl-model-07 (work in progress), March
2015. 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, J., Bogdanovic, D., and K.
Koushik, "Yang Data Model for OSPF Protocol", draft-ietf- 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., [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<http://www.rfc-editor.org/info/rfc6241>. <http://www.rfc-editor.org/info/rfc6241>.
[RFC7223] Bjorklund, M., "A YANG Data Model for Interface [RFC7223] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 7223, DOI 10.17487/RFC7223, May 2014, Management", RFC 7223, DOI 10.17487/RFC7223, May 2014,
<http://www.rfc-editor.org/info/rfc7223>. <http://www.rfc-editor.org/info/rfc7223>.
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