Internet DRAFT - draft-bogdanovic-netmod-yang-model-classification
draft-bogdanovic-netmod-yang-model-classification
NETMOD D. Bogdanovic
Internet-Draft
Intended status: Informational B. Claise
Expires: April 19, 2016 C. Moberg
Cisco Systems, Inc.
October 17, 2015
YANG Model Classification
draft-bogdanovic-netmod-yang-model-classification-05
Abstract
The YANG [RFC6020] data modeling language is currently being
considered for a wide variety of applications throughout the
networking industry at large. Many standards defining organizations,
open source projects, and vendors are using YANG to develop and
publish models of configuration, state data and operations for a wide
variety of applications. At the same time, there is currently no
well-known terminology to categorize various types of YANG models.
A consistent terminology would help with the categorization of
models, assist in the analysis the YANG data modeling efforts in the
IETF and other organizations, and bring clarity to the YANG-related
discussions between the different groups.
This document describes a set of concepts and associated terms to
support consistent classification of YANG models.
Status of This Memo
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 April 19, 2016.
Bogdanovic, et al. Expires April 19, 2016 [Page 1]
Internet-Draft YANG Model Classification October 2015
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. First Dimension: YANG Model Abstraction Layers . . . . . . . 3
2.1. Network Service YANG Data Models . . . . . . . . . . . . 4
2.2. Network Element YANG Data models . . . . . . . . . . . . 5
3. Second Dimension: Model Types . . . . . . . . . . . . . . . . 6
3.1. Standard YANG Models . . . . . . . . . . . . . . . . . . 6
3.2. Vendor-specific YANG Models . . . . . . . . . . . . . . . 6
3.3. Vendor-specific Extensions . . . . . . . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
7. Change log [RFC Editor: Please remove] . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
The Internet Engineering Steering Group (IESG) has been actively
encouraging IETF working groups to use the NETCONF [RFC6241] and YANG
standards for configuration management purposes, especially in new
working group charters [Writable-MIB-Module-IESG-Statement].
YANG is also gaining wide acceptance as the de-facto standard
modeling language in the broader industry. This extends beyond the
IETF, including many standards development organizations, industry
consortia, ad hoc groups, open source projects and vendors.
There are currently no clear guidelines on how to classify the
layering of YANG models according to abstraction, or how to classify
Bogdanovic, et al. Expires April 19, 2016 [Page 2]
Internet-Draft YANG Model Classification October 2015
models along the continuum spanning formal standards publications and
vendor-specific models.
This document presents a set of concepts and terms to form a useful
taxonomy for consistent classification of YANG models in two
dimensions:
o The layering of models based on their abstraction levels
o The type of model based on the nature and intent of the content
The two categories are covered in the next two sections.
2. First Dimension: YANG Model Abstraction Layers
Model developers have taken two approaches to developing YANG model:
top-down and bottom-up. The top-down approach starts with high level
abstractions modeling business or customer requirements and maps them
to specific networking technologies. The bottom-up approach starts
with fundamental networking technologies and maps them into more
abstract constructs.
There are currently no specific requirements on, or well-defined best
practices around the development of models. For the purpose of this
document we assume that both approaches (bottom-up and top-down) will
be used as they both provide benefits that appeals to different
groups.
For layering purposes, this documents suggests the classification of
data models into two distinct abstraction layers:
o Network Element YANG Models describe the configuration, state data
and operations of a specific device-centric technology or feature.
o Network Service YANG Models describes the configuration, state
data and operations of an abstract representation of a service
implemented on one or multiple network elements
Figure 1 illustrates the application of YANG models at different
layers of abstraction. Layering of models allow for reusability of
existing lower layer models by higher level models while limiting
duplication of features across layers.
For model developers, per-layer modeling allows for separation of
concern across editing teams focusing on specific areas.
As an example, experience from the IETF shows that creating useful
network element YANG models for e.g routing or switching protocols
Bogdanovic, et al. Expires April 19, 2016 [Page 3]
Internet-Draft YANG Model Classification October 2015
requires teams that include developers with experience from
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.
+-----------------------+
| |
| OSS/BSS |
| |
+-----------------------+
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Network Service YANG data models
+------------+ +-------------+ +-------------+
| | | | | |
| - VPWS | | - VPLS | | L3VPN |
| - L2VPN | | - L2VPN | | |
| | | | | |
+------------+ +-------------+ +-------------+
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Network Element YANG data models
+------------+ +------------+ +-------------+ +------------+
| | | | | | | |
| MPLS | | BGP | | IPv4 & IPv6 | | Ethernet |
| | | | | | | |
+------------+ +------------+ +-------------+ +------------+
Fig. 1 YANG Model Layers
2.1. Network Service YANG Data Models
Network Service YANG Data Models 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.
Bogdanovic, et al. Expires April 19, 2016 [Page 4]
Internet-Draft YANG Model Classification October 2015
As an example, the Network Service model included in
[YANG-Data-Model-for-L3VPN-service-delivery] provides an abstracted
model for Layer 3 IP VPN service configuration. An orchestrator
receives operations on service instances according to the service
model and decomposes the data into specific Network Element models to
configure the participating network elements to perform the intent of
the service.
Network Service YANG models defines services models to be consumed by
external systems. These models are commonly designed, developed and
deployed by network infrastructure teams.
YANG allows for different design patterns to describe network
services, ranging from monolithic to component-based approaches.
The monolithic approach captures the entire service in a single model
and does not put focus on reusability of internal data definitions
and groupings. The monolithic approach has the advantages of single-
purpose development including speed at the expense of reusability.
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
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
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.
Bogdanovic, et al. Expires April 19, 2016 [Page 5]
Internet-Draft YANG Model Classification October 2015
The decomposition, ordering and execution of changes to the operating
system, and application configuration is the task of the management
framework that implements the YANG model.
3. Second Dimension: Model Types
This document suggests classifying YANG model types as either
standard YANG models, vendor-specific YANG models, or vendor-specific
extensions.
The suggested classification applies to both Network Element YANG
Data Models and to Network Service YANG Data Models.
It is to be expected that real-world implementations of both Network
Service and Network Element models will include a mix of all three
types of models.
3.1. Standard YANG Models
Standard YANG models are published by standards defining
organizations (SDOs). While there is no formal definition of what
construes an SDO, a common feature is that they publish
specifications along specific processes with content that reflects
some sort of membership consensus. The specifications are developed
for wide use among the membership or for audiences beyond that.
The lifecycle of these models are driven by the editing cycle of the
specification and not tied to a specific implementation.
Examples of SDOs in the networking industry are the IETF, the IEEE
and the MEF.
3.2. Vendor-specific YANG Models
Vendor-specific YANG models are developed by organizations with the
intent to support a specific set of implementations under control of
that organization. The intent of these models range from providing
openly published YANG models that may eventually be contributed back
to, or adopted by an SDO, to strictly internal YANG models not
intended for external consumption.
The lifecycle of these models are generally aligned with the release
cycle of the product or open source software project deliverables.
It is worth noting that there is an increasing amount of interaction
between OSS projects and SDOs in the networking industry. This
includes OSS projects implementing published standards as well as OSS
Bogdanovic, et al. Expires April 19, 2016 [Page 6]
Internet-Draft YANG Model Classification October 2015
projects contributing content to standards defining organization
processes.
3.3. Vendor-specific Extensions
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
allows locally defined data trees to be augmented into locations in
externally defined data trees.
Vendors use this to extend standard data models to cover the full
scope of features in implementations, which commonly is broader than
what is covered by the standard model.
4. Security Considerations
At this stage, authors of the draft didn't look into security
considerations.
5. IANA Considerations
This document requests no action by IANA.
6. Acknowledgements
Thanks to David Ball for his enlightenments on Metro Ethernet Forum
service aspects.
7. Change log [RFC Editor: Please remove]
version 1: restructure the document, add the two dimensions, add the
interaction with the different SDOs and opensource projects, add the
definitions.
version 2: added definitions for config and service models clarified
second dimension of model classification. fixed typos
version 3: restructure and partial rewrite of section 2.
version 4: Language fixes
8. References
Bogdanovic, et al. Expires April 19, 2016 [Page 7]
Internet-Draft YANG Model Classification October 2015
8.1. 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,
<http://www.rfc-editor.org/info/rfc6020>.
8.2. Informative References
[I-D.ietf-netmod-acl-model]
Bogdanovic, D., Sreenivasa, K., Huang, L., and D. Blair,
"Network Access Control List (ACL) YANG Data Model",
draft-ietf-netmod-acl-model-03 (work in progress), June
2015.
[I-D.ietf-ospf-yang]
Yeung, D., Qu, Y., Zhang, J., Bogdanovic, D., and K.
Koushik, "Yang Data Model for OSPF Protocol", draft-ietf-
ospf-yang-02 (work in progress), September 2015.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<http://www.rfc-editor.org/info/rfc6241>.
[RFC7223] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 7223, DOI 10.17487/RFC7223, May 2014,
<http://www.rfc-editor.org/info/rfc7223>.
[Writable-MIB-Module-IESG-Statement]
"Writable MIB Module IESG Statement",
<https://www.ietf.org/iesg/statement/writable-mib-
module.html>.
[YANG-Data-Model-for-L3VPN-service-delivery]
"YANG Data Model for L3VPN service delivery",
<https://tools.ietf.org/id/draft-l3vpn-service-yang>.
Authors' Addresses
Dean Bogdanovic
Email: ivandean@gmail.com
Bogdanovic, et al. Expires April 19, 2016 [Page 8]
Internet-Draft YANG Model Classification October 2015
Benoit Claise
Cisco Systems, Inc.
Email: bclaise@cisco.com
Carl Moberg
Cisco Systems, Inc.
Email: camoberg@cisco.com
Bogdanovic, et al. Expires April 19, 2016 [Page 9]
