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Versions: (draft-bogdanovic-netmod-yang-model-classification)
00 01 02 03 04 05 06 07 08 RFC 8199
NETMOD D. Bogdanovic
Internet-Draft Volta Networks, Inc.
Intended status: Informational B. Claise
Expires: December 24, 2016 C. Moberg
Cisco Systems, Inc.
June 22, 2016
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 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 modules.
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 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 December 24, 2016.
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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
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 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
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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 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
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.
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.
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.
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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 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
YANG modules into two distinct abstraction layers:
o Network Element YANG Modules describe the configuration, state
data and operations of specific device-centric technologies or
features
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 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.
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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
requires teams that include developers with experience of
implementing those protocols.
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 Modules
+------------+ +-------------+ +-------------+
| | | | | |
| - L2VPN | | - L2VPN | | L3VPN |
| - VPWS | | - VPLS | | |
| | | | | |
+------------+ +-------------+ +-------------+
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Network Element YANG Modules
+------------+ +------------+ +-------------+ +------------+
| | | | | | | |
| 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
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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 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 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 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
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 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.
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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 Modules
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 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: Module Types
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
Modules and Network Service YANG Modules.
It is to be expected that real-world implementations of both Network
Service and Network Element YANG Modules will include a mix of all
three types of modules.
Figure 2 illustrates the relationship between the three types of
modules.
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+--------------+
| 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 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
(Institute of Electrical and Electronics Engineers) and the MEF.
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.
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
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as well as open source projects contributing content to SDO
processes.
Vendors also develop Vendor-specific Extensions to standard modules
using YANG constructs for extending data definitions of previously
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 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 Modules and Extensions
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 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 module to configuration decomposition in
devices.
The lifecycle of these modules are generally aligned with the change
cadence of the infrastructure.
4. Adding The Classification Type to YANG Module Catalogs
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]:
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leaf module-class{
type enum {
service
device
notApplicable
}
description
"Categorization of the YANG module based on
draft-ietf-netmod-yang-model-classification.";
}
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.
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.
5. Security Considerations
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.
8. Change log [RFC Editor: Please remove]
version 00: Renamed and small fixes based on WG feedback.
version 01: Language fixes, collapsing of vendor data models and
extensions, and the introduction of user data models and extensions.
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.
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9. 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,
<http://www.rfc-editor.org/info/rfc6020>.
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, 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
(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>.
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[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
Volta Networks, Inc.
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
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