wdiff rfc8199.original rfc8199.txt

NETMOD
Internet Engineering Task Force (IETF) D. Bogdanovic
Internet-Draft
Request for Comments: 8199 Volta Networks, Inc.
Intended status:
Category: Informational B. Claise
Expires: December 15, 2017
ISSN: 2070-1721 C. Moberg
Cisco Systems, Inc.
June 13,
July 2017

YANG Module Classification
draft-ietf-netmod-yang-model-classification-08

Abstract

The YANG data modeling language is currently being considered for a
wide variety of applications throughout the networking industry at
large. Many standards development organizations (SDOs), open source open-source
software projects, vendors vendors, and users are using YANG to develop and
publish YANG modules for a wide variety of applications. At the same
time, there is currently no well-known terminology to categorize
various types of YANG modules.

A consistent terminology would help with the categorization of YANG
modules, assist in the analysis of 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 document is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents not an Internet Standards Track specification; it is
published for informational purposes.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a maximum candidate for any level of Internet
Standard; see Section 2 of six months RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained 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 15, 2017.
http://www.rfc-editor.org/info/rfc8199.

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
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. First Dimension: YANG Module Abstraction Layers . . . . . . . 4
2.1. Network Service YANG Modules . . . . . . . . . . . . . . 6
2.2. Network Element YANG Modules . . . . . . . . . . . . . . 7
3. Second Dimension: YANG Module Origin Types . . . . . . . . . . . . 7
3.1. Standard YANG Modules . . . . . . . . . . . . . . . . . . 8
3.2. Vendor-specific Vendor-Specific YANG Modules and Extensions . . . . . . . 8
3.3. User-specific User-Specific YANG Modules and Extensions . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Acknowledgements . . . . . . . . References . . . . . . . . . . . . . . 9
7. Change log [RFC Editor: Please remove] . . . . . . . . . . . 9
8.
6.1. Normative References . . . . . . . . . . . . . . . . . . 9
6.2. Informative References . . . . . . . 10
8.1. Normative References . . . . . . . . . . . 10
Acknowledgements . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 10

1. Introduction

The Internet Engineering Steering Group (IESG) has been actively
encouraging IETF working groups to use the YANG data modeling
language [RFC7950], [RFC7950] and NETCONF protocol the Network Configuration Protocol (NETCONF)
[RFC6241] for configuration management purposes, especially in new
working group charters [Writable-MIB-Module-IESG-Statement]. [IESG-Statement].

YANG is also gaining wide acceptance as the de-facto de facto standard data
modeling language in the broader industry. This extends beyond the
IETF, including
IETF to include many standards development organizations, SDOs, industry consortia, ad hoc groups, open open-
source projects, vendors, and end- end users.

There are currently no clear guidelines on how to classify the
layering of YANG modules according to abstraction, abstraction or how to classify
modules along the continuum spanning formal standards publications,
vendor-specific modules modules, and modules provided by end-users. 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 module origin type based on the nature and intent of the
content

The intent of this document is to provide a taxonomy to simplify
human communication around YANG modules. While the classification
boundaries are at times blurry, this document should provide a robust
starting point as the YANG community gains further experience with
designing and deploying modules. To be more explicit, it is expected
that the classification criteria will change over time.

A number of modules, for example, modules have concerned with topologies,
created substantial discussion during the development of this document: for examples, modules concerned with
topologies.
document. Topology modules are useful both on the Network Element network element
level (e.g. (e.g., link-state database content) as well as and on the Network
Service network service
level (e.g. (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 discussions among SDOs and
industry consortia discussions,
whose consortia; the goals of such discussions are determined in their
by the respective areas of work.

o Second, operators might look at the YANG module abstraction layers
to understand which Network Service YANG modules Modules and Network
Element YANG modules 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 a
Layer 2 Virtual Private Network (L2VPN) YANG module might be a
Network Service YANG module, Module, ready to be used as a service model
by a network operator. Alternatively, it might be a Network
Element YANG module Module that contains the L2VPN data definitions
required to be configured on a single device.

o And thirdly, Third, this taxonomy would will help equipment vendors (whether physical
or virtual), controller vendors, and orchestrator vendors to
explain to their customers the relationship between the different
YANG modules they support in their products.

1.1. Terminology

[RFC7950] specifies:

o data model: A data model describes how data is represented and
accessed.

o module: A YANG module defines hierarchies of schema nodes. With
its definitions and the definitions it imports or includes from
elsewhere, a module is self-contained and "compilable".

2. First Dimension: YANG Module Abstraction Layers

Module developers have taken two approaches to developing YANG
modules: top-down and bottom-up. The top-down approach starts with
high level
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 for the development of YANG modules. This document
considers both bottom-up and top-down approaches as they are both
used and they each 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, operations operations, and notifications of specific device-centric
technologies or features features.

o Network Service YANG Modules describe the configuration, state
data, operations operations, and notifications of abstract representations of
services implemented on one or multiple network elements elements.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Network Service YANG Modules

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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 Abstraction Layers

Figure 1 illustrates the application of YANG modules at different
layers of abstraction. Layering of modules allows for reusability of
existing lower layer lower-layer modules by higher level higher-level modules while limiting
duplication of features across layers.

For module developers, per-layer modeling allows for separation of
concern across editing teams focusing on specific areas.

As an example, experience from the IETF shows that creating useful
Network Element YANG modules Modules (e.g., for e.g. routing or switching protocols
protocols) requires teams that include developers with experience of
implementing those protocols.

On the other hand, Network Service YANG modules Modules are best developed by
network operators experienced in defining network services for
consumption by programmers programmers, e.g., those developing e.g. flow-through
provisioning systems or self-service portals.

2.1. Network Service YANG Modules

Network Service YANG Modules describe the characteristics of a
service, as agreed upon with consumers of that service. That is, a
service module does not expose the detailed configuration parameters
of all participating network elements and features, features but describes an
abstract model that allows instances of the service to be decomposed
into instance data according to the Network Element YANG Modules of
the participating network elements. The service-to-element
decomposition is a separate process with process; the details depending depend on how the
network operator chooses to realize the service. For the purpose of
this document, the term "orchestrator" is used to describe to
describe a system
implementing such a process.

Network Service YANG Modules define service models to be consumed by
external systems.

External systems can be provisioning systems, service orchestrators,
Operations Support Systems, Business Support
Systems Systems, and
applications exposed to network service consumers, being
either consumers (either internal
network operations people or external customers. customers). These modules are
commonly designed, developed 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 development, including development speed
at the expense of reusability.

The component-based approach captures device-centric features (e.g.
the definition of a (e.g.,
VPN Routing and Forwarding (VRF), routing protocols, or packet
filtering) in a vendor-independent manner. The components are
designed for reuse across many service modules. The set of
components required for a specific service is then composed into the
higher-level service. The component-based approach has the
advantages of modular development development, including a higher degree of
reusability at the expense of initial development speed.

As an example, an L2VPN service can be built on many different types
of transport network technologies, including e.g. including, e.g., MPLS or carrier
ethernet. Carrier
Ethernet. A component-based approach would allow for reuse of e.g.
User-Network User-
Network Interface (UNI) definitions independent of definitions, such as the
underlying transport network (e.g. MEF UNI interface or
MPLS
interface). interface, independent of the underlying transport network. The
monolithic approach would assume a specific set of transport
technologies and interface definitions.

An example of a Network Service YANG module Module is in [RFC8049]. It
provides an abstract model for Layer 3 IP VPN service configuration.
This module includes e.g. the concept of a 'site-network-access' to
represent bearer and connection parameters. An orchestrator receives
operations on service instances according to the service module and
decomposes the data into configuration data according to specific
Network Element YANG Modules to configure the participating network
elements to the service. In the case of the L3VPN module, this would
include translating the 'site-network-access' parameters to the
appropriate parameters in the Network Element YANG Module implemented
on the constituent elements.

2.2. Network Element YANG Modules

Network Element YANG Modules describe the characteristics of a
network device as defined by the vendor of that device. The modules
are commonly structured around features of the device, e.g. e.g.,
interface configuration [RFC7223], OSPF configuration [I-D.ietf-ospf-yang], [OSPF-YANG],
and
firewall rules definitions [I-D.ietf-netmod-acl-model]. access control list (ACL) configuration [ACL-YANG].

The module Network Element YANG Module provides a coherent data model
representation of the software environment consisting of the
operating system and applications running on the device. The
decomposition, ordering, and execution of changes to the operating
system and application configuration is the task of the agent that
implements the module.

3. Second Dimension: YANG Module Origin Types

This document suggests classifying YANG module origin types as
standard
Standard YANG modules, vendor-specific Modules, Vendor-Specific YANG modules Modules and extensions, Extensions,
or user-specific User-Specific YANG modules Modules and extensions Extensions.

The suggested classification applies to both Network Element YANG
Modules and Network Service YANG Modules.

It is to be expected that real-world implementations of both Network
Service YANG Modules and Network Element YANG Modules will include a
mix of all three module origin types.

Figure 2 illustrates the relationship between the three types of
modules.

Figure 2: YANG Module Origin Types

3.1. Standard YANG Modules

Standard YANG Modules are published by standards development
organizations (SDOs). SDOs. Most SDOs create
specifications according to a formal process in order to produce a
standard that is useful for their constituencies.

The lifecycle lifecycles of these modules is are driven by the editing cycle cycles of
the
specification specifications and not tied to a specific implementation.

Examples of SDOs in the networking industry are the IETF and the
IEEE.

3.2. Vendor-specific Vendor-Specific YANG Modules and Extensions

Vendor-specific

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 organization, for example, vendors of virtual or physical
equipment, industry consortia, and opensource open-source projects. The intent
of these modules range ranges from providing openly published YANG modules
that may eventually be contributed back to, to or adopted by, by an SDO, SDO to
strictly internal YANG modules not intended for external consumption.

The lifecycle lifecycles of these modules are generally aligned with the
release
cycle cycles of the product or open source open-source software project
deliverables.

It is worth noting that there is an increasing amount of interaction
between open source open-source projects and SDOs in the networking industry.
This includes open source open-source projects implementing published standards
as well as open source open-source projects contributing content to SDO
processes.

Vendors also develop Vendor-specific Extensions 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 added 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 that
covered by the standard module.

3.3. User-specific User-Specific YANG Modules and Extensions

User-specific

User-Specific YANG Modules are developed by organizations that
operate YANG-based infrastructure including devices and
orchestrators. For
orchestrators, for example, network administrators in enterprises, enterprises or
at 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 the ability to describe the service-to-network decomposition
in orchestrators and the module to configuration module-to-configuration decomposition in
devices.

The lifecycles of these modules are generally aligned with the change
cadence of the infrastructure.

4. Security Considerations

This document doesn't have any Security Considerations.

5. IANA Considerations

This document has no does not require any IANA actions.

6. Acknowledgements

Thanks to David Ball and Jonathen Hansford for feedback and
suggestions.

7. 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), explain 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.

version 06: updates based on comments from Adrian Farrel about YANG
Data Model for L3VPN Service Delivery.

version 07: updates based on comments from Pete Resnick

8. References

8.1.

6.1. Normative References

[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>.

[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<http://www.rfc-editor.org/info/rfc7950>.

[RFC8049] Litkowski, S., Tomotaki, L., and K. Ogaki, "YANG Data
Model for L3VPN Service Delivery", RFC 8049,
DOI 10.17487/RFC8049, February 2017,
<http://www.rfc-editor.org/info/rfc8049>.

8.2.

6.2. Informative References

[I-D.ietf-netmod-acl-model]

[ACL-YANG]
Bogdanovic, D., Koushik, K., Jethanandani, M., Huang, L., Agarwal, S.,
and D. Blair, "Network Access Control List (ACL) YANG Data
Model",
draft-ietf-netmod-acl-model-10 (work Work in progress), March Progress, draft-ietf-netmod-acl-model-11,
June 2017.

[I-D.ietf-ospf-yang]

[IESG-Statement]
"Writable MIB Module IESG Statement",
<https://www.ietf.org/iesg/statement/writable-mib-
module.html>.

[OSPF-YANG]
Yeung, D., Qu, Y., Zhang, Z., Chen, I., and A. Lindem,
"Yang Data Model for OSPF Protocol", draft-ietf-ospf-
yang-07 (work Work in progress), March Progress,
draft-ietf-ospf-yang-08, July 2017.

[Writable-MIB-Module-IESG-Statement]
"Writable MIB Module IESG Statement",
<https://www.ietf.org/iesg/statement/writable-mib-
module.html>.

Acknowledgements

Thanks to David Ball and Jonathan Hansford for feedback and
suggestions.

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