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Differences from draft-bogdanovic-netmod-yang-model-classification-01.txt
NETMOD D. Bogdanovic
Internet-Draft Juniper Networks
Intended status: Informational B. Claise
Expires: September 24, 2015 C. Moberg
Cisco Systmes, Inc.
March 23, 2015
YANG model classification
draft-bogdanovic-netmod-yang-model-classification-02
Abstract
YANG became de facto standard language for data modeling in the
industry. More and more groups uses YANG to create protocol and
service models, both for configuration and operational models.
Currently there is a lack of consistent terminology to categorize
those models. A consistent terminology would help models
categorization, assist in the analysis the YANG data modeling effort
in the IETF and in the industry, and facilitate the YANG-related
discussions between different groups.
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
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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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 24, 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
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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. First Dimension: Network YANG Data Model Layering . . . . . . 3
2.1. Network Service YANG Data Models . . . . . . . . . . . . 4
2.2. Network Element YANG Data models . . . . . . . . . . . . 5
3. Second Dimension: Model Type . . . . . . . . . . . . . . . . 5
3.1. Standard YANG model . . . . . . . . . . . . . . . . . . . 6
3.2. Standard Extension YANG Model . . . . . . . . . . . . . . 6
3.3. Proprietary Extension to Standard YANG Model . . . . . . 6
3.4. Vendor configuration model . . . . . . . . . . . . . . . 7
3.5. Proprietary YANG Model . . . . . . . . . . . . . . . . . 8
4. Typical Architecture . . . . . . . . . . . . . . . . . . . . 8
5. IETF, Other SDOs, and open source . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
9. Change log [RFC Editor: Please remove] . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
10.1. Normative References . . . . . . . . . . . . . . . . . . 11
10.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
YANG [RFC6020] became de-facto standard language for data modeling in
the industry. Not only at the IETF, but also in multiple Standard
Development Organizations, different consortia, ad hoc groups, and
OSP. Therefore, many YANG models are being developed and published.
Today, there is no classification of models, there are no clear
guidelines on how to layer models on each other, or how to classify
existing or new models. With this document, the authors propose a
new way to classify the YANG model, along with a taxonomy.
Acknowledging that the YANG became the de-facto standard language for
data modeling, the Internet Engineering Steering Group (IESG) has
been encouraging the working groups to use the NETCONF [RFC6241] and
YANG standards for configuration, especially in new charters
[Writable-MIB-Module-IESG-Statement].
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YANG Models can be classified according to two dimensions: based on
the layer in the hierarchy of models, and based on the model type.
Those two categories are covered in the next two sections.
2. First Dimension: Network YANG Data Model Layering
When developing models, there are two approaches possible, top down
and bottom up. Top down approach is driven by business requirements
and bottom up is driven by technological ones.
There are no hard requirements on how to create models, but it would
be useful to have a classification and how to create models that can
be easily reused, as with this time and energy will be saved in
future development. We should stimulate both development styles,
bottom up and top down, as each has its benefits and groups to which
a certain style will be more appealing than the other.
For layering purposes, we can classify data models into two layers:
o Network Service YANG Model: an abstract view, in YANG, of a
service deployed on one or multiple network elements.
o Network Element YANG Model: describe the configuration parameters,
in YANG, of a specific device technology or feature.
Figure 1 displays example YANG models at different layers. By
layering the models, it is easier to achieve reusability of existing
lower layer models in higher level models and preventing duplication
of same features modeled in different layers. When developing models
per layers, it allows creating very focused groups in specific areas.
As an example, creating protocol data definitions network equipment
YANG data models should involve people that have intimate experience
of implemention details. On the other hand, network service models
are best developed by people experienced in network operations. Same
network service, can be implemented and modeled using different
Network Element YANG models.
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+-----------------------+
| |
| OSS/BSS |
| |
+-----------------------+
Network Service YANG data models -------------------------------
+------------+ +-------------+ +-------------+
| | | | | |
| - VPWS | | - VPLS | | L3VPN |
| - L2VPN | | - L2VPN | | |
| | | | | |
+------------+ +-------------+ +-------------+
Network Element YANG data models ---------------------------------
+------------+ +------------+ +--------------+ +-----------+
| | | | | | | |
| MPLS | | BGP | | Interface | | Routing |
| | | | | | | |
+------------+ +------------+ +--------------+ +-----------+
Fig. 1 YANG Model layers
2.1. Network Service YANG Data Models
Network Service YANG models are created by network operators to
contain the characteristics of a service, as discussed with their
customers. That is, it does not provide details for configuring
network elements or protocols. A separate process is responsible for
mapping this Network Service Model onto the Network Element YANG
Models, depending on how the network operator chooses to realize the
service.
For example, http://datatracker.ietf.org/doc/draft-l3vpn-service-
yang/ provides an abstracted view of the Layer 3 IP VPN service
configuration components. It will be up to an orchestrator to take
this as an input and use specific configurations models on the
network element layer to configure the different network elements to
deliver the service.
Network Service YANG models can be developed in multiple ways.
Building them monolithic from vendor models or by combining one or
more service components into an end to end service data model. It
specifies complete service that is provided by the network operator.
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Building monolithic network service model has an advantage of doing
it fast, but at the expense of flexibility of updating the service
later or changing equipment vendors. Such an end to end service can
be VPLS/VPWS, L2VPN, IPsec, etc. If we take into example VPLS L2VPN
service, it can be built as a single network service model or it can
be built from several service components. VPWS L2VPN service can be
built on top of MPLS or IP network core. When building such a
network service model, network variations have to be taken into the
account and by creating service components modle, such as MPLS, BGP
service component models, it is easier to build a network service
model, such as VPWS L2VPN.
2.2. Network Element YANG Data models
This is base model for all higher models. It fully describes a
protocol or technology, such as OSPF [I-D.ietf-ospf-yang], ISIS
[I-D.ietf-isis-yang-isis-cfg] or feature, such as the access control
list [I-D.ietf-netmod-acl-model].
3. Second Dimension: Model Type
At very high level, models can be divided into proprietary and
standard. Each vendor, consortium, open source project can publish
their models and those are considered proprietary models. When an
SDO, such as IETF or IEEE, publishes an accepted model document, then
this is a standard model. There are use cases where a consortium has
published work which de facto became standard, such as Linux kernel,
but for the clarity in this document, authors are making a separation
between models based on the above description.
Standard YANG Model: YANG model defined by an Standard Development
organization (SDO), e.g. IETF, IEEE.
Standard Extension YANG Model: YANG Model that describes a
standard extension, example route filter, to standard filter YANG
model.
Proprietary Extension to Standard YANG Model: As the Standard YANG
Models contains a subset of all the Vendor Configuration Models,
proprietary extensions must complement the Standard YANG Models to
represent a Vendor Configuration Model.
Proprietary YANG Model: A non Standard YANG Model.
Vendor Configuration Model: It describes all configurable
capabilities of the device and what device vendor exposes for
configuration. The vendor configuration model can be CLI or YANG-
based.
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As mentioned earlier in this document, there are two ways of
designing models, top down and bottom up with one restriction.
Everything is dependent on the vendor data model. That model
describes all the possibilities and if model developers prefers, they
can use vendor model only to design service components, network
service and business service. Using vendor model provides all
capabilities today, but it comes with restrictions of portability
between vendors and to certain extent devices. On the other hand,
only standard models and standard extensions can be used, but this
might result in less feature rich or less efficient services.
Service model developer has a choice to reuse service components or
write a model completely based on vendor data model.
3.1. Standard YANG model
With YANG we have a common language, that enables different
communities to express data models that are widely understandable
without lot of additional explanation. This enables different
groups, such as IETF, to standardize data models, defined as an IETF
RFC, and vendors to support them, which will make it easier to for
network operators to manage their network configuration
programmatically. The Standard YANG Models can distinguished between
the core YANG models, such as the YANG Data Model for Interface
Management [RFC7223], and the technology specific YANG models, such
as the Configuration Data Model for the IP Flow Information Export
(IPFIX) and Packet Sampling (PSAMP) Protocols [RFC6728].
3.2. Standard Extension YANG Model
Standard Extension is the conditional portion of a Standard YANG
Model, expressed with the feature, if-feature, augment YANG
statements [RFC6020]. An example of such standard extension is
policy based routing (PBR). PBR is found in many vendor
implementations and have many common features, but not all vendors
support PBR on all of their devices.
3.3. Proprietary Extension to Standard YANG Model
Proprietary extension is a conditional portion of a Standard YANG
Model, expressed with feature, if-feature, augment YANG statements
[RFC6020]. Proprietary extensions are required as the Standard YANG
model will not cover all the possible configuration parameters of the
different vendors. Proprietary extension can be a feature depending
on hardware platform capabilities and it is not available by other
vendors. Such an example could be match condition for packet
classification used for PBR.
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3.4. Vendor configuration model
Base model for all other models is the vendor configuration model.
It describes all configurable capabilities of the device and what
device vendor exposes for configuration.
The standard configuration model is a subset of vendor configuration
model. The standard configuration model can be broken into base
model and standard extension models, where the base is common data
model and standard extensions are standard features that are not
implemented by all vendors. Example of standard base model is Access
Control List and routing filter is a standard extension on ACL. Or
another example: encryption algorithm is standard feature, but the
different types, like md5, hmac-md5, hmac-sha1, etc are standard
extensions, as it is not that all vendors have all encryption
algorithm types implemented.
Although all vendors provide very similar functionality using
standards, implementations are different. One of basic examples are
dynamic routing protocols. We can see today two main types of
routing protocol configuration.
protocol centric - all the protocol related config is contained
with the protocol itself. Especially in case of multiple
instances of the routing protocol running in different routing-
instances (routing-instance as described in core routing model
[I-D.ietf-netmod-routing-cfg]), all the routing-instance protocol
config is contained in the default routing instance.
Router ospf 10
Default-metric 100
Address-family ipv4 vrf VRF1
Network x.x.x.x area 0
Address-family ipv4 vrf VRF2
Network x.x.x.x area 0
Address-family ipv4
Network x.x.x.x area 1
In term of YANG model, the routing protocol configuration will be
defined within the default routing-instance and the routing-
protocol config will contain multiple instances referring to other
routing-instances.
VRF centric - All the protocol related config for a routing-
instance is contained within this routing-instance.
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Routing-instance VRF1 {
Protocols isis {
}
}
Routing-instance VRF2 {
Protocols isis {
}
}
In terms of YANG model, the routing protocol configuration for a
routing-instance will be defined within the associated routing-
instance.
The bottom line message is that, even if YANG models are
standardized, they will provide different CLI outcomes, simply
because the CLI among vendors is not standardized.
3.5. Proprietary YANG Model
While waiting for the Standard YANG Models to be published, the
different vendors might offer Proprietary YANG Models.
4. Typical Architecture
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+--------------------------------------------------------+
| OSS/BSS |
+--------------------------------------------------------+
+--------------------------------------------------------+
| Orchestrator |
| +------------------------------------------------+ |
| | network service model | |
| | | |
| +------------------------------------------------+ |
+--------------------------------------------------------+
+--------------------------------------------------------+
| Network element |
| | |
| +-----------------------+ | +-------------------+ |
| | Standard YANG model | | | Proprietary | |
| | | | | YANG model | |
| +-----------------------+ | | | |
| | | | |
| +-----------------------+ | | | |
| | Proprietary Extension | | | | |
| | To YANG Standard | | | | |
| | Model | | | | |
| +-----------------------+ | +-------------------+ |
| | |
| +-------------------------------------------------+ |
| | Vendor Configuration Model | |
| +-------------------------------------------------+ |
+--------------------------------------------------------+
Fig. 2 Typical Architecture
The OSS/BSS may contains business related models. Those models,
which may or may not be written in YANG, are outside the scope of the
IETF work
5. IETF, Other SDOs, and open source
IETF, as a standard defining organization (SDO), is well positioned
to standardize Network Element YANG models. With a wide range of
expertise found within its working groups focused on those technology
definitions. As IETF participants implement those protocols, they
have deep expertise about the implementation and finding a common
base standard configuration model between vendors should be a very
viable goal.
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In some situation where the protocols are standardized by different
SDOs, those SDOs should be responsible for its YANG data modeling
effort. For example, the IETF has transferred the responsibility for
some IEEE technology-related MIB modules to the IEEE 802.1 and 802.3
Working Group [RFC4663], [RFC7448]. Similarly, the IEEE should be
responsible for similar YANG data modeling efforts.
Developing Network Service YANG Models requires network operations
expertise. When those operators participate in IETF work, the right
working group can be formed, and those Service YANG Models can be
developed within IETF. However, some other groups, like Metro
Ethernet Forum or CableLabs, could be better positioned for service
modeling related to their area of expertise.
Today there are many open source projects and some of them are
becoming de facto standards, like the Linux kernel. Many such open
source projects, like Open Daylight, OpenStack, etc, are doing very
good work and their work is being accepted and deployed in production
environments. They bring a lot of very valuable experience to other
groups. From IETF perspective, if there is such a work present, it
can be used as a very good starting point for modeling within IETF.
6. Security Considerations
At this stage, authors of the draft didn't look into security
considerations.
7. IANA Considerations
This document requests no action by IANA.
8. Acknowledgements
Thanks to David Ball for his enlightenments on Metro Ethernet Forum
service aspects.
9. 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
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10. References
10.1. Normative References
[RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the
Network Configuration Protocol (NETCONF)", RFC 6020,
October 2010.
10.2. Informative References
[I-D.ietf-isis-yang-isis-cfg]
Litkowski, S., Yeung, D., Lindem, A., Zhang, J., and L.
Lhotka, "YANG Data Model for ISIS protocol", draft-ietf-
isis-yang-isis-cfg-01 (work in progress), October 2014.
[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-01 (work in progress),
February 2015.
[I-D.ietf-netmod-routing-cfg]
Lhotka, L., "A YANG Data Model for Routing Management",
draft-ietf-netmod-routing-cfg-16 (work in progress),
October 2014.
[I-D.ietf-ospf-yang]
Yeung, D., Qu, Y., Zhang, J., Bogdanovic, D., and K.
Sreenivasa, "Yang Data Model for OSPF Protocol", draft-
ietf-ospf-yang-00 (work in progress), March 2015.
[RFC4663] Harrington, D., "Transferring MIB Work from IETF Bridge
MIB WG to IEEE 802.1 WG", RFC 4663, September 2006.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
Bierman, "Network Configuration Protocol (NETCONF)", RFC
6241, June 2011.
[RFC6728] Muenz, G., Claise, B., and P. Aitken, "Configuration Data
Model for the IP Flow Information Export (IPFIX) and
Packet Sampling (PSAMP) Protocols", RFC 6728, October
2012.
[RFC7223] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 7223, May 2014.
[RFC7448] Taylor, T. and D. Romascanu, "MIB Transfer from the IETF
to the IEEE 802.3 WG", RFC 7448, February 2015.
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[Writable-MIB-Module-IESG-Statement]
"Writable MIB Module IESG Statement", <https://www.ietf
.org/iesg/statement/writable-mib-module.html>.
Authors' Addresses
Dean Bogdanovic
Juniper Networks
Email: deanb@juniper.net
Benoit Claise
Cisco Systmes, Inc.
Email: bclaise@cisco.com
Carl Moberg
Cisco Systmes, Inc.
Email: camoberg@cisco.com
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