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YANG model classification
draft-bogdanovic-netmod-yang-model-classification-01

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This is an older version of an Internet-Draft whose latest revision state is "Replaced".
Authors Dean Bogdanović , Benoît Claise , Carl Moberg
Last updated 2015-03-09
Replaced by draft-ietf-netmod-yang-model-classification, draft-ietf-netmod-yang-model-classification, RFC 8199
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draft-bogdanovic-netmod-yang-model-classification-01
NETMOD                                                     D. Bogdanovic
Internet-Draft                                          Juniper Networks
Intended status: Informational                                 B. Claise
Expires: September 10, 2015                                    C. Moberg
                                                     Cisco Systmes, Inc.
                                                          March 09, 2015

                       YANG model classification
          draft-bogdanovic-netmod-yang-model-classification-01

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
   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 September 10, 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
   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.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   2
   3.  First Dimension: Network YANG Data Model Layering . . . . . .   3
     3.1.  Network Service YANG Data Models  . . . . . . . . . . . .   4
     3.2.  Network Element YANG Data models  . . . . . . . . . . . .   5
   4.  Second Dimension: Model Type  . . . . . . . . . . . . . . . .   5
     4.1.  Standard YANG model . . . . . . . . . . . . . . . . . . .   6
     4.2.  Standard Extension YANG Model . . . . . . . . . . . . . .   6
     4.3.  Proprietary Extension to Standard YANG Model  . . . . . .   6
     4.4.  Vendor configuration model  . . . . . . . . . . . . . . .   7
     4.5.  Proprietary YANG Model  . . . . . . . . . . . . . . . . .   8
   5.  Typical Architecture  . . . . . . . . . . . . . . . . . . . .   8
   6.  IETF, Other SDOs, and open source . . . . . . . . . . . . . .   9
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   10. Change log [RFC Editor: Please remove]  . . . . . . . . . . .  10
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     11.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   With more and more data models being described with YANG [RFC6020], a
   taxonomy for the models is needed.  In this draft, authors try to
   propose a taxonomy for YANG models.

2.  Problem Statement

   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 are
   proposing a new way for YANG model classifications.

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   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].

   YANG Models can 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.

3.  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 modeling, but it
   would be useful to have a classification and 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:

      Network Service YANG Model

      Network Element YANG Model

   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
   protocol and feature YANG models.

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                       +-----------------------+
                         |                       |
                         |        OSS/BSS        |
                         |                       |
                         +-----------------------+

      Network Service YANG data models -------------------------------

                  +------------+      +-------------+
                  |            |      |             |
                  |  - VPWS    |      |   - VPLS    |
                  |  - L2VPN   |      |   - L2VPN   |
                  |            |      |             |
                  +------------+      +-------------+

      Network Element YANG data models ---------------------------------

    +------------+    +------------+   +--------------+  +-----------+
    |            |    |            |   |              |  |           |
    |     MPLS   |    |    BGP     |   |  Interface   |  |  Routing  |
    |            |    |            |   |              |  |           |
    +------------+    +------------+   +--------------+  +-----------+

3.1.  Network Service YANG Data Models

   Network Service YANG models are created by network operators when
   they choose how to configure their network from technology point of
   view.  They decide which technology is best match for their business
   needs and based on that create network service data models.  With
   more and more configuration models being available, both vendor and
   standards one, network service model developer can create reusable
   components based on the configuration models, and use those service
   components data models to create end to end service model.

   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 elementlayer 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 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.

3.2.  Network Element YANG Data models

   This is base model for all higher models.  It fully describes
   protocol, such as OSPF [I-D.yeung-netmod-ospf], ISIS
   [I-D.ietf-isis-yang-isis-cfg] or feature, example access control list
   [I-D.ietf-netmod-acl-model].  The base model can be either vendor
   specific, which then describes vendor implementation of the protocol
   or feature or standard model.  Key difference between those two is
   what is implemented.  Vendor device model will always describe what
   is implemented, which can ber more or even less then in standard
   model.  Standard model describes what is agreed in the industry to be
   accepted as base description.

4.  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 ITU, 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:

      Standard Extension 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.

      Vendor Configuration Model: It describes all configurable
      capabilities of the device and what device vendor exposes for

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      configuration.  The vendor configuration model can be CLI or YANG-
      based.

      Proprietary YANG Model: A non Standard YANG Model.

   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.

4.1.  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.  For example, A YANG Data Model for Interface
   Management [RFC7223], or the Configuration Data Model for the IP Flow
   Information Export (IPFIX) and Packet Sampling (PSAMP) Protocols
   [RFC6728].

4.2.  Standard Extension YANG Model

   Standard Extension is a 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.

4.3.  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 extension can be a feature depending on
   harward 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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4.4.  Vendor configuration model

   Base model for all other models is the vendor configuration model.
   It describes all configurable capabalities 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 term 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.

4.5.  Proprietary YANG Model

   While waiting for the Standard YANG Models to be published, the
   different vendors might offer Proprietary YANG Models.

5.  Typical Architecture

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          +--------------------------------------------------------+
          |                      OSS/BSS                           |
          +--------------------------------------------------------+

          +--------------------------------------------------------+
          | Orchestrator                                           |
          |   +------------------------------------------------+   |
          |   | network service model                          |   |
          |   | +-------------------+   +-------------------+  |   |
          |   | | Service Component |   | Service Component |  |   |
          |   | | Model             |   | Model             |  |   |
          |   | |                   |   |                   |  |   |
          |   | +-------------------+   +-------------------+  |   |
          |   +------------------------------------------------+   |
              +--------------------------------------------------------+

              +--------------------------------------------------------+
          | Network element                                        |
          |                             |                          |
          |  +-----------------------+  |  +-------------------+   |
          |  | Standard YANG model   |  |  |   Proprietary     |   |
          |  |                       |  |  |   YANG model      |   |
              |  +-----------------------+  |  |                   |   |
          |                             |  |                   |   |
          |  +-----------------------+  |  |                   |   |
          |  | Proprietary Extension |  |  |                   |   |
          |  | To YANG Standard      |  |  |                   |   |
          |  | Model                 |  |  |                   |   |
          |  +-----------------------+  |  +-------------------+   |
          |                             |                          |
          |  +-------------------------------------------------+   |
          |  |          Vendor Configuration Model             |   |
          |  +-------------------------------------------------+   |
          +--------------------------------------------------------+

6.  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 WGs 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.

   In some situation where the protocols are standardized by different
   SDOs, those SDOs should be responsible for its YANG data modeling

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   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.

   Although many network operators participate in IETF work, developing
   higher level models requires network operations expertise.  If such
   teams within right WG can be formed, then some service models can be
   developed within IETF, but some groups, like Metro Ethernet Forum or
   CableLabs could be better positioned for service modeling.

   Today there are many open source projects and some of them are
   becoming de facto standards, like the Linux kernel.  Many such open
   source projecs, 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.

7.  Security Considerations

   At this stage, authors of the draft didn't look into security
   considerations.

8.  IANA Considerations

   This document requests no action by IANA.

9.  Acknowledgements

   Thanks to David Ball for his enlightenments on Metro Ethernet Forum
   service aspects.

10.  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.

11.  References

11.1.  Normative References

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

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11.2.  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.yeung-netmod-ospf]
              Yeung, D., Qu, Y., Zhang, J., Bogdanovic, D., and K.
              Sreenivasa, "Yang Data Model for OSPF Protocol", draft-
              yeung-netmod-ospf-02 (work in progress), October 2014.

   [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.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, June 2011.

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536, March
              2012.

   [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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