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Network Working Group                                     A. Lindem, Ed.
Internet-Draft                                             Cisco Systems
Intended status: Informational                            L. Berger, Ed.
Expires: August 26, 2016                         LabN Consulting, L.L.C.
                                                           D. Bogdanovic

                                                                C. Hopps
                                                        Deutsche Telekom
                                                       February 23, 2016


               Network Device YANG Organizational Models
                 draft-rtgyangdt-rtgwg-device-model-03

Abstract

   This document presents an approach for organizing YANG models in a
   comprehensive structure that may be used to configure and operate
   network devices.  The structure is itself represented as a YANG
   model, with all of the related component models logically organized
   in a way that is operationally intuitive, but this model is not
   expected to be implemented.  The identified component modules are
   expected to be defined and implemented on common network devices.

   This document also defines two modules that can be used to model the
   logical and virtual resource representations that may be present on a
   network device.  Examples of common industry terms for logical
   resource representations are Logical Systems or Routers.  Examples of
   of common industry terms for virtual resource representations are
   Virtual Routing and Forwarding (VRF) instances and Virtual Switch
   Instances (VSIs).

   This document is derived from work submitted to the IETF by members
   of the informal OpenConfig working group of network operators and is
   a product of the Routing Area YANG Architecture design team.

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



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   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 August 26, 2016.

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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Status of Work and Open Issues  . . . . . . . . . . . . .   4
   2.  Module Overview . . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Interface Model Components  . . . . . . . . . . . . . . .   8
     2.2.  System Management . . . . . . . . . . . . . . . . . . . .  10
     2.3.  Network Services  . . . . . . . . . . . . . . . . . . . .  10
     2.4.  OAM Protocols . . . . . . . . . . . . . . . . . . . . . .  11
     2.5.  Routing . . . . . . . . . . . . . . . . . . . . . . . . .  11
     2.6.  MPLS  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   3.  Logical Network Elements  . . . . . . . . . . . . . . . . . .  13
     3.1.  LNE Management - Host Network Device View . . . . . . . .  14
     3.2.  LNE Management - LNE View . . . . . . . . . . . . . . . .  15
     3.3.  LNE Instantiation . . . . . . . . . . . . . . . . . . . .  16
   4.  Network Instances . . . . . . . . . . . . . . . . . . . . . .  16
     4.1.  Network Instance Policy . . . . . . . . . . . . . . . . .  17
     4.2.  Network Instance Management . . . . . . . . . . . . . . .  17
     4.3.  Network Instance Instantiation  . . . . . . . . . . . . .  18
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   7.  YANG Modules  . . . . . . . . . . . . . . . . . . . . . . . .  18
     7.1.  Network Device Model Structure  . . . . . . . . . . . . .  18
     7.2.  Logical Network Element Model . . . . . . . . . . . . . .  25
     7.3.  Network Instance Model  . . . . . . . . . . . . . . . . .  27
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  32
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  32
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  33



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   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  34
   Appendix B.  Contributors . . . . . . . . . . . . . . . . . . . .  35
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  36

1.  Introduction

   "Operational Structure and Organization of YANG Models" [OC-STRUCT],
   highlights the value of organizing individual, self-standing YANG
   [RFC6020] models into a more comprehensive structure.  This document
   builds on that work and presents a derivative structure for use in
   representing the networking infrastructure aspects of physical and
   virtual devices.  [OC-STRUCT] and earlier versions of this document
   presented a single device-centric model root, this document no longer
   contains this element.  Such an element would have translated to a
   single device management model that would be the root of all other
   models and was judged to be overly restrictive in terms of
   definition, implementation, and operation.

   The document first presents a notional network device YANG
   organizational structure that provides a conceptual framework for the
   models that may be used to configure and operate network devices.
   The structure is itself presented as a YANG module, with all of the
   related component modules logically organized in a way that is
   operationally intuitive.  This network device model is not expected
   to be implemented, but rather provide as context for the identified
   representative component modules with are expected to be defined, and
   supported on typical network devices.

   This document also defines two new modules that are expected to be
   implemented.  These models are defined to support the configuration
   and operation of network-devices that allow for the partitioning of
   resources from both, or either, management and networking
   perspectives.  Both make use of emerging YANG functionality supported
   by either structural mount [STRUCTURAL-MOUNT]  or YANG Schema
   Dispatching Language (YSDL) [YANG-YSDL].  The function provided by
   these documents are collectively refered to as "Schema Mount".  This
   document is expected to use whatever Schema Mount solution is adopted
   by the Netmod Working Group.

   Two forms of resource partitioning are supported:

   The first form provides a logical partitioning of a network device
   where each partition is separately managed as essentially an
   independent network element which is 'hosted' by the base network
   device.  These hosted network elements are referred to as logical
   network elements, or LNEs, and are supported by the logical-network-
   element module defined below.  The module is used to identify LNEs
   and associate resources from the network-device with each LNE.  LNEs



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   themselves are represented in YANG as independent network devices;
   each accessed independently.  Optionally, and when supported by the
   implementation, they may also be accessed from the host system.
   Examples of vendor terminology for an LNE include logical system or
   router, and virtual switch, chassis, or fabric.

   The second form provides support what is commonly referred to as
   Virtual Routing and Forwarding (VRF) instances as well as Virtual
   Switch Instances (VSI), see [RFC4026].  In this form of resource
   partitioning multiple control plane and forwarding/bridging instances
   are provided by and managed via a single (physical or logical)
   network device.  This form of resource partitioning is referred to as
   Network Instances and are supported by the network-instance module
   defined below.  Configuration and operation of each network-instance
   is always via the network device and the network-instance module.

   This document was motivated by, and derived from, [OC-STRUCT].  The
   requirements from that document have been combined with the
   requirements from "Consistent Modeling of Operational State Data in
   YANG", [OC-OPSTATE], into "NETMOD Operational State Requirements",
   [NETMOD-OPSTATE].  This document is aimed at the requirement related
   to a common model-structure, currently Requirement 7, and also aims
   to provide a modeling base for Operational State representation.

   The approach taken in this (and the original) document is to organize
   the models describing various aspects of network infrastructure,
   focusing on devices, their subsystems, and relevant protocols
   operating at the link and network layers.  The proposal does not
   consider a common model for higher level network services.  We focus
   on the set of models that are commonly used by network operators, and
   suggest a corresponding organization.

   A significant portion of the text and model contained in this
   document was taken from the -00 of [OC-STRUCT].

1.1.  Status of Work and Open Issues

   This version of the document and structure are a product of the
   Routing Area YANG Architecture design team and is very much a work in
   progress rather than a final proposal.  This version is a major
   change from the prior version and this change was enabled by the work
   on the previously mentioned Schema Mount.

   Schema Mount enables a dramatic simplification of the presented
   device model, particularly for "lower-end" devices which are unlikely
   to support multiple network instances or logical network elements.
   Should structural-mount/YSDL not be available, the more explicit tree




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   structure presented in earlier versions of this document will need to
   be utilized.

   The top open issues are:

   1.  The use of YSDL vs Structural Mount, i.e., a Netmod defined
       Schema Mount solution, needs to be resolved as does ensuring that
       the selected approach has the needed capabilities.

   2.  This document will need to match the evolution and
       standardization of [OC-OPSTATE] or [NETMOD-OPSTATE] by the Netmod
       WG.

   3.  Interpretation of different policy containers requires
       clarification.

   4.  It may make sense to use the identityref structuring with
       hardware and QoS model.

   5.  Which document(s) define the base System management, network
       services, and oam protocols modules is TBD.  This includes the
       possibility of simply using RFC7317 in place of the presented
       System management module.

   6.  The model will be updated once the "opstate" requirements are
       addressed.

   7.  It may make sense to publish the network-instance and logical-
       network-element modules separately, as different devices may not
       implement both, and network providers may only require one or the
       other.

2.  Module Overview

   In this document, we consider network devices that support protocols
   and functions defined within the IETF Routing Area, e.g, routers,
   firewalls and hosts.  Such devices may be physical or virtual, e.g.,
   a classic router with custom hardware or one residing within a
   server-based virtual machine implementing a virtual network function
   (VNF).  Each device may sub-divide their resources into logical
   network elements (LNEs) each of which provides a managed logical
   device.  Examples of vendor terminology for an LNE include logical
   system or router, and virtual switch, chassis, or fabric.  Each LNE
   may also support virtual routing and forwarding (VRF) and virtual
   switching instance (VSI) functions, which are referred to below as a
   network instances (NIs).  This breakdown is represented in Figure 1.





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              ,''''''''''''''''''''''''''''''''''''''''''''''`.
              |      Network Device (Physical or Virtual)     |
              | .....................   ..................... |
              | :  Logical Network  :   :  Logical Network  : |
              | :      Element      :   :      Element      : |
              | :+-----+-----+-----+:   :+-----+-----+-----+: |
              | :| Net | Net | Net |:   :| Net | Net | Net |: |
              | :|Inst.|Inst.|Inst.|:   :|Inst.|Inst.|Inst.|: |
              | :+-----+-----+-----+:   :+-----+-----+-----+: |
              | :  | |   | |   | |  :   :  | |   | |   | |  : |
              | :..|.|...|.|...|.|..:   :..|.|...|.|...|.|..: |
              |    | |   | |   | |         | |   | |   | |    |
               `'''|'|'''|'|'''|'|'''''''''|'|'''|'|'''|'|'''''
                   | |   | |   | |         | |   | |   | |
                      Interfaces              Interfaces

   Figure 1: Module Element Relationships

   A model for LNEs is described in Section 3 and the model for network
   instances is covered in Section 4.

   The presented notional network device module can itself be thought of
   as a "meta-model" as it describes the relationships between
   individual models.  We choose to represent it also as a simple YANG
   module consisting of other models, which are in fact independent top
   level individual models.  Although it is never expected to be
   implemented.

   The presented modules do not follow the hierarchy of any particular
   implementation, and hence is vendor-neutral.  Nevertheless, the
   structure should be familiar to network operators and also readily
   mapped to vendor implementations.

   The overall structure is:

















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       module: network-device
          +--rw ietf-yang-library
          |
          +--rw interfaces
          +--rw hardware
          +--rw qos
          |
          +--rw system-management
          +--rw network-services
          +--rw oam-protocols
          |
          +--rw routing
          +--rw mpls
          +--rw ieee-dot1Q
          |
          +--rw ietf-acl
          +--rw ietf-key-chain
          |
          +--rw logical-network-element
          +--rw network-instance

   The network device is composed of top level modules that can be used
   to configure and operate a network device.  (This is a significant
   difference from earlier versions of this document where there was a
   strict model hierarchy.)  Importantly the network device structure is
   the same for a physical network device or a logical network device,
   such as those instantiated via the logical-network-element model.
   Extra spacing is included to denote different types of modules
   included.

   YANG library [YANG-LIBRARY] is included as it used to identify
   details of the top level modules supported by the (physical or
   logical) network device.  Th ability to identify supported modules is
   particularly important for LNEs which may have a set of supported
   modules which differs from the set supported by the host network
   device.

   The interface management model [RFC7223] is included at the top
   level.  The hardware module is a placeholder for a future device-
   specific configuration and operational state data model.  For
   example, a common structure for the hardware model might include
   chassis, line cards, and ports, but we leave this unspecified.  The
   quality of service (QoS) section is also a placeholder module for
   device configuration and operational state data which relates to the
   treatment of traffic across the device.  This document defines
   augmentations to the interface module to support LNEs and NIs.
   Similar elements, although perhaps only for LNEs, may also need to be




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   included as part of the definition of the future hardware and QoS
   modules.

   System management, network services, and oam protocols represent new
   top level modules that are used to organize data models of similar
   functions.  Additional information on each is provided below.

   The routing and MPLS modules provide core support for the
   configuration and operation of a devices control plane and data plane
   functions.  IEEE dot1Q [IEEE-8021Q] is an example of another module
   that provides similar functions for VLAN bridging, and other similar
   modules are also possible.  Each of these modules is expected to be
   LNE and NI unaware, and to be instantiated as needed as part of the
   LNE and NI configuration and operation supported by the logical-
   network-element and network-instance modules.  (Note that this is a
   change from [RTG-CFG] which is currently defined with VRF/NI
   semantics.)

   The access control list (ACL) and key chain modules are included as
   examples of other top level modules that may be supported by a
   network device.

   The logical network element and network instance modules enable LNEs
   and NIs respectively and are defined below.

2.1.  Interface Model Components

   Interfaces are a crucial part of any network device's configuration
   and operational state.  They generally include a combination of raw
   physical interfaces, link-layer interfaces, addressing configuration,
   and logical interfaces that may not be tied to any physical
   interface.  Several system services, and layer 2 and layer 3
   protocols may also associate configuration or operational state data
   with different types of interfaces (these relationships are not shown
   for simplicity).  The interface management model is defined by
   [RFC7223].

   The logical-network-element and network-instance modules defined in
   this document augment the existing interface management model in two
   ways: The first, by the logical-network-element module, adds an
   identifier which is used on physical interface types to identify an
   associated LNE.  The second, by the network-instance module, adds a
   name which is used on sub-interface types to identify an associated
   network instance.  Similarly, this name is also added for IPv4 and
   IPv6 types, as defined in [RFC7277].

   The interface related augmentations are as follows:




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       augment /if:interfaces/if:interface:
          +--rw bind-lne-name?   string

       augment /if:interfaces/if:interface:
          +--rw bind-network-instance-name?   string
       augment /if:interfaces/if:interface/ip:ipv4:
          +--rw bind-network-instance-name?   string
       augment /if:interfaces/if:interface/ip:ipv6:
          +--rw bind-network-instance-name?   string

   The following is an example of envisioned combined usage.  The
   interfaces container includes a number of commonly used components as
   examples:

             +--rw interfaces
             |  +--rw interface* [name]
             |     +--rw name                       string
             |     +--rw bind-lne-name?             string
             |     +--rw ethernet
             |     |  +--rw bind-network-instance-name?   string
             |     |  +--rw aggregates
             |     |  +--rw rstp
             |     |  +--rw lldp
             |     |  +--rw ptp
             |     +--rw vlans
             |     +--rw tunnels
             |     +--rw ipv4
             |     |  +--rw bind-network-instance-name?   string
             |     |  +--rw arp
             |     |  +--rw icmp
             |     |  +--rw vrrp
             |     |  +--rw dhcp-client
             |     +--rw ipv6
             |        +--rw bind-network-instance-name?   string
             |        +--rw vrrp
             |        +--rw icmpv6
             |        +--rw nd
             |        +--rw dhcpv6-client

   The [RFC7223] defined interface model is structured to include all
   interfaces in a flat list, without regard to logical or virtual
   instances (e.g., VRFs) supported on the device.  The bind-lne-name
   and bind-network-instance-name leaves provide the association between
   an interface and its associated LNE and NI (e.g., VRF or VSI).







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2.2.  System Management

   [Editor's note: need to discuss and resolve relationship between this
   structure and RFC7317 and determine if 7317 is close enough to simply
   use as is.]

   System management is expected to reuse definitions contained in
   [RFC7317].  It is expected to be instantiated per device and LNE.
   Its structure is shown below:

       module: network-device
          +--rw system-management
          |  +--rw system-management-global
          |  +--rw system-management-protocol* [type]
          |     +--rw type    identityref

   System-management-global is used for configuration information and
   state that is independent of a particular management protocol.
   System-management-protocol is a list of management protocol specific
   elements.  The type-specific sub-modules are expected to be defined.

   The following is an example of envisioned usage:

       module: network-device
          +--rw system-management
             +--rw system-management-global
             |  +--rw statistics-collection
             |  ...
             +--rw system-management-protocol* [type]
             |  +--rw type=syslog
             |  +--rw type=dns
             |  +--rw type=ntp
             |  +--rw type=ssh
             |  +--rw type=tacacs
             |  +--rw type=snmp
             |  +--rw type=netconf


2.3.  Network Services

   A device may provide different network services to other devices, for
   example a device my act as a DHCP server.  The model may be
   instantiated per device, LNE, and NI.  An identityref is used to
   identify the type of specific service being provided and its
   associated configuration and state information.  The defined
   structure is as follows:





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       module: network-device
          +--rw network-services
          |  +--rw network-service* [type]
          |     +--rw type    identityref

   The following is an example of envisioned usage: Examples shown below
   include a device-based Network Time Protocol (NTP) server, a Domain
   Name System (DNS) server, and a Dynamic Host Configuration Protocol
   (DHCP) server:

       module: network-device
          +--rw network-services
             +--rw network-service* [type]
                +--rw type=ntp-server
                +--rw type=dns-server
                +--rw type=dhcp-server

2.4.  OAM Protocols

   OAM protocols that may run within the context of a device are grouped
   within the oam-protocols model.  The model may be instantiated per
   device, LNE, and NI.  An identifyref is used to identify the
   information and state that may relate to a specific OAM protocol.
   The defined structure is as follows:

       module: network-device
          +--rw oam-protocols
             +--rw oam-protocol* [type]
                +--rw type    identityref


   The following is an example of envisioned usage.  Examples shown
   below include Bi-directional Forwarding Detection (BFD), Ethernet
   Connectivity Fault Management (CFM), and Two-Way Active Measurement
   Protocol (TWAMP):

       module: network-device
          +--rw oam-protocols
             +--rw oam-protocol* [type]
                +--rw type=bfd
                +--rw type=cfm
                +--rw type=twamp

2.5.  Routing

   Routing protocol and IP forwarding configuration and operation
   information is modeled via a routing model, such as the one defined
   in [RTG-CFG].  Although, the defined routing module includes support



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   for NIs, which it refers to as Routing Instances, while the approach
   presented in this document presumes that the routing module is
   unaware of LNEs and NIs.

   The routing module is expected to include all IETF defined control
   plane protocols, such as BGP, OSPF, LDP and RSVP-TE.  It is also
   expected to support configuration and operation of or more routing
   information bases (RIB).  A RIB is a list of routes complemented with
   administrative data.  Finally, policy is expected to be represented
   within each control plane protocol and RIB.

   The anticipated structure is as follows:

      module: network-device
          +--rw routing
             +--rw control-plane-protocols
             |  +--rw control-plane-protocol* [type]
             |     +--rw type      identityref
             |     +--rw policy
             +--rw ribs
                +--rw rib* [name]
                   +--rw name           string
                   +--rw description?   string
                   +--rw policy

2.6.  MPLS

   MPLS data plane related information is grouped together, as with the
   previously discussed modules, is unaware of VRFs/NIs.  The model may
   be instantiated per device, LNE, and NI.  MPLS control plane
   protocols are expected to be included in Section 2.5.  MPLS may reuse
   and build on [OC-MPLS] or other emerging models and has an
   anticipated structure as follows:

     module: network-device
          +--rw mpls
             +--rw global
             +--rw lsps* [type]
                +--rw type    identityref

   Type refers to LSP type, such as static, traffic engineered or
   routing congruent.  The following is an example of such usage:









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     module: network-device
          +--rw mpls
             +--rw global
             +--rw lsps* [type]
                 +--rw type=static
                 +--rw type=constrained-paths
                 +--rw type=igp-congruent

3.  Logical Network Elements

   A logical network element is a network-device which is contained
   within another network-device.  Using host-virtualization terminology
   one could refer to an LNE as a "Guest", and the containing network-
   device as the "Host".  While LNEs may be implemented via host-
   virtualization technologies this is not a requirement.

   Logical network elements represent the capability of some devices to
   partition resources into independent logical routers and/or switches.
   Device support for multiple logical network elements is
   implementation specific.  Systems without such capabilities need not
   include support for the logical-network-element module.  In physical
   devices, some hardware features are shared across partitions, but
   control plane (e.g., routing) protocol instances, tables, and
   configuration are managed separately.  For example, in virtual
   routers or VNFs, this may correspond to establishing multiple logical
   instances using a single software installation.  The model supports
   configuration of multiple instances on a single device by creating a
   list of logical network elements, each with their own configuration
   and operational state related to routing and switching protocols, as
   shown below:

       module: logical-network-element
          +--rw logical-network-inventory
             +--rw logical-network-element* [name]
                +--rw name?   string
                +--rw description? string
                +--rw managed?     boolean
                +--rw root?        schema-mount
       augment /if:interfaces/if:interface:
          +--rw bind-lne-name?     string

   `name` identifies the logical network element.  `managed` indicates
   if the host network device is able to manage the LNE via the `root`
   structure.







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3.1.  LNE Management - Host Network Device View

   There are multiple implementation approaches possible to enable a
   network device to support the logical-network-element module and
   multiple LNEs.  Some approaches will allow the management functions
   operating at network device level to access LNE configuration and
   operation information, while others will not.  Similarly, even when
   LNE management from the network device is supported by the
   implementation, it may be prohibited by user policy.

   The `managed` boolean mentioned above is used to indicate when LNE
   management from the network device context is possible.  When the
   `managed` is `false`, the LNE cannot be managed by the host system
   and can only be managed from within the context of the LNE as
   described in the next section, Section 3.2.

   When `managed` is `true`, the LNE can be managed from both the
   context of the LNE and the host network device.  In this case, the
   same information that is available from within the LNE context is
   made available via the `root` element, with paths modified as
   described in [STRUCTURAL-MOUNT].

   As an example, consider the case where an LNE with a `name` of "one"
   is defined on a network device.  In this case the following structure
   might be made available:


























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    .................................................................
                                             [ network-device state ]
       module: logical-network-element
          +--rw logical-network-inventory
             +--rw logical-network-element* [name]
                +--rw name="one"          string
                +--rw manged=true         boolean
                +--rw root                schema-mount

    .................................................................
                               [ LNE state exposed to network-device]

                   +--rw ietf-yang-library
                   +--rw interfaces
                   +--rw hardware
                   +--rw qos
                   +--rw system-management
                   +--rw network-services
                   +--rw oam-protocols
                   +--rw routing
                   +--rw mpls
                   +--rw ieee-dot1Q
                   +--rw network-instance
    .................................................................

   As an LNE is a network device itself, all modules that may be present
   at the top level network device may also be present for the LNE, be
   made available under `root`, and be accessible via paths modified per
   [STRUCTURAL-MOUNT].  The list of available modules is expected to be
   implementation dependent.  As is the method used by an implementation
   to support LNEs.

   Resources assigned to the LNE will be represented in that LNE's
   resource modules. e.g., an LNE's interfaces module will contain the
   interfaces assigned to that LNE from the containing network-device.

3.2.  LNE Management - LNE View

   Management functions operating with the context of an LNE are
   accessed through standard LNE's management interfaces, e.g., NETCONF
   and SNMP.  When accessing an LNE via an LNE's management interface, a
   network-device representation will be presented, but its scope will
   be limited to the specific LNE.  Normal YANG/NETCONF mechanisms,
   together with ietf-yang-library, can be used to identify the
   available modules.  Each supported module will be presented as a top
   level module.  Only LNE associated resources will be reflected in
   resource related modules, e.g., interfaces, hardware and perhaps QoS.
   From the management perspective, there will be no difference between



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   the available LNE view (information) and an a physical network
   device.

   Multiple implementation approaches are possible to provide LNE views,
   and these are outside the scope of this document.

3.3.  LNE Instantiation

   TBD -- need to resolve if instantiation is based on new list entry
   creation per the pending Schema Mount solution definition.

4.  Network Instances

   The network instance container is used to represent virtual routing
   and forwarding instances (VRFs) and virtual switching instances
   (VSIs), [RFC4026].  VRFs and VSIs are commonly used to isolate
   routing and switching domains, for example to create virtual private
   networks, each with their own active protocols and routing/switching
   policies.  The model represents both core/provider and virtual
   instances.  Network instances reuse and build on [RTG-CFG] and are
   shown below:

       module: network-instance
          +--rw network-instances
             +--rw network-instance* [name]
                +--rw name                         string
                +--rw type?                        identityref
                +--rw enabled?                     boolean
                +--rw description?                 string
                +--rw network-instance-policy
                |  ...
                +--rw root?                      schema-mount
                |  ...
       augment /if:interfaces/if:interface:
          +--rw bind-network-instance-name?   string
       augment /if:interfaces/if:interface/ip:ipv4:
          +--rw bind-network-instance-name?   string
       augment /if:interfaces/if:interface/ip:ipv6:
          +--rw bind-network-instance-name?   string

   A network instance is identified by a `name` string.  This string is
   used both as an index within the network-instance module and to
   associate resources with a network instance is shown above in the
   interface augmentation.  Type is used to indicate the type NI, such
   as L3-VRF, VPLS, L2-VSI, etc.  Network instance policy and root are
   discussed in greater detail below.





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4.1.  Network Instance Policy

   Network instance policies are used to control how NI information is
   represented at the device level, VRF routing policies, and VRF/VSI
   identifiers.  Examples include BGP route targets (RTs) and route
   distinguishers (RDs), virtual network identifiers (VN-IDs), VPLS
   neighbors, etc.  The structure is expected to be:

       module: network-instance
          +--rw network-instances
             +--rw network-instance* [name]
                +--rw network-instance-policy
                   (TBD)

4.2.  Network Instance Management

   Modules that may be used to represent network instance specific
   information will be available under `root`.  As with LNEs, actual
   module availability is expected to be implementation dependent.  The
   ietf-yang-library module is expected to be the primary method used to
   identify supported modules.  Resource related control and assignment
   is expected to be managed at the network-device level, not the
   network instance level, based on the `bind-network-instance-name`
   augmentation mentioned above.

   As an example, consider the case where a network instance with a
   `name` of "green" is defined on a network device.  In this case the
   following structure might be made available:

       module: network-instance
          +--rw ietf-yang-library
          +--rw interfaces
          |  +--rw bind-network-instance-name="green"  string
          +--rw system-management
          +--rw network-instances
             +--rw network-instance* [name]
                +--rw name="green"    string
                +--rw type?                               identityref
                +--rw enabled=true                        boolean
                +--rw description="The Green VRF"         string
                +--rw network-instance-policy
                |  ... (RT=1000:1, RD=1.2.3.4)
                +--rw root?                               schema-mount
                   +--rw ietf-yang-library
                   +--rw network-services
                   +--rw oam-protocols
                   +--rw routing
                   +--rw mpls



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   All modules that represent control-plane and data-plane information
   may be present at the `root`, and be accessible via paths modified
   per [STRUCTURAL-MOUNT].  The list of available modules is expected to
   be implementation dependent.  As is the method used by an
   implementation to support NIs.

4.3.  Network Instance Instantiation

   TBD -- need to resolve if instantiation is based on new list entry
   creation per the pending Schema Mount solution definition.

5.  Security Considerations

   The network-device model structure described in this document does
   not define actual configuration and state data, hence it is not
   directly responsible for security risks.

   Each of the component models that provide the corresponding
   configuration and state data should be considered sensitive from a
   security standpoint since they generally manipulate aspects of
   network configurations.  Each component model should be carefully
   evaluated to determine its security risks, along with mitigations to
   reduce such risks.

   LNE portion is TBD

   NI portion is TBD

6.  IANA Considerations

   This YANG model currently uses a temporary ad-hoc namespace.  If it
   is placed or redirected for the standards track, an appropriate
   namespace URI will be registered in the "IETF XML Registry"
   [RFC3688].  The YANG structure modules will be registered in the
   "YANG Module Names" registry [RFC6020].

7.  YANG Modules

   The structure of the models defined in this document are described by
   the YANG module below.

7.1.  Network Device Model Structure

   <CODE BEGINS> file "network-device@2016-02-22.yang"
   module network-device {

     yang-version "1";




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     // namespace
     namespace "urn:ietf:params:xml:ns:yang:network-device";

     prefix "struct";

     // import some basic types

     // meta
     organization "IETF RTG YANG Design Team Collaboration
                   with OpenConfig";

     contact
         "Routing Area YANG Architecture Design Team -
          <rtg-dt-yang-arch@ietf.org>";

     description
       "This module describes a model structure for YANG
        configuration and operational state data models. Its intent is
        to describe how individual device protocol and feature models
        fit together and interact.";

     revision "2016-02-22" {
       description
         "IETF Routing YANG Design Team Meta-Model";
       reference "TBD";
     }

     // extension statements

     // identity statements

     identity oam-protocol-type {
         description
             "Base identity for derivation of OAM protocols";
     }

     identity network-service-type {
         description
             "Base identity for derivation of network services";
     }

      identity system-management-protocol-type {
         description
             "Base identity for derivation of system management
              protocols";
      }

      identity oam-service-type {



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         description
             "Base identity for derivation of Operations,
              Administration, and Maintenance (OAM) services.";
      }

      identity control-plane-protocol-type {
         description
             "Base identity for derivation of control-plane protocols";
      }

      identity mpls-lsp-type {
         description
             "Base identity for derivation of MPLS LSP typs";
      }

     // typedef statements

     // grouping statements

     grouping control-plane-protocols {
         description
             "Grouping for control plane protocols configured for
              a network-instance";
         container control-plane-protocols {
             description
                 "Container for control plane protocols configured for
                  a network instance.";
             list control-plane-protocol {
                 key "type";
                 description
                     "List of control plane protocols configured for
                      a network instance.";
                 leaf type {
                     type identityref {
                         base control-plane-protocol-type;
                     }
                     mandatory true;
                     description
                         "The control plane protocol type, e.g., BGP,
                          OSPF IS-IS, etc";
                 }
                 container policy {
                     description
                         "Protocol specific policy,
                         reusing [RTG-POLICY]";
                 }
             }
         }



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     }

     grouping ribs {
       description
         "Routing Information Bases (RIBs) supported by a
          network-instance";
       container ribs {
           description
               "RIBs supported by a network-instance";
           list rib {
               key "name";
               min-elements "1";
               description
                   "Each entry represents a RIB identified by the
                  'name' key. All routes in a RIB must belong to the
                   same address family.

                   For each routing instance, an implementation should
                   provide one system-controlled default RIB for each
                   supported address family.";
               leaf name {
                   type string;
                   description
                       "The name of the RIB.";
               }
               reference "draft-ietf-netmod-routing-cfg";
               leaf description {
                   type string;
                   description
                       "Description of the RIB";
               }
               // Note that there is no list of interfaces within
               container policy {
                   description "Policy specific to RIB";
               }
           }
       }
     }

     // top level device definition statements
     container ietf-yang-library {
       description
         "YANG Module Library as defined in
          draft-ietf-netconf-yang-library";
     }

     container interfaces {
       description



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        "Interface list as defined by RFC7223/RFC7224";
     }

     container hardware {
       description
         "Hardware / vendor-specific data relevant to the platform.
         This container is an anchor point for platform-specific
         configuration and operational state data.  It may be further
         organized into chassis, line cards, ports, etc.  It is
         expected that vendor or platform-specific augmentations
         would be used to populate this part of the device model";
     }

     container qos {
       description "QoS features, for example policing, shaping, etc.";
     }

     container system-management {
         description
           "System management for physical or virtual device.";
         container system-management-global {
             description "System management - with reuse of RFC 7317";
         }
         list system-management-protocol {
             key "type";
             leaf type {
                 type identityref {
                     base system-management-protocol-type;
                 }
                 mandatory true;
                 description
                     "Syslog, ssh, TACAC+, SNMP, NETCONF, etc.";
             }
             description "List of system management protocol
                          configured for a logical network
                          element.";
         }
     }

     container network-services {
         description
             "Container for list of configured network
              services.";
         list network-service {
             key "type";
             description
                 "List of network services configured for a
                  network instance.";



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             leaf type {
                 type identityref {
                     base network-service-type;
                 }
                 mandatory true;
                 description
                     "The network service type supported within
                      a network instance, e.g., NTP server, DNS
                      server, DHCP server, etc.";
             }
         }
     }

     container oam-protocols {
         description
             "Container for configured OAM protocols.";
         list oam-protocol {
             key "type";
             leaf type {
                 type identityref {
                     base oam-protocol-type;
                 }
                 mandatory true;
                 description
                     "The Operations, Administration, and
                      Maintenance (OAM) protocol type, e.g., BFD,
                      TWAMP, CFM, etc.";
             }
             description
                 "List of configured OAM protocols.";
         }
     }

     container routing {
       description
         "The YANG Data Model for Routing Management revised to be
          Network Instance / VRF independent. ";
       // Note that there is no routing or network instance
       uses control-plane-protocols;
       uses ribs;
     }

     container mpls {
         description "MPLS and TE configuration";
         container global {
             description "Global MPLS configuration";
         }
         list lsps {



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             key "type";
             description
                 "List of LSP types.";
             leaf type {
                 type identityref {
                     base mpls-lsp-type;
                 }
                 mandatory true;
                 description
                     "MPLS and Traffic Engineering protocol LSP types,
                      static, LDP/SR (igp-congruent),
                      RSVP TE (constrained-paths) , etc.";
             }
         }
     }

     container ieee-dot1Q {
       description
         "The YANG Data Model for VLAN bridges as defined by the IEEE";
     }

     container ietf-acl {
       description "Packet Access Control Lists (ACLs) as specified
                      in draft-ietf-netmod-acl-model";
     }

     container ietf-key-chain {
       description "Key chains as specified in
                    draft-ietf-rtgwg-yang-key-chain;";
     }

     container logical-network-element {
       description
         "This module is used to support multiple logical network
          elements on a single physical or virtual system.";
     }

     container network-instance {
       description
         "This module is used to support multiple network instances
          within a single physical or virtual device.  Network
          instances are commonly know as VRFs (virtual routing
          and forwarding) and VSIs (virtual switching instances).";
     }
     // rpc statements

     // notification statements




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   }
   <CODE ENDS>

7.2.  Logical Network Element Model

   <CODE BEGINS> file "logical-network-element@2016-01-19.yang"
   module logical-network-element {

     yang-version "1";

     // namespace
     namespace "urn:ietf:params:xml:ns:yang:logical-network-element";

     prefix "struct";

     // import some basic types
     import ietf-interfaces {
       prefix if;
     }

     // meta
     organization "IETF RTG YANG Design Team Collaboration
                   with OpenConfig";

     contact
         "Routing Area YANG Architecture Design Team -
          <rtg-dt-yang-arch@ietf.org>";

     description
       "This module is used to support multiple logical network
        elements on a single physical or virtual system.";

     revision "2016-01-19" {
       description
         "IETF Routing YANG Design Team Meta-Model";
       reference "TBD";
     }

     // extension statements

     // feature statements
     feature bind-network-element-id {
       description
         "Logical network element ID to which an interface is bound";
     }

     // identity statements




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     identity logical-network-element-type {
       description
        "Identify type of logical-network-element";
     }

     identity lne-managed {
       base logical-network-element-type;
       description
         "A Logical Network Element that can
          be managed by the host system";
     }

     identity lne-unmanaged {
       base logical-network-element-type;
       description
         "A Logical Network Element that cannot
          be managed by the host system";
     }

     // typedef statements

     // grouping statements

     // top level device definition statements
     container logical-network-inventory {
       description "Allows a network device to support multiple logical
                    network element (device) instances";
       list logical-network-element {
         key lne-id;
         description "List of logical network elements";
         leaf lne-id {
           type uint16; // expect a small number of logical routers
           description "Device-wide unique identifier for the
                        logical network element";
         }
         leaf lne-name {
           type string;
           description "Descriptive name for the logical network
                        element";
         }
         leaf lne-type {
           type identityref {
             base logical-network-element-type;
           }
           description "Type of logical-network-element";
         }
         leaf lne-root {
           type schema-mount;



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           description "Root for models supported per logical
                        network element";
         }
       }
     }

     // augment statements
     augment "/if:interfaces/if:interface" {
       description
           "Add a node for the identification of the logical network
           element associated with an interface. Applies to interfaces
           that can be assigned on a per logical network element basis.
           A <TBD> error is returned when the interface type cannot be
           assigned.";

       leaf bind-lne-id {
         type uint16;
         description
           "Logical network element ID to which interface is bound";
       }
     }

     // rpc statements

     // notification statements

   }
   <CODE ENDS>

7.3.  Network Instance Model

   <CODE BEGINS> file "network-instance@2016-02-22.yang"
   module network-instance {

     yang-version "1";

     // namespace
     namespace "urn:ietf:params:xml:ns:yang:network-instance";

     prefix "struct";

     // import some basic types
     import ietf-interfaces {
       prefix if;
     }

     import ietf-ip {
       prefix ip;



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     }

     // meta
     organization "IETF RTG YANG Design Team Collaboration
                   with OpenConfig";

     contact
         "Routing Area YANG Architecture Design Team -
          <rtg-dt-yang-arch@ietf.org>";

     description
       "This module is used to support multiple network instances
        within a single physical or virtual device.  Network
        instances are commonly know as VRFs (virtual routing
        and forwarding) and VSIs (virtual switching instances).";

     revision "2016-02-22" {
       description
         "IETF Routing YANG Design Team Meta-Model";
       reference "TBD";
     }

     // extension statements

     feature bind-network-instance-name {
       description
         "Network Instance to which an interface instance is bound";
     }

     // identity statements

     identity network-instance-type {
         description
            "Base identity from which identities describing
             network instance types are derived.";
     }

      identity ipv4-interface-protocol-type {
         description
             "Base identity for derivation of IPv4 interface
              protocols";
      }

      identity ipv6-interface-protocol-type {
         description
             "Base identity for derivation of IPv6 interface
              protocols";
      }



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     // typedef statements

     // grouping statements

     grouping interface-ip-common {
       description
         "interface-specific configuration for IP interfaces, IPv4 and
         IPv6";

     }

     grouping ipv4-interface-protocols {
         container ipv4-interface-protocols {
             list ipv4-interface-protocol {
                 key "type";
                 leaf type {
                     type identityref {
                         base ipv4-interface-protocol-type;
                     }
                     mandatory true;
                     description
                         "ARP, ICMP, VRRP, DHCP Client, etc.";
                 }
                 description
                     "List of IPv4 protocols configured
                      on an interface";
             }
             description
                 "Container for list of IPv4 protocols configured
                   on an interface";
         }
         description
             "Grouping for IPv4 protocols configured on an interface";
     }

     grouping ipv6-interface-protocols {
         description
             "Grouping for IPv6 protocols configured on
              an interface.";
         container ipv6-interface-protocols {
             description
                 "Container for list of IPv6 protocols configured
                   on an interface.";
             list ipv6-interface-protocol {
                 key "type";
                 description
                     "List of IPv6 protocols configured
                      on an interface";



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                 leaf type {
                     type identityref {
                         base ipv6-interface-protocol-type;
                     }
                     mandatory true;
                     description
                         "ND, ICMPv6, VRRP, DHCPv6 Client, etc.";
                 }
             }
         }
     }

     grouping network-instance-policy {
       description
           "Network instance policies such as route
            distinguisher, route targets, VPLS ID and neighbor,
            Ethernet ID, etc. ";
       reference
           "RFC 4364 - BGP/MPLS Virtual Private Networks (VPNs)
            RFC 6074 - Provisioning, Auto-Discovery, and Signaling
                 in Layer 2 Virtual Private Networks (L2VPNs)
            RFC 7432 - BGP MPLS-Based Ethernet VPN";
       container network-instance-policy {
           description "Network Instance Policy -- details TBD";
       }
     }

     // top level device definition statements
     container network-instances {
         description "Network instances each of which have
                      an independent IP/IPv6 addressing space
                      and protocol instantiations. For layer 3,
                      this consistent with the routing-instance
                      definition in ietf-routing";
         reference "draft-ietf-netmod-routing-cfg";
         list network-instance {
             key name;
             description "List of network-instances";
             leaf name {
                 type string;
                 description "device scoped
                              identifier for the network
                              instance";
             }
             leaf type {
                 type identityref {
                     base network-instance-type;
                 }



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                 description
                     "The network instance type -- details TBD
                      Likely types include core, L3-VRF, VPLS,
                      L2-cross-connect, L2-VSI, etc.";
             }
             leaf enabled {
                 type boolean;
                 default "true";
                 description
                   "Flag indicating whether or not the network
                    instance is enabled.";
             }
             leaf description {
                 type string;
                 description
                   "Description of the network instance
                   and its intended purpose";
             }
             uses network-instance-policy;
             leaf root {
               type schema-mount;
               description "Root for models supported per
                            network instance";
             }
         }
     }

     // augment statements

     augment "/if:interfaces/if:interface" {
       description
           "Add a node for the identification of the logical network
           instance (which is within the interface's identified logical
           network element) associated with the IP information
           configured on an interface";

       leaf bind-network-instance-name {
         type string;
         description
           "Network Instance to which an interface is bound";
       }
     }

     augment "/if:interfaces/if:interface/ip:ipv4" {
       description
           "Add a node for the identification of the logical
           network instance (which is within the interface's
           identified physical or virtual device) associated with



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           the IP information configured on an interface";

       leaf bind-network-instance-name {
         type string;
         description
           "Network Instance to which IPv4 interface is bound";

       }
     }

     augment "/if:interfaces/if:interface/ip:ipv6" {
       description
           "Add a node for the identification of the logical
           network instance (which is within the interface's
           identified physical or virtual device) associated with
           the IP information configured on an interface";

       leaf bind-network-instance-name {
         type string;
         description
           "Network Instance to which IPv6 interface is bound";

       }
     }

     // rpc statements

     // notification statements

   }
   <CODE ENDS>

8.  References

8.1.  Normative References

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

   [RFC4026]  Andersson, L. and T. Madsen, "Provider Provisioned Virtual
              Private Network (VPN) Terminology", RFC 4026, March 2005.

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

   [RFC7223]  Bjorklund, M., "A YANG Data Model for Interface
              Management", RFC 7223, May 2014.



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   [RFC7277]  Bjorklund, M., "A YANG Data Model for IP Management",
              RFC 7277, June 2014.

   [RFC7317]  Bierman, A. and M. Bjorklund, "A YANG Data Model for
              System Management", RFC 7317, August 2014.

   [STRUCTURAL-MOUNT]
              Bjorklund, M., "YANG Structural Mount", draft-bjorklund-
              netmod-structural-mount-00.txt (work in progress),
              December 2015.

   [YANG-YSDL]
              Lhotha, L., "YANG Schema Dispatching Language", draft-
              lhotka-netmod-ysdl-00.txt (work in progress), November
              2015.

8.2.  Informative References

   [IEEE-8021Q]
              Holness, M., "IEEE 802.1Q YANG Module Specifications",
              IEEE-Draft http://www.ieee802.org/1/files/public/docs2015/
              new-mholness-yang-8021Q-0515-v04.pdf, May 2015.

   [NETMOD-OPSTATE]
              Watsen, K. and T. Nadeau, "NETMOD Operational State
              Requirements", draft-ietf-netmod-opstate-reqs-03.txt (work
              in progress), January 2016.

   [OC-MPLS]  George, J., Fang, L., Osborne, E., and R. Shakir, "MPLS /
              TE Model for Service Provider Networks", draft-openconfig-
              mpls-consolidated-model-02.txt (work in progress), October
              2015.

   [OC-OPSTATE]
              Shakir, R., Shaikh, A., and M. Hines, "Consistent Modeling
              of Operational State Data in YANG", draft-openconfig-
              netmod-opstate-01.txt (work in progress), July 2015.

   [OC-STRUCT]
              Shaikh, A., Shakir, R., D'Souza, K., and L. Fang,
              "Consistent Modeling of Operational State Data in YANG",
              draft-openconfig-netmod-model-structure-00.txt (work in
              progress), March 2015.

   [RTG-CFG]  Lhotha, L. and A. Lindem, "A YANG Data Model for Routing
              Management", draft-ietf-netmod-routing-cfg-20.txt (work in
              progress), October 2015.




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   [YANG-LIBRARY]
              Bierman, A., Bjorklund, M., and K. Watsen, "YANG Module
              Library", draft-ietf-netconf-yang-library-03.txt (work in
              progress), December 2015.

Appendix A.  Acknowledgments

   This document is derived from draft-openconfig-netmod-model-
   structure-00.  The Authors of that document who are not also authors
   of this document are listed as Contributors to this work.

   The original stated: The authors are grateful for valuable
   contributions to this document and the associated models from: Deepak
   Bansal, Paul Borman, Chris Chase, Josh George, Marcus Hines, and Jim
   Uttaro.

   The Routing Area Yang Architecture design team members included Acee
   Lindem, Anees Shaikh, Christian Hopps, Dean Bogdanovic, Lou Berger,
   Qin Wu, Rob Shakir, Stephane Litkowski, and Yan Gang.

   The identityref approach was proposed by Mahesh Jethanandani.

   The RFC text was produced using Marshall Rose's xml2rfc tool.




























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Appendix B.  Contributors

   Contributors' Addresses

      Anees Shaikh
      Google
      1600 Amphitheatre Pkwy
      Mountain View, CA  94043
      United States
      Email: aashaikh@google.com


      Rob Shakir
      Jive Communications, Inc.
      1275 W 1600 N, Suite 100
      Orem, UT  84057
      United States
      Email: rjs@rob.sh


      Kevin D'Souza
      AT&T
      200 S. Laurel Ave
      Middletown, NJ
      United States
      Email: kd6913@att.com

      Luyuan Fang
      Microsoft
      205 108th Ave. NE, Suite 400
      Bellevue, WA
      United States
      Email: lufang@microsoft.com

      Qin Wu
      Huawei Technologies
      101 Software Avenue, Yuhua District
      Nanjing, Jiangsu  210012
      China

      Email: bill.wu@huawei.com










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      Stephane Litkowski
      Orange
      9 rue du chene germain
      Cesson Sevigne  35512
      France

      Email: stephane.litkowski@orange.com


      Gang Yan
      Huawei Technologies
      Huawei Bld., No.156 Beiqing Rd.
      Beijing  100095
      China

      Email: yangang@huawei.com


Authors' Addresses

   Acee Lindem (editor)
   Cisco Systems
   301 Midenhall Way
   Cary, NC  27513
   USA

   Email: acee@cisco.com


   Lou Berger (editor)
   LabN Consulting, L.L.C.

   Email: lberger@labn.net


   Dean Bogdanovic

   Email: ivandean@gmail.com


   Christan Hopps
   Deutsche Telekom

   Email: chopps@chopps.org







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