<pre>Internet Engineering Task Force (IETF)                         Y. Zhuang
Request for Comments: 8542                                        D. Shi
Category: Standards Track                                         Huawei
ISSN: 2070-1721                                                    R. Gu
                                                            China Mobile
                                                      H. Ananthakrishnan
                                                                 Netflix
                                                              March 2019


     <span class="h1">A YANG Data Model for Fabric Topology in Data-Center Networks</span>

Abstract

   This document defines a YANG data model for fabric topology in data-
   center networks and represents one possible view of the data-center
   fabric.  This document focuses on the data model only and does not
   endorse any kind of network design that could be based on the
   abovementioned model.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in <a href="./rfc7841#section-2">Section&nbsp;2 of RFC 7841</a>.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   <a href="https://www.rfc-editor.org/info/rfc8542">https://www.rfc-editor.org/info/rfc8542</a>.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a> and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (<a href="https://trustee.ietf.org/license-info">https://trustee.ietf.org/license-info</a>) 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.



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Table of Contents

   <a href="#section-1">1</a>.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   <a href="#page-2">2</a>
   <a href="#section-2">2</a>.  Definitions and Acronyms  . . . . . . . . . . . . . . . . . .   <a href="#page-3">3</a>
     <a href="#section-2.1">2.1</a>.  Key Words . . . . . . . . . . . . . . . . . . . . . . . .   <a href="#page-3">3</a>
     <a href="#section-2.2">2.2</a>.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   <a href="#page-3">3</a>
   <a href="#section-3">3</a>.  Model Overview  . . . . . . . . . . . . . . . . . . . . . . .   <a href="#page-4">4</a>
     <a href="#section-3.1">3.1</a>.  Topology Model Structure  . . . . . . . . . . . . . . . .   <a href="#page-4">4</a>
     <a href="#section-3.2">3.2</a>.  Fabric Topology Model . . . . . . . . . . . . . . . . . .   <a href="#page-4">4</a>
       <a href="#section-3.2.1">3.2.1</a>.  Fabric Topology . . . . . . . . . . . . . . . . . . .   <a href="#page-5">5</a>
       <a href="#section-3.2.2">3.2.2</a>.  Fabric Node Extension . . . . . . . . . . . . . . . .   <a href="#page-6">6</a>
       <a href="#section-3.2.3">3.2.3</a>.  Fabric Termination-Point Extension  . . . . . . . . .   <a href="#page-7">7</a>
   <a href="#section-4">4</a>.  Fabric YANG Modules . . . . . . . . . . . . . . . . . . . . .   <a href="#page-8">8</a>
   <a href="#section-5">5</a>.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  <a href="#page-21">21</a>
   <a href="#section-6">6</a>.  Security Considerations . . . . . . . . . . . . . . . . . . .  <a href="#page-22">22</a>
   <a href="#section-7">7</a>.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  <a href="#page-23">23</a>
     <a href="#section-7.1">7.1</a>.  Normative References  . . . . . . . . . . . . . . . . . .  <a href="#page-23">23</a>
     <a href="#section-7.2">7.2</a>.  Informative References  . . . . . . . . . . . . . . . . .  <a href="#page-24">24</a>
   <a href="#appendix-A">Appendix A</a>.  Non-NMDA-State Modules . . . . . . . . . . . . . . .  <a href="#page-25">25</a>
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  <a href="#page-32">32</a>
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  <a href="#page-32">32</a>

<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>.  Introduction</span>

   A data-center (DC) network can be composed of single or multiple
   fabrics, which are also known as Points Of Delivery (PODs).  These
   fabrics may be heterogeneous due to implementation of different
   technologies when a DC network is upgraded or new techniques and
   features are rolled out.  For example, within a DC network, Fabric A
   may use Virtual eXtensible Local Area Network (VXLAN) while Fabric B
   may use VLAN.  Likewise, an existing fabric may use VXLAN while a new
   fabric (for example, a fabric introduced for DC upgrade and
   expansion) may implement a technique discussed in the NVO3 Working
   Group, such as Geneve [<a href="#ref-GENEVE" title="&quot;Geneve: Generic Network Virtualization Encapsulation&quot;">GENEVE</a>].  The configuration and management of
   such DC networks with heterogeneous fabrics could result in
   considerable complexity.

   For a DC network, a fabric can be considered as an atomic structure
   for management purposes.  From this point of view, the management of
   the DC network can be decomposed into a set of tasks to manage each
   fabric separately, as well as the fabric interconnections.  The
   advantage of this method is to make the overall management tasks
   flexible and easy to extend in the future.

   As a basis for DC fabric management, this document defines a YANG
   data model [<a href="./rfc6020" title="&quot;YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)&quot;">RFC6020</a>] [<a href="./rfc7950" title="&quot;The YANG 1.1 Data Modeling Language&quot;">RFC7950</a>] for a possible view of the fabric-
   based data-center topology.  To do so, it augments the generic




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   network and network topology data models defined in [<a href="./rfc8345" title="&quot;A YANG Data Model for Network Topologies&quot;">RFC8345</a>] with
   information that is specific to data-center fabric networks.

   The model defines the generic configuration and operational state for
   a fabric-based network topology, which can subsequently be extended
   by vendors with vendor-specific information as needed.  The model can
   be used by a network controller to represent its view of the fabric
   topology that it controls and expose this view to network
   administrators or applications for DC network management.

   Within the context of topology architecture defined in [<a href="./rfc8345" title="&quot;A YANG Data Model for Network Topologies&quot;">RFC8345</a>],
   this model can also be treated as an application of the Interface to
   the Routing System (I2RS) network topology model [<a href="./rfc8345" title="&quot;A YANG Data Model for Network Topologies&quot;">RFC8345</a>] in the
   scenario of data-center network management.  It can also act as a
   service topology when mapping network elements at the fabric layer to
   elements of other topologies, such as L3 topologies as defined in
   [<a href="./rfc8346" title="&quot;A YANG Data Model for Layer 3 Topologies&quot;">RFC8346</a>].

   By using the fabric topology model defined in this document, people
   can treat a fabric as a holistic entity and focus on its
   characteristics (such as encapsulation type and gateway type) as well
   as its connections to other fabrics, while putting the underlay
   topology aside.  As such, clients can consume the topology
   information at the fabric level with no need to be aware of the
   entire set of links and nodes in the corresponding underlay networks.
   A fabric topology can be configured by a network administrator using
   the controller by adding physical devices and links into a fabric.
   Alternatively, fabric topology can be learned from the underlay
   network infrastructure.

<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>.  Definitions and Acronyms</span>

<span class="h3"><a class="selflink" id="section-2.1" href="#section-2.1">2.1</a>.  Key Words</span>

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a> [<a href="./rfc2119" title="&quot;Key words for use in RFCs to Indicate Requirement Levels&quot;">RFC2119</a>] [<a href="./rfc8174" title="&quot;Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words&quot;">RFC8174</a>] when, and only when, they appear in all
   capitals, as shown here.

<span class="h3"><a class="selflink" id="section-2.2" href="#section-2.2">2.2</a>.  Terminology</span>

   POD: a module of network, compute, storage, and application
   components that work together to deliver networking services.  It
   represents a repeatable design pattern.  Its components maximize the
   modularity, scalability, and manageability of data centers.

   Fabric: composed of several PODs to form a data-center network.



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<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>.  Model Overview</span>

   This section provides an overview of the DC fabric topology model and
   its relationship with other topology models.

<span class="h3"><a class="selflink" id="section-3.1" href="#section-3.1">3.1</a>.  Topology Model Structure</span>

   The relationship of the DC fabric topology model and other topology
   models is shown in Figure 1.

             +------------------------+
             |      network model     |
             +------------------------+
                          |
                          |
             +------------V-----------+
             | network topology model |
             +------------------------+
                          |
        +-----------+-----+------+-------------+
        |           |            |             |
    +---V----+  +---V----+   +---V----+   +----V---+
    |   L1   |  |   L2   |   |   L3   |   | Fabric |
    |topology|  |topology|   |topology|   |topology|
    |  model |  |  model |   |  model |   |  model |
    +--------+  +--------+   +--------+   +--------+

                Figure 1: The Network Data Model Structure

   From the perspective of resource management and service provisioning
   for a data-center network, the fabric topology model augments the
   basic network topology model with definitions and features specific
   to a DC fabric, to provide common configuration and operations for
   heterogeneous fabrics.

<span class="h3"><a class="selflink" id="section-3.2" href="#section-3.2">3.2</a>.  Fabric Topology Model</span>

   The fabric topology model module is designed to be generic and can be
   applied to data-center fabrics built with different technologies,
   such as VLAN and VXLAN.  The main purpose of this module is to
   configure and manage fabrics and their connections.  It provides a
   fabric-based topology view for data-center applications.









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<span class="h4"><a class="selflink" id="section-3.2.1" href="#section-3.2.1">3.2.1</a>.  Fabric Topology</span>

   In the fabric topology module, a fabric is modeled as a node of a
   network; as such, the fabric-based data-center network consists of a
   set of fabric nodes and their connections.  The following depicts a
   snippet of the definitions to show the main structure of the model.
   The notation syntax follows [<a href="./rfc8340" title="&quot;YANG Tree Diagrams&quot;">RFC8340</a>].

       module: ietf-dc-fabric-topology
       augment /nw:networks/nw:network/nw:network-types:
          +--rw fabric-network!
       augment /nw:networks/nw:network/nw:node:
          +--rw fabric-attributes
             +--rw fabric-id?   fabric-id
             +--rw name?        string
             +--rw type?        fabrictype:underlay-network-type
             +--rw description?    string
             +--rw options
             +--...
       augment /nw:networks/nw:network/nw:node/nt:termination-point:
          +--ro fport-attributes
             +--ro name?          string
             +--ro role?          fabric-port-role
             +--ro type?          fabric-port-type

   The fabric topology module augments the generic ietf-network and
   ietf-network-topology modules as follows:

   o  A new topology type, "ietf-dc-fabric-topology", is defined and
      added under the "network-types" container of the ietf-network
      module.

   o  Fabric is defined as a node under the network/node container.  A
      new container, "fabric-attributes", is defined to carry attributes
      for a fabric such as gateway mode, fabric types, involved device
      nodes, and links.

   o  Termination points (in the network topology module) are augmented
      with fabric port attributes defined in a container.  The
      "termination-point" here is used to represent a fabric "port" that
      provides connections to other nodes, such as an internal device,
      another fabric externally, or end hosts.

   Details of the fabric node and the fabric termination point extension
   will be explained in the following sections.






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<span class="h4"><a class="selflink" id="section-3.2.2" href="#section-3.2.2">3.2.2</a>.  Fabric Node Extension</span>

   As an atomic network (that is, a set of nodes and links that composes
   a POD and also supports a single overlay/underlay instance), a fabric
   itself is composed of a set of network elements, i.e., devices and
   related links.  The configuration of a fabric is contained under the
   "fabric-attributes" container depicted as follows.  The notation
   syntax follows [<a href="./rfc8340" title="&quot;YANG Tree Diagrams&quot;">RFC8340</a>].

       +--rw fabric-attributes
          +--rw fabric-id?      fabrictypes:fabric-id
          +--rw name?           string
          +--rw type?           fabrictype:underlay-network-type
          +--rw vni-capacity
          |  +--rw min?   int32
          |  +--rw max?   int32
          +--rw description?    string
          +--rw options
          |  +--rw gateway-mode?           enumeration
          |  +--rw traffic-behavior?       enumeration
          |  +--rw capability-supported* fabrictype:service-capabilities
          +--rw device-nodes* [device-ref]
          |  +--rw device-ref    fabrictype:node-ref
          |  +--rw role*?         fabrictype:device-role
          +--rw device-links* [link-ref]
          |  +--rw link-ref    fabrictype:link-ref
          +--rw device-ports* [port-ref]
             +--rw port-ref     fabrictype:tp-ref
             +--rw port-type?   fabrictypes:port-type
             +--rw bandwidth?   fabrictypes:bandwidth


   In the module, additional data objects for fabric nodes are
   introduced by augmenting the "node" list of the network module.  New
   objects include fabric name, type of the fabric, and descriptions of
   the fabric, as well as a set of options defined in an "options"
   container.  The "options" container includes the gateway-mode type
   (centralized or distributed) and traffic behavior (whether an Access
   Control List (ACL) is needed for the traffic).  Also, it includes a
   list of device nodes and related links as "supporting-node" to form a
   fabric network.  These device nodes and links are represented as
   leaf-refs of existing nodes and links in the underlay topology.  For
   the device node, the "role" object is defined to represent the role
   of a device within the fabric, such as "SPINE" or "LEAF", which
   should work together with the gateway-mode.






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<span class="h4"><a class="selflink" id="section-3.2.3" href="#section-3.2.3">3.2.3</a>.  Fabric Termination-Point Extension</span>

   Since a fabric can be considered as a node, "termination-points" can
   represent fabric "ports" that connect to other fabrics and end hosts,
   as well as devices inside the fabric.

   As such, the set of "termination-points" of a fabric indicate all of
   its connections, including its internal connections, interconnections
   with other fabrics, and connections to end hosts.

   The structure of fabric ports is as follows.  The notation syntax
   follows [<a href="./rfc8340" title="&quot;YANG Tree Diagrams&quot;">RFC8340</a>].

       augment /nw:networks/nw:network/nw:node/nt:termination-point:
           +--ro fport-attributes
              +--ro name?          string
              +--ro role?          fabric-port-role
              +--ro type?          fabric-port-type
              +--ro device-port?   tp-ref
              +--ro (tunnel-option)?

   This structure augments the termination points (in the network
   topology module) with fabric port attributes defined in a container.

   New nodes are defined for fabric ports, including fabric name, role
   of the port within the fabric (internal port, external port to
   outside network, access port to end hosts), and port type (L2
   interface, L3 interface).  By defining the device port as a tp-ref, a
   fabric port can be mapped to a device node in the underlay network.

   Additionally, a new container for tunnel-options is introduced to
   present the tunnel configuration on a port.

   The termination point information is learned from the underlay
   networks, not configured by the fabric topology layer.
















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<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>.  Fabric YANG Modules</span>

   This module imports typedefs from [<a href="./rfc8345" title="&quot;A YANG Data Model for Network Topologies&quot;">RFC8345</a>], and it references
   [<a href="./rfc7348" title="&quot;Virtual eXtensible Local Area Network (VXLAN): A Framework for Overlaying Virtualized Layer 2 Networks over Layer 3 Networks&quot;">RFC7348</a>] and [<a href="./rfc8344" title="&quot;A YANG Data Model for IP Management&quot;">RFC8344</a>].

&lt;CODE BEGINS&gt; file "ietf-dc-fabric-types@2019-02-25.yang"
module ietf-dc-fabric-types {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-dc-fabric-types";
  prefix fabrictypes;

  import ietf-network {
    prefix nw;
    reference
      "<a href="./rfc8345">RFC 8345</a>: A YANG Data Model for Network Topologies";
  }

  organization
    "IETF I2RS (Interface to the Routing System) Working Group";
  contact
    "WG Web:    &lt;<a href="https://datatracker.ietf.org/wg/i2rs/">https://datatracker.ietf.org/wg/i2rs/</a>&gt;
     WG List:   &lt;mailto:i2rs@ietf.org&gt;

     Editor:    Yan Zhuang
                &lt;mailto:zhuangyan.zhuang@huawei.com&gt;

     Editor:    Danian Shi
                &lt;mailto:shidanian@huawei.com&gt;";
  description
    "This module contains a collection of YANG definitions for
     fabric.

     Copyright (c) 2019 IETF Trust and the persons identified
     as authors of the code.  All rights reserved.

     Redistribution and use in source and binary forms, with
     or without modification, is permitted pursuant to, and
     subject to the license terms contained in, the Simplified
     BSD License set forth in <a href="#section-4">Section 4</a>.c of the IETF Trust's
     Legal Provisions Relating to IETF Documents
     (<a href="https://trustee.ietf.org/license-info">https://trustee.ietf.org/license-info</a>).

     This version of this YANG module is part of <a href="./rfc8542">RFC 8542</a>;
     see the RFC itself for full legal notices.";

  revision 2019-02-25 {
    description
      "Initial revision.";



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    reference
      "<a href="./rfc8542">RFC 8542</a>: A YANG Data Model for Fabric Topology
       in Data-Center Networks";
  }

  identity fabric-type {
    description
      "Base type for fabric networks";
  }

  identity vxlan-fabric {
    base fabric-type;
    description
      "VXLAN fabric";
  }

  identity vlan-fabric {
    base fabric-type;
    description
      "VLAN fabric";
  }

  identity trill-fabric {
    base fabric-type;
    description
      "TRILL fabric";
  }

  identity port-type {
    description
      "Base type for fabric port";
  }

  identity eth {
    base port-type;
    description
      "Ethernet";
  }

  identity serial {
    base port-type;
    description
      "Serial";
  }

  identity bandwidth {
    description
      "Base for bandwidth";



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  }

  identity bw-1M {
    base bandwidth;
    description
      "1M";
  }

  identity bw-10M {
    base bandwidth;
    description
      "10Mbps";
  }

  identity bw-100M {
    base bandwidth;
    description
      "100Mbps";
  }

  identity bw-1G {
    base bandwidth;
    description
      "1Gbps";
  }

  identity bw-10G {
    base bandwidth;
    description
      "10Gbps";
  }

  identity bw-25G {
    base bandwidth;
    description
      "25Gbps";
  }

  identity bw-40G {
    base bandwidth;
    description
      "40Gbps";
  }

  identity bw-100G {
    base bandwidth;
    description
      "100Gbps";



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  }

  identity bw-400G {
    base bandwidth;
    description
      "400Gbps";
  }

  identity device-role {
    description
      "Base for the device role in a fabric.";
  }

  identity spine {
    base device-role;
    description
      "This is a spine node in a fabric.";
  }

  identity leaf {
    base device-role;
    description
      "This is a leaf node in a fabric.";
  }

  identity border {
    base device-role;
    description
      "This is a border node to connect to other
       fabric/network.";
  }

  identity fabric-port-role {
    description
      "Base for the port's role in a fabric.";
  }

  identity internal {
    base fabric-port-role;
    description
      "The port is used for devices to access each
       other within a fabric.";
  }

  identity external {
    base fabric-port-role;
    description
      "The port is used for a fabric to connect to



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       outside network.";
  }

  identity access {
    base fabric-port-role;
    description
      "The port is used for an endpoint to connect
       to a fabric.";
  }

  identity service-capability {
    description
      "Base for the service of the fabric ";
  }

  identity ip-mapping {
    base service-capability;
    description
      "NAT.";
  }

  identity acl-redirect {
    base service-capability;
    description
      "ACL redirect, which can provide a Service Function Chain (SFC).";
  }

  identity dynamic-route-exchange {
    base service-capability;
    description
      "Dynamic route exchange.";
  }

  /*
   * Typedefs
   */

  typedef fabric-id {
    type nw:node-id;
    description
      "An identifier for a fabric in a topology.
       This identifier can be generated when composing a fabric.
       The composition of a fabric can be achieved by defining an
       RPC, which is left for vendor specific implementation
       and not provided in this model.";
  }

  typedef service-capabilities {



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    type identityref {
      base service-capability;
    }
    description
      "Service capability of the fabric";
  }

  typedef port-type {
    type identityref {
      base port-type;
    }
    description
      "Port type: ethernet or serial or others.";
  }

  typedef bandwidth {
    type identityref {
      base bandwidth;
    }
    description
      "Bandwidth of the port.";
  }

  typedef node-ref {
    type instance-identifier;
    description
      "A reference to a node in topology";
  }

  typedef tp-ref {
    type instance-identifier;
    description
      "A reference to a termination point in topology";
  }

  typedef link-ref {
    type instance-identifier;
    description
      "A reference to a link in topology";
  }

  typedef underlay-network-type {
    type identityref {
      base fabric-type;
    }
    description
      "The type of physical network that implements
       this fabric.  Examples are VLAN and TRILL.";



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  }

  typedef device-role {
    type identityref {
      base device-role;
    }
    description
      "Role of the device node.";
  }

  typedef fabric-port-role {
    type identityref {
      base fabric-port-role;
    }
    description
      "Role of the port in a fabric.";
  }

  typedef fabric-port-type {
    type enumeration {
      enum layer2interface {
        description
          "L2 interface";
      }
      enum layer3interface {
        description
          "L3 interface";
      }
      enum layer2Tunnel {
        description
          "L2 tunnel";
      }
      enum layer3Tunnel {
        description
          "L3 tunnel";
      }
    }
    description
      "Fabric port type";
  }

  grouping fabric-port {
    description
      "Attributes of a fabric port.";
    leaf name {
      type string;
      description
        "Name of the port.";



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    }
    leaf role {
      type fabric-port-role;
      description
        "Role of the port in a fabric.";
    }
    leaf type {
      type fabric-port-type;
      description
        "Type of the port";
    }
    leaf device-port {
      type tp-ref;
      description
        "The device port it mapped to.";
    }
    choice tunnel-option {
      description
        "Tunnel options to connect two fabrics.
         It could be L2 Tunnel or L3 Tunnel.";
    }
  }
}

&lt;CODE ENDS&gt;

   &lt;CODE BEGINS&gt; file "ietf-dc-fabric-topology@2019-02-25.yang"
   module ietf-dc-fabric-topology {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-dc-fabric-topology";
     prefix fabric;

     import ietf-network {
       prefix nw;
       reference
         "<a href="./rfc8345">RFC 8345</a>: A YANG Data Model for Network Topologies";
     }
     import ietf-network-topology {
       prefix nt;
       reference
         "<a href="./rfc8345">RFC 8345</a>: A YANG Data Model for Network Topologies";
     }
     import ietf-dc-fabric-types {
       prefix fabrictypes;
       reference
         "<a href="./rfc8542">RFC 8542</a>: A YANG Data Model for Fabric Topology in
          Data-Center Networks";
     }



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     organization
       "IETF I2RS (Interface to the Routing System) Working Group";
     contact
       "WG Web:    &lt;<a href="https://datatracker.ietf.org/wg/i2rs/">https://datatracker.ietf.org/wg/i2rs/</a>&gt;
        WG List:   &lt;mailto:i2rs@ietf.org&gt;

        Editor:    Yan Zhuang
                   &lt;mailto:zhuangyan.zhuang@huawei.com&gt;

        Editor:    Danian Shi
                   &lt;mailto:shidanian@huawei.com&gt;";
     description
       "This module contains a collection of YANG definitions for
        fabric.

        Copyright (c) 2019 IETF Trust and the persons identified
        as authors of the code.  All rights reserved.

        Redistribution and use in source and binary forms, with
        or without modification, is permitted pursuant to, and
        subject to the license terms contained in, the Simplified
        BSD License set forth in <a href="#section-4">Section 4</a>.c of the IETF Trust's
        Legal Provisions Relating to IETF Documents
        (<a href="https://trustee.ietf.org/license-info">https://trustee.ietf.org/license-info</a>).

        This version of this YANG module is part of <a href="./rfc8542">RFC 8542</a>;
        see the RFC itself for full legal notices.";

     revision 2019-02-25 {
       description
         "Initial revision.";
       reference
         "<a href="./rfc8542">RFC 8542</a>: A YANG Data Model for Fabric Topology
          in Data-Center Networks";
     }

     //grouping statements

     grouping fabric-network-type {
       description
         "Identify the topology type to be fabric.";
       container fabric-network {
         presence "indicates fabric Network";
         description
           "The presence of the container node indicates
            fabric topology";
       }
     }



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     grouping fabric-options {
       description
         "Options for a fabric";
       leaf gateway-mode {
         type enumeration {
           enum centralized {
             description
               "The Fabric uses centralized
                gateway, in which gateway is deployed on SPINE
                node.";
           }
           enum distributed {
             description
               "The Fabric uses distributed
                gateway, in which gateway is deployed on LEAF
                node.";
           }
         }
         default "distributed";
         description
           "Gateway mode of the fabric";
       }
       leaf traffic-behavior {
         type enumeration {
           enum normal {
             description
               "Normal means no policy is needed
                for all traffic";
           }
           enum policy-driven {
             description
               "Policy driven means policy is
                needed for the traffic; otherwise, the traffic
                will be discarded.";
           }
         }
         default "normal";
         description
           "Traffic behavior of the fabric";
       }
       leaf-list capability-supported {
         type fabrictypes:service-capabilities;
         description
           "It provides a list of supported services of the
            fabric.  The service-capabilities is defined as
            identity-ref.  Users can define more services
            by defining new identities.";
       }



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     }

     grouping device-attributes {
       description
         "device attributes";
       leaf device-ref {
         type fabrictypes:node-ref;
         description
           "The device that the fabric includes that refers
            to a node in another topology.";
       }
       leaf-list role {
         type fabrictypes:device-role;
         default "fabrictypes:leaf";
         description
           "It is a list of device roles to represent the roles
            that a device plays within a POD, such as SPINE,
            LEAF, Border, or Border-Leaf.
            The device role is defined as identity-ref.  If more
            than 2 stages are used for a POD, users can
            define new identities for the device role.";
       }
     }

     grouping link-attributes {
       description
         "Link attributes";
       leaf link-ref {
         type fabrictypes:link-ref;
         description
           "The link that the fabric includes that refers to
            a link in another topology.";
       }
     }

     grouping port-attributes {
       description
         "Port attributes";
       leaf port-ref {
         type fabrictypes:tp-ref;
         description
           "The port that the fabric includes that refers to
            a termination-point in another topology.";
       }
       leaf port-type {
         type fabrictypes:port-type;
         description
           "Port type is defined as identity-ref.  The current



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            types include ethernet or serial.  If more types
            are needed, developers can define new identities.";
       }
       leaf bandwidth {
         type fabrictypes:bandwidth;
         description
           "Bandwidth of the port.  It is defined as identity-ref.
            If more speeds are introduced, developers can define
            new identities for them.  Current speeds include 1M, 10M,
            100M, 1G, 10G, 25G, 40G, 100G, and 400G.";
       }
     }

     grouping fabric-attributes {
       description
         "Attributes of a fabric";
       leaf fabric-id {
         type fabrictypes:fabric-id;
         description
           "An identifier for a fabric in a topology.
            This identifier can be generated when composing a fabric.
            The composition of a fabric can be achieved by defining an
            RPC, which is left for vendor-specific implementation and
            not provided in this model.";
       }
       leaf name {
         type string;
         description
           "Name of the fabric";
       }
       leaf type {
         type fabrictypes:underlay-network-type;
         description
           "The type of physical network that implements this
            fabric.  Examples are VLAN and TRILL.";
       }
       container vni-capacity {
         description
           "The range of the VXLAN Network Identifier
            (VNI) defined in <a href="./rfc7348">RFC 7348</a> that the POD uses.";
         leaf min {
           type int32;
           description
             "The lower-limit VNI.";
         }
         leaf max {
           type int32;
           description



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             "The upper-limit VNI.";
         }
       }
       leaf description {
         type string;
         description
           "Description of the fabric";
       }
       container options {
         description
           "Options of the fabric";
         uses fabric-options;
       }
       list device-nodes {
         key "device-ref";
         description
           "Device nodes that are included in a fabric.";
         uses device-attributes;
       }
       list device-links {
         key "link-ref";
         description
           "Links that are included within a fabric.";
         uses link-attributes;
       }
       list device-ports {
         key "port-ref";
         description
           "Ports that are included in the fabric.";
         uses port-attributes;
       }
     }

     // augment statements

     augment "/nw:networks/nw:network/nw:network-types" {
       description
         "Introduce a new network type for fabric-based topology";
       uses fabric-network-type;
     }

     augment "/nw:networks/nw:network/nw:node" {
       when '/nw:networks/nw:network/nw:network-types/'
          + 'fabric:fabric-network' {
         description
           "Augmentation parameters apply only for networks
            with fabric topology";
       }



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       description
         "Augmentation for fabric nodes created by
          fabric topology.";
       container fabric-attributes {
         description
           "Attributes for a fabric network";
         uses fabric-attributes;
       }
     }

     augment "/nw:networks/nw:network/nw:node/nt:termination-point" {
       when '/nw:networks/nw:network/nw:network-types/'
          + 'fabric:fabric-network' {
         description
           "Augmentation parameters apply only for networks
            with fabric topology";
       }
       description
         "Augmentation for port on fabric.";
       container fport-attributes {
         config false;
         description
           "Attributes for fabric ports";
         uses fabrictypes:fabric-port;
       }
     }
   }
   &lt;CODE ENDS&gt;

<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>.  IANA Considerations</span>

   This document registers the following namespace URIs in the "IETF XML
   Registry" [<a href="./rfc3688" title="&quot;The IETF XML Registry&quot;">RFC3688</a>]:

   URI:urn:ietf:params:xml:ns:yang:ietf-dc-fabric-types
   Registrant Contact: The IESG.
   XML: N/A; the requested URI is an XML namespace.

   URI:urn:ietf:params:xml:ns:yang:ietf-dc-fabric-topology
   Registrant Contact: The IESG.
   XML: N/A; the requested URI is an XML namespace.

   URI:urn:ietf:params:xml:ns:yang:ietf-dc-fabric-topology-state
   Registrant Contact: The IESG.
   XML: N/A; the requested URI is an XML namespace.






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   This document registers the following YANG modules in the "YANG
   Module Names" registry [<a href="./rfc6020" title="&quot;YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)&quot;">RFC6020</a>]:

   Name: ietf-dc-fabric-types
   Namespace: urn:ietf:params:xml:ns:yang:ietf-dc-fabric-types
   Prefix: fabrictypes
   Reference: <a href="./rfc8542">RFC 8542</a>

   Name: ietf-dc-fabric-topology
   Namespace: urn:ietf:params:xml:ns:yang:ietf-dc-fabric-topology
   Prefix: fabric
   Reference: <a href="./rfc8542">RFC 8542</a>

   Name: ietf-dc-fabric-topology-state
   Namespace: urn:ietf:params:xml:ns:yang:ietf-dc-fabric-topology-state
   Prefix: sfabric
   Reference: <a href="./rfc8542">RFC 8542</a>

<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>.  Security Considerations</span>

   The YANG module defined in this document is designed to be accessed
   via network management protocols such as NETCONF [<a href="./rfc6241" title="&quot;Network Configuration Protocol (NETCONF)&quot;">RFC6241</a>] or
   RESTCONF [<a href="./rfc8040" title="&quot;RESTCONF Protocol&quot;">RFC8040</a>].  The lowest NETCONF layer is the secure transport
   layer, and the mandatory-to-implement secure transport is Secure
   Shell (SSH) [<a href="./rfc6242" title="&quot;Using the NETCONF Protocol over Secure Shell (SSH)&quot;">RFC6242</a>].  The lowest RESTCONF layer is HTTPS, and the
   mandatory-to-implement secure transport is TLS [<a href="./rfc8446" title="&quot;The Transport Layer Security (TLS) Protocol Version 1.3&quot;">RFC8446</a>].

   The Network Configuration Access Control Model (NACM) [<a href="./rfc8341" title="&quot;Network Configuration Access Control Model&quot;">RFC8341</a>]
   provides the means to restrict access for particular NETCONF or
   RESTCONF users to a preconfigured subset of all available NETCONF or
   RESTCONF protocol operations and content.

   There are a number of data nodes defined in this YANG module that are
   writable/creatable/deletable (i.e., config true, which is the
   default).  These data nodes may be considered sensitive or vulnerable
   in some network environments.  Write operations (e.g., edit-config)
   to these data nodes without proper protection can have a negative
   effect on network operations.  The subtrees and data nodes and their
   sensitivity/vulnerability in the ietf-dc-fabric-topology module are
   as follows:

   fabric-attributes: A malicious client could attempt to sabotage the
   configuration of important fabric attributes, such as device nodes or
   type.

   Some of the readable data nodes in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control read access (e.g., via get, get-config, or



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   notification) to these data nodes.  The subtrees and data nodes and
   their sensitivity/vulnerability in the ietf-dc-fabric-topology module
   are as follows:

   fport-attributes: A malicious client could attempt to read the
   connections of fabrics without permission, such as device-port and
   name.

<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>.  References</span>

<span class="h3"><a class="selflink" id="section-7.1" href="#section-7.1">7.1</a>.  Normative References</span>

   [<a id="ref-RFC2119">RFC2119</a>]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>,
              DOI 10.17487/RFC2119, March 1997,
              &lt;<a href="https://www.rfc-editor.org/info/rfc2119">https://www.rfc-editor.org/info/rfc2119</a>&gt;.

   [<a id="ref-RFC3688">RFC3688</a>]  Mealling, M., "The IETF XML Registry", <a href="https://www.rfc-editor.org/bcp/bcp81">BCP 81</a>, <a href="./rfc3688">RFC 3688</a>,
              DOI 10.17487/RFC3688, January 2004,
              &lt;<a href="https://www.rfc-editor.org/info/rfc3688">https://www.rfc-editor.org/info/rfc3688</a>&gt;.

   [<a id="ref-RFC6020">RFC6020</a>]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", <a href="./rfc6020">RFC 6020</a>,
              DOI 10.17487/RFC6020, October 2010,
              &lt;<a href="https://www.rfc-editor.org/info/rfc6020">https://www.rfc-editor.org/info/rfc6020</a>&gt;.

   [<a id="ref-RFC6241">RFC6241</a>]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", <a href="./rfc6241">RFC 6241</a>, DOI 10.17487/RFC6241, June 2011,
              &lt;<a href="https://www.rfc-editor.org/info/rfc6241">https://www.rfc-editor.org/info/rfc6241</a>&gt;.

   [<a id="ref-RFC6242">RFC6242</a>]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", <a href="./rfc6242">RFC 6242</a>, DOI 10.17487/RFC6242, June 2011,
              &lt;<a href="https://www.rfc-editor.org/info/rfc6242">https://www.rfc-editor.org/info/rfc6242</a>&gt;.

   [<a id="ref-RFC7950">RFC7950</a>]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              <a href="./rfc7950">RFC 7950</a>, DOI 10.17487/RFC7950, August 2016,
              &lt;<a href="https://www.rfc-editor.org/info/rfc7950">https://www.rfc-editor.org/info/rfc7950</a>&gt;.

   [<a id="ref-RFC8040">RFC8040</a>]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", <a href="./rfc8040">RFC 8040</a>, DOI 10.17487/RFC8040, January 2017,
              &lt;<a href="https://www.rfc-editor.org/info/rfc8040">https://www.rfc-editor.org/info/rfc8040</a>&gt;.

   [<a id="ref-RFC8174">RFC8174</a>]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in <a href="./rfc2119">RFC</a>
              <a href="./rfc2119">2119</a> Key Words", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc8174">RFC 8174</a>, DOI 10.17487/RFC8174,
              May 2017, &lt;<a href="https://www.rfc-editor.org/info/rfc8174">https://www.rfc-editor.org/info/rfc8174</a>&gt;.





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   [<a id="ref-RFC8341">RFC8341</a>]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, <a href="./rfc8341">RFC 8341</a>,
              DOI 10.17487/RFC8341, March 2018,
              &lt;<a href="https://www.rfc-editor.org/info/rfc8341">https://www.rfc-editor.org/info/rfc8341</a>&gt;.

   [<a id="ref-RFC8342">RFC8342</a>]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore Architecture
              (NMDA)", <a href="./rfc8342">RFC 8342</a>, DOI 10.17487/RFC8342, March 2018,
              &lt;<a href="https://www.rfc-editor.org/info/rfc8342">https://www.rfc-editor.org/info/rfc8342</a>&gt;.

   [<a id="ref-RFC8345">RFC8345</a>]  Clemm, A., Medved, J., Varga, R., Bahadur, N.,
              Ananthakrishnan, H., and X. Liu, "A YANG Data Model for
              Network Topologies", <a href="./rfc8345">RFC 8345</a>, DOI 10.17487/RFC8345, March
              2018, &lt;<a href="https://www.rfc-editor.org/info/rfc8345">https://www.rfc-editor.org/info/rfc8345</a>&gt;.

   [<a id="ref-RFC8346">RFC8346</a>]  Clemm, A., Medved, J., Varga, R., Liu, X.,
              Ananthakrishnan, H., and N. Bahadur, "A YANG Data Model
              for Layer 3 Topologies", <a href="./rfc8346">RFC 8346</a>, DOI 10.17487/RFC8346,
              March 2018, &lt;<a href="https://www.rfc-editor.org/info/rfc8346">https://www.rfc-editor.org/info/rfc8346</a>&gt;.

   [<a id="ref-RFC8446">RFC8446</a>]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", <a href="./rfc8446">RFC 8446</a>, DOI 10.17487/RFC8446, August 2018,
              &lt;<a href="https://www.rfc-editor.org/info/rfc8446">https://www.rfc-editor.org/info/rfc8446</a>&gt;.

<span class="h3"><a class="selflink" id="section-7.2" href="#section-7.2">7.2</a>.  Informative References</span>

   [<a id="ref-GENEVE">GENEVE</a>]   Gross, J., Ganga, I., and T. Sridhar, "Geneve: Generic
              Network Virtualization Encapsulation", Work in Progress,
              <a href="./draft-ietf-nvo3-geneve-12">draft-ietf-nvo3-geneve-12</a>, March 2019.

   [<a id="ref-RFC7348">RFC7348</a>]  Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
              L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
              eXtensible Local Area Network (VXLAN): A Framework for
              Overlaying Virtualized Layer 2 Networks over Layer 3
              Networks", <a href="./rfc7348">RFC 7348</a>, DOI 10.17487/RFC7348, August 2014,
              &lt;<a href="https://www.rfc-editor.org/info/rfc7348">https://www.rfc-editor.org/info/rfc7348</a>&gt;.

   [<a id="ref-RFC8340">RFC8340</a>]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              <a href="https://www.rfc-editor.org/bcp/bcp215">BCP 215</a>, <a href="./rfc8340">RFC 8340</a>, DOI 10.17487/RFC8340, March 2018,
              &lt;<a href="https://www.rfc-editor.org/info/rfc8340">https://www.rfc-editor.org/info/rfc8340</a>&gt;.

   [<a id="ref-RFC8344">RFC8344</a>]  Bjorklund, M., "A YANG Data Model for IP Management",
              <a href="./rfc8344">RFC 8344</a>, DOI 10.17487/RFC8344, March 2018,
              &lt;<a href="https://www.rfc-editor.org/info/rfc8344">https://www.rfc-editor.org/info/rfc8344</a>&gt;.







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<span class="h2"><a class="selflink" id="appendix-A" href="#appendix-A">Appendix A</a>.  Non-NMDA-State Modules</span>

   The YANG module, ietf-dc-fabric-topology, defined in this document
   augments two modules, ietf-network and ietf-network-topology, that
   are designed to be used in conjunction with implementations that
   support the Network Management Datastore Architecture (NMDA) defined
   in [<a href="./rfc8342" title="&quot;Network Management Datastore Architecture (NMDA)&quot;">RFC8342</a>].  In order to allow implementations to use the model
   even in cases when NMDA is not supported, a set of companion modules
   have been defined that represent a state model of networks and
   network topologies: ietf-network-state and ietf-network-topology-
   state, respectively.

   In order to be able to use the model for fabric topologies defined in
   this document in conjunction with non-NMDA-compliant implementations,
   a corresponding companion module needs to be introduced as well.
   This companion module, ietf-dc-fabric-topology-state, mirrors ietf-
   dc-fabric-topology.  However, the ietf-dc-fabric-topology-state
   module augments ietf-network-state (instead of ietf-network and ietf-
   network-topology), and all of its data nodes are non-configurable.

   Like ietf-network-state and ietf-network-topology-state, ietf-dc-
   fabric-topology-state SHOULD NOT be supported by implementations that
   support NMDA.  It is for this reason that the module is defined in
   the Appendix.

   The definition of the module follows.  As the structure of the module
   mirrors that of its underlying module, the YANG tree is not depicted
   separately.

&lt;CODE BEGINS&gt; file "ietf-dc-fabric-topology-state@2019-02-25.yang"
module ietf-dc-fabric-topology-state {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-dc-fabric-topology-state";
  prefix sfabric;

  import ietf-network-state {
    prefix nws;
    reference
      "<a href="./rfc8345">RFC 8345</a>: A Data Model for Network Topologies";
  }
  import ietf-dc-fabric-types {
    prefix fabrictypes;
    reference
      "<a href="./rfc8542">RFC 8542</a>: A YANG Data Model for Fabric Topology in
       Data-Center Networks";
  }

  organization



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    "IETF I2RS (Interface to the Routing System) Working Group";
  contact
    "WG Web:    &lt;<a href="https://datatracker.ietf.org/wg/i2rs/">https://datatracker.ietf.org/wg/i2rs/</a>&gt;
     WG List:   &lt;mailto:i2rs@ietf.org&gt;

     Editor:    Yan Zhuang
                &lt;mailto:zhuangyan.zhuang@huawei.com&gt;

     Editor:    Danian Shi
                &lt;mailto:shidanian@huawei.com&gt;";
  description
    "This module contains a collection of YANG definitions for
     fabric state, representing topology that either is learned
     or results from applying topology that has been
     configured per the ietf-dc-fabric-topology model, mirroring
     the corresponding data nodes in this model.

     This model mirrors the configuration tree of ietf-dc-fabric
     -topology but contains only read-only state data.  The model
     is not needed when the implementation infrastructure supports
     the Network Management Datastore Architecture (NMDA).

     Copyright (c) 2019 IETF Trust and the persons identified as
     authors of the code.  All rights reserved.

     Redistribution and use in source and binary forms, with or
     without modification, is permitted pursuant to, and subject
     to the license terms contained in, the Simplified BSD
     License set forth in <a href="#section-4">Section 4</a>.c of the IETF Trust's Legal
     Provisions Relating to IETF Documents
     (<a href="https://trustee.ietf.org/license-info">https://trustee.ietf.org/license-info</a>).

     This version of this YANG module is part of <a href="./rfc8542">RFC 8542</a>;
     see the RFC itself for full legal notices.";

  revision 2019-02-25 {
    description
      "Initial revision.";
    reference
      "<a href="./rfc8542">RFC 8542</a>: A YANG Data Model for Fabric Topology in
       Data-Center Networks";
  }

  //grouping statements

  grouping fabric-network-type {
    description
      "Identify the topology type to be fabric.";



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    container fabric-network {
      presence "indicates fabric Network";
      description
        "The presence of the container node indicates
         fabric topology";
    }
  }

  grouping fabric-options {
    description
      "Options for a fabric";
    leaf gateway-mode {
      type enumeration {
        enum centralized {
          description
            "The fabric uses centralized
             gateway, in which gateway is deployed on SPINE
             node.";
        }
        enum distributed {
          description
            "The fabric uses distributed
             gateway, in which gateway is deployed on LEAF
             node.";
        }
      }
      default "distributed";
      description
        "Gateway mode of the fabric";
    }
    leaf traffic-behavior {
      type enumeration {
        enum normal {
          description
            "Normal means no policy is needed
             for all traffic";
        }
        enum policy-driven {
          description
            "Policy driven means policy is
             needed for the traffic; otherwise, the traffic
             will be discarded.";
        }
      }
      default "normal";
      description
        "Traffic behavior of the fabric";
    }



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    leaf-list capability-supported {
      type fabrictypes:service-capabilities;
      description
        "It provides a list of supported services of the
         fabric.  The service-capabilities is defined as
         identity-ref.  Users can define more services
         by defining new identities.";
    }
  }

  grouping device-attributes {
    description
      "device attributes";
    leaf device-ref {
      type fabrictypes:node-ref;
      description
        "The device that the fabric includes that refers
         to a node in another topology.";
    }
    leaf-list role {
      type fabrictypes:device-role;
      default "fabrictypes:leaf";
      description
        "It is a list of device roles to represent the roles
         that a device plays within a POD, such as SPINE,
         LEAF, Border, or Border-Leaf.
         The device role is defined as identity-ref.  If more
         than 2 stages are used for a POD, users can
         define new identities for the device role.";
    }
  }

  grouping link-attributes {
    description
      "Link attributes";
    leaf link-ref {
      type fabrictypes:link-ref;
      description
        "The link that the fabric includes that refers to
         a link in another topology.";
    }
  }

  grouping port-attributes {
    description
      "Port attributes";
    leaf port-ref {
      type fabrictypes:tp-ref;



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      description
        "The port that the fabric includes that refers to
         a termination-point in another topology.";
    }
    leaf port-type {
      type fabrictypes:port-type;
      description
        "Port type is defined as identity-ref.  The current
         types include ethernet or serial.  If more types
         are needed, developers can define new identities.";
    }
    leaf bandwidth {
      type fabrictypes:bandwidth;
      description
        "Bandwidth of the port.  It is defined as
         identity-ref.  If more speeds are introduced,
         developers can define new identities for them.  Current
         speeds include 1M, 10M, 100M, 1G, 10G,
         25G, 40G, 100G, and 400G.";
    }
  }

  grouping fabric-attributes {
    description
      "Attributes of a fabric";
    leaf fabric-id {
      type fabrictypes:fabric-id;
      description
        "Fabric ID";
    }
    leaf name {
      type string;
      description
        "Name of the fabric";
    }
    leaf type {
      type fabrictypes:underlay-network-type;
      description
        "The type of physical network that implements this
         fabric.  Examples are VLAN and TRILL.";
    }
    container vni-capacity {
      description
        "The range of the VXLAN Network
         Identifier (VNI) defined in <a href="./rfc7348">RFC 7348</a> that the POD uses.";
      leaf min {
        type int32;
        description



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          "The lower-limit VNI.";
      }
      leaf max {
        type int32;
        description
          "The upper-limit VNI.";
      }
    }

    leaf description {
      type string;
      description
        "Description of the fabric";
    }
    container options {
      description
        "Options of the fabric";
      uses fabric-options;
    }
    list device-nodes {
      key "device-ref";
      description
        "Device nodes that are included in a fabric.";
      uses device-attributes;
    }
    list device-links {
      key "link-ref";
      description
        "Links that are included within a fabric.";
      uses link-attributes;
    }
    list device-ports {
      key "port-ref";
      description
        "Ports that are included in the fabric.";
      uses port-attributes;
    }
  }

  // augment statements

  augment "/nws:networks/nws:network/nws:network-types" {
    description
      "Introduce a new network type for fabric-based logical
       topology";
    uses fabric-network-type;
  }




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  augment "/nws:networks/nws:network/nws:node" {
    when '/nws:networks/nws:network/nws:network-types'
       + '/sfabric:fabric-network' {
      description
        "Augmentation parameters apply only for
         networks with fabric topology.";
    }
    description
      "Augmentation for fabric nodes.";
    container fabric-attributes-state {
      description
        "Attributes for a fabric network";
      uses fabric-attributes;
    }
  }
}
&lt;CODE ENDS&gt;


































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Acknowledgements

   We wish to acknowledge the helpful contributions, comments, and
   suggestions that were received from Alexander Clemm, Donald E.
   Eastlake 3rd, Xufeng Liu, Susan Hares, Wei Song, Luis M. Contreras,
   and Benoit Claise.

Authors' Addresses

   Yan Zhuang
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   Email: zhuangyan.zhuang@huawei.com


   Danian Shi
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   Email: shidanian@huawei.com


   Rong Gu
   China Mobile
   32 Xuanwumen West Ave, Xicheng District
   Beijing, Beijing  100053
   China

   Email: gurong_cmcc@outlook.com


   Hariharan Ananthakrishnan
   Netflix

   Email: hari@netflix.com











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</pre>