    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

         A YANG Data Model for Fabric Topology in Data-Center Networks

    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 Section 2 of RFC 7841.

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

    Copyright Notice

       Copyright (c) 2019 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
       (https://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.

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    RFC 8542            Data Model for DC Fabric Topology         March 2019

    Table of Contents

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

    1.  Introduction

       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 [GENEVE].  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 [RFC6020] [RFC7950] 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 [RFC8345] 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 [RFC8345],
       this model can also be treated as an application of the Interface to
       the Routing System (I2RS) network topology model [RFC8345] 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
       [RFC8346].

       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.

    2.  Definitions and Acronyms

    2.1.  Key Words

       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
       BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
       capitals, as shown here.

    2.2.  Terminology

       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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    3.  Model Overview

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

    3.1.  Topology Model Structure

       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.

    3.2.  Fabric Topology Model

       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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    3.2.1.  Fabric Topology

       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 [RFC8340].

           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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    3.2.2.  Fabric Node Extension

       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 [RFC8340].

           +--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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    3.2.3.  Fabric Termination-Point Extension

       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 [RFC8340].

           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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    4.  Fabric YANG Modules

       This module imports typedefs from [RFC8345], and it references
       [RFC7348] and [RFC8344].

    <CODE BEGINS> 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
          "RFC 8345: A YANG Data Model for Network Topologies";
      }

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

         Editor:    Yan Zhuang
                    <mailto:zhuangyan.zhuang@huawei.com>

         Editor:    Danian Shi
                    <mailto:shidanian@huawei.com>";
      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 Section 4.c of the IETF Trust's
         Legal Provisions Relating to IETF Documents
         (https://trustee.ietf.org/license-info).

         This version of this YANG module is part of RFC 8542;
         see the RFC itself for full legal notices.";

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

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        reference
          "RFC 8542: 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.";
        }
      }
    }

    <CODE ENDS>

       <CODE BEGINS> 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
             "RFC 8345: A YANG Data Model for Network Topologies";
         }
         import ietf-network-topology {
           prefix nt;
           reference
             "RFC 8345: A YANG Data Model for Network Topologies";
         }
         import ietf-dc-fabric-types {
           prefix fabrictypes;
           reference
             "RFC 8542: 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:    <https://datatracker.ietf.org/wg/i2rs/>
            WG List:   <mailto:i2rs@ietf.org>

            Editor:    Yan Zhuang
                       <mailto:zhuangyan.zhuang@huawei.com>

            Editor:    Danian Shi
                       <mailto:shidanian@huawei.com>";
         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 Section 4.c of the IETF Trust's
            Legal Provisions Relating to IETF Documents
            (https://trustee.ietf.org/license-info).

            This version of this YANG module is part of RFC 8542;
            see the RFC itself for full legal notices.";

         revision 2019-02-25 {
           description
             "Initial revision.";
           reference
             "RFC 8542: 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 RFC 7348 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;
           }
         }
       }
       <CODE ENDS>

    5.  IANA Considerations

       This document registers the following namespace URIs in the "IETF XML
       Registry" [RFC3688]:

       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 [RFC6020]:

       Name: ietf-dc-fabric-types
       Namespace: urn:ietf:params:xml:ns:yang:ietf-dc-fabric-types
       Prefix: fabrictypes
       Reference: RFC 8542

       Name: ietf-dc-fabric-topology
       Namespace: urn:ietf:params:xml:ns:yang:ietf-dc-fabric-topology
       Prefix: fabric
       Reference: RFC 8542

       Name: ietf-dc-fabric-topology-state
       Namespace: urn:ietf:params:xml:ns:yang:ietf-dc-fabric-topology-state
       Prefix: sfabric
       Reference: RFC 8542

    6.  Security Considerations

       The YANG module defined in this document is designed to be accessed
       via network management protocols such as NETCONF [RFC6241] or
       RESTCONF [RFC8040].  The lowest NETCONF layer is the secure transport
       layer, and the mandatory-to-implement secure transport is Secure
       Shell (SSH) [RFC6242].  The lowest RESTCONF layer is HTTPS, and the
       mandatory-to-implement secure transport is TLS [RFC8446].

       The Network Configuration Access Control Model (NACM) [RFC8341]
       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.

    7.  References

    7.1.  Normative References

       [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119,
                  DOI 10.17487/RFC2119, March 1997,
                  <https://www.rfc-editor.org/info/rfc2119>.

       [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
                  DOI 10.17487/RFC3688, January 2004,
                  <https://www.rfc-editor.org/info/rfc3688>.

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

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

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

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

       [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
                  Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
                  <https://www.rfc-editor.org/info/rfc8040>.

       [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
                  2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
                  May 2017, <https://www.rfc-editor.org/info/rfc8174>.

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

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

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

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

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

    7.2.  Informative References

       [GENEVE]   Gross, J., Ganga, I., and T. Sridhar, "Geneve: Generic
                  Network Virtualization Encapsulation", Work in Progress,
                  draft-ietf-nvo3-geneve-12, March 2019.

       [RFC7348]  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", RFC 7348, DOI 10.17487/RFC7348, August 2014,
                  <https://www.rfc-editor.org/info/rfc7348>.

       [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
                  BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
                  <https://www.rfc-editor.org/info/rfc8340>.

       [RFC8344]  Bjorklund, M., "A YANG Data Model for IP Management",
                  RFC 8344, DOI 10.17487/RFC8344, March 2018,
                  <https://www.rfc-editor.org/info/rfc8344>.

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    Appendix A.  Non-NMDA-State Modules

       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 [RFC8342].  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.

    <CODE BEGINS> 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
          "RFC 8345: A Data Model for Network Topologies";
      }
      import ietf-dc-fabric-types {
        prefix fabrictypes;
        reference
          "RFC 8542: 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:    <https://datatracker.ietf.org/wg/i2rs/>
         WG List:   <mailto:i2rs@ietf.org>

         Editor:    Yan Zhuang
                    <mailto:zhuangyan.zhuang@huawei.com>

         Editor:    Danian Shi
                    <mailto:shidanian@huawei.com>";
      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 Section 4.c of the IETF Trust's Legal
         Provisions Relating to IETF Documents
         (https://trustee.ietf.org/license-info).

         This version of this YANG module is part of RFC 8542;
         see the RFC itself for full legal notices.";

      revision 2019-02-25 {
        description
          "Initial revision.";
        reference
          "RFC 8542: 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 RFC 7348 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;
        }
      }
    }
    <CODE ENDS>

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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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