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Versions: (draft-dong-i2rs-l2-network-topology) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18

Network Working Group                                            J. Dong
Internet-Draft                                                    X. Wei
Intended status: Standards Track                                   Q. Wu
Expires: January 13, 2021                                         Huawei
                                                            M. Boucadair
                                                                  Orange
                                                                  A. Liu
                                                                  Tecent
                                                           July 12, 2020


            A YANG Data Model for Layer 2 Network Topologies
              draft-ietf-i2rs-yang-l2-network-topology-15

Abstract

   This document defines a YANG data model for Layer 2 network
   topologies.  In particular, this data model augments the generic
   network and network topology data models with Layer 2 specific
   topology attributes.

Editorial Note (To be removed by RFC Editor)

   Please update these statements within the document with the RFC
   number to be assigned to this document:

   o  "This version of this YANG module is part of RFC XXXX;"

   o  "RFC XXXX: A YANG Data Model for Layer 2 Network Topologies";

   o  reference: RFC XXXX

   Please update the "revision" date of the YANG module.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."



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   This Internet-Draft will expire on January 13, 2021.

Copyright Notice

   Copyright (c) 2020 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Layer 2 Topology Model  . . . . . . . . . . . . . . . . . . .   3
   4.  Layer 2 Topology YANG Module  . . . . . . . . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  23
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  23
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  23
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  24
   Appendix A.  Companion YANG Module for Non-NMDA Compliant
                Implementations  . . . . . . . . . . . . . . . . . .  25
   Appendix B.  An Example . . . . . . . . . . . . . . . . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  34

1.  Introduction

   [RFC8345] defines the YANG [RFC6020] [RFC7950] data models of the
   abstract (generic) network and network topology.  Such models can be
   augmented with technology-specific details to build more specific
   topology models.

   This document defines the YANG data model for Layer 2 (L2) network
   topologies by augmenting the generic network (Section 6.1 of
   [RFC8345]) and network topology (Section 6.2 of [RFC8345]) data
   models with L2-specific topology attributes.  An example is provided
   in Appendix B.





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   There are multiple applications for such a data model.  For example,
   within the context of Interface to the Routing System (I2RS), nodes
   within the network can use the data model to capture their
   understanding of the overall network topology and expose it to a
   network controller.  A network controller can then use the
   instantiated topology data to compare and reconcile its own view of
   the network topology with that of the network elements that it
   controls.  Alternatively, nodes within the network may compare and
   reconcile this understanding either among themselves or with the help
   of a controller.  Beyond the network element and the immediate
   context of I2RS itself, a network controller might even use the data
   model to represent its view of the topology that it controls and
   expose it to external applications.  Further use cases where the data
   model can be applied are described in [I2RS-UR].

   This document uses the common YANG types defined in [RFC6991] and
   adopts the Network Management Datastore Architecture (NMDA)
   [RFC8342].

2.  Terminology

   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.

   The terminology for describing YANG modules is defined in [RFC7950].
   The meanings of the symbols used in the tree diagram are defined in
   [RFC8340].

3.  Layer 2 Topology Model

   The Layer 2 network topology YANG module is designed to be generic
   and applicable to Layer 2 networks built with different Layer 2
   technologies.  It can be used to describe both the physical and the
   logical (virtual) Layer 2 network topologies.

   The relationship between the Layer 2 topology module and the generic
   network and network topology module is shown in Figure 1.  In order
   to represent a Layer 2 network topology, the generic network and
   topology models are augmented with Layer 2 specific information, such
   as the identifiers, identities (e.g., Provider Backbone Bridging
   [IEEE802.1ah], QinQ [IEEE802.1ad], or VXLAN [RFC7348]), attributes,
   and states of the Layer 2 networks, nodes, links, and termination
   points.  Some of the information may be collected via Link Layer
   Discovery Protocol (LLDP) [IEEE802.1AB] or other Layer 2 protocols,
   and some of them may be locally configured.



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                                 +---------------------+
                                 |    ietf-network     |
                                 +----------^----------+
                                            |
                                            |
                                 +---------------------+
                                 |ietf-network-topology|
                                 +----------^----------+
                                            |
                                            |
                                 +----------^----------+
                                 |   ietf-l2-topology  |
                                 +---------------------+

             Figure 1: Layer 2 Topology YANG Module Structure

   The structure of the "ietf-l2-topology" YANG module is depicted in
   the following tree diagram:

module: ietf-l2-topology
  augment /nw:networks/nw:network/nw:network-types:
    +--rw l2-network!
  augment /nw:networks/nw:network:
    +--rw l2-topology-attributes
       +--rw name?    string
       +--rw flags*   l2-flag-type
  augment /nw:networks/nw:network/nw:node:
    +--rw l2-node-attributes
       +--rw name?                 string
       +--rw description?          string
       +--rw management-address*   inet:ip-address
       +--rw sys-mac-address?      yang:mac-address
       +--rw management-vlan-id?   dot1q-types:vlanid {VLAN}?
       +--rw flags*                node-flag-type
  augment /nw:networks/nw:network/nt:link:
    +--rw l2-link-attributes
       +--rw name?    string
       +--rw flags*   link-flag-type
       +--rw rate?    uint64
       +--rw delay?   uint32
  augment /nw:networks/nw:network/nw:node/nt:termination-point:
    +--rw l2-termination-point-attributes
       +--rw description?                   string
       +--rw maximum-frame-size?            uint32
       +--rw (l2-termination-point-type)?
       |  +--:(ethernet)
       |  |  +--rw mac-address?             yang:mac-address
       |  |  +--rw eth-encapsulation?       identityref



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       |  |  +--rw lag?                     boolean
       |  |  +--rw member-link-tp*          -> /nw:networks/network
                                            /node/nt:termination-point/tp-id
       |  |  +--rw auto-negotiation?        boolean
       |  |  +--rw duplex?                  duplex-mode
       |  |  +--rw default-untagged-vlan?   dot1q-types:vlanid {VLAN}?
       |  |  +--rw vlans* [vlan-id] {VLAN}?
       |  |  |  +--rw vlan-id    dot1q-types:vlanid
       |  |  |  +--rw name?      string
       |  |  +--rw qinq* [svlan-id cvlan-id] {QinQ}?
       |  |  |  +--rw svlan-id    dot1q-types:vlanid
       |  |  |  +--rw cvlan-id    dot1q-types:vlanid
       |  |  +--rw vxlan {VXLAN}?
       |  |     +--rw vni-id?   vni
       |  +--:(legacy)
       |     +--rw layer-2-address?         yang:phys-address
       |     +--rw encapsulation?           identityref
       +--ro tp-state?                      identityref

  notifications:
    +---n l2-node-event
    |  +--ro event-type?           l2-network-event-type
    |  +--ro node-ref?             -> /nw:networks/network
                               [nw:network-id=current()/../network-ref]/node/node-id
    |  +--ro network-ref?          -> /nw:networks/network/network-id
    |  +--ro l2-network!
    |  +--ro l2-node-attributes
    |     +--ro name?                 string
    |     +--ro description?          string
    |     +--ro management-address*   inet:ip-address
    |     +--ro sys-mac-address?      yang:mac-address
    |     +--ro management-vlan-id?   dot1q-types:vlanid {VLAN}?
    |     +--ro flags*                node-flag-type
    +---n l2-link-event
    |  +--ro event-type?           l2-network-event-type
    |  +--ro link-ref?             -> /nw:networks/network
                              [nw:network-id=current()/../network-ref]/nt:link/link-id
    |  +--ro network-ref?          -> /nw:networks/network/network-id
    |  +--ro l2-network!
    |  +--ro l2-link-attributes
    |     +--ro name?    string
    |     +--ro flags*   link-flag-type
    |     +--ro rate?    uint64
    |     +--ro delay?   uint32
    +---n l2-termination-point-event
       +--ro event-type?                        l2-network-event-type
       +--ro tp-ref?                            -> /nw:networks/network
                              [nw:network-id=current()/../network-ref]/node



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                          [nw:node-id=current()/../node-ref]/nt:termination-point/tp-id
       +--ro node-ref?                          -> /nw:networks/network
                              [nw:network-id=current()/../network-ref]/node/node-id
       +--ro network-ref?                       -> /nw:networks/network/network-id
       +--ro l2-network!
       +--ro l2-termination-point-attributes
          +--ro description?                   string
          +--ro maximum-frame-size?            uint32
          +--ro (l2-termination-point-type)?
          |  +--:(ethernet)
          |  |  +--ro mac-address?             yang:mac-address
          |  |  +--ro eth-encapsulation?       identityref
          |  |  +--ro lag?                     boolean
          |  |  +--ro member-link-tp*          -> /nw:networks/network
                                               /node/nt:termination-point/tp-id
          |  |  +--ro auto-nego?               boolean
          |  |  +--ro duplex?                  duplex-mode
          |  |  +--ro default-untagged-vlan?   dot1q-types:vlanid {VLAN}?
          |  |  +--ro vlans* [vlan-id] {VLAN}?
          |  |  |  +--ro vlan-id    dot1q-types:vlanid
          |  |  |  +--ro name?      string
          |  |  +--ro qinq* [svlan-id cvlan-id] {QinQ}?
          |  |  |  +--ro svlan-id    dot1q-types:vlanid
          |  |  |  +--ro cvlan-id    dot1q-types:vlanid
          |  |  +--ro vxlan {VXLAN}?
          |  |     +--ro vni-id?   vni
          |  +--:(legacy)
          |     +--ro layer-2-address?         yang:phys-address
          |     +--ro encapsulation?           identityref
          +--ro tp-state?                      identityref

   The Layer 2 topology YANG module augments the "ietf-network" and
   "ietf-network-topology" YANG modules as follows:

   o  A new network type "l2-network-type" is introduced.  This is
      represented by a container object, and is inserted under the
      "network-types" container of the generic "ietf-network" module
      defined in Section 6.1 of [RFC8345].

   o  Additional network attributes are introduced in a grouping "l2-
      network-attributes", which augments the "network" list of the
      "ietf-network" module.  The attributes include Layer 2 network
      name and a set of flags.  Each type of flag is represented by a
      separate identity.

   o  Additional data objects for Layer 2 nodes are introduced by
      augmenting the "node" list of the generic "ietf-network" module.




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      New objects include Layer 2 node identifier, description,
      management address, and a set of flags.

   o  Additional data objects for Layer 2 termination points are
      introduced by augmenting the "termination-point" list of the
      "ietf-network-topology" module defined in Section 6.2 of
      [RFC8345].  New objects include Layer 2 termination point
      descriptions, Layer 2 termination point type specific attributes
      and Layer 2 termination point states.

   o  Links in the "ietf-network-topology" module are augmented as well
      with a set of Layer 2 parameters, allowing to associate a link
      with a name, a set of Layer 2 link attributes, and flags.

   o  Some optional Layer 2 technology specific attributes are
      introduced in this module as Layer 2 features because these
      attributes may be useful to expose to above services/applications.
      Note that learning or configuring advanced Layer 2 technology-
      specific attributes is not within the scope of the Layer 2
      Topology YANG module; dedicated YANG modules should be used
      instead (e.g., [I-D.ietf-trill-yang]).

4.  Layer 2 Topology YANG Module

   This module uses types defined in [RFC6991], [RFC7224],
   [IEEE802.1Qcp], and [RFC8345].  It also references [RFC4761],
   [RFC4762], and [RFC4202].

<CODE BEGINS> file "ietf-l2-topology@2020-06-29.yang"
module ietf-l2-topology {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-l2-topology";
  prefix l2t;

  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-inet-types {
    prefix inet;
    reference
      "RFC 6991:Common YANG Data Types";



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  }
  import ietf-yang-types {
    prefix yang;
    reference
      "RFC 6991:Common YANG Data Types";
  }
  import iana-if-type {
    prefix ift;
    reference
      "RFC 7224: IANA Interface Type YANG Module";
  }
  import ieee802-dot1q-types {
    prefix dot1q-types;
    reference
      "IEEE Std 802.1Qcp-2018: Bridges and Bridged
       Networks - Amendment: YANG Data Model";
  }

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

     Editor:    Jie Dong
               <mailto:jie.dong@huawei.com>

     Editor:    Xiugang Wei
               <mailto:weixiugang@huawei.com>

     Editor:    Qin Wu
               <mailto:bill.wu@huawei.com>

     Editor:    Mohamed Boucadair
               <mailto:mohamed.boucadair@orange.com>

     Editor:   Anders Liu
               <andersliu@tencent.com>";
  description
    "This module defines a basic model for the Layer 2 topology
     of a network.

     Copyright (c) 2020 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



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     set forth in Section 4.c of the IETF Trust's Legal Provisions
     Relating to IETF Documents
     (http://trustee.ietf.org/license-info).

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

  revision 2020-06-29 {
    description
      "Initial revision";
    reference
      "RFC XXXX: A YANG Data Model for Layer 2
       Network Topologies";
  }

  feature VLAN {
    description
      "Enables VLAN tag support as defined in IEEE 802.1Q.";
    reference
      "IEEE Std 802.1Q-2014: Bridges and Bridged Networks";
  }

  feature QinQ {
    description
      "Enables QinQ double tag support as defined in IEEE 802.1ad.";
    reference
      "IEEE Std 802.1ad: Provider Bridges";
  }

  feature VXLAN {
    description
      "Enables VXLAN support as defined in RFC7348.";
    reference
      "RFC 7348: Virtual eXtensible Local Area  Network (VXLAN):
       A Framework for Overlaying Virtualized Layer 2
       Networks over Layer 3 Networks";
  }

  identity flag-identity {
    description
      "Base type for flags.";
  }

  identity eth-encapsulation-type {
    base ift:iana-interface-type;
    description
      "Base identity from which specific Ethernet
       encapsulation types are derived.";



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    reference
      "RFC 7224: IANA Interface Type YANG Module";
  }

  identity ethernet {
    base eth-encapsulation-type;
    description
      "Native Ethernet encapsulation.";
  }

  identity vlan {
    base eth-encapsulation-type;
    description
      "VLAN encapsulation.";
  }

  identity qinq {
    base eth-encapsulation-type;
    description
      "QinQ encapsulation.";
  }

  identity pbb {
    base eth-encapsulation-type;
    description
      "Provider-backbone-bridging (PBB) encapsulation.
       The PBB functions are developed in IEEE 802.1ah.";
  }

  identity trill {
    base eth-encapsulation-type;
    description
      "TRILL encapsulation.";
  }

  identity vpls {
    base eth-encapsulation-type;
    description
      "Ethernet VPLS interface encapsulation.";
  }

  identity vxlan {
    base eth-encapsulation-type;
    description
      "VXLAN MAC in UDP encapsulation.";
    reference
      "RFC 7348: Virtual eXtensible Local Area  Network (VXLAN):
       A Framework for Overlaying Virtualized Layer 2



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       Networks over Layer 3 Networks";
  }

  identity tp-state-type {
    description
      "Base type for termination point state.";
  }

  identity inuse {
    base tp-state-type;
    description
      "The termination point is in forwarding state.";
  }

  identity blocking {
    base tp-state-type;
    description
      "The termination point is in blocking state.";
  }

  identity down {
    base tp-state-type;
    description
      "The termination point is in down state.";
  }

  identity unknown {
    base tp-state-type;
    description
      "The termination point is in unknown state.";
  }

  typedef vni {
    type uint32 {
      range "0..16777215";
    }
    description
      "VXLAN Network Identifier or VXLAN Segment ID.
       It allows up to 16 M VXLAN segments to coexist
       within the same administrative domain.

       The use of value '0' is implementation-specific.";
    reference
      "RFC 7348: Virtual eXtensible Local Area  Network (VXLAN):
                 A Framework for Overlaying Virtualized Layer 2
                 Networks over Layer 3 Networks";
  }




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  typedef l2-flag-type {
    type identityref {
      base flag-identity;
    }
    description
      "Base type for L2 flags. One example of L2 flag
       type is trill which represents trill topology
       type.";
  }

  typedef node-flag-type {
    type identityref {
      base flag-identity;
    }
    description
      "Node flag attributes. The physical node can be
       one example of node flag attribute.";
  }

  typedef link-flag-type {
    type identityref {
      base flag-identity;
    }
    description
      "Link flag attributes. One example of link flag
       attribute is the pseudowire.";
  }

  typedef l2-network-event-type {
    type enumeration {
      enum addition {
        value 0;
        description
          "A Layer 2 node or link or termination-point
           has been added.";
      }
      enum removal {
        value 1;
        description
          "A Layer 2 node or link or termination-point
           has been removed.";
      }
      enum update {
        value 2;
        description
          "A Layer 2 node or link or termination-point
           has been updated.";
      }



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    }
    description
      "Layer 2 network event type for notifications.";
  }

  typedef duplex-mode {
    type enumeration {
      enum full-duplex {
        description
          "Indicates full-duplex mode.";
      }
      enum half-duplex {
        description
          "Indicates half-duplex mode.";
      }
    }
    description
      "Indicates the type of the duplex mode.";
  }

  grouping l2-network-type {
    description
      "Indicates the topology type to be L2.";
    container l2-network {
      presence "Indicates L2 Network";
      description
        "The presence of the container node indicates
         L2 Topology.";
    }
  }

  grouping l2-topology-attributes {
    description
      "L2 Topology scope attributes.";
    container l2-topology-attributes {
      description
        "Contains L2 topology attributes.";
      leaf name {
        type string;
        description
          "Name of the topology.";
      }
      leaf-list flags {
        type l2-flag-type;
        description
          "Topology flags.";
      }
    }



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  }

  grouping l2-node-attributes {
    description
      "L2 node attributes";
    container l2-node-attributes {
      description
        "Contains L2 node attributes.";
      leaf name {
        type string;
        description
          "Node name.";
      }
      leaf description {
        type string;
        description
          "Node description.";
      }
      leaf-list management-address {
        type inet:ip-address;
        description
          "IP address used for
           management purpose.";
      }
      leaf sys-mac-address {
        type yang:mac-address;
        description
          "MAC address used to identify layer 2 node.
           This MAC address can be used as interface
           MAC address.";
      }
      leaf management-vlan-id {
        if-feature "VLAN";
        type dot1q-types:vlanid;
        description
          "VLAN ID used for management
           purpose.";
      }
      leaf-list flags {
        type node-flag-type;
        description
          "Node flags. It can be used to indicates
           node flag attributes.";
      }
    }
  }

  grouping l2-link-attributes {



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    description
      "L2 link attributes";
    container l2-link-attributes {
      description
        "Contains L2 link attributes.";
      leaf name {
        type string;
        description
          "Link name.";
      }
      leaf-list flags {
        type link-flag-type;
        description
          "Link flags. It can be used to indicate
           link flag attributes.";
      }
      leaf rate {
        type uint64;
        units "Kbps";
        description
          "Link rate. It specifies bandwidth requirements
           associated with the specific link. The link
           contains a source and a destination.";
      }
      leaf delay {
        type uint32;
        units "microseconds";
        description
          "Unidirectional Link delay in
           microseconds.";
      }
    }
  }

  grouping l2-termination-point-attributes {
    description
      "L2 termination point attributes";
    container l2-termination-point-attributes {
      description
        "Containing L2 termination point attributes.";
      leaf description {
        type string;
        description
          "L2 termination point description. It also
           can be seen as port description.";
      }
      leaf maximum-frame-size {
        type uint32;



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        description
          "Maximum L2 frame size that can be transported on
           the data link layer, e.g. Ethernet frame.
           If L2 frame is an Ethernet frame, the maximum frame size
           should include Frame Check Sequence(FCS) and should not
           include preamble,Start Frame Delimiter and Inter frame
           gap.";
      }
      choice l2-termination-point-type {
        description
          "Indicates termination-point type
           specific attributes.";
        case ethernet {
          leaf mac-address {
            type yang:mac-address;
            description
              "Interface MAC address.";
          }
          leaf eth-encapsulation {
            type identityref {
              base eth-encapsulation-type;
            }
            description
              "Encapsulation type of this
               termination point.";
          }
          leaf lag {
            type boolean;
            default "false";
            description
              "Defines whether lag is enabled or disabled.
               When it is set to true, the lag is enabled.";
          }
          leaf-list member-link-tp {
            when "../lag = 'true'" {
              description
                "Relevant only when the lag interface is enabled.";
            }
            type leafref {
              path "/nw:networks/nw:network/nw:node/nt:termination-point/nt:tp-id";
            }
            description
              "Member link termination points.";
          }
          leaf auto-nego {
            type boolean;
            default "true";
            description



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              "Set to true if auto negotiation is supported.
               Set to false if auto negotiation is not supported.";
          }
          leaf duplex {
            type duplex-mode;
            description
              "Expose the duplex mode, full duplex or half-duplex.";
          }
          leaf default-untagged-vlan {
            when "derived-from-or-self(../eth-encapsulation, 'l2t:vlan')" {
              description
                "Only applies when the type of the Ethernet
                 encapsulation is 'vlan'.";
            }
            if-feature "VLAN";
            type dot1q-types:vlanid;
            description
              "Port VLAN ID is the VLAN identifier that
               will be assigned to any untagged frames entering
               the switch on the specific port.";
          }
          list vlans {
            when "derived-from-or-self(../eth-encapsulation, 'l2t:vlan')" {
              description
                "Only applies when the type of the Ethernet
                 encapsulation is 'vlan'.";
            }
            if-feature "VLAN";
            key "vlan-id";
            description
              "Interface configured VLANs.";
            leaf vlan-id {
              type dot1q-types:vlanid;
              description
                "VLAN ID.";
            }
            leaf name {
              type string {
                length "1..31";
              }
              description
                "VLAN name.";
            }
          }
          list qinq {
            when "derived-from-or-self(../eth-encapsulation, 'l2t:qinq')" {
              description
                "Only applies when the type of the Ethernet



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                 encapsulation is 'qinq'.";
            }
            if-feature "QinQ";
            key "svlan-id cvlan-id";
            description
              "Interface configured SVLANs and CVLANs.";
            leaf svlan-id {
              type dot1q-types:vlanid;
              description
                "Service VLAN ID.";
            }
            leaf cvlan-id {
              type dot1q-types:vlanid;
              description
                "Customer VLAN ID.";
            }
          }
          container vxlan {
            when "derived-from-or-self(../eth-encapsulation, 'l2t:vxlan')" {
              description
                "Only applies when the type of the Ethernet
                 encapsulation is 'vxlan'.";
            }
            if-feature "VXLAN";
            leaf vni-id {
              type vni;
              description
                "VXLAN Network Identifier (VNI).";
            }
            description
              "Vxlan encapsulation type.";
          }
        }
        case legacy {
          leaf layer-2-address {
            type yang:phys-address;
            description
              "Interface Layer 2 address.";
          }
          leaf encapsulation {
            type identityref {
              base ift:iana-interface-type;
            }
            description
              "Other legacy encapsulation type of this
               termination point.";
          }
        }



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      }
      leaf tp-state {
        type identityref {
          base tp-state-type;
        }
        config false;
        description
          "State of the termination point.";
      }
    }
  }

  augment "/nw:networks/nw:network/nw:network-types" {
    description
      "Introduces new network type for L2 topology.";
    uses l2-network-type;
  }
  augment "/nw:networks/nw:network" {
    when '/nw:networks/nw:network/nw:network-types/l2t:l2-network' {
      description
        "Augmentation parameters apply only for networks
         with L2 topology.";
    }
    description
      "Configuration parameters for the L2 network
       as a whole.";
    uses l2-topology-attributes;
  }
  augment "/nw:networks/nw:network/nw:node" {
    when '/nw:networks/nw:network/nw:network-types/l2t:l2-network' {
      description
        "Augmentation parameters apply only for networks
         with L2 topology.";
    }
    description
      "Configuration parameters for L2 at the node
       level.";
    uses l2-node-attributes;
  }
  augment "/nw:networks/nw:network/nt:link" {
    when '/nw:networks/nw:network/nw:network-types/l2t:l2-network' {
      description
        "Augmentation parameters apply only for networks
         with L2 topology.";
    }
    description
      "Augments L2 topology link information.";
    uses l2-link-attributes;



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  }
  augment "/nw:networks/nw:network/nw:node/nt:termination-point" {
    when '/nw:networks/nw:network/nw:network-types/l2t:l2-network' {
      description
        "Augmentation parameters apply only for networks
         with L2 topology.";
    }
    description
      "Augments L2 topology termination point information.";
    uses l2-termination-point-attributes;
  }

  notification l2-node-event {
    description
      "Notification event for L2 node.";
    leaf event-type {
      type l2-network-event-type;
      description
        "Event type.";
    }
    uses nw:node-ref;
    uses l2-network-type;
    uses l2-node-attributes;
  }

  notification l2-link-event {
    description
      "Notification event for L2 link.";
    leaf event-type {
      type l2-network-event-type;
      description
        "Event type.";
    }
    uses nt:link-ref;
    uses l2-network-type;
    uses l2-link-attributes;
  }

  notification l2-termination-point-event {
    description
      "Notification event for L2 termination point.";
    leaf event-type {
      type l2-network-event-type;
      description
        "Event type.";
    }
    uses nt:tp-ref;
    uses l2-network-type;



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    uses l2-termination-point-attributes;
  }
}

<CODE ENDS>

5.  IANA Considerations

   This document requests IANA to register the following URIs in the
   "ns" subregistry within the "IETF XML Registry" [RFC3688]:

      URI: urn:ietf:params:xml:ns:yang:ietf-l2-topology
      Registrant Contact: The IESG.
      XML: N/A; the requested URI is an XML namespace.

      URI: urn:ietf:params:xml:ns:yang:ietf-l2-topology-state
      Registrant Contact: The IESG.
      XML: N/A; the requested URI is an XML namespace.

   This document requests IANA to register the following YANG modules in
   the "YANG Module Names" subregistry [RFC6020] within the "YANG
   Parameters" registry.

     name: ietf-l2-topology
     namespace: urn:ietf:params:xml:ns:yang:ietf-l2-topology
     prefix: l2t
     reference: RFC XXXX

     name: ietf-l2-topology-state
     namespace: urn:ietf:params:xml:ns:yang:ietf-l2-topology-state
     prefix: l2t-s
     reference: RFC XXXX

   These modules are not maintained by IANA.

6.  Security Considerations

   The YANG module specified in this document defines a schema for data
   that 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




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   RESTCONF users to a preconfigured subset of all available NETCONF or
   RESTCONF protocol operations and content.

   The Layer 2 topology module defines information that can be
   configurable in certain instances, for example in the case of virtual
   topologies that can be created by client applications.  In such
   cases, a malicious client could introduce topologies that are
   undesired.  Specifically, a malicious client could attempt to remove
   or add a node, a link, a termination point, by creating or deleting
   corresponding elements in the node, link, and termination point
   lists, respectively.  In the case of a topology that is learned, the
   server will automatically prohibit such misconfiguration attempts.
   In the case of a topology that is configured, i.e. whose origin is
   "intended", the undesired configuration could become effective and be
   reflected in the operational state datastore [RFC8342], leading to
   disruption of services provided via this topology.  For those
   reasons, it is important that the NACM is vigorously applied to
   prevent topology misconfiguration by unauthorized clients.

   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.  These are the subtrees and data nodes
   and their sensitivity/vulnerability:

   o  l2-network-attributes: A malicious client could attempt to
      sabotage the configuration of any of the contained attributes,
      such as the name or the flag data nodes.

   o  l2-node-attributes: A malicious client could attempt to sabotage
      the configuration of important node attributes, such as the name
      or the management-address.

   o  l2-link-attributes: A malicious client could attempt to sabotage
      the configuration of important link attributes, such as the rate
      or the delay data nodes.

   o  l2-termination-point-attributes: A malicious client could attempt
      to sabotage the configuration of important termination point
      attributes (e.g., 'maximum-frame-size').

   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
   notification) to these data nodes.  In particular, the YANG model for
   layer 2 topology may expose sensitive information, for example the



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   MAC addresses of devices, VLAN/VXLAN identifiers.  Unrestricted use
   of such information can lead to privacy violations.  For example,
   listing MAC addresses in a network allows monitoring of devices and
   their movements.  Location information can be derived from MAC
   addresses of network devices, bypassing protection of location
   information by the Operating System.

7.  Acknowledgements

   The authors would like to acknowledge the comments and suggestions
   received from Susan Hares, Alia Atlas, Juergen Schoenwaelder, Mach
   Chen, Alexander Clemm, Sriganesh Kini, Oscar Gonzalez de Dios, Stig
   Venaas, Christian Huitema, and Meral Shirazipour,Benjamin Kaduk.

   Many thanks to Ladislav Lhotka for the yang-doctors review.

8.  References

8.1.  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>.

   [RFC4202]  Kompella, K., Ed. and Y. Rekhter, Ed., "Routing Extensions
              in Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 4202, DOI 10.17487/RFC4202, October 2005,
              <https://www.rfc-editor.org/info/rfc4202>.

   [RFC4761]  Kompella, K., Ed. and Y. Rekhter, Ed., "Virtual Private
              LAN Service (VPLS) Using BGP for Auto-Discovery and
              Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007,
              <https://www.rfc-editor.org/info/rfc4761>.

   [RFC4762]  Lasserre, M., Ed. and V. Kompella, Ed., "Virtual Private
              LAN Service (VPLS) Using Label Distribution Protocol (LDP)
              Signaling", RFC 4762, DOI 10.17487/RFC4762, January 2007,
              <https://www.rfc-editor.org/info/rfc4762>.

   [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>.

   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
              RFC 6991, DOI 10.17487/RFC6991, July 2013,
              <https://www.rfc-editor.org/info/rfc6991>.



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   [RFC7224]  Bjorklund, M., "IANA Interface Type YANG Module",
              RFC 7224, DOI 10.17487/RFC7224, May 2014,
              <https://www.rfc-editor.org/info/rfc7224>.

   [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>.

   [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>.

   [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>.

   [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>.

   [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>.

   [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>.

8.2.  Informative References

   [I-D.ietf-trill-yang]
              Weiguo, H., Yizhou, L., Kumar, D., Durrani, M., Zhai, H.,
              and L. Xia, "TRILL YANG Data Model", draft-ietf-trill-
              yang-04 (work in progress), December 2015.

   [I2RS-UR]  Hares, S. and M. Chen, "Summary of I2RS Use Case
              Requirements", draft-ietf-i2rs-usecase-reqs-summary-03
              (work in progress), November 2016.

   [IEEE802.1AB]
              "Station and Media Access Control Connectivity Discovery",
              IEEE Std 802.1AB-2016, March 2016.




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   [IEEE802.1ad]
              "Virtual Bridged Local Area Networks Amendment 4: Provider
              Bridges", IEEE Std 802.1ad-2005, May 2006.

   [IEEE802.1ah]
              "Virtual Bridged Local Area Networks Amendment 4: Provider
              Bridges", IEEE Std 802.1ah-2008, August 2008.

   [IEEE802.1Qcp]
              "Bridges and Bridged Networks - Amendment: YANG Data
              Model", IEEE Std 802.1Qcp-2018, September 2018.

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

   [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>.

   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              RFC 7951, DOI 10.17487/RFC7951, August 2016,
              <https://www.rfc-editor.org/info/rfc7951>.

   [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>.

   [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>.

   [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>.

Appendix A.  Companion YANG Module for Non-NMDA Compliant
             Implementations

   The YANG module ietf-l2-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



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   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 layer 2 topologies defined
   in this document in conjunction with non-NMDA compliant
   implementations, a corresponding companion module is defined that
   represents the operational state of layer 2 network topologies.  The
   module "ietf-l2-topology-state" mirrors the module "ietf-l2-topology"
   defined in Section 4.  However, it augments "ietf-network-state" and
   "ietf-network-topology-state" (instead of "ietf-network" and "ietf-
   network-topology") and all its data nodes are non-configurable.

   The companion module "ietf-l2-topology" SHOULD NOT be supported by
   implementations that support NMDA.  It is for this reason that this
   module is defined in the informative Appendix.

   As the structure of this modules mirrors that of its underlying
   modules, the YANG tree is not depicted separately.

   <CODE BEGINS> file "ietf-l2-topology-state@2020-06-29.yang"
   module ietf-l2-topology-state {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-l2-topology-state";
     prefix l2t-s;

     import ietf-network-state {
       prefix nw-s;
       reference
         "RFC 8345: A YANG Data Model for Network Topologies";
     }
     import ietf-network-topology-state {
       prefix nt-s;
       reference
         "RFC 8345: A YANG Data Model for Network Topologies";
     }
     import ietf-l2-topology {
       prefix l2t;
       reference
         "RFC XXXX: A YANG Data Model for Layer 2 Network
                    Topologies";
     }

     organization
       "IETF I2RS (Interface to the Routing System) Working Group";



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     contact
       "WG Web:   <http://tools.ietf.org/wg/i2rs/>
        WG List:  <mailto:i2rs@ietf.org>

        Editor:    Jie Dong
                  <mailto:jie.dong@huawei.com>
        Editor:    Xiugang Wei
                  <mailto:weixiugang@huawei.com>
        Editor:    Qin Wu
                  <mailto:bill.wu@huawei.com>
        Editor:    Mohamed Boucadair
                  <mailto:mohamed.boucadair@orange.com>
        Editor:   Anders Liu
                  <andersliu@tencent.com>";
     description
       "This module defines a model for Layer 2 Network Topology
        state, representing topology that either is learned or
        results from applying topology that has been configured per
        the 'ietf-l2-topology' model, mirroring the
        corresponding data nodes in this model.

        This model mirrors 'ietf-l2-topology' but contains only
        read-only state data.  The model is not needed when the
        underlying implementation infrastructure supports the
        Network Management Datastore Architecture (NMDA).

        Copyright (c) 2020 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
        (http://trustee.ietf.org/license-info).

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

     revision 2020-06-29 {
       description
         "Initial revision";
       reference
         "RFC XXXX: A YANG Data Model for Layer 2 Network
                    Topologies";
     }

     /*



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      * Data nodes
      */

     augment "/nw-s:networks/nw-s:network/nw-s:network-types" {
       description
         "Introduces a new network type for L2 topology.";
       uses l2t:l2-network-type;
     }

     augment "/nw-s:networks/nw-s:network" {
       when '/nw-s:networks/nw-s:network/nw-s:network-types/'
          + 'l2t-s:l2-network' {
         description
           "Augmentation parameters apply only for networks
            with L2 topology.";
       }
       description
         "Configuration parameters for the L2 network
          as a whole.";
       uses l2t:l2-network-attributes;
     }

     augment "/nw-s:networks/nw-s:network/nw-s:node" {
       when '../nw-s:network-types/l2t-s:l2-network' {
         description
           "Augmentation parameters apply only for networks
            with L2 topology.";
       }
       description
         "Configuration parameters for L2 at the node
          level.";
       uses l2t:l2-node-attributes;
     }

     augment "/nw-s:networks/nw-s:network/nt-s:link" {
       when '../nw-s:network-types/l2t-s:l2-network' {
         description
           "Augmentation parameters apply only for networks
            with L2 topology.";
       }
       description
         "Augments L2 topology link information.";
       uses l2t:l2-link-attributes;
     }

     augment "/nw-s:networks/nw-s:network/nw-s:node/"
           + "nt-s:termination-point" {
       when '../../nw-s:network-types/l2t-s:l2-network' {



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         description
           "Augmentation parameters apply only for networks
            with L2 topology.";
       }
       description
         "Augments L2 topology termination point information.";
       uses l2t:l2-termination-point-attributes;
     }

     /*
      * Notifications
      */

     notification l2-node-event {
       description
         "Notification event for L2 node.";
       leaf event-type {
         type l2t:l2-network-event-type;
         description
           "Event type.";
       }
       uses nw-s:node-ref;
       uses l2t:l2-network-type;
       uses l2t:l2-node-attributes;
     }

     notification l2-link-event {
       description
         "Notification event for a L2 link.";
       leaf event-type {
         type l2t:l2-network-event-type;
         description
           "Event type.";
       }
       uses nt-s:link-ref;
       uses l2t:l2-network-type;
       uses l2t:l2-link-attributes;
     }

     notification l2-termination-point-event {
       description
         "Notification event for L2 termination point.";
       leaf event-type {
         type l2t:l2-network-event-type;
         description
           "Event type.";
       }
       uses nt-s:tp-ref;



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       uses l2t:l2-network-type;
       uses l2t:l2-termination-point-attributes;
     }
   }
   <CODE ENDS>

Appendix B.  An Example

   This section contains an example of an instance data tree in JSON
   encoding [RFC7951].  The example instantiates "ietf-l2-topology" for
   the topology that is depicted in the following diagram.  There are
   three nodes: D1, D2, and D3.  D1 has three termination points: 1-0-1,
   1-2-1, and 1-3-1.  D2 has three termination points as well: 2-1-1,
   2-0-1, and 2-3-1.  D3 has two termination points: 3-1-1 and 3-2-1.
   In addition, there are six links, two between each pair of nodes,
   with one going in each direction.

                   +------------+                   +------------+
                   |     D1     |                   |     D2     |
                  /-\          /-\                 /-\          /-\
                  | | 1-0-1    | |---------------->| | 2-1-1    | |
                  | |    1-2-1 | |<----------------| |    2-0-1 | |
                  \-/  1-3-1   \-/                 \-/  2-3-1   \-/
                   |   /----\   |                   |   /----\   |
                   +---|    |---+                   +---|    |---+
                       \----/                           \----/
                        A  |                             A  |
                        |  |                             |  |
                        |  |                             |  |
                        |  |       +------------+        |  |
                        |  |       |     D3     |        |  |
                        |  |      /-\          /-\       |  |
                        |  +----->| | 3-1-1    | |-------+  |
                        +---------| |    3-2-1 | |<---------+
                                  \-/          \-/
                                   |            |
                                   +------------+

                      Figure 2. A Network Topology Example

   The corresponding instance data tree is depicted below:

    {
     "ietf-network:networks": {
       "network": [
         {
           "network-types": {
             "ietf-l2-topology:l2-network": {}



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           },
           "network-id": "l2-topo-example",
           "node": [
             {
               "node-id": "D1",
               "ietf-network-topology:termination-point": [
                 {
                   "tp-id": "1-0-1",
                   "ietf-l2-topology:l2-termination-point-attributes": {
                     "mac-address": "00:00:5E:00:53:D0"
                   }
                 },
                 {
                   "tp-id": "1-2-1",
                   "ietf-l2-topology:l2-termination-point-attributes": {
                     "mac-address": "00:00:5E:00:53:D1"
                   }
                 },
                 {
                   "tp-id": "1-3-1",
                   "ietf-l2-topology:l2-termination-point-attributes": {
                     "mac-address": "00:00:5E:00:53:D2"
                   }
                 }
               ],
               "ietf-l2-topology:l2-node-attributes": {
                 "management-address": [
                   "192.0.2.1",
                   "2001:db8:0:1::/64"
                 ]
               }
             },
             {
               "node-id": "D2",
               "ietf-network-topology:termination-point": [
                 {
                   "tp-id": "2-0-1",
                   "ietf-l2-topology:l2-termination-point-attributes": {
                     "mac-address": "00:00:5E:00:53:E0"
                   }
                 },
                 {
                   "tp-id": "2-1-1",
                   "ietf-l2-topology:l2-termination-point-attributes": {
                     "mac-address": "00:00:5E:00:53:E1"
                   }
                 },
                 {



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                   "tp-id": "2-3-1",
                   "ietf-l2-topology:l2-termination-point-attributes": {
                     "mac-address": "00:00:5E:00:53:E2"
                   }
                 }
               ],
               "ietf-l2-topology:l2-node-attributes": {
                 "management-address": [
                   "192.0.2.2",
                   "2001:db8:0:2::/64"
                 ]
               }
             },
             {
               "node-id": "D3",
               "ietf-network-topology:termination-point": [
                 {
                   "tp-id": "3-1-1",
                   "ietf-l2-topology:l2-termination-point-attributes": {
                     "mac-address": "00:00:5E:00:53:F0"
                   }
                 },
                 {
                   "tp-id": "3-2-1",
                   "ietf-l2-topology:l2-termination-point-attributes": {
                     "mac-address": "00:00:5E:00:53:F1"
                   }
                 }
               ],
               "ietf-l2-topology:l2-node-attributes": {
                 "management-address": [
                   "192.0.2.3",
                  "2001:db8:0:3::/64"
                 ]
               }
             }
           ],
           "ietf-network-topology:link": [
             {
               "link-id": "D1,1-2-1,D2,2-1-1",
               "source": {
                 "source-node": "D1",
                 "source-tp": "1-2-1"
               },
               "destination": {
                 "dest-node": "D2",
                 "dest-tp": "2-1-1"
               },



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               "ietf-l2-topology:l2-link-attributes": {
                 "rate": "1000"
               }
             },
             {
               "link-id": "D2,2-1-1,D1,1-2-1",
               "source": {
                 "source-node": "D2",
                 "source-tp": "2-1-1"
               },
               "destination": {
                 "dest-node": "D1",
                 "dest-tp": "1-2-1"
               },
               "ietf-l2-topology:l2-link-attributes": {
                 "rate": "1000"
               }
             },
             {
               "link-id": "D1,1-3-1,D3,3-1-1",
               "source": {
                 "source-node": "D1",
                 "source-tp": "1-3-1"
               },
               "destination": {
                 "dest-node": "D3",
                 "dest-tp": "3-1-1"
               },
               "ietf-l2-topology:l2-link-attributes": {
                 "rate": "1000"
               }
             },
             {
               "link-id": "D3,3-1-1,D1,1-3-1",
               "source": {
                 "source-node": "D3",
                 "source-tp": "3-1-1"
               },
               "destination": {
                 "dest-node": "D1",
                 "dest-tp": "1-3-1"
               },
               "ietf-l2-topology:l2-link-attributes": {
                 "rate": "1000"
               }
             },
             {
               "link-id": "D2,2-3-1,D3,3-2-1",



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               "source": {
                 "source-node": "D2",
                 "source-tp": "2-3-1"
               },
               "destination": {
                 "dest-node": "D3",
                 "dest-tp": "3-2-1"
               },
               "ietf-l2-topology:l2-link-attributes": {
                 "rate": "1000"
               }
             },
             {
               "link-id": "D3,3-2-1,D2,2-3-1",
               "source": {
                 "source-node": "D3",
                 "source-tp": "3-2-1"
               },
               "destination": {
                 "dest-node": "D2",
                 "dest-tp": "2-3-1"
               },
               "ietf-l2-topology:l2-link-attributes": {
                 "rate": "1000"
               }
             }
           ]
         }
       ]
     }
   }

Authors' Addresses

   Jie Dong
   Huawei
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: jie.dong@huawei.com










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   Xiugang Wei
   Huawei
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: weixiugang@huawei.com


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

   Email: bill.wu@huawei.com


   Mohamed Boucadair
   Orange
   Rennes 35000
   France

   Email: mohamed.boucadair@orange.com


   Anders Liu
   Tecent
   Yinke Building 38 Haidian St, Haidian District
   Beijing  100080
   China

   Email: andersliu@tencent.com


















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