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Versions: (draft-dong-i2rs-l2-network-topology) 00 01 02 03 04 05 06 07 08 09

Network Working Group                                            J. Dong
Internet-Draft                                                    X. Wei
Intended status: Standards Track                                   Q. Wu
Expires: December 26, 2019                                        Huawei
                                                            M. Boucadair
                                                                  Orange
                                                                  A. Liu
                                                                  Tecent
                                                           June 24, 2019


            A YANG Data Model for Layer-2 Network Topologies
              draft-ietf-i2rs-yang-l2-network-topology-07

Abstract

   This document defines a YANG data model for Layer 2 network
   topologies.

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."

   This Internet-Draft will expire on December 26, 2019.



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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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Layer 2 Topology Model  . . . . . . . . . . . . . . . . . . .   3
   4.  Layer 2 Topology YANG Module  . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  20
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  20
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  21
   Appendix A.  Companion YANG Module for Non-NMDA Compliant
                Implementations  . . . . . . . . . . . . . . . . . .  22
   Appendix B.  An Example . . . . . . . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  30

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 network
   topologies by augmenting the generic network and network topology
   data models with L2 specific topology attributes.  A sample example
   is provided in Appendix B.

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




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

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.

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 L2
   technologies.  It can be used to describe both the physical and the
   logical (virtual) L2 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, descriptions, 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)
   or other Layer-2 protocols, and some of them may be locally
   configured.

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

                Figure 1: L2-topology YANG Module Structure

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




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   module: ietf-l2-topology
     augment /nw:networks/nw:network/nw:network-types:
       +--rw l2-network!
     augment /nw:networks/nw:network:
       +--rw l2-network-attributes
          +--rw name?   string
          +--rw flag*   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-vid?       vlan {VLAN}?
          +--rw flag*                 node-flag-type
     augment /nw:networks/nw:network/nt:link:
       +--rw l2-link-attributes
          +--rw name?    string
          +--rw flag*    link-flag-type
          +--rw rate?    decimal64
          +--rw delay?   uint32
          +--rw srlg*    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
          |  |  +--rw port-vlan-id?         vlan {VLAN}?
          |  |  +--rw vlan-id-name* [vlan-id] {VLAN}?
          |  |     +--rw vlan-id      vlan
          |  |     +--rw vlan-name?   string
          |  +--:(legacy)
          |     +--rw layer-2-address?      yang:phys-address
          |     +--rw encapsulation?        identityref
          +--ro tp-state?             enumeration
     notifications:
       +---n l2-node-event
       |  +--ro event-type?
       |  +--ro node-ref?
       |  +--ro network-ref?
       |  +--ro l2-network!
       |  +--ro l2-node-attributes
       +---n l2-link-event
       |  +--ro event-type?
       |  +--ro link-ref?



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       |  +--ro network-ref?
       |  +--ro l2-network!
       |  +--ro l2-link-attributes
       +---n l2-termination-point-event
          +--ro event-type?
          +--ro tp-ref?
          +--ro node-ref?
          +--ro network-ref?
          +--ro l2-network!
          +--ro l2-termination-point-attributes

   The L2-topology module augments the generic 'ietf-network' and 'ietf-
   network-topology' 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
      defned in [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.
      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 [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  The optional L2 technology specific attributes are introduced in
      this module as Layer-2 features.








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4.  Layer 2 Topology YANG Module

   This module uses the common YANG types defined in [RFC6991] and types
   defined in [RFC8345].

<CODE BEGINS> file "ietf-l2-topology@2019-06-21.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 "Section 4 of RFC 6991";
    }
    import ietf-yang-types {
      prefix "yang";
      reference "Section 3 of RFC 6991";
    }

    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



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                 <andersliu@tencent.com>";

    description
      "This module defines a basic model for
       the layer-2 topology of a network.

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

       This version of this YANG module is part of
       draft-ietf-i2rs-yang-l2-network-topo-07;
       see the RFC itself for full legal notices.";

    revision "2019-06-04" {
      description "Initial revision";
      reference
        "RFC XXXX: A YANG Data Model for Layer-2 Network Topologies";
    }

   /*
    * Typedefs
    */

    typedef vlan {
      type uint16 {
        range "1..4094";
      }
      description "VLAN ID";
      reference "IEEE 802.1Q";
    }

    typedef trill-nickname {
      type uint16;
      description "TRILL Nickname";
      reference "RFC 6326";
    }

    typedef vni {
      type uint32 {
       range "1..16777215";
      }



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      description "VxLAN Network Identifier";
      reference "RFC 7348";
    }

    typedef l2-flag-type {
      type identityref {
        base "flag-identity";
      }
      description "Base type for l2 flags";
    }
   typedef node-flag-type {
       type identityref {
         base "flag-identity";
       }
       description "Node flag attributes";
     }
   typedef link-flag-type {
       type identityref {
         base "flag-identity";
       }
       description "Link flag attributes";
     }

    typedef l2-network-event-type {
      type enumeration {
        enum "add" {
          value 0;
          description "An L2 node or link or termination-point
          has been added";
        }
        enum "remove" {
          value 1;
          description "An L2 node or link or termination-point
          has been removed";
        }
        enum "update" {
          value 2;
          description "An L2 node or link or termination-point
          has been updated";
        }
      }
      description "l2 network event type for notifications";
    } // l2-topology-event-type


    /*
    * Features
    */



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    feature VLAN {
      description
        "Indicates that the system supports the
         vlan functions.";
    }

    feature QinQ {
      description
        "Indicates that the system supports the
         qinq functions";
      reference "IEEE 802.1ad.";
    }

    feature PBB {
      description
       "Indicates that the device supports the
        provider-backbone-bridging functions";
      reference "IEEE 802.1ah.";
    }

    feature VPLS {
      description
        "Indicates that the device supports the
         VPLS functions.";
      reference "RFC 4761, RFC 4762";
    }

    feature TRILL {
      description
        "Indicates that the device supports the
         TRILL functions.";
      reference "RFC 6325";
    }

    feature VXLAN {
      description
        "Indicates that the device supports the
         VXLAN functions.";
      reference "RFC 7348";
    }

   /*
    * Identities
    */

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



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    /*Consider udpating this part to make use of draft-ietf-softwire-iftunnel*/

    identity encapsulation-type {
      description
        "Base identity from which specific encapsulation
         types are derived.";
    }

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

    }

    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
        "PBB encapsulation.";
    }

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

    identity vpls {
      base eth-encapsulation-type;



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      description
        "VPLS encapsulation.";
    }

    identity vxlan {
      base eth-encapsulation-type;
      description
        "VXLAN encapsulation.";
    }

    identity frame-relay {
      base encapsulation-type;
      description
        "Frame Relay encapsulation.";
    }

    identity ppp {
      base encapsulation-type;
      description
        "PPP encapsulation";
    }

    identity hdlc {
      base encapsulation-type;
      description
        "HDLC encapsulation.";
    }

    identity atm {
      base encapsulation-type;
      description
        "Base identity from which specific ATM
         encapsulation types are derived.";

    }

    identity pwe3 {
      base encapsulation-type;
      description
        "Base identity from which specific PW
         encapsulation types are derived.";
    }


   /*
    * Groupings
    */




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    grouping l2-network-type {
      description "Identify 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-network-attributes {
      description "L2 Topology scope attributes";
      container l2-network-attributes {
        description "Containing L2 network attributes";
        leaf name {
          type string;
          description "Name of the L2 network.";
        }

        leaf-list flag {
          type l2-flag-type;
          description "L2 network flags";
        }
      }
    }

    grouping l2-node-attributes {
      description "L2 node attributes";
      container l2-node-attributes {
        description "Containing 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 "System management address.";
        }
        leaf sys-mac-address {
          type yang:mac-address;
          description "System MAC-address.";
        }
        leaf management-vid {
          if-feature VLAN;



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          type vlan;
          description "System management VID.";
        }
        leaf-list flag {
          type node-flag-type;
          description "Node operational flags.";
        }
      }
    }  // grouping l2-node-attributes

    grouping l2-link-attributes {
      description "L2 link attributes";
      container l2-link-attributes {
        description "Containing L2 link attributes.";
        leaf name {
          type string;
          description "Link name.";
        }
        leaf-list flag {
          type link-flag-type;
          description "Link flags.";
        }
        leaf rate {
          type decimal64 {
            fraction-digits 2;
          }
          description "Link rate.";

        }
        leaf delay {
          type uint32;
          description "Link delay in microseconds.";
        }
        leaf-list srlg {
          type uint32;
          description
            "List of Shared Risk Link Groups
             this link belongs to.";
          reference "RFC 4202";
        }
      }
    } // grouping l2-link-attributes

    grouping l2-termination-point-attributes {
      description "L2 termination point attributes";
      container l2-termination-point-attributes {
        description "Containing L2 TP attributes";
        leaf description {



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          type string;
          description "Port description.";
        }

        leaf maximum-frame-size {
          type uint32;
          description "Maximum frame size.";
        }

        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
                 ternimation point.";
            }

            leaf port-vlan-id {
              if-feature VLAN;
              type vlan;
              description "Port VLAN ID is the VLAN id that
              will be assigned to any untagged frames entering
              the switch on the specific port.";
            }

            list vlan-id-name {
              if-feature VLAN;
              key "vlan-id";
              description "Interface configured VLANs.";
              leaf vlan-id {
                type vlan;
                description "VLAN ID.";
              }
              leaf vlan-name {
                type string;
                description "VLAN name.";
              }



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            }
          } //case ethernet

          case legacy {
            leaf layer-2-address {
              type yang:phys-address;
              description "Interface Layer 2 address.";
            }

            leaf encapsulation {
              type identityref {
                base encapsulation-type;
              }
              description
                "Encapsulation type of this termination point.";
            }
          } //case legacy such as atm, ppp, hdlc,etc.

        } //choice termination-point-type

        leaf tp-state {
          type enumeration {
            enum in-use {
              value 0;
              description
                "the termination point is in forwarding state.";
            }
            enum blocking {
              value 1;
              description
                "the termination point is in blocking state.";
            }
            enum down {
              value 2;
              description
                "the termination point is in down state.";
            }
            enum others {
              value 3;
              description
                "the termination point is in other state.";
            }
          }
          config false;
          description "State of the termination point";
        }
      }
    } // grouping l2-termination-point-attributes



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   /*
    * Data nodes
    */


    augment "/nw:networks/nw:network/nw:network-types" {
      description
        "Introduce 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-network-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 "Augment L2 topology link information";
      uses l2-link-attributes;
    }

    augment "/nw:networks/nw:network/nw:node/nt:termination-point" {
      when "/nw:networks/nw:network/nw:network-types/l2t:l2-network" {
        description



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

   /*
    * Notifications
    */

    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;
      uses l2-termination-point-attributes;
    }

}  // module l2-topology
<CODE ENDS>




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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 [RFC7950] 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
   RESTCONF users to a preconfigured subset of all available NETCONF or
   RESTCONF protocol operations and content.

   In general, Layer 2 network topologies are system-controlled and
   provide ephemeral topology information.  In an NMDA-complient server,
   they are only part of <operational> which provides read-only access




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   to clients, they are less vulnerable.  That said, the YANG module
   does in principle allow information to be configurable.

   The Layer 2 topology module define 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, leading to disruption
   of services provided via this topology might be disrupted.  For those
   reasons, it is important that the NETCONF access control model 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 in the ietf-network module:

   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, such as the maximum-frame-size.








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7.  Acknowledgements

   The authors would like to acknowledge the comments and suggestions
   received from Susan Hares, Alia Atlas, Juergen Schoenwaelder, Mach
   Chen, Alexander Clemm and Sriganesh Kini.

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>.

   [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>.

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

   [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>.

   [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>.

   [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>.







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   [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

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [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>.

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536,
              DOI 10.17487/RFC6536, March 2012,
              <https://www.rfc-editor.org/info/rfc6536>.

   [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>.









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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
   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
   represent the operational state of layer 2 network topologies.  The
   module ietf-l2-topology-state mirrors the module ietf-l2-topology
   defined earlier in this document.  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 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@2019-06-04.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";
       }

       import ietf-network-topology-state {
         prefix "nt-s";
       }

       import ietf-l2-topology {
         prefix "l2t";
       }

       organization



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         "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>";

       description
         "This module defines a basic model for
          the layer-2 topology of a network.

          Copyright (c) 2018 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
          draft-ietf-i2rs-yang-l2-network-topo-07;
          see the RFC itself for full legal notices.";

       revision "2019-06-04" {
         description "Initial revision";
         reference "draft-ietf-i2rs-l2-network-topology-07";
       }



      /*
       * Data nodes
       */


       augment "/nw-s:networks/nw-s:network/nw-s:network-types" {
         description
           "Introduce 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" {



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           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: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 L2 at the node
            level";
         uses l2t:l2-node-attributes;
       }

       augment "/nw-s:networks/nw-s:network/nt-s:link" {
         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 "Augment 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:networks/nw-s:network/nw-s:network-types/"+
           "l2t-s:l2-network" {
           description
             "Augmentation parameters apply only for networks
              with L2 topology";
         }
         description
           "Augment L2 topology termination point information";
         uses l2t:l2-termination-point-attributes;
       }

      /*



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       * 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 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;
         uses l2t:l2-network-type;
         uses l2t:l2-termination-point-attributes;
       }

   }  // module l2-topology-state
   <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.




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   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 as below.  Note that
   some lines have been wrapped to adhere to the 72-character line
   limitation of RFCs.

    {
        "ietf-network:networks": {
          "network": [
            {
              "network-types": {
                "ietf-l2-topology:l2-network": {}
              },
              "network-id": "l2-topo-example",
              "node": [
                {
                  "node-id": "D1",
                  "termination-point": [
                    {
                      "tp-id": "1-0-1",
                      "ietf-l2-topology:
                        l2-termination-point-attributes": {
                        "mac-address": "A1:B2:C3:D4:E5:F0"
                      }



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                    },
                    {
                      "tp-id": "1-2-1",
                      "ietf-l2-topology:
                        l2-termination-point-attributes": {
                        "mac-address": "A1:B2:C3:D4:E5:F1"
                      }
                    },
                    {
                      "tp-id": "1-3-1",
                      "ietf-l2-topology:
                        l2-termination-point-attributes": {
                        "mac-address": "A1:B2:C3:D4:E5:F2"
                      }
                    }
                  ],
                  "ietf-l2-topology:l2-node-attributes": {
                    "management-address": ["10.1.1.1"]
                  }
                },
                {
                  "node-id": "D2",
                  "termination-point": [
                    {
                      "tp-id": "2-0-1",
                      "ietf-l2-topology:
                        l2-termination-point-attributes": {
                        "mac-address": "A2:B2:C3:D4:E5:F0"
                      }
                    },
                    {
                      "tp-id": "2-1-1",
                      "ietf-l2-topology:
                        l2-termination-point-attributes": {
                        "mac-address": "A2:B2:C3:D4:E5:F2"
                      }
                    },
                    {
                      "tp-id": "2-3-1",
                      "ietf-l2-topology:
                        l2-termination-point-attributes": {
                        "mac-address": "A2:B2:C3:D4:E5:F3"
                      }
                    }
                  ],
                  "ietf-l2-topology:l2-node-attributes": {
                    "management-address": ["10.1.1.2"]
                  }



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                },
                {
                  "node-id": "D3",
                  "termination-point": [
                    {
                      "tp-id": "3-1-1",
                      "ietf-l2-topology:
                        l2-termination-point-attributes": {
                        "mac-address": "A3:B2:C3:D4:E5:F0"
                      }
                    },
                    {
                      "tp-id": "3-2-1",
                      "ietf-l2-topology:
                        l2-termination-point-attributes": {
                        "mac-address": "A3:B2:C3:D4:E5:F1"
                      }
                    }
                  ],
                  "ietf-l2-topology:l2-node-attributes": {
                    "management-address": ["10.1.1.3"]
                  }
                }
              ],
              "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"
                  },
                  "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"



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                  },
                  "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",
                  "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"
                  }
                },
                {



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                  "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


   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





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   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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