A VTN Network YANG Module

Document Type Active Internet-Draft (individual)
Authors Bo Wu  , Dhruv Dhody 
Last updated 2021-06-06
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Network Working Group                                              B. Wu
Internet-Draft                                                  D. Dhody
Intended status: Experimental                        Huawei Technologies
Expires: December 8, 2021                                   June 6, 2021

                       A VTN Network YANG Module


   This document defines a virtual transport network (VTN) network YANG
   module for retrieving and manipulating VTN topology and resource
   allocation.  The model can be used to implement the provisioning of
   IETF network slice services.

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 8, 2021.

Copyright Notice

   Copyright (c) 2021 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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
     2.1.  Tree Diagrams . . . . . . . . . . . . . . . . . . . . . .   3
   3.  VTN Network Yang Module Consideration . . . . . . . . . . . .   3
     3.1.  VTN Operation . . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  VTN Network Modeling Design . . . . . . . . . . . . . . .   7
   4.  Description of the VTN Network YANG Module  . . . . . . . . .   7
   5.  VTN Yang Module Tree  . . . . . . . . . . . . . . . . . . . .   8
   6.  VTN Yang Module . . . . . . . . . . . . . . . . . . . . . . .  10
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   9.  Contributor . . . . . . . . . . . . . . . . . . . . . . . . .  19
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     10.2.  Informative References . . . . . . . . . . . . . . . . .  21
   Appendix A.  Example VTN Network Model  . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   [I-D.ietf-teas-ietf-network-slices] defines IETF network slice
   services that provide connectivity coupled with network resources
   commitment between a number of endpoints over a shared network
   infrastructure, and also defines the IETF Network Slice controller
   (NSC) to realize the network slice services by mapping it to a
   suitable underlying technology.

   [I-D.ietf-teas-enhanced-vpn] describes that enhanced VPN (VPN+)
   services can be used to realize IETF network slice services.  To
   improve service scalability, The virtual transport network (VTN),
   which has a customized network topology and a group of dedicated or
   shared nodes and links of the physical network, is introduced for
   multiple VPN+ services with similar connection and SLA requirements.
   For the control and management of these VTN resources,
   [I-D.dong-teas-enhanced-vpn-vtn-scalability] gives a detailed
   analysis and description.

   This document defines VTN network model that the NSC can use to
   create and manage VTN instances to realize the network slicing
   services.  According to the YANG model classification of [RFC8309],
   VTN network model is a network configuration model.

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2.  Conventions used in this document

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in
   BCP14, [RFC2119], [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   The following terms are defined in [RFC6241] and are used in this

   o  configuration data

   o  state data

   The following terms are defined in [RFC7950] and are used in this

   o  augment

   o  data model

   o  data node

   The terminology for describing YANG data models is found in

2.1.  Tree Diagrams

   The tree diagram used in this document follows the notation defined
   in [RFC8340].

3.  VTN Network Yang Module Consideration

   To realize the IETF Network Slice based on the reference framework
   defined in [I-D.ietf-teas-ietf-network-slices] , the Figure 1 shows
   an approach with VPN network model and VTN network YANG module.

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          |                 Customer                 |
          |                                          |
                               | NSC NBI
          |    IETF Network Slice Controller (NSC)   |
                  LxNM model   | NSC SBI  VTN network module
                               V          VTN as VPN underlay
          |           Network Controller(s)          |
              Device model     |       VTN device model

                    Figure 1: Reference Module Use Case

   The VTN network model can be used in the following ways:

   o  Static VTN configuration: A VTN instance can be created before
      processing IETF Network Slice service request by a network

   o  Dynamic VTN configuration: A VTN instance can be initiated along
      with configuring IETF Network Slice service request by a network

   In the process of realizing an IETF network slice service, when
   creating a Layer 3 VPN or Layer 2 VPN instance, The NSC can use a
   static VTN instance or dynamically create one as the VPN underlay
   transport.  Compared with existing VPN underlying full mesh tunneling
   mechanisms, the VTN could provide resource isolation, topology
   constraints, and simplified configuration.  Additionally, specific
   service flows of a VPN can be further optimized using SR policies
   defined in [I-D.dong-idr-sr-policy-vtn].

   And also in multi-domain network slicing cases, instead of mapping
   the overlay VPN to the intra-domain VTNs at the edge of each domain,
   an inter-domain VTN could be used directly for inter-domain
   interconnection, which is described in

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   [I-D.li-teas-e2e-ietf-network-slicing] . The network controller
   serving the transit domain can only manage the VTNs.  A 5G end-to-end
   network slicing scenario is shown in the following figure.

    /----\        /----\         /----\          /----\         /----\
   /      \     //      \\     //      \\      //      \\      /      \
  |  RAN   |---|   NW-1   |---|   NW-2   |----|   NW-3   |----|  Core  |
   \      /     \\      //     \\      //      \\      //      \      /
    \----/        \----/         \----/          \----/         \----/

             IETF Network Slice (VPN+)
                Global VTN
               Domain VTN-1   Domain VTN-2    Domain VTN-3
              o************o o************o   o***********o

                  5G end-to-end network slicing scenario

   In addition to providing VTN network configuration, VTN network model
   also provides monitoring details of the underlying resource created
   to meet the requirements of IETF network slice service.

   An example of VTN instances and a physical network is illustrated in
   Figure 2.

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               ++++   ++++   ++++
               ++++   +++\\  ++++
                ||     || \\  ||             Physical
                ||     ||  \\ ||             Network
        ++++   ++++   ++++  \\+++   ++++
        +  +===+--+===+--+===+--+===+  +
        +  +===+--+===+--+===+--+===+  +
        ++++   ++++   ++++   ++++   ++++
         PE1                         PE2

               /          /              VTN-1

               /    / \                  VTN-2


                    /    /               VTN-n

           o   is a virtual node
           --- is a virtual link

                          Figure 2: A VTN example

   In the example, each VTN instance has a customized network topology
   comprised of a set of links and nodes in the physical network.  In
   control plane, each VTN is associated with a multi-topology or a
   Flex-Algo.  And it also has its own forwarding plane resources and
   identifiers which provide VTN-specific packet processing.

3.1.  VTN Operation

   There are multiple modes of VTN operations to be supported as

   o  New VTN Binding: In realization, a NSC could request a set of
      underlay resources that are unaffected by other slice services.  A

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      new VTN could be created and bound to a VPN per the network slice
      service and not used for any other VPNs.

   o  VTN Sharing: A NSC could decide to use allocated underlay
      resources to meet the requirements of an IETF network slice.
      Therefore, an existing VTN instance can be reused and multiple
      VPNs in the VTN instance can share same VTN resources.  In some
      cases, the properties of the existing VTN (e.g., link bandwidth)
      need modification.

   o  VTN Deletion: If the NSC determines that no VPN service is using a
      VTN, the NSC can delete the VTN instance.

   o  VTN Monitoring: The NSC could also use the VTN network model to
      track and monitor VTN resource status and usage.

3.2.  VTN Network Modeling Design

   A VTN network is modeled as network topology defined in [RFC8345]
   with augmentations.  A new network type "vtn" is defined in this
   document.  When a network topology data instance contains the vtn
   network type, it represents an instance of a VTN.

   Each VTN consists of a set of nodes and a set of links.  Each node
   and link have different attributes that represent the allocated
   resources or the operational status of the VTN network.  VTN supports
   several resource partition methods, which are defined by 'interface-
   partition-capability'' under a link, which can further be supported
   by FlexE and independent queue techniques.

   The container "vtn" under 'network' of [RFC8345] defines global
   parameters for a VTN, which defines the specific control plane
   technique of the VTN and a unique "vtn-data-plane identifier" for
   data plane.  And also, a color attribute for steering traffic, such
   as VPN traffic, into a VTN is also defined.

4.  Description of the VTN Network YANG Module

   The description of the VTN data nodes are as follows:

   o  "vtn-id": Is an identifier that is used to uniquely identify the
      VTN instance within the network scope.

   o  VTN allocation resources: The nodes and links represent the
      network resource allocated for a VTN instance.  'bandwidth-
      reservation' specifies the bandwidth allocated to a VTN network,
      or is overridden by the configuration of the VTN link.

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      'interface-partition-capability' specifies the resource partition
      capability of the physical interfaces associated with a VTN link.

   o  VTN control plane: Based on the existing work in IETF, control
      plane mechanism of VTN could be implemented by Multi-Topology
      Routing (MTR) which defined in [RFC4915], [RFC5120], and
      [I-D.ietf-lsr-isis-sr-vtn-mt] or Flex-algo which is defined in
      [I-D.ietf-lsr-flex-algo].  With these control plane technologies,
      VTN nodes of each VTN instance will create their own VTN-specific
      forwarding tables.

   o  VTN data plane: Defines the data plane mechanism and the VTN
      identifier of the network domain managed by the network
      controller.  The data plane mechanism could be baed on MPLS or
      IPv6 forwarding.  "vtn-domain-identifier" is used to identify
      network resource of data plane that has been allocated for the
      VTN.  In the case of IPv6 based forwarding, VTN data plane
      identifier is defined in [I-D.dong-6man-enhanced-vpn-vtn-id].  If
      a network slice service traverses multiple network domains, a
      global VTN identifier across the domains may be defined.  For
      example, [I-D.li-6man-e2e-ietf-network-slicing] defines a IPv6
      extension header to carry the global VTN identifier.

   o  VTN steering policy: "vtn-color-id" is the color attribute of VTN
      for traffic steering.

5.  VTN Yang Module Tree

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module: ietf-vtn-ntw
  augment /nw:networks/nw:network/nw:network-types:
    +--rw vtn!
  augment /nw:networks/nw:network:
    +--rw vtn
       +--rw vtn-id?                  uint32
       +--rw vtn-name?                string
       +--rw bandwidth-reservation
       |  +--rw (bandwidth-type)?
       |     +--:(bandwidth-value)
       |     |  +--rw bandwidth-value?     uint64
       |     +--:(bandwidth-percentage)
       |        +--rw bandwidth-percent?   rt-types:percentage
       +--rw control-plane
       |  +--rw (vtn-cp-type)?
       |     +--:(flex-algo)
       |     |  +--rw flex-algo
       |     |     +--rw flex-algo-id?   uint32
       |     +--:(multi-topology)
       |        +--rw multi-topology-id?   uint32
       +--rw data-plane
       |  +--rw vtn-global-identifier?   uint32
       |  +--rw domain-data-plane
       |     +--rw data-plane-type?         identityref
       |     +--rw vtn-domain-identifier?   uint32
       +--rw steering-policy
          +--rw vtn-color-id?   uint32
  augment /nw:networks/nw:network/nw:node:
    +--rw vtn
  augment /nw:networks/nw:network/nt:link:
    +--rw vtn
    |  +--rw interface-partition-capability?   identityref
    |  +--rw bandwidth-reservation
    |     +--rw (bandwidth-type)?
    |        +--:(bandwidth-value)
    |        |  +--rw bandwidth-value?     uint64
    |        +--:(bandwidth-percentage)
    |           +--rw bandwidth-percent?   rt-types:percentage
    +--ro statistics
       +--ro admin-status?                  te-types:te-admin-status
       +--ro oper-status?                   te-types:te-oper-status
       +--ro one-way-available-bandwidth?   rt-types:bandwidth-ieee-float32
       +--ro one-way-utilized-bandwidth?    rt-types:bandwidth-ieee-float32
       +--ro one-way-min-delay?             uint32
       +--ro one-way-max-delay?             uint32
       +--ro one-way-delay-variation?       uint32
       +--ro one-way-packet-loss?           decimal64

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6.  VTN Yang Module

   <CODE BEGINS> file "ietf-vtn-ntw@2021-06-04.yang"

module ietf-vtn-ntw {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-vtn-ntw";
  prefix vtn-ntw;

  import ietf-network {
    prefix nw;
      "RFC 8345: A YANG Data Model for Network Topologies";
  import ietf-network-topology {
    prefix nt;
      "RFC 8345: A YANG Data Model for Network Topologies";
  import ietf-routing-types {
    prefix rt-types;
      "RFC 8294: Common YANG Data Types for the Routing Area";
  import ietf-te-types {
    prefix te-types;
      "RFC 8776: Traffic Engineering Common YANG Types";
  import ietf-te-packet-types {
    prefix te-packet-types;
      "RFC 8776: Traffic Engineering Common YANG Types";

    "IETF TEAS Working Group";
     WG Web: <http://tools.ietf.org/wg/teas/>
     WG List:<mailto:teas@ietf.org>

     Editor: Bo Wu <lana.wubo@huawei.com>
           : Dhruv Dhody <dhruv.ietf@gmail.com>";
    "This YANG module defines a network data module for
     VTN(Virtual Transport Network)";

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  revision 2021-06-04 {
      "This is the initial version of VTN network yang module";
      "RFC XXX: YANG Data module for VTN network";

  identity interface-partition-capability {
      "Base identity for interface partition capability.";

  identity flexe-partition {
    base interface-partition-capability;
      "Identity for FlexE partition capability.";

  identity queue-partition {
    base interface-partition-capability;
      "Identity for queue partition capability.";

  identity vtn-data-plane-type {
      "Base identity for VTN data plane type.";

  identity vtn-data-plane-vtn-ipv6 {
    base vtn-data-plane-type;
      "Identity for VTN based packet forwarding of IPv6.";

  identity vtn-data-plane-vtn-mpls {
    base vtn-data-plane-type;
      "Identity for VTN based packet forwarding of MPLS.";

  identity vtn-data-plane-sr-mpls {
    base vtn-data-plane-type;
      "Identity for SR MPLS forwarding mechanism.";

  identity vtn-data-plane-srv6 {

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    base vtn-data-plane-type;
      "Identity for SRv6 forwarding mechanism.";

   * Groupings

  grouping traffic-steering-policy {
      "Configuration of the traffic mapping policy.";
    container steering-policy {
        "Policy set that matches to a VTN.";
      leaf vtn-color-id {
        type uint32;
          "VTN color ID for VTN traffic steering";

  grouping vtn-bandwidth-reservation {
      "Grouping for VTN bandwidth reservation.";
    container bandwidth-reservation {
        "Container for VTN bandwidth reservation.";
      choice bandwidth-type {
          "Choice of bandwidth reservation type.";
        case bandwidth-value {
          leaf bandwidth-value {
            type uint64;
            units "bps";
              "Bandwidth allocation for the VTN as absolute value.";
        case bandwidth-percentage {
          leaf bandwidth-percent {
            type rt-types:percentage;
              "Bandwidth allocation for the VTN as a percentage of a link.";

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  grouping vtn-control-plane-attributes {
      "VTN topology control plane attributes.";
    container control-plane {
        "vtn control plane mechanism.";
      choice vtn-cp-type {
          "Choice of vtn control plane.";
        case flex-algo {
          container flex-algo {
              "A VTN could use flex-algo as a control plane
            leaf flex-algo-id {
              type uint32;
                "flex-algo-id for VTN";
        case multi-topology {
            "A VTN could use MT (Multi-Topology) as a control
             plane mechanism.";
          leaf multi-topology-id {
            type uint32;
              "MT-id for VTN";

  grouping vtn-data-plane-attributes {
      "Grouping for VTN topology data plane attributes.";
    container data-plane {
        "VTN data plane mechanism.";
      leaf vtn-global-identifier {
        type uint32;
          "The global VTN identifier for multi-domain is specified.";

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      container domain-data-plane {
          "VTN data plane mechanism per network domain.";
        leaf data-plane-type {
          type identityref {
            base vtn-data-plane-type;
            "Specifies the data plane forwarding mechanism of the VTN.
             The mechanism consists of VTN based Packet Forwarding or
             existing Segment Routing with MPLS data plane or IPv6 data
        leaf vtn-domain-identifier {
          type uint32;
            "The domain VTN identifier is specified for
             VTN based Packet Forwarding of a network domain.
             The forwarding plane could be with
             the MPLS Data Plane or IPv6";
             Carrying Virtual Transport Network identifier
             in MPLS Packet
             Carrying Virtual Transport Network Identifier
             in IPv6 Extension Header";

  grouping vtn-topology-attributes {
      "VTN topology scope attributes.";
    container vtn {
        "Containing VTN topology attributes.";
      leaf vtn-id {
        type uint32;
          "VTN identifier";
      leaf vtn-name {
        type string;
          "VTN Name";

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      uses vtn-bandwidth-reservation;
      uses vtn-control-plane-attributes;
      uses vtn-data-plane-attributes;
      uses traffic-steering-policy;
    // vtn

  // vtn-node-attributes

  grouping vtn-node-attributes {
      "VTN node scope attributes.";
    container vtn {
        "Containing VTN attributes.";

  // vtn-node-attributes

  grouping vtn-link-attributes {
      "VTN link scope attributes";
    container vtn {
        "Containing VTN attributes.";
      leaf interface-partition-capability {
        type identityref {
          base interface-partition-capability;
          "Describes different resource partition type of a link.";
      uses vtn-bandwidth-reservation;

  // vtn-statistics

  grouping statistics-per-vtn {
      "Statistics attributes per VTN.";

  // vtn-node-statistics

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  grouping statistics-per-node {
      "Statistics attributes per VTN node.";

  // one-way-performance-metrics

  grouping one-way-performance-bandwidth {
      "Grouping for one-way performance bandwidth .";
    leaf one-way-available-bandwidth {
      type rt-types:bandwidth-ieee-float32;
      units "bytes per second";
      default "0x0p0";
        "Available bandwidth that is defined to be VTN link
         bandwidth minus bandwidth utilization.  For a
         bundled link, available bandwidth is defined to be the
         sum of the component link available bandwidths.";
    leaf one-way-utilized-bandwidth {
      type rt-types:bandwidth-ieee-float32;
      units "bytes per second";
      default "0x0p0";
        "Bandwidth utilization that represents the actual
         utilization of the link (i.e. as measured in the router).
         For a bundled link, bandwidth utilization is defined to
         be the sum of the component link bandwidth

  // vtn-link-statistics

  grouping vtn-statistics-per-link {
      "Statistics attributes per VTN link.";
    container statistics {
      config false;
        "Statistics for VTN link.";
      leaf admin-status {
        type te-types:te-admin-status;
          "The administrative state of the link.";
      leaf oper-status {

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        type te-types:te-oper-status;
          "The current operational state of the link.";
      uses one-way-performance-bandwidth;
      uses te-packet-types:one-way-performance-metrics-packet;

  augment "/nw:networks/nw:network/nw:network-types" {
      "Defines the VTN topology type.";
    container vtn {
      presence "Indicates VTN topology";
        "Its presence identifies the VTN type.";

  augment "/nw:networks/nw:network" {
    when 'nw:network-types/vtn-ntw:vtn' {
        "Augment only for VTN topology.";
      "Augment VTN configuration and state.";
    uses vtn-topology-attributes;

  augment "/nw:networks/nw:network/nw:node" {
    when '../nw:network-types/vtn-ntw:vtn' {
        "Augment only for VTN topology.";
      "Augment node configuration and state.";
    uses vtn-node-attributes;

  augment "/nw:networks/nw:network/nt:link" {
    when '../nw:network-types/vtn-ntw:vtn' {
        "Augment only for VTN topology.";
      "Augment link configuration and state.";
    uses vtn-link-attributes;
    uses vtn-statistics-per-link;

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7.  Security Considerations

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

   The NETCONF access control model [RFC8341] provides the means to
   restrict access for particular NETCONF or RESTCONF users to a
   preconfigured subset of all available NETCONF or RESTCONF protocol
   operations and content.

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

   vtn-link: A malicious client could attempt to remove a link from a
   topology, add a new link.  In each case, the structure of the
   topology would be sabotaged, and this scenario could, for example,
   result in an VTN topology that is less than optimal.

   The entries in the nodes above include the whole network
   configurations corresponding with the VTN, and indirectly create or
   modify the PE or P device configurations.  Unexpected changes to
   these entries could lead to service disruption and/or network

8.  IANA Considerations

   This document registers a URI in the IETF XML registry [RFC3688].
   Following the format in [RFC3688], the following registration is
   requested to be made:

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      URI: urn:ietf:params:xml:ns:yang:ietf-vtn-ntw
      Registrant Contact: The IESG.
      XML: N/A, the requested URI is an XML namespace.

   This document requests to register a YANG module in the YANG Module
   Names registry [RFC7950].

              Name: ietf-vtn-ntw
              Namespace: urn:ietf:params:xml:ns:yang:ietf-vtn-ntw
              Prefix: vtn-ntw
              Reference: RFC XXXX

9.  Contributor

      Zhenbin Li

      Email: lizhenbin@huawei.com

      Jie Dong

      Email: jie.dong@huawei.com

10.  References

10.1.  Normative References

              Dong, J., Li, Z., Xie, C., and C. Ma, "Carrying Virtual
              Transport Network Identifier in IPv6 Extension Header",
              draft-dong-6man-enhanced-vpn-vtn-id-03 (work in progress),
              February 2021.

              Dong, J., Hu, Z., and R. Pang, "BGP SR Policy Extensions
              for Virtual Transport Network", draft-dong-idr-sr-policy-
              vtn-00 (work in progress), October 2020.

              Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
              A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
              algo-15 (work in progress), April 2021.

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              Xie, C., Ma, C., Dong, J., and Z. Li, "Using IS-IS Multi-
              Topology (MT) for Segment Routing based Virtual Transport
              Network", draft-ietf-lsr-isis-sr-vtn-mt-00 (work in
              progress), March 2021.

              Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", draft-
              ietf-spring-segment-routing-policy-11 (work in progress),
              April 2021.

              Li, Z. and J. Dong, "Encapsulation of End-to-End IETF
              Network Slice Information in IPv6", draft-li-6man-e2e-
              ietf-network-slicing-00 (work in progress), April 2021.

              Zhu, Y., Dong, J., and Z. Hu, "Using Flex-Algo for Segment
              Routing based VTN", draft-zhu-lsr-isis-sr-vtn-flexalgo-02
              (work in progress), February 2021.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,

   [RFC4915]  Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
              Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
              RFC 4915, DOI 10.17487/RFC4915, June 2007,

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120,
              DOI 10.17487/RFC5120, February 2008,

   [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,

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   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,

   [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>.

   [RFC8309]  Wu, Q., Liu, W., and A. Farrel, "Service Models
              Explained", RFC 8309, DOI 10.17487/RFC8309, January 2018,

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,

   [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,

10.2.  Informative References

              Dong, J., Li, Z., Qin, F., Yang, G., and J. N. Guichard,
              "Scalability Considerations for Enhanced VPN (VPN+)",
              draft-dong-teas-enhanced-vpn-vtn-scalability-02 (work in
              progress), February 2021.

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              Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
              Framework for Enhanced Virtual Private Network (VPN+)
              Services", draft-ietf-teas-enhanced-vpn-07 (work in
              progress), February 2021.

              Farrel, A., Gray, E., Drake, J., Rokui, R., Homma, S.,
              Makhijani, K., Contreras, L. M., and J. Tantsura,
              "Framework for IETF Network Slices", draft-ietf-teas-ietf-
              network-slices-00 (work in progress), April 2021.

              Li, Z. and J. Dong, "Framework for End-to-End IETF Network
              Slicing", draft-li-teas-e2e-ietf-network-slicing-00 (work
              in progress), April 2021.

Appendix A.  Example VTN Network Model

   Device could map

Authors' Addresses

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

   Email: lana.wubo@huawei.com

   Dhruv Dhody
   Huawei Technologies
   Divyashree Techno Park
   Bangalore, Karnataka  560066

   Email: dhruv.ietf@gmail.com

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