Skip to main content

YANG Data Model for SD-WAN VPN service model delivery
draft-sun-opsawg-sdwan-service-model-00

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft whose latest revision state is "Expired".
Authors Qiong Sun , Bo Wu
Last updated 2018-06-27
RFC stream (None)
Formats
Additional resources
Stream Stream state (No stream defined)
Consensus boilerplate Unknown
RFC Editor Note (None)
IESG IESG state I-D Exists
Telechat date (None)
Responsible AD (None)
Send notices to (None)
draft-sun-opsawg-sdwan-service-model-00
Operations and Management Area Working Group                      Q. Sun
Internet-Draft                                             China Telecom
Intended status: Standards Track                                   B. Wu
Expires: December 29, 2018                                        Huawei
                                                           June 27, 2018

         YANG Data Model for SD-WAN VPN service model delivery
                draft-sun-opsawg-sdwan-service-model-00

Abstract

   This document defines a YANG data model that can be used for
   communication between customers and network operators to deliver
   agile, assured IP connectivity, overlay VPN service, which is also
   referred to as SD-WAN VPN Service.  This model provides an abstracted
   view of the SD-WAN service configuration components.  It will be up
   to the management system to take this model as input and use specific
   configuration models to configure the different network elements to
   deliver the service.  How the configuration of network elements is
   done is out of scope for this document.

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 29, 2018.

Copyright Notice

   Copyright (c) 2018 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

Sun & Wu                Expires December 29, 2018               [Page 1]
Internet-Draft          SD-WAN Service YANG Model              June 2018

   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
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Design of the Data Model  . . . . . . . . . . . . . . . . . .   4
     2.1.  SD-WAN service  . . . . . . . . . . . . . . . . . . . . .   6
     2.2.  Site  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.3.  Segment networks  . . . . . . . . . . . . . . . . . . . .   7
     2.4.  Policies  . . . . . . . . . . . . . . . . . . . . . . . .   8
       2.4.1.  Path selection policies . . . . . . . . . . . . . . .   8
       2.4.2.  Qos bandwidth policies  . . . . . . . . . . . . . . .   9
       2.4.3.  Traffic filter  . . . . . . . . . . . . . . . . . . .   9
       2.4.4.  Internet access . . . . . . . . . . . . . . . . . . .   9
       2.4.5.  Interworking with traditional VPN . . . . . . . . . .   9
   3.  Modules Tree Structure  . . . . . . . . . . . . . . . . . . .  10
   4.  YANG Modules  . . . . . . . . . . . . . . . . . . . . . . . .  13
     4.1.  IETF-sd-wan . . . . . . . . . . . . . . . . . . . . . . .  13
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  34
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  34
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  35
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  35
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .  35
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  36

1.  Introduction

   BGP/MPLS IP VPNs [RFC4364] as widely deployed technology can provide
   IP network connectivity over the backbone between IP VPN sites.
   Though having some similarity with the connectivity services offered
   by BGP/MPLS IP VPNs, SD-WAN(software-defined wide-area network)
   utilizes overlay networking technology and enable application driven
   networking to deliver agile, assured IP connectivity services for
   enterprise customer.

   SD-WAN can be built on top of various underlay networks and allow
   multiple parallel paths between two or more sites . More
   specifically, two sites can be interconnected by a traditional MPLS
   VPN ([RFC4364] or [RFC4664]),or by public Internet using fiber,
   cable, DSL-based Internet access, WiFi, or 4G/Long Term Evolution
   (LTE)as well as by overlay tunnels.  The overlay is possibly further
   secured by IPsec tunnels [RFC6071].Typical SD-WAN use cases are

Sun & Wu                Expires December 29, 2018               [Page 2]
Internet-Draft          SD-WAN Service YANG Model              June 2018

   providing SD-WAN sites with secure multi-site VPN service between
   them, access to Internet or interconnection with traditional VPN
   sites.

   In addition to basic connection service, SD-WAN can use policies to
   prioritize traffic for diverse applications used in enterprises, such
   as VoIP calling, videoconferencing, streaming media etc.  Therefore,
   application traffic can be forwarded over different WANs or overlay
   connections based on QoS, Security and other constraints and
   dynamically switched among them depending on real-time measurement of
   the user traffic flowing through.

   This draft specifies SD-WAN VPN service YANG model . This model can
   be used as a input to automated control and configuration
   applications to manage SD-WAN VPN services.

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC2119 [RFC2119].

1.2.  Definitions

   Customer Edge (CE) Device: A CE is equipment dedicated to a
   particular customer; it is directly connected (at Layer 3) to one or
   more PE devices via attachment circuits.

   Provider Edge (PE) Device: A PE is equipment managed by the SP; it
   can support multiple VPNs for different customers and is directly
   connected (at Layer 3) to one or more CE devices via attachment
   circuits.  A PE is usually located at an SP point of presence (POP)
   and is managed by the SP.

   CE-based VPN: Refers to an approach in which the PE devices do not
   know anything about the routing or the addressing of the customer
   networks.  The PE devices offer a simple IP service, and expect to
   receive IP packets whose headers contain only globally unique IP
   addresses.  What makes a CE-based VPN into a Provider-Provisioned VPN
   is that the SP takes on the task of managing and provisioning the CE
   devices

   PE-Based VPNs: The PE devices know that certain traffic is VPN
   traffic.  They forward the traffic (through tunnels) based on the
   destination IP address of the packet and, optionally, based on other
   information in the IP header of the packet.  The PE devices are
   themselves the tunnel endpoints.  The tunnels may make use of various

Sun & Wu                Expires December 29, 2018               [Page 3]
Internet-Draft          SD-WAN Service YANG Model              June 2018

   encapsulations to send traffic over the SP network (such as, but not
   restricted to, GRE, IP-in-IP, IPsec, or MPLS tunnels).

   SD-WAN:An automated, programmatic approach to managing enterprise
   network connectivity and circuit usage.  It extends software-defined
   networking (SDN) into an application that businesses can use to
   quickly create a smart "hybrid WAN"- a WAN that comprises business-
   grade IP VPN, broadband Internet, and wireless services.  SD-WAN is
   also deemed as extended CE-based VPN.

   Underlay network: The network that provides the connectivity among
   SD-WAN VPN sites and that the customer network packets are tunneled
   over.  The underlay network does not need to be aware that it is
   carrying overlay customer network packets.  Addresses on the underlay
   network appear as "outer addresses" in encapsulated overlay packets.
   In general, the underlay network can use a completely different
   protocol (and address family) from that of the overlay network.

   Overlay network: A virtual network in which the separation of cutomer
   networks is hidden from the underlying physical infrastructure.  That
   is, the underlying transport network does not need to know about
   customer separation to correctly forward traffic.  IPsec tunnels
   [RFC6071] is an example of an L3 overlay network .

2.  Design of the Data Model

   L3VPN Service Model defined in [RFC8299] is used for communication
   between customers and network operators and to deliver a Layer 3
   provider-provisioned VPN service.

   SD-WAN VPN is also a layer 3 VPN service provided between two or more
   SD-WAN sites and offers basic logic IP connection service among the
   sites and advanced application aware services for traffic flowing
   into or out of the connection as well.

   In L3VPN service model, the "vpn-services" and "sites" are defined as
   two core parameters.The vpn-services container defines general
   service parameters such as VPN topology for a virtual IP connection
   and other common service descriptions like multicast, extranet etc.
   And the "sites" container is used to describe customer sites
   interconnected by the virtual IP connection.  Furthermore, sites
   contains the IP connection parameters including routing protocol
   needed to expose to an enterprise customer network.  This draft uses
   them as basis to define IP connectivity service in SD-WAN VPN.

   In addition, Application application aware policy services are
   defined as advanced SD-WAN services.  The policies consist of path
   selection policy, QoS policy, security policy, Internet access policy

Sun & Wu                Expires December 29, 2018               [Page 4]
Internet-Draft          SD-WAN Service YANG Model              June 2018

   and VPN interworking policy.  A path selection policy is used to
   perform an application dynamic control behavior using multiple WAN
   links located at a specific site.  A QoS policy is used to specify
   QoS requirements, such as bandwidth of a specific application or an
   application group within a segment.  And security policy is used to
   filter specific traffic in terms of security consideration.Internet
   access policy and VPN interworking policy are parameters used to
   access external resources in Internet or traditional VPN.

   Moreover, to provide fine granularity of traffic isolation within a
   tenant, a "segment-networks" container under the "sdwan-vpn" is
   proposed and represent virtual network services within each
   enterprise customer network, including parameters like segment
   topology and routing protocols of customer network attached.

   Figure 1 below shows an example of the enterprise customer with four
   sites.  Site 1 to site 3 are all SD-WAN sites, and site 1 and site 3
   both have two WAN links connected to underlay transport networks, one
   is IP/MPLS VPN and the other is Internet.  Site 2 has only one
   Internet WAN link.  Unlike the others, site 4 is a traditional MPLS
   VPN site.  And this customer needs to build up three segments to
   separate its traffic flowing over WAN tranport network.

Sun & Wu                Expires December 29, 2018               [Page 5]
Internet-Draft          SD-WAN Service YANG Model              June 2018

                      SD-WAN
                     segment1
   ----------------------------------------------------
                     segment2
   ----------------------------------------------------
                     segment3
   ----------------------------------------------------
             |                            |
      site4  |       ------------------   |      site 3
     +-----+       /+---+         +---+ \ |       +-----+
   --|  CE |--------|PE |         |PE |-----------| CE  |---
     +-----+      | +---+         +---+ |        /+-----+
      site1       |        IP/MPLS      |      /
     +-----+      |        +---+        |    /
   --| CE  |-------------- |PE |       /    /
     +-----+\       \      +---+      /   /
             \        --------------     /
              \          --------      /
                -------/          \  /
                       |  Internet|
     site2             |          |
    +-----+          /  \         /
   -| CE  |--------/     --------
    +-----+
    Figure 1 SD-WAN VPN service

2.1.  SD-WAN service

   The "sdvpn-vpn-svc" list item contains generic information about the
   SD-WAN VPN service.  The "vpn-id" provided in the vpn-service list
   refers to an internal reference for this VPN service, while the
   customer name refers to a more-explicit reference to a customer.

   A WAN transport network list under the root container is used to
   describe different WAN network information to specify which links are
   reachable.  In many cases, enterprise customers could have business
   relationship with multiple WAN network services providers for example
   broadband internet service and MPLS VPN service .

2.2.  Site

   A site represents a customer office located at a specific location.
   A site could have one or more devices and one or more transport
   network links.

   The "sites" container contains device, location parameters and the
   "transport-network" container.

Sun & Wu                Expires December 29, 2018               [Page 6]
Internet-Draft          SD-WAN Service YANG Model              June 2018

   The transport-network container is used to specify underlay network
   link parameters.  It consists of the following categories of
   parameters:

   o  Access type: defines requirements of the attachment (below Layer
      3)bearer type including Ethernet, LTE, DSL.

   o  IP Connection: defines Layer 3 parameters of the attachment

   o  Routing protocol: includes OSPF, BGP or static routing.

   o  Bandwidth: spcifies the bandwidth of the attachment, including
      inbound and outbound traffic bandwidth.

2.3.  Segment networks

   The "segment-networks" is a container directly under the "sdwan-vpn-
   svc" and it is used to represent logical networks in a particular
   enterprise SD-WAN network.  The intention of segment network is to
   separate one SD-WAN network into multiple virtual networks to ensure
   per segment traffic separation in site to site or site to external
   network interconnection.

   Each segment has its own service topology.  The type of VPN service
   topology is required for configuration.  Our proposed model supports
   any-to-any, Hub and Spoke (where Hubs can exchange traffic).By
   default, the any-to-any VPN service topology is used.  New topologies
   could be added via augmentation.

   Based on the requested VPN service topology and the site list,
   overlay tunnels could be set up between sites over underlay networks
   automatically.

   The "lan-network" list under the "segment-network" is used to
   represent one or more customer LAN networks attached from different
   sites belonged to a segment network.  The list is composed of VLAN ,
   IP connection and routing protocol parameters exposed by the customer
   networks.

   In the figure below, there are three segments constructed for a
   customer between two sites to separate the traffic from three
   departments.

Sun & Wu                Expires December 29, 2018               [Page 7]
Internet-Draft          SD-WAN Service YANG Model              June 2018

            site 1--------|                            |------site 2
           +------+       |             +----------+   |    +------+
LAN1-------|----- |---------------------+ segment A+--------|------|-----LAN1
           | CE   |****(TN#1 MPLS VPN)  +----------+    ****|  CE  |
LAN2-------|----- |****(TN#2 Internet) -+ segment B+------- |------|-----LAN2
           |      |****(TN#3 LTE     )  +----------+    ****|      |
LAN3--- ---|----- |---------------------+ segment C+--------|------|-----LAN3
           +------+       |             +----------+   |    +------+
                          |                            |

2.4.  Policies

   The "policies" container under the "sdwan-vpn" list is used contain
   all the policies and all the policy templates defined in a SD-WAN VPN
   service.

   The policy templates have application group, classification profile
   and qos profile.

   The"application-group" is used to describe all the application
   categories, e.g.  VOIP, email, games etc.

   The "classification-profile" container defines flow classification
   rules to be handled and it has a rule list and the corresponding flow
   class name.  This draft borrows the flow classification profile
   defined in RFC8299 to specify flow classification criteria.  The flow
   classification rule are supposed to be used together with other
   policies including path-selection-policy, QoS policy and traffic
   filter policy.

   The "qos-profile" is used to specify the bandwidth requirements for a
   certain flow or other criteria.

2.4.1.  Path selection policies

   The path-selection-policy container is under policies container, and
   it has the following parameters:

   o  Flow classification rule.

   o  Traffic SLA profile, including delay, jitter and loss sub
      parameters.

   o  Primary and secondary path.

   Path selection policy is an ordered list.  For the traffic specified
   by the flow classification rule, traffic SLA profile related status

Sun & Wu                Expires December 29, 2018               [Page 8]
Internet-Draft          SD-WAN Service YANG Model              June 2018

   will be collected and based on the measurement result calculated from
   the collected information, primary path or secondary path will be
   selected.

2.4.2.  Qos bandwidth policies

   The qos-bandwidth policy container is used to describe parameter to
   guarantee bandwidth for specific traffic flowing through a SD-WAN VPN
   connection.  It has three categories parameters, including priority,
   DSCP parameters, traffic rate limit (CAR traffic policy or traffic
   shaping) and bandwidth represented by percentage value or absolute
   value.

2.4.3.  Traffic filter

   Traffic filter is a class of security policy used to filter flow
   either over overlay network or underlay network.

2.4.4.  Internet access

   The "internet-access" container contains internet access option and
   Internet-gateway-IP list.  And Internet-gateway-IP is only used for
   the central Internet access case.  A central internet access means
   traffic from different sites aggregates to central Internet access
   gateway and forwards via the gateway.  An internet access service can
   include Network Address Translation (NAT) to enable the customer to
   use private IP addresses within their networks.

   In addition, each site could have its own Internet access links.  In
   case of local break-out for Internet access, traffic from specific
   site could access the internet directly by setting access option as
   local.

   In Implementation, service provider could combine two options to
   fulfill customer needs.

2.4.5.  Interworking with traditional VPN

   In some cases, there is a need that certain SD-WAN sites or segments
   communicate with traditional VPN sites.  An interworking-gateway
   allows sites interconnected via the MPLS VPN to communicate with
   sites interconnected via SD-WAN tunnels over the Internet.  A
   interworking-gateway or several gateways could be specified to serve
   this requirment.

   The "vpn-interworking" container contains "interworking-gateway-IP"
   used to connect a specific segment located at a site to the legacy
   VPN network.

Sun & Wu                Expires December 29, 2018               [Page 9]
Internet-Draft          SD-WAN Service YANG Model              June 2018

3.  Modules Tree Structure

   This document defines sd-wan yang data model.

  module: ietf-sdwan-vpn-svc
     +--rw sdwan-vpn-svc
        +--rw sdwan-vpn* [vpn-id]
           +--rw vpn-id                    svc-id
           +--rw customer-name?            svc-id
           +--rw wan-transport-networks* [wan-transport-name]
           |  +--rw wan-transport-name    string
           |  +--rw wan-transport-type?   identityref
           +--rw sites
           |  +--rw site* [site-id]
           |     +--rw site-id              svc-id
           |     +--rw location* [email]
           |     |  +--rw email       string
           |     |  +--rw postcode?   string
           |     |  +--rw address?    string
           |     +--rw device* [name]
           |     |  +--rw name    string
           |     |  +--rw type?   string
           |     +--rw transport-network* [name]
           |        +--rw name                string
           |        +--rw access-type?        identityref
           |        +--rw ip-connection
           |        |  +--rw type?     identityref
           |        |  +--rw static
           |        |     +--rw customer-addr?   inet:ip-address
           |        |     +--rw prefix?          inet:ip-prefix
           |        |     +--rw provider-addr?   inet:ip-address
           |        +--rw routing-protocol* [type]
           |        |  +--rw type      identityref
           |        |  +--rw ospf
           |        |  |  +--rw address-family*   address-family
           |        |  |  +--rw area-address      yang:dotted-quad
           |        |  |  +--rw metric?           uint16
           |        |  +--rw bgp
           |        |  |  +--rw autonomous-system    uint32
           |        |  |  +--rw address-family*      address-family
           |        |  +--rw static
           |        |     +--rw ip-lan-prefixes* [lan next-hop]
           |        |        +--rw lan         inet:ip-prefix
           |        |        +--rw next-hop    inet:ipv4-address
           |        |        +--rw priority?   uint16
           |        +--rw bandwidth
           |           +--rw input-bandwidth?    uint64
           |           +--rw output-bandwidth?   uint64

Sun & Wu                Expires December 29, 2018              [Page 10]
Internet-Draft          SD-WAN Service YANG Model              June 2018

           |           +--rw mtu?                uint16
           +--rw segment-networks* [segment-id]
           |  +--rw segment-id      svc-id
           |  +--rw topology?       identityref
           |  +--rw sites* [site-id]
           |  |  +--rw site-id      leafref
           |  |  +--rw site-role?   identityref
           |  +--rw lan-networks* [site-id]
           |     +--rw site-id             leafref
           |     +--rw vlan-tag?           uint16
           |     +--rw ip-address?         inet:ip-address
           |     +--rw ip-prefix?          inet:ip-prefix
           |     +--rw routing-protocol* [type]
           |        +--rw type      identityref
           |        +--rw ospf
           |        |  +--rw address-family*   address-family
           |        |  +--rw area-address      yang:dotted-quad
           |        |  +--rw metric?           uint16
           |        +--rw bgp
           |        |  +--rw autonomous-system    uint32
           |        |  +--rw address-family*      address-family
           |        +--rw static
           |           +--rw ip-lan-prefixes* [lan next-hop]
           |              +--rw lan         inet:ip-prefix
           |              +--rw next-hop    inet:ipv4-address
           |              +--rw priority?   uint16
           +--rw policies
              +--rw path-selection-policy* [name]
              |  +--rw name               string
              |  +--rw segment-network?   leafref
              |  +--rw site*              leafref
              |  +--rw rule* [rule-id]
              |     +--rw rule-id                string
              |     +--rw priority?              uint32
              |     +--rw classification-name?   leafref
              |     +--rw traffic-sla-profile* [name]
              |     |  +--rw name                string
              |     |  +--rw latency?            uint32
              |     |  +--rw jitter?             uint32
              |     |  +--rw packet-loss-rate?   uint32
              |     +--rw path-primary?          string
              |     +--rw path-sencondry?        string
              +--rw qos-bandwidth-policy* [name]
              |  +--rw name       string
              |  +--rw priorty?   uint32
              |  +--rw qos
              |     +--rw classification-name?   leafref
              |     +--rw qos-profile-name?      leafref

Sun & Wu                Expires December 29, 2018              [Page 11]
Internet-Draft          SD-WAN Service YANG Model              June 2018

              +--rw traffic-filter* [site-id]
              |  +--rw site-id                leafref
              |  +--rw classification-name?   leafref
              |  +--rw direction?             identityref
              |  +--rw action?                identityref
              +--rw internet-access* [site-id]
              |  +--rw site-id                leafref
              |  +--rw access-option?         uint32
              |  +--rw internet-gateway-ip*   inet:ip-address
              |  +--rw nat?                   uint32
              |  +--rw nat44-ip-addr?         inet:ip-address
              +--rw vpn-interworking* [site-id]
              |  +--rw site-id           leafref
              |  +--rw vpn-gateway-ip?   inet:ip-address
              +--rw application-group* [group-name]
              |  +--rw group-name          string
              |  +--rw application-name*   string
              +--rw classification-profile* [name]
              |  +--rw name    string
              |  +--rw rule* [id]
              |     +--rw id                         string
              |     +--rw (match-type)?
              |        +--:(match-flow)
              |        |  +--rw match-flow
              |        |     +--rw dscp?                inet:dscp
              |        |     +--rw dot1p?               uint8
              |        |     +--rw ipv4-src-prefix?     inet:ipv4-prefix
              |        |     +--rw ipv6-src-prefix?     inet:ipv6-prefix
              |        |     +--rw ipv4-dst-prefix?     inet:ipv4-prefix
              |        |     +--rw ipv6-dst-prefix?     inet:ipv6-prefix
              |        |     +--rw l4-src-port?         inet:port-number
              |        |     +--rw l4-src-port-range
              |        |     |  +--rw lower-port?   inet:port-number
              |        |     |  +--rw upper-port?   inet:port-number
              |        |     +--rw l4-dst-port?         inet:port-number
              |        |     +--rw l4-dst-port-range
              |        |     |  +--rw lower-port?   inet:port-number
              |        |     |  +--rw upper-port?   inet:port-number
              |        |     +--rw protocol-field?      union
              |        +--:(match-application-group)
              |           +--rw match-application-group?   string
              +--rw qos-profile* [name]
                 +--rw name             string
                 +--rw bd-limit-type?   identityref
                 +--rw percent
                 |  +--rw width-percent?   uint32
                 +--rw value
                    +--rw cir?   uint32

Sun & Wu                Expires December 29, 2018              [Page 12]
Internet-Draft          SD-WAN Service YANG Model              June 2018

                    +--rw pir?   uint32

4.  YANG Modules

4.1.  IETF-sd-wan

   <CODE BEGINS> file "ietf-sdwan-vpn-svc@2018-06-13.yang

module ietf-sdwan-vpn-svc {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-sdwan-vpn-svc";
  prefix sdwan-svc;

  import ietf-inet-types {
    prefix inet;
  }
  import ietf-yang-types {
    prefix yang;
  }

  organization "IETF foo Working Group.";
  contact
    "WG List: foo@ietf.org
     Editor:  ";
  description
    "The YANG module defines a generic service configuration
     model for SD-WAN VPN.";

  revision 2018-06-13 {
    description
      "Initial revision";
    reference "A YANG Data Model for SD-WAN VPN.";
  }

  typedef svc-id {
    type string;
    description
      "Type definition for servicer identifier";
  }

  typedef address-family {
    type enumeration {
      enum "ipv4" {
        description
          "IPv4 address family.";
      }
      enum "ipv6" {

Sun & Wu                Expires December 29, 2018              [Page 13]
Internet-Draft          SD-WAN Service YANG Model              June 2018

        description
          "IPv6 address family.";
      }
    }
    description
      "Defines a type for the address family.";
  }

  identity vpn-topology {
    description
      "Base identity for vpn topology.";
  }

  identity any-to-any {
    base vpn-topology;
    description
      "Identity for any-to-any VPN topology.";
  }

  identity hub-spoke {
    base vpn-topology;
    description
      "Identity for Hub-and-Spoke VPN topology.";
  }

  identity site-role {
    description
      "Site Role";
  }

  identity any-to-any-role {
    base site-role;
    description
      "Site in an any-to-any IP VPN.";
  }

  identity hub {
    base site-role;
    description
      "Hob Role";
  }

  identity spoke {
    base site-role;
    description
      "Spoke Role";
  }

Sun & Wu                Expires December 29, 2018              [Page 14]
Internet-Draft          SD-WAN Service YANG Model              June 2018

  identity access-type {
    description
      "Access type";
  }

  identity ge {
    base access-type;
    description
      "GE";
  }

  identity ef {
    base access-type;
    description
      "EF";
  }

  identity xge {
    base access-type;
    description
      "XGE";
  }

  identity lte {
    base access-type;
    description
      "LTE";
  }

  identity xdsl-atm {
    base access-type;
    description
      "xDSL(ATM)";
  }

  identity xdsl-ptm {
    base access-type;
    description
      "xDSL(PTM)";
  }

  identity routing-protocol-type {
    description
      "Base identity for routing protocol type.";
  }

  identity ospf {
    base routing-protocol-type;

Sun & Wu                Expires December 29, 2018              [Page 15]
Internet-Draft          SD-WAN Service YANG Model              June 2018

    description
      "Identity for OSPF protocol type.";
  }

  identity bgp {
    base routing-protocol-type;
    description
      "Identity for BGP protocol type.";
  }

  identity static {
    base routing-protocol-type;
    description
      "Identity for static routing protocol type.";
  }

  identity addr-allocation {
    description
      "Base identity for address allocation";
  }

  identity addr-allocation-static {
    base addr-allocation;
    description
      "Static";
  }

  identity traffic-direction {
    description
      "Base identity for traffic direction";
  }

  identity inbound {
    base traffic-direction;
    description
      "Identity for inbound";
  }

  identity outbound {
    base traffic-direction;
    description
      "Identity for outbound";
  }

  identity both {
    base traffic-direction;
    description
      "Identity for both";

Sun & Wu                Expires December 29, 2018              [Page 16]
Internet-Draft          SD-WAN Service YANG Model              June 2018

  }

  identity traffic-action {
    description
      "Base identity for traffic action";
  }

  identity permit {
    base traffic-action;
    description
      "Identity for permit action";
  }

  identity deny {
    base traffic-action;
    description
      "Identity for deny action";
  }

  identity bd-limit-type {
    description
      "base identity for bd limit type";
  }

  identity percent {
    base bd-limit-type;
    description
      "Identity for percent";
  }

  identity value {
    base bd-limit-type;
    description
      "Identity for value";
  }

  grouping qos-bandwidth-policy {
    list qos-bandwidth-policy {
      key "name";
      leaf name {
        type string;
        description
          "QoS name";
      }
      leaf priorty {
        type uint32;
        description
          "Priorty";

Sun & Wu                Expires December 29, 2018              [Page 17]
Internet-Draft          SD-WAN Service YANG Model              June 2018

      }
      container qos {
        leaf classification-name {
          type leafref {
            path "/sdwan-vpn-svc/sdwan-vpn/policies"+"
             /classification-profile/name";
          }
          description
            "Qos Classification name";
        }
        leaf qos-profile-name {
          type leafref {
            path "/sdwan-vpn-svc/sdwan-vpn/policies/qos-profile/name";
          }
          description
            "Qos profile name";
        }
        description
          "Container for QOS";
      }
      description
        "List for qos policy";
    }
    description
      "Gourping for qos-bandwidth-policy";
  }

  grouping qos-profile {
    list qos-profile {
      key "name";
      leaf name {
        type string;
        description
          "QOS profile name";
      }
      leaf bd-limit-type {
        type identityref {
          base bd-limit-type;
        }
        description
          "bd limit type";
      }
      container percent {
        when "../bd-limit-type = 'percent'";
        leaf width-percent {
          type uint32;
          description
            "Width percent";

Sun & Wu                Expires December 29, 2018              [Page 18]
Internet-Draft          SD-WAN Service YANG Model              June 2018

        }
        description
          "Container for percent";
      }
      container value {
        when "../bd-limit-type = 'value'";
        leaf cir {
          type uint32;
          description
            "CIR";
        }
        leaf pir {
          type uint32;
          description
            "PIR";
        }
        description
          "Container for value";
      }
      description
        "List for qos profile";
    }
    description
      "Grouping for qos profile";
  }

  grouping application-group {
    list application-group {
      key "group-name";
      leaf group-name {
        type string;
        description
          "Gourp name";
      }
      leaf-list application-name {
        type string;
        description
          "Application name";
      }
      description
        "List for application group";
    }
    description
      "Grouping for application-group";
  }

  grouping path-selection-policy {
    list path-selection-policy {

Sun & Wu                Expires December 29, 2018              [Page 19]
Internet-Draft          SD-WAN Service YANG Model              June 2018

      key "name";
      leaf name {
        type string;
        description
          "Policy name";
      }
      leaf segment-network {
        type leafref {
          path "/sdwan-vpn-svc/sdwan-vpn/segment-networks/segment-id";
        }
        description
          "segment network identifier";
      }
      leaf-list site {
        type leafref {
          path "/sdwan-vpn-svc/sdwan-vpn/sites/site/site-id";
        }
        description
          "Site list ";
      }
      list rule {
        key "rule-id";
        leaf rule-id {
          type string;
          description
            "Rule id";
        }
        leaf priority {
          type uint32;
          description
            "Priority";
        }
        leaf classification-name {
          type leafref {
            path "/sdwan-vpn-svc/sdwan-vpn/policies"+
           "/classification-profile/name";
          }
          description
            "QOS Classification NAME";
        }
        list traffic-sla-profile {
          key "name";
          leaf name {
            type string;
            description
              "traffic sla profile";
          }
          leaf latency {

Sun & Wu                Expires December 29, 2018              [Page 20]
Internet-Draft          SD-WAN Service YANG Model              June 2018

            type uint32;
            description
              "latency";
          }
          leaf jitter {
            type uint32;
            description
              "jitter";
          }
          leaf packet-loss-rate {
            type uint32;
            description
              "packet loss rate";
          }
          description
            "traffic sla profile";
        }
        leaf path-primary {
          type string;
          description
            "Path primary";
        }
        leaf path-sencondry {
          type string;
          description
            "Path sencondry";
        }
        description
          "List for Rule";
      }
      description
        "List for path selection policy";
    }
    description
      "Grouping for path-selection-policy";
  }

  grouping internet-access {
    list internet-access {
      key "site-id";
      leaf site-id {
        type leafref {
          path "/sdwan-vpn-svc/sdwan-vpn/sites/site/site-id";
        }
        description
          "Site id";
      }
      leaf access-option {

Sun & Wu                Expires December 29, 2018              [Page 21]
Internet-Draft          SD-WAN Service YANG Model              June 2018

        type uint32;
        description
          "internet access via local breakout or central gateway";
      }
      leaf-list internet-gateway-ip {
        type inet:ip-address;
        description
          "Internet gateway IP";
      }
      leaf nat {
        type uint32;
        description
          "NAT";
      }
      leaf nat44-ip-addr {
        type inet:ip-address;
        description
          "Static nat custom internet IP.
           Address to be used for network address translation from IPv4 to
           IPv4.  This is to be used if the customer is providing the IPv4
           address.  If the customer address is not set, the model assumes
           that the provider will allocate the address.";
      }
      description
        "List for internet access";
    }
    description
      "Grouping for internet-access";
  }

  grouping vpn-interworking {
    list vpn-interworking {
      key "site-id";
      leaf site-id {
        type leafref {
          path "/sdwan-vpn-svc/sdwan-vpn/sites/site/site-id";
        }
        description
          "Site id";
      }
      leaf vpn-gateway-ip {
        type inet:ip-address;
        description
          "traditional MPLS VPN gateway IP";
      }
      description
        "List for traditional MPLS VPN interworking";
    }

Sun & Wu                Expires December 29, 2018              [Page 22]
Internet-Draft          SD-WAN Service YANG Model              June 2018

    description
      "Grouping for vpn-interworking";
  }

  grouping traffic-filter-policy {
    list traffic-filter {
      key "site-id";
      leaf site-id {
        type leafref {
          path "/sdwan-vpn-svc/sdwan-vpn/sites/site/site-id";
        }
        description
          "Site id";
      }
      leaf classification-name {
        type leafref {
          path "/sdwan-vpn-svc/sdwan-vpn/policies"+
           "/classification-profile/name";
        }
        description
          "Classification profile name";
      }
      leaf direction {
        type identityref {
          base traffic-direction;
        }
        description
          "Traffic direction";
      }
      leaf action {
        type identityref {
          base traffic-action;
        }
        description
          "Action";
      }
      description
        "List for traffic filter";
    }
    description
      "Grouping for traffic filter";
  }

  grouping flow-definition {
    container match-flow {
      leaf dscp {
        type inet:dscp;
        description

Sun & Wu                Expires December 29, 2018              [Page 23]
Internet-Draft          SD-WAN Service YANG Model              June 2018

          "DSCP value.";
      }
      leaf dot1p {
        type uint8 {
          range "0..7";
        }
        description
          "802.1p matching.";
      }
      leaf ipv4-src-prefix {
        type inet:ipv4-prefix;
        description
          "Match on IPv4 src address.";
      }
      leaf ipv6-src-prefix {
        type inet:ipv6-prefix;
        description
          "Match on IPv6 src address.";
      }
      leaf ipv4-dst-prefix {
        type inet:ipv4-prefix;
        description
          "Match on IPv4 dst address.";
      }
      leaf ipv6-dst-prefix {
        type inet:ipv6-prefix;
        description
          "Match on IPv6 dst address.";
      }
      leaf l4-src-port {
        type inet:port-number;
        must "'.' <= '../l4-src-port-range/lower-port' and'.'>="+
        " '../l4-src-port-range/upper-port'" {
          description
            " If l4-src-port and l4-src-port-range/lower-port and
                upper-port are set at the same time, l4-src-port
                should not overlap with l4-src-port-range. ";
        }
        description
          "Match on Layer 4 src port.";
      }
      container l4-src-port-range {
        leaf lower-port {
          type inet:port-number;
          description
            "Lower boundary for port.";
        }
        leaf upper-port {

Sun & Wu                Expires December 29, 2018              [Page 24]
Internet-Draft          SD-WAN Service YANG Model              June 2018

          type inet:port-number;
          must ". >= ../lower-port" {
            description
              " Upper boundary for port. If it
                   exists, upper boundary must be
                       higher than lower boundary.";
          }
          description
            "Upper boundary for port.";
        }
        description
          "Match on Layer 4 src port range. When only lower-port
              is present, it represents a single port. When both
              lower-port and upper-port are specified, it implies
              a range inclusive of both values.";
      }
      leaf l4-dst-port {
        type inet:port-number;
        must ". <= ../l4-dst-port-range/lower-port and.>="+
        " ../l4-dst-port-range/upper-port" {
          description
            " If l4-dst-port and l4-dst-port-range/lower-port and
                upper-port are set at the same time, l4-dst-port
                should not overlap with l4-src-port-range. ";
        }
        description
          "Match on Layer 4 dst port.";
      }
      container l4-dst-port-range {
        leaf lower-port {
          type inet:port-number;
          description
            "Lower boundary for port.";
        }
        leaf upper-port {
          type inet:port-number;
          must ". >= ../lower-port" {
            description
              "Upper boundary must be
                  higher than lower boundary.";
          }
          description
            "Upper boundary for port. If it exists, upper boundary
                must be higher than lower boundary.";
        }
        description
          "Match on Layer 4 dst port range. When only lower-port is
              present, it represents a single port. When both lower-port

Sun & Wu                Expires December 29, 2018              [Page 25]
Internet-Draft          SD-WAN Service YANG Model              June 2018

              and upper-port are specified, it implies a range inclusive
              of both values.";
      }
      leaf protocol-field {
        type union {
          type uint8;
          type identityref {
            base routing-protocol-type;
          }
        }
        description
          "Match on IPv4 protocol or IPv6 Next Header field.";
      }
      description
        "Describes flow-matching criteria.";
    }
    description
      "Flow definition based on criteria.";
  }

  grouping classification-profile {
    list classification-profile {
      key "name";
      leaf name {
        type string;
        description
          "classification name";
      }
      list rule {
        key "id";
        ordered-by user;
        leaf id {
          type string;
          description
            "A description identifying qos classification
             policy rule.";
        }
        choice match-type {
          default "match-flow";
          case match-flow {
            uses flow-definition;
          }
          case match-application-group {
            leaf match-application-group {
              type string;
              description
                "Defines the application to match.";
            }

Sun & Wu                Expires December 29, 2018              [Page 26]
Internet-Draft          SD-WAN Service YANG Model              June 2018

          }
          description
            "Choice for classification.";
        }
        description
          "List of marking rules.";
      }
      description
        "List for classification profile";
    }
    description
      "Gourping for classification profile";
  }

  grouping routing-protocol {
    list routing-protocol {
      key "type";
      leaf type {
        type identityref {
          base routing-protocol-type;
        }
        description
          "Routing protocol type";
      }
      container ospf {
        when "derived-from-or-self(../type, 'sdwan-svc:ospf')" {
          description
            "Only applies when protocol is OSPF.";
        }
        leaf-list address-family {
          type address-family;
          min-elements 1;
          description
            "If OSPF is used on this site, this node
             contains a configured value.  This node
             contains at least one address family
             to be activated.";
        }
        leaf area-address {
          type yang:dotted-quad;
          mandatory true;
          description
            "Area address.";
        }
        leaf metric {
          type uint16;
          default "1";
          description

Sun & Wu                Expires December 29, 2018              [Page 27]
Internet-Draft          SD-WAN Service YANG Model              June 2018

            "Metric of the PE-CE link.  It is used
             in the routing state calculation and
             path selection.";
        }
        description
          "OSPF-specific configuration.";
      }
      container bgp {
        when "derived-from-or-self(../type, 'sdwan-svc:bgp')" {
          description
            "Only applies when protocol is BGP.";
        }
        leaf autonomous-system {
          type uint32;
          mandatory true;
          description
            "Customer AS number in case the customer
             requests BGP routing.";
        }
        leaf-list address-family {
          type address-family;
          min-elements 1;
          description
            "If BGP is used on this site, this node
             contains a configured value.  This node
             contains at least one address family
             to be activated.";
        }
        description
          "BGP-specific configuration.";
      }
      container static {
        when "derived-from-or-self(../type, 'sdwan-svc:static')" {
          description
            "Only applies when protocol is static.
             BGP activation requires the SP to know
             the address of the customer peer.  When
             BGP is enabled, the 'static-address'
             allocation type for the IP connection
             MUST be used.";
        }
        list ip-lan-prefixes {
          key "lan next-hop";
          leaf lan {
            type inet:ip-prefix;
            description
              "LAN prefixes.";
          }

Sun & Wu                Expires December 29, 2018              [Page 28]
Internet-Draft          SD-WAN Service YANG Model              June 2018

          leaf next-hop {
            type inet:ipv4-address;
            description
              "Next-hop address to use on the customer side.";
          }
          leaf priority {
            type uint16;
            description
              "Prority";
          }
          description
            "List of LAN prefixes for the site.";
        }
        description
          "Configuration specific to static routing.";
      }
      description
        "List for Routing Protocol";
    }
    description
      "Grouping for routing protocol";
  }

  container sdwan-vpn-svc {
    list sdwan-vpn {
      key vpn-id;
      leaf vpn-id {
      type svc-id;
      description
      "VPN identifier.  Local administration meaning.";
      }

      leaf customer-name {
        type svc-id;
        description
          "Id for customer";
      }

      list wan-transport-networks {
        key "wan-transport-name";
        leaf wan-transport-name {
          type string;
          description
            "WAN transport network name";
        }
        leaf wan-transport-type {
          type identityref {
            base access-type;

Sun & Wu                Expires December 29, 2018              [Page 29]
Internet-Draft          SD-WAN Service YANG Model              June 2018

          }
          description
            "Access type";
        }
      }

      container sites {
        list site {
          key "site-id";
          leaf site-id {
            type svc-id;
            description
              "Site Name";
          }
          list location {
            key "email";
            leaf email {
              type string;
              description
                "List for email";
            }
            leaf postcode {
              type string;
              description
                "Post code";
            }
            leaf address {
              type string;
              description
                "Location address";
            }
            description
              "List for location";
          }
          list device {
            key "name";
            leaf name {
              type string;
              description
                "Device Name";
            }
            leaf type {
              type string;
              description
                "Device Type";
            }
            description
              "List for device";

Sun & Wu                Expires December 29, 2018              [Page 30]
Internet-Draft          SD-WAN Service YANG Model              June 2018

          }
          list transport-network {
            key "name";
            leaf name {
              type string;
              description
                "transport network port name";
            }
            leaf access-type {
              type identityref {
                base access-type;
              }
              description
                "Access type";
            }
            container ip-connection {
              leaf type {
                type identityref {
                  base addr-allocation;
                }
                description
                  "Address allocation type";
              }
              container static {
                when "../type = 'addr-allocation-static'";
                leaf customer-addr {
                  type inet:ip-address;
                  description
                    "Customer address";
                }
                leaf prefix {
                  type inet:ip-prefix;
                  description
                    "IP Prefix";
                }
                leaf provider-addr {
                  type inet:ip-address;
                  description
                    "Provider address";
                }
                description
                  "Container for static";
              }
              description
                "Container for ip connection";
            }
            uses routing-protocol;
            container bandwidth {

Sun & Wu                Expires December 29, 2018              [Page 31]
Internet-Draft          SD-WAN Service YANG Model              June 2018

              leaf input-bandwidth {
                type uint64;
                description
                  "input bandwidth";
              }
              leaf output-bandwidth {
                type uint64;
                description
                  "output bandwidth";
              }
              leaf mtu {
                type uint16;
                description
                  "MTU";
              }
              description
                "Container for service";
            }
            description
              "List for transport network ports";
          }
          description
            "List for sites";
        }
        description
          "Container for sites";
      }

      list segment-networks {
        key "segment-id";
        leaf segment-id {
          type svc-id;
          description
            "segment network identifier";
        }
        leaf topology {
          type identityref {
            base vpn-topology;
          }
          description
            "vpn segment topology: hub&spoke or any-to-any";
        }
        list sites {
          key "site-id";
          leaf site-id {
            type leafref {
              path "/sdwan-vpn-svc/sdwan-vpn/sites/site/site-id";
            }

Sun & Wu                Expires December 29, 2018              [Page 32]
Internet-Draft          SD-WAN Service YANG Model              June 2018

            mandatory true;
            description
              "Reference to a site.";
          }
          leaf site-role {
            type identityref {
              base site-role;
            }
            default "any-to-any-role";
            description
              "Role of the site in the segment.";
          }
          description
            "List of sites the segment is associated with.";
        }
        list lan-networks {
          key "site-id";
          leaf site-id {
            type leafref {
              path "/sdwan-vpn-svc/sdwan-vpn/sites/site/site-id";
            }
          }
          leaf vlan-tag {
            type uint16;
            description
              "VLAN TAG";
          }
          leaf ip-address {
            type inet:ip-address;
            description
              "IP Address";
          }
          leaf ip-prefix {
            type inet:ip-prefix;
            description
              "IP Prefix";
          }
          uses routing-protocol;
          description
            "container for lan network";
        }
        description
          "List for segment network";
      }
      container policies {
        uses path-selection-policy;
        uses qos-bandwidth-policy;
        uses traffic-filter-policy;

Sun & Wu                Expires December 29, 2018              [Page 33]
Internet-Draft          SD-WAN Service YANG Model              June 2018

        uses internet-access;
        uses vpn-interworking;
        uses application-group;
        uses classification-profile;
        uses qos-profile;
      }

      description
        "List for SD-WAN";
    }
    description
      "Container for SD-WAN VPN service";
  }
}

   &lt;CODE ENDS&gt;

5.  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
   [RFC5246].

   The NETCONF access control model [RFC6536]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.  These are the subtrees and data nodes
   and their sensitivity/vulnerability.

6.  IANA Considerations

   IANA has assigned a new URI from the "IETF XML Registry" [RFC3688].

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

Sun & Wu                Expires December 29, 2018              [Page 34]
Internet-Draft          SD-WAN Service YANG Model              June 2018

   IANA has recorded a YANG module name in the "YANG Module Names"
   registry [RFC6020] as follows:

              Name: ietf-sdwan-vpn-svc
              Namespace: urn:ietf:params:xml:ns:yang:ietf-sdwan-vpn-svc
              Prefix: sdwan-svc
              Reference: RFC xxxx

7.  Acknowledgments

   This work has benefited from the discussions of xxxx.

8.  Contributors

   The authors would like to thank Zitao Wang and Qin Wu for their major
   contributions to the initial modeling.

9.  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>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [RFC4664]  Andersson, L., Ed. and E. Rosen, Ed., "Framework for Layer
              2 Virtual Private Networks (L2VPNs)", RFC 4664,
              DOI 10.17487/RFC4664, September 2006,
              <https://www.rfc-editor.org/info/rfc4664>.

   [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>.

   [RFC6071]  Frankel, S. and S. Krishnan, "IP Security (IPsec) and
              Internet Key Exchange (IKE) Document Roadmap", RFC 6071,
              DOI 10.17487/RFC6071, February 2011,
              <https://www.rfc-editor.org/info/rfc6071>.

   [RFC8299]  Wu, Q., Ed., Litkowski, S., Tomotaki, L., and K. Ogaki,
              "YANG Data Model for L3VPN Service Delivery", RFC 8299,
              DOI 10.17487/RFC8299, January 2018,
              <https://www.rfc-editor.org/info/rfc8299>.

Sun & Wu                Expires December 29, 2018              [Page 35]
Internet-Draft          SD-WAN Service YANG Model              June 2018

Authors' Addresses

   Qiong Sun
   China Telecom
   Beijing
   China

   Email: sunqiong.bri@chinatelecom.cn

   Bo Wu
   Huawei
   Nanjing
   China

   Email: lana.wubo@huawei.com

Sun & Wu                Expires December 29, 2018              [Page 36]