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Enable RDP ShortPath for Windows Virtual Desktop on an image version automated

Since Windows Virtual Desktop is generally available a lot of improvements has been done. Think about ARM template deployment, MSIX app attach through the Azure portal and performance improvements in the WVD client and latency improvements at the most of the regions.
Since 16 November 2020 a really nice improvement has been added to the list, Windows Virtual Desktop RDP Short path. In this blogpost I will show you how to configure this feature with some automation tasks.

Introduction

First some basic background information about Windows Virtual Desktop and default network connectivity. A Windows Virtual Desktop environment consists of hostpools, session hosts, workspaces and application groups. If everything has been configured correctly you will be able to connect with a domain account to https://rdweb.wvd.microsoft.com/arm/webclient/index.html. After connecting you will able to connect workspaces and/or applications.

The user validation, securing and other connection needs will be handled by the Windows Virtual Desktop gateway and broker. Because I am an automation guy and not a networking guy I will stop talking about networking now :). For a complete networking overview please check the Windows Virtual Desktop network connectivity page.

RDP Shortpath is a feature of Windows Virtual Desktop that establishes a direct UDP-based transport between Remote Desktop Client and Session host. RDP uses this transport to deliver Remote Desktop and RemoteApp while offering better reliability and consistent latency. For a complete overview please check the Shortpath overview.

Prerequisites

Before continuing you will need:

Table of contents

For enabling RDP ShortPath in a new image version you do the following steps:

Create new virtual machine

For creating a new virtual I worte a blogpost earlier. Please check my blogpost Windows Virtual Desktop Image Management Automated – Part 1 – Create WVD image version based on existing config with PowerShell. In that post I will explain how to create a new virtual machine based on a existing sessionhost. The only thing you need know is the Windows Virtual Desktop hostpool.
After following that post at the end you will have an output somthing like this:

image-version-output

Use the information for the rest of this article.

Local tasks on the virtual machine

For enabling the RDP shortpath feature you will need to execute some command on the local virtual machine. Because I don’t want to login I’m using remote PowerShell which allows me to run commands with login into the virtual machine with RDP.
First of all I created a PowerShell script for the local machine. Before you are able to setup a remote PowerShell connection you will need some parameters first. These are the parameters you received from the create new virtual machine part. Beside that you also need some modules and the add-firewallRule function.

param(
    [parameter(mandatory = $true, ValueFromPipelineByPropertyName)]$virtualMachineName,
    [parameter(mandatory = $true, ValueFromPipelineByPropertyName)]$resourceGroupName,
    [parameter(mandatory = $true, ValueFromPipelineByPropertyName)]$password,
    [parameter(mandatory = $true, ValueFromPipelineByPropertyName)]$username
)

import-module az.desktopvirtualization
import-module az.network
import-module az.compute


function add-firewallRule() {
    param(
    [parameter(mandatory = $true, ValueFromPipelineByPropertyName)]$NSG,
    [parameter(mandatory = $true, ValueFromPipelineByPropertyName)]$Name,
    [parameter(mandatory = $true, ValueFromPipelineByPropertyName)]$Port,
    [parameter(mandatory = $true, ValueFromPipelineByPropertyName)]$Protocol,
    [parameter(mandatory = $false, ValueFromPipelineByPropertyName)]$Source

)
    if ($null -eq $Source){$Source = "*";$SourceReadable="Any"}
    # Pick random number for setting priority. It will exclude current priorities.
    $InputRange = 100..200
    $Exclude = ($NSG | Get-AzNetworkSecurityRuleConfig | select Priority).priority
    $RandomRange = $InputRange | Where-Object { $Exclude -notcontains $_ }
    $priority = Get-Random -InputObject $RandomRange
    $nsgParameters = @{
        Name                     = $Name
        Description              = $Name
        Access                   = 'Allow'
        Protocol                 = $Protocol 
        Direction                = "Inbound" 
        Priority                 = $priority 
        SourceAddressPrefix      = $Source 
        SourcePortRange          = "*"
        DestinationAddressPrefix = "*" 
        DestinationPortRange     = $Port
    }
    $NSG | Add-AzNetworkSecurityRuleConfig @NSGParameters  | Set-AzNetworkSecurityGroup 
}

The code below will take care about enabling remote PowerShell on the virtual machine by installing the EnableRemotePS extention. It will also create a NSG rule which allows you to connect. For security reasons I recommend providing a source from where the remote PowerShell connection will be made instead of any. In this example I’m using 127.0.0.1, you will need to change that source of course.


$vm = Get-AzVM -name $virtualMachineName -ResourceGroupName $resourceGroupName
$virtualNetworkSubnet = (Get-AzNetworkInterface -ResourceId $vm.NetworkProfile.NetworkInterfaces.id).IpConfigurations.subnet.id
$NSG = Get-AzNetworkSecurityGroup | ? { $_.subnets.id -eq $virtualNetworkSubnet }# Enabling Powershell Remote Extention
$virtualMachinePublicIp = (Get-AzPublicIpAddress | where { $_.name -match $VirtualMachineName }).IpAddress

$connectionUri = "https://" + $virtualMachinePublicIp + ":5986" 
[securestring]$secStringPassword = ConvertTo-SecureString $password -AsPlainText -Force
[pscredential]$creds = New-Object System.Management.Automation.PSCredential ($userName, $secStringPassword)
$session = $null


# Adding Remote PowerShell Extention and NSG configuration
Write-Output "Enabling Powershell Remote Extention"
Invoke-AzVMRunCommand -CommandId "EnableRemotePS" -VM $vm
add-firewallRule -NSG $NSG -port 5986 -Source 127.0.0.1
 -Protocol "TCP" -Name "Allow-port-5986"

After the extention has been installed and the NSG has been configured you can setup a remote PowerShell connection.

while (!($session)) {
    $session = New-PSSession -ConnectionUri $connectionUri -Credential $creds -SessionOption (New-PSSessionOption -SkipCACheck -SkipCNCheck -SkipRevocationCheck)
    Write-Output "Creating Remote Powershell session"
    $session
}

After the session has been established we are able to execute remote commands.
In the first place I will set the execution policy to unrestricted so my script will run. Next the script will test if there is a C:\Scripts directory allready, if it does not exist we will create one.
The next part will download the real script which will configure the needed register keys and the local Windows Firewall. At last it will execute the script.


# Configure base needs
Invoke-Command -Session $session -ScriptBlock { Set-ExecutionPolicy -ExecutionPolicy Unrestricted }
Invoke-Command -Session $session -ScriptBlock { if(!(Test-Path C:\Scripts)){New-Item -ItemType "directory" -Path "C:\Scripts" } }
# RDP Short path
Invoke-Command -Session $session -ScriptBlock { Invoke-WebRequest -uri https://raw.githubusercontent.com/srozemuller/Windows-Virtual-Desktop/master/SessionHost-Management/Prepare-ForRDPShortPath.ps1 -OutFile C:\Scripts\Perpare-ForRDPShortPath.ps1} 
Invoke-Command -Session $session -ScriptBlock { C:\Scripts\Perpare-ForRDPShortPath.ps1 } 

Disconnect-PSSession -Session $session
Remove-PSSession -Session $session

After the script has run locally you will see the prepare script in C:\Scripts. The Prepare-ForRDPShortpath.ps1 content will take care of the register keys and the local Windows Firewall

$WinstationsKey = 'HKLM:\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations'
if(Test-Path $WinstationsKey){
    New-ItemProperty -Path $WinstationsKey -Name 'fUseUdpPortRedirector' -ErrorAction:SilentlyContinue -PropertyType:dword -Value 1 -Force
    New-ItemProperty -Path $WinstationsKey -Name 'UdpPortNumber' -ErrorAction:SilentlyContinue -PropertyType:dword -Value 3390 -Force
}

New-NetFirewallRule -DisplayName 'Remote Desktop - Shortpath (UDP-In)'  -Action Allow -Description 'Inbound rule for the Remote Desktop service to allow RDP traffic. [UDP 3390]' -Group '@FirewallAPI.dll,-28752' -Name 'RemoteDesktop-UserMode-In-Shortpath-UDP'  -PolicyStore PersistentStore -Profile Domain, Private -Service TermService -Protocol udp -LocalPort 3390 -Program '%SystemRoot%\system32\svchost.exe' -Enabled:True
Restart-Computer $env:computername -Force

The local Windows Firewall has been set.

The needed registry keys.

Configure Network Security Group

After the local settings has been done the next step is to add port 3390 to the correct NSG. In this step we will execute the add-firewallRule function again, this time without a source.


# Adding the role for RDP Shortpath
add-firewallRule -NSG $NSG -port 3390 -Protocol "UDP" -Name "Allow-3390"

Finalizing the virtual machine

The second last step is Sysprep the virtual machine and create a new version into the Shared Image Gallery. I talked about how to Sysprep and create a new version automatically in part 2 of Windows Virtual Desktop Image Management Automated.

The very last step is adding the new virtual machines to the Windows Virtual Desktop hostpool. How to achieve that goal fully automatically please check part 3 Create WVD sessionhosts on image version

Verify connection

At the end after connecting with the Windows Remote Client (download via Windows desktop client page) and the Workspace tab you are able to view the connection settings.

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