Powershell P2P with UPnP hole punching - powershell

Question

I'm trying to get my head around how P2P works and how one can implement working P2P without having to forward ports on the router. As far as I know to do this we need to "punch holes" and one of the means of doing this is with NATUPnP.
Below I've got some powershell code which sets up a TCP listener on local port 42008:
$port = 42008
# Punch hole
$upnp = New-Object -ComObject "HNetCfg.NATUPnP"
$upnp.StaticPortMappingCollection.Add(42002, "TCP", $port, "localhost", $true, "Socket test")
# Create a TCP listener object
$listener = New-Object System.Net.Sockets.TcpListener([System.Net.IPAddress]::Any, $port)
# Start the listener
$listener.Start()
# Wait for incoming connections
while ($true) {
# Accept incoming connections
$client = $listener.AcceptTcpClient()
# Get the stream for the client
$stream = $client.GetStream()
# Read data from the stream
$buffer = New-Object byte[] 1024
$read = $stream.Read($buffer, 0, 1024)
# Convert the data to a string and print it
$data = [System.Text.Encoding]::ASCII.GetString($buffer, 0, $read)
Write-Host "Received: $data"
# Close the stream and the client
$stream.Close()
$client.Close()
}
As far as I understand it the hole punching above should redirect messages sent to <publicIP>:42002 to localhost:<$port> where the TCP Listener is listening. I then run the following client:
$upnp = New-Object -ComObject "HNetCfg.NATUPnP"
$externalIP = $upnp.StaticPortMappingCollection.item(42002, "TCP").ExternalIPAddress
$externalPort = 42002
# Connect to the remote machine
$client = New-Object System.Net.Sockets.TcpClient($externalIP, $externalPort)
# Get the stream for the client
$stream = $client.GetStream()
# Write data to the stream
$data = "Hello, World 2!"
$buffer = [System.Text.Encoding]::ASCII.GetBytes($data)
$stream.Write($buffer, 0, $buffer.Length)
# Close the stream and the client
$stream.Close()
$client.Close()
In this example I open up upnp just to grab the external IP and the external port, then I ping a message via TcpClient.
As far as I know this should work? But I keep getting the following exception:
New-Object : Exception calling ".ctor" with "2" argument(s): "No connection could be made because the target machine actively refused it <XX.XX.XX.XX>:42002"
At C:\Users\sancarn\Desktop\tbd\Powershell\SocketClient.ps1:7 char:11
+ $client = New-Object System.Net.Sockets.TcpClient($externalIP, $exter ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (:) [New-Object], MethodInvocationException
+ FullyQualifiedErrorId : ConstructorInvokedThrowException,Microsoft.PowerShell.Commands.NewObjectCommand
Why is my machine actively refusing connection? I've actively disabled my firewall just to check whether that was the issue, but to no avail. I can't think what else could be wrong unless I've just got the wrong end of the stick as to how to use it? Any ideas?