With complex infrastructure, firewalls are often bothersome.
Is it our application or the network?
Powershell TcpListener class can help us.
Here is a sample script opening a specific port and printing incoming data along with connection information.
The Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 | #region Hardcoded Parameters$iPortToTest = 6666#endregion#region Internal Parameters$_Listener#endregion#region Internal FunctionFunction Open-TCPPort { [CmdletBinding()] Param ( [Parameter(Mandatory=$true, Position=0)] [ValidateNotNullOrEmpty()] [int] $Port ) Process { Try { # Start Listener $endpoint = new-object System.Net.IPEndPoint([ipaddress]::any,$Port) $listener = new-object System.Net.Sockets.TcpListener $endpoint $listener.start() Write-Verbose ("[$(Get-Date)] Listener started on port {0} " -f $Port) -Verbose Return $listener } Catch { $mess = "Couldn't start listener : " + $Error[0] Write-Error -Message $mess -ErrorAction Stop } }}Function Receive-TCPMessage { [CmdletBinding()] Param ( [Parameter(Mandatory=$true, Position=0)] [ValidateNotNullOrEmpty()] [System.Net.Sockets.TcpListener] $listener ) Process { Try { # Accept connection $data = $listener.AcceptTcpClient() Write-Verbose ("[$(Get-Date)] New Connection from {0} Source port <{1}>" -f $data.Client.RemoteEndPoint.Address, $Data.Client.RemoteEndPoint.Port) -Verbose # Stream setup $stream = $data.GetStream() $bytes = New-Object System.Byte[] 1024 # Read Data from stream and write it to host while (($i = $stream.Read($bytes,0,$bytes.Length)) -ne 0){ $EncodedText = New-Object System.Text.ASCIIEncoding $data = $EncodedText.GetString($bytes,0, $i) Write-Output $data } } Catch { $mess = "Receive Message failed with: `n" + $Error[0] Write-Error -Message $mess -ErrorAction Stop } Finally { # Close stream $stream.close() } }}#endregion Internal Function#----------------------------------------------#region Main Block#----------------------------------------------$_Listener = Open-TCPPort($iPortToTest)try{ while($true) { try{ # Test for pending connection if($_Listener.Pending()){ Receive-TCPMessage($_Listener) } Start-Sleep -Milliseconds 50 } catch { $mess = "Receive Message failed with: `n" + $Error[0] Write-Error -Message $mess -ErrorAction Stop } }}finally{ $_Listener.stop()}#----------------------------------------------#endregion Main Block#---------------------------------------------- |
The usage
Set the port you want to listen to in script parameter: $iPortToTest.
Run the script. A message should display the port is now listening.
Connection request will be displayed (machine, source port and incoming data).
A simple test, in local using putty:
