Listen and send basic messages over TCP to see if your ports are open

1_client.ps1

&{ Param($hostname, $port)
	$socket = $NULL
	$stream = $NULL
	try {
		$socket = [System.Net.Sockets.TCPClient]::new(
			[System.Net.IPAddress]::Parse(
				[System.Net.Dns]::GetHostAddresses($hostname)
			),
			$port
		)
		$stream = $socket.GetStream()

		$writer = [System.IO.StreamWriter]::new($stream)
		'Connected! Send something to the server'
		'Hit enter with no text to exit'
		for ($line = $NULL; $line = Read-Host; $writer.Flush()) {
			$writer.WriteLine($line)
		}
	}
	finally {
		$stream.Close()
		$socket.Close()
	}
} -hostname (iwr -Uri 'https://ifconfig.me/ip').Content -port 17011

1_server.ps1

&{ Param($ip, $port)
	$listener = [System.Net.Sockets.TcpListener]::new(
		[System.Net.IPEndPoint]::new($ip, $port)
	)

	$listener.Start()

	$client = $NULL
	$stream = $NULL
	$reader = $NULL
	try {
		$client = $listener.AcceptTcpClient()
		$stream = $client.GetStream()
		$reader = [System.IO.StreamReader]::new($stream)

		'Connected!'
		'The client will send text and close this session'
		for (
			$line = $NULL;
			$line = $reader.ReadLine();
			Write-Host $line -fore cyan
		) {}
	}
	finally {
		$reader.Dispose()
		$stream.Dispose()
		$client.Dispose()
	}

	$listener.Stop()
} -ip ([System.Net.IPAddress]::Any) -port 17011

2_client.ps1

&{ Param($hostname, $port)
	Write-Host 'Connecting, ctrl+c to exit' -fore cyan
	
	$socket = $NULL
	$stream = $NULL
	$writer = $NULL
	$response = $NULL
	$chat = $NULL
	try {
		$socket = [System.Net.Sockets.TCPClient]::new(
			[System.Net.IPAddress]::Parse(
				[System.Net.Dns]::GetHostAddresses($hostname)
			),
			$port
		)
		$stream = $socket.GetStream()
		$writer = [System.IO.StreamWriter]::new($stream)
		$response = [System.IO.StreamReader]::new($stream)
		Write-Host 'Connected!' -fore cyan

		$line = 'Type and hit enter to send a message to the client, requests are then shown'
		while ($socket.Connected) {
			if ($line) {
				$writer.WriteLine($line)
				$writer.Flush()
				Sleep -Milliseconds 100
			}
			while ($stream.DataAvailable) {
				$line = $response.ReadLine()
				if (!$line) {
					exit
				}
				Write-Host $line -fore green
			}
			$line = Read-Host
		}
	}
	finally {
		try {
			$writer.WriteLine('')
			$writer.Flush()
		}
		catch {}
		$response.Close()
		$writer.Close()
		$socket.Close()
	}
} -hostname (iwr -Uri 'https://ifconfig.me/ip').Content -port 30120

2_server.ps1

&{ Param($ip, $port)
	$listener = [System.Net.Sockets.TcpListener]::new(
		[System.Net.IPEndPoint]::new($ip, $port)
	)
	$listener.Start()
	Write-Host 'Listening, ctrl+c to exit' -fore cyan

	$client = $NULL
	$stream = $NULL
	$reader = $NULL
	$response = $NULL
	$chat = $NULL
	try {
		$client = $listener.AcceptTcpClient()
		$stream = $client.GetStream()
		$response = [System.IO.StreamWriter]::new($stream)
		$reader = [System.IO.StreamReader]::new($stream)
		Write-Host 'Connected!' -fore cyan

		$line = 'Type and hit enter to send a message to the server, responses are then shown'
		while ($client.Connected) {
			if ($line) {
				$response.WriteLine($line)
				$response.Flush()
				Sleep -Milliseconds 100
			}
			while ($stream.DataAvailable) {
				$line = $reader.ReadLine()
				if (!$line) {
					exit
				}
				Write-Host $line -fore green
			}
			$line = Read-Host
		}
	}
	finally {
		try {
			$response.WriteLine('')
			$response.Flush()
		}
		catch {}
		$reader.Close()
		$response.Close()
		$client.Close()
		$listener.Stop()
	}
} -ip ([System.Net.IPAddress]::Any) -port 30120

3_client.ps1

#NetStream doesn't support ReadStream & WriteStream operating at the same time
#so instead of writing directly here we have to use a queue later
$queue = [System.Collections.Queue]@('Type and hit enter to send a message to the client, enter no message to terminate')

$chat = $NULL
if ($MyInvocation.ExpectingInput) {
	$chat = [PSCustomObject]@{Input=$Input} `
	| Add-Member `
		-MemberType ScriptProperty `
		-Name       'HasExited' `
		-Value      {
			if (!$this.Input) {
				return $True
			}
			
			if ($this.Input.MoveNext()) {
				$queue.Enqueue($this.Input.Current)
			}
			else {
				$queue.Enqueue('')
				$this.Kill()
			}
			return $False
		} `
		-PassThru `
	| Add-Member `
		-MemberType ScriptMethod `
		-Name       'Kill' `
		-Value      { $this.Input = $NULL } `
		-PassThru
}

&{ Param($hostname, $port)
	Write-Host 'Connecting' -fore cyan
	
	$socket   = $NULL
	$stream   = $NULL
	$writer   = $NULL
	$response = $NULL
	try {
		$socket = [System.Net.Sockets.TCPClient]::new(
			[System.Net.IPAddress]::Parse(
				[System.Net.Dns]::GetHostAddresses($hostname)
			),
			$port
		)
		$stream = $socket.GetStream()
		$writer = [System.IO.StreamWriter]::new($stream)
		$writer.NewLine = "`n"
		$response = [System.IO.StreamReader]::new($stream)
		Write-Host 'Connected!' -fore cyan
		
		if (!$chat) {
			$chat = [Diagnostics.Process]::new()
			$chat.StartInfo `
			| %{
				$_.UseShellExecute        = $False
				$_.RedirectStandardOutput = $True
				$_.FileName               = 'powershell'
				$_.Arguments              = '-Command "&{$line=$NULL;do{$line=Read-Host;$line}while($line);1|sleep}"'
			}
			Register-ObjectEvent `
				-InputObject $chat `
				-EventName   'OutputDataReceived' `
				-MessageData $queue `
				-Action      {
					$Event.MessageData.Enqueue($EventArgs.Data)
				} `
			| Out-Null
			$chat.Start() | Out-Null
			$chat.BeginOutputReadLine()
		}
		
		$line = $NULL
		do {
			while ($queue.Count) {
				$line = $queue.Dequeue()
				$writer.WriteLine($line)
				$writer.Flush()
			}
			while ($stream.DataAvailable) {
				$line = $response.ReadLine()
				if ($line) {
					Write-Host $line -fore green
				}
				else {
					$chat.Kill()
				}
			}
			sleep -Milliseconds 500
		} while (!$chat.HasExited)
	}
	finally {
		if (!$chat.HasExited) {
			$chat.Kill()
		}
		$response.Close()
		$writer.Close()
		$socket.Close()
	}
} -hostname (iwr -Uri 'https://ifconfig.me/ip').Content -port 30120

3_server.ps1

#NetStream doesn't support ReadStream & WriteStream operating at the same time
#so instead of writing directly here we have to use a queue later
$queue = [System.Collections.Queue]@('Type and hit enter to send a message to the server, enter no message to disconnect')

$chat = $NULL
if ($MyInvocation.ExpectingInput) {
	$chat = [PSCustomObject]@{Input=$Input} `
	| Add-Member `
		-MemberType ScriptProperty `
		-Name       'HasExited' `
		-Value      {
			if (!$this.Input) {
				return $True
			}
			
			if ($this.Input.MoveNext()) {
				$queue.Enqueue($this.Input.Current)
			}
			else {
				$queue.Enqueue('')
				$this.Kill()
			}
			return $False
		} `
		-PassThru `
	| Add-Member `
		-MemberType ScriptMethod `
		-Name       'Kill' `
		-Value      { $this.Input = $NULL } `
		-PassThru
}

&{ Param($ip, $port)
	$listener = [System.Net.Sockets.TcpListener]::new(
		[System.Net.IPEndPoint]::new($ip, $port)
	)
	$listener.Start()
	Write-Host 'Listening' -fore cyan

	$client   = $NULL
	$stream   = $NULL
	$reader   = $NULL
	$response = $NULL
	try {
		$client = $listener.AcceptTcpClient()
		$stream = $client.GetStream()
		$response = [System.IO.StreamWriter]::new($stream)
		$response.NewLine = "`n"
		$reader = [System.IO.StreamReader]::new($stream)
		Write-Host 'Connected!' -fore cyan

		if (!$chat) {
			$chat = [Diagnostics.Process]::new()
			$chat.StartInfo `
			| %{
				$_.UseShellExecute        = $False
				$_.RedirectStandardOutput = $True
				$_.FileName               = 'powershell'
				$_.Arguments              = '-Command "&{$line=$NULL;do{$line=Read-Host;$line}while($line);1|sleep}"'
			}
			Register-ObjectEvent `
				-InputObject $chat `
				-EventName   'OutputDataReceived' `
				-MessageData $queue `
				-Action      {
					$Event.MessageData.Enqueue($EventArgs.Data)
				} `
			| Out-Null
			$chat.Start() | Out-Null
			$chat.BeginOutputReadLine()
		}

		$line = $NULL
		do {
			while ($queue.Count) {
				$line = $queue.Dequeue()
				$response.WriteLine($line)
				$response.Flush()
			}
			while ($stream.DataAvailable) {
				$line = $reader.ReadLine()
				if ($line) {
					Write-Host $line -fore green
				}
				else {
					$chat.Kill()
				}
			}
			sleep -Milliseconds 500
		} while (!$chat.HasExited)
	}
	finally {
		if (!$chat.HasExited) {
			$chat.Kill()
		}
		$reader.Close()
		$response.Close()
		$client.Close()
		$listener.Stop()
	}
} -ip ([System.Net.IPAddress]::Any) -port 30120

bash <(echo 'exec 3<>/dev/tcp/IP/PORT; cat <&3 & while read line; do echo "$line" >&3; done')

is a good client alternative for linux if you dont have nc

bash <(echo 'exec 3<>/dev/tcp/IP/PORT; cat <&3 & echo "$$ $!"; line="Type and hit enter to send a message to the client, enter no message to terminate"; while : ; do echo "$line" >&3; if [ -z "$line" ]; then break; fi; read line; done; kill $!') | bash <(echo 'echo -e "\e[01;36mConnecting\e[0m"; read pid1 pid2; echo -e "\e[01;36mConnected!\e[0m"; while read line; do if [ -z "$line" ]; then kill $pid1 $pid2; fi; echo -e "\e[01;32m$line\e[0m"; done')

emulates 3_client very closely

---

awk 'BEGIN { print "Listening"; start=1; line="-"; while (length(line)) { ARGV[1] |& getline line; if (start) { start=0; print "Connected!"; print line; print "Enter - to await next message" } else print "\x1B[A"line; while (length(line)) { getline line <"-"; if (line == "-") break; print line |& ARGV[1] } } }' '/inet/tcp/PORT/0/0'

is an okay server