Question

In C# to use a TcpClient or generally to connect to a socket how can I first check if a certain port is free on my machine?

more info: This is the code I use:

TcpClient c; //I want to check here if port is free. c = new TcpClient(ip, port); 

Answer 1

Since you’re using a TcpClient, that means you’re checking open TCP ports. There are lots of good objects available in the System.Net.NetworkInformation namespace.

Use the IPGlobalProperties object to get to an array of TcpConnectionInformation objects, which you can then interrogate about endpoint IP and port.

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 int port = 456; //<--- This is your value  bool isAvailable = true;   // Evaluate current system tcp connections. This is the same information provided  // by the netstat command line application, just in .Net strongly-typed object  // form.  We will look through the list, and if our port we would like to use  // in our TcpClient is occupied, we will set isAvailable to false.  IPGlobalProperties ipGlobalProperties = IPGlobalProperties.GetIPGlobalProperties();  TcpConnectionInformation[] tcpConnInfoArray = ipGlobalProperties.GetActiveTcpConnections();   foreach (TcpConnectionInformation tcpi in tcpConnInfoArray)  {    if (tcpi.LocalEndPoint.Port==port)    {      isAvailable = false;      break;    }  }   // At this point, if isAvailable is true, we can proceed accordingly.