I am getting an exception when my tcp client connects to the server with ip address but works with "localhost"

Question

I am writing a simple C# tcp client and server program. The server will eventually be on a different machine but now I am just testing on the same machine. I am getting an exception error "Only one usage of each socket address (protocol/network address/port) is normally permitted" when I create my TcpClient using the ip address. But it works if I use "localhost" instead of ip address. I get the ip address from ipconfig. I also try having the server running on a different machine and my TcpClient gets the same exception when I specify the remote machine's ip address. How do I make the connection using ip address? thanks.

Below is the code where I create the TcpClient

            IPAddress ipaddr = IPAddress.Parse("192.168.128.100");
            int port = 3000;


            int tries = 0;
            client = null;
            while (tries < 6) // try for 3 seconds
            {
                try
                {
                    tries++;
                    IPEndPoint ipEndpt = new IPEndPoint(ipaddr, port);
                    client = new TcpClient(ipEndpt);
                }
                catch (Exception ex)
                {
                    client = null;
                    Thread.Sleep(500);
                }
            }

Answer 1

when you create tcp client, are you defining a port? if so, you should not. instead, you will connect to the port of the server.

Answer 2

There is probably another service listening on the interface on that port.

You should try

netstat -oan

and search for port 3000. If you found a line in the result the last file is the pid of the process which you can also find in the taskmanager.

TCP    192.168.128.100:3000         0.0.0.0:0              LISTEN         4711

4711 = PID