Why is my tcp client unable to connect to my server

Question

I am having trouble with my c# tcp code. When I run the server and the client on the same computer, it will connect just fine. But when I run the client on a different PC or on a phone, I get: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.

Here is the server code:

        private static void CreateServer()
        {
            TcpListener server = null;
            try
            {

                Int32 port = 13000;
                IPAddress localAddr = IPAddress.Parse("127.0.0.1");


                server = new TcpListener(localAddr, port);

                server.Start();


                Byte[] bytes = new Byte[256];
                String data = null;

                while (true)
                {
                    Console.Write("Waiting for a connection... ");
                    /*
                    IPHostEntry ipHostInfo = Dns.GetHostEntry(Dns.GetHostName());
                    var ipAddress = ipHostInfo.AddressList;
                    Console.WriteLine(ipHostInfo.HostName);
                    Console.WriteLine(ipAddress[0]);
                    */


                    TcpClient client = server.AcceptTcpClient();
                    Console.WriteLine("Connected!");

                    data = null;


                    NetworkStream stream = client.GetStream();

                    int i;


                    try
                    {
                        while ((i = stream.Read(bytes, 0, bytes.Length)) != 0)
                        {

                            data = System.Text.Encoding.ASCII.GetString(bytes, 0, i);
                            Console.WriteLine("Received: {0}", data);


                            data = data.ToUpper();

                            byte[] msg = System.Text.Encoding.ASCII.GetBytes(data);


                            stream.Write(msg, 0, msg.Length);

                        }
                    }
                    catch(IOException e)
                    {
                        //Console.WriteLine(e);
                        Console.WriteLine("Restarting Server");
                        //client.Close();
                        //CreateServer();
                    }

                    // Shutdown and end connection
                    client.Close();
                }
            }
            catch (SocketException e)
            {
                //Console.WriteLine("SocketException: {0}", e);
            }
            finally
            {
                // Stop listening for new clients.
                server.Stop();
            }

            Console.WriteLine("\nHit enter to continue...");
            Console.Read();
        }

I removed most of the comments. But that is the basic example for a tcp server from the documentation.

the client connect code is very simple:

            tcpClient = new TcpClient();
            tcpClient.Connect("192.168.0.7", 13000);

with the declaration for tcpClient saved in a less local spot for retaining and quickly reconnecting.

What I have tried: I have made sure the IP address is correct, I even port forwarded and used my external IP, but got the same issue. I made sure the firewall is not blocking the app on either device. I tried using either device as the server.

I've looked up the problem and the only other person to have this issue needed to make sure he put in the correct IP and fix his firewall settings. I'm probably missing something super obvious.

One final piece of information, one device is wired to the router, I don't know if that is messing with anything.

One other thing, I tried:

tcpClient.Connect(new IPEndPoint(IPAddress.Parse("192.168.0.7"), 13000));

as well.

Answer 1

Whelp I was right. It was something very obvious and honestly dumb on my part.

on the server side:

IPAddress localAddr = IPAddress.Parse("127.0.0.1");

does not result in the server listening on its ipv4, instead it listens on an ipv6 so what you want: Remove the localAddr declaration, as it is not important, and instead of calling:

server = new TcpListener(localAddr, port);

call:

server = new TcpListener(IPAddress.Any, port);

IPAddress.Any is used to listen across all of the network interfaces the device has.