No connection could be made because the target machine actively refused it - using Socket or TcpClient

Question

Many people have this same problem, but everyone's implementation is different.

I need help with my implementation of it.

void sendUsingTcp() 
{
    try 
    {
        Socket sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        IPEndPoint endPoint = new IPEndPoint(IPAddress.Parse(172.16.8.200), 8000);
        sock.Connect(endPoint);
        // code past this never hits because the line above fails
    } 
    catch (SocketException err) 
    {
        MessageBox.Show(err.Message);
    }
}

I have also tried the TCP Client directly with the same error results:

void sendUsingTcp() 
{
    try 
    {
        using (TcpClient client = new TcpClient()) 
        {
            IPEndPoint endPoint = new IPEndPoint(IPAddress.Parse(172.16.8.200), 8000);
            client.Connect(endPoint);
            // code past this never hits because the line above fails
        }
    } 
    catch (SocketException err) 
    {
        MessageBox.Show(err.Message);
    }
}

The IP Address of my PC is 172.16.11.144.

Solution 1

i) it's quite possible that port 8000 is used for something else. Pick another (large) number and see whether the same thing occurs ii) use the loopback address to connect to your own machine - IPAddress.Loopback

Solution 2

For me it turned out, my Server was listening for incoming connections only from the same IP. I had to change the code for it to listen from any IP.

Before and Wrong:

IPEndPoint endPoint = new IPEndPoint(IPAddress.Parse(172.16.8.200), 8000);

After with problem fixed:

IPEndPoint endPoint = new IPEndPoint(IPAddress.Any, 8000);

Solution 3

Have you checked to make sure port 8000 is open on the remote machine? If so, it could be a firewall issue or even something with the network. More details about what's running on the remote machine would help.

Solution 4

Not sure if this was ever answered properly BUT you cannot use a TCPClient to set up a listener - you need a TCPListener class - https://docs.microsoft.com/en-us/dotnet/api/system.net.sockets.tcplistener?redirectedfrom=MSDN&view=netframework-4.7.2

Otherwise, you just get an exception when the TCP handshake fails.

Solution 5

Commonly the problem is that the port is closed. Nothing is listening on the other side.

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