Question

I’m trying to program a (simple, for starters) server-client thingy, just to establish a connection and see if it works. And it does. As long as I stay inside my own four walls/network. As soon as I try to go via my routers IP the client produces a mighty fine error message. All the usual suspects have been eliminated: Router Port forwarding is on, the firewall doesn’t interfere (well, it still doesn’t work when I turn it off), and canyouseeme.org says that it can establish a connection to my chosen port when the server runs.

Here is the source code for the server, since I figured out it was possible to just go via the command line with a little telnetting.
When I try to establish a connection, it just says Could not open connection to the host, on port 49163:Connection failed

Server:

import java.net.*;
import java.io.*;

public class ChatServer {
    public static void main(String[] args) throws IOException {

        ServerSocket server = null;

        try {
            System.setProperty("java.net.preferIPv4Stack" , "true");
            server = new ServerSocket(49163);
        } catch (IOException e) {
            System.err.println("Could not listen on port: 49163.");
            System.exit(1);
        }

        Socket client = null;
        try {
            client = server.accept();
        } catch (IOException e) {
            System.err.println("Accept failed.");
            System.exit(1);
        }

        PrintWriter out = new PrintWriter(client.getOutputStream(), true);
        BufferedReader in = new BufferedReader(newInputStreamReader(client.getInputStream()));
        String inputLine;
        String outputLine;

        out.println("Connection established");
        while ((inputLine = in.readLine()) != null) {
            if (inputLine.equals("exit")) {
                break;
            }
        outputLine = inputLine;
        out.println(outputLine);
        }
        out.close();
        in.close();
        client.close();
        server.close();
        System.out.println("Server offline");
    }
}

Oh yeah, preferIP4vStack was something I picked up on Stackoverflow, but it doesn’t seem to work for me.

For some reason I’m not able to inlcude the code for the client, I keep getting messages about formatting, and I just can’t figure it out. But the way I see it is that I’m not even able to connect via the command line (when I try to connect to the “real” IP), so the client doesn’t have to get involved. But for you who want to see the error anyway:

java.net.ConnectException: Connection refused: connect
  at java.net.PlainSocketImpl.socketConnect(Native Method)
  at java.net.PlainSocketImpl.doConnect(Unknown Source)
  at java.net.PlainSocketImpl.connectToAddress(Unknown Source)
  at java.net.PlainSocketImpl.connect(Unknown Source)
  at java.net.SocksSocketImpl.connect(Unknown Source)
  at java.net.Socket.connect(Unknown Source)
  at java.net.Socket.connect(Unknown Source)
  at java.net.Socket.<init>(Unknown Source)
  at java.net.Socket.<init>(Unknown Source)
  at ChatClient.main(ChatClient.java:12)

Answer 1

I don’t know if I’m suposed to laugh or cry now.
A friend told me that MAYBE, maybe the problem might be that I try to log in with the external IP from a network-intern PC, which for some mysterious reason can’t get out or can’t get back in.
Got someone to try and login from somewhere else, and voila! Works like a charm.