Java networking server-client error

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

Could not open connection to the host, on port 49163:Connection failed

No it didn't. Thats not a Java message. Your code said that, when you caught a ConnectException that had a much more detailed message of its own. Print that and you might have some hope of finding what went wrong. Making up your own messages and suppressing what the exception tells you is rarely if ever a good idea.

The message will probably be one of:

• 'connection refused', which means you got the target host or port wrong, or there is a firewall
• 'connection timed out', which is a network connectivity problem
• 'no route to host', which is an IP routing problem
• 'unknown host', which again means you got the server name wrong.

Answer 2

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.