Connection refused to host: connection timed out

Question

I have been struggling with this problem a couple of days now so I really hope someone can help me. I am trying to get rmi to work in a NAT environment. We use a firewall, so I have opened port 1099 and 2020 which I use as a fixed port for communication (just to be sure it is not a firewall thing); I use the following code:
//server
public class ComputeEngine extends UnicastRemoteObject
implements Compute
public ComputeEngine() throws RemoteException {
super();
public String getMessage() {
return "you have successfully connected to the server";
public static void main(String[] args) {
if (System.getSecurityManager() == null) {
System.setSecurityManager(new RMISecurityManager());
try {
String port = args[0];
try {
RMISocketFactory.setSocketFactory(new FixedPortRMISocketFactory(Integer.parseInt(port)));
} catch (IOException e) {
e.printStackTrace();
LocateRegistry.createRegistry( 1099 );
catch (RemoteException e1) {
e1.printStackTrace();
String name = "rmi://localhost/Compute";
try {
Compute engine = new ComputeEngine();
Naming.rebind(name, engine);
System.out.println("ComputeEngine bound");
while(true); //stay alive
} catch (Exception e) {
System.err.println("ComputeEngine exception: " + e.getMessage());
e.printStackTrace();
public Socket createSocket(String host, int port)
throws IOException {
System.out.println("creating socket to host : " + host + " on port " + port);
return new Socket(host, port);
* Create a server socket on the specified port (port 0 indicates
* an anonymous port) and writes out some debugging info
* @param port the port number
* @return the server socket on the specified port
* @exception IOException if an I/O error occurs during server socket
* creation
* @since JDK1.1
public ServerSocket createServerSocket(int port)
throws IOException {
port = (port == 0 ? portnumber : port);
System.out.println("creating ServerSocket on port " + port);
return new ServerSocket(port);
//client
public class ComputePi {
public static void main(String args[]) {
if (System.getSecurityManager() == null) {
System.setSecurityManager(new RMISecurityManager());
try {
String name = "rmi://" + args[0] + "/Compute";
Compute comp = (Compute) Naming.lookup(name);
System.out.println("connected to server");
System.out.println(comp.getMessage());
} catch (Exception e) {
System.err.println("ComputePi exception: " + e.getMessage());
e.printStackTrace();
I start the client with:
java -Djava.security.policy=policy.all -jar client.jar 194.2.4.6:1099
I start the server with:
java -Djava.rmi.server.codebase="file:/C:\RMI\\server.jar" -Djava.rmi.server.hostname="194.2.4.6" -Djava.security.policy=policy.all -jar server.jar 2020
As you can see I set the "-Djava.rmi.server.hostname" property which should be a solution to the NAT problem. However I keep getting the following exception!!??!!:
ComputePi exception: Connection refused to host: 194.2.4.6; nested exception is:
     java.net.ConnectException: Connection timed out: connect
java.rmi.ConnectException: Connection refused to host: 194.2.4.6; nested exception is:
     java.net.ConnectException: Connection timed out: connect
     at sun.rmi.transport.tcp.TCPEndpoint.newSocket(Unknown Source)
     at sun.rmi.transport.tcp.TCPChannel.createConnection(Unknown Source)
     at sun.rmi.transport.tcp.TCPChannel.newConnection(Unknown Source)
     at sun.rmi.server.UnicastRef.newCall(Unknown Source)
     at sun.rmi.registry.RegistryImpl_Stub.lookup(Unknown Source)
     at java.rmi.Naming.lookup(Unknown Source)
     at client.ComputePi.main(ComputePi.java:14)
Caused by: java.net.ConnectException: Connection timed out: 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.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 sun.rmi.transport.proxy.RMIDirectSocketFactory.createSocket(Unknown Source)
     at sun.rmi.transport.proxy.RMIMasterSocketFactory.createSocket(Unknown Source)
     ... 7 more
Can anyone help me with this, please??????
kind regards,
Christiaan

Answer 1

Yes, i can ping it from the client.
I have also noticed that when i run my server with the option -Djava.rmi.server.hostname=IP the applications stops automatically after a few minuts...
I'm not using nothing about codebase. I have the stub and skel classes in server and client machines..
I add the complete exception:
Client exception: java.rmi.ConnectException: Connection refused to host: external_IP; nested exception is:
java.net.ConnectException: Connection timed out: connect
java.rmi.ConnectException: Connection refused to host: external_IP; nested exception is:
java.net.ConnectException: Connection timed out: connect
at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:567)
at sun.rmi.transport.tcp.TCPChannel.createConnection(TCPChannel.java:185
at sun.rmi.transport.tcp.TCPChannel.newConnection(TCPChannel.java:171)
at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:101)
at example.hello.Server_Stub.sayHello(Unknown Source)
at example.hello.Client.main(Client.java:55)
Caused by: java.net.ConnectException: Connection timed out: connect
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:305)
at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:171)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:158)
at java.net.Socket.connect(Socket.java:426)
at java.net.Socket.connect(Socket.java:376)
at java.net.Socket.<init>(Socket.java:291)
at java.net.Socket.<init>(Socket.java:119)
at sun.rmi.transport.proxy.RMIDirectSocketFactory.createSocket(RMIDirect
SocketFactory.java:22)
at sun.rmi.transport.proxy.RMIMasterSocketFactory.createSocket(RMIMaster
SocketFactory.java:128)
at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:562)
... 5 more