Communication Error with Host and Remote Object

Question

Hi,
I was executing my RMI program in a Linux Grid Network environment and the communication was no problem and the code did work.
However I have switched to the same code to another network with linux machines and when try to execute the code I get the Error:
java.rmi.ConnectIOException: Exception creating connection to: 136.186.14.96; nested exception is: java.net.NoRouteToHostException: No route to host
136.186.14.96 is the place where the registry is running and Server Object is bound
Client Locate the Registry as below
LocateRegistry.getRegistry("136.186.14.96",1099);
ACTUAL CODE:
+//Pass The Remote Reference+
+try {+
oClient.registry = LocateRegistry.getRegistry(oClient.o_RegistryReference,oClient.i_Port);
oClient.server = (ART_Interface) oClient.registry.lookup("Server_Obj");
oClient.server.clientRegister(oClient.i_ClientID, oClient);
System.out.println("SEQUENCE <1>  Client [" iID + "] Request to Register");+
+} catch (Exception e) {+
System.out.println("Client [" oClient.i_ClientID + "]Registration Error: " + e);+
+}+
Client Code Execution....
+#ART_CLIENT <HOST> <PORT> <Client ID> <slavesPerClient>+
java -cp /home/research/mbcooray/network/mercury/GRID/ -Djava.rmi.server.codebase=file:/home/research/mbcooray/network/mercury/GRID/ -Djava.security.policy=/home/research/mbcooray/network/mercury/GRID/Policy.txt ART_Client 136.186.14.96 1099 0 1 &

Answer 1

No for multiple instances of clients communicating (Reporting) to Server, wouldn't server have a dedicated port for them?No. A remote object is exported on port X, the client forms an inbound (from the server's point of view) connection to it, an accepted-socket is created, also on X. netstat -an will show you that: X LISTENING and zero or more X ESTABLISHED. A TCP connection consists of the tuple {TCP, client-address, client-port, server-address, server-port}. Here 'server-port' is X, 'client-port' is allocated by the system. So there can exist multiple inbound connections to X, and the server-port number is always X.
For Call backs I guess JVM gets hold of a random free portFor all outbound connections, TCP gets hold of a random free port.
as it is running on a separate thread (I assume)Threads have nothing to do with it.
Is this done by using socketfactory? Forget it. You don't want to do this, for the reasons I have. You probably don't need to do it, and if you do need to do it you should shoot the netadmin instead.
Yes, the server exports the object and binds it in the local registryThat's not the same thing as exporting it on port 1099. You can specify a port number when exporting, or when calling super() if your remote objects extend UnicastRemoteObject. If you are using LocateRegistry.createRegistry(), port 1099 will get reused automatically for all subsequently-exported remote objects unless you are using a socket factory, which you aren't. If you are using a separate Registry you should specify the export port number yourself, and you can't re-use 1099.
The background to this is that firewalls often contain rule configurations about what remote port numbers may be connected to, which corresponds to the reality that Internet services have fixed port numbers, so you can decide e.g. to allow your users to connect to HTTP servers (80,443,8080,8443) and SSH (22) but not for example Telnet (23). However by symmetry they often also allow similar rules for outbound port numbers, which are completely useless as they do not correspond to any reality whatsoever. If you have a netadmin who is enforcing outbound port number rules, just tell him to stop it.