Re: rmi application thru NAT

Tom Forsmo <>
Tue, 31 Oct 2006 01:19:22 +0100
first off, I don't think you can not bind to an ip+port that is not on
the local machine, at least I think so. Because it would undermine any
local control of the machine/device.

In any case, correct me if I am wrong here, but it seems to me that you
have misunderstood how NAT works. You are trying to bind an rmi server
to the NATed networks public ip address? the problem is that the port is
not open because you have to open it by opening a socket connection to
an external server, only by doing this will the NAT device open an
external port with which the remote server will try to respond through.

So in essence you can not forcibly open an external port on a NAT device
by just binding to it, you have to first open a connection/port from the
client, then you can try to use it. But that leaves you with one
problem, you have to figure out what port the NAT will be using, which
is an algorithmic problem that has not yet been solved.

So your solution is to get a range of static ip addresses to use on the
devices instead of having a NATed network.


polaris wrote:

I have rmi application which is running correctly
inside LAN where im starting the server using lan
address: like the following:

RemoteInterface remoteReference = (RemoteInterface)
UnicastRemoteObject.exportObject(new Server());
System.getProperties().put("java.rmi.server.hostname", "");

with this command: java -Djava.rmi.server.hostname= remoteSever

but when it try to rebind using public IP (I get it from some web
sites) instead I get this error:

Exception in thread "main" java.lang.RuntimeException:
java.rmi.ConnectException: Connection refused to host:
***.***.***.***; nested exception is:
Connection timed out: connect

Is the problem from NAT setting where i need to
redirect the incomming traffic and how can i do that?

also i tried to bind server with 1099 port in the following code:

UnicastRemoteObject.exportObject(new Server(),1099);

but i get "Port already in use: 1099" error where i started
rmiregistry with this port.

i need to know the right way to bind remote server with specific
port (shoudl i use another port for rmiregistry e.g. 1500)
and what port i should use in client lookup: Server bind port or
rmiregistry started port?


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