RMI, NAT firewall, and callbacks

Question

Hi,
My problem is similar to many other problems that have been posted over the span of nearly a decade on this forum. However, I'm starting this thread because my search through the forum didn't make me happy, and because I hope that with new versions of Java new things might be possible.
My setting: the server has a public IP, a client is behind a NAT firewall. The client passes a Remote object to the server so that the server can call back the client some time later. This setting is nowadays very common in Internet: clients are run on ubiquitous home routers with NAT, and servers are available on public IP addresses.
One way to solve this problem is to instruct the server to use the TCP connection already established by the client when the server wants to call back the client. This way the NAT firewall will not block the server communication, because it will be part of the connection initiated by the client. So it looks like using a socket factory might be a solution.
Is the solution with socket factories possible?
Thanks,
Irek
Edited by: 893951 on 2011-10-31 04:44
Edited by: 893951 on 2011-10-31 04:52

Answer 1

EJP wrote:
the seconds one fails.Fails how?Well, the server can´t connect to client. That is, i have a server in 193.136.205.20 a a client in 193.136.205.20 (same host). The client connects to server and the server callback the client. I have another client in 193.136.205.128 and it connects do server too, but when the server callback this client, i have the exception "No connection to route host".
Is it because of firewall?Impossible to say until you tell us how it fails.
If i kill the firewall in both server and clients, does it work?I don't know, it's your firewall. Does it?
Or is there any solution, making the client as a server?A callback is a server.Yes, i understood that. I have expressed myself in a bad way. A callback is a server indeed. When i create the client callback object, i export it, creating the object and in the login method (existent in server) i send this object so the server adds it to a hashtable to callback later.
>
It sounds like a strange design. How come the client has the datase?, not the server? and why can't the client just push the database updates to the server? How can the server know when to callback the client to get more updates?Well, i have a local database for each client and a large database in server. I said the clients fetch database just as a example. The real deal is that a client fetches values from devices that measure energy values (electricity, gas, water, temperature, etc...). It fetches all connected devices in 5 minutes interval and saves values in the local database. 3 minutes after that synchronize, the server fetches all connected clients for all values from all proxys (clients). This is done using callback. It´s why i have this design. I thought on pushing values to the server. And it´s an idea that could be implemented. But this is how my company wants this testing project implemented...
However i have managed to correct this error. I have tried with another host 193.136.205.106 and it connected to server and the server could callback it. I then assumed that the host 193.136.205.128 had firewall permission problems. I solved this, creating the server registry in port 1099 and fixed the object port to 2000. Then, everytime i create a client, i fixed the export callback object in port 2004. I have set the permissions in both firewalls (server and clients) to accept connections in por 1099, 2000 and 2004 and it functions all correctly!! =)
Thanks for the help.