Client-Server Chat application JAVA

Question

I have a simple java written client and server chat application(with sockets). When running on the same network/computer it works fine. However when i try to run the client from a different network it doesn't connect. I tried using the public IP address of the server to connect the client to the server but without luck. How would I be able to connect to the server app from a different network? any help would be appreciated.

Answer 1

It worked after I did port forwarding on router. Most of the ISP provided modem/routers wont let you manipulate ports so had to buy my own modem/router, forwarded the port and worked like a charm. Information on what port forwarding is can be found here : http://www.howtogeek.com/66214/how-to-forward-ports-on-your-router/

Answer 2

It sounds like you have more of a firewall issue than a problem with the application. Instead of trying to connect with the Java client, first try connecting with Telnet to the server from the same computer, then from the other computer. The first effort will show you what to expect when it works. For instance, if your server is running on port 999, use telnet server.example.com 999.

If the machines are Linux boxes, use iptables -L to see whether there is a block on the port you are trying to access.

If you're still having problems reaching the server, run tcpdump -i tcp:999 on the server host to see what traffic is making it to your server socket, then run the telnet commands again. You should see the tcp connection established when connecting from the local machine, maybe or maybe not when connecting from other machines. If you don't see it while connecting from other machines, run tcpdump there too to make sure the client is definitely sending the traffic to the server.

After you are sure that the server can receive traffic and that your client is sending the traffic, there are no mysteries about what is actually going on and you should find your problem.