Making a TCP connection through a restrictive outbound firewall

Question

I'm using Java to create a client/server application that communicates using TCP. The network that the client is running on has an outbound firewall that prevents the client from connecting to the server. Is there any way/workaround to create a TCP connection through this firewall?

I have tried to use common ports that are open such as port 80, 443, and 113, however the firewall appears to drop the connection once it is made (possibly by detecting non-protocol packets).

An alternative would be to have the client software run as a Java applet hosted from an external website, however I'm not sure if the outbound firewall would still be able to block this connection.

Any help would be greatly appreciated.

Answer 1

You can try to communicate using http or https. By tunneling your protocol over these, it might be possible that the firewall lets your traffic through.

Answer 2

Assuming that the users have internet access, and you can't telnet through port 80/443, it probably mean that the users connect through an HTTP Proxy configured in the browser. You could try to research on various tunneling methods via an HTTP Proxy... Though, that will be a very unstable hack.

I recommend contacting the system administrator, explaining your needs, and see what he/she suggests.