The client might be able to connect to port 3380, while a connection from the server to the client might be forbidden. In other words the firewall might (and they usually do) implement a different ruleset for outgoing connections and incoming ones. Therefore I wager there is no way you can achieve what you want, short of asking the client to connect (or triggering that with a Java applet) and seeing if it comes through.

In reply to Re: Testing for a firewall by echo
in thread Testing for a firewall by akm2

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