JFirewallTest is a free Java webstart application that tests for holes or open ports in your firewall. Unlike other solutions, JFirewallTest uses a two stage testing procedure that tests all 65,536 ports very rapidly.
After testing is complete, JFirewallTest will present a page of results reporting exactly what ports are open and accessible to others on the Internet. The list includes information about common services associated with each port and an estimate of the vulnerability. JFirewallTest can be launched directly from this web site and will run on Windows, Linux and Mac computers.
JFirewallTest proves that testing all network ports does not need to take hours but can be done in minutes! Using a simple two phase approach, JFirewallTest completes a full TCP port scan in under 10 minutes.
The first stage creates a list of ports that are listening for connections locally. JFirewallTest performs this action by making dummy connections to all ports on your local machine. To speed up operation JFirewallTest uses multiple threads and is therefore not slowed down by pending responses. The list of open ports is sent to a WikiWebServer for the second stage. The second stage tests each open port to see if it is accessible from the Internet. The results are displayed live to the user.