If your firewall uses network address translation to tranlate your local ip to a internet global ip you will have to go into the tools-options menu, click on firewalls, fill in force local ip with the global ip address provided by your isp. Make sure your router/firewall is port forwarding 6346 to your local ip. Example 10.0.0.1. This should open up a hole for other users to download files from you. If your isp uses DHCP, you can go to grc.com, run shields-up and it will tell you your ip address to force.