Firewall Configuration and Troubleshooting*  
If you have a firewall, be sure that it is set up to allow for outgoing connections on ports 3724, 6112, and 6881-6999 for the TCP (also called TCP/IP) protocol. More information on how to open ports for some popular firewalls can be found on our Blizzard Downloader Networking Help page under the Firewalls section. If your firewall is not listed there or you need more help, please refer to your firewall documentation or contact the manufacturer.  
Important note: Please be aware that many popular firewalls will become very restrictive to traffic when 'disabled', including shutting down all traffic on some ports. Please be sure any firewalls you have installed are enabled and configured correctly in order to use the downloader effectively.