multi-NAT functionality comes into play
Some routers allow you to type in port ranges instead of individual ports. This can be important for getting some applications like ICQ to work. ICQ needs about 10 contiguous ports forwarded. It is much easier to specify a range than each one. Occasionally 100 or more ports need to be opened and 'ranges' become the only real option.
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For ICQ to successfully work behind a firewall the following system configurations must be set by the System Administrator for the systems network.
Client to server Communication:
* This is done via port 5190 TCP to login.icq.com (please note- allow a bi-directional connection to the port for login.icq.com and not any specific IP address, since it stands for more than one IP address).
Client to client communication:
* Client to client connection is done using the TCP protocol, using port range 1024-65535. This means that the client needs an open listening port within the mentioned range-- 1024-65535.
http://www.icq.com/icqtour/firewall/netadmin.html
1. Open the ICQ Menu and select Preferences.
2. Select the Connection feature.
3. Click on the User tab.
4. By default the Use sever proxy settings (recommended) is set.
Not Using a Proxy
1. Click on the radio button Not using a proxy. Incoming ports are needed only for communication with users that are behind a firewall.
2. Use dynamically allocated port numbers (default).
3. Clicks on radio button Use the following TCP listen port for incoming event. Insert the port numbers From to To for the port to set your port range.
The ICQ Video feature is designed to automatically work with most domestic firewalls and routers without any configuration, since most of them allow outgoing UDP packets by default.
However, some firewalls, especially corporate firewalls, are configured to block all outgoing UDP traffic. For the ICQ Video feature to work with such firewalls, they need to be configured to allow outgoing UDP packets from a specific port range; starting from 5190 and up. Chances are that they will find available UDP ports in the 5190-5200 range, therefore it is recommended to enable outgoing UDP packets in this range. The wider the port range, the greater the chance that the ICQ Video feature will work behind the firewall.
Note that port-forwarding (static port mapping) is not generally required. However, some types of personal routers may require setting of static mapping of these local ports.
Milos