Glad to hear your IPCOP's up and running, Lindows. I don't actually think IPCOP has got an IP Forwarding option. You may be referring to the "Port Forwarding" Option under the "Firewall" Menu. This screen allows you to redirect any packets which hit your firewall's external interface to selected machines within your network. The basis of selection is by TCP or UDP port. For example, if you have a web server behind your firewall, you would redirect port 80 to the IP address of the internal web server.
IPCOP also allows you to handle more than one IP address on your external interface using the "Aliases" option under the "Network" Menu. Once these have been set up, you can also forward specific ports using the "Port Forwarding" Option.
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