To support ISP connections with multiple static IP addresses, allow the router configuration to optionally choose which of the WAN's public IP addresses to use for Port Forwarding rule. Currently, only one public IP address is assumed and all Port Forwarding rules assume it as the inbound address. Configuration that have multiple public addresses must resort to using iptables rules in the Administration Scripts to achieve this, which can be very complex and create inadvertent issues.
I hope, it would be possible to replace the "External Port" input text-box on the Port Forwarding rules with an "External Address:Port" . If the address was left empty, it would function the same as today and use the default (or dynamically assigned) IP address. However, if the address was provided in the GUI input then the parser would recognize and associate accordingly it in the iptables command.