To enable inbound traffic for a client network follow these steps.
1) On the ATT Modem > Home Network > IP Allocation > Find the mac address of the device and choose Allocate > Select the Public Fixed address from the list to map to the client router’s outside interface. DO NOT enable IP Passthrough under the Firewall
2) On the clients firewall set the outside interface IP to DHCP and reboot.
3) Enable Remote Access to the firewall under Device > Remote Access > Use our default password and router port (User name is tech). Save a shortcut: T:\RDP\Client\@ ATT DSL modem