Modem not passing port 515
I have a SMC modem. I have port forwards set up for RDP to certain computers on the network. I also have a zyxel firewall that has been setup for the RDP as well. Currently the RDP works correctly, but I'm trying to port forward port 515 for remote printing. I have matched the settings on both the modem and the firewall to the working RDP settings but the modem appears (per the logs on the firewall) not to be passing the info. I am wondering if setting the modem to true bridge mode would help. I have reached the extent of my knowledge on what to do. Any help would be appreciated.