Assing Extern IP via MASTER/Slave port

Hello everyone!
I need to make the following configuration:
Eth1 = Wan link
Eth2 = Lan Link
Eth5 = DMZ
In DMZ I need to pass the external IP directly to the computers connected to this port. It works by enabling the master port option for Eth1 and thus configuring the direct IP. Problem is that I can not create firewall rules that reach the connections to the devices connected through the Eth5 port.
What i need to do?
Thx!