Installation

Hello, I am new to monowall and was hoping if someone could help me. I am trying to utilize monowall within my network containing 5 vlans and I have a Cisco router providing dhcp and vlan routing to each of these vlans (Cisco's term - router on a stick). Where would I place the monowall in such a scenario? The Cisco router is also my path to Internet via my serial port.

Any help is greatly appreciated.