I have an old pix515e with inside interface 192.168.1.230 / 255.255.255.0, DMZ interface 10.10.20.1 / 255.255.255.248 and outside interface.
Behind this pix there is a 1921 router with interface 0/0: 10.10.20.2 / 255.255.255.248, interface 0/1: 192.1...