1 ETH0 192.168.1.0/24 – GW 192.168.1.1
2 ETH1 192.168.2.0/24 – GW 192.168.2.1
On dhcp server side create 2 subnet with for each Zeroshell adress as GW and a range of IP that can be distributed.
If you don’t change firewall rules (by default permit), it will forward IP from one network to the other.
It’s just ipforward activated on linux.