I had the same confusion, but the below worked for me. This is for using Keexybox as primary entry point for all devices (DNS/DHCP/Gateway).
1) set Input network to different subnet then your primary router.
ex. Router IP is 192.168.1.1
interface eth0 (for both input and output)
input to 192.168.2.254
output to 192.168.1.254
1) set Input network to different subnet then your primary router.
ex. Router IP is 192.168.1.1
interface eth0 (for both input and output)
input to 192.168.2.254
output to 192.168.1.254