Trying to setup the Linksys gear to be back the BBOX3 with all kind of ethernet settings but seems not to accept nor DHCP, no dhcp, static ip, etc

My goal would be to set up a BBOX network in the range of 192.168.1.x and get the WRT1200AC to be connected through a static route to the BBOX3 as gateway and teh WRT would be a DHCP server in the 192.168.1.2xx range.

Any idea ? Does anyone use the WRT1200AC ?