How config network WAN and LAN in ReadyNas 3130 or 2120 ver. 6.6.1

I have problems with the red configuration, I have a wan network to go to the internet and another lan network to manage the internal network, I want to put a card with the lan network and another network card with the wan, as soon as I do this the ReadyNas Is very slow and stops responding to the active directory service, someone can explain in detail what would be the ideal configuration for this scenario.

thanks.