DMZ

I’m trying to set up a DMZ. I put 3 NICS in my firewall (Raptor 6.5) box and configure them with different subnets. The outside NIC has a gateway defined. The inside and DMZ NIC do not. I ‘m having trouble pinging…I can only ping with success with the proper address in the arp table. When that entry expires I get a request timed out. Do I need to have gateways defined for my other NIC cards or perhaps just one NIC card. If so.. then what should the gateway be? Confused.. Can anyone help?

Thank you

-Dave