I'm trying to set up an application server with two NICS

I want ETH1 to only answer and respond to internal network requests eg 192.168.0.1/24

and ETH2 to service requests from the Internet, routed from my firewall

I can only get one or other to work, not both at the same time. It seems to hinge on the gateway settings, if I have a gateway on ETH1, the server does not respond to internet requests, if I have a gateway on ETH2, the server doesn't respond to internal requests.

Can you point me in the right direction?

Thanks