2 Ethernet cards, 2 networks

Hi All,
Would it be easy and possible to run 2 ethernet networks with a device with 2 ethernet interfaces?
I want to be able to connect one ethernet card to the internet and make a second internal network for TCP modbus slaves on the other interface.

Have you read this topic (Bridged network configuration), which whilst not an exact match, does tackle the issue of having more than one network (in their case for a proxy server, but I’d imagine an public / private without through traffic might be easier)