[CentOS] Multiple NICs, different IP Networks and routing centos 8

Hi all

Recently I installed a new server with a network setup I never had or needed till now.

The server has three interfaces, which all should have their own IP from different networks. Two interfaces are „user faced“ one is so to say „backend faced“.

The backend faced just needs to find hosts in the same subnet.

The two user faced networks should be accessible from different other (client) networks and the traffic should also go outband from the same interface it came in.

Till now I was not able to figure that out, how do I configure such a setup in centos?

Thanks for hints and suggestions and best regards . Götz