I have 3 Raspberry, of which one to use as a firewall with iptables, connected to others via switch.
Internet--> A (firewall) --> (switch) --> B \-> C
I would like all the traffic directed to the other raspberries (B-C) to pass through the firewall A first. Now: I realized that once the traffic reaches the firewall, I can redirect it to others Raspb via NAT iptables. But my doubt is: how to make the traffic, before reaching the raspberries B and C to their IP, pass through the Firewall first? The only solution I found is the one in which only the IP of the firewall appears externally and based on the ports to which it is contacted it is forwarded to the other Raspbs. My other doubt: should B and C be connected to the Internet with their IP, or should only a local IP visible to the Firewall be visible? Sorry for too many questions but I am approaching the world of networks recently.
EDIT: I noticed that all devices connected to my ISP's modem have the same public IP 85.X.X.56 My Switch is Tp Link TL-SG105E and supports both Port Based VLAN and 802.1Q VLAN. I don't know if it supports Trunked VLAN, I don't understand much about networks :(