Traffic Accounting based on iptables

Dear all, I am thinking about different options to do a traffic accounting for each ip adress in my network consisting of green, blue and orange.

The next try shall be a traffic accounting based on iptables.

That is what I want to try: iptables -N INET_OUT iptables -N INET_IN iptables -I FORWARD -j INET_IN iptables -I FORWARD -j INET_OUT

iptables -I INET_OUT -s "$ip" iptables -I INET_IN -d "$ip"

My question is, what is the correct "Forward" chain which directs the whole (external) traffic to device red0?

Best regards Ben