I have a new question about iptables.

I have a router/internet gateway that has several different networks connected to it. There is, and The network has a branch router of that is connected to a network. I would like to block access of the network to the network. What type of iptables command would I use on my gateway/router to do this?

Something like this:

iptables -A INPUT -s -i eth2 -p all -d -j DROP