You need to allow related and established packets back. There is a generic rule there already but your DROP rules are being inserted before it so the packets get dropped. You cant really use the default rules either as these allow traffic between all the LAN's. You also need to think of the order the rules are being applied. As you have used -I on its own for each rule they are added one by one to the top of your rules so the drop rules end up above the allow rules. Try something like:
| Code: |
iptables -I FORWARD -i eth2 -o eth1 -j DROP
iptables -I FORWARD -i eth3 -o eth2 -j DROP
iptables -I FORWARD -i eth3 -o eth1 -j DROP
iptables -I FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -I FORWARD -i eth1 -o eth2 -j ALLOW
iptables -I FORWARD -i eth1 -o eth3 -j ALLOW
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