More useful examples


iptables -A INPUT -i $EXTERNAL_ETH -p icmp --icmp-type 8 -j DROP


iptables -A INPUT -i $EXTERNAL_ETH -p tcp --dport 25 -j DROP


iptables -A INPUT -i $EXTERNAL_ETH -p tcp --dport ! smtp -j DROP


iptables -D INPUT -i $EXTERNAL_ETH -p tcp --dport 25 -j DROP


iptables -A INPUT -s 192.168.1.1 -p tcp --syn -j DROP


iptables -A INPUT -m mac --mac-source ! 00:E0:63:82:4C:71 -j DROP