... # Default rules $IPTABLES --append INPUT --protocol tcp --match state --state ESTABLISHED,RELATED --jump ACCEPT $IPTABLES --append INPUT --protocol udp --match state --state ESTABLISHED,RELATED --jump ACCEPT $IPTABLES --append INPUT --protocol icmp --match state --state ESTABLISHED,RELATED --jump ACCEPT ...
I tried to tune iptables config, so I have such lines to allow only ESTABLISHED connections in input chain: