$IPT -t filter -A INPUT -m state --state INVALID -j DROP
$IPT -t filter -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-$IPT -t filter -A INPUT -p icmp -j ACCEPT
+$IPT -t filter -A INPUT -p icmp -j ACCEPT
+$IPT -t filter -A INPUT -p 47 -j ACCEPT # allow GRE
$IPT -t filter -A INPUT -i $WAN -p tcp -j REJECT --reject-with tcp-reset
$IPT -t filter -A INPUT -i $WAN -j REJECT --reject-with icmp-port-unreachable
$IPT -t filter -A FORWARD -m state --state INVALID -j DROP