iptables -P FORWARD ACCEPT
iptables -P INPUT ACCEPT
iptables -P OUTPUT ACCEPT
iptables -t nat -P PREROUTING ACCEPT
iptables -t nat -P POSTROUTING ACCEPT
iptables -t nat -P OUTPUT ACCEPT

# Creation des chaines personnalisees
iptables -N lan-wan
iptables -N lan-fw
iptables -N wan-fw
iptables -N wan-lan

# Redirection vers les chaines
iptables -A INPUT -i lo -j ACCEPT
iptables -A INPUT -i $wan -j wan-fw
iptables -A INPUT -i $lan -j lan-fw
iptables -A FORWARD -i $lan -o $wan -j lan-wan
iptables -A FORWARD -i $wan -o $lan -j wan-lan

iptables -A wan-lan -p tcp --dport 21 -j ACCEPT
iptables -A wan-lan -p tcp --dport 20 -j ACCEPT
iptables -A wan-lan -m state --state ESTABLISHED,RELATED -j ACCEPT

iptables -t nat -A PREROUTING -d 1.2.3.4 -p tcp --dport 21 -j DNAT --to-destination 10.0.1.3:21
iptables -t nat -A PREROUTING -d 1.2.3.4 -p tcp --dport 20 -j DNAT --to-destination 10.0.1.3:20