Simple iptable gateway script

It’s the second time I must setup a Linux gateway connected to a DSL line. The DSL modem interface is ppp0 and the LAN interface is eth0. Here is the script I use to setup the iptables :

echo "1" > /proc/sys/net/ipv4/ip_forward

modprobe ip_conntrack_ftp

export EXT=ppp0

/sbin/iptables -F
/sbin/iptables -t nat -F
/sbin/iptables -t mangle -F
/sbin/iptables -X

/sbin/iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
/sbin/iptables -A INPUT -m state --state NEW -i ! $EXT -j ACCEPT
/sbin/iptables -P INPUT DROP

/sbin/iptables -A FORWARD -i $EXT -o eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT
/sbin/iptables -A FORWARD -i eth0 -o $EXT -j ACCEPT

/sbin/iptables -t nat -A POSTROUTING -o $EXT -j MASQUERADE

/sbin/iptables -A FORWARD -i $EXT -o $EXT -j REJECT