Originariamente inviato da pilovis
Esempio:

echo "1" > /proc/sys/net/ipv4/ip_forward
modprobe ip_tables
modprobe ip_conntrack
modprobe iptable_nat
modprobe ipt_MASQUERADE
iptables -t nat -A POSTROUTING -d ! 192.168.1.0/24 -j MASQUERADE
iptables -A FORWARD -s 192.168.1.0/24 -j ACCEPT
iptables -A FORWARD -d 192.168.1.0/24 -j ACCEPT
iptables -A FORWARD -j DROP
iptables -t nat -A PREROUTING -d xxx.xxx.xxx.xxx -p tcp --dport 3389 -j
DNAT --to-destination 192.168.0.1:3389
Questo sopra se hai due schede di rete.

Nel tuo caso se hai un modem ADSL metti

iptables -t nat -A PREROUTING -i ppp0 -p tcp --dport 6699 -j DNAT --to-destination 192.168.0.3:6699