io usavo questo script, provalo un po'

codice:
#! /bin/bash
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 ! 192.168.0.1/24 -j MASQUERADE
iptables -A FORWARD -s 192.168.0.1/24 -j ACCEPT
iptables -A FORWARD -d 192.168.0.1/24 -j ACCEPT
iptables -A FORWARD -j DROP
Se non funziona rimaneggialo in base ai tuoi indirizzi ip.