echo 1 > /proc/sys/net/ipv4/ip_forward
# limpa regras existentes no iptables
iptables -F
# cria regras (politicas) padrao
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT ACCEPT
# Libera input para solicitacoes da rede interna
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -m state --state NEW -i $INTERNAL_INTERFACE -j ACCEPT
# Liberando comunicacao entres as interfaces interna e internet (FORWARD)
iptables -A FORWARD -i eth1 -o eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A FORWARD -i eth0 -o eth1_1 -j ACCEPT
# Abilitando o NAT
iptables -t nat -A POSTROUTING -s 0/0 -j MASQUERADE