Someone

modprobe ip_tables
modprobe ip_conntrack
modprobe ip_conntrack_ftp
modprobe iptable_nat
modprobe ip_nat_ftp
modprobe ip_gre
IR0="eth1"
IR1="eth0"
RINTERNA="192.168.10.0/24"
ENDREMOTO="0.0.0.0"
UP_PORTS="1024:"
D_PORTS=":1024"
IP_EXT="200.xxx.xxx.xxx"
CONECTIVIDADE="200.201.165.0/24 200.201.173.0/24 200.201.174.0/24"
iptables -F
iptables -F -t nat
iptables -t filter -P INPUT ACCEPT
iptables -t filter -P OUTPUT ACCEPT
iptables -t filter -P FORWARD ACCEPT
iptables -t nat -P PREROUTING ACCEPT
iptables -t nat -P OUTPUT ACCEPT
iptables -t nat -P POSTROUTING ACCEPT
for i in /proc/sys/net/ipv4/conf/*/rp_filter; do
 echo 1 >$i
done
echo "1" >/proc/sys/net/ipv4/ip_forward
echo "4096" > /proc/sys/net/ipv4/ip_conntrack_max
iptables -A INPUT -i lo -j ACCEPT
iptables -A INPUT -s $RINTERNA -i $IR0 -j ACCEPT
iptables -A INPUT -i $IR1 -j ACCEPT
iptables -A INPUT -i $IR0 -j ACCEPT
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
for no_proxy in $CONECTIVIDADE; do
        iptables -t nat -A PREROUTING -p tcp -s $RINTERNA -d $no_proxy -j ACCEPT
done
iptables -t nat -A PREROUTING -p tcp -i $IR0 --dport 80 -j REDIRECT --to-port 3128
iptables -t nat -A POSTROUTING -o $IR1 -j MASQUERADE
iptables -t nat -A POSTROUTING -p tcp --dport 1723 -j MASQUERADE
iptables -t nat -A POSTROUTING -p 47 -j MASQUERADE
iptables -t nat -I PREROUTING -p tcp --dport 1723 -d $IP_EXT -j DNAT --to-destination 192.168.10.1:1723
iptables -t nat -I PREROUTING -p 47 -d $IP_EXT -j DNAT --to-destination 192.168.10.1