Algo sobre iptables y /etc/rc.local

cat /etc/rc.local 


#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.

#Configurar el IP de la interfaz eth0
  ifconfig eth0 192.168.0.1 netmask 255.255.255.0


   iptables -F
   iptables -X
   iptables -Z
   iptables -t nat -F

  # EXTERNAL -> external network interface
  # INTERNAL -> internal network interface
  EXTERNAL=wlan0
  INTERNAL=eth0
  echo 1 > /proc/sys/net/ipv4/ip_forward
  echo "Setting up NAT (Network Address Translation)..."
  # by default, nothing is forwarded.
  iptables -P FORWARD DROP
  # Allow all connections OUT and only related ones IN
  iptables -A FORWARD -i $EXTERNAL -o $INTERNAL -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
  iptables -A FORWARD -i $INTERNAL -o $EXTERNAL -j ACCEPT
  # enable MASQUERADING
  iptables -t nat -A POSTROUTING -o $EXTERNAL -j MASQUERADE
  

# para proxy transparente, leer sobre squid transparente.
iptables -t nat -A PREROUTING -i $INTERNAL -p tcp --dport 80 -j REDIRECT --to-port 3128
exit 0