Iptables (rc.firewall)

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#!/bin/bash
# Script de Firewall

#####################################
### Passo 1: Primeiro vamos arrumar a casa :) ###
#####################################

# Limpando as Regras
iptables -F INPUT
iptables -F OUTPUT
iptables -F FORWARD

# Definindo a Politica Default das Cadeias
iptables -P INPUT DROP
iptables -P OUTPUT ACCEPT
iptables -P FORWARD DROP


######################################
### Passo 2: Antes de Servir, vamos nos proteger ! ###
######################################

# Desabilitando o trafego IP Entre as Placas de Rede
echo "0" > /proc/sys/net/ipv4/ip_forward

# Configurando a Protecao anti-spoofing
echo "Setting anti-spoofing .....[ OK ]"
for spoofing in /proc/sys/net/ipv4/conf/*/rp_filter; do
        echo "1" > $spoofing
done


#######################################
### Passo 3: Carregando os modulos do iptables ###
#######################################

modprobe ip_tables
modprobe iptable_filter
modprobe iptable_mangle
modprobe iptable_nat
modprobe ipt_MASQUERADE
echo "Setting rules .............[ OK ]"

#######################################
### Passo 4: Agora, vamos definir o que pode passar e o que nao ###
#######################################

# Cadeia de Entrada. Esta cadeia, so vale para o proprio host

# Qualquer pacote IP que venha do localhost, Ok.
iptables -A INPUT -i lo -j ACCEPT

# REDE INTERNA LIBERADA
iptables -A INPUT -i eth1 -j ACCEPT

# No iptables, temos de dizer quais sockets sao validos em uma conexao
iptables -A INPUT -m state --state ESTABLISHED,RELATED,NEW -j ACCEPT


# Cadeia de Reenvio (FORWARD)

# Primeiro, ativar o mascaramento (nat).
iptables -t nat -F POSTROUTING
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

# Agora dizemos quem e o que podem acessar externamente
# No iptables, o controle do acesso a rede externa e feito na cadeia "FORWARD"

# Redireciona porta 80 para 3128 (squid)
iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 80 -j REDIRECT --to-port 3128

# REDE INTERNA LIBERADA
iptables -A FORWARD -i eth1 -j ACCEPT

# No iptables, temos de dizer quais sockets sao validos em uma conexao
iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT

########################################
### Finalmente, podemos "Ligar" o foward (clientes) :) ###
########################################

# Habilitando o trafego Ip, entre as Interfaces de rede
echo "1" > /proc/sys/net/ipv4/ip_forward
echo "Firewall OK ...............[ OK ]"