==== Exemplo de Script ====
<code bash>
# cat /etc/init.d/firewall
</code>

<code bash firewall.sh>
#!/bin/bash
#
### BEGIN INIT INFO
# Provides:          firewall
# Required-Start:    networking
# Required-Stop: 
# Should-Start:      S
# Should-Stop:       
# Default-Start:     2 3 4 5
# Default-Stop:
# Short-Description: Firewall 
# Description:       Firewall 
#                   
### END INIT INFO
  
## Variáveis 
IPT=$(which iptables) 
NET="0/0" 
PA="1024:65535"
LO="127.0.0.1" 
FW="192.168.200.1"
AUDIT="192.168.200.5"
DMZ="192.168.200.3"
WAN1="200.100.50.99"
WAN2="10.0.3.50"
REDE="192.168.200.0/24"
#----------------------------------------------------------------------- 
modulos() 
 { 
#### CARREGANDO MÓDULOS #### 
modprobe ip_conntrack_ftp 
modprobe ip_nat_ftp 
 } 
  
nega() 
 { 
#### FECHANDO O FIREWALL #### 
$IPT -P INPUT DROP 
$IPT -P OUTPUT DROP 
$IPT -P FORWARD DROP 
 } 
 
limpa()
 { 
#### ABRINDO O FIREWALL #### 
$IPT -X 
$IPT -F 
$IPT -F -t nat 
$IPT -F -t mangle 
$IPT -P INPUT ACCEPT 
$IPT -P OUTPUT ACCEPT 
$IPT -P FORWARD ACCEPT 
 } 
  
loop() 
 {
#### LIBERANDO A LOOP BACK #### 
$IPT -A INPUT -i lo -d $LO -j ACCEPT 
$IPT -A OUTPUT -o lo -d $LO -j ACCEPT 
 } 
 
input() 
 { 
#### ESTABILIZANDO AS CONEXÕES DE INPUT #### 
$IPT -A INPUT -i eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT 
 } 
  
output() 
 { 
#### ESTABILIZANDO AS CONEXÕES DE OUTPUT #### 
$IPT -A OUTPUT -o eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT 
 } 
  
forward() 
 { 
#### ESTABILIZANDO AS CONEXÕES DE FORWARD ####
$IPT -A FORWARD -i eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT 
 } 
 
icmps() 
 { 
##### LIBERANDO ICMPS #### 
for tipo in 0 3/0 3/1 3/2 3/3 3/4 4 5 11 12 
do 
$IPT -A INPUT -p icmp -s $NET -d $FW --icmp-type $tipo -m limit --limit 1/s  -j ACCEPT 
$IPT -A INPUT -p icmp -s $NET -d $WAN1 --icmp-type $tipo -m limit --limit 1/s  -j ACCEPT 
$IPT -A INPUT -p icmp -s $NET -d $WAN2 --icmp-type $tipo -m limit --limit 1/s  -j ACCEPT 
done 

$IPT -A OUTPUT -p icmp --icmp-type 8 -s $FW -d $NET -j ACCEPT 
$IPT -A OUTPUT -p icmp --icmp-type 8 -s $WAN1 -d $NET -j ACCEPT 
$IPT -A OUTPUT -p icmp --icmp-type 8 -s $WAN2 -d $NET -j ACCEPT 
 } 

pt_web_firewall() 
 { 
#### LIBERANDO CONEXÃO WEB PARA O FIREWALL #### 
$IPT -A INPUT -p tcp -s $NET --sport 80 -d $WAN2 --dport $PA -j ACCEPT 
$IPT -A OUTPUT -p tcp -s $WAN2 --sport $PA -d $NET --dport 80 -j ACCEPT 
$IPT -A INPUT -p tcp -s $NET --sport $PA -d $FW --dport 80 -j ACCEPT 
$IPT -A OUTPUT -p tcp -s $FW --sport 80 -d $NET --dport $PA -j ACCEPT
$IPT -A INPUT -p tcp -s $NET --sport $PA -d $FW --dport 8080 -j ACCEPT 
$IPT -A OUTPUT -p tcp -s $FW --sport 8080 -d $NET --dport $PA -j ACCEPT
 } 
  	 
pt_dns_firewall() 
 { 
#### LIBERANDO CONEXÃO DNS NO FIREWALL#### 
$IPT -A INPUT -p udp -s $NET --sport 53 -d $WAN2 --dport $PA -j ACCEPT 
$IPT -A INPUT -p icmp --icmp-type 3 -s $NET -d $WAN2 -j ACCEPT 
$IPT -A OUTPUT -p udp -s $WAN2 --sport $PA -d $NET --dport 53 -j ACCEPT 
$IPT -A OUTPUT -p udp -s $FW --sport $PA -d $NET --dport 53 -j ACCEPT 
$IPT -A INPUT -p udp --sport 53 -s $DMZ -d $FW --dport $PA -j ACCEPT
$IPT -A OUTPUT -p udp --sport $PA -s $FW -d $DMZ --dport 53 -j ACCEPT
$IPT -A FORWARD -p udp --sport 53 -s $DMZ  -d $NET --dport $PA -j  ACCEPT
$IPT -A FORWARD -p udp --sport $PA -s $NET -d $DMZ  --dport 53 -j ACCEPT

}

pt_ntp_firewall() 
 { 
#### LIBERANDO CONEXÃO NTP NO FIREWALL#### 
$IPT -A INPUT -i eth2 -p udp -s $AUDIT --sport 123 -d $FW --dport 123 -j ACCEPT
$IPT -A OUTPUT -o eth2 -p udp -s $FW --sport 123 -d $AUDIT --dport 123 -j ACCEPT
$IPT -A INPUT -p udp --sport 123 -s $AUDIT -d $REDE --dport $PA -j ACCEPT
$IPT -A OUTPUT -p udp --sport $PA -s $REDE -d $AUDIT --dport 123 -j ACCEPT
 } 
  
pt_ssh_firewall() 
 { 
#### LIBERANDO CONEXÃO SSH NO FIREWALL#### 
$IPT -A INPUT -p tcp -s $NET --sport $PA -d $WAN1 --dport 51000 -j ACCEPT 
$IPT -A OUTPUT -p tcp -s $WAN1 --sport 51000 -d $NET --dport $PA -j ACCEPT
$IPT -A INPUT -p tcp -s $NET --sport $PA -d $FW --dport 51000 -j ACCEPT 
$IPT -A OUTPUT -p tcp -s $FW --sport 51000 -d $NET --dport $PA -j ACCEPT
 } 

pt_proxy_firewall() 
 { 
#### LIBERANDO CONEXÃO PROXY NO FIREWALL#### 
$IPT -A INPUT -p tcp -s $NET --sport $PA -d $FW --dport 3128 -j ACCEPT 
$IPT -A OUTPUT -p tcp -s $FW --sport 3128 -d $NET --dport $PA -j ACCEPT
 } 

pt_ldap_firewall() 
 { 
#### LIBERANDO CONEXÃO LDAP NO FIREWALL#### 
$IPT -A INPUT -p tcp -s $REDE --sport 389 -d $NET --dport $PA -j ACCEPT 
$IPT -A OUTPUT -p tcp -s $NET --sport $PA -d $REDE --dport 389 -j ACCEPT
 } 

pt_mysql_firewall() 
 { 
#### LIBERANDO CONEXÃO MYSQL NO FIREWALL#### 
$IPT -A INPUT -p tcp -s $REDE --sport 3306 -d $NET --dport $PA -j ACCEPT 
$IPT -A OUTPUT -p tcp -s $NET --sport $PA -d $REDE --dport 3306 -j ACCEPT
}
flags_invalidas() 
 { 
##### ATIVANDO CONTROLE DE FLAGS INVALIDAS #### 
for FLAGS in SYN,RST SYN,FIN SYN,PSH SYN,URG FIN,RST FIN,URG,PSH 
 do 
for CHAINS in INPUT FORWARD 
   do 
$IPT -A $CHAINS -p tcp -d $FW -m state --state NEW --tcp-flags $FLAGS $FLAGS -j LOG --log-prefix "FLAG_$FLAGS" 
$IPT -A $CHAINS -p tcp -d $FW -m state --state NEW --tcp-flags $FLAGS $FLAGS -j DROP 

$IPT -A $CHAINS -p tcp -d $WAN1 -m state --state NEW --tcp-flags $FLAGS $FLAGS -j LOG --log-prefix "FLAG_$FLAGS" 
$IPT -A $CHAINS -p tcp -d $WAN1 -m state --state NEW --tcp-flags $FLAGS $FLAGS -j DROP 

$IPT -A $CHAINS -p tcp -d $WAN2 -m state --state NEW --tcp-flags $FLAGS $FLAGS -j LOG --log-prefix "FLAG_$FLAGS" 
$IPT -A $CHAINS -p tcp -d $WAN2 -m state --state NEW --tcp-flags $FLAGS $FLAGS -j DROP 
 done 
 done 
 } 

nat () 
 { 
#### COMPARTILHANDO CONEXÃO DA INTERNET ####   
$IPT -A FORWARD -s $REDE -d $NET -j ACCEPT 
$IPT -A FORWARD -s $NET -d $REDE -j ACCEPT 
  
$IPT -t nat -A POSTROUTING -s $REDE -o eth1 -j MASQUERADE 
 } 

pre_ssh () 
 { 
#### REDIRECIONAMENTO DE PORTAS DO SSH PARA MAQUINA INTERNAS #### 
for ip in 2 3 4 5 
do 
$IPT -A OUTPUT -p tcp -s $NET --sport $PA -d 192.168.200.$ip --dport 5$ip'000' -j ACCEPT
$IPT -A INPUT -p tcp --sport 5$ip'000' -s 192.168.200.$ip -d $NET --dport $PA -j  ACCEPT
$IPT -A FORWARD -p tcp  --sport 5$ip'000' -s 192.168.200.$ip -d $NET --dport $PA -j  ACCEPT
$IPT -A FORWARD -p tcp --sport $PA -s $NET -d 192.168.200.$ip --dport 5$ip'000' -j ACCEPT
$IPT -t nat -A PREROUTING -p tcp --sport $PA -s $NET -d $WAN1 --dport 5$ip'000' -j DNAT --to-destination 192.168.200.$ip':'5$ip'000'
done
 } 

pre_dns () 
 { 
#### REDIRECIONAMENTO DA PORTA DNS PARA MAQUINA DMZ #### 
$IPT -t nat -A PREROUTING -p udp --sport $PA -s $NET -d $WAN1 --dport 53 -j DNAT --to-destination $DMZ:53
 }

pre_web () 
 { 
#### REDIRECIONAMENTO DE PORTAS WEB PARA MAQUINA DMZ #### 
for httpports in  80 443 
do
$IPT -t nat -A PREROUTING -p tcp --sport $PA -s $NET -d $WAN1 --dport $httpports -j DNAT --to-destination $DMZ:$httpports
done
 }

pre_mail () 
 {
#### REDIRECIONAMENTO DE PORTAS MAIL PARA MAQUINA DMZ #### 
for mailports in  25 110 143 993 995 
do
$IPT -t nat -A PREROUTING -p tcp --sport $PA -s $NET -d $WAN1 --dport $mailports -j DNAT --to-destination $DMZ:$mailports
done
 }

pre_ftp ()
 {
#### REDIRECIONAMENTO DE PORTAS FTP PARA MAQUINA DMZ #### 
for ftpports in  20 21 
do
$IPT -t nat -A PREROUTING -p tcp --sport $PA -s $NET -d $WAN1 --dport $ftpports -j DNAT --to-destination $DMZ:$ftpports
 done
 }
#----------------------------------------------------------------------- 
case $1 in 
 start) 
 modulos 
 nega 
 loop 
 input 
 output 
 forward 
 icmps 
 pt_web_firewall 
 pt_dns_firewall 
 pt_ntp_firewall 
 pt_ssh_firewall 
 pt_proxy_firewall 
 pt_ldap_firewall 
 pt_mysql_firewall
 flags_invalidas 
 nat
 pre_ssh
 pre_dns
 pre_web
 pre_mail
 pre_ftp
 
echo " ******* FIREWAL ATIVADO ******* " 
 	;; 
 stop) 
 limpa 
  
echo " ******* FIREWALL DESATIVADO ******* " 
  	;; 
filter) $IPT -nL  
  	;; 
nat) $IPT -nL -t nat 
  	;; 
mangle) $IPT -nL -t mangle  
 	;; 
restart) $0 stop 
	 $0 start 
  	;; 
*) echo "erro use $0 {start|stop|filter|nat|mangle|restart}" 
  	;; 
esac 
</code>