6. Permitir HTTP entrante
iptables -A INPUT -i eth0 -p tcp –dport 80 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 80 -m state –state ESTABLISHED -j ACCEPT

7. Permitir HTTPS entrante
iptables -A INPUT -i eth0 -p tcp –dport 443 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 443 -m state –state ESTABLISHED -j ACCEPT

8. Multipuerto (Permitir entrantes SSH, HTTP y HTTPS)
iptables -A INPUT -i eth0 -p tcp -m multiport –dports 22,80,443 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp -m multiport –sports 22,80,443 -m state –state ESTABLISHED -j ACCEPT

9. Permitir salir SSH
iptables -A OUTPUT -o eth0 -p tcp –dport 22 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp –sport 22 -m state –state ESTABLISHED -j ACCEPT

10. Permitir salir SSH sólo a una red específica
iptables -A OUTPUT -o eth0 -p tcp -d 192.168.101.0/24 –dport 22 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp –sport 22 -m state –state ESTABLISHED -j ACCEPT

11. Permitir salir HTTPS
iptables -A OUTPUT -o eth0 -p tcp –dport 443 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp –sport 443 -m state –state ESTABLISHED -j ACCEPT

12. Carguar tráfico HTTPS balanceado
iptables -A PREROUTING -i eth0 -p tcp –dport 443 -m state –state NEW -m nth –counter 0 –every 3 –packet 0 -j DNAT –to-destination 192.168.1.101:443
iptables -A PREROUTING -i eth0 -p tcp –dport 443 -m state –state NEW -m nth –counter 0 –every 3 –packet 1 -j DNAT –to-destination 192.168.1.102:443
iptables -A PREROUTING -i eth0 -p tcp –dport 443 -m state –state NEW -m nth –counter 0 –every 3 –packet 2 -j DNAT –to-destination 192.168.1.103:443

13. Permitir ping desde el interior al exterior
iptables -A OUTPUT -p icmp –icmp-type echo-request -j ACCEPT
iptables -A INPUT -p icmp –icmp-type echo-reply -j ACCEPT

14. Permitir ping desde el exterior al interior
iptables -A INPUT -p icmp –icmp-type echo-request -j ACCEPT
iptables -A OUTPUT -p icmp –icmp-type echo-reply -j ACCEPT

15. Permitir el acceso loopback
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT

16. Permitir que los paquetes de red interna salgan a la red externa.
# if eth1 is connected to external network (internet)
# if eth0 is connected to internal network (192.168.1.x)
iptables -A FORWARD -i eth0 -o eth1 -j ACCEPT

16. Permitir consultas DNS
iptables -A OUTPUT -p udp -o eth0 –dport 53 -j ACCEPT
iptables -A INPUT -p udp -i eth0 –sport 53 -j ACCEPT

17. Permitir conexiones NIS
#rpcinfo -p | grep ypbind ; This port is 853 and 850
iptables -A INPUT -p tcp –dport 111 -j ACCEPT
iptables -A INPUT -p udp –dport 111 -j ACCEPT
iptables -A INPUT -p tcp –dport 853 -j ACCEPT
iptables -A INPUT -p udp –dport 853 -j ACCEPT
iptables -A INPUT -p tcp –dport 850 -j ACCEPT
iptables -A INPUT -p udp –dport 850 -j ACCEPT

18. Permitir rsync de una red específica
iptables -A INPUT -i eth0 -p tcp -s 192.168.101.0/24 –dport 873 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 873 -m state –state ESTABLISHED -j ACCEPT

19. Permitir conexión MySQL sólo desde una red específica
iptables -A INPUT -i eth0 -p tcp -s 192.168.200.0/24 –dport 3306 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 3306 -m state –state ESTABLISHED -j ACCEPT

20. Permitir Sendmail o Postfix
iptables -A INPUT -i eth0 -p tcp –dport 25 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 25 -m state –state ESTABLISHED -j ACCEPT

21. Permitir IMAP y IMAPS
iptables -A INPUT -i eth0 -p tcp –dport 143 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 143 -m state –state ESTABLISHED -j ACCEPT

iptables -A INPUT -i eth0 -p tcp –dport 993 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 993 -m state –state ESTABLISHED -j ACCEPT

22. Permitir POP3 y POP3S
iptables -A INPUT -i eth0 -p tcp –dport 110 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 110 -m state –state ESTABLISHED -j ACCEPT

iptables -A INPUT -i eth0 -p tcp –dport 995 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 995 -m state –state ESTABLISHED -j ACCEPT

23. Prevenir ataques DoS
iptables -A INPUT -p tcp –dport 80 -m limit –limit 25/minute –limit-burst 100 -j ACCEPT

24. Reenvío de puertos 422 to 22
iptables -t nat -A PREROUTING -p tcp -d 192.168.102.37 –dport 422 -j DNAT –to 192.168.102.37:22
iptables -A INPUT -i eth0 -p tcp –dport 422 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 422 -m state –state ESTABLISHED -j ACCEPT

25. Log de paquetes rechazados
iptables -N LOGGING
iptables -A INPUT -j LOGGING
iptables -A LOGGING -m limit –limit 2/min -j LOG –log-prefix “IPTables Packet Dropped: ” –log-level 7
iptables -A LOGGING -j DROP