Iptables

La herramienta para manejar el modulo de netfilter del kernel. En otras palabras el firewall a mano

La entrada de una direccion

/sbin/iptables -I INPUT 1 -s 172.24.2.238 -j DROP

Bloquear la salida a google

/sbin/iptables -I FORWARD 1 -s 192.168.0.0/16 -d www.google.com -j DROP

o

/sbin/iptables -I ZINTERNA-ZEXTERNA 1 -s 192.168.0.0/16 -d www.google.com -j DROP

Puede usar DROP o REJECT, le primero no avisa, el segundo si

/sbin/iptables -A FORWARD -p TCP -i eth0 -d 172.14.1.1 --dport 80 -j ACCEPT

/sbin/iptables -t nat -I PREROUTING -s 192.168.0.0/16 -i ! eth2 -d ! 192.168.0 .0/24 -p tcp --dport 80 -j REDIRECT --to-port 3128 

/sbin/iptables -t nat -A POSTROUTING -s 192.168.0.0/16 -j MASQUERADE
/sbin/iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

/sbin/iptables -t nat -A PREROUTING -p TCP -i eth1 -d 200.41.79.34 --dport 53 -j DNAT --to-destination 172.24.13.4

/sbin/iptables -t nat -A POSTROUTING -o eth1 -j SNAT --to-source 200.41.79.35

/sbin/iptables 

 /sbin/iptables 

/sbin/iptables -t nat -I PREROUTING -s 192.168.0.0/16 -i ! eth2 -d ! 192.168.0 .0/24 -p tcp --dport 80 -j REDIRECT --to-port 3128

https://kodeslogic.medium.com/how-to-fix-nf-conntrack-table-full-dropping-packet-a5fedc6c463d

• 25 Useful IPtable Firewall Rules Every Linux Administrator Should Know https://www.tecmint.com/linux-iptables-firewall-rules-examples-commands
• https://www.unixmen.com/iptables-vs-firewalld/

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