iptables and redirection traffic from one PC to another

[Aleksander Kurczyk <akurczyk@outlook.com>]

Hello,

This is my firewall script:

sudo iptables -F
sudo iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
sudo iptables -A INPUT -i lo -j ACCEPT
sudo iptables -A INPUT -s 192.168.0.0/24 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 22005 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 80 -j ACCEPT
sudo iptables -A INPUT -j DROP
sudo iptables -t nat -A PREROUTING -p tcp --dport 81 -j DNAT --to 192.168.1.2:80
sudo iptables -A FORWARD -p tcp -d 192.168.1.10 --dport 80 -j ACCEPT
sudo iptables -L

I want to run it on Raspbian which is behind my home router. I forwarded the whole incoming traffic from my router to the RPI using the DMZ function (NAT 1:1).

The "-A INPUT" part of the script works! :) I can access only 22005 and 80 from the Internet and every other port on the LAN subnet and lo interface. The thing is that the port forwarding part isn't working :(

sudo iptables -t nat -A PREROUTING -p tcp --dport 81 -j DNAT --to 192.168.1.2:80
sudo iptables -A FORWARD -p tcp -d 192.168.1.10 --dport 80 -j ACCEPT

I want to redirect the 81 port of my RPI to my home PC's 80 port (web serwer). I found this in Google.

Of course I also enabled IPv4 forwarding in sysclt:

sudo sysctl -w net.ipv4.ip_forward=1

And am I dropping the packets correctly or should I use default policy instead? This way is simpler to understand. Is there something that I am doing wrong in this script?

--
Best regards,
Aleksander Kurczyk