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Summary of Setting up Firewall on Different Distros

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iptables firewalld ufw firewall security
Hugo
Author
Hugo
DevOps Engineer in London
Table of Contents

In this article, I will cover the basics of setting up firewalls on different distros, including firewalld, ufw, and iptables.

We will also discuss the daily tasks of firewall management, such as allowing or blocking specific source addresses/destination ports, port forwarding, and NAT.

Web Application Example:
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  • A web server at 192.168.0.100
  • A node.js app at 192.168.0.200:8000 that is not publicly accessible

Tasks:

Allow port 80 from public:
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iptables -A INPUT -p tcp -m tcp --dport 80 -j ACCEPT

firewall-cmd --zone=public --add-port=80/tcp --permanent

ufw allow 80/tcp

Allow SSH only from a trusted IP, e.g., 43.164.66.12:
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iptables -A INPUT -p tcp -s 43.164.66.12 --dport 22 -j ACCEPT

firewall-cmd --zone=public --add-rich-rule 'rule family="ipv4" source address=43.164.66.12 port port=22 accept'

ufw allow from 43.164.66.12 to any port 22/tcp

Forward port 8080 requests to 192.168.0.200:8000:
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iptables -t nat -A PREROUTING -p tcp --dport 8080 \
       -j DNAT --to-destination 192.168.0.200:8000
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

firewall-cmd --zone=public --add-masquerade
firewall-cmd --zone="public" --add-forward-port=port=8080:proto=tcp:toaddr=198.51.100.0:toport=8000

Drop traffic from bad IP, e.g., 233.228.5.86:
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firewall-cmd --zone=public --add-rich-rule 'rule family="ipv4" source address=233.228.5.86 drop'

ufw deny from 233.228.5.86

When working with the NAT table, we need to enable ip_forward as well in /etc/ufw/sysctl.conf:

net.ipv4.ip_forward = 1

NAT Example:
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  • A Linux router with IP 192.160.0.100 with internet access
  • Internal servers 192.160.0.200, 192.160.0.201, 192.160.0.203 using 192.160.0.100 as router.

Tasks:

Config NAT for internal server to have internet access:
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iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

firewall-cmd --zone=public --add-masquerade

By following these guidelines, you can set up your firewall effectively and ensure the security of your system.

Reference:
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