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This paper shows how to use iptables to set up a secure firewall on your Linux home computer(s). It contains plenty of configuration examples and command output. If you follow the examples, you will be able to build and deploy a robust and flexible firewall of your own.
You Should Know:
Basic iptables Commands
1. List Current Rules
sudo iptables -L -v -n
Lists all active rules with verbose output.
2. Block a Specific IP Address
sudo iptables -A INPUT -s 192.168.1.100 -j DROP
Drops all incoming traffic from `192.168.1.100`.
3. Allow SSH (Port 22)
sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT
4. Allow HTTP/HTTPS Traffic
sudo iptables -A INPUT -p tcp --dport 80 -j ACCEPT sudo iptables -A INPUT -p tcp --dport 443 -j ACCEPT
5. Enable NAT (Network Address Translation)
sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
6. Save iptables Rules
sudo iptables-save > /etc/iptables.rules
Restore them on reboot:
sudo iptables-restore < /etc/iptables.rules
Advanced iptables Configurations
- Rate Limiting Connections
sudo iptables -A INPUT -p tcp --dport 22 -m limit --limit 3/min --limit-burst 3 -j ACCEPT
-
Block ICMP (Ping) Requests
sudo iptables -A INPUT -p icmp --icmp-type echo-request -j DROP
-
Log Dropped Packets
sudo iptables -A INPUT -j LOG --log-prefix "IPTABLES-DROP: " --log-level 4 sudo iptables -A INPUT -j DROP
Troubleshooting Commands
-
Check Packet Counters
sudo iptables -L -v
-
Flush All Rules
sudo iptables -F
-
Delete a Specific Rule
sudo iptables -D INPUT 2
(Deletes the 2nd rule in the INPUT chain)
What Undercode Say
A well-configured `iptables` firewall is essential for securing Linux systems. Always test rules before applying them in production. Use logging to monitor suspicious activity and regularly update rules to adapt to new threats. Combining `iptables` with tools like `fail2ban` enhances security further.
Expected Output:
A functional firewall setup with logged and secured traffic, preventing unauthorized access while allowing legitimate services.
<h1>Example of a secure baseline iptables configuration</h1> sudo iptables -P INPUT DROP sudo iptables -A INPUT -i lo -j ACCEPT sudo iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT sudo iptables -A INPUT -p tcp --dport 80 -j ACCEPT sudo iptables -A INPUT -p tcp --dport 443 -j ACCEPT sudo iptables -A INPUT -j LOG --log-prefix "DENIED: " sudo iptables -A INPUT -j DROP
For persistent rules, install `iptables-persistent` (Debian/Ubuntu):
sudo apt install iptables-persistent sudo netfilter-persistent save
Further Reading:
References:
Reported By: Ahmed Ali – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
