Iptables Cheatsheet

iptables is a user-space utility program that allows a system administrator to configure the IP packet filter rules of the Linux kernel firewall.

Basic Commands

sudo iptables -L               # List all rules
sudo iptables -L -v -n         # List rules with verbosity and numeric IPs/ports
sudo iptables -S               # Print rules in command format
sudo iptables -F               # Flush (delete) all rules

Default Policies

sudo iptables -P INPUT DROP    # Drop incoming traffic by default
sudo iptables -P FORWARD DROP  # Drop forwarding traffic by default
sudo iptables -P OUTPUT ACCEPT # Allow outgoing traffic by default

Allowing Traffic

# Allow Loopback (localhost)
sudo iptables -A INPUT -i lo -j ACCEPT
 
# Allow established and related connections (Crucial!)
sudo iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
 
# Allow SSH (Port 22)
sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT
 
# Allow HTTP and HTTPS
sudo iptables -A INPUT -p tcp --dport 80 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 443 -j ACCEPT
 
# Allow Ping (ICMP)
sudo iptables -A INPUT -p icmp --icmp-type echo-request -j ACCEPT

Dropping and Blocking

# Drop traffic from a specific IP
sudo iptables -A INPUT -s 192.168.1.100 -j DROP
 
# Drop a specific port
sudo iptables -A INPUT -p tcp --dport 23 -j DROP

Saving Rules

Rules added via command line are lost on reboot. You must save them.