Firewall

# Check status
ufw status verbose

# Enable the firewall
ufw enable

# Disable the firewall
ufw disable

# Reset to default (removes all rules)
ufw reset

# By port number
ufw allow 80/tcp       # HTTP
ufw allow 443/tcp      # HTTPS
ufw allow 22/tcp       # SSH
ufw allow 3306/tcp     # MySQL (only if necessary!)

# By service name
ufw allow ssh
ufw allow http
ufw allow https

# Port range
ufw allow 8000:9000/tcp

ufw deny 3306/tcp
ufw deny from 1.2.3.4    # Block a specific IP

# First display the numbered rules
ufw status numbered

# Then delete by number
ufw delete 3

ufw default deny incoming
ufw default allow outgoing
ufw allow ssh
ufw allow http
ufw allow https
ufw enable

# Check status
firewall-cmd --state
firewall-cmd --list-all

# Open a port (permanent)
firewall-cmd --permanent --add-port=80/tcp
firewall-cmd --permanent --add-port=443/tcp
firewall-cmd --permanent --add-service=ssh

# Apply the changes
firewall-cmd --reload

# Block an IP
firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="1.2.3.4" drop'
firewall-cmd --reload

# View rules
iptables -L -n -v

# Open a port
iptables -A INPUT -p tcp --dport 80 -j ACCEPT

# Block an IP
iptables -A INPUT -s 1.2.3.4 -j DROP

# Save the rules (Debian/Ubuntu)
apt install iptables-persistent
netfilter-persistent save