ufw

sudo apt update && sudo apt install ufw -y

# Enable
sudo ufw enable
# Disable
sudo ufw disable
# Reload
sudo ufw reload

# default rule - allow all outgoing, deny all incoming
sudo ufw default allow outgoing
sudo ufw default deny incoming

sudo editor /etc/ufw/ufw.conf
# Edit: ENABLED=yes

# Simple
sudo ufw status
# Including ID
sudo ufw status numbered

# Allow port
sudo ufw allow $PORT_NUMBER
sudo ufw allow $PORT_NUMBER/tcp
# note: must allow the modified port of ssh first before restarting SSH

# Allow IP
sudo ufw allow from $IP_ADDRESS

# Allow IP range
sudo ufw allow from $IP/$CIDR

# Allow IP range on one port
sudo ufw allow from $IP/$CIDR to any port $PORT_NUMBER

# Block incoming requests from IP
sudo ufw insert 1 deny from $IP_ADDRESS
# note: insert 1 for on top of rule list, ufw follows the order of the rules
sudo ufw deny from $IP_ADDRESS # when there is no rule

# Block outgoing requests to IP
sudo ufw deny out from any to $IP_ADDRESS

# note: ssh is always an alias of 22
sudo ufw allow ssh
#sudo ufw allow 22

sudo ufw delete $RULE_NUMBER