If your firewalld is installed, there here are the commands useful in daily management
Check state of firewall
sudo firewall-cmd --state
Start firewall
sudo systemctl start firewalld
Stop firewall
sudo systemctl stop firewalld
Enable to autostart with system start
sudo systemctl enable firewalld
Add rule for given port number
sudo firewall-cmd --zone=public --add-port=80/tcp --permanent
sudo firewall-cmd --reload
sudo firewall-cmd --zone=public --list-ports
The last line is responsible of listing all available ports for verification
Remove rule for given port number
sudo firewall-cmd --zone=public --remove-port=80/tcp --permanent
sudo firewall-cmd --reload
Ubuntu firewalld – few useful commands