Nmap is a free and very popular network security scanner. It is easy to use and very powerful. This article will explain the installation and usage of Nmap for testing firewall configurations. Even though you can check which ports are open through your firewall, testing it by scanning can be very useful. For example, if you have a firewall rule that disables outside access to your MariaDB service, Nmap can help you make sure that the firewall is working as intended. **NOTE:** *You should nev......