One of the most effective ways to protect an application server is to use a screened subnet. A screened subnet is a network segment that is isolated from both the internet and the internal network by two firewalls. The application server is placed in the screened subnet, also known as the demilitarized zone (DMZ), and only the necessary ports are opened for communication. This way, the application server is shielded from external attacks and internal breaches, and the impact of a compromise is minimized.