John works as a Network Administrator for Perfect Solutions Inc.

John works as a Network Administrator for Perfect Solutions Inc. The company has a Linux-based network. The company is aware of various types of security attacks and wants to impede them. Hence, management has assigned John a project to port scan the company's Web Server. For this, he uses the nmap port scanner and issues the following command to perform idle port scanning:

nmap -PN -p- -sI IP_Address_of_Company_Server

He analyzes that the server's TCP ports 21, 25, 80, and 111 are open.

Which of the following security policies is the company using during this entire process to mitigate the risk of hacking attacks?