According to the question, you are required to prevent outside computers from accessing your network. You should therefore configure the

switch's port access based on the MAC address, which can be done by configuring port security. Port security is a feature of Cisco Catalyst

series switches. Port security is used to block input based on the media access control (MAC) address to an Ethernet, Fast Ethernet, or Gigabit

Ethernet port. It denies the port access to a workstation when the MAC address of the station attempting to access the port is different from

any of the MAC addresses specified for that port.

Answer B and C are incorrect. A firewall is used to protect an internal network or intranet against unauthorized access from the

Internet or other outside networks.

Answer D is incorrect. A port scanner is a software tool that is designed to search a network host for open ports. This tool is often used

by administrators to check the security of their networks. It is also used by hackers to compromise the network and systems.