Which of the following would be MOST appropriate to secure an existing SCADA system by preventing
connections from unauthorized networks?

A.
Implement a HIDS to protect the SCADA system

B.
Implement a Layer 2 switch to access the SCADA system

C.
Implement a firewall to protect the SCADA system

D.
Implement a NIDS to protect the SCADA system

Explanation:
Firewalls manage traffic using filters, which is just a rule or set of rules. A recommended guideline for
firewall rules is, “deny by default; allow by exception”. This means that if a network connection is not
specifically allowed, it will be denied.
Incorrect Answers:
A: A HIDS monitors the inbound and outbound packets from a host device only and will alert the user or
administrator if suspicious activity is detected.
B: A switch is a networking device used to connect other devices together and potentially implement
traffic management on their communications.
D: A NIDS monitor traffic to and from all devices on the network and will alert the administrator if
suspicious activity is detected.

Stewart, James Michael, CompTIA Security+ Review Guide, Sybex, Indianapolis, 2014, pp. 6, 9, 23https://en.wikipedia.org/wiki/Intrusion_detection_system