hardMultiple SelectObjective-mapped
CAS-004 Practice Question: A security architect is reviewing the network…
A security architect is reviewing the network security controls for a critical industrial control system (ICS) environment. The architect must select two controls that are most effective at preventing unauthorized access to the ICS network from the corporate IT network, while still allowing necessary monitoring traffic. Which TWO controls should be implemented? (Choose two.)
⚠ Common exam trap
A common mix-up: candidates choose a VPN (Option A) thinking encryption equals security, but encryption does not prevent unauthorized access—it only protects data in transit, and a VPN still allows bidirectional communication, which is the opposite of what is needed for ICS isolation.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Deploy a unidirectional gateway (data diode) between the networks
A unidirectional gateway (data diode) physically enforces one-way data flow, ensuring that no traffic can originate from the corporate IT network into the ICS network. This prevents unauthorized access while allowing monitoring data (e.g., syslog, SNMP traps) to be sent out from the ICS side. It is the most effective control for preventing any inbound attack vectors while preserving outbound monitoring traffic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure a site-to-site VPN from the corporate network to the ICS network
Why it's wrong here
VPN would allow inbound connections, increasing risk.
- ✗
Implement a network-based intrusion prevention system (IPS) on the ICS network
Why it's wrong here
IPS is reactive and may not prevent all unauthorized access.
- ✓
Deploy a unidirectional gateway (data diode) between the networks
Why this is correct
Ensures traffic can only flow out, preventing inbound access.
- ✓
Place a bastion host in a DMZ accessible from both networks for monitoring traffic
Why this is correct
Allows necessary monitoring without exposing the ICS network directly.
- ✗
Segment the networks using VLANs only
Why it's wrong here
VLANs without additional controls can be bypassed.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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