The correct controls are a data diode and a bastion host placed in a DMZ. A data diode, or unidirectional gateway, physically enforces one-way data flow from the ICS network to the corporate IT network, ensuring that no traffic can originate from the corporate side into the ICS environment while still allowing outbound monitoring data like syslog or SNMP traps. The bastion host, positioned in a DMZ accessible from both networks, provides a secure, audited point for authorized monitoring traffic without exposing the ICS directly. On the CompTIA SecurityX CAS-004 exam, this pairing tests your understanding of defense-in-depth for critical infrastructure, where a common trap is to choose a firewall alone—firewalls can be misconfigured or bypassed, but a data diode provides physical isolation. Remember the memory tip: "Diode for direction, bastion for inspection"—the diode blocks inbound attacks, and the bastion safely handles monitoring.
CAS-004 Security Architecture Practice Question
This CAS-004 practice question tests your understanding of security architecture. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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.)
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Related concept
Read the scenario before looking for a memorised answer.
✓
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.
Related concept
Read the scenario before looking for a memorised answer.
✗
Segment the networks using VLANs only
Why it's wrong here
VLANs without additional controls can be bypassed.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often 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.
Detailed technical explanation
How to think about this question
Data diodes typically use optical fiber transceivers with the transmit pair physically removed or disabled on the receiving side, ensuring data can only flow in one direction at the physical layer. In ICS environments like power grids or water treatment plants, this prevents any possibility of a remote attacker sending commands from the IT network, even if the corporate network is compromised. The monitoring traffic is often sent via a separate outbound-only path, such as a syslog forwarder or a read-only historian that pulls data through the diode.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security Architecture — This question tests Security Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this CAS-004 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This CAS-004 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CAS-004 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.