The most likely cause is that the web server is not listening on port 8443. When a web server is not listening on a specific port, it simply ignores incoming connection attempts on that port, even if the firewall permits the traffic. In this scenario, the firewall ACL correctly allows both ports 443 and 8443 from any source, so the network layer is not blocking the request; the issue lies at the application layer where the server’s service or daemon has not been configured to bind to port 8443. On the CompTIA SecurityX CAS-004 exam, this question tests your ability to distinguish between firewall misconfigurations and server-side listening issues—a common trap is to immediately blame the ACL when the server itself is the culprit. Remember the troubleshooting mantra: just because the firewall says yes does not mean the server is listening. A useful memory tip is “Port open at the wall, but no one home in the hall”—the firewall is the wall, and the listening service is the occupant.
CAS-004 Security Architecture Practice Question
This CAS-004 practice question tests your understanding of security architecture. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Exhibit
access-list extended OUTSIDE-IN
permit tcp any host 10.0.1.100 eq 443
permit tcp any host 10.0.1.100 eq 8443
deny ip any any
Refer to the exhibit. A security analyst notices that users from the internet can reach the web server at 10.0.1.100 on port 443, but they cannot reach it on port 8443. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The web server is not listening on port 8443
The firewallACL permits both ports, so the firewall is not the issue. The most likely cause is that the web server is not listening on port 8443. Option A is incorrect because the ACL permits it. Option C is incorrect because the ACL order is fine. Option D is incorrect because the ACL permits any source.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The ACL only permits traffic from specific source IPs
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related CAS-004 ACL questions on filtering logic and placement.
Security Architecture — This question tests Security Architecture — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The web server is not listening on port 8443 — The firewall ACL permits both ports, so the firewall is not the issue. The most likely cause is that the web server is not listening on port 8443. Option A is incorrect because the ACL permits it. Option C is incorrect because the ACL order is fine. Option D is incorrect because the ACL permits any source.
What should I do if I get this CAS-004 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related CAS-004 ACL questions on filtering logic and placement.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Standard ACLs match source addresses.
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