The answer is that the ACL is applied to the wrong interface or direction. This is correct because the ACL permits HTTP (TCP 80) but does not explicitly permit HTTPS (TCP 443), yet the issue is that HTTPS is blocked while HTTP works. If the ACL were applied inbound on the inside interface, it would filter outbound traffic from the 192.168.1.0/24 network, blocking HTTPS requests before they leave the internal network. On the ISC2 Certified in Cybersecurity CC exam, this scenario tests your understanding of ACL placement and direction, a common trap where candidates focus only on missing permit statements rather than where the ACL is applied. The implicit deny at the end of the ACL always blocks unpermitted traffic, but the key is that HTTP works, so the problem is not the rules themselves but their application point. Memory tip: think “direction dictates destination”—if traffic is blocked leaving, check the inbound direction on the inside interface.
ISC2 CC Business Continuity, DR & Incident Response Practice Question
This CC practice question tests your understanding of business continuity, dr & incident response. 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
Refer to the exhibit.
! Configuration snippet from router R1
access-list 100 permit tcp 192.168.1.0 0.0.0.255 any eq 80
access-list 100 permit tcp 192.168.1.0 0.0.0.255 any eq 443
access-list 100 deny ip any any log
!
interface GigabitEthernet0/0
ip access-group 100 in
!
Refer to the exhibit. A security analyst observes that users from the 192.168.1.0/24 network cannot access HTTPS websites, but HTTP access works fine. 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.
Refer to the exhibit.
! Configuration snippet from router R1
access-list 100 permit tcp 192.168.1.0 0.0.0.255 any eq 80
access-list 100 permit tcp 192.168.1.0 0.0.0.255 any eq 443
access-list 100 deny ip any any log
!
interface GigabitEthernet0/0
ip access-group 100 in
!
A
The ACL is applied to the wrong interface or direction.
If the ACL is applied inbound on the internal interface, it should work; if applied outbound on the external interface, it may block return traffic. The most likely issue is misapplication.
B
The implicit deny at the end of the ACL blocks HTTPS traffic.
Why wrong: The permit for port 443 comes before the deny, so HTTPS is allowed.
C
The ACL is missing a permit statement for TCP port 443 return traffic.
Why wrong: ACLs filter based on source/destination; return traffic is handled separately.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The ACL is applied to the wrong interface or direction.
The exhibit shows an ACL that permits HTTP (TCP 80) but does not explicitly permit HTTPS (TCP 443). However, the question states that HTTP works and HTTPS does not, which suggests the ACL is correctly filtering inbound traffic on the outside interface. The most likely cause is that the ACL is applied to the wrong interface or direction, because if it were applied inbound on the inside interface, it would block outbound HTTPS traffic from the 192.168.1.0/24 network. The implicit deny at the end of the ACL would block any traffic not explicitly permitted, but since HTTP works, the issue is not the implicit deny itself but rather the placement of the ACL.
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.
✓
The ACL is applied to the wrong interface or direction.
Why this is correct
If the ACL is applied inbound on the internal interface, it should work; if applied outbound on the external interface, it may block return traffic. The most likely issue is misapplication.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The implicit deny at the end of the ACL blocks HTTPS traffic.
Why it's wrong here
The permit for port 443 comes before the deny, so HTTPS is allowed.
✗
The ACL is missing a permit statement for TCP port 443 return traffic.
Why it's wrong here
ACLs filter based on source/destination; return traffic is handled separately.
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the concept that an ACL applied to the wrong interface or direction can cause selective service failures, leading candidates to mistakenly focus on missing permit statements or the implicit deny rather than the ACL placement.
Detailed technical explanation
How to think about this question
In Cisco IOS, ACLs are applied to interfaces in a specific direction (inbound or outbound) relative to the router. When an ACL is applied inbound on the inside interface, it filters traffic entering the router from the internal network; if it only permits HTTP, outbound HTTPS packets are dropped. Conversely, if applied outbound on the outside interface, it filters traffic leaving the router toward the internet, which would not affect internal users' outbound requests. The implicit deny at the end of every ACL is a standard behavior (RFC 1700), but it only blocks traffic that reaches the ACL; if the ACL is applied in the wrong direction, the traffic never hits the permit statements correctly.
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 security analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CC question in full detail.
Business Continuity, DR & Incident Response — This question tests Business Continuity, DR & Incident Response — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The ACL is applied to the wrong interface or direction. — The exhibit shows an ACL that permits HTTP (TCP 80) but does not explicitly permit HTTPS (TCP 443). However, the question states that HTTP works and HTTPS does not, which suggests the ACL is correctly filtering inbound traffic on the outside interface. The most likely cause is that the ACL is applied to the wrong interface or direction, because if it were applied inbound on the inside interface, it would block outbound HTTPS traffic from the 192.168.1.0/24 network. The implicit deny at the end of the ACL would block any traffic not explicitly permitted, but since HTTP works, the issue is not the implicit deny itself but rather the placement of the ACL.
What should I do if I get this CC question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
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 CC practice question is part of Courseiva's free ISC2 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 CC 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.