The answer is that the ACL is not blocking traffic because the deny line has 0 matches. This output indicates that no packets have been evaluated against that specific deny entry, meaning the rule is effectively inactive despite being applied inbound on the external interface. In ACL processing, counters increment only when a packet matches a given line; a zero match count for a deny rule targeting traffic to a malicious host on port 443 proves that no such traffic has been inspected by that rule. On the Cisco CyberOps Associate 200-201 exam, this scenario tests your ability to interpret ACL counters as operational evidence, not just configuration—a common trap is assuming a configured ACL is automatically blocking traffic without verifying the match counters. Remember the memory tip: "Zero matches means zero blocks; counters tell the story, not the config."
200-201 Security Monitoring Practice Question
This 200-201 practice question tests your understanding of security monitoring. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.
```
Router# show ip access-lists
Extended IP access list BLOCK_MALICIOUS
10 deny tcp any host 203.0.113.5 eq 443
20 permit ip any any (2623 matches)
```
Refer to the exhibit. An analyst configures an ACL to block traffic to a malicious host on port 443. After applying it inbound on the external interface, the analyst sees the ACL counters. What does the output indicate?
Refer to the exhibit.
```
Router# show ip access-lists
Extended IP access list BLOCK_MALICIOUS
10 deny tcp any host 203.0.113.5 eq 443
20 permit ip any any (2623 matches)
```
A
The ACL is working correctly; traffic to the malicious host is blocked.
Why wrong: Deny line has no matches, so no traffic is being denied.
B
The ACL is not blocking traffic because the deny line has 0 matches.
Indicates the rule is not being hit; possible wrong direction.
C
The ACL needs to be applied outbound to work.
Why wrong: Could be, but the exhibit does not specify direction.
D
The ACL is blocking all traffic because the permit line is never used.
Why wrong: Permit line has matches; traffic is passing.
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 not blocking traffic because the deny line has 0 matches.
Option B is correct because the ACL counters show 0 matches for the deny line that is intended to block traffic to the malicious host on port 443. This indicates that no traffic matching the deny condition has been processed by the ACL, meaning the rule is not being triggered. Since the ACL is applied inbound on the external interface, traffic from the external network destined for the malicious host should match the deny line if it is correctly configured; the 0 matches suggest the ACL is not blocking the intended 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.
✗
The ACL is working correctly; traffic to the malicious host is blocked.
Why it's wrong here
Deny line has no matches, so no traffic is being denied.
✓
The ACL is not blocking traffic because the deny line has 0 matches.
Why this is correct
Indicates the rule is not being hit; possible wrong direction.
Related concept
Read the scenario before looking for a memorised answer.
✗
The ACL needs to be applied outbound to work.
Why it's wrong here
Could be, but the exhibit does not specify direction.
✗
The ACL is blocking all traffic because the permit line is never used.
Why it's wrong here
Permit line has matches; traffic is passing.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that an ACL with 0 matches on a deny line is still blocking traffic, when in fact the counters prove the rule is not being hit, so the traffic is passing through unblocked.
Detailed technical explanation
How to think about this question
ACL counters increment only when a packet matches a specific ACE (Access Control Entry). In this scenario, the 0 matches on the deny line could be due to incorrect source/destination IP addresses, wrong port specification (e.g., using 'eq 443' instead of 'eq https'), or the traffic not traversing the interface where the ACL is applied. In real-world deployments, ACLs are often misconfigured with reversed source/destination fields, especially when applied inbound on an external interface, where the source should be the external host and the destination the internal host.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security Monitoring — This question tests Security Monitoring — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The ACL is not blocking traffic because the deny line has 0 matches. — Option B is correct because the ACL counters show 0 matches for the deny line that is intended to block traffic to the malicious host on port 443. This indicates that no traffic matching the deny condition has been processed by the ACL, meaning the rule is not being triggered. Since the ACL is applied inbound on the external interface, traffic from the external network destined for the malicious host should match the deny line if it is correctly configured; the 0 matches suggest the ACL is not blocking the intended traffic.
What should I do if I get this 200-201 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.
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