The answer is that ACL hit counts not incrementing for expected traffic is a key symptom of a misconfigured IPv4 ACL. This occurs because a router processes ACL entries sequentially, so if a deny statement appears before a permit statement for the same traffic, the permit rule is never reached, causing legitimate packets to be silently dropped without incrementing the expected hit counter. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your ability to troubleshoot ACL application direction and entry order, often appearing in scenario-based questions where traffic fails to pass despite a seemingly correct permit line. A common trap is assuming an ACL is working simply because it is applied to an interface, but the hit counts reveal the truth. Remember the memory tip: "If the hits don't match the traffic, your ACL logic is tragic."
300-410 IPv4 Access Control Lists Practice Question
This 300-410 practice question tests your understanding of ipv4 access control lists. 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.
Which THREE symptoms indicate that an IPv4 access control list may be misconfigured or not applied correctly? (Choose THREE.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Traffic that should be permitted is being blocked.
Option A is correct because a primary symptom of a misconfigured or incorrectly applied ACL is that it blocks traffic that should be permitted. This typically occurs when the ACL's sequence of permit and deny statements does not match the intended policy, or when the ACL is applied in the wrong direction (inbound vs. outbound) on an interface. The router processes ACL entries sequentially, so a deny statement placed before a permit statement for the same traffic will cause legitimate packets to be dropped.
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.
✓
Traffic that should be permitted is being blocked.
Why this is correct
This indicates the ACL may have an incorrect deny statement or order.
Related concept
Read the scenario before looking for a memorised answer.
✗
The interface is flapping up and down.
Why it's wrong here
Interface flapping is usually due to physical or Layer 2 issues, not ACLs.
✓
High CPU utilization on the router due to ACL processing.
Why this is correct
Inefficient or large ACLs can cause high CPU, especially with logging enabled.
Related concept
Read the scenario before looking for a memorised answer.
✓
ACL hit counts are not incrementing for expected traffic.
Why this is correct
This suggests the ACL may not be applied to the correct interface or direction.
Related concept
Read the scenario before looking for a memorised answer.
✗
Routing protocol neighbors are dropping.
Why it's wrong here
Neighbor drops are usually due to protocol timers, authentication, or MTU issues, not ACLs.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between direct symptoms of ACL misconfiguration (blocking permitted traffic, no hit counts, high CPU) and indirect or unrelated issues (interface flapping, neighbor drops) that candidates might incorrectly associate with ACLs due to a superficial understanding of ACL behavior.
Detailed technical explanation
How to think about this question
ACL hit counts are maintained per entry in the ACL and can be viewed with the 'show access-lists' command. If expected traffic does not increment the hit count, it suggests the ACL is not being matched—either because it is applied to the wrong interface, in the wrong direction, or because the traffic does not match any entry (e.g., due to incorrect source/destination IPs or port numbers). High CPU utilization due to ACL processing occurs when ACLs are very long or when the router must process many packets through the ACL, especially if the ACL is applied to a high-traffic interface; this can indicate that the ACL is not optimized (e.g., frequently matched entries should be placed earlier) or that it is applied where not needed.
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 network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
IPv4 Access Control Lists — This question tests IPv4 Access Control Lists — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Traffic that should be permitted is being blocked. — Option A is correct because a primary symptom of a misconfigured or incorrectly applied ACL is that it blocks traffic that should be permitted. This typically occurs when the ACL's sequence of permit and deny statements does not match the intended policy, or when the ACL is applied in the wrong direction (inbound vs. outbound) on an interface. The router processes ACL entries sequentially, so a deny statement placed before a permit statement for the same traffic will cause legitimate packets to be dropped.
What should I do if I get this 300-410 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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