This CC practice question tests your understanding of network security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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
Mar 15 14:23:45 192.168.1.1 %FW-3-DENY: deny tcp 10.0.0.10:12345 -> 203.0.113.5:80 due to access-group INTERNET_IN
Refer to the exhibit. Based on the exhibit, why was the packet denied?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The packet was blocked by an inbound access list
The exhibit shows an inbound access list applied to the interface, and the packet is denied because its source IP matches a deny entry in that inbound ACL. Inbound access lists filter traffic before it is processed by the router, so the packet is dropped upon arrival. The correct answer is D because the packet was blocked by an inbound access list, as indicated by the ACL configuration and the deny action.
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.
✗
Source IP is internal
Why it's wrong here
The source IP 10.0.0.10 is internal, but that is not the reason for denial; the access list denied it.
✗
The packet was blocked by an outbound access list
Why it's wrong here
The access-group is named INTERNET_IN, indicating it is an inbound access list.
✗
Destination IP is external
Why it's wrong here
The destination is external (203.0.113.5), but that alone does not cause denial; the access list rule caused it.
✓
The packet was blocked by an inbound access list
Why this is correct
The message specifies 'due to access-group INTERNET_IN', which is applied inbound.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the distinction between inbound and outbound ACLs, and the trap here is that candidates may confuse the direction of the ACL application (inbound vs. outbound) or assume that a packet is denied because of the source or destination IP alone, rather than focusing on the ACL rule that explicitly denies the traffic.
Detailed technical explanation
How to think about this question
Inbound ACLs on Cisco routers process packets immediately upon ingress, before any routing decision is made, which can conserve CPU resources by dropping unwanted traffic early. The ACL is evaluated sequentially from top to bottom, and the first matching entry (permit or deny) determines the action; if no match is found, an implicit deny all at the end blocks the packet. In real-world scenarios, inbound ACLs are commonly used on external interfaces to block malicious traffic before it enters the network, reducing the load on internal security devices.
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.
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The packet was blocked by an inbound access list — The exhibit shows an inbound access list applied to the interface, and the packet is denied because its source IP matches a deny entry in that inbound ACL. Inbound access lists filter traffic before it is processed by the router, so the packet is dropped upon arrival. The correct answer is D because the packet was blocked by an inbound access list, as indicated by the ACL configuration and the deny action.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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