The correct answer is that network ACL rule 100 denies traffic from 10.0.0.0/8, which includes the source IP 10.0.1.5, so the traffic is denied. This is because network ACL rule order evaluation follows a first-match determination principle: rules are evaluated in ascending order by number, and the first rule that matches the traffic dictates the action, regardless of any subsequent allow rules. Since network ACLs are stateless, they do not track connection state, so a deny on rule 100 immediately blocks the traffic. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this concept tests your understanding of stateless filtering and the critical importance of rule numbering—a common trap is assuming later allow rules override earlier denies. Remember the memory tip: “First match wins, so number your denies low.”
ANS-C01 Network Design Practice Question
This ANS-C01 practice question tests your understanding of network design. 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.
Network Topology
A network administrator is troubleshooting connectivity to a web server in subnet with network ACL 'acl-12345678'. The web server is on port 443. The administrator finds that traffic from IP 10.0.1.5 is being denied. Why is the traffic being denied?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The network ACL rule 100 denies traffic from 10.0.0.0/8, which includes the IP 10.0.1.5.
Option C is correct because network ACLs are stateless and evaluated in ascending order by rule number. Rule 100 denies traffic from 10.0.0.0/8, which includes the source IP 10.0.1.5, so any traffic from that IP is denied regardless of later allow rules. Since network ACLs do not track connection state, the deny is applied immediately upon matching rule 100.
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 subnet is not associated with this network ACL.
Why it's wrong here
Assuming it is associated.
✗
The security group attached to the web server is blocking the traffic.
Why it's wrong here
Not indicated in exhibit.
✓
The network ACL rule 100 denies traffic from 10.0.0.0/8, which includes the IP 10.0.1.5.
Why this is correct
Rule 100 matches and denies.
Related concept
Read the scenario before looking for a memorised answer.
✗
The network ACL rule 100 allows traffic from 0.0.0.0/0, but rule 200 denies traffic from 10.0.0.0/8, and rule 200 is evaluated first.
Why it's wrong here
Rule 100 is lower number and evaluated first.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the evaluation order of network ACL rules (ascending by rule number) with the order of security group rules (all evaluated until a match), or mistakenly think that a higher-numbered allow rule overrides a lower-numbered deny rule.
Detailed technical explanation
How to think about this question
Network ACLs are stateless packet filters applied at the subnet boundary, meaning each packet is evaluated independently without regard to connection state. Rule numbers (e.g., 100, 200) determine evaluation order, with lower numbers processed first; AWS recommends incrementing rules by 100 to allow insertion of new rules later. In real-world scenarios, a common misconfiguration is placing a broad deny rule (e.g., 10.0.0.0/8) with a low rule number, inadvertently blocking legitimate traffic from a subset of that range.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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.
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The network ACL rule 100 denies traffic from 10.0.0.0/8, which includes the IP 10.0.1.5. — Option C is correct because network ACLs are stateless and evaluated in ascending order by rule number. Rule 100 denies traffic from 10.0.0.0/8, which includes the source IP 10.0.1.5, so any traffic from that IP is denied regardless of later allow rules. Since network ACLs do not track connection state, the deny is applied immediately upon matching rule 100.
What should I do if I get this ANS-C01 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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