- A
The security group is blocking SSH traffic
Why wrong: Incorrect. The security group allows inbound SSH, so it is not blocking the traffic.
- B
The network ACL is not associated with the subnet
Why wrong: Incorrect. The subnet is associated with the network ACL shown; if no custom NACL were associated, the default NACL (allow all) would apply, but the custom NACL is associated as per the question.
- C
The network ACL has a rule that denies all traffic (rule 300) which overrides the allow rule
Why wrong: Incorrect. While rule 300 denies all traffic, it is evaluated after rule 100 and rule 200. Since rule 100 does not match SSH and rule 200 matches and denies, rule 300 is not reached for SSH traffic.
- D
The network ACL rule 200 denies SSH traffic, overriding rule 100
Correct. The network ACL has rule 200 that explicitly denies SSH traffic. Because rule 100 only allows HTTP, not SSH, rule 200 is the first matching rule for SSH and denies it.
ANS-C01 NACL Rule Evaluation Order Practice Question
This ANS-C01 practice question tests your understanding of network management and operations. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: nACL Rule Evaluation Order. 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.
A network engineer is troubleshooting SSH connectivity to an EC2 instance in subnet subnet-0abcd1234efgh5678, which is associated with the network ACL shown. The security group allows inbound SSH. Why can't the engineer SSH to the instance?
Answer choices
Why each option matters
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 200 denies SSH traffic, overriding rule 100
The correct answer is D. The network ACL exhibit shows inbound rule 100 allowing HTTP traffic (port 80) and rule 200 denying SSH traffic (port 22). Since NACL rules are evaluated in ascending order, when an SSH packet arrives, rule 100 does not match (it allows HTTP, not SSH), so rule 200 matches and denies the traffic. Thus, SSH is blocked. Option A is wrong because the security group allows SSH. Option B is wrong because the subnet is associated with the NACL as stated. Option C is wrong because rule 300 is a higher-numbered rule and would only be evaluated if no earlier rule matched; here rule 200 already matches and denies SSH.
Key principle: NACL Rule Evaluation Order
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 security group is blocking SSH traffic
Why it's wrong here
Incorrect. The security group allows inbound SSH, so it is not blocking the traffic.
- ✗
The network ACL is not associated with the subnet
Why it's wrong here
Incorrect. The subnet is associated with the network ACL shown; if no custom NACL were associated, the default NACL (allow all) would apply, but the custom NACL is associated as per the question.
- ✗
The network ACL has a rule that denies all traffic (rule 300) which overrides the allow rule
Why it's wrong here
Incorrect. While rule 300 denies all traffic, it is evaluated after rule 100 and rule 200. Since rule 100 does not match SSH and rule 200 matches and denies, rule 300 is not reached for SSH traffic.
- ✓
The network ACL rule 200 denies SSH traffic, overriding rule 100
Common exam traps
Common exam trap: answer the scenario, not the keyword
Candidates often assume that an allow rule with a lower number always overrides a deny rule with a higher number. However, the allow rule must match the specific traffic; if it does not, the deny rule will apply.
Trap categories for this question
Command / output trap
Incorrect. The subnet is associated with the network ACL shown; if no custom NACL were associated, the default NACL (allow all) would apply, but the custom NACL is associated as per the question.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- NACL Rule Evaluation Order
- NACL vs Security Group
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
NACL Rule Evaluation Order
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.
Visual reference
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
What to study next
Got this wrong? Here's your next step.
Review nACL Rule Evaluation Order, then practise related ANS-C01 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Management and Operations — This question tests Network Management and Operations — NACL Rule Evaluation Order.
What is the correct answer to this question?
The correct answer is: The network ACL rule 200 denies SSH traffic, overriding rule 100 — The correct answer is D. The network ACL exhibit shows inbound rule 100 allowing HTTP traffic (port 80) and rule 200 denying SSH traffic (port 22). Since NACL rules are evaluated in ascending order, when an SSH packet arrives, rule 100 does not match (it allows HTTP, not SSH), so rule 200 matches and denies the traffic. Thus, SSH is blocked. Option A is wrong because the security group allows SSH. Option B is wrong because the subnet is associated with the NACL as stated. Option C is wrong because rule 300 is a higher-numbered rule and would only be evaluated if no earlier rule matched; here rule 200 already matches and denies SSH.
What should I do if I get this ANS-C01 question wrong?
Review nACL Rule Evaluation Order, then practise related ANS-C01 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
NACL Rule Evaluation Order
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Last reviewed: Jun 20, 2026
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