- A
The instance's operating system firewall is blocking the traffic.
OS-level firewalls (e.g., iptables, Windows Firewall) can block traffic even if AWS firewalls allow it.
- B
The network ACL is not associated with the subnet correctly.
Why wrong: Since the NACL allows all traffic, association is not the issue.
- C
VPC Flow Logs are misconfigured.
Why wrong: Flow logs do not affect traffic; they only capture metadata.
- D
The route table does not have a default route to an internet gateway.
Why wrong: Route tables do not block inbound traffic; they route outbound traffic.
Question 407 of 1,546
SOA-C02 Networking and Content Delivery Practice Question
This SOA-C02 practice question tests your understanding of networking and content delivery. 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.
A SysOps administrator notices that traffic to an Amazon EC2 instance is being blocked even though the security group allows all inbound traffic. The subnet's network ACL allows all inbound and outbound traffic. What could be the issue?
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 instance's operating system firewall is blocking the traffic.
The security group and network ACL both allow all traffic, so the issue must be at the instance level. The operating system's built-in firewall (e.g., iptables for Linux, Windows Firewall for Windows) can block inbound traffic independently of AWS networking constructs. Since the OS firewall is not managed by AWS, it can override security group rules, causing traffic to be dropped even when AWS-side configurations are permissive.
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 instance's operating system firewall is blocking the traffic.
Why this is correct
OS-level firewalls (e.g., iptables, Windows Firewall) can block traffic even if AWS firewalls allow it.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The network ACL is not associated with the subnet correctly.
Why it's wrong here
Since the NACL allows all traffic, association is not the issue.
- ✗
VPC Flow Logs are misconfigured.
Why it's wrong here
Flow logs do not affect traffic; they only capture metadata.
- ✗
The route table does not have a default route to an internet gateway.
Why it's wrong here
Route tables do not block inbound traffic; they route outbound traffic.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume AWS-side controls (security groups and network ACLs) are the only layers that can block traffic, overlooking the instance's own OS firewall, which operates independently and can override permissive AWS rules.
Detailed technical explanation
How to think about this question
Under the hood, the OS firewall operates at Layer 4 (transport layer) or Layer 3 (network layer) and can filter based on port, protocol, source IP, or state. For example, iptables rules in Linux are evaluated before the application receives the packet, and a default DROP policy on the INPUT chain will silently discard traffic even if AWS security groups allow it. In a real-world scenario, a SysOps administrator might enable the Windows Firewall with default block rules after provisioning an EC2 instance, causing RDP or HTTP access to fail despite correct security group settings.
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.
Visual reference
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.
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FAQ
Questions learners often ask
What does this SOA-C02 question test?
Networking and Content Delivery — This question tests Networking and Content Delivery — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The instance's operating system firewall is blocking the traffic. — The security group and network ACL both allow all traffic, so the issue must be at the instance level. The operating system's built-in firewall (e.g., iptables for Linux, Windows Firewall for Windows) can block inbound traffic independently of AWS networking constructs. Since the OS firewall is not managed by AWS, it can override security group rules, causing traffic to be dropped even when AWS-side configurations are permissive.
What should I do if I get this SOA-C02 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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Last reviewed: Jul 4, 2026
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