- A
Modify the network ACL to deny traffic from that IP.
Why wrong: Incorrect because network ACLs apply at the subnet level, not the instance level. They cannot block traffic to a specific instance.
- B
Use AWS WAF to block the IP address.
Why wrong: Incorrect because AWS WAF is used to protect web applications from common web exploits and is associated with ALB, CloudFront, or API Gateway, not directly with an EC2 instance.
- C
Install a third-party firewall on the instance.
Correct because a third-party firewall installed on the instance can block traffic from a specific IP at the operating system level, fulfilling the 'instance level' requirement.
- D
Update the security group to deny traffic from that IP.
Why wrong: Incorrect because security groups only allow traffic and cannot explicitly deny traffic from a specific IP address.
SOA-C02 Instance-level firewall Practice Question
This SOA-C02 practice question tests your understanding of security and compliance. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: instance-level firewall. 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 an EC2 instance running a web server is receiving unexpected traffic from an IP address that is known to be malicious. The administrator wants to block this IP address at the instance level. Which solution should be used?
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
Install a third-party firewall on the instance.
Option C is correct because a host-based firewall (such as a third-party firewall installed on the instance) can block traffic from a specific IP address at the instance level. Option A is incorrect because network ACLs operate at the subnet level, not the instance level. Option B is incorrect because AWS WAF is designed to filter web requests at the application layer and is typically associated with load balancers or CloudFront, not directly with an individual EC2 instance. Option D is incorrect because security groups do not support deny rules; they only allow traffic, so they cannot be used to block specific IPs.
Key principle: Instance-level firewall
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Modify the network ACL to deny traffic from that IP.
Why it's wrong here
Incorrect because network ACLs apply at the subnet level, not the instance level. They cannot block traffic to a specific instance.
- ✗
Use AWS WAF to block the IP address.
Why it's wrong here
Incorrect because AWS WAF is used to protect web applications from common web exploits and is associated with ALB, CloudFront, or API Gateway, not directly with an EC2 instance.
- ✓
Install a third-party firewall on the instance.
- ✗
Update the security group to deny traffic from that IP.
Why it's wrong here
Incorrect because security groups only allow traffic and cannot explicitly deny traffic from a specific IP address.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The question specifies 'at the instance level,' which disqualifies subnet-level solutions like network ACLs. Candidates often overlook this detail and choose NACLs because they support explicit deny.
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
- Instance-level firewall
- Network ACL
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
Instance-level firewall
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
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
What to study next
Got this wrong? Here's your next step.
Review instance-level firewall, then practise related SOA-C02 questions on the same topic to reinforce the concept.
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Security and Compliance — study guide chapter
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FAQ
Questions learners often ask
What does this SOA-C02 question test?
Security and Compliance — This question tests Security and Compliance — Instance-level firewall.
What is the correct answer to this question?
The correct answer is: Install a third-party firewall on the instance. — Option C is correct because a host-based firewall (such as a third-party firewall installed on the instance) can block traffic from a specific IP address at the instance level. Option A is incorrect because network ACLs operate at the subnet level, not the instance level. Option B is incorrect because AWS WAF is designed to filter web requests at the application layer and is typically associated with load balancers or CloudFront, not directly with an individual EC2 instance. Option D is incorrect because security groups do not support deny rules; they only allow traffic, so they cannot be used to block specific IPs.
What should I do if I get this SOA-C02 question wrong?
Review instance-level firewall, then practise related SOA-C02 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Instance-level firewall
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Last reviewed: Jun 20, 2026
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