← SOA-C02·Amazon Web Services

Question 918 of 1,546

Networking and Content Delivery →hardMultiple ChoiceObjective-mapped

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 company is using an Application Load Balancer (ALB) to distribute traffic to a fleet of EC2 instances. The security team reports that the ALB is receiving a high number of requests with suspicious User-Agent strings. The SysOps team needs to block these requests at the load balancer level without changing the application code. Which action should be taken?

A
Modify the security group of the ALB to deny traffic from User-Agent strings.
Why wrong: Security groups operate at the network layer and cannot inspect HTTP headers like User-Agent. They can only filter traffic based on IP addresses and ports.
B
Update the target group health check to filter out suspicious User-Agent strings.
Why wrong: Target group health checks are used to determine the health of instances and do not inspect or filter incoming requests.
C
Add a listener rule on the ALB that checks the User-Agent header and returns a fixed response.
ALB listener rules can evaluate conditions such as the User-Agent header and perform actions like returning a fixed response, effectively blocking requests without changing application code.
D
Deploy AWS WAF and associate it with the ALB.
Why wrong: While AWS WAF can inspect HTTP headers and block requests, it is an additional service that adds cost and complexity. The question asks for an action at the load balancer level, and ALB rules provide a more direct solution.

Full breakdown with real-world context →

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

✓

Add a listener rule on the ALB that checks the User-Agent header and returns a fixed response.

Option C is correct because ALB listener rules can evaluate conditions like the User-Agent header and perform actions such as returning a fixed response, which effectively blocks requests. Option A is incorrect because security groups operate at the network layer and cannot inspect HTTP headers; they filter traffic based on IP addresses and ports. Option B is incorrect because target group health checks determine instance health and do not filter incoming requests based on headers. Option D is incorrect because while AWS WAF can inspect headers and block requests, it is a separate service that adds complexity and cost; the question asks for an action at the load balancer level, and ALB rules provide a simpler direct solution.

Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

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 security group of the ALB to deny traffic from User-Agent strings.
Why it's wrong here
Security groups operate at the network layer and cannot inspect HTTP headers like User-Agent. They can only filter traffic based on IP addresses and ports.
✗
Update the target group health check to filter out suspicious User-Agent strings.
Why it's wrong here
Target group health checks are used to determine the health of instances and do not inspect or filter incoming requests.
✓
Add a listener rule on the ALB that checks the User-Agent header and returns a fixed response.
Why this is correct
ALB listener rules can evaluate conditions such as the User-Agent header and perform actions like returning a fixed response, effectively blocking requests without changing application code.
Related concept
Standard ACLs match source addresses.
✗
Deploy AWS WAF and associate it with the ALB.
Why it's wrong here
While AWS WAF can inspect HTTP headers and block requests, it is an additional service that adds cost and complexity. The question asks for an action at the load balancer level, and ALB rules provide a more direct solution.

Common exam traps

Common exam trap: ACLs stop at the first match

ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.

Detailed technical explanation

How to think about this question

ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.

KKey Concepts to Remember

Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.

TExam Day Tips

Check inbound versus outbound direction.
Read the ACL from top to bottom.
Look for a broader permit or deny above the intended line.

Key takeaway

ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

Real-world example

How this comes up in practice

A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.

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 ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related SOA-C02 ACL questions on filtering logic and placement.

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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 — Standard ACLs match source addresses..

What is the correct answer to this question?

The correct answer is: Add a listener rule on the ALB that checks the User-Agent header and returns a fixed response. — Option C is correct because ALB listener rules can evaluate conditions like the User-Agent header and perform actions such as returning a fixed response, which effectively blocks requests. Option A is incorrect because security groups operate at the network layer and cannot inspect HTTP headers; they filter traffic based on IP addresses and ports. Option B is incorrect because target group health checks determine instance health and do not filter incoming requests based on headers. Option D is incorrect because while AWS WAF can inspect headers and block requests, it is a separate service that adds complexity and cost; the question asks for an action at the load balancer level, and ALB rules provide a simpler direct solution.

What should I do if I get this SOA-C02 question wrong?

What is the key concept behind this question?

Standard ACLs match source addresses.

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