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Network Security, Compliance and Governance →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the ALB security group is not set as the source for inbound traffic; instead, traffic reaches the ALB directly from the internet. This occurs because an internet-facing Application Load Balancer has public IP addresses and its nodes reside in public subnets, meaning the security group rules are applied to the ALB’s elastic network interfaces, not to the listener itself. If the security group allows traffic only from a VPN CIDR but the ALB is still reachable from the internet, the most likely cause is that the security group is either misconfigured to allow 0.0.0.0/0 as a secondary rule or is not attached to the ALB’s ENIs at all. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding that security groups for ALBs operate at the network interface level, not the DNS or listener level—a common trap is assuming the security group alone blocks internet traffic when the ALB is internet-facing. Remember: security groups are stateful firewalls for ENIs, not for the ALB’s public DNS endpoint. Memory tip: “SG on the ENI, not on the listener—if the ALB is public, the SG must explicitly deny the internet.”

ANS-C01 Network Security, Compliance and Governance Practice Question

This ANS-C01 practice question tests your understanding of network security, compliance and governance. 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 runs a web application on EC2 instances behind an Application Load Balancer (ALB). The application must be accessible only from a specific AWS Client VPN endpoint. The security team has configured the ALB security group to allow inbound traffic from the Client VPN CIDR range, but users report that they can still access the application from outside the VPN. What is the MOST likely cause of this issue?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

Question 1mediummultiple choice

Read the full VPN explanation →

A
The ALB security group is not set as the source for inbound traffic; instead, traffic reaches the ALB directly from the internet.
If the ALB security group does not restrict inbound traffic, traffic can bypass the Client VPN.
B
The network ACL is stateless and requires separate inbound and outbound rules for return traffic.
Why wrong: NACL statelessness is not the issue here; the problem is with the ALB security group.
C
The subnet's network ACL allows inbound HTTP/HTTPS traffic from 0.0.0.0/0.
Why wrong: Network ACLs apply to all traffic entering the subnet, but the ALB security group should be the primary control.
D
The EC2 instances' security group allows inbound traffic from 0.0.0.0/0.
Why wrong: The EC2 security group is not the first line of defense; the ALB security group controls access to the ALB.

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

✓

The ALB security group is not set as the source for inbound traffic; instead, traffic reaches the ALB directly from the internet.

Option A is correct because the ALB security group is configured to allow inbound traffic from the Client VPN CIDR range, but if the ALB itself is internet-facing (i.e., it has public IP addresses and is deployed in public subnets), traffic can bypass the security group rules if the security group is not actually applied to the ALB's network interfaces. The most likely cause is that the ALB security group is not set as the source for inbound traffic; instead, traffic reaches the ALB directly from the internet, meaning the security group rules are not being enforced on the ALB's listener. This allows users outside the VPN to access the application because the ALB accepts traffic from any source unless the security group explicitly restricts it.

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 ALB security group is not set as the source for inbound traffic; instead, traffic reaches the ALB directly from the internet.
Why this is correct
If the ALB security group does not restrict inbound traffic, traffic can bypass the Client VPN.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The network ACL is stateless and requires separate inbound and outbound rules for return traffic.
Why it's wrong here
NACL statelessness is not the issue here; the problem is with the ALB security group.
✗
The subnet's network ACL allows inbound HTTP/HTTPS traffic from 0.0.0.0/0.
Why it's wrong here
Network ACLs apply to all traffic entering the subnet, but the ALB security group should be the primary control.
✗
The EC2 instances' security group allows inbound traffic from 0.0.0.0/0.
Why it's wrong here
The EC2 security group is not the first line of defense; the ALB security group controls access to the ALB.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates assume the ALB security group is automatically enforced, but Cisco tests the nuance that an internet-facing ALB can still receive traffic from the internet if the security group is not properly applied or if the ALB is not configured to restrict traffic to the VPN CIDR.

Detailed technical explanation

How to think about this question

An internet-facing ALB has public IP addresses on its network interfaces and accepts traffic directly from the internet. The ALB's security group acts as a virtual firewall for the ALB's endpoints; if the security group is not applied to the ALB's network interfaces (e.g., if it is misconfigured or missing), the ALB will accept traffic from any source. Under the hood, the ALB's listener evaluates incoming connections against the security group rules; if the security group is not attached, the default behavior is to allow all traffic. In a real-world scenario, this often occurs when the security group is created but not associated with the ALB, or when the ALB is deployed in a public subnet without proper security group assignment.

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.

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FAQ

Questions learners often ask

What does this ANS-C01 question test?

Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The ALB security group is not set as the source for inbound traffic; instead, traffic reaches the ALB directly from the internet. — Option A is correct because the ALB security group is configured to allow inbound traffic from the Client VPN CIDR range, but if the ALB itself is internet-facing (i.e., it has public IP addresses and is deployed in public subnets), traffic can bypass the security group rules if the security group is not actually applied to the ALB's network interfaces. The most likely cause is that the ALB security group is not set as the source for inbound traffic; instead, traffic reaches the ALB directly from the internet, meaning the security group rules are not being enforced on the ALB's listener. This allows users outside the VPN to access the application because the ALB accepts traffic from any source unless the security group explicitly restricts it.

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.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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