ANS-C01 Network Management and Operations 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. 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 has a VPC with an Application Load Balancer (ALB) in front of EC2 instances. The security group for the ALB allows inbound HTTP traffic from 0.0.0.0/0. The security group for the EC2 instances allows inbound traffic only from the ALB security group. However, the health checks are failing. What is the most likely cause?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The EC2 security group does not allow inbound traffic from the ALB security group
Option C is correct because ALB health checks come from the ALB's private IP addresses, which are in the VPC CIDR; the security group must allow traffic from the ALB security group, not from the internet. Option A is wrong because the ALB security group is correct. Option B is wrong because the ALB subnet is not relevant. Option D is wrong because the target group configuration is separate.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 target group is not configured with the correct health check path
Why it's wrong here
While possible, the most likely cause is security group misconfiguration.
✗
The ALB is in a private subnet
Why it's wrong here
ALB can be in private or public; health checks still work.
✓
The EC2 security group does not allow inbound traffic from the ALB security group
Why this is correct
Health checks originate from ALB; security group must allow from ALB.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The ALB security group does not allow outbound traffic
Why it's wrong here
Security groups are stateful; outbound is allowed by default.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Management and Operations — This question tests Network Management and Operations — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The EC2 security group does not allow inbound traffic from the ALB security group — Option C is correct because ALB health checks come from the ALB's private IP addresses, which are in the VPC CIDR; the security group must allow traffic from the ALB security group, not from the internet. Option A is wrong because the ALB security group is correct. Option B is wrong because the ALB subnet is not relevant. Option D is wrong because the target group configuration is separate.
What should I do if I get this ANS-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
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?
CIDR notation defines the prefix length.
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