This ANS-C01 practice question tests your understanding of network implementation. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 public and private subnets across two Availability Zones. They have a Network Load Balancer (NLB) in the public subnets. The NLB has a target group of EC2 instances in the private subnets. The NLB is configured with TLS listeners and uses a certificate from AWS Certificate Manager (ACM). Clients connect to the NLB over the internet. Some clients report connection timeouts. The NLB access logs show that the connections are established but then hang. The target instances are healthy. The security groups for the instances allow inbound TCP/443 from the NLB's private IPs. 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 target group is configured with protocol TLS instead of TCP
NLB with TLS termination requires that the target group uses TCP protocol (not TLS) because NLB terminates TLS and forwards plain TCP to targets. If the target group is configured with TLS protocol, the NLB will attempt to initiate a TLS handshake with the targets, which may fail if targets are not expecting TLS (or if certificates mismatch). This can cause connections to hang. Option B (cross-zone load balancing) would not cause hang. Option C (idle timeout) would cause disconnects, not hang. Option D (security group) is correct as described.
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 configured with protocol TLS instead of TCP
Cross-zone load balancing is disabled, causing uneven distribution
Why it's wrong here
Would cause some instances to receive no traffic, not hang.
✗
The security group for the NLB is blocking traffic from clients
Why it's wrong here
NLB does not use security groups; it's layer 4.
✗
The NLB idle timeout is set too low
Why it's wrong here
Would cause disconnects, not hang.
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 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.
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 Implementation — This question tests Network Implementation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The target group is configured with protocol TLS instead of TCP — NLB with TLS termination requires that the target group uses TCP protocol (not TLS) because NLB terminates TLS and forwards plain TCP to targets. If the target group is configured with TLS protocol, the NLB will attempt to initiate a TLS handshake with the targets, which may fail if targets are not expecting TLS (or if certificates mismatch). This can cause connections to hang. Option B (cross-zone load balancing) would not cause hang. Option C (idle timeout) would cause disconnects, not hang. Option D (security group) is correct as described.
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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