This ANS-C01 practice question tests your understanding of network implementation. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 multiple subnets across three Availability Zones. The company wants to deploy a Network Load Balancer (NLB) to distribute TCP traffic to a fleet of EC2 instances. The NLB must preserve the source IP address of the client. Which configuration is required?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create the NLB with a TCP listener and register the EC2 instances as targets in a target group.
Option A is correct because NLB preserves the source IP address by default when using TCP traffic and target group with instance targets. Option B is wrong because enabling Proxy Protocol would add a proxy header, but NLB still preserves source IP. Option C is wrong because an NLB does not use security groups. Option D is wrong because cross-zone load balancing does not affect source IP preservation.
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.
✗
Enable Proxy Protocol v2 on the NLB target group.
Why it's wrong here
Proxy Protocol adds a header but is not required for source IP preservation; NLB preserves IP by default.
✗
Enable cross-zone load balancing on the NLB.
Why it's wrong here
Cross-zone load balancing distributes traffic across AZs but does not affect source IP preservation.
✗
Attach a security group to the NLB that allows inbound traffic from the client IP range.
Why it's wrong here
NLBs do not use security groups; they are not stateful.
✓
Create the NLB with a TCP listener and register the EC2 instances as targets in a target group.
Why this is correct
NLB preserves source IP for TCP traffic when targets are instances.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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: Create the NLB with a TCP listener and register the EC2 instances as targets in a target group. — Option A is correct because NLB preserves the source IP address by default when using TCP traffic and target group with instance targets. Option B is wrong because enabling Proxy Protocol would add a proxy header, but NLB still preserves source IP. Option C is wrong because an NLB does not use security groups. Option D is wrong because cross-zone load balancing does not affect source IP preservation.
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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