- A
Enable Proxy Protocol v2 on the NLB target group.
Why wrong: Proxy Protocol adds a header but is not required for source IP preservation; NLB preserves IP by default.
- B
Enable cross-zone load balancing on the NLB.
Why wrong: Cross-zone load balancing distributes traffic across AZs but does not affect source IP preservation.
- C
Attach a security group to the NLB that allows inbound traffic from the client IP range.
Why wrong: NLBs do not use security groups; they are not stateful.
- D
Create the NLB with a TCP listener and register the EC2 instances as targets in a target group.
NLB preserves source IP for TCP traffic when targets are instances.
Question 1,699 of 1,705
NLB Source IP Preservation — TCP Listener Default Behavior
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 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
✓
Create the NLB with a TCP listener and register the EC2 instances as targets in a target group.
Network Load Balancers (NLBs) preserve the source IP address of clients by default when using a TCP listener. No additional configuration is required to enable this behavior; the NLB forwards packets with the original source IP intact. Therefore, simply creating the NLB with a TCP listener and registering EC2 instances as targets is sufficient.
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.
- ✗
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.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The ANS-C01 exam often tests the misconception that Proxy Protocol v2 must be enabled for source IP preservation on an NLB, when in fact NLBs preserve the source IP by default and Proxy Protocol is only needed for ALBs or when additional metadata is required.
Detailed technical explanation
How to think about this question
NLBs operate at Layer 4 and use a flow hash algorithm to route packets; they do not perform NAT on the source IP, so the original client IP is visible to the backend instances. This is in contrast to Application Load Balancers (ALBs), which terminate the TCP connection and replace the source IP with their own private IP unless X-Forwarded-For headers are used. In real-world scenarios, this is critical for applications that require client IP logging or geo-location without additional proxy configuration.
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
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.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..
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. — Network Load Balancers (NLBs) preserve the source IP address of clients by default when using a TCP listener. No additional configuration is required to enable this behavior; the NLB forwards packets with the original source IP intact. Therefore, simply creating the NLB with a TCP listener and registering EC2 instances as targets is sufficient.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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