The answer is NLB, because it preserves the client source IP by default, while GWLB does not. NLB operates at Layer 4 and forwards packets directly to targets, keeping the original source IP intact—critical for applications that log or process client addresses. GWLB, in contrast, uses GENEVE encapsulation on UDP port 6081 to tunnel traffic to backend appliances, which replaces the client source IP with the NLB’s private IP unless you explicitly configure Proxy Protocol. On the ANS-C01 exam, this distinction tests your understanding of how each load balancer handles traffic flow and IP preservation, especially in migration scenarios requiring low latency and many short-lived TCP connections. A common trap is assuming both preserve source IP equally; remember that GWLB’s encapsulation inherently obscures it. Memory tip: “NLB keeps it real; GWLB keeps it sealed.”
ANS-C01 Network Design Practice Question
This ANS-C01 practice question tests your understanding of network design. 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 is migrating a legacy on-premises application to AWS. The application uses a large number of short-lived TCP connections and requires low latency. The network team is considering using either a Network Load Balancer (NLB) or a Gateway Load Balancer (GWLB). Which of the following is a key advantage of using NLB over GWLB for this use case?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
NLB preserves the client source IP, while GWLB does not by default.
For an application using a large number of short-lived TCP connections requiring low latency, NLB is the optimal choice because it operates at Layer 4 and preserves the client source IP address by default, which is critical for applications that need to log or process the original client IP. GWLB, by design, uses GENEVE encapsulation (UDP port 6081) to tunnel traffic to backend appliances, which replaces the client source IP with the NLB's private IP unless explicit configuration (e.g., proxy protocol) is used. This makes NLB the better fit for preserving source IP without additional overhead.
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.
✗
NLB can forward traffic to third-party virtual appliances.
Why it's wrong here
GWLB is specifically designed for that purpose, not NLB.
✗
NLB can handle higher throughput than GWLB.
Why it's wrong here
Both can handle high throughput; NLB is not necessarily higher.
✓
NLB preserves the client source IP, while GWLB does not by default.
Why this is correct
NLB preserves source IP; GWLB uses GENEVE encapsulation and hides original source IP.
Related concept
Read the scenario before looking for a memorised answer.
✗
NLB supports TLS termination, while GWLB does not.
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse GWLB's transparent inline appliance support with NLB's source IP preservation, assuming that GWLB also preserves source IP by default, when in fact it uses GENEVE encapsulation that obscures the original client IP unless additional configuration is applied.
Detailed technical explanation
How to think about this question
NLB preserves the client source IP by using the same IP header in the forwarded packets, which is essential for applications that rely on source IP-based logging, security rules, or session affinity. In contrast, GWLB encapsulates traffic using GENEVE (RFC 8926) with a 42-byte header, which hides the original client IP unless the appliance or target explicitly parses the GENEVE header or uses proxy protocol v2. For short-lived TCP connections, the additional encapsulation overhead of GWLB can also introduce slight latency and packet processing overhead, making NLB more suitable for low-latency requirements.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: NLB preserves the client source IP, while GWLB does not by default. — For an application using a large number of short-lived TCP connections requiring low latency, NLB is the optimal choice because it operates at Layer 4 and preserves the client source IP address by default, which is critical for applications that need to log or process the original client IP. GWLB, by design, uses GENEVE encapsulation (UDP port 6081) to tunnel traffic to backend appliances, which replaces the client source IP with the NLB's private IP unless explicit configuration (e.g., proxy protocol) is used. This makes NLB the better fit for preserving source IP without additional overhead.
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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Question Discussion
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