The answer is to enable cross-zone load balancing on the NLB (which is on by default) and set the ALB idle timeout to a fixed value. Cross-zone load balancing ensures that each NLB node distributes traffic evenly across targets in all three Availability Zones, preventing uneven load distribution and supporting high availability. The ALB idle timeout is a fixed, configurable setting (default 60 seconds, range 1–4000 seconds) that closes connections after a period of inactivity, meeting the requirement for a predictable response timeout. On the ANS-C01 exam, this question tests your understanding of default NLB behavior versus ALB timeout mechanics—a common trap is assuming cross-zone balancing must be manually enabled on NLBs, when in fact it is enabled by default. Remember the mnemonic: “NLB spreads by default, ALB times out by design.”
ANS-C01 Network Design Practice Question
This ANS-C01 practice question tests your understanding of network design. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 designing a network for a critical application that requires high availability across three Availability Zones in a single AWS Region. The application uses Network Load Balancers (NLBs) and Application Load Balancers (ALBs). The company must ensure that cross-zone load balancing is enabled for the NLBs and that the ALBs have a fixed response timeout. Which combination of settings meets these requirements?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable cross-zone load balancing on the NLB (default) and set the idle timeout on the ALB to a fixed value.
Option B is correct because cross-zone load balancing is enabled by default on Network Load Balancers (NLBs) and ensures traffic is distributed evenly across targets in all Availability Zones, which is critical for high availability across three AZs. The idle timeout on an Application Load Balancer (ALB) is a fixed value (default 60 seconds, configurable from 1 to 4000 seconds) that controls how long the ALB keeps a connection open without data transfer, meeting the requirement for a fixed response timeout. This combination satisfies both requirements without conflicting settings.
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.
✗
Disable cross-zone load balancing on the ALB and set the idle timeout on the NLB.
Why it's wrong here
ALB cross-zone cannot be disabled; NLB does not have idle timeout.
✓
Enable cross-zone load balancing on the NLB (default) and set the idle timeout on the ALB to a fixed value.
Why this is correct
Correct: NLB cross-zone is on by default; ALB idle timeout is configurable.
Related concept
Read the scenario before looking for a memorised answer.
✗
Disable cross-zone load balancing on the NLB and set the connection timeout on the ALB.
Enable cross-zone load balancing on the ALB and set the connection timeout on the NLB.
Why it's wrong here
ALB cross-zone is always on; NLB does not have connection timeout.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the cross-zone load balancing capability of NLBs (which can be toggled) with ALBs (which inherently distribute across AZs via target groups), and they mistakenly think ALBs have a 'connection timeout' setting when the correct term is 'idle timeout'.
Detailed technical explanation
How to think about this question
Under the hood, NLB cross-zone load balancing is enabled by default for new NLBs (since 2018) and distributes traffic evenly across all registered targets in all enabled AZs, regardless of the client's source AZ; this is crucial for three-AZ architectures to avoid uneven load. The ALB idle timeout is a layer-7 setting that closes HTTP/HTTPS connections after a period of inactivity, and it must be set to a fixed value (e.g., 60 seconds) to prevent long-lived idle connections from consuming resources—this is distinct from the NLB's idle timeout (default 350 seconds) which operates at layer 4. In a real-world scenario, if the NLB's cross-zone load balancing were disabled, traffic would only be routed to targets in the same AZ as the client, causing potential imbalance and failure if one AZ goes down.
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.
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: Enable cross-zone load balancing on the NLB (default) and set the idle timeout on the ALB to a fixed value. — Option B is correct because cross-zone load balancing is enabled by default on Network Load Balancers (NLBs) and ensures traffic is distributed evenly across targets in all Availability Zones, which is critical for high availability across three AZs. The idle timeout on an Application Load Balancer (ALB) is a fixed value (default 60 seconds, configurable from 1 to 4000 seconds) that controls how long the ALB keeps a connection open without data transfer, meeting the requirement for a fixed response timeout. This combination satisfies both requirements without conflicting settings.
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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