- A
Launch instances in a cluster placement group with Enhanced Networking (ENA) enabled.
Why wrong: Cluster placement group provides low latency, but ENA is standard; EFA provides even lower latency.
- B
Launch instances in a spread placement group with SR-IOV enabled.
Why wrong: SR-IOV is not a separate feature; it's similar to ENA. Spread placement group increases latency.
- C
Launch instances in a spread placement group with Enhanced Networking (ENA) enabled.
Why wrong: Spread placement group spreads instances to reduce risk of simultaneous failure, but increases latency.
- D
Launch instances in a cluster placement group with Elastic Fabric Adapter (EFA) enabled.
Cluster placement group minimizes network distance, and EFA provides OS-bypass for low latency.
Question 1,656 of 1,705
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 designing a network architecture for a critical application that requires sub-millisecond latency between EC2 instances in the same placement group. The instances will be launched in a single Availability Zone in us-east-1. Which combination of features should be used to achieve the lowest latency?
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
✓
Launch instances in a cluster placement group with Elastic Fabric Adapter (EFA) enabled.
Option D is correct because Elastic Fabric Adapter (EFA) provides OS-bypass capabilities that enable HPC and machine learning workloads to achieve sub-millisecond latency by bypassing the operating system kernel for inter-instance communication. Combined with a cluster placement group, which ensures instances are in close physical proximity within a single Availability Zone, this configuration delivers the lowest possible latency for tightly coupled applications.
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.
- ✗
Launch instances in a cluster placement group with Enhanced Networking (ENA) enabled.
Why it's wrong here
Cluster placement group provides low latency, but ENA is standard; EFA provides even lower latency.
- ✗
Launch instances in a spread placement group with SR-IOV enabled.
Why it's wrong here
SR-IOV is not a separate feature; it's similar to ENA. Spread placement group increases latency.
- ✗
Launch instances in a spread placement group with Enhanced Networking (ENA) enabled.
Why it's wrong here
Spread placement group spreads instances to reduce risk of simultaneous failure, but increases latency.
- ✓
Launch instances in a cluster placement group with Elastic Fabric Adapter (EFA) enabled.
Why this is correct
Cluster placement group minimizes network distance, and EFA provides OS-bypass for low latency.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume Enhanced Networking (ENA) is the best option for low latency because it is widely used for high-throughput workloads, but they overlook that EFA's OS-bypass is specifically designed for sub-millisecond latency in tightly coupled HPC applications.
Trap categories for this question
Similar concept trap
SR-IOV is not a separate feature; it's similar to ENA. Spread placement group increases latency.
Detailed technical explanation
How to think about this question
EFA uses a custom network interface that leverages the AWS Scalable Reliable Datagram (SRD) protocol, which is a transport protocol designed for high-performance computing that provides low-latency, reliable, and ordered delivery without the overhead of TCP. In practice, EFA can achieve latencies as low as 10-20 microseconds between instances in the same cluster placement group, whereas ENA typically delivers latencies in the hundreds of microseconds. This makes EFA essential for applications like distributed machine learning training or tightly coupled HPC simulations that require frequent, small message exchanges.
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.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
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: Launch instances in a cluster placement group with Elastic Fabric Adapter (EFA) enabled. — Option D is correct because Elastic Fabric Adapter (EFA) provides OS-bypass capabilities that enable HPC and machine learning workloads to achieve sub-millisecond latency by bypassing the operating system kernel for inter-instance communication. Combined with a cluster placement group, which ensures instances are in close physical proximity within a single Availability Zone, this configuration delivers the lowest possible latency for tightly coupled applications.
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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