The correct combination is a cluster placement group with Elastic Fabric Adapter (EFA) enabled. This works because a cluster placement group packs instances close together within a single Availability Zone, minimizing network hops, while EFA provides a user-space networking interface that bypasses the operating system kernel to achieve sub-millisecond latency and high throughput. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how placement group strategies and specialized network interfaces interact for HPC and ML workloads; a common trap is assuming Enhanced Networking or SR-IOV alone is sufficient, but those still rely on kernel-level processing. Remember the mnemonic "Cluster + EFA = Lowest Latency" to avoid confusing spread or partition groups, which intentionally increase latency for fault isolation.
ANS-C01 Network Design Practice Question
This ANS-C01 practice question tests your understanding of network design. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 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 C is correct. A placement group with a cluster strategy places instances in a low-latency group within a single AZ, and Elastic Fabric Adapter (EFA) provides high-throughput, low-latency networking for HPC and ML workloads. Option A is wrong because Enhanced Networking alone does not guarantee sub-millisecond latency; EFA is needed. Option B is wrong because Spread placement group spreads instances across hardware, increasing latency. Option D is wrong because a spread placement group with SR-IOV is not as low-latency as cluster placement with EFA.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
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
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related ANS-C01 NAT questions on configuration and troubleshooting.
Network Design — This question tests Network Design — Static NAT maps one inside address to one outside address..
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 C is correct. A placement group with a cluster strategy places instances in a low-latency group within a single AZ, and Elastic Fabric Adapter (EFA) provides high-throughput, low-latency networking for HPC and ML workloads. Option A is wrong because Enhanced Networking alone does not guarantee sub-millisecond latency; EFA is needed. Option B is wrong because Spread placement group spreads instances across hardware, increasing latency. Option D is wrong because a spread placement group with SR-IOV is not as low-latency as cluster placement with EFA.
What should I do if I get this ANS-C01 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related ANS-C01 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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