Quick Answer
The answer is to set up an IPsec VPN between the EC2 instances. This is correct because IPsec operates at the network layer and provides end-to-end encryption of all IP traffic between the two instances, ensuring that data in transit is fully protected regardless of the underlying network path or subnet boundaries. On the AWS Certified Security Specialty SCS-C02 exam, this question tests your understanding of encryption mechanisms versus network segmentation controls—a common trap is confusing VPC Peering, security groups, or NACLs with encryption, as none of those services encrypt traffic; they only control access or routing. Remember that VPC Peering connects networks but leaves traffic unencrypted, while IPsec VPNs explicitly add that cryptographic layer. For the exam, a quick memory tip is: “Peering for paths, IPsec for privacy.”
This SCS-C02 practice question tests your understanding of infrastructure security. 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 security engineer needs to ensure that all traffic between two EC2 instances in different subnets is encrypted in transit. What is the most secure and efficient solution?
Configure network ACLs to allow traffic
Why wrong: NACLs do not encrypt.
Use VPC Peering
Why wrong: VPC Peering does not encrypt traffic.
Set up an IPsec VPN between the instances
IPsec encrypts all IP traffic between the endpoints.
Configure security groups to allow traffic
Why wrong: Security groups only filter, not encrypt.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Set up an IPsec VPN between the instances
Option A is correct because an IPSec VPN provides encryption in transit. Option B is wrong because VPC Peering does not encrypt traffic. Option C is wrong because security groups do not encrypt. Option D is wrong because NACLs do not encrypt.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Configure network ACLs to allow traffic
Why it's wrong here
NACLs do not encrypt.
Use VPC Peering
Why it's wrong here
VPC Peering does not encrypt traffic.
Set up an IPsec VPN between the instances
Configure security groups to allow traffic
Why it's wrong here
Security groups only filter, not encrypt.
Common exam traps
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
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
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Infrastructure Security — This question tests Infrastructure Security — CIDR notation defines the prefix length..
The correct answer is: Set up an IPsec VPN between the instances — Option A is correct because an IPSec VPN provides encryption in transit. Option B is wrong because VPC Peering does not encrypt traffic. Option C is wrong because security groups do not encrypt. Option D is wrong because NACLs do not encrypt.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
CIDR notation defines the prefix length.
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Last reviewed: Jun 20, 2026
This SCS-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SCS-C02 exam.
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