- A
Use security groups to allow traffic.
Why wrong: Security groups are firewalls, not encryption.
- B
Use VPC Peering.
Why wrong: VPC Peering does not encrypt traffic.
- C
Use network ACLs to allow traffic.
Why wrong: NACLs are stateless firewalls, not encryption.
- D
Use IPsec VPN between the instances.
IPsec provides encryption for traffic between instances.
Question 756 of 1,705
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 wants to ensure that traffic between EC2 instances in the same VPC but different subnets is encrypted. Which solution should be used?
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
✓
Use IPsec VPN between the instances.
Option D is correct because an IPsec VPN between EC2 instances creates an encrypted tunnel at Layer 3, ensuring that all traffic between the instances is encrypted regardless of the underlying network path. This is necessary because traffic within a VPC traversing different subnets is not encrypted by default, even though it stays within the AWS network.
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.
- ✗
Use security groups to allow traffic.
Why it's wrong here
Security groups are firewalls, not encryption.
- ✗
Use VPC Peering.
Why it's wrong here
VPC Peering does not encrypt traffic.
- ✗
Use network ACLs to allow traffic.
Why it's wrong here
NACLs are stateless firewalls, not encryption.
- ✓
Use IPsec VPN between the instances.
Why this is correct
IPsec provides encryption for traffic between instances.
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 confuse network-layer access control (security groups, NACLs) with encryption, assuming that allowing traffic through a firewall or using VPC Peering inherently secures the data, when in fact neither provides confidentiality or integrity of the payload.
Detailed technical explanation
How to think about this question
IPsec operates in either transport mode (encrypting only the payload) or tunnel mode (encrypting the entire IP packet), and when used between EC2 instances, it typically requires configuring strongSwan or similar software on each instance. A subtle behavior is that IPsec can introduce MTU issues if the encryption overhead exceeds the path MTU, requiring MSS clamping or fragmentation handling. In a real-world scenario, this is often used to meet compliance requirements like PCI DSS or HIPAA that mandate encryption of data in transit even within a trusted network boundary.
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.
Visual reference
Quick reference
VPN Protocol Comparison
| Protocol | Port | Encryption | Authentication | Use Case |
|---|---|---|---|---|
| IKEv2 / IPsec | UDP 500 / 4500 | AES-256 | Certificates / PSK | Site-to-site & remote access |
| SSL / TLS VPN | TCP 443 | TLS 1.3 | Certificates / MFA | Clientless remote access |
| L2TP / IPsec | UDP 1701 | AES (IPsec) | PSK / Certificates | Legacy remote access |
| WireGuard | UDP 51820 | ChaCha20 | Public keys | Modern high-performance VPN |
| PPTP | TCP 1723 | MPPE (weak) | MS-CHAPv2 | Legacy — avoid in production |
PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.
What to study next
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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: Use IPsec VPN between the instances. — Option D is correct because an IPsec VPN between EC2 instances creates an encrypted tunnel at Layer 3, ensuring that all traffic between the instances is encrypted regardless of the underlying network path. This is necessary because traffic within a VPC traversing different subnets is not encrypted by default, even though it stays within the AWS network.
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
This ANS-C01 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 ANS-C01 exam.
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