- A
Place the instance in a private subnet with a route to an internet gateway, and add a security group rule that allows SSH inbound from 198.51.100.0/24.
Why wrong: A private subnet should not have a route to an internet gateway; that would make it a public subnet.
- B
Place the instance in a public subnet, and add a network ACL rule that denies all inbound traffic from 0.0.0.0/0.
Why wrong: NACL would block SSH from corporate IP as well.
- C
Place the instance in a private subnet, and add a security group rule that allows SSH inbound from 198.51.100.0/24.
The instance is in a private subnet, and the security group restricts SSH to the corporate IP range.
- D
Place the instance in a public subnet, and add a security group rule that allows SSH inbound from 0.0.0.0/0.
Why wrong: This would expose the instance to the internet.
Quick Answer
The correct answer is to place the EC2 instance in a private subnet and add a security group rule allowing SSH inbound from the corporate IP range 198.51.100.0/24. This configuration ensures the instance remains inaccessible from the internet while permitting SSH traffic directly from the trusted corporate network, as security groups act as a virtual firewall at the instance level. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of subnet isolation versus security group controls—a common trap is assuming a public subnet is required for connectivity, but a private subnet with a properly scoped security group provides the necessary access without exposing the instance to the internet. Remember that private subnets lack a direct route to an internet gateway, so the security group rule alone is sufficient when the corporate network reaches the instance via a VPN or Direct Connect. Memory tip: “Private subnet, public access denied—security group is your trusted guide.”
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. 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 wants to launch an Amazon EC2 instance that must be accessible via SSH from the company's corporate network (IP range 198.51.100.0/24). The instance should not be accessible from the internet. Which network configuration should the security engineer recommend?
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
Place the instance in a private subnet, and add a security group rule that allows SSH inbound from 198.51.100.0/24.
The instance should be placed in a private subnet with a security group allowing SSH from the corporate IP range. A bastion host or VPN could be used, but the question asks for the instance's network configuration. Option A is correct. Option B is incorrect because placing in a public subnet exposes it to the internet. Option C is incorrect because a public subnet with a NACL blocking everything would block SSH. Option D is incorrect because a private subnet with a route to an internet gateway would still be private? Actually, private subnets do not have direct internet access, but a route to an internet gateway would make it a public subnet. So D is wrong.
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
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Place the instance in a private subnet with a route to an internet gateway, and add a security group rule that allows SSH inbound from 198.51.100.0/24.
Why it's wrong here
A private subnet should not have a route to an internet gateway; that would make it a public subnet.
- ✗
Place the instance in a public subnet, and add a network ACL rule that denies all inbound traffic from 0.0.0.0/0.
Why it's wrong here
NACL would block SSH from corporate IP as well.
- ✓
Place the instance in a private subnet, and add a security group rule that allows SSH inbound from 198.51.100.0/24.
- ✗
Place the instance in a public subnet, and add a security group rule that allows SSH inbound from 0.0.0.0/0.
Why it's wrong here
This would expose the instance to the internet.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
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
How to think about this question
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.
KKey Concepts to Remember
- CIDR notation defines the prefix length.
- Block size helps identify subnet boundaries.
- Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
- The required host count determines the smallest suitable subnet.
TExam Day Tips
- Write the block size before choosing the subnet.
- Check whether the question asks for hosts, subnets or a specific address range.
- Do not confuse /24, /25, /26 and /27 host counts.
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
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
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
Questions learners often ask
What does this SCS-C02 question test?
Infrastructure Security — This question tests Infrastructure Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Place the instance in a private subnet, and add a security group rule that allows SSH inbound from 198.51.100.0/24. — The instance should be placed in a private subnet with a security group allowing SSH from the corporate IP range. A bastion host or VPN could be used, but the question asks for the instance's network configuration. Option A is correct. Option B is incorrect because placing in a public subnet exposes it to the internet. Option C is incorrect because a public subnet with a NACL blocking everything would block SSH. Option D is incorrect because a private subnet with a route to an internet gateway would still be private? Actually, private subnets do not have direct internet access, but a route to an internet gateway would make it a public subnet. So D is wrong.
What should I do if I get this SCS-C02 question wrong?
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
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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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