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 allow its developers to SSH into EC2 instances only from the corporate network IP range (203.0.113.0/24). Which configuration should be used to enforce this restriction?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a security group rule that allows inbound SSH (port 22) from the corporate IP range.
Option C is correct because a security group rule can restrict inbound SSH to the specific IP range. Option A is wrong because IAM policies do not control network access. Option B is wrong because NACLs are stateless and require separate inbound and outbound rules. Option D is wrong because Systems Manager Session Manager does not use SSH.
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.
✗
Configure a network ACL on the subnet to allow inbound SSH from the corporate range and deny all other inbound traffic.
Why it's wrong here
NACLs are stateless and require outbound rules; security groups are simpler.
✗
Use AWS Systems Manager Session Manager to connect to instances instead of SSH.
Why it's wrong here
This bypasses SSH but does not enforce the restriction if SSH is still open.
✗
Add an IAM policy that allows `ec2:RunInstances` only if the request includes the corporate IP.
Why it's wrong here
IAM policies do not control network access to running instances.
✓
Add a security group rule that allows inbound SSH (port 22) from the corporate IP range.
Why this is correct
Security groups are stateful and can restrict inbound traffic to a specific source.
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.
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: Add a security group rule that allows inbound SSH (port 22) from the corporate IP range. — Option C is correct because a security group rule can restrict inbound SSH to the specific IP range. Option A is wrong because IAM policies do not control network access. Option B is wrong because NACLs are stateless and require separate inbound and outbound rules. Option D is wrong because Systems Manager Session Manager does not use SSH.
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.
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Question Discussion
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