The answer is to add an inbound rule to the security group associated with the EC2 instance, allowing traffic from the 203.0.113.0/24 IP range. This is correct because security groups act as a virtual firewall at the instance level, providing stateful filtering that automatically tracks connection state and returns traffic, making them the precise tool for controlling host-level access from a specific CIDR block. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this question tests your understanding of the distinction between security groups and network ACLs—a common trap is confusing the two, as ACLs are stateless and applied at the subnet level, requiring separate inbound and outbound rules. Remember that security groups are the go-to for instance-level allow rules, while route tables handle traffic paths and IAM policies manage permissions, not network access. A useful memory tip: “Security groups secure the instance; ACLs access the subnet.”
SOA-C02 Networking and Content Delivery Practice Question
This SOA-C02 practice question tests your understanding of networking and content delivery. 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 SysOps administrator needs to allow traffic from a specific IP address range (203.0.113.0/24) to access an Amazon EC2 instance in a VPC. Which configuration step should be performed?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add an inbound rule to the security group associated with the EC2 instance allowing traffic from 203.0.113.0/24.
Option B is correct because a security group inbound rule allows traffic from the specified CIDR. Option A is wrong because network ACLs are stateless and less granular; security groups are preferred for host-level control. Option C is wrong because route tables control traffic flow between subnets, not access to instances. Option D is wrong because IAM policies do not control network traffic.
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.
✗
Create an IAM policy that allows inbound traffic from 203.0.113.0/24.
Why it's wrong here
IAM policies control API access, not network traffic.
✗
Add a rule to the network ACL associated with the subnet to allow inbound traffic from 203.0.113.0/24.
Why it's wrong here
Network ACLs are stateless and apply at subnet level; security groups are stateful and instance-level.
✗
Modify the route table of the subnet to include a route for 203.0.113.0/24 to the internet gateway.
Why it's wrong here
Route tables control traffic leaving the subnet, not inbound access to instances.
✓
Add an inbound rule to the security group associated with the EC2 instance allowing traffic from 203.0.113.0/24.
Why this is correct
Security groups act as a virtual firewall for the instance, and stateful rules are appropriate.
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 SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Networking and Content Delivery — This question tests Networking and Content Delivery — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Add an inbound rule to the security group associated with the EC2 instance allowing traffic from 203.0.113.0/24. — Option B is correct because a security group inbound rule allows traffic from the specified CIDR. Option A is wrong because network ACLs are stateless and less granular; security groups are preferred for host-level control. Option C is wrong because route tables control traffic flow between subnets, not access to instances. Option D is wrong because IAM policies do not control network traffic.
What should I do if I get this SOA-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 SOA-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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