The correct answer involves verifying that the route tables for both subnets have routes to each other's CIDR, alongside checking security groups and network ACLs. This is because EC2 connectivity between subnets in a VPC depends on three distinct layers: security groups act as a virtual firewall at the instance level, network ACLs provide stateless traffic control at the subnet boundary, and route tables dictate the path network traffic takes between subnets. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this question tests your understanding of the VPC troubleshooting hierarchy, where misconfigured routes are a common root cause for inter-subnet failures. A frequent trap is assuming NAT Gateways or flow logs are relevant—NAT Gateways only handle outbound internet traffic, and flow logs are diagnostic tools, not configuration fixes. Remember the mnemonic "RAN" for Routes, ACLs, and Network security groups—these three always govern internal VPC communication.
SOA-C02 Networking and Content Delivery Practice Question
This SOA-C02 practice question tests your understanding of networking and content delivery. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 troubleshoot connectivity between two EC2 instances in the same VPC but different subnets. The instances cannot communicate. Which THREE checks should the administrator perform? (Choose three.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Verify that the network ACLs for both subnets allow the required traffic
Correct answers: A, B, and D. Option A is correct because security groups control traffic at the instance level. Option B is correct because network ACLs control traffic at the subnet level. Option D is correct because route tables determine if the subnets can route to each other. Option C is wrong because NAT Gateways are for internet access, not internal VPC communication. Option E is wrong because flow logs are for monitoring, not a direct cause.
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.
✓
Verify that the network ACLs for both subnets allow the required traffic
Why this is correct
Network ACLs are stateless and filter traffic at the subnet boundary.
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: Verify that the network ACLs for both subnets allow the required traffic — Correct answers: A, B, and D. Option A is correct because security groups control traffic at the instance level. Option B is correct because network ACLs control traffic at the subnet level. Option D is correct because route tables determine if the subnets can route to each other. Option C is wrong because NAT Gateways are for internet access, not internal VPC communication. Option E is wrong because flow logs are for monitoring, not a direct cause.
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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Question Discussion
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