ANS-C01 Network Security, Compliance and Governance Practice Question
A security engineer is troubleshooting why an EC2 instance cannot communicate with the internet. The instance is in a private subnet with a route table that has a default route (0.0.0.0/0) pointing to a NAT gateway. The security group for the instance allows all outbound traffic. What should the engineer check NEXT?
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
✓
Check the network ACL associated with the private subnet
Network ACLs are stateless and must allow both inbound and outbound traffic for the response. Option A is wrong because security group already allows outbound. Option B is wrong because the route is configured. Option D is wrong because flow logs are for analysis, not a next step in troubleshooting connectivity.
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 security group inbound rules allow return traffic
Why it's wrong here
Security groups are stateful, so inbound rules do not affect outbound-initiated traffic.
- ✗
Verify that the NAT gateway has an Elastic IP
Why it's wrong here
A NAT gateway requires an EIP to communicate with the internet, but the route is already configured.
- ✓
Check the network ACL associated with the private subnet
Why this is correct
Network ACLs are stateless and must allow inbound ephemeral ports for return traffic.
- ✗
Enable VPC Flow Logs to analyze traffic
Why it's wrong here
Flow logs are useful for analysis but not a first troubleshooting step.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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