ANS-C01 Network Implementation Practice Question
A company has a VPC with a CIDR block of 10.0.0.0/16. The VPC has three subnets: 10.0.1.0/24, 10.0.2.0/24, and 10.0.3.0/24. An EC2 instance in subnet 10.0.1.0/24 needs to send traffic to an on-premises server at 10.0.0.5/32 via a VPN connection. The VPC route table has a route to the VPN gateway for 10.0.0.0/8. What is the expected behavior?
⚠ Common exam trap
The ANS-C01 exam often tests the misconception that a route to a larger CIDR (like 10.0.0.0/8) will override a more specific local route (like 10.0.0.0/16), but AWS always uses the longest prefix match, so the local route takes precedence.
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
✓
Traffic to 10.0.0.5 stays within the VPC.
The VPC's CIDR is 10.0.0.0/16, and the destination 10.0.0.5/32 falls within this range. AWS VPCs use the most specific route that matches the destination IP, and the local route (10.0.0.0/16) is automatically added to all VPC route tables. Since 10.0.0.5/32 is a subset of 10.0.0.0/16, the local route takes precedence over the VPN route (10.0.0.0/8) because it is more specific (longer prefix length). Therefore, traffic destined to 10.0.0.5 stays within the VPC and is not sent to the VPN gateway.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Traffic to 10.0.0.5 is sent to the internet gateway.
Why it's wrong here
No route to IGW for 10.0.0.5.
- ✗
Traffic to 10.0.0.5 is routed through the VPN gateway.
Why it's wrong here
The local route is more specific.
- ✓
Traffic to 10.0.0.5 stays within the VPC.
Why this is correct
The VPC's local route matches 10.0.0.5.
- ✗
Traffic to 10.0.0.5 is dropped because there is no matching route.
Why it's wrong here
There is a local route.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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