ANS-C01 Network Implementation Practice Question
A company has a Direct Connect connection with a private VIF to a VPC in us-east-1. The VPC has two subnets: a public subnet and a private subnet. The public subnet has an internet gateway attached. The private subnet has a NAT gateway. The company's on-premises network uses the 10.0.0.0/8 IP range. The VPC CIDR is 10.1.0.0/16. The on-premises router is advertising 10.1.0.0/16 over BGP to the Direct Connect router. The company needs EC2 instances in the private subnet to initiate outbound connections to the internet for updates. The NAT gateway is in the public subnet. The route table for the private subnet has a default route (0.0.0.0/0) pointing to the NAT gateway. However, the on-premises network team reports that they can ping the private IP of the NAT gateway (10.1.0.10) but not the private IP of an EC2 instance in the private subnet (10.1.1.50). The EC2 instance's security group allows ICMP from the on-premises IP range. The VPC's main route table has a route for 10.0.0.0/8 pointing to the virtual private gateway. The VPC is attached to a virtual private gateway. What is the most likely cause?
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
✓
The private subnet's route table does not have a route for the on-premises CIDR (10.0.0.0/8) pointing to the virtual private gateway.
The on-premises network can ping the NAT gateway because the NAT gateway is in the public subnet, and the route table for the public subnet likely has a route to the virtual private gateway for the on-premises CIDR. However, the EC2 instance is in the private subnet, and the private subnet's route table does not have a route for the on-premises CIDR (10.0.0.0/8) pointing to the virtual private gateway. The VPC's main route table has such a route, but the private subnet is not using the main route table; it likely has a custom route table that only has the default route to the NAT gateway. Therefore, traffic from on-premises to the EC2 instance's private IP is not routed to the virtual private gateway. Option D is correct. Option A is incorrect because the security group allows ICMP. Option B is incorrect because the NAT gateway is reachable. Option C is incorrect because the virtual private gateway is attached.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The virtual private gateway is not attached to the VPC.
Why it's wrong here
The VPC is attached to a virtual private gateway, as stated.
- ✗
The NAT gateway is not reachable from the on-premises network.
Why it's wrong here
The on-premises network can ping the NAT gateway, so it is reachable.
- ✗
The security group on the EC2 instance is blocking ICMP from the on-premises IP range.
Why it's wrong here
The security group allows ICMP from the on-premises IP range, as stated.
- ✓
The private subnet's route table does not have a route for the on-premises CIDR (10.0.0.0/8) pointing to the virtual private gateway.
Why this is correct
Without a route for the on-premises CIDR in the private subnet's route table, traffic from on-premises to the EC2 instance is not forwarded to the VGW.
Visual reference
Go deeper
Related to this question
About these practice questions
Courseiva writes every ANS-C01 question from scratch — 1,621 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ANS-C01 exam.