ANS-C01 Network Management and Operations Practice Question
A company has a Direct Connect connection with a private VIF to a VPC. The on-premises network uses BGP to advertise the 10.0.0.0/8 prefix to AWS. The VPC has a route table that includes a route to the Virtual Private Gateway for 10.0.0.0/8. On-premises hosts can ping EC2 instances in the VPC, but EC2 instances cannot ping on-premises hosts. The VPC has an Internet Gateway and a NAT Gateway. The EC2 instances are in private subnets with routes to the NAT Gateway for 0.0.0.0/0. 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 VPC route table has a more specific local route (10.0.0.0/16) that overrides the route to the VGW for part of the on-premises CIDR.
For EC2 instances to reach on-premises hosts, the VPC route table must have a route for the on-premises CIDR pointing to the Virtual Private Gateway. The engineer has that route. However, the on-premises hosts are in the 10.0.0.0/8 range, and the VPC also uses 10.0.0.0/16. The issue is that the VPC route table has a local route for 10.0.0.0/16, which is more specific than the 10.0.0.0/8 route to the VGW. Traffic from EC2 to on-premises hosts within the 10.0.0.0/16 range will be routed locally within the VPC, not through the VGW. The on-premises hosts must be in a different CIDR than the VPC's CIDR, or the VPC must use a different CIDR. Since the VPC uses 10.0.0.0/16, any on-premises host with an IP in that range will be considered local and won't go through the VGW. The solution is to ensure the VPC CIDR does not overlap with the on-premises CIDR.
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 Direct Connect virtual interface is configured for public VIF instead of private VIF.
Why it's wrong here
A public VIF would not allow private IP communication.
- ✗
The EC2 instances' security group outbound rules are blocking ICMP.
Why it's wrong here
If blocked, the ping would fail, but the question states on-premises can ping EC2, so ICMP is allowed inbound.
- ✓
The VPC route table has a more specific local route (10.0.0.0/16) that overrides the route to the VGW for part of the on-premises CIDR.
Why this is correct
Because the VPC uses 10.0.0.0/16, any on-premises IP within that range is considered local and not forwarded to the VGW.
- ✗
The on-premises router is not advertising the 10.0.0.0/8 route to AWS.
Why it's wrong here
The engineer stated BGP is advertising 10.0.0.0/8, and on-premises can ping EC2, so route exists.
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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.