ANS-C01 Network Management and Operations Practice Question
A company has an AWS Site-to-Site VPN connection between an on-premises network and a VPC. The VPN uses virtual private gateways and static routes. The network team reports that the VPN tunnel is up, but traffic from the on-premises network cannot reach some EC2 instances in the VPC. The EC2 instances have security groups that allow inbound traffic from the on-premises network. The VPC route table has a route pointing to the virtual private gateway for the on-premises CIDR. The tunnel status shows 'UP' from both sides. What is the MOST likely cause of the connectivity issue?
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 does not have a route for the on-premises subnet that the traffic originates from, but only for a larger CIDR.
The security group may be allowing traffic from the on-premises CIDR but not from the tunnel endpoint IP. However, the more common issue is that the on-premises network's source IP is being translated or the VPC route table is missing a route for the specific subnet. Option A is a typical cause: if the on-premises CIDR is not exactly matched, the VPC may not route traffic back. Option C could cause issues if the VPN is not in the main route table. Option D would cause tunnel issues.
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 VPC route table does not have a route for the on-premises subnet that the traffic originates from, but only for a larger CIDR.
Why this is correct
If the route is for a different CIDR, traffic may not be routed correctly.
- ✗
The VPC has a network ACL that denies inbound traffic from the on-premises CIDR.
Why it's wrong here
Would block all traffic, not just some instances.
- ✗
The customer gateway device is using a different pre-shared key than configured in AWS.
Why it's wrong here
Would cause tunnel to be down.
- ✗
The virtual private gateway is not attached to the correct VPC.
Why it's wrong here
Would cause tunnel failure or no connectivity at all.
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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.