- A
The customer gateway is not configured with the correct public IP address of the VGW.
Why wrong: The tunnel is UP, so the IP is correct.
- B
The VPN tunnel is not configured with the correct pre-shared key.
Why wrong: The tunnel status is UP, so the key is correct.
- C
The security group for the EC2 instances does not allow inbound ICMP from the on-premises network.
Why wrong: The scenario states ICMP is allowed.
- D
The VPC route table does not have a route for the on-premises CIDR (192.168.0.0/16) pointing to the virtual private gateway.
Option D is correct because, despite the scenario stating that the VPC route table has the route, the route table associated with the EC2 instances' subnet likely does not. This missing route prevents return traffic from being routed through the VPN tunnel, causing the ping failure.
SCS-C02 Site-to-Site VPN Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: site-to-Site VPN. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company is migrating its on-premises data center to AWS. The company has a VPC with a CIDR of 10.0.0.0/16 and needs to connect its on-premises network (192.168.0.0/16) to the VPC using an AWS Site-to-Site VPN. The security engineer has configured the virtual private gateway (VGW) and the customer gateway (CGW) with the correct settings. The VPN tunnel status is UP, but the on-premises servers cannot ping the EC2 instances in the VPC. The EC2 instances have security groups that allow ICMP traffic from the on-premises network. The VPC route table has a route for the on-premises network pointing to the VGW. What is the most likely cause of the issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 CIDR (192.168.0.0/16) pointing to the virtual private gateway.
The correct answer is D. While the scenario states that the VPC route table has a route for the on-premises CIDR pointing to the VGW, this refers to the main route table. The EC2 instances are likely in a subnet that uses a custom route table, which may not have this route. Without the route in the subnet's route table, the VPC cannot forward reply traffic from the EC2 instances back to the on-premises network via the VPN tunnel, causing ping failures. The tunnel status (UP) and security group configuration are correct, so the issue is the missing route in the subnet's route table.
Key principle: Site-to-Site VPN
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 customer gateway is not configured with the correct public IP address of the VGW.
Why it's wrong here
The tunnel is UP, so the IP is correct.
- ✗
The VPN tunnel is not configured with the correct pre-shared key.
Why it's wrong here
The tunnel status is UP, so the key is correct.
- ✗
The security group for the EC2 instances does not allow inbound ICMP from the on-premises network.
Why it's wrong here
The scenario states ICMP is allowed.
- ✓
The VPC route table does not have a route for the on-premises CIDR (192.168.0.0/16) pointing to the virtual private gateway.
Why this is correct
Option D is correct because, despite the scenario stating that the VPC route table has the route, the route table associated with the EC2 instances' subnet likely does not. This missing route prevents return traffic from being routed through the VPN tunnel, causing the ping failure.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Site-to-Site VPN
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap is that the scenario states the VPC route table has a route for on-premises CIDR pointing to the VGW, leading candidates to assume routing is not the issue. However, the VPC has multiple route tables; the EC2 instances might be in a subnet associated with a different route table that lacks this route. Thus, the most likely cause is a missing route in the subnet's route table, even though the main VPC route table has it.
Trap categories for this question
Scenario analysis trap
The scenario states ICMP is allowed.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Site-to-Site VPN
- Virtual Private Gateway (VGW)
- VPC Route Table
- Return Traffic Routing
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Site-to-Site VPN
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review site-to-Site VPN, then practise related SCS-C02 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this SCS-C02 question test?
Infrastructure Security — This question tests Infrastructure Security — Site-to-Site VPN.
What is the correct answer to this question?
The correct answer is: The VPC route table does not have a route for the on-premises CIDR (192.168.0.0/16) pointing to the virtual private gateway. — The correct answer is D. While the scenario states that the VPC route table has a route for the on-premises CIDR pointing to the VGW, this refers to the main route table. The EC2 instances are likely in a subnet that uses a custom route table, which may not have this route. Without the route in the subnet's route table, the VPC cannot forward reply traffic from the EC2 instances back to the on-premises network via the VPN tunnel, causing ping failures. The tunnel status (UP) and security group configuration are correct, so the issue is the missing route in the subnet's route table.
What should I do if I get this SCS-C02 question wrong?
Review site-to-Site VPN, then practise related SCS-C02 questions on the same topic to reinforce the concept.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Site-to-Site VPN
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Last reviewed: Jun 20, 2026
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