The answer is a missing route in the subnet’s route table directing traffic to the on-premises network via the VPN. This is correct because the VPN tunnel is up, yet the on-premises firewall sees packets from the VM’s public IP—even though the VM resides in a private subnet with no public IP. That mismatch proves the VM’s traffic is escaping through the internet gateway instead of the VPN tunnel, where it gets source-NATed to a public IP. On the CompTIA Cloud+ CV0-004 exam, this scenario tests your ability to troubleshoot VPN routing misconfiguration in hybrid cloud environments, a common trap where engineers focus on tunnel status rather than subnet routing. A key memory tip: “Tunnel up, traffic lost? Check the route table cost.”
CV0-004 Operations and Support Practice Question
This CV0-004 practice question tests your understanding of operations and support. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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 cloud engineer is troubleshooting an issue where a virtual machine (VM) in a VPC cannot communicate with an on-premises database server through a site-to-site VPN. The VPN tunnel status shows 'UP' and the on-premises firewall logs show packets from the VM's public IP (but the VM is in a private subnet with no public IP). What is the MOST likely cause?
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The route table for the subnet is missing a route to the on-premises network via the VPN.
The VPN tunnel status is 'UP' and the on-premises firewall sees packets from the VM's public IP, but the VM is in a private subnet with no public IP. This indicates that the VM's traffic is being sent to the internet instead of through the VPN tunnel. The most likely cause is that the subnet's route table lacks a specific route directing traffic destined for the on-premises network to the virtual private gateway (VGW) or VPN connection, causing the traffic to be routed to the internet gateway (IGW) and source-NATed to the public IP.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 on-premises firewall is blocking the VM's private IP address.
Why it's wrong here
Firewall logs show packets from public IP, indicating traffic is not arriving via VPN tunnel.
✗
The VM's security group is blocking outbound traffic to the on-premises subnet.
Why it's wrong here
Security groups would drop traffic entirely, not cause it to appear from a public IP.
✓
The route table for the subnet is missing a route to the on-premises network via the VPN.
Why this is correct
Without proper route, traffic may exit through an internet gateway or NAT, resulting in public IP source.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The VPN tunnel is misconfigured with mismatched pre-shared keys.
Why it's wrong here
Mismatched keys would prevent the tunnel from establishing; tunnel status is UP.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates see 'VPN tunnel UP' and assume the VPN is fully functional, overlooking that routing (the route table) is a separate layer that must direct traffic into the tunnel; the tunnel being up does not guarantee traffic is being sent through it.
Trap categories for this question
Command / output trap
Firewall logs show packets from public IP, indicating traffic is not arriving via VPN tunnel.
Detailed technical explanation
How to think about this question
In AWS, when a VM in a private subnet sends traffic to an on-premises network, the subnet's route table must have a route with destination the on-premises CIDR and target the virtual private gateway (VGW). Without this route, traffic defaults to the internet gateway (IGW) and undergoes source NAT (SNAT) to the VM's public IP if an Elastic IP or NAT gateway is involved. This explains why the on-premises firewall sees the VM's public IP despite the VM having no public IP assigned. The VPN tunnel being 'UP' confirms the IPSec/IKE configuration is correct, isolating the issue to routing.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Operations and Support — This question tests Operations and Support — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The route table for the subnet is missing a route to the on-premises network via the VPN. — The VPN tunnel status is 'UP' and the on-premises firewall sees packets from the VM's public IP, but the VM is in a private subnet with no public IP. This indicates that the VM's traffic is being sent to the internet instead of through the VPN tunnel. The most likely cause is that the subnet's route table lacks a specific route directing traffic destined for the on-premises network to the virtual private gateway (VGW) or VPN connection, causing the traffic to be routed to the internet gateway (IGW) and source-NATed to the public IP.
What should I do if I get this CV0-004 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
Read the scenario before looking for a memorised answer.
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Question Discussion
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