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 administrator manages a hybrid cloud environment where on-premises servers connect to a VPC in AWS via a VPN connection. The on-premises network uses IP range 10.0.0.0/16. The VPC uses 172.16.0.0/16. The VPN is established and the tunnel status is UP. However, on-premises hosts cannot ping EC2 instances in the VPC. The administrator logs into an EC2 instance and can ping the on-premises VPN gateway IP. The security groups and network ACLs are configured to allow all traffic. The route tables in the VPC have a route to the on-premises network via the virtual private gateway. The on-premises firewall logs show that packets from the VPC are being dropped. 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 on-premises firewall is blocking traffic from the VPC CIDR range.
The on-premises firewall logs explicitly show that packets from the VPC are being dropped, indicating the firewall is filtering traffic from the VPC CIDR range (172.16.0.0/16). Since the VPN tunnel is UP, the EC2 instance can ping the on-premises VPN gateway IP, and security groups/network ACLs allow all traffic, the only remaining point of failure is the on-premises firewall blocking the return traffic.
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 VPN tunnel is misconfigured and not passing traffic.
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The security group attached to the EC2 instance is blocking inbound ICMP.
Why it's wrong here
Security groups allow all traffic.
✗
The VPC route table does not have a route to the on-premises network.
Why it's wrong here
Route exists.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a UP VPN tunnel guarantees end-to-end connectivity, ignoring that on-premises firewalls often require explicit allow rules for the VPC CIDR, even when the tunnel is established.
Detailed technical explanation
How to think about this question
In a hybrid cloud VPN, the tunnel being UP only confirms the IKE/IPsec phase 1 and 2 negotiations succeeded, but traffic can still be blocked by stateful firewalls on either side if they lack rules for the remote CIDR. The on-premises firewall must have an inbound rule allowing ICMP (or the specific protocol) from the VPC CIDR (172.16.0.0/16) to the on-premises hosts, and the return traffic must be permitted by the VPC's security groups and network ACLs.
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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
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 on-premises firewall is blocking traffic from the VPC CIDR range. — The on-premises firewall logs explicitly show that packets from the VPC are being dropped, indicating the firewall is filtering traffic from the VPC CIDR range (172.16.0.0/16). Since the VPN tunnel is UP, the EC2 instance can ping the on-premises VPN gateway IP, and security groups/network ACLs allow all traffic, the only remaining point of failure is the on-premises firewall blocking the return traffic.
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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