The answer is that VPC peering is not established between the two VPCs. Without an active VPC peering connection, no direct network path exists between the separate virtual networks, so instances in different VPCs cannot communicate using private IP addresses, regardless of route tables or security group rules. On the CompTIA Cloud+ CV0-004 exam, this scenario tests your understanding that VPC peering is a prerequisite for cross-VPC connectivity; security groups and route tables only control traffic once the peering link is in place. A common trap is assuming that simply having overlapping security group rules or correct routes enables communication, but without the peering attachment, those configurations are irrelevant. Remember the peering-first principle: you must establish the bridge before you can configure the guards. A useful memory tip is “Peer before you steer”—the peering connection must exist before you can steer traffic with routes and security groups.
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 administrator is troubleshooting connectivity issues between two virtual networks in a public cloud. The networks are in the same region but different VPCs. Both VPCs have route tables and security groups configured. Instances in VPC A cannot ping instances in VPC B. Which of the following 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
✓
VPC peering is not established between the two VPCs.
VPC peering is a direct network connection between two VPCs that enables routing of traffic using private IPv4 or IPv6 addresses. Without an established VPC peering connection, instances in different VPCs cannot communicate, even if they are in the same region. Since the question states the VPCs are separate and no peering is mentioned, this is the most likely root cause of the connectivity failure.
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.
✓
VPC peering is not established between the two VPCs.
Why this is correct
Without peering, traffic is isolated between VPCs.
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 instances are not assigned public IP addresses.
Why it's wrong here
Private IP communication does not require public IPs.
✗
Security groups are blocking ICMP traffic.
Why it's wrong here
Security groups are permissive by default; this could be a cause but is less likely if other traffic also fails.
✗
Network ACLs are not configured to allow the traffic.
Why it's wrong here
NACLs are stateless but default to allow all; misconfiguration is possible but less common than missing peering.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often focus on security groups or ACLs as the default answer for connectivity issues, but the fundamental prerequisite for cross-VPC communication is the existence of a VPC peering connection or a transit gateway, not just network access controls.
Detailed technical explanation
How to think about this question
VPC peering uses the existing infrastructure of the cloud provider to route traffic between VPCs without a VPN or physical gateway. It relies on route table entries pointing to the peering attachment, and it does not support transitive routing—meaning if VPC A is peered with VPC B and VPC B with VPC C, VPC A cannot reach VPC C unless a direct peering exists. In real-world scenarios, administrators often forget to add the necessary routes in both VPC route tables after creating the peering connection, which is a common pitfall.
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: VPC peering is not established between the two VPCs. — VPC peering is a direct network connection between two VPCs that enables routing of traffic using private IPv4 or IPv6 addresses. Without an established VPC peering connection, instances in different VPCs cannot communicate, even if they are in the same region. Since the question states the VPCs are separate and no peering is mentioned, this is the most likely root cause of the connectivity failure.
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.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A systems administrator is troubleshooting a network connectivity issue between two peered VPCs in different regions. The VPC peering connection is established and the route tables are configured. However, instances cannot communicate. What should be checked NEXT?
hard
A.The route propagation of the peering connection
B.The network ACLs at the subnet level
✓ C.The security group rules on the instances
D.The MTU settings on the instances
Why C: Since the VPC peering connection is established and route tables are configured, the next likely cause is that security group rules on the instances are blocking traffic. Security groups act as virtual firewalls at the instance level, and by default they deny all inbound traffic; explicit rules must allow traffic from the peered VPC's CIDR or security group. This is a common oversight when peering VPCs across regions, as security groups do not automatically permit cross-peering traffic.
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Question Discussion
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