The answer is a missing route in the web servers' subnet route table to the application servers' subnet. This is correct because in a three-tier VPC routing misconfiguration, public subnets typically have a default route (0.0.0.0/0) pointing to an internet gateway for outbound internet access, but they lack an explicit route to the private subnet's CIDR block. Without that route, the web tier's traffic to the application tier is dropped at the subnet boundary, even though security groups and network ACLs are permissive. On the CompTIA Cloud+ CV0-004 exam, this scenario tests your understanding of VPC routing fundamentals versus common missteps—many candidates mistakenly blame security groups or ACLs first, but the core issue is that the route table doesn't know where to send packets destined for the private subnet. A common trap is assuming a default route handles all internal traffic, but it only covers internet-bound traffic. Memory tip: "Default gets you out, explicit gets you in"—always verify that each subnet's route table includes a local route or explicit entry for every other subnet it must reach.
CV0-004 Deployment Practice Question
This CV0-004 practice question tests your understanding of deployment. 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 company is migrating its on-premises e-commerce application to a public cloud provider. The application consists of a web tier, an application tier, and a database tier. The cloud architect has designed a three-tier architecture using virtual machines (VMs) in a virtual private cloud (VPC). During the deployment, the web servers are placed in a public subnet, the application servers in a private subnet, and the database servers in a separate private subnet. All security groups and network ACLs have been configured to allow the required traffic. After deploying the application, the operations team reports that the web servers cannot communicate with the application servers. The web servers are able to reach the internet, and the application servers can be reached from the operations team's management bastion host. Which of the following 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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The route table associated with the web servers' subnet is missing a route to the application servers' subnet.
The web servers are in a public subnet with a route table that typically includes a default route (0.0.0.0/0) pointing to an internet gateway, enabling internet access. However, for the web servers to reach the application servers in a private subnet, the route table associated with the web servers' subnet must also contain a route to the destination CIDR block of the application servers' subnet, pointing to a local route or a virtual private cloud (VPC) peering connection. Without this explicit route, traffic from the web servers to the application servers is dropped because the route table does not know how to forward packets to that subnet, even though security groups and network ACLs are correctly configured.
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 route table associated with the web servers' subnet is missing a route to the application servers' subnet.
Why this is correct
Correct: Without a route to the private subnet, traffic is dropped.
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 web servers do not have a route to the internet gateway.
Why it's wrong here
Incorrect: The web servers can reach the internet, so the route to IGW is functional.
✗
The network ACL on the application servers' subnet is blocking inbound traffic from the web servers.
Why it's wrong here
Incorrect: If NACLs were blocking, the bastion host (same subnet) would also be blocked.
✗
The security group on the web servers is blocking outbound traffic to the application servers.
Why it's wrong here
Incorrect: Security groups are stateful; if outbound is allowed, return traffic is automatically allowed.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the misconception that security groups or network ACLs are the primary cause of connectivity issues between subnets, when in reality the missing route in the subnet's route table is the root cause, especially when internet access works but inter-subnet communication fails.
Detailed technical explanation
How to think about this question
In AWS VPC routing, each subnet is associated with a route table that determines where network traffic is directed. For traffic to flow between subnets, the route table must have a route that matches the destination subnet's CIDR block, typically pointing to the local VPC router (local route). If a public subnet's route table only has a default route to an internet gateway and lacks the explicit local route for the private subnet's CIDR, packets destined for the private subnet are dropped because the route table does not have a matching entry. This is a common misconfiguration when custom route tables are created and not properly populated with the necessary local routes.
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.
Deployment — This question tests Deployment — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The route table associated with the web servers' subnet is missing a route to the application servers' subnet. — The web servers are in a public subnet with a route table that typically includes a default route (0.0.0.0/0) pointing to an internet gateway, enabling internet access. However, for the web servers to reach the application servers in a private subnet, the route table associated with the web servers' subnet must also contain a route to the destination CIDR block of the application servers' subnet, pointing to a local route or a virtual private cloud (VPC) peering connection. Without this explicit route, traffic from the web servers to the application servers is dropped because the route table does not know how to forward packets to that subnet, even though security groups and network ACLs are correctly configured.
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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