Quick Answer
The answer is a misconfigured default gateway. Even with a correct IP address and subnet mask, a VM cannot communicate outside its local subnet without a properly configured default gateway, which serves as the router for all outbound traffic. When the gateway is incorrect or missing, the VM can send packets but cannot receive return traffic from remote networks, making it appear unreachable despite being running and locally configured. On the CompTIA Cloud+ CV0-004 exam, this question tests your understanding of Layer 3 routing fundamentals versus common red herrings like DNS or firewall rules—DNS only affects name resolution, not raw connectivity, and firewalls typically block specific ports rather than all traffic. A frequent trap is assuming a running VM with a valid IP must have network access, but the gateway is the critical bridge to external networks. Remember the mnemonic: IP gets you local, gateway gets you global.
This CV0-004 practice question tests your understanding of troubleshooting. 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 notices that a virtual machine is running but cannot be reached over the network. The administrator verifies that the VM is configured with the correct IP address and subnet mask. Which of the following is the MOST likely cause of this 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.
Cloud provider firewall blocking all traffic
Why wrong: Firewalls usually block by rule, not by default gateway misconfiguration.
Incorrect DNS server settings
Why wrong: DNS does not affect basic IP connectivity.
Missing port forwarding rule
Why wrong: Port forwarding is for inbound access, not general connectivity.
Misconfigured default gateway
Without a correct gateway, traffic cannot exit the subnet.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Misconfigured default gateway
Option B is correct because a misconfigured default gateway is a common cause of network unreachability when IP and subnet are correct. Option A is wrong because incorrect DNS would affect name resolution, not basic connectivity. Option C is wrong because firewall rules within the cloud provider may block traffic, but the question suggests the VM itself is reachable? Actually, if the VM is running but cannot be reached, a misconfigured gateway prevents return traffic. Option D is wrong because port forwarding is not typically used for general network connectivity.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Cloud provider firewall blocking all traffic
Why it's wrong here
Firewalls usually block by rule, not by default gateway misconfiguration.
Incorrect DNS server settings
Why it's wrong here
DNS does not affect basic IP connectivity.
Missing port forwarding rule
Why it's wrong here
Port forwarding is for inbound access, not general connectivity.
Misconfigured default gateway
Common exam traps
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
What to study next
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related CV0-004 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Troubleshooting — This question tests Troubleshooting — CIDR notation defines the prefix length..
The correct answer is: Misconfigured default gateway — Option B is correct because a misconfigured default gateway is a common cause of network unreachability when IP and subnet are correct. Option A is wrong because incorrect DNS would affect name resolution, not basic connectivity. Option C is wrong because firewall rules within the cloud provider may block traffic, but the question suggests the VM itself is reachable? Actually, if the VM is running but cannot be reached, a misconfigured gateway prevents return traffic. Option D is wrong because port forwarding is not typically used for general network connectivity.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related CV0-004 subnetting questions on CIDR, address ranges, and subnet selection.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
CIDR notation defines the prefix length.
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Last reviewed: Jun 24, 2026
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