The answer is that the instance's security group does not allow inbound HTTP/HTTPS traffic from 0.0.0.0/0. Even when a VM is running in a public subnet with an internet gateway attached, the security group acts as a virtual firewall at the instance level, and if it lacks an inbound rule permitting web traffic from the internet, the web application remains unreachable. This scenario tests your understanding of the layered security model in cloud networking, where the subnet’s route table and internet gateway handle network-layer connectivity, while the security group controls host-level access. On the CompTIA Cloud+ CV0-004 exam, a common trap is to assume that a public subnet alone guarantees internet reachability, but you must verify both the route table and the security group rules. A helpful memory tip is “route to the subnet, filter at the instance”—the internet gateway gets traffic to the subnet, but the security group decides if the instance accepts it.
CV0-004 Operations and Support Practice Question
This CV0-004 practice question tests your understanding of operations and support. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Refer to the exhibit. A cloud administrator runs the command to inspect an instance and notices that it is running, but the web application hosted on it is unreachable from the internet. The instance is in a public subnet with an internet gateway attached to the VPC. 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.
The instance type t2.medium does not support public IP addresses.
Why wrong: t2.medium supports public IP addresses; the instance likely has a public IP if in a public subnet.
B
The instance's security group does not allow inbound HTTP/HTTPS traffic from 0.0.0.0/0.
Correct. Security group rules control inbound traffic; missing HTTP/HTTPS rules would prevent internet access.
C
The subnet subnet-abc is not associated with a route table that has a route to the internet gateway.
Why wrong: The stem states the internet gateway is attached to the VPC, but the subnet route table may still be misconfigured; however, security group is a more common first check.
D
The volume vol-111 is not encrypted.
Why wrong: Volume encryption does not affect network reachability.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The instance's security group does not allow inbound HTTP/HTTPS traffic from 0.0.0.0/0.
The instance has a security group named "sg-web" which likely does not allow inbound HTTP/HTTPS traffic from the internet. Other options are less plausible given the configuration.
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
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The instance type t2.medium does not support public IP addresses.
Why it's wrong here
t2.medium supports public IP addresses; the instance likely has a public IP if in a public subnet.
✓
The instance's security group does not allow inbound HTTP/HTTPS traffic from 0.0.0.0/0.
Why this is correct
Correct. Security group rules control inbound traffic; missing HTTP/HTTPS rules would prevent internet access.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The subnet subnet-abc is not associated with a route table that has a route to the internet gateway.
Why it's wrong here
The stem states the internet gateway is attached to the VPC, but the subnet route table may still be misconfigured; however, security group is a more common first check.
✗
The volume vol-111 is not encrypted.
Why it's wrong here
Volume encryption does not affect network reachability.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
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
How to think about this question
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.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
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
How this comes up in practice
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
Got this wrong? Here's your next step.
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.
Operations and Support — This question tests Operations and Support — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The instance's security group does not allow inbound HTTP/HTTPS traffic from 0.0.0.0/0. — The instance has a security group named "sg-web" which likely does not allow inbound HTTP/HTTPS traffic from the internet. Other options are less plausible given the configuration.
What should I do if I get this CV0-004 question wrong?
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.
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?
CIDR notation defines the prefix length.
About these practice questions
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Variation 1. A cloud administrator is troubleshooting an issue where a virtual machine (VM) cannot connect to the internet. Which TWO of the following are valid first steps to diagnose the problem?
easy
✓ A.Verify the VM's network interface is attached to the correct subnet.
B.Check the VM's OS firewall settings.
C.Create a new VM.
✓ D.Check the VM's security group rules.
E.Reboot the VM.
Why A: Option A is correct because verifying the VM's network interface is attached to the correct subnet is a fundamental first step in diagnosing internet connectivity issues. If the VM is on an isolated or mismatched subnet, it cannot route traffic to the internet gateway, regardless of other configurations. This check ensures the VM's virtual NIC is connected to the appropriate virtual network and subnet that has a route to the internet.
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Question Discussion
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