The answer is to check the network ACL inbound rules. This is correct because network ACLs are stateless, meaning they evaluate traffic in both directions independently, and a default deny rule can silently block inbound HTTP traffic even when the associated security group permits it from 0.0.0.0/0. On the CompTIA Cloud+ CV0-004 exam, this scenario tests your understanding of the layered security model in cloud networking, where security groups act as instance-level firewalls and network ACLs serve as subnet-level filters—a common trap is assuming a security group allow rule alone guarantees access. Remember that stateless ACLs require explicit allow rules for both inbound and outbound traffic, while security groups are stateful and automatically allow return traffic. A helpful memory tip: “ACLs are stateless, so check both ways; SGs are stateful, so they track the plays.”
CV0-004 Operations and Support Practice Question
This CV0-004 practice question tests your understanding of operations and support. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 deployed a web application on an EC2 instance in a public subnet. The instance passes status checks and has a public IP address. The security group allows HTTP (80) from 0.0.0.0/0. Users report that the website is not accessible. What should the administrator check next?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The network ACL inbound rules.
Option A is correct because network ACLs are stateless and can block traffic even if the security group allows it. Options B, C, and D are less likely or secondary steps.
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 network ACL inbound rules.
Why this is correct
Network ACLs are stateless and can block inbound traffic even if the security group allows it.
The route table likely already has a default route to the internet gateway for a public subnet.
✗
The instance's operating system firewall.
Why it's wrong here
The OS firewall could block traffic, but it is usually not the first thing to check when security groups and NACLs are in place.
✗
The instance's user data script.
Why it's wrong here
User data script only runs at launch and does not affect network connectivity.
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 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.
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 network ACL inbound rules. — Option A is correct because network ACLs are stateless and can block traffic even if the security group allows it. Options B, C, and D are less likely or secondary steps.
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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