The answer is the network ACLs for both subnets, because when troubleshooting intra-VPC connectivity between VMs in different subnets, network ACLs are the first check due to their stateless nature. Unlike security groups, which are stateful and automatically allow return traffic, network ACLs require explicit allow rules for both inbound and outbound traffic; if either direction is blocked, the connection fails even if security groups permit all traffic from the VPC CIDR. On the CompTIA Cloud+ CV0-004 exam, this question tests your understanding of the fundamental difference between stateful and stateless filtering—a common trap is assuming security groups alone control all traffic, but intra-VPC routing is automatic, so ACL misconfigurations are the primary culprit. Remember the mnemonic: "ACLs are the gatekeepers, SGs are the bouncers"—gatekeepers check both ways, bouncers only check who enters.
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 a connectivity issue between two virtual machines in the same VPC but different subnets. Both VMs have security groups that allow all traffic from the VPC CIDR. What should the administrator check first?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The network ACLs for both subnets.
Option A is correct because network ACLs are stateless and must explicitly allow traffic in both directions. Option B is unlikely due to the automatic local route. Options C and D are not the first step.
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 VPC flow logs.
Why it's wrong here
Flow logs are useful for diagnosis but not the first thing to check; checking NACLs is more direct.
✓
The network ACLs for both subnets.
Why this is correct
NACLs are stateless and may be blocking traffic even if security groups allow it.
Clue confirmation
The clue word "first" in the question point toward this answer.
VPC automatically adds a local route, so route tables are unlikely to be the issue.
✗
The DHCP option set.
Why it's wrong here
DHCP options are for DNS and domain, not connectivity between subnets.
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 ACLs for both subnets. — Option A is correct because network ACLs are stateless and must explicitly allow traffic in both directions. Option B is unlikely due to the automatic local route. Options C and D are not the first step.
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: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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