The answer is a host-based firewall on the target instance blocking ping and misconfigured network ACLs (NACLs) blocking ICMP. This is correct because while security groups are stateful and automatically allow return traffic, NACLs are stateless and require explicit rules for both inbound and outbound ICMP traffic; if either direction is missing, ping fails. Additionally, even with perfect cloud-level networking, the operating system’s own firewall (like iptables or Windows Firewall) can independently block ICMP at the instance level. On the CompTIA Cloud+ CV0-004 exam, this question tests your ability to distinguish between stateful security groups and stateless NACLs, a classic trap where candidates assume security group rules alone guarantee connectivity. A common memory tip is “NACLs need two rules, firewalls are local”—always check both the subnet’s stateless ACL and the instance’s OS firewall when VPC peering ping fails.
CV0-004 Troubleshooting Practice Question
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 is troubleshooting a network connectivity issue between two VPCs connected via a VPC peering connection. The administrator has verified that the route tables are correct and that the security groups allow traffic. However, instances in VPC A cannot ping instances in VPC B. Which TWO of the following could be causing the issue? (Choose TWO.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Network ACLs in VPC B are blocking inbound ICMP
Network ACLs are stateless and must allow both inbound and outbound traffic; if they block ICMP, ping fails. Firewall rules within the OS can also block ping. Option A is wrong because security groups are stateful and would allow return traffic if outbound is allowed. Option D is wrong because routing is verified. Option E is wrong because VPC peering does not depend on IGW.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Network ACLs in VPC B are blocking inbound ICMP
Why this is correct
Network ACLs are stateless; they must explicitly allow both inbound and outbound ICMP.
Related concept
Standard ACLs match source addresses.
✗
Security groups in VPC A are blocking inbound ICMP
Why it's wrong here
Security groups are stateful; if outbound is allowed, return traffic is automatically allowed.
✓
Host-based firewall on the target instance is blocking ping
Why this is correct
The OS firewall (e.g., iptables) can block ICMP despite cloud-level rules.
Related concept
Standard ACLs match source addresses.
✗
VPC peering connection does not support ICMP
Why it's wrong here
VPC peering supports all protocols, including ICMP.
✗
Route tables are misconfigured
Why it's wrong here
Route tables have been verified as correct.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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 ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related CV0-004 ACL questions on filtering logic and placement.
Troubleshooting — This question tests Troubleshooting — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Network ACLs in VPC B are blocking inbound ICMP — Network ACLs are stateless and must allow both inbound and outbound traffic; if they block ICMP, ping fails. Firewall rules within the OS can also block ping. Option A is wrong because security groups are stateful and would allow return traffic if outbound is allowed. Option D is wrong because routing is verified. Option E is wrong because VPC peering does not depend on IGW.
What should I do if I get this CV0-004 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related CV0-004 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A cloud administrator is troubleshooting a connectivity issue between two VPCs in the same region. Which TWO actions should the administrator verify? (Choose two.)
medium
✓ A.VPC peering connection status
✓ B.Route table entries
C.Security group rules
D.VPN tunnel configuration
E.Internet gateway attachment
Why A: Options A and C are correct because route tables must have routes to the peering connection, and the VPC peering connection must be in the 'active' state. Option B is wrong because security groups don't block traffic between peered VPCs unless explicitly configured, but they are not the primary check. Option D is wrong because an internet gateway is not required for VPC peering. Option E is wrong because VPN tunnel is a different connectivity method.
Variation 2. A cloud administrator is troubleshooting connectivity issues between two virtual networks in different regions. The VNets are peered, but instances cannot communicate. The administrator verifies that the peering status is 'Connected' and route tables appear correct. Which of the following should be checked next?
medium
✓ A.Network Security Group (NSG) rules on the instances and subnets
B.DNS resolution settings
C.Gateway subnet configuration
D.Service endpoint status
Why A: Even when VNet peering status shows 'Connected' and route tables are correct, Network Security Group (NSG) rules can still block traffic. NSGs act as a stateful firewall at the subnet or NIC level, and by default they deny all inbound traffic unless explicitly allowed. Since the administrator has already verified routing, the next logical step is to check NSG rules for any implicit deny or missing allow rules that could be dropping the inter-region traffic.
Last reviewed: Jun 24, 2026
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This CV0-004 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CV0-004 exam.
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