hardMultiple ChoiceObjective-mapped
CV0-004 Practice Question: A systems administrator is troubleshooting a…
A systems administrator is troubleshooting a network connectivity issue between two peered VPCs in different regions. The VPC peering connection is established and the route tables are configured. However, instances cannot communicate. What should be checked NEXT?
⚠ Common exam trap
The trap here is that candidates often focus on network ACLs or route propagation first, forgetting that security groups are the most granular and commonly misconfigured firewall layer that can silently block traffic even when routes and ACLs are correct.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The security group rules on the instances
Since the VPC peering connection is established and route tables are configured, the next likely cause is that security group rules on the instances are blocking traffic. Security groups act as virtual firewalls at the instance level, and by default they deny all inbound traffic; explicit rules must allow traffic from the peered VPC's CIDR or security group. This is a common oversight when peering VPCs across regions, as security groups do not automatically permit cross-peering traffic.
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 route propagation of the peering connection
Why it's wrong here
VPC peering does not use route propagation; routes must be added manually.
- ✗
The network ACLs at the subnet level
Why it's wrong here
NACLs are stateless and can also block traffic, but security groups are more commonly the issue; however, checking security groups is a standard next step.
- ✓
The security group rules on the instances
Why this is correct
Security groups are stateful firewalls that can block inter-VPC traffic if not explicitly allowed.
- ✗
The MTU settings on the instances
Why it's wrong here
MTU mismatch could cause packet loss but is not the most likely next step for general connectivity failure.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.