Google Cloud Professional Cloud Security Engineer Practice Exam

What is a likely reason for VM instances being able to communicate freely despite existing VPC firewall rules?

1. Service accounts not being configured

2. All VM instances are missing the respective network tags

3. Firewall rules are not applied to the entire network

4. The firewall rules have incorrect priorities

The correct answer is: All VM instances are missing the respective network tags

VM instances being able to communicate freely despite existing VPC firewall rules is likely due to all VM instances missing the respective network tags. In Google Cloud, firewall rules can be configured to apply to specific instances based on network tags. If the instances do not have the correct tags that match any firewall rules, those rules will not be applied to the instances. Thus, the absence of the necessary network tags means the firewall rules do not take effect for those VM instances, allowing unrestricted communication between them. Properly configured network tags are critical for controlling traffic as they serve as labels assigned to VM instances. By using tags, specific firewall rules can be created to allow or deny traffic based on these assigned labels. If a VM instance is not tagged appropriately, it may fall into a default rule that permits communication, explaining why the firewall rules appear ineffective in regulating traffic between these instances. This situational understanding highlights the importance of management and configuration practices concerning network tags when establishing security measures in a Virtual Private Cloud (VPC) environment.