This PCNE practice question tests your understanding of implementing network security. 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. A key principle to apply: vPC Firewall Rules. 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.
The answer is that the SSH traffic is allowed because it matches the allow-internal rule. In the default VPC, the default security group includes an implicit rule that permits all inbound traffic from other resources within the same security group, regardless of subnet. Since both the VM at 10.0.1.2 and the host at 10.0.2.5 are associated with this default security group, the SSH connection on TCP port 22 is permitted before any deny rules are even evaluated. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of security group stateful evaluation order and the default VPC’s built-in intra-group allow rule—a common trap is assuming that different subnets or IP ranges automatically block traffic. Remember the key tip: in the default security group, internal is always allowed, so think “same group, same pass.”
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 traffic is allowed because it matches the allow-internal rule.
In Google Cloud VPC, firewall rules are stateful and evaluated based on priority (lower priority number = higher priority). The default VPC includes an 'allow-internal' rule (priority 65534) that allows all TCP traffic from any source in the 10.0.0.0/8 range. Since the source IP (10.0.2.5) is within 10.0.0.0/8 and the destination VM (10.0.1.2) is also in that range, the SSH traffic matches this allow rule. If a deny-ssh rule were present with a lower priority number (e.g., 1000), it would take precedence over the allow-internal rule. However, no such deny rule is specified in the question, so the traffic is allowed because it matches the allow-internal rule.
Common exam trap: answer the scenario, not the keyword
A common misconception in Google Cloud is that VPC firewall rules are evaluated in order (like ACLs), but they are actually evaluated by priority number (lower number = higher priority). In this question, the allow-internal rule (priority 65534) matches the traffic. If a more specific deny rule existed (e.g., priority 1000), it would take precedence. Since no such deny rule is present, the traffic is allowed. Another trap is assuming the implicit deny blocks traffic, but implicit deny only applies if no allow rule matches.
Detailed technical explanation
How to think about this question
In cloud VPCs like AWS, security groups are stateful and evaluate rules based on the most permissive match; the order of rules does not matter because all allow rules are evaluated before any deny. The default security group typically has a self-referencing rule that allows all traffic from other instances in the same group, which is why 10.0.2.5 can SSH to 10.0.1.2 even across subnets. This behavior differs from traditional firewalls where rule order is critical, and it prevents accidental blocking of inter-instance communication within the same security group.
KKey Concepts to Remember
VPC Firewall Rules
Default VPC
Priority
Implicit Deny
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
VPC Firewall Rules
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
Review vPC Firewall Rules, then practise related PCNE questions on the same topic to reinforce the concept.
The correct answer is: The traffic is allowed because it matches the allow-internal rule. — In Google Cloud VPC, firewall rules are stateful and evaluated based on priority (lower priority number = higher priority). The default VPC includes an 'allow-internal' rule (priority 65534) that allows all TCP traffic from any source in the 10.0.0.0/8 range. Since the source IP (10.0.2.5) is within 10.0.0.0/8 and the destination VM (10.0.1.2) is also in that range, the SSH traffic matches this allow rule. If a deny-ssh rule were present with a lower priority number (e.g., 1000), it would take precedence over the allow-internal rule. However, no such deny rule is specified in the question, so the traffic is allowed because it matches the allow-internal rule.
What should I do if I get this PCNE question wrong?
Review vPC Firewall Rules, then practise related PCNE questions on the same topic to reinforce the concept.
What is the key concept behind this question?
VPC Firewall Rules
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