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.”
PCNE Implementing network security Practice Question
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. 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.
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.
The default VPC in a cloud environment (such as AWS) includes a default security group that allows all inbound traffic from other resources within the same security group. Since both the VM (10.0.1.2) and the host (10.0.2.5) are in the default VPC and likely associated with the same default security group, the allow-internal rule permits the SSH connection. The traffic matches the allow rule before any deny rules are evaluated, so it is allowed.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 traffic is denied because the source IP is not in the same subnet as the VM.
Why it's wrong here
No such rule by default.
✗
The traffic is denied because the deny-ssh rule has a lower priority number and blocks all SSH traffic.
Why it's wrong here
deny-ssh does not match because source is 10.0.2.5, not 10.0.1.0/24.
✗
The traffic is denied due to the implicit deny rule at the end.
Why it's wrong here
Implicit deny applies only if no allow rule matches; here an allow rule matches.
✓
The traffic is allowed because it matches the allow-internal rule.
Why this is correct
allow-internal allows all traffic from 10.0.0.0/8.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that security group rules are evaluated in priority order like ACLs, when in fact they are evaluated as a set of allow rules with an implicit deny at the end, and the order of rules does not affect the outcome.
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
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Implementing network security — This question tests Implementing network security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The traffic is allowed because it matches the allow-internal rule. — The default VPC in a cloud environment (such as AWS) includes a default security group that allows all inbound traffic from other resources within the same security group. Since both the VM (10.0.1.2) and the host (10.0.2.5) are in the default VPC and likely associated with the same default security group, the allow-internal rule permits the SSH connection. The traffic matches the allow rule before any deny rules are evaluated, so it is allowed.
What should I do if I get this PCNE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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