The answer is to verify that the default route (0.0.0.0/0) exists in the VPC route table pointing to the internet gateway. This is correct because Cloud NAT requires a default route to internet to function; while Cloud NAT handles source network address translation for private instances, it does not create the path for packets to leave the VPC. The default route acts as the next-hop instruction, directing all outbound traffic to the internet gateway, without which packets from your instances are simply dropped. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding that Cloud NAT is a translation service, not a routing service—a common trap is assuming a correctly configured NAT alone enables internet access. Remember the memory tip: “NAT translates, routes direct”—you must have both the translation rule and the default route for outbound connectivity to work.
PCNE Implementing network security Practice Question
This PCNE practice question tests your understanding of implementing network security. 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 company has a VPC with a subnet in us-central1. They have several private Compute Engine instances (no external IP) that need to download updates from a public repository on the internet. The network engineer has created a Cloud NAT gateway in the same region and attached it to the subnet. However, the instances still cannot reach the internet. The engineer has confirmed that the Cloud NAT gateway is correctly configured and that the subnet's Private Google Access is not relevant for this traffic. What should the engineer check first to resolve the issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Verify that the default route (0.0.0.0/0) is present in the VPC route table pointing to the internet gateway.
Option A is correct because even with a properly configured Cloud NAT, instances require a default route (0.0.0.0/0) in the VPC route table that points to the internet gateway (IGW) to direct outbound traffic to the internet. Cloud NAT translates private IPs to public IPs, but it does not create the route; the route must exist for packets to leave the VPC. Without this route, traffic from the instances to 0.0.0.0/0 will be dropped, as there is no next-hop to forward packets to the internet.
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.
✓
Verify that the default route (0.0.0.0/0) is present in the VPC route table pointing to the internet gateway.
Why this is correct
The default route is essential for internet-bound traffic to be routed to the NAT gateway.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Confirm that the Cloud NAT router is configured with the correct network and subnet.
Why it's wrong here
The engineer already confirmed the NATgateway is correctly configured.
✗
Ensure that the Cloud NAT gateway has a static external IP.
Why it's wrong here
Static IP is optional; Cloud NAT works with ephemeral IPs.
✗
Check that the firewall rules allow egress traffic for the instances to the internet.
Why it's wrong here
While needed, the first check should be the route; missing route is a more fundamental issue.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that Cloud NAT alone provides internet connectivity, but the trap here is that candidates overlook the fundamental requirement of a default route in the VPC route table, assuming NAT configuration is sufficient for outbound traffic.
Detailed technical explanation
How to think about this question
In Google Cloud VPCs, a default route (0.0.0.0/0) with a next-hop of the internet gateway is automatically created for new VPCs, but if it is deleted or misconfigured, outbound traffic fails even with Cloud NAT. Cloud NAT operates at the network address translation layer, but it relies on the VPC routing table to direct packets; without a route, packets are discarded before reaching the NAT gateway. This is analogous to on-premises routing where a default gateway must be set for internet-bound traffic.
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: Verify that the default route (0.0.0.0/0) is present in the VPC route table pointing to the internet gateway. — Option A is correct because even with a properly configured Cloud NAT, instances require a default route (0.0.0.0/0) in the VPC route table that points to the internet gateway (IGW) to direct outbound traffic to the internet. Cloud NAT translates private IPs to public IPs, but it does not create the route; the route must exist for packets to leave the VPC. Without this route, traffic from the instances to 0.0.0.0/0 will be dropped, as there is no next-hop to forward packets to the internet.
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.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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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