- A
Grant the service project's compute engine default service account the Compute Network User role on the host project.
Without this role, the service project's instances cannot use the VPC resources, including the VPC peering routes to Cloud SQL.
- B
Enable Private Google Access on the vm-analytics subnet.
Why wrong: Private Google Access is for Google APIs, not for Cloud SQL private IP connectivity.
- C
Create a firewall rule in the host project allowing ingress from the service project's subnets to the Cloud SQL subnet.
Why wrong: The firewall rule already exists allowing all traffic from the VPC range, so this is not the issue.
- D
Configure a Cloud Router in the service project to advertise routes to the Cloud SQL subnet.
Why wrong: Cloud Router is not needed; the VPC peering handles routes.
Why Can't a VM in a Service Project Connect to Cloud SQL Private IP? | Google PCNE
This PCNE practice question tests your understanding of implementing a virtual private cloud. 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 large enterprise has a Google Cloud environment with multiple projects under an organization. They have a Shared VPC host project with a VPC named 'shared-vpc' that has subnets in us-central1 and europe-west1. Several service projects are attached to this host project. One service project, 'proj-analytics', has a Compute Engine instance 'vm-analytics' in us-central1 that needs to connect to a Cloud SQL PostgreSQL instance (private IP) also in us-central1, but within a different service project 'proj-db'. The Cloud SQL instance is configured with a private IP address 10.0.1.5 from a subnet in 'shared-vpc' (the same VPC). The vm-analytics instance has an internal IP 10.0.0.5 from a different subnet in 'shared-vpc'. The two subnets are in the same region, and there is a firewall rule allowing all traffic from 10.0.0.0/16 (the entire VPC range) to the Cloud SQL subnet. However, vm-analytics cannot connect to the Cloud SQL instance. The error on vm-analytics is 'Connection timed out'. There are no firewall rules blocking egress from vm-analytics. What is the most likely cause and solution?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Quick Answer
The answer is granting the service project’s Compute Engine default service account the Compute Network User role on the host project. This is correct because Cloud SQL private IP connectivity relies on Private Service Access, which establishes a VPC peering between the Shared VPC and Google’s producer VPC. While the peering routes exist in the host project, service projects attached to the Shared VPC do not automatically inherit the IAM permissions needed to use those routes—the VM’s service account must have the compute.networkUser role on the host project to access the peered network. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of how Shared VPC, IAM, and Private Service Access interact; a common trap is assuming that being in the same VPC guarantees connectivity, when in fact the service project lacks the IAM binding to the host project’s network. Remember the mnemonic: “Peering needs permission, not just position.”
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
Grant the service project's compute engine default service account the Compute Network User role on the host project.
The most likely cause is that the service project's Compute Engine default service account lacks the necessary IAM permissions to use the Shared VPC network resources. The Cloud SQL instance with a private IP is accessible via the Shared VPC, but the service project's instances need the Compute Network User role on the host project to allow them to use the VPC network and its subnets. Without this role, the traffic from vm-analytics cannot reach the Cloud SQL private IP, resulting in a timeout. Option A is correct because granting the Compute Network User role to the service project's default compute service account enables the necessary network access. Option B is incorrect because Private Google Access is for accessing Google APIs without external IPs, not for Cloud SQL private connectivity. Option C is unnecessary because firewall rules already allow traffic from the entire VPC range to the Cloud SQL subnet. Option D is incorrect because Cloud Router is used for hybrid connectivity and dynamic routing, but the issue is IAM, not routing.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Grant the service project's compute engine default service account the Compute Network User role on the host project.
Why this is correct
Without this role, the service project's instances cannot use the VPC resources, including the VPC peering routes to Cloud SQL.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
- ✗
Enable Private Google Access on the vm-analytics subnet.
Why it's wrong here
Private Google Access is for Google APIs, not for Cloud SQL private IP connectivity.
- ✗
Create a firewall rule in the host project allowing ingress from the service project's subnets to the Cloud SQL subnet.
Why it's wrong here
The firewall rule already exists allowing all traffic from the VPC range, so this is not the issue.
- ✗
Configure a Cloud Router in the service project to advertise routes to the Cloud SQL subnet.
Why it's wrong here
Cloud Router is not needed; the VPC peering handles routes.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
- CIDR notation defines the prefix length.
- Block size helps identify subnet boundaries.
- Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
- The required host count determines the smallest suitable subnet.
TExam Day Tips
- Write the block size before choosing the subnet.
- Check whether the question asks for hosts, subnets or a specific address range.
- Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related PCNE subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this PCNE question test?
Implementing a Virtual Private Cloud — This question tests Implementing a Virtual Private Cloud — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Grant the service project's compute engine default service account the Compute Network User role on the host project. — The most likely cause is that the service project's Compute Engine default service account lacks the necessary IAM permissions to use the Shared VPC network resources. The Cloud SQL instance with a private IP is accessible via the Shared VPC, but the service project's instances need the Compute Network User role on the host project to allow them to use the VPC network and its subnets. Without this role, the traffic from vm-analytics cannot reach the Cloud SQL private IP, resulting in a timeout. Option A is correct because granting the Compute Network User role to the service project's default compute service account enables the necessary network access. Option B is incorrect because Private Google Access is for accessing Google APIs without external IPs, not for Cloud SQL private connectivity. Option C is unnecessary because firewall rules already allow traffic from the entire VPC range to the Cloud SQL subnet. Option D is incorrect because Cloud Router is used for hybrid connectivity and dynamic routing, but the issue is IAM, not routing.
What should I do if I get this PCNE question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related PCNE subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Last reviewed: Jun 24, 2026
This PCNE practice question is part of Courseiva's free Google Cloud 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 PCNE exam.
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