- A
Enable Cloud NAT on each service project and configure a default route to the firewall appliance.
Why wrong: Cloud NAT is for outbound internet access, not for internal traffic steering.
- B
Set up VPC network peering between service projects and route traffic through the host project via a VPN tunnel.
Why wrong: Service projects already share the VPC via Shared VPC; peering is unnecessary and not allowed.
- C
Create a policy-based route in the host project that matches traffic between service project subnets and has a next hop to the firewall appliance's internal IP.
Policy-based routes can direct specific inter-subnet traffic to a next-hop instance for inspection.
- D
Create a firewall rule in the host project that allows traffic between service projects only if the source is the firewall appliance.
Why wrong: Firewall rules cannot force traffic to go through an intermediary; they only allow or deny.
Using Policy-Based Routes in Shared VPC for Traffic Inspection
This PCSE practice question tests your understanding of pcse exam topics. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 uses Shared VPC in a host project with multiple service projects. The security team wants to ensure that all traffic between service projects is inspected by a third-party firewall appliance deployed in the host project. Which configuration should be implemented?
Quick Answer
The correct answer is to create a policy-based route in the host project that matches traffic between service project subnets and has a next hop to the firewall appliance's internal IP. This configuration works because a policy-based route allows you to define traffic inspection criteria based on source and destination subnets, overriding the default VPC routing to force inter-service-project traffic through the third-party firewall appliance deployed in the host project. On the Google Professional Cloud Security Engineer exam, this scenario tests your understanding of Shared VPC route priority and the distinction between policy-based and tag-based routes; a common trap is assuming a standard static route in the service project would suffice, but only a policy-based route in the host project can selectively redirect traffic between different service projects without affecting other flows. Remember the key distinction: policy-based routes match on source and destination, while tag-based routes match on VM instance tags—for firewall inspection between service projects, always think “policy-based in the host project.”
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
Create a policy-based route in the host project that matches traffic between service project subnets and has a next hop to the firewall appliance's internal IP.
Option C is correct because a policy-based route in the host project can match traffic based on source and destination subnets from different service projects and force that traffic to be forwarded to the next-hop IP of the third-party firewall appliance. This ensures all inter-service-project traffic is inspected by the firewall, as the route overrides the default VPC routing behavior within the Shared VPC environment.
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.
- ✗
Enable Cloud NAT on each service project and configure a default route to the firewall appliance.
Why it's wrong here
Cloud NAT is for outbound internet access, not for internal traffic steering.
- ✗
Set up VPC network peering between service projects and route traffic through the host project via a VPN tunnel.
Why it's wrong here
Service projects already share the VPC via Shared VPC; peering is unnecessary and not allowed.
- ✓
Create a policy-based route in the host project that matches traffic between service project subnets and has a next hop to the firewall appliance's internal IP.
Why this is correct
Policy-based routes can direct specific inter-subnet traffic to a next-hop instance for inspection.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Create a firewall rule in the host project that allows traffic between service projects only if the source is the firewall appliance.
Why it's wrong here
Firewall rules cannot force traffic to go through an intermediary; they only allow or deny.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between firewall rules (which filter traffic) and routes (which direct traffic); the trap here is that candidates mistakenly think a firewall rule can force traffic through an appliance, when in fact only a route can change the path traffic takes.
Detailed technical explanation
How to think about this question
Policy-based routes in Google Cloud are static routes that match on source IP ranges, destination IP ranges, and optionally protocol/port, and they override the default VPC routing table for matched traffic. In a Shared VPC, the host project owns the VPC network, so a policy-based route defined there can match traffic between subnets from different service projects and set the next hop to the firewall appliance's internal IP, effectively creating a forced forwarding path. This is similar to policy-based routing (PBR) in traditional networking, where traffic is steered based on criteria beyond the destination prefix.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
Visual reference
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.
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FAQ
Questions learners often ask
What does this PCSE question test?
Read the scenario before looking for a memorised answer.
What is the correct answer to this question?
The correct answer is: Create a policy-based route in the host project that matches traffic between service project subnets and has a next hop to the firewall appliance's internal IP. — Option C is correct because a policy-based route in the host project can match traffic based on source and destination subnets from different service projects and force that traffic to be forwarded to the next-hop IP of the third-party firewall appliance. This ensures all inter-service-project traffic is inspected by the firewall, as the route overrides the default VPC routing behavior within the Shared VPC environment.
What should I do if I get this PCSE 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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Last reviewed: Jun 30, 2026
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