PCNE Practice Question: Designing, Planning, and Prototyping a GCP Network
A company has two VPCs in the same project, VPC-A and VPC-B. They have set up VPC peering between them. In VPC-A, there is a subnet 10.0.1.0/24. In VPC-B, there are subnets 10.0.2.0/24 and 10.0.3.0/24. A compute instance in VPC-A can ping an instance in VPC-B with IP 10.0.2.10, but fails to ping an instance in VPC-B with IP 10.0.3.10. All subnets are in the same region. Firewall rules allow all traffic between VPC-A and VPC-B. What is the most likely cause?
⚠ Common exam trap
A common mix-up: candidates assume VPC peering automatically works for all subnets in the peered VPC, forgetting that static routes with more specific prefixes can override peering routes, even when firewall rules are permissive.
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
✓
VPC-A has a static route to 10.0.3.0/24 that preempts the peering route.
VPC peering routes are automatically added to the route tables of both VPCs when the peering is established. However, if a more specific static route (e.g., to 10.0.3.0/24) exists in VPC-A, it will take precedence over the peering route due to longest prefix match routing. Since the instance in VPC-A can reach 10.0.2.10 but not 10.0.3.10, the most likely cause is that VPC-A has a static route that preempts the peering route for the 10.0.3.0/24 subnet.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
VPC-A has a static route to 10.0.3.0/24 that preempts the peering route.
Why this is correct
Static routes have higher priority than peering routes, causing traffic to go elsewhere.
- ✗
The peering is not bidirectional; VPC-B is not exporting routes.
Why it's wrong here
By default, both sides export routes.
- ✗
The firewall rules in VPC-B block ICMP from VPC-A to 10.0.3.0/24.
Why it's wrong here
Firewall rules allow all traffic.
- ✗
The subnet 10.0.3.0/24 was added after the peering, and the peering routes were not updated. Recreate the peering.
Why it's wrong here
VPC peering automatically updates routes when subnets are added.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.