Quick Answer
The answer is VPC peering with firewall rules, as this combination provides the direct, private inter-VPC connectivity required while enabling granular traffic control at the VM level. By configuring ingress and egress firewall rules on peered VPCs, you can restrict communication based on source and destination tags, service accounts, or CIDR ranges, giving you fine-grained control over which specific VMs can talk to each other. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of when to use VPC peering versus Shared VPC—a common trap is assuming Shared VPC offers the same per-VM granularity across separate VPC networks, but Shared VPC centralizes management within a single host project and does not inherently allow selective filtering between independent VPCs. Remember the key distinction: VPC peering with firewall rules gives you VM-level control across VPC boundaries, while Shared VPC is about centralized administration within one network. A helpful memory tip is “Peer and filter, don’t share and blur”—peering lets you apply precise rules, whereas sharing blurs the lines between projects.
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.
An organization has multiple VPC networks and wants to allow traffic between them with fine-grained control over which VMs can communicate. Which solution should they implement?
Cloud Interconnect.
Why wrong: Cloud Interconnect is for on-premises connectivity.
Shared VPC.
Why wrong: Shared VPC combines networks, not multiple separate VPCs.
VPC peering with firewall rules.
VPC peering connects networks and firewall rules provide granular control.
Cloud VPN between VPCs.
Why wrong: Cloud VPN is unnecessary; VPC peering is simpler.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
VPC peering with firewall rules.
VPC peering with firewall rules is the correct solution because it allows direct, private connectivity between two VPC networks while enabling fine-grained control over which specific VMs can communicate via firewall rules (ingress/egress). Unlike Shared VPC, which centralizes management but does not inherently provide per-VM granularity across separate VPCs, VPC peering combined with firewall rules allows you to restrict traffic based on source and destination tags, service accounts, or CIDR ranges. This meets the requirement for both inter-VPC traffic and granular VM-level control.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Cloud Interconnect.
Why it's wrong here
Cloud Interconnect is for on-premises connectivity.
Shared VPC.
Why it's wrong here
Shared VPC combines networks, not multiple separate VPCs.
VPC peering with firewall rules.
Why this is correct
VPC peering connects networks and firewall rules provide granular control.
Related concept
Read the scenario before looking for a memorised answer.
Cloud VPN between VPCs.
Why it's wrong here
Cloud VPN is unnecessary; VPC peering is simpler.
Common exam traps
Google Cloud often tests the misconception that Shared VPC is the solution for inter-VPC traffic, but Shared VPC actually consolidates multiple projects into a single VPC, not connecting separate VPCs, while VPC peering with firewall rules provides the required granular control across distinct VPC networks.
Detailed technical explanation
VPC peering uses the Google Cloud internal, private IP infrastructure (RFC 1918) to route traffic between VPCs without needing a VPN or external gateway, and it supports transitive peering only if explicitly configured via a hub-and-spoke model. Firewall rules in VPC peering are evaluated at the VM instance level, using hierarchical firewall policies or network tags, allowing you to permit or deny traffic based on source and destination tags (e.g., only allow traffic from VMs tagged 'web' to VMs tagged 'db'). A subtle behavior is that VPC peering does not support global routing unless using a shared VPC or a network appliance, so you must ensure subnets do not overlap to avoid routing conflicts.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
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Implementing network security — study guide chapter
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FAQ
Implementing network security — This question tests Implementing network security — Read the scenario before looking for a memorised answer..
The correct answer is: VPC peering with firewall rules. — VPC peering with firewall rules is the correct solution because it allows direct, private connectivity between two VPC networks while enabling fine-grained control over which specific VMs can communicate via firewall rules (ingress/egress). Unlike Shared VPC, which centralizes management but does not inherently provide per-VM granularity across separate VPCs, VPC peering combined with firewall rules allows you to restrict traffic based on source and destination tags, service accounts, or CIDR ranges. This meets the requirement for both inter-VPC traffic and granular VM-level control.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 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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