PCNE Implementing hybrid interconnectivity Practice Question
This PCNE practice question tests your understanding of implementing hybrid interconnectivity. 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 wants to use a third-party VPN appliance on Google Cloud (Compute Engine) to connect to an on-premises network. Which networking feature must be enabled to allow the VPN appliance to forward traffic between VPC subnets and the tunnel?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable IP forwarding on the VPN appliance VM instance.
Option C is correct because a third-party VPN appliance running as a Compute Engine VM must have IP forwarding enabled to act as a router. Without this setting, the VM will drop any traffic that is not destined to its own IP address, even if the kernel is configured to forward packets. Enabling IP forwarding (via the `canIpForward` flag or the `gcloud compute instances create --can-ip-forward` option) allows the VM to forward traffic between the VPC subnets and the VPN tunnel interfaces.
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.
✗
Create a custom route in the VPC pointing to the VPN appliance's internal IP.
Why it's wrong here
While a route is needed, IP forwarding is the prerequisite; the route alone won't work without it.
✗
Enable Private Google Access on the subnet hosting the VPN appliance.
Why it's wrong here
Private Google Access is unrelated to VPN forwarding.
✓
Enable IP forwarding on the VPN appliance VM instance.
Why this is correct
IP forwarding is required for the VM to act as a router.
Related concept
Read the scenario before looking for a memorised answer.
✗
Create a firewall rule allowing traffic from the on-premises network to the VPC subnets.
Why it's wrong here
Firewall rules are needed but not the primary enabler for forwarding.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between network-level configurations (routes, firewall rules) and instance-level capabilities (IP forwarding), trapping candidates who assume that creating a route or firewall rule alone is sufficient for a VM to act as a gateway.
Detailed technical explanation
How to think about this question
Under the hood, IP forwarding on a Compute Engine VM sets the `net.ipv4.ip_forward` sysctl parameter on the instance and also configures the hypervisor to allow the VM to receive packets not addressed to its own MAC/IP. In a real-world scenario, if you deploy a VPN appliance like a Cisco CSR 1000V or a strongSwan instance, you must enable IP forwarding both in the OS (e.g., `sysctl -w net.ipv4.ip_forward=1`) and at the GCP instance metadata level via the `canIpForward` flag; otherwise, the appliance will silently drop encapsulated 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 hybrid interconnectivity — This question tests Implementing hybrid interconnectivity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Enable IP forwarding on the VPN appliance VM instance. — Option C is correct because a third-party VPN appliance running as a Compute Engine VM must have IP forwarding enabled to act as a router. Without this setting, the VM will drop any traffic that is not destined to its own IP address, even if the kernel is configured to forward packets. Enabling IP forwarding (via the `canIpForward` flag or the `gcloud compute instances create --can-ip-forward` option) allows the VM to forward traffic between the VPC subnets and the VPN tunnel interfaces.
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.
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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