The answer is that you must verify the VPC has a custom route with destination 10.1.0.0/16 and next-hop set to the specific VPN tunnel interface. This is required because HA VPN tunnels in Google Cloud do not automatically route traffic to on-premises destinations; you must explicitly create a custom route that points the desired destination prefix to the correct next-hop tunnel interface. Without this route, the VPC has no path for traffic destined to 10.1.0.0/16, causing it to be dropped. On the Google Professional Cloud Network Engineer exam, this tests your understanding that routing and firewall rules are separate concerns—firewalls control access, but routes control the path. A common trap is assuming that BGP advertisements from on-premises will automatically install a route for a Google Cloud subnet, but BGP only advertises on-premises prefixes, not VPC subnets. Memory tip: think of the custom route as a signpost—without it, traffic has no direction to the tunnel interface.
PCNE Implementing a Virtual Private Cloud Practice Question
This PCNE practice question tests your understanding of implementing a virtual private cloud. 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.
A company has an HA VPN tunnel between on-premises and Google Cloud. They want traffic destined to 10.1.0.0/16 (a subnet in their VPC) to go through a specific next-hop VPN tunnel interface, but currently traffic is being dropped. What should they verify?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The VPC has a custom route with destination 10.1.0.0/16 and next-hop set to the correct VPN tunnel interface.
Option B is correct because a custom route with destination 10.1.0.0/16 and next-hop set to the specific VPN tunnel interface is required to direct traffic through that interface. Option A is incorrect because firewall rules control access but not routing. Option C is incorrect because on-premises BGP advertisement is for routes from on-premises, not Google Cloud routes. Option D is incorrect because Cloud NAT is used for outbound internet access, not routing to on-premises.
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.
✓
The VPC has a custom route with destination 10.1.0.0/16 and next-hop set to the correct VPN tunnel interface.
Why this is correct
A custom route with the correct next-hop is necessary to direct traffic through the specific VPN tunnel.
Cloud NAT is for outbound internet from instances without external IPs, not for routing to on-premises.
✗
Firewall rules allow ingress from on-premises IPs.
Why it's wrong here
Firewall rules control access but not the specific route taken.
✗
The on-premises router is advertising the route via BGP.
Why it's wrong here
BGP advertising is for on-premises routes, not for Google Cloud 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.
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.
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: The VPC has a custom route with destination 10.1.0.0/16 and next-hop set to the correct VPN tunnel interface. — Option B is correct because a custom route with destination 10.1.0.0/16 and next-hop set to the specific VPN tunnel interface is required to direct traffic through that interface. Option A is incorrect because firewall rules control access but not routing. Option C is incorrect because on-premises BGP advertisement is for routes from on-premises, not Google Cloud routes. Option D is incorrect because Cloud NAT is used for outbound internet access, not routing to on-premises.
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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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.
Question Discussion
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