- A
The advertised route from the on-premises router is a default route.
Why wrong: BGP is established, so routes are exchanged; whether it is default or not, on-premises can still initiate traffic.
- B
The MTU size of the VPN tunnel.
Why wrong: MTU mismatch can cause issues but is less likely than firewall rules.
- C
The Cloud VPN gateway is assigned an external IP address.
Why wrong: The gateway's external IP is required for the tunnel; if the tunnel is up, it must have one.
- D
The firewall rules in the VPC allowing incoming traffic from the on-premises CIDR.
Firewall rules control inbound traffic; without an allow rule, traffic is denied.
Question 887 of 1,000
PCNE Cloud VPN firewall rules Practice Question
This PCNE practice question tests your understanding of implementing a virtual private cloud. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: cloud VPN firewall rules. 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 engineer is troubleshooting connectivity between an on-premises network and a GCP VPC over a Cloud VPN tunnel with dynamic routing (BGP). The tunnel is established and BGP session is up, but on-premises hosts cannot reach instances in the VPC. What should the engineer check first?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"first"Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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
✓
The firewall rules in the VPC allowing incoming traffic from the on-premises CIDR.
The first thing to check is the VPC firewall rules because even if BGP routes are exchanged and the tunnel is up, traffic can be blocked by firewall rules if there is no ingress rule allowing traffic from the on-premises CIDR. The tunnel being established and BGP session up indicates Layer 3 connectivity, but Layer 4 filtering via firewall rules can still block traffic. Option A is incorrect: a default route advertised from on-premises is fine as long as the route is learned and points to the correct next hop. Option B is incorrect: MTU issues would typically cause fragmentation problems, not complete inability to reach instances. Option C is incorrect: the Cloud VPN gateway must have an external IP for the tunnel to be established; if it were missing, the tunnel wouldn't be up.
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 advertised route from the on-premises router is a default route.
Why it's wrong here
BGP is established, so routes are exchanged; whether it is default or not, on-premises can still initiate traffic.
- ✗
The MTU size of the VPN tunnel.
- ✗
The Cloud VPN gateway is assigned an external IP address.
Why it's wrong here
The gateway's external IP is required for the tunnel; if the tunnel is up, it must have one.
- ✓
The firewall rules in the VPC allowing incoming traffic from the on-premises CIDR.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Cloud VPN firewall rules
- BGP routing and firewall interaction
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
Cloud VPN firewall rules
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.
Review cloud VPN firewall rules, then practise related PCNE questions on the same topic to reinforce the concept.
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Implementing a Virtual Private Cloud — study guide chapter
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FAQ
Questions learners often ask
What does this PCNE question test?
Implementing a Virtual Private Cloud — This question tests Implementing a Virtual Private Cloud — Cloud VPN firewall rules.
What is the correct answer to this question?
The correct answer is: The firewall rules in the VPC allowing incoming traffic from the on-premises CIDR. — The first thing to check is the VPC firewall rules because even if BGP routes are exchanged and the tunnel is up, traffic can be blocked by firewall rules if there is no ingress rule allowing traffic from the on-premises CIDR. The tunnel being established and BGP session up indicates Layer 3 connectivity, but Layer 4 filtering via firewall rules can still block traffic. Option A is incorrect: a default route advertised from on-premises is fine as long as the route is learned and points to the correct next hop. Option B is incorrect: MTU issues would typically cause fragmentation problems, not complete inability to reach instances. Option C is incorrect: the Cloud VPN gateway must have an external IP for the tunnel to be established; if it were missing, the tunnel wouldn't be up.
What should I do if I get this PCNE question wrong?
Review cloud VPN firewall rules, then practise related PCNE questions on the same topic to reinforce the concept.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
Cloud VPN firewall rules
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Last reviewed: Jun 24, 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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