PCNE Cloud VPN firewall rules Practice Question
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?
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.
Why it's wrong here
MTU mismatch can cause issues but is less likely than firewall rules.
- ✗
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.
Why this is correct
Firewall rules control inbound traffic; without an allow rule, traffic is denied.
Visual reference
Go deeper
Related to this question
About these practice questions
This PCNE question is part of Courseiva's 961-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
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.