- A
The VPC firewall rules are blocking outbound traffic from the new subnet.
Why wrong: VPC firewall rules apply to ingress and egress; but Google Cloud can initiate outbound traffic unless explicitly blocked.
- B
The on-premises firewall is blocking traffic initiated from the 192.168.100.0/24 subnet because it is not in the permitted list.
On-premises firewalls often have stateful inspection; new subnet traffic may not be allowed.
- C
There is a route conflict between the 192.168.100.0/24 route and an existing route in the on-premises routing table.
Why wrong: A route conflict would affect traffic in both directions.
- D
The on-premises BGP router is not advertising the 10.0.0.0/8 network because a mask mismatch.
Why wrong: BGP can advertise the /8 if configured; mask mismatch would cause other issues.
PCNE Implementing hybrid interconnectivity Practice Question
This PCNE practice question tests your understanding of implementing hybrid interconnectivity. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 a hybrid network with multiple VPN tunnels connecting their on-premises network to Google Cloud. They use Cloud Router with BGP to propagate routes. They recently added a new subnet 192.168.100.0/24 in Google Cloud. On-premises devices can reach resources in the new subnet, but Google Cloud resources cannot initiate traffic to certain on-premises hosts in the 10.0.0.0/8 subnet. BGP sessions are all established. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 on-premises firewall is blocking traffic initiated from the 192.168.100.0/24 subnet because it is not in the permitted list.
The issue is that on-premises hosts in 10.0.0.0/8 can be reached from the new Google Cloud subnet (192.168.100.0/24) because BGP routes are propagated, but return traffic initiated from on-premises hosts is blocked by the on-premises firewall. Since BGP sessions are established and routes are exchanged, the problem is not routing but stateful firewall filtering: the on-premises firewall likely has a rule that permits traffic from known subnets but does not include 192.168.100.0/24, so return packets for connections initiated from Google Cloud are dropped.
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.
- ✗
The VPC firewall rules are blocking outbound traffic from the new subnet.
Why it's wrong here
VPC firewall rules apply to ingress and egress; but Google Cloud can initiate outbound traffic unless explicitly blocked.
- ✓
The on-premises firewall is blocking traffic initiated from the 192.168.100.0/24 subnet because it is not in the permitted list.
Why this is correct
On-premises firewalls often have stateful inspection; new subnet traffic may not be allowed.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
There is a route conflict between the 192.168.100.0/24 route and an existing route in the on-premises routing table.
Why it's wrong here
A route conflict would affect traffic in both directions.
- ✗
The on-premises BGP router is not advertising the 10.0.0.0/8 network because a mask mismatch.
Why it's wrong here
BGP can advertise the /8 if configured; mask mismatch would cause other issues.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between routing (BGP/route tables) and firewall filtering, leading candidates to incorrectly blame route advertisement or VPC firewall rules when the actual issue is a missing permit entry in the on-premises firewall for the new subnet.
Detailed technical explanation
How to think about this question
In hybrid networks using Cloud Router and BGP, route exchange ensures reachability, but stateful firewalls (on-premises) track connection state and require explicit permit rules for source subnets that initiate traffic. Even if routes are correct, a firewall without a rule for 192.168.100.0/24 will drop packets from that subnet, causing one-way connectivity. This is a common scenario where BGP convergence is fine but security policies are misaligned.
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 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.
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.
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Implementing hybrid interconnectivity — study guide chapter
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FAQ
Questions learners often ask
What does this PCNE question test?
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: The on-premises firewall is blocking traffic initiated from the 192.168.100.0/24 subnet because it is not in the permitted list. — The issue is that on-premises hosts in 10.0.0.0/8 can be reached from the new Google Cloud subnet (192.168.100.0/24) because BGP routes are propagated, but return traffic initiated from on-premises hosts is blocked by the on-premises firewall. Since BGP sessions are established and routes are exchanged, the problem is not routing but stateful firewall filtering: the on-premises firewall likely has a rule that permits traffic from known subnets but does not include 192.168.100.0/24, so return packets for connections initiated from Google Cloud are dropped.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
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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