- A
The VLAN attachment is in the wrong region
Why wrong: VLAN attachments are regional, but this would affect connectivity to all on-premises subnets, not just one.
- B
The GCE instance does not have a route to the on-premises subnet
If the Cloud Router is not advertising the on-premises subnet correctly, or custom route propagation is not enabled, the VPC may lack a route to 10.0.0.0/24.
- C
The on-premises firewall is blocking ICMP
Why wrong: Firewall blocking ICMP would affect ping, but they can ping the gateway, so not likely the issue.
- D
The on-premises router is not using the correct BGP AS number
Why wrong: Incorrect AS number would prevent BGP session establishment, but they can ping the gateway, so BGP is up.
Question 301 of 1,000
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 engineer has set up a Dedicated Interconnect with a VLAN attachment and a Cloud Router BGP session. They can ping the on-premises gateway IP but cannot reach an on-premises subnet 10.0.0.0/24 from a GCE instance. The on-premises router is advertising the subnet via BGP. 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 GCE instance does not have a route to the on-premises subnet
The GCE instance can ping the on-premises gateway IP because the Cloud Router has a BGP session and the gateway IP is directly reachable via the VLAN attachment. However, to reach the on-premises subnet 10.0.0.0/24, the GCE VPC needs a route for that subnet pointing to the Cloud Router as the next hop. Without an automatically propagated or manually configured route in the VPC, traffic from the GCE instance to 10.0.0.0/24 will be dropped, even though the on-premises router is advertising the subnet via BGP.
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 VLAN attachment is in the wrong region
Why it's wrong here
VLAN attachments are regional, but this would affect connectivity to all on-premises subnets, not just one.
- ✓
The GCE instance does not have a route to the on-premises subnet
Why this is correct
If the Cloud Router is not advertising the on-premises subnet correctly, or custom route propagation is not enabled, the VPC may lack a route to 10.0.0.0/24.
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.
- ✗
The on-premises firewall is blocking ICMP
- ✗
The on-premises router is not using the correct BGP AS number
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that BGP route advertisement alone ensures reachability, but in Google Cloud, the VPC route table must explicitly include the learned prefix via dynamic route propagation or a static route.
Detailed technical explanation
How to think about this question
In Google Cloud, BGP routes learned from an on-premises peer via a Cloud Router are not automatically added to the VPC route table unless the Cloud Router is configured with 'global dynamic routing' or the VPC has 'dynamic routing mode' set to 'global'. Even then, the learned routes must match the VPC's 'advertised route priority' and 'route propagation' settings. A common real-world scenario is that the VPC uses 'regional dynamic routing' and the GCE instance is in a different region than the Cloud Router, causing the learned route for 10.0.0.0/24 to not be installed in the instance's region.
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.
Visual reference
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 GCE instance does not have a route to the on-premises subnet — The GCE instance can ping the on-premises gateway IP because the Cloud Router has a BGP session and the gateway IP is directly reachable via the VLAN attachment. However, to reach the on-premises subnet 10.0.0.0/24, the GCE VPC needs a route for that subnet pointing to the Cloud Router as the next hop. Without an automatically propagated or manually configured route in the VPC, traffic from the GCE instance to 10.0.0.0/24 will be dropped, even though the on-premises router is advertising the subnet via BGP.
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: Jul 4, 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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