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.
A network engineer is configuring a Cloud VPN tunnel with route-based VPN and BGP. The tunnel is established, but the Cloud Router does not learn any routes from the on-premises peer. 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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
All of the above are possible causes.
Option C is correct because both A and B are independently plausible causes for the Cloud Router not learning routes from the on-premises peer. Firewall rules blocking UDP port 179 would prevent BGP session establishment entirely, while failing to configure the BGP session on the VPN tunnel interface means the BGP peering cannot form even if the tunnel is up. Since the question asks for the 'most likely cause' and both are valid, 'All of the above are possible causes' is the best answer.
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.
✗
Firewall rules on the on-prem router block UDP port 179.
The BGP session is not configured on the VPN tunnel.
Why it's wrong here
This is a possible cause but not the most likely on its own.
✓
All of the above are possible causes.
Why this is correct
Multiple factors commonly cause BGP route learning failure, including missing BGP config, ASN mismatch, firewall blocking TCP 179, etc.
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 Cloud Router does not have an ASN configured.
Why it's wrong here
While missing ASN prevents BGP, it is less common than other issues.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that BGP uses UDP port 179 (it uses TCP), and that a VPN tunnel being 'established' automatically implies BGP is configured, when in fact BGP configuration is a separate step required for route exchange.
Detailed technical explanation
How to think about this question
In route-based VPNs with BGP, the VPN tunnel interface acts as the underlay for BGP peering. BGP uses TCP port 179, not UDP, so the reference to UDP in option A is a deliberate red herring—BGP relies on TCP for reliable transport. Additionally, the BGP session must be configured with the peer IP address (the tunnel endpoint IP) and the correct remote ASN; misconfiguration of either will prevent route exchange even if the tunnel is established.
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.
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: All of the above are possible causes. — Option C is correct because both A and B are independently plausible causes for the Cloud Router not learning routes from the on-premises peer. Firewall rules blocking UDP port 179 would prevent BGP session establishment entirely, while failing to configure the BGP session on the VPN tunnel interface means the BGP peering cannot form even if the tunnel is up. Since the question asks for the 'most likely cause' and both are valid, 'All of the above are possible causes' is the best answer.
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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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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