- A
Firewall rules on the on-prem router block UDP port 179.
Why wrong: Blocking UDP port 179 is not relevant because BGP uses TCP port 179. Even if the firewall blocks both TCP and UDP on the same port, this is not the most likely cause given the tunnel is established.
- B
The BGP session is not configured on the VPN tunnel.
The BGP session must be configured on the VPN tunnel interface. Without this configuration, the Cloud Router cannot exchange routes with the on-premises peer, making this the most likely cause.
- C
All of the above are possible causes.
Why wrong: This option is incorrect because not all of the options are possible causes. Option A is not a direct cause (BGP uses TCP), and Option D is not a possible cause in this context.
- D
The Cloud Router does not have an ASN configured.
Why wrong: A Cloud Router without an ASN would not establish a BGP session, but this is not listed as a typical cause in the other options. Given the tunnel is established, the missing BGP session configuration is more likely.
PCNE BGP port Practice Question
This PCNE practice question tests your understanding of bgp port. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. A key principle to apply: bGP port. 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 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 BGP session is not configured on the VPN tunnel.
Option B is the most likely cause because the BGP session must be explicitly configured on the VPN tunnel interface for route exchange. Option A is incorrect because BGP uses TCP port 179, not UDP. Option D is incorrect because a Cloud Router without an ASN would not establish a BGP session, but this is not a given in the scenario; however, the question asks for the most likely cause, and the tunnel being established suggests the VPN is up, but BGP configuration is missing. Option C is incorrect because not all options are possible causes (A and D are not valid).
Key principle: BGP port
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 this is correct
The BGP session must be configured on the VPN tunnel interface. Without this configuration, the Cloud Router cannot exchange routes with the on-premises peer, making this the most likely cause.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
BGP port
- ✗
All of the above are possible causes.
- ✗
The Cloud Router does not have an ASN configured.
Why it's wrong here
A Cloud Router without an ASN would not establish a BGP session, but this is not listed as a typical cause in the other options. Given the tunnel is established, the missing BGP session configuration is more likely.
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
- BGP port
- Cloud Router BGP configuration
- Route-based VPN
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
BGP port
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.
Review bGP port, then practise related PCNE questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this PCNE question test?
BGP port
What is the correct answer to this question?
The correct answer is: The BGP session is not configured on the VPN tunnel. — Option B is the most likely cause because the BGP session must be explicitly configured on the VPN tunnel interface for route exchange. Option A is incorrect because BGP uses TCP port 179, not UDP. Option D is incorrect because a Cloud Router without an ASN would not establish a BGP session, but this is not a given in the scenario; however, the question asks for the most likely cause, and the tunnel being established suggests the VPN is up, but BGP configuration is missing. Option C is incorrect because not all options are possible causes (A and D are not valid).
What should I do if I get this PCNE question wrong?
Review bGP port, 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: "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?
BGP port
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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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