The answer is an incorrect BGP peer IP address configured on the Cloud Router. This is the most likely cause because a BGP session stuck in the Active state means the router has sent an Open message but has not received a valid response, which directly points to a TCP connection failure on port 179. Since the HA VPN tunnel itself is established, the issue is isolated to the BGP layer, not the IPsec tunnel. On the Google Professional Cloud Network Engineer exam, this scenario tests your ability to distinguish between tunnel-level and BGP-level problems—a common trap is assuming a working tunnel guarantees BGP peering. Remember that Active state always indicates a peer IP mismatch or unreachable peer, while Idle state often points to a configuration or authentication issue. Memory tip: “Active means the IP is inactive”—if the BGP session is Active, verify the peer IP address first.
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 configured an HA VPN tunnel between an on-premises network and Google Cloud. The tunnel status shows as established, but traffic is not flowing. The engineer checks the Cloud Router BGP session and sees it is in the Active state. 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
✓
The Cloud Router is not configured with the correct BGP IP address for the on-premises side.
The BGP session being in the Active state indicates that the Cloud Router has sent an Open message but has not received a valid response from the on-premises peer. This most commonly occurs when the BGP peer IP address configured on the Cloud Router does not match the IP address the on-premises router is using for BGP peering, preventing the TCP connection on port 179 from completing. Since the tunnel is established (IPsec is up), the issue is at the BGP layer, not the tunnel layer.
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 tunnel's shared secret (pre-shared key) is mismatched.
Why it's wrong here
PSK mismatch would prevent tunnel from establishing, not cause BGP Active state.
✗
The Cloud Router is not advertising the VPC subnet routes.
Why it's wrong here
Route advertisement does not affect BGP session state; session can be Active with no routes.
✗
The on-premises router is not allowing BGP traffic on UDP port 179.
Why it's wrong here
Blocking BGP port would prevent session from establishing at all, not just Active state.
✓
The Cloud Router is not configured with the correct BGP IP address for the on-premises side.
Why this is correct
Incorrect peer IP is a common cause of BGP Active state.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between IPsec tunnel states and BGP session states, trapping candidates who assume a working tunnel means BGP must also be working, when in fact BGP has its own TCP-based connectivity requirements independent of the encrypted tunnel.
Detailed technical explanation
How to think about this question
BGP uses TCP port 179 for session establishment; the Active state means the router is actively trying to initiate a TCP connection but has not received a SYN-ACK from the peer. In HA VPN, the Cloud Router BGP peer IP must match the tunnel interface IP of the on-premises router (often a loopback or interface IP), and a mismatch causes the TCP handshake to fail. A common real-world scenario is when the on-premises router uses a different source IP for BGP than the one configured in the Cloud Router's BGP peer definition, often due to NAT or interface misconfiguration.
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: The Cloud Router is not configured with the correct BGP IP address for the on-premises side. — The BGP session being in the Active state indicates that the Cloud Router has sent an Open message but has not received a valid response from the on-premises peer. This most commonly occurs when the BGP peer IP address configured on the Cloud Router does not match the IP address the on-premises router is using for BGP peering, preventing the TCP connection on port 179 from completing. Since the tunnel is established (IPsec is up), the issue is at the BGP layer, not the tunnel layer.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.