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.
Network Topology
Refer to the exhibit. An engineer has configured HA VPN with two tunnels (tunnel-a and tunnel-b) to an on-premises network. The BGP session for peer-b is in IDLE 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 on-premises router's BGP configuration for peer-b has a wrong IP address.
The BGP session for peer-b is in IDLE state, which typically indicates a TCP connection failure. Since tunnel-a is working, the Cloud Router and VPNgateway are correctly configured, and the issue is specific to peer-b. The most likely cause is that the on-premises router's BGP configuration for peer-b has the wrong IP address (e.g., the wrong BGP peer IP or the wrong Cloud Router interface IP), preventing the TCP handshake from completing.
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 Cloud Router is not in the same region as the VPN gateway.
Why it's wrong here
Region mismatch would affect both tunnels, but tunnel-a BGP is established.
✗
The on-premises router is not advertising any routes.
Why it's wrong here
Missing routes would not prevent BGP session from establishing; session can be up without routes.
✗
The pre-shared key for tunnel-b is incorrect.
Why it's wrong here
Incorrect PSK would prevent the tunnel from establishing, but both tunnels show ESTABLISHED.
✓
The on-premises router's BGP configuration for peer-b has a wrong IP address.
Why this is correct
IP mismatch causes BGP IDLE state; tunnel status indicates VPN is up, so BGP configuration is likely the issue.
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 BGP session states and tunnel/encryption failures; the trap here is that candidates assume any BGP issue is caused by route advertisement problems, when in fact the IDLE state points to a TCP connectivity issue, such as a wrong peer IP address.
Trap categories for this question
Command / output trap
Incorrect PSK would prevent the tunnel from establishing, but both tunnels show ESTABLISHED.
Detailed technical explanation
How to think about this question
BGP uses TCP port 179 to establish a session; the IDLE state means BGP is waiting for a start event (e.g., neighbor configuration) and has not yet initiated a TCP connection. In HA VPN, each tunnel has its own BGP session with a specific peer IP address (the on-premises BGP speaker's tunnel interface IP). If the peer IP is misconfigured, the TCP SYN packet is sent to the wrong destination, causing the connection to time out or be rejected. This is distinct from IKE/IPsec failures, which would prevent the tunnel from coming up entirely.
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 on-premises router's BGP configuration for peer-b has a wrong IP address. — The BGP session for peer-b is in IDLE state, which typically indicates a TCP connection failure. Since tunnel-a is working, the Cloud Router and VPN gateway are correctly configured, and the issue is specific to peer-b. The most likely cause is that the on-premises router's BGP configuration for peer-b has the wrong IP address (e.g., the wrong BGP peer IP or the wrong Cloud Router interface IP), preventing the TCP handshake from completing.
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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Question Discussion
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