The answer is that the on-premises router lacks a BGP configuration for the second peer IP address, causing the HA VPN BGP session to stay in Active state. In a dual-tunnel HA VPN, each tunnel uses a distinct link-local peer IP from the 169.254.x.x range, and Cloud Router expects both BGP sessions to be configured on the on-premises side. When the on-premises router only has a neighbor statement for the first peer IP, it silently drops BGP OPEN messages from the second peer, leaving Cloud Router stuck in Active state as it never receives a response. This scenario tests your understanding of HA VPN BGP peering requirements for the Google Professional Cloud Network Engineer exam, where a common trap is assuming both tunnels share the same BGP configuration. Remember the memory tip: “Two tunnels, two peers—if one peer is missing, the session stays kissing.”
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.
Exhibit
Refer to the exhibit.
Output from a Cloud Router BGP session:
```
show ip bgp summary
BGP router identifier 10.0.0.1, local AS number 64512
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
169.254.1.1 4 65001 10 12 0 0 0 00:01:23 1
169.254.1.1 4 65001 0 0 0 0 0 00:00:34 Active
```
Refer to the exhibit. An engineer is troubleshooting a dual-tunnel HA VPN. The BGP session on one interface is established (State/PfxRcd 1) but the other is stuck in Active state. What can cause this?
Refer to the exhibit.
Output from a Cloud Router BGP session:
```
show ip bgp summary
BGP router identifier 10.0.0.1, local AS number 64512
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
169.254.1.1 4 65001 10 12 0 0 0 00:01:23 1
169.254.1.1 4 65001 0 0 0 0 0 00:00:34 Active
```
A
The on-premises router does not have a BGP configuration for the second peer IP address (169.254.x.x).
If the on-premises router is not expecting a connection from the second peer IP, it will not respond, leaving the Cloud Router in Active state.
B
The Cloud Router is using the same BGP identifier for both sessions, causing a conflict.
Why wrong: Cloud Router uses the same router ID for both interfaces; but that is allowed and shouldn't cause Active state.
C
The on-premises router is configured with BGP MD5 authentication that only matches the first peer.
Why wrong: MD5 mismatch would result in an Open message error, not persistent Active state.
D
The MTU on the second tunnel is not matching between the two ends.
Why wrong: MTU mismatch would affect data traffic, not BGP session establishment.
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 does not have a BGP configuration for the second peer IP address (169.254.x.x).
In a dual-tunnel HA VPN, each tunnel uses a separate BGP session with its own peer IP address (typically from the 169.254.x.x link-local range). If the on-premises router only has a BGP neighbor statement for the first peer IP, it will ignore incoming BGP packets from the second peer. The Cloud Router sees the session stuck in Active state because it is sending BGP OPEN messages but never receiving a response, as the on-premises router is not listening on that IP.
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 on-premises router does not have a BGP configuration for the second peer IP address (169.254.x.x).
Why this is correct
If the on-premises router is not expecting a connection from the second peer IP, it will not respond, leaving the Cloud Router in Active state.
Related concept
Read the scenario before looking for a memorised answer.
✗
The Cloud Router is using the same BGP identifier for both sessions, causing a conflict.
Why it's wrong here
Cloud Router uses the same router ID for both interfaces; but that is allowed and shouldn't cause Active state.
✗
The on-premises router is configured with BGP MD5 authentication that only matches the first peer.
Why it's wrong here
MD5 mismatch would result in an Open message error, not persistent Active state.
✗
The MTU on the second tunnel is not matching between the two ends.
Why it's wrong here
MTU mismatch would affect data traffic, not BGP session establishment.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between BGP session states — Active specifically means the TCP connection is not being completed by the remote end, often due to missing neighbor configuration or ACL blocking, not authentication or MTU issues.
Detailed technical explanation
How to think about this question
The BGP Active state indicates that the router has started the TCP three-way handshake (sent SYN) but has not received a SYN-ACK. In a dual-tunnel HA VPN, each tunnel endpoint uses a unique 169.254.x.x/30 link-local address. If the on-premises router lacks a 'neighbor 169.254.x.x remote-as' statement for the second peer, it will not respond to TCP SYN packets from that IP, leaving the Cloud Router stuck in Active. This is a common misconfiguration when copying a single-tunnel config to a dual-tunnel setup without adding the second BGP peer.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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 does not have a BGP configuration for the second peer IP address (169.254.x.x). — In a dual-tunnel HA VPN, each tunnel uses a separate BGP session with its own peer IP address (typically from the 169.254.x.x link-local range). If the on-premises router only has a BGP neighbor statement for the first peer IP, it will ignore incoming BGP packets from the second peer. The Cloud Router sees the session stuck in Active state because it is sending BGP OPEN messages but never receiving a response, as the on-premises router is not listening on that IP.
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.
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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