PCNE Implementing hybrid interconnectivity Practice Question
This PCNE practice question tests your understanding of implementing hybrid interconnectivity. 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. 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 company has deployed Cloud HA VPN between their on-premises network and Google Cloud. They have two tunnels from the on-premises VPN appliance to the HA VPN gateway. The on-premises appliance uses a single public IP address for both tunnels, while the Cloud VPN gateway uses two different public IPs. BGP sessions are established over both tunnels, and the Cloud Router is configured with 'active/active' mode. The network team notices that all outbound traffic from Google Cloud to on-premises is using only one of the two tunnels, even though both tunnels are up. BGP metrics are identical for routes received over both sessions. 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 does not support ECMP when both BGP sessions have the same peer IP address.
Option C is correct because Cloud Router uses the BGP peer IP address as part of the ECMP hash key. When both BGP sessions originate from the same on-premises public IP (the single IP used for both tunnels), Cloud Router sees them as the same peer and does not load-balance across them. Even though the tunnels use different Cloud VPNgatewayIPs, the BGP sessions share a common peer IP, which prevents ECMP from being enabled.
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 BGP sessions have different hold timers causing one to be preferred.
Why it's wrong here
Hold timers do not affect route selection.
✗
The on-premises appliance must use two different public IPs for ECMP to work.
Why it's wrong here
Cloud HA VPN can support multiple tunnels from the same IP, but ECMP may not function as expected.
✓
The Cloud Router does not support ECMP when both BGP sessions have the same peer IP address.
Why this is correct
Even if routes are identical, ECMP may not work if the next hop is the same; Cloud Router uses flow-based hashing that may not balance in this case.
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 must be configured with 'active/standby' mode instead of 'active/active'.
Why it's wrong here
'active/active' is correct to use both tunnels, but the limitation is the peer IP.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that ECMP requires different tunnel endpoints or different BGP metrics, when the actual requirement is that the BGP peer IP addresses must be unique for the Cloud Router to treat the sessions as separate multipath candidates.
Detailed technical explanation
How to think about this question
Cloud Router implements ECMP based on the BGP next-hop and peer IP; when both BGP sessions have the same peer IP, the router treats them as a single multipath candidate and does not install multiple paths. This behavior aligns with RFC 4271, which states that BGP routes with the same next-hop are considered for multipath only if the peer IP differs. In practice, using two distinct on-premises public IPs (or using a separate loopback for each tunnel) would allow ECMP to function correctly.
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 does not support ECMP when both BGP sessions have the same peer IP address. — Option C is correct because Cloud Router uses the BGP peer IP address as part of the ECMP hash key. When both BGP sessions originate from the same on-premises public IP (the single IP used for both tunnels), Cloud Router sees them as the same peer and does not load-balance across them. Even though the tunnels use different Cloud VPN gateway IPs, the BGP sessions share a common peer IP, which prevents ECMP from being enabled.
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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