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 network engineer has configured a Dedicated Interconnect with a VLAN attachment and Cloud Router. BGP sessions are up and routes are exchanged. However, traffic from a specific on-premises subnet is not reaching a VPC instance. The route table shows a custom static route with priority 1000 for that subnet pointing to a VPN tunnel, and a BGP learned route with priority 100 for the same subnet via Interconnect. What is the most likely reason for the traffic not using the Interconnect route?
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 BGP route's next hop is not reachable due to a missing firewall rule on the on-premises side
The BGP route with priority 100 is preferred over the static route with priority 1000. However, if the BGP route's next hop is not reachable (e.g., due to a missing firewall rule on the on-premises side blocking the necessary ICMP or BGP session traffic), the route will be considered invalid and not installed in the routing table. This causes traffic to fall back to the less preferred static route via the VPN tunnel, explaining why the Interconnect path is not used.
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 route's next hop is not reachable due to a missing firewall rule on the on-premises side
Why this is correct
If the on-premises next hop is unreachable, Cloud Router cannot forward traffic, causing blackhole.
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.
✗
Route propagation is disabled on the Cloud Router
Why it's wrong here
Route propagation is enabled by default and needed for BGP routes.
✗
VPC firewall rules are blocking traffic on the Interconnect VLAN attachment
Why it's wrong here
Firewall rules are applied to traffic entering the VPC, but routing decision is made before firewall.
✗
The BGP route has a lower MED than the static route
Why it's wrong here
MED is not compared between static and dynamic routes; BGP routes (priority 100) win over static (1000).
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that route priority alone determines path selection, but the trap here is that a BGP route with a lower priority can still be invalid if its next hop is unreachable, causing the router to use a higher-priority static route instead.
Detailed technical explanation
How to think about this question
In Google Cloud, route priority values range from 0 to 65535, with lower numbers indicating higher preference. A BGP-learned route has a default priority of 100, while custom static routes default to 1000. For a BGP route to be installed in the routing table, its next hop must be reachable via a connected route or a static route with a valid next hop. If the on-premises firewall blocks the necessary traffic (e.g., UDP 179 for BGP or ICMP for next-hop validation), the route is marked as invalid, and the router falls back to the next best route.
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 BGP route's next hop is not reachable due to a missing firewall rule on the on-premises side — The BGP route with priority 100 is preferred over the static route with priority 1000. However, if the BGP route's next hop is not reachable (e.g., due to a missing firewall rule on the on-premises side blocking the necessary ICMP or BGP session traffic), the route will be considered invalid and not installed in the routing table. This causes traffic to fall back to the less preferred static route via the VPN tunnel, explaining why the Interconnect path is not used.
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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