PCNE Implementing hybrid interconnectivity Practice Question
This PCNE practice question tests your understanding of implementing hybrid interconnectivity. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 customer reports that after setting up HA VPN, some on-premises subnets are not reachable from Google Cloud. The Cloud Router shows the missing routes. 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.
Why wrong: If the tunnel were down, no routes would be learned, not just some.
B
The on-premises router is not configured to advertise those subnets.
Why wrong: If not advertised, the Cloud Router would not show them, but it shows missing routes? Actually, if not advertised, they wouldn't appear. The question says Cloud Router shows missing routes, meaning routes are expected but not present. So filter is more likely.
C
BGP route filters are blocking the advertisement of those subnets.
Route filters on the Cloud Router or on-premises router can selectively allow or deny routes.
D
The shared secret is incorrect.
Why wrong: Incorrect shared secret would prevent the tunnel from establishing, so no routes at all.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
BGP route filters are blocking the advertisement of those subnets.
Option C is correct because the Cloud Router shows the missing routes, indicating that the VPN tunnel and BGP session are up, but the routes are not being installed. BGP route filters on the Cloud Router or on-premises router can explicitly block the advertisement of specific subnets, preventing them from being learned and installed in the routing table even though the BGP session is established.
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 VPN tunnel is down.
Why it's wrong here
If the tunnel were down, no routes would be learned, not just some.
✗
The on-premises router is not configured to advertise those subnets.
Why it's wrong here
If not advertised, the Cloud Router would not show them, but it shows missing routes? Actually, if not advertised, they wouldn't appear. The question says Cloud Router shows missing routes, meaning routes are expected but not present. So filter is more likely.
✓
BGP route filters are blocking the advertisement of those subnets.
Why this is correct
Route filters on the Cloud Router or on-premises router can selectively allow or deny routes.
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 shared secret is incorrect.
Why it's wrong here
Incorrect shared secret would prevent the tunnel from establishing, so no routes at all.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume missing routes are due to a tunnel or BGP session failure, but Cisco tests the distinction between routes being received (BGP table) versus being installed (routing table), which points to route filtering as the cause.
Trap categories for this question
Command / output trap
If not advertised, the Cloud Router would not show them, but it shows missing routes? Actually, if not advertised, they wouldn't appear. The question says Cloud Router shows missing routes, meaning routes are expected but not present. So filter is more likely.
Detailed technical explanation
How to think about this question
BGP route filters can be applied using prefix-lists, route-maps, or as-path filters to control which prefixes are advertised or accepted. In Google Cloud, Cloud Router uses BGP to exchange routes with on-premises routers, and if a route filter is configured to deny certain prefixes, those routes will be present in the BGP table (show ip bgp) but not in the routing table (show ip route). This is a common troubleshooting scenario where 'show ip bgp' shows the prefix but 'show ip route' does not, pointing to a filter issue.
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: BGP route filters are blocking the advertisement of those subnets. — Option C is correct because the Cloud Router shows the missing routes, indicating that the VPN tunnel and BGP session are up, but the routes are not being installed. BGP route filters on the Cloud Router or on-premises router can explicitly block the advertisement of specific subnets, preventing them from being learned and installed in the routing table even though the BGP session is established.
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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