The answer is to configure BGP route filtering on the Cloud Router to accept only specific prefixes from each on-premises site. This is correct because Cloud Router allows you to define inbound route policies that explicitly match and permit only the desired prefixes from a BGP peer, preventing any unwanted or overlapping routes from being installed into the VPC route table. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of granular route control versus broader security measures like firewall rules or VPN tunnel configurations—a common trap is assuming that VPN tunnels or firewall policies alone can filter BGP-advertised routes, but they cannot; only Cloud Router policies control prefix acceptance at the routing layer. Remember the memory tip: "Filter at the Router, not the Tunnel"—route filtering must happen at the BGP peering level, not at the VPN gateway or firewall, to ensure only authorized prefixes populate your VPC routes.
PCNE Implementing network security Practice Question
This PCNE practice question tests your understanding of implementing network security. 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 multiple on-premises networks connected to a Cloud VPN hub in GCP. Each on-premises site uses BGP to advertise its prefixes. The security team wants to ensure that only specific prefixes from each site are accepted into the VPC routes. What should they configure?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure BGP route filtering on the Cloud Router to accept only specific prefixes from each on-premises site.
Option A is correct because Cloud Router supports BGP route filtering, allowing you to define inbound route policies that accept only specific prefixes from each on-premises BGP peer. This ensures that only the desired prefixes are installed into the VPC route table, providing granular control over route advertisement acceptance without affecting the VPN tunnel or firewall state.
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.
✓
Configure BGP route filtering on the Cloud Router to accept only specific prefixes from each on-premises site.
Why this is correct
Cloud Router allows filtering inbound and outbound routes.
Related concept
Read the scenario before looking for a memorised answer.
✗
Create firewall rules to block traffic from unwanted prefixes.
Why it's wrong here
Firewall rules control traffic, but routes are still learned; this is less efficient.
✗
Set up a separate VPN tunnel for each prefix.
Why it's wrong here
Not scalable and not a routing filter.
✗
Use VPC Service Controls to restrict the prefixes.
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between route filtering (control plane) and firewall rules (data plane), so the trap here is that candidates mistakenly think firewall rules can prevent unwanted route injection, when in fact they only block traffic after the route is already learned.
Detailed technical explanation
How to think about this question
Cloud Router uses BGP with support for route policies via the `bgp-route-selection` and `advertised-route-priority` features, but for inbound filtering you configure a `router` resource with a `bgp` section that includes `advertise_mode` and `advertised_ip_ranges`, or use the `router` `bgp` `route_policy` to match on community attributes or prefix lists. In a real-world scenario, an enterprise might use BGP communities from each site to tag prefixes and then apply a route policy on the Cloud Router to accept only those with a specific community value, preventing route leaks from misconfigured peers.
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 network security — This question tests Implementing network security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure BGP route filtering on the Cloud Router to accept only specific prefixes from each on-premises site. — Option A is correct because Cloud Router supports BGP route filtering, allowing you to define inbound route policies that accept only specific prefixes from each on-premises BGP peer. This ensures that only the desired prefixes are installed into the VPC route table, providing granular control over route advertisement acceptance without affecting the VPN tunnel or firewall state.
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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