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 a Cloud VPN between their on-premises network and Google Cloud. They want to ensure that traffic flows symmetrically, meaning that traffic from Google Cloud to on-premises uses the same VPN tunnel as traffic from on-premises to Google Cloud. Which best practice should they implement?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Implement policy-based routing that forces traffic to and from specific subnets to use the same tunnel.
Option B is correct because policy-based routing (PBR) allows you to explicitly define forwarding rules based on source/destination IP addresses, ensuring that traffic from Google Cloud to on-premises uses the same VPN tunnel as the reverse direction. This enforces symmetric flow, which is critical for stateful firewalls and NAT devices that expect packets to arrive on the same interface they left. Dynamic routing (BGP) or static routes alone do not guarantee symmetry unless combined with PBR or tunnel interface configurations.
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.
✗
Use dynamic routing with BGP and ensure that the AS path length is the same on both sides.
Why it's wrong here
BGP does not inherently enforce symmetric routing.
✓
Implement policy-based routing that forces traffic to and from specific subnets to use the same tunnel.
Why this is correct
Policy-based routing can enforce symmetric flows.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Deploy multiple VPN tunnels and use different priorities for each.
Why it's wrong here
Multiple tunnels with different priorities can cause asymmetry if traffic takes different paths in each direction.
✗
Use static routes pointing to the VPN tunnel on both sides.
Why it's wrong here
Static routes can lead to asymmetry if there are multiple paths.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that dynamic routing protocols like BGP inherently provide symmetric routing, but in reality, BGP only controls the best path selection independently on each router, so without additional configuration (e.g., PBR or tunnel interface binding), traffic can easily become asymmetric.
Detailed technical explanation
How to think about this question
Policy-based routing (PBR) works by matching traffic based on ACLs (access control lists) and then applying a 'set ip next-hop' or 'set interface' command to force the packet out a specific tunnel. In Google Cloud, symmetric routing is enforced by Cloud Router's BGP session configuration, but when using policy-based VPNs (route-based VPNs with static routing), you must manually configure PBR on both sides to ensure the same tunnel is used for bidirectional traffic. A real-world scenario is when an on-premises firewall performs stateful inspection and drops return packets that arrive on a different interface than the original outbound flow.
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: Implement policy-based routing that forces traffic to and from specific subnets to use the same tunnel. — Option B is correct because policy-based routing (PBR) allows you to explicitly define forwarding rules based on source/destination IP addresses, ensuring that traffic from Google Cloud to on-premises uses the same VPN tunnel as the reverse direction. This enforces symmetric flow, which is critical for stateful firewalls and NAT devices that expect packets to arrive on the same interface they left. Dynamic routing (BGP) or static routes alone do not guarantee symmetry unless combined with PBR or tunnel interface configurations.
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: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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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