Quick Answer
The answer is on-premises router CPU capacity. This factor directly impacts throughput because the router must process encryption, decryption, and packet forwarding for the VPN tunnel; if its CPU is overloaded, it becomes a bottleneck regardless of cloud-side resources. Additionally, tunnel type matters: route-based tunnels support ECMP and avoid per-packet policy lookups, reducing CPU overhead, while policy-based tunnels force the gateway to evaluate each packet against a security policy, adding latency and limiting throughput under high traffic. On the Google Professional Cloud Network Engineer exam, this question tests your understanding of how on-premises hardware constraints interplay with cloud VPN design—a common trap is focusing only on bandwidth or cloud-side limits while ignoring the router’s processing power. Remember the mnemonic “TEC” for Tunnel type, Encryption overhead, and CPU capacity—the three core throughput factors.
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.
Which THREE factors can affect the throughput of a Cloud VPN tunnel? (Choose three.)
VM instance types
Why wrong: VPN gateway is managed; VMs are not directly involved.
Number of tunnels
Why wrong: Number of tunnels affects aggregate throughput but not per-tunnel.
Tunnel type (route-based vs policy-based)
Different tunnel types have different overheads.
Encryption algorithm
Stronger algorithms use more CPU and reduce throughput.
On-premises router CPU capacity
On-premises device is a common bottleneck.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Tunnel type (route-based vs policy-based)
Tunnel type (route-based vs policy-based) affects throughput because route-based tunnels (e.g., using BGP or static routes) can leverage ECMP and do not require per-flow policy lookups, reducing CPU overhead. Policy-based tunnels require the VPN gateway to evaluate each packet against a security policy, which adds latency and can limit throughput, especially under high traffic loads.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
VM instance types
Number of tunnels
Why it's wrong here
Number of tunnels affects aggregate throughput but not per-tunnel.
Tunnel type (route-based vs policy-based)
Why this is correct
Different tunnel types have different overheads.
Related concept
Read the scenario before looking for a memorised answer.
Encryption algorithm
Why this is correct
Stronger algorithms use more CPU and reduce throughput.
Related concept
Read the scenario before looking for a memorised answer.
On-premises router CPU capacity
Why this is correct
On-premises device is a common bottleneck.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Google Cloud often tests the misconception that VM instance types or the number of tunnels directly control VPN throughput, when in reality the tunnel type, encryption algorithm, and on-premises router CPU are the primary factors that limit or enhance throughput.
Detailed technical explanation
Route-based tunnels (VTI) use a virtual interface and routing table to forward traffic, allowing for ECMP and dynamic routing protocols like BGP, which can distribute load across multiple paths. Policy-based tunnels require the VPN gateway to match traffic against a policy (e.g., source/destination IP, port) before encryption, which introduces per-packet processing overhead that can become a bottleneck in high-throughput scenarios. In GCP, Cloud VPN supports both types, but route-based tunnels are recommended for higher throughput and scalability.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
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FAQ
Implementing hybrid interconnectivity — This question tests Implementing hybrid interconnectivity — Read the scenario before looking for a memorised answer..
The correct answer is: Tunnel type (route-based vs policy-based) — Tunnel type (route-based vs policy-based) affects throughput because route-based tunnels (e.g., using BGP or static routes) can leverage ECMP and do not require per-flow policy lookups, reducing CPU overhead. Policy-based tunnels require the VPN gateway to evaluate each packet against a security policy, which adds latency and can limit throughput, especially under high traffic loads.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This PCNE practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCNE exam.
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