HA VPN Design for 99.99% Availability
A company is designing an HA VPN to connect their on-premises data center to Google Cloud VPC. The on-premises router supports two independent interfaces with public IPs. They want to achieve 99.99% availability for the VPN connection, understanding that HA VPN uses two tunnels and two Cloud Router instances. Which configuration meets this goal?
Quick Answer
The correct configuration is four tunnels: one tunnel from each on-premises interface to each Cloud Router instance, totaling four BGP sessions. This meets the 99.99% availability goal because HA VPN design for high availability requires full mesh redundancy between the two on-premises interfaces and the two Cloud Router instances, ensuring that any single failure—whether an on-premises interface, a Cloud Router, or a tunnel—still leaves at least one active path for traffic. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding that HA VPN’s SLA is achieved only when both Cloud Routers and both on-premises interfaces are fully utilized with distinct BGP sessions; a common trap is assuming two tunnels (one per Cloud Router) are sufficient, but that leaves a single point of failure on the on-premises side. Remember the memory tip: “two times two equals four tunnels” — each on-premises interface must talk to each Cloud Router to eliminate all single points of failure.
⚠ Common exam trap
Candidates often think two tunnels (one per interface) to the same Cloud Router is sufficient, but they overlook that the Cloud Router itself is a single point of failure, and HA VPN requires redundancy at both the on-premises and Cloud Router layers to achieve 99.99% availability.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Four tunnels: one tunnel from each on-premises interface to each Cloud Router instance, totaling four BGP sessions
HA VPN requires at least two Cloud Router instances and two tunnels from each on-premises interface to each Cloud Router instance to achieve 99.99% availability. This configuration creates four BGP sessions, ensuring that if one on-premises interface, one Cloud Router, or one tunnel fails, traffic can still flow through the remaining paths. The design leverages both redundancy of interfaces and redundancy of Cloud Routers to meet the high availability SLA.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Two tunnels: both tunnels from the same on-premises interface to two different Cloud Router instances
Why it's wrong here
Sharing the same interface creates a single point of failure.
- ✗
Two tunnels: each tunnel from a separate on-premises interface to the same Cloud Router instance
Why it's wrong here
All tunnels terminate on one Cloud Router, single point of failure.
- ✗
Four tunnels: two tunnels from each on-premises interface to the same Cloud Router instance
Why it's wrong here
Two tunnels to the same Cloud Router instance still has a single point of failure at the Cloud Router level.
- ✓
Four tunnels: one tunnel from each on-premises interface to each Cloud Router instance, totaling four BGP sessions
Why this is correct
This provides full device and path redundancy suitable for 99.99% availability.
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Variation 1. A company wants to connect its on-premises data center to Google Cloud. They have a single VPN appliance on-premises and need high availability for the connection. Which architecture provides the most cost-effective high availability solution?
easy- ✓ A.Deploy Cloud HA VPN with two interfaces, each with its own external IP address, and configure two tunnels to the on-premises VPN appliance.
- B.Use a single Cloud Classic VPN tunnel with a static route.
- C.Deploy two Cloud Classic VPN gateways in the same region, each with one tunnel to the on-premises VPN appliance.
- D.Deploy Cloud HA VPN with one interface and one external IP address, and configure a single tunnel to the on-premises appliance.
Why A: Cloud HA VPN provides high availability by using two interfaces with two external IP addresses, and you can configure two tunnels to a single on-premises VPN appliance. This architecture is cost-effective because it uses a single Cloud VPN gateway (HA VPN) and does not require additional infrastructure. Option B is incorrect because a single Classic VPN tunnel does not provide high availability. Option C is incorrect because deploying two Classic VPN gateways is more expensive and still requires multiple tunnels to the same on-premises appliance, but it does not leverage the built-in HA capabilities of HA VPN. Option D is incorrect because Cloud HA VPN requires at least two interfaces (with separate IPs) to provide high availability; a single interface would be a single point of failure.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.