Google Cloud Cross-Cloud Interconnect Protected Bandwidth Calculation

PCNE By islever Editorial Last updated

Configuring Cloud Interconnect. Configuring VPCs.

Short answer

A Provision 40 Gbps total bandwidth (20 Gbps per zone) for both CSPs in Frankfurt and attach them to a Cloud Router in europe-west3 to meet the 20 Gbps protected bandwidth and 99.9% SLA requirements.

Question

You are configuring a Cross-Cloud Interconnect connection for your Google Cloud organization with two public cloud service providers (CSPs)–CSP 1 and CSP 2. The CSP 1 and CSP 2 environments are closest to Frankfurt, Germany. You can choose between two common colocation locations, Frankfurt and Munich. Your organization's Google Cloud infrastructure is deployed in the North American region, us-east4, which is located in Virginia, USA. The VPC dynamic routing mode has been set to GLOBAL. Your organization requires 20 Gbps of protected bandwidth with a 99.9% Google Cloud SLA. You want to minimize costs where possible. What should you do?
    1. Create two Cross-Cloud Interconnect connections to CSP 1, with 40 Gbps of total bandwidth (20 Gbps in zone 1 and 20 Gbps in zone 2) in a common co-location facility located in Frankfurt, Germany. 2. Create two Cross-Cloud Interconnect connections to CSP 2, with 40 Gbps of total bandwidth (20 Gbps in zone 1 and 20 Gbps in zone 2) in a common co-location facility located in Frankfurt, Germany. 3. Create a Cloud Router in europe-west3 (Frankfurt), and configure two VLAN attachments for CSP 1 and two VLAN attachments for CSP 2.
    Correct Answer
    1. Create two Cross-Cloud Interconnect connections to CSP 1, with 20 Gbps of total bandwidth (10 Gbps in zone 1 and 10 Gbps in zone 2) in a common co-location facility located in Frankfurt, Germany. 2. Create two Cross-Cloud Interconnect connections to CSP 2, with 20 Gbps of total bandwidth (10 Gbps in zone 1 and 10 Gbps in zone 2) in a common co-location facility located in Frankfurt, Germany. 3. Create a Cloud Router in europe-west3 (Frankfurt), and configure two VLAN attachments for CSP 1 and two VLAN attachments for CSP 2.
    1. Create two Cross-Cloud Interconnect connections to CSP 1, with 40 Gbps of total bandwidth (20 Gbps in zone 1) in a common co-location facility located in Frankfurt, Germany and (20 Gbps in zone 2) in a common co-location facility located in Munich, Germany. 2. Create two Cross-Cloud Interconnect connections to CSP 2, with 40 Gbps of total bandwidth (20 Gbps in zone 1) in a common co-location facility located in Frankfurt, Germany and (20 Gbps in zone 2) in a common co-location facility located in Munich, Germany. 3. Create a Cloud Router in europe-west3 (Frankfurt), and configure two VLAN attachments for CSP 1 and two VLAN attachments for CSP 2.
    1. Create two Cross-Cloud Interconnect connections to CSP 1, with 40 Gbps of total bandwidth (20 Gbps in zone 1 and 20 Gbps in zone 2) in a common co-location facility located in Frankfurt, Germany. 2. Create two Cross-Cloud Interconnect connections to CSP 2, with 40 Gbps of total bandwidth (20 Gbps in zone 1 and 20 Gbps in zone 2) in a common co-location facility located in Frankfurt, Germany. 3. Create a Cloud Router in us-east4 (Ashburn, Virginia, USA), and configure two VLAN attachments for CSP 1 and two VLAN attachments for CSP 2.

Key Takeaways

Protected bandwidth requires double the provisioned capacity because the design must sustain the full required throughput even if one of the redundant links fails.

This page explains how to calculate bandwidth provisioning for Google Cloud Cross-Cloud Interconnect to meet protected bandwidth and SLA requirements. The correct answer involves doubling the required bandwidth to ensure redundancy.

Common mistake: Many candidates choose Option B (20 Gbps total, 10 Gbps per zone) assuming that splitting the required 20 Gbps evenly across two zones satisfies the requirement. This is incorrect because 'protected' implies resilience against a single failure; losing one 10 Gbps link would result in only 10 Gbps available, violating the 20 Gbps protected requirement.

Expert Analysis

The question requires a design for Cross-Cloud Interconnect (CCI) with specific constraints: 20 Gbps of protected bandwidth, a 99.9% SLA, and cost minimization. The key to this problem lies in understanding Google Cloud's redundancy model for interconnects.

To achieve the 99.9% SLA, connections must be deployed as a high-availability pair across two different availability zones within the same region. This is a standard requirement for protected connectivity on Google Cloud.

The critical technical detail is the definition of Protected Bandwidth. In Google Cloud's Cross-Cloud Interconnect, "protected" means that if one link fails, the remaining link(s) can sustain the traffic. Therefore, the total provisioned bandwidth must be at least double the required protected bandwidth to ensure that a single failure does not drop below the service level agreement. For a requirement of 20 Gbps protected, you need a total capacity of 40 Gbps (20 Gbps in Zone 1 + 20 Gbps in Zone 2). If you only provisioned 20 Gbps total (e.g., 10 Gbps per zone), a single failure would leave you with only 10 Gbps, failing the 20 Gbps protected requirement.

Option A correctly provisions 40 Gbps total bandwidth (20 Gbps in each zone) for both CSPs, ensuring that if one zone fails, the other still provides the full 20 Gbps. It places both connections in Frankfurt, which is cost-effective compared to spreading them across Munich (Option C). Option B incorrectly calculates the bandwidth as 20 Gbps total (10 Gbps per zone), which would fail the protected bandwidth requirement upon a single link failure. Option D incorrectly places the Cloud Router in us-east4; VLAN attachments for regional interconnects must be associated with a Cloud Router in the same region as the attachment (europe-west3).

Therefore, Option A is the correct configuration.

Official Reference

These links open the official vendor documentation in a new tab.

Exam Strategy

When designing for 'protected' or 'high-availability' bandwidth in Google Cloud exams, always remember the 50% rule: provision twice the required throughput. If you need N Gbps protected, you must have at least 2N Gbps total capacity distributed across redundant paths. Additionally, ensure VLAN attachments are created in the same region as the Cloud Router they connect to.

Frequently Asked Questions

What does 'protected bandwidth' mean in Google Cloud Interconnect?

Protected bandwidth means the connection is designed to maintain the specified throughput even if one of the redundant links fails. You must provision enough total bandwidth so that a single failure leaves enough capacity to meet the requirement.

Why must VLAN attachments be in the same region as the Cloud Router?

In Google Cloud, a VLAN attachment is a regional resource. It must be associated with a Cloud Router in the same region (e.g., europe-west3) to establish routing adjacency and manage the interconnect session.

More PCNE FAQ →

Community Votes

A
57%
B
43%

57% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 7 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 7

  1. mohitms1996 👍 4 Answered B
    Bandwidth + Redundancy: You need 20 Gbps of protected bandwidth, which means two 10 Gbps connections (one per zone) per CSP is sufficient when protected with redundancy. Google Cloud achieves 99.9% SLA when connections are deployed in redundant pairs (HA) across different edge availability zones. Location: Both CSP 1 and CSP 2 are closest to Frankfurt → no need to use Munich, which would increase complexity and cost. Though your GCP infra is in us-east4 (Virginia), your Cloud Router must be located in the same region as the VLAN attachments (i.e., europe-west3, Frankfurt), which is where the interconnects terminate. Routing mode: With Global dynamic routing, prefixes learned from europe-west3 will be available in us-east4, so you don’t need to place the Cloud Router in us-east4 (which would actually not work due to region mismatch).
  2. n2183712847 👍 2 Answered B
    20gb & 20gb
  3. researched_answer_boi 👍 1 Answered B
    Based on the documentation below, and the facts that global dynamic routing is enabled and Cloud Routers must be in the same GCP region as the VLAN attachment for the interconnect, I'd opt for "B" as the correct answer: https://docs.cloud.google.com/network-connectivity/docs/interconnect/concepts/cci-overview#capacity https://docs.cloud.google.com/network-connectivity/docs/interconnect/concepts/cci-overview#minimum-requirements
  4. ulkerra 👍 1 Answered A
    For 99.9% avalibility, one region, two zones and two vlan attachments are enough. For protected 20 Gbps, 40 Gbps of total bandwidth (20 Gbps in zone 1 and 20 Gbps in zone 2) required
  5. 0d2fdfa 👍 1 Answered A
    keyword is the protected bandwidth it reduces the capacity by 50% so remember the 50% rule for protected bandwidth
Show 2 more comments
  1. Gwendal 👍 1 Answered A
    https://cloud.google.com/network-connectivity/docs/interconnect/concepts/cci-overview#minimum-requirements
  2. 1f01b87 👍 1 Answered A
    Option A is the correct answer

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