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Scenario-based practice

Troubleshooting Scenario Questions

Practise Google Professional Cloud Network Engineer practice questions — original exam-style scenarios covering every exam domain, with detailed explanations, wrong-answer analysis, and common exam traps.

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Google Cloud
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Scenario guide

How to approach troubleshooting scenario questions

These questions describe a network symptom and ask you to identify the root cause or the correct fix. They appear across all certification exams and reward systematic thinking over memorisation. The best candidates follow a consistent troubleshooting framework even under time pressure.

Quick answer

Troubleshooting Scenario Questions questions test whether you can apply the concept in context, not just recognise a definition.

How the topic appears in realistic exam-style scenarios.

Which detail in the question changes the correct answer.

How to eliminate plausible but wrong options.

How to connect the question back to the wider exam objective.

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Practice set

Practice scenarios

Question 1hardmultiple choice
Review the full subnetting walkthrough →

A network engineer is troubleshooting connectivity issues between two Compute Engine instances in the same VPC but different subnets (us-east1 and europe-west1). The engineer suspects an MTU issue. What is the default MTU for traffic within Google Cloud, and what MTU should the engineer expect when packets traverse the internet?

Question 2mediummultiple choice
Open the full BGP breakdown →

A company is using Cloud VPN to connect to Google Cloud. They notice that traffic from their on-premises network to Google Cloud is not being routed correctly after a recent change. On the on-premises router, they verify that the BGP session is established and routes are received. Which step should they take next to troubleshoot?

Question 3hardmultiple choice
Review the full subnetting walkthrough →

An engineer is troubleshooting a VPC Network Peering connection between two VPCs. The peering is established, but traffic from VPC A to VPC B is not reaching a specific subnet. Both VPCs have custom routes. What is the most likely cause?

Question 4hardmulti select
Open the full BGP breakdown →

A network engineer is troubleshooting a BGP session between an on-premises router and a Cloud Router. The BGP session state is 'CONNECT' and never transitions to 'ESTABLISHED'. The engineer has verified that the Cloud Router and on-premises router have the same BGP ASN, and that the peer IP addresses are correctly configured. Which two additional steps should the engineer take to resolve this issue? (Choose TWO.)

Question 5hardmulti select
Open the full BGP breakdown →

An engineer is troubleshooting a High Availability VPN setup. The VPN tunnels are established, but the BGP sessions are flapping. Which THREE factors could cause this? (Choose THREE.)

Question 6mediummulti select
Open the full BGP breakdown →

A company has a Dedicated Interconnect connection between their on-premises data center and Google Cloud. They are experiencing intermittent connectivity issues on a specific VLAN attachment. The VLAN attachment is configured with a single Cloud Router and BGP sessions are established. Which two steps should they take to troubleshoot the issue? (Choose two.)

Question 7mediummultiple choice
Open the full BGP breakdown →

An engineer has set up a Dedicated Interconnect with a VLAN attachment and a Cloud Router BGP session. They can ping the on-premises gateway IP but cannot reach an on-premises subnet 10.0.0.0/24 from a GCE instance. The on-premises router is advertising the subnet via BGP. What is the most likely cause?

Question 8hardmulti select
Full question →

A network engineer is troubleshooting a global HTTPS load balancer that is not serving traffic to some users. The load balancer has a backend service with a zonal NEG in us-central1-a. Users report intermittent 502 errors. Which two checks should the engineer perform? (Choose two.)

Question 9mediummultiple choice
Read the full NAT/PAT explanation →

A company uses Cloud NAT to allow instances without external IPs to access the internet. They have a managed instance group (MIG) in us-central1 with 10 instances, all using the same Cloud NAT configured with a single NAT IP address. They notice that some instances are unable to connect to a specific external API endpoint, while others can. The error on the failing instances is 'Cannot connect to host'. The NAT IP is not blacklisted by the API. The Cloud NAT gateway has default settings with a minimum port per VM of 64 and a maximum of 65536. What is the most likely cause?

Question 10mediummultiple choice
Read the full NAT/PAT explanation →

An engineer is troubleshooting outbound connectivity from a Compute Engine instance that has no external IP. The instance needs to reach an external service on the internet. Cloud NAT is configured on the VPC network. However, the instance cannot connect. What is the most likely cause?

Question 11mediummultiple choice
Open the full BGP breakdown →

A company is migrating its on-premises data center to Google Cloud. They currently have a Cloud VPN tunnel with dynamic routing (BGP) connecting their on-premises router (ASN 65001) to a Cloud Router in us-central1 (ASN 64512). The on-premises network uses IP range 10.0.0.0/8, and the Google Cloud VPC uses 172.16.0.0/12. After migration, they notice intermittent connectivity issues: traffic from on-premises to a new VM (172.16.1.2) is sometimes dropped, while other VMs in the same subnet work fine. The VM 172.16.1.2 is fine when accessed from other Google Cloud VMs. The team suspects asymmetric routing. Investigation shows that the on-premises router receives two routes for 172.16.1.2/32: one with next-hop as the Cloud VPN tunnel and another with next-hop as the internet (default route). No custom route advertisements are configured on the Cloud Router. The VPC has a default route (0.0.0.0/0) pointing to the internet gateway. What should the network engineer do to resolve the issue without breaking other connectivity?

Question 12hardmultiple choice
Open the full BGP breakdown →

A network engineer is troubleshooting BGP session flaps between a Cloud Router and an on-premises router. The Cloud Router logs show that the session goes down and up repeatedly every few minutes. What is the most common cause of such flapping?

Question 13hardmultiple choice
Open the full BGP breakdown →

A large e-commerce company has a hybrid cloud setup with a Dedicated Interconnect between their on-premises data center in Dallas and Google Cloud us-central1 region. They have a single VLAN attachment with a Cloud Router that uses BGP to exchange routes. The on-premises network uses 10.0.0.0/8, and Google Cloud VPC uses 172.16.0.0/16. They recently deployed a new application in us-west1 that uses IP range 172.17.0.0/16. They created a VPC peering between the us-central1 VPC and the us-west1 VPC. On-premises users can reach the us-central1 workloads but cannot reach the us-west1 application. There are no firewall rules blocking traffic. The on-premises router has a default route pointing to the Interconnect. What is the most likely cause of the issue?

Question 14hardmultiple choice
Review the full routing breakdown →

An engineer is troubleshooting asymmetric routing between two VPCs connected via VPC peering. They notice that return traffic takes a different path. What is a common cause of asymmetric routing in this scenario?

Question 15easymultiple choice
Open the full BGP breakdown →

You are troubleshooting an HA VPN connection between Google Cloud and on-premises. The tunnels appear as 'UP' but no routes are exchanged. The Cloud Router logs show 'BGP session state: IDLE'. What is the most likely cause?

These PCNE practice questions are part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style PCNE questions with detailed explanations, topic-based practice, mock exams, readiness tracking, and study analytics.