Professional-Cloud-Network-Engineer Exam Dumps : Google Cloud Certified - Professional Cloud Network Engineer

how-to/dedicated/using-interconnects-other-projects

Using Cloud Interconnect with Shared VPC You can use Shared VPC to share your VLAN attachment in a project with other VPC networks. Choosing Shared VPC is preferable if you need to create many projects and would like to prevent individual project owners from managing their connectivity back to your on-premises network. In this scenario, the host project contains a common Shared VPC network usable by VMs in service projects. Because VMs in the service projects use this network, Service Project Admins don't need to create other VLAN attachments or Cloud Routers in the service projects. In this scenario, you must create VLAN attachments and Cloud Routers for a Cloud Interconnect connection only in the Shared VPC host project. The combination of a VLAN attachment and its associated Cloud Router are unique to a given Shared VPC network.

docs/shared-vpc

The problem description indicates that VMs in VPC2 receive traffic but their replies don't reach VPC1, especially when a VPN gateway fails. This strongly suggests an asymmetric routing issue, where VPC2's routing table might not be aware of all necessary routes to send return traffic to VPC1, particularly in a multi-region setup with failover. By default, VPC networks are in regional dynamic routing mode, meaning they only learn routes from Cloud Routers in the same region. To ensure that routes learned from one region (where the active VPN tunnel might be) are available globally across the VPC, you need to enable global dynamic routing mode in the VPC that is experiencing the return traffic issue (VPC2 in this case). This allows VPC2 to learn and apply routes from Cloud Routers in all regions, ensuring that even if a VPN tunnel fails in one region, the routes learned from the active tunnel in another region are still available for return traffic.

Exact Extract:

"A VPC network's dynamic routing mode controls whether routes learned by Cloud Routers in one region are available to VMs in other regions. By default, VPC networks are in regional dynamic routing mode, which means Cloud Routers in a region only advertise routes to and learn routes from other Cloud Routers in the same region. This can lead to asymmetric routing issues in multi-region deployments."

"To ensure that routes learned from Cloud Routers are propagated to all regions within a VPC network, you must set the dynamic routing mode to global."Reference: Google Cloud VPC Documentation - Dynamic routing mode