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

The most effective long-term solution to address IPv4 address exhaustion in GKE clusters, while still ensuring routability and unique ranges per cluster, is to transition to dual-stack IPv4/IPv6 clusters and leverage IPv6 for Pods and Services. This allows you to conserve IPv4 addresses for critical use cases while providing a vast address space with IPv6 for pods and services, significantly reducing the pressure on your private IPv4 ranges. Google Cloud GKE fully supports dual-stack networking.

Exact Extract:

"Dual-stack clusters enable you to assign both IPv4 and IPv6 addresses to Pods and Services. This approach helps conserve IPv4 address space by shifting a significant portion of the network communication to IPv6, particularly for internal cluster communication or communication with other IPv6-enabled services."

"When you enable dual-stack networking, GKE assigns an IPv6 address range to your Pods and can also assign IPv6 addresses to Services. This significantly expands the available addressing capacity within your cluster."Reference: Google Kubernetes Engine Documentation - Dual-stack networking

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