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Zorluk: OrtaPlanning Virtual Private Cloud (VPC) Networks and Subnets

A cloud engineer is preparing to integrate a Google Cloud environment with an on-premises network via Cloud VPN. The current GCP deployment uses an auto-mode Virtual Private Cloud (VPC) network. To prevent future IP CIDR collisions with on-premises subnets and gain control over subnet creation, the engineer must convert the auto-mode VPC to a custom-mode VPC and provision a new subnet in a new region. What is the correct sequence of steps to execute this migration safely?

  1. 1Audit the existing on-premises IP address space and verify that currently deployed auto-mode subnets do not conflict with remote routes.
  2. 2Switch the VPC network mode from auto to custom using the gcloud command-line tool or Google Cloud Console.
  3. 3Plan and define a unique primary CIDR block for the target expansion region that does not overlap with any existing GCP or on-premises subnets.
  4. 4Create the new custom subnet in the target region within the converted VPC network using the allocated non-overlapping CIDR block.

Cevap

The correct sequence begins with auditing existing network IP space for conflicts, followed by converting the VPC network from auto to custom mode, then planning a unique non-overlapping CIDR block for the target region, and finally creating the new custom subnet.
To safely transition a GCP VPC for hybrid connectivity, an engineer must first audit existing IP allocations against on-premises routes to identify potential conflicts. Next, the VPC network mode must be converted from auto to custom mode, which retains existing subnets while granting administrative control over future subnet creation. After conversion, the engineer plans a distinct, non-overlapping CIDR block for the new region, and finally provisions the new custom subnet using that range.

Adım Adım Çözüm

1
Audit current IP address space against on-premises routes.
Identified any potential IP collisions before modifying VPC architecture.
Existing subnets must be validated first so active traffic is not disrupted when establishing hybrid connectivity.
2
Convert the VPC network from auto mode to custom mode.
The VPC network is switched to custom mode, preserving existing subnets while disabling automatic subnet creation in new regions.
Auto-mode VPCs automatically create subnets with fixed /20 CIDR blocks in every region, which often overlap with enterprise networks.
3
Plan a non-overlapping IP range for the new region.
A specific, non-colliding CIDR block is allocated for the target expansion region.
Custom-mode VPCs require explicit IP range planning to support scalable hybrid networking.
4
Provision the custom subnet using the planned CIDR block.
The new custom subnet is created and ready to host workloads in the specified region.
Subnets can only be custom created after the VPC network mode has been updated to custom.

Anahtar Kavram

Converting Auto-Mode VPC to Custom-Mode VPC for Hybrid Network Planning
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