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Difficulty: MediumPlanning Virtual Private Cloud (VPC) Networks and Subnets

A cloud architect is planning to expand an existing primary subnet CIDR range in a custom-mode Virtual Private Cloud (VPC) that is connected to an on-premises data center via Cloud VPN. To ensure uninterrupted connectivity and prevent IP routing conflicts across the hybrid environment, in what sequence should these steps be executed?

  1. 1Audit existing on-premises IP subnets and active GCP network ranges to identify available contiguous CIDR blocks.
  2. 2Select an expanded primary subnet CIDR block (e.g., expanding from /24 to /22) that completely contains the original range and avoids on-premises routes.
  3. 3Execute the subnet IP range expansion operation to update the primary IP address range of the subnet.
  4. 4Update Cloud Router BGP advertisements or on-premises static routes to propagate the expanded subnet prefix across the VPN.

Answer

The correct order of steps is: 1) Audit existing on-premises IP subnets and active GCP network ranges to identify available contiguous CIDR blocks. 2) Select an expanded primary subnet CIDR block (e.g., expanding from /24 to /22) that completely contains the original range and avoids on-premises routes. 3) Execute the subnet IP range expansion operation to update the primary IP address range of the subnet. 4) Update Cloud Router BGP advertisements or on-premises static routes to propagate the expanded subnet prefix across the VPN.
The correct sequence follows a logical lifecycle for hybrid cloud networking: first audit existing address space to prevent overlaps, next select a valid expanded CIDR block that encompasses the original range, then perform the actual subnet expansion in GCP, and finally update hybrid BGP or static routes so the on-premises network can reach the newly expanded address range.

Step-by-Step Solution

1
Audit current hybrid network address space
Identified available non-overlapping CIDR space in both GCP and on-premises environments.
Prevents IP collisions between on-premises subnets and newly allocated GCP addresses.
2
Plan the target CIDR block for expansion
Selected a broader netmask (e.g., /22) that encompasses the current primary range (e.g., /24).
GCP subnet expansion rules require that the existing subnet range must be a subset of the new expanded range.
3
Apply the IP range expansion to the primary subnet
GCP updates the primary IP range for the subnet without destroying existing resources.
Modifies the subnet definition in GCP live environment without causing VM downtime.
4
Update hybrid routing configurations
On-premises networks are notified of the expanded IP range via BGP or updated static routes.
Ensures return traffic from on-premises to newly provisioned IPs in the expanded subnet range is routed correctly.

Key Concept

Planning and expanding GCP VPC subnets in a hybrid environment requires verifying CIDR non-overlap, adhering to GCP expansion rules (must encompass original range), applying the expansion, and updating hybrid BGP/static routing.
Estimated Time:1m 30s
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Topics

Planning Virtual Private Cloud (VPC) Networks and Subnets

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