A cloud administration team needs to expand the primary IP address range of an existing su… — Google Cloud Associate Cloud Engineer

A cloud administration team needs to expand the primary IP address range of an existing subnet in a custom-mode Virtual Private Cloud (VPC) network. The subnet is currently configured with the primary CIDR block $10.20.1.0/24$ . Which CIDR range can be specified to successfully expand this existing subnet's primary IP range?

$10.20.0.0/23$ Answer
B
$10.20.1.0/25$
C
$10.20.2.0/24$
D
$10.20.1.128/25$

Answer

The CIDR range

10.20.0.0/23

correctly expands the existing subnet.

In Google Cloud VPC networks, expanding an existing primary subnet CIDR block requires providing a larger CIDR range (smaller netmask prefix length) that entirely includes the original IP range. The CIDR

10.20.0.0/23

spans from

10.20.0.0

10.20.1.255

, which fully encapsulates the existing

10.20.1.0/24

block.

Step-by-Step Solution

Identify the existing subnet primary IP range

The current subnet uses

10.20.1.0/24

, which covers IP addresses

10.20.1.0

through

10.20.1.255

Expanding a subnet requires selecting a broader network block that contains the original block.

Evaluate valid expansion constraints in Google Cloud VPC

To expand a primary subnet IP range, the netmask must be decreased (e.g., /24 to /23), and the start of the new block must align properly while containing the original addresses.

Subnet ranges can only be expanded, never shrunk or replaced with non-contiguous blocks.

Verify candidate CIDR blocks

10.20.0.0/23

covers

10.20.0.0

10.20.1.255

, successfully encompassing the original

10.20.1.0/24

block while doubling the available IP capacity.

This meets all VPC primary IP range expansion requirements.

Key Concept

VPC Subnet Primary CIDR Expansion Rules

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