In a scenario with four environments and multiple VPCs, what is the minimum CIDR network subnet for each VPC?

In a scenario with four environments and multiple VPCs, what is the minimum CIDR network subnet for each VPC?

• A. /22
• B. /23
• C. /24
• D. /25

Answer: (B)

Planning IP space for VPCs means sizing the VPC CIDR to hold all the subnets you’ll create inside it, while keeping room for growth and avoiding overlaps with other VPCs. In this scenario you typically want subnets that correspond to different environments or tiers, often across multiple Availability Zones. A /23 gives you 512 total IP addresses, which is enough to carve out two /24 subnets (two environments, for example) inside the VPC, with AWS reserving 5 addresses in each subnet. That leaves about 502 usable addresses across those two subnets, which is a practical amount for a compact, multi-environment setup. If you used a /24, you’d have only a single /24 subnet to work with, which isn’t enough when you need more than one environment or additional subnets inside the same VPC. A /22 would certainly work, but it’s larger than necessary for just two subnets and is not the minimum required. Therefore, the smallest VPC CIDR that reliably accommodates the typical two-subnet-per-VPC arrangement in this four-environments/multiple-VPC context is a /23.

Planning IP space for VPCs means sizing the VPC CIDR to hold all the subnets you’ll create inside it, while keeping room for growth and avoiding overlaps with other VPCs. In this scenario you typically want subnets that correspond to different environments or tiers, often across multiple Availability Zones. A /23 gives you 512 total IP addresses, which is enough to carve out two /24 subnets (two environments, for example) inside the VPC, with AWS reserving 5 addresses in each subnet. That leaves about 502 usable addresses across those two subnets, which is a practical amount for a compact, multi-environment setup.

If you used a /24, you’d have only a single /24 subnet to work with, which isn’t enough when you need more than one environment or additional subnets inside the same VPC. A /22 would certainly work, but it’s larger than necessary for just two subnets and is not the minimum required. Therefore, the smallest VPC CIDR that reliably accommodates the typical two-subnet-per-VPC arrangement in this four-environments/multiple-VPC context is a /23.