What is the smallest CIDR network subnet block you can allocate for your VPC?

The smallest CIDR network subnet block that can be allocated for a Virtual Private Cloud (VPC) is typically a /28. This allows for a smaller number of usable IPs within the subnet. In a /28 subnet, which provides 16 IP addresses in total, 14 are available for assignment after accounting for the network and broadcast addresses.

While /24, /20, and /16 subnets are valid options and are larger subnet sizes providing more IP addresses, they are not the smallest allowed for a VPC. A /24 allows for 256 total addresses (with 254 usable), /20 allows for 4096 addresses (with 4094 usable), and /16 allows for 65,536 addresses (with 65,534 usable).

Choosing a /28 block gives you the ability to fit smaller applications or portions of your architecture within a confined space, ideal for allocating specific services or features that don’t require a large number of IPs. Therefore, while /24 is a common choice, it is not the smallest option available for CIDR allocation in a VPC.