2026/09/25

That the smallest possible IPv4 CIDR AWS allows is /28, (16 addresses):

The allowed block size is between a /16 netmask (65,536 IP addresses) and /28 netmask (16 IP addresses)

– https://docs.aws.amazon.com/vpc/latest/userguide/vpc-cidr-blocks.html#:~:text=The%20allowed%20block%20size%20is%20between%20a%20%2F16%20netmask%20%2865%2C536%20IP%20addresses%29%20and%20%2F28%20netmask%20%2816%20IP%20addresses%29%2E