VPC IPV4 CIDR Block Range - Student Inquiry (HELP! Due Tomorrow)

Question

Hi, can someone please help me?  I created a VPC for a school project, and specified an IP range of 192.168.0.0/24. That part went fine. But when I try to create a subnet that has a CIDR block that is contained within (and is smaller than) the VPC's CIDR range, I am unable to do so. Subnetting is a whole new concept for me. Is there someone that can give me a CIDR block that will work, and also a small summary of how to do this so that I do not struggle in the future?

kentrad · Answer

Use a CIDR calculator such as, [cidr / vlsm supernet calculator](https://www.subnet-calculator.com/cidr.php).

```
192.168.0.0/24 gives 256 addresses, address range of 192.168.0.0 - 192.168.0.255
```
If we want to split that into 4 subnets:
```
192.168.0.0/26 gives 64 addresses, address range of 192.168.0.0 - 192.168.0.63
192.168.0.64/26 gives 64 addresses, address range of 192.168.0.64 - 192.168.0.127
192.168.0.128/26 gives 64 addresses, address range of 192.168.0.128 - 192.168.0.191
192.168.0.192/26 gives 64 addresses, address range of 192.168.0.192 - 192.168.0.255
```
The size of a CIDR is 2**(32-width of prefix). For instance 192.168.0.0/24 is 2**(32-24) = 2**8 = 256.

VPC IPV4 CIDR Block Range - Student Inquiry (HELP! Due Tomorrow)

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