VPC/CIDR IPv4 issue

Question

Hello, Good day. Just started learning how to write IAAC on Cloud Formation using my text editor and I noticed something I don't understand.

Scenario 1 : If i create a VPC with an IPv4 CIDR (10.0.1.0/16) it rejects on the AWS console as invalid.

Scenario 2 : But if i run it as IAAC (Cloud formation) on a connected text editor, it corrects the mistake and works but the error remains in the CFN template

why?

I have screenshots incase this is needed.

Thank you

Answer

This is because CloudFormation corrects the VPC CIDR to its canonical form.  See https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-ec2-vpc.html

*CidrBlock
    The IPv4 network range for the VPC, in CIDR notation. For example, 10.0.0.0/16. We modify the specified CIDR block to its canonical form; for example, if you specify 100.68.0.18/18, we modify it to 100.68.0.0/18.*

VPC/CIDR IPv4 issue

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