AWS Certified Solutions Architect – Professional SAP-C01 – Question331

A user has created a VPC with CIDR 20.0.0.0/16. The user has created one subnet with CIDR 20.0.0.0/16 by mistake. The user is trying to create another subnet of CIDR 20.0.1.0/24.
How can the user create the second subnet?

A. The user can modify the first subnet CIDR with AWS CLI
B. The user can modify the first subnet CIDR from the console
C. There is no need to update the subnet as VPC automatically adjusts the CIDR of the first subnet based on the second subnet's CIDR
D. It is not possible to create a second subnet with overlapping IP CIDR without deleting the first subnet.

Correct Answer: D

Explanation:

Explanation: A Virtual Private Cloud (VPC) is a virtual network dedicated to the user’s AWS account. A user can create a subnet with VPC and launch instances inside the subnet. The user can create a subnet with the same size of VPC. However, he cannot create any other subnet since the CIDR of the second subnet will conflict with the first subnet. The user cannot modify the CIDR of a subnet once it is created. Thus, in this case if required, the user has to delete the subnet and create new subnets.
Reference:
http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Subnets.html