How can the user create the second subnet?
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
The user can modify the first subnet CIDR from the console
It is not possible to create a second subnet as one subnet with the same CIDR as the VPC has been created
The user can modify the first subnet CIDR with AWS CLI
Explanations:
AWS does not automatically adjust the CIDR of existing subnets when a new subnet is created. The CIDR of subnets must not overlap, and the VPC will not change the existing subnet’s CIDR.
The first subnet’s CIDR cannot be modified to allow for another subnet within the same CIDR range, as subnets must be smaller and distinct from the VPC CIDR and other subnets.
It is not possible to create a second subnet with a CIDR that overlaps with the CIDR of the VPC or any existing subnet. Since the first subnet uses the entire range of the VPC, no additional subnets can be created.
The AWS CLI cannot be used to modify a subnet’s CIDR. Once a subnet is created, its CIDR cannot be changed, meaning the existing subnet’s CIDR cannot be adjusted to allow for a new subnet.
I assess that the answer is:
It is not possible to create a second subnet as one subnet with the same CIDR as the VPC has been created