AWS Certified SysOps Administrator SOA-C01 – Question091

A user has created a VPC with CIDR 20.0.0.0/24. The user has created a public subnet with CIDR 20.0.0.0/25. The user is trying to create the private subnet with CIDR 20.0.0.128/25. Which of the below mentioned statements is true in this scenario?

A. It will not allow the user to create the private subnet due to a CIDR overlap
B. It will allow the user to create a private subnet with CIDR as 20.0.0.128/25
C. This statement is wrong as AWS does not allow CIDR 20.0.0.0/25
D. It will not allow the user to create a private subnet due to a wrong CIDR range

Correct Answer: B

Explanation:

Explanation: When the user creates a subnet in VPC, he specifies the CIDR block for the subnet. The CIDR block of a subnet can be the same as the CIDR block for the VPC (for a single subnet in the VPC., or a subset (to enable multiple subnets. If the user creates more than one subnet in a VPC, the CIDR blocks of the subnets must not overlap. Thus, in this case the user has created a VPC with the CIDR block 20.0.0.0/24, which supports 256 IP addresses (20.0.0.0 to 20.0.0.255. The user can break this CIDR block into two subnets, each supporting 128 IP addresses. One subnet uses the CIDR block 20.0.0.0/25 (for addresses
20.0.0.0 – 20.0.0.127. and the other uses the CIDR block 20.0.0.128/25 (for addresses 20.0.0.128 20.0.0.255.