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 and a private subnet with CIDR 20.0.0.128/25. The user has launched one instance each in the private and public subnets. Which of the below mentioned options cannot be the correct IP address (private IP. assigned to an instance in the public or private subnet?

Answer options:

A.20.0.0.255
B.20.0.0.132
C.20.0.0.122
D.20.0.0.55

Answer – A
As per the AWS documentation there is a reservation of IP addresses. Hence option A is right because this IP address will be reserved by AWS.
The first four IP addresses and the last IP address in each subnet CIDR block are not available for you to use, and cannot be assigned to an instance. For example, in a subnet with CIDR block 10.0.0.0/24, the following five IP addresses are reserved:
· 10.0.0.0: Network address.
· 10.0.0.1: Reserved by AWS for the VPC router.
· 10.0.0.2: Reserved by AWS. The IP address of the DNS server is always the base of the VPC network range plus two; however, we also reserve the base of each subnet range plus two. 10.0.0.3: Reserved by AWS for future use.
· 10.0.0.255: Network broadcast address. We do not support broadcast in a VPC, therefore we reserve this address.
For more information on IP Reservation, please visit the link:
http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Subnets.html