AWS Certified SysOps Administrator – Associate (legacy) — Question 290

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

Correct answer: A

Explanation

In any AWS VPC subnet, the first four IP addresses and the last IP address are reserved and cannot be assigned to an instance. For the private subnet (20.0.0.128/25), the IP address 20.0.0.255 is the network broadcast address and is reserved by AWS. The other options (20.0.0.132, 20.0.0.122, and 20.0.0.55) fall within the usable ranges of their respective subnets.