When you create a VPC you assign it a CIDR block (an IP range), then divide it into subnets. The exam expects you to understand how ranges are split and reserved.
What to know
A VPC CIDR can be /16 to /28. Each subnet takes a slice of it, and AWS reserves 5 IPs per subnet (network, VPC router, DNS, future use, broadcast). Public subnets route to an Internet Gateway; private ones don’t. The tell is planning address space so subnets don’t overlap and leave room to grow.
Test yourself
How many IP addresses does AWS reserve in every subnet, reducing the usable count?
- 2
- 5
- 1
- 10
👉 Click to reveal the answer & explanation
Correct answer: B. AWS reserves 5 IP addresses in each subnet (network address, VPC router, DNS, a reserved address, and broadcast), so a /28 subnet’s 16 addresses yield 11 usable. The other counts are incorrect.
Related topics
Amazon VPC · VPC peering · NAT Gateway
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