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Question 7 of 65

Part 2: Networking, VPC & Traffic Routing (6 - 20)

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AWS Cloud Architecture•Part 2: Networking, VPC & Traffic Routing (6 - 20)

How many IP addresses does AWS reserve in each subnet CIDR block?

In Simple Words: AWS reserves 5 IP addresses in every subnet (e.g. in 10.0.0.0/24):

  1. .0: Network address.
  2. .1: Reserved by AWS for VPC router.
  3. .2: Reserved by AWS for DNS (AmazonProvidedDNS).
  4. .3: Reserved by AWS for future use.
  5. .255: Network broadcast address (VPCs do not support broadcast).
bash
# Calculate usable IPs in AWS subnet:
# /24 gives 256 addresses -> 256 - 5 = 251 usable IP addresses!
aws ec2 describe-subnets --subnet-ids subnet-12345678   --query "Subnets[0].AvailableIpAddressCount"
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