How Clouds Slice Up IP Addresses (CIDR)

easy

Learn with your AI

Pick a depth. Each prompt opens in your AI pre-loaded with the lesson. Click a row to preview the prompt.

Or teach me the whole lesson:

Why this matters

Every VPC, subnet, and peering connection is a CIDR decision you can't easily undo. A /16 gives you 65k addresses but burns a private-IP block; a /24 gives you 254 hosts but caps your autoscaling group before you notice. Multi-cloud peering fails on day one if two clouds picked overlapping ranges.

Demo

Create non-overlapping VPC CIDRs across two clouds and verify the math.

Try it yourself

Calculate usable hosts in 10.0.0.0/22 (hint: 1022 in standard, 1019 in AWS) — verify with ipcalc 10.0.0.0/22.
Sketch a plan that gives 4 clouds a /14 each from the 10.0.0.0/8 space without overlap.
Try creating an AWS subnet at 10.10.1.0/24 inside a VPC of 10.10.0.0/24 — observe the rejection and explain why.

References

# AWS VPC at 10.10.0.0/16 (65,536 addresses, 65,531 usable per subnet)
aws ec2 create-vpc --cidr-block 10.10.0.0/16 \
  --tag-specifications 'ResourceType=vpc,Tags=[{Key=Name,Value=prod-aws}]'

# Subnet a /24 carve-out (256 addresses, 251 usable — AWS reserves 5)
aws ec2 create-subnet --vpc-id <vpc-id> \
  --cidr-block 10.10.1.0/24 --availability-zone us-east-1a

# Verify no overlap with peer
aws ec2 describe-vpcs --query 'Vpcs[*].[VpcId,CidrBlock]' --output table