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Subnet Calculator
AWS • Azure • GCP Cloud Architecture

Cloud VPC CIDR Calculator & Subnet Planner

Plan non-overlapping, high-availability subnets for AWS VPCs, Azure VNets, and Google Cloud networks across multiple Availability Zones. Accurately factors in cloud provider reserved IP addresses and exports ready-to-use Terraform configuration code.

Subnet Sizing Tiers per AZ:
Public (ALB/NAT)
Private App (EC2)
Private DB (RDS)

Generated Subnet Architecture

Subnet NameAZCIDR BlockUsable Hosts
✓All subnets fit seamlessly within base VPC CIDR without overlapping.

Cloud Provider Reserved IP Addresses Explained

Unlike traditional on-premises networking where only 2 addresses per subnet are reserved (Network ID and Directed Broadcast), major cloud providers reserve additional IP addresses at the beginning of every subnet:

AWS: 5 Reserved IPs per Subnet

  • .0: Network address.
  • .1: Reserved by AWS for the VPC router.
  • .2: Reserved by AWS for Amazon Provided DNS (Route 53 Resolver).
  • .3: Reserved by AWS for future use.
  • .255: Network broadcast address (broadcast is not supported in a VPC).

Azure: 5 Reserved IPs per VNet Subnet

  • .0: Network address.
  • .1: Reserved by Azure for the default gateway.
  • .2 and .3: Reserved by Azure to map Azure DNS IPs to the VNet space.
  • .255: Network broadcast address.

Google Cloud (GCP): 4 Reserved IPs per Subnet

  • .0: Network address.
  • .1: Reserved by GCP for the default gateway.
  • .254: Reserved by GCP for future use.
  • .255: Network broadcast address.

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