// tools/subnets

Azure subnet planner

Enter a virtual network address space and the subnets you need. Each subnet gets the first free range that fits, with usable addresses after the five Azure reserves.

Runs entirely in your browser. Nothing you paste is sent anywhere.

Virtual network address space

Subnets, one per line: name and size (/24) or number of addresses needed (60)

Presets:

Plan

Subnet	CIDR	Usable range	Usable IPs

Azure rules worth knowing. Azure reserves five addresses in every subnet: the network address, the next three (default gateway and Azure DNS) and the broadcast address. The smallest IPv4 subnet is a /29. GatewaySubnet should be /27 or larger, AzureFirewallSubnet and AzureBastionSubnet need /26, and those three names must be exact.