unofficial visual subnet calculator for Azure virtual networks, available at https://cidr.duckiesfarm.com
Azure holds 5 IP addresses for every subnet. The first and last IP in each subnet is reserved for the network identification and for broadcast, respectively. Azure also holds 3 additional addresses for internal use starting from the first address in the subnet. In Azure subnets are created using classless internet domain routing (CIDR) blocks of the address space that was designed for the Virtual Network. As an example, the smallest range you can specify for a subnet is /29, which provides eight IP addresses.
This tool simplifies the job of segmenting an Azure virtual network into subnets by showing the addresses that can actually be used.
Based on the work of David C A Croft.