Azure VNet Subnet Planner
VNet subnet allocation accurately accounting for Microsoft Azure 5 reserved IPs (.0, .1, .2, .3, and .255) with Bicep export.
Azure Virtual Network IP Reservation Architecture
When architects size subnets for Microsoft Azure, standard subnet calculators fail because they only deduct 2 addresses (network and directed broadcast). In Azure, the fabric SDN reserves exactly 5 IP addresses across every subnet regardless of prefix size. Calculating capacity with standard tools leads to deployment failures when provisioning VMs, Private Endpoints, or container instances.
Exact 5-IP Offset Accounting
Reflects offsets .0 (network), .1 (gateway), .2 & .3 (Azure DNS mapping), and the broadcast address so you never run out of IPs for production workloads.
Dedicated Azure Subnet Rules
One-click addition of mandatory enterprise subnets: GatewaySubnet (/27), AzureFirewallSubnet (/26), and AzureBastionSubnet (/26).
Bicep & Terraform Generation
Export your validated topology directly into production-grade infrastructure-as-code files ready to paste into your CI/CD repository.
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Frequently Asked Questions
Which 5 IP addresses does Microsoft Azure reserve in every subnet?
In Azure, the first 4 and the last IP in every subnet are reserved: (1) .0 - Network address; (2) .1 - Default gateway; (3) .2 - Azure DNS; (4) .3 - Azure DNS; (5) .255 - Broadcast address. The first usable host in an Azure subnet is always .4.
What is the minimum subnet size supported in an Azure VNet?
The smallest supported subnet in Azure is /29, which contains 8 total IP addresses and 3 usable IP addresses (8 minus 5 reserved). Subnets smaller than /29 cannot be created in Azure VNets.
What are the minimum subnet sizes for Azure GatewaySubnet and AzureFirewallSubnet?
Azure GatewaySubnet requires a minimum of /29, but Microsoft strongly recommends /27 or larger. AzureFirewallSubnet and AzureBastionSubnet both require a minimum prefix of /26.
Need this designed for a real production environment?
Consult with Gurinder Singh and vetted cloud specialists for Azure Landing Zones, AWS VPC peering, and hybrid connectivity.