Visual Subnet Calculator (Azure Edition)
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Enter the network you wish to subnet: Click below to split and join subnets.
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Tips for Azure Virtual Network
Azure Reserved Subnet Name
| Reserved Subnet Name | min. Size of Subnet | Max. Size of Subnet | Recommand Size of Subnet | Related Azure Services |
|---|---|---|---|---|
| GatewaySubnet | /29 | /26 | /27 | Azure Virtual Network Gateway / ExpressRoute / Site-to-Site VPN |
| RouteServerSubnet | /27 | /24 | /27 | Azure Route Server |
| AzureBastionSubnet | /26 | /24 | /26 | Azure Bastion |
| AzureFirewallSubnet | /26 | /26 | /26 | Azure Firewall |
| AzureFirewallManagementSubnet | /29 | /26 | /29 | Azure Firewall Manager |
Common Subnet Size
| Common Subnet Name | min. Size of Subnet | Max. Size of Subnet | Recommand Size of Subnet | Related Azure Services |
|---|---|---|---|---|
| snet-in-dns-resolver | /28 | /24 | /28 | Azure Private DNS Resolver |
| snet-out-dns-resolver | /28 | /24 | /28 | Azure Private DNS Resolver |
Sample CIDR Plan
If you only have one /24 that can be designed...
Rule
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Based on Are there any restrictions on using IP addresses within these subnets?, Azure Subnet reserves 5 IP addresses in each subnet for internal use: the first 4 (Network ID, Default Gateway IP, Azure DNS reserved-1, Azure DNS reserved-2) and the last 1 (Network broadcast address) IP addresses.
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Based on Azure VMet - How small and how large can VNets and subnets be?, The smallest supported IPv4 subnet is /29, and the largest is /2 (using CIDR subnet definitions). IPv6 subnets must be exactly /64 in size.
Spotlight
Special Thanks to davidc + ChatGPT
The source code for Azure Edition page has been forked and ported from davidc/subnets. If you're searching for the original Visual Subnet Calculator, I encourage you to check out Visual Subnet Calculator. Furthermore, as I am not a front-end engineer, the project utilized ChatGPT for suggestions on modifications to HTML / CSS / Javascript.