Subnet

Overview

A subnet is a slice of the IP range inside a virtual network. When you create a VM and pick a subnet, the VM is assigned an address from that subnet's range automatically.

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Creating a subnet

1. Under Network > Subnets, click Create Subnet.

2. Configure the following:

   Field	Description	Example
   Subnet name	An identifying name	prod-subnet-a
   Linked network	The virtual network it belongs to	prod-vnet
   Network CIDR	Subnet range, within the virtual network	192.168.0.0/24
   Gateway	Default gateway IP (one IP inside the subnet CIDR)	192.168.0.1

3. Click Create.

Subnet CIDR and gateway rules

• The subnet CIDR must be a subset of the virtual network CIDR. If the virtual network is 192.168.0.0/16, subnets can be 192.168.0.0/24, 192.168.1.0/24, etc.
• If the gateway IP is outside the subnet CIDR, you'll see networkCidrMismatch.

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CIDR sizing guide

The subnet size can't be changed later, so estimate how many IPs you need before creating it.

CIDR	Usable IPs	Typical use
/23	~512	Large environments (hundreds of VMs)
/24	~256	General use (dozens of VMs; default)
/25	~128	Smaller, isolated environments
/26	~64	Secondary subnets for DB / admin nodes

Splitting subnets by role makes firewall rules easier (e.g. web-subnet, app-subnet, db-subnet, mgmt-subnet).

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Managing subnets

• List: shows name, CIDR, parent virtual network, and IPs in use
• Delete: only possible when no network interfaces are attached

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Next steps

• Virtual network: creating a virtual network and designing the CIDR
• Public IP: allocating an IP for internet access