To increase the number of physical FortiGate units, you need more rack space, cables, and power to install the new units. You also need to change your network configuration to accommodate the new physical units. In the future, if you need fewer physical units you are left with expensive hardware that is idle.

Increasing VDOMs involves no additional hardware, no additional cabling, and very few changes to existing networking configurations. VDOMs save physical space and power. You are limited only by the size of the VDOM license you buy and the physical resources on the FortiGate unit.

For example, if you are using one FortiGate 620B unit with 10 VDOMs instead of 10 physical units, over a year you will save an estimated 18,000 kWh. You could potentially save ten times that amount with a 100 VDOM license.

By default, FortiGate units support a maximum of 10 VDOMs in any combination of NAT/Route and Transparent modes. For FortiGate models numbered 3000 and higher, you can purchase a license key to increase the maximum number of VDOMs beyond 10. For more information on VDOM licences, see “Virtual Domain Licensing”.