Chapter 10 Install and System Administration for FortiOS 5.0 : VLANs : Example VLAN configuration in NAT mode : General configuration steps
  
General configuration steps
The following steps provide an overview of configuring and testing the hardware used in this example. For best results in this configuration, follow the procedures in the order given. Also, note that if you perform any additional actions between procedures, your configuration may have different results.
1. Configure the FortiGate unit
Configure the external interface
Add two VLAN subinterfaces to the internal network interface
Add firewall addresses and address ranges for the internal and external networks
Add security policies to allow:
the VLAN networks to access each other
the VLAN networks to access the external network.
2. Configure the VLAN switch
See Also
Configure the FortiGate unit
Configure the VLAN switch
Test the configuration