Chapter 10 Install and System Administration for FortiOS 5.0 : VLANs : Example VLAN configuration in NAT mode : Configure the FortiGate unit : Configure the external interface
  
Configure the external interface
The FortiGate unit’s external interface will provide access to the Internet for all internal networks, including the two VLANs.
To configure the external interface - web-based manager
1. Go to System > Network > Interface.
2. Select Edit for the external interface.
3. Enter the following information and select OK:
Addressing mode
Manual
IP/Network Mask
172.16.21.2/255.255.255.0
To configure the external interface - CLI
config system interface
edit external
set mode static
set ip 172.16.21.2 255.255.255.0
end
See Also
Configure the FortiGate unit
Add VLAN subinterfaces
Add the firewall addresses
Add the security policies