FortiGuard Management : Advanced settings : FortiGuard antivirus and IPS settings : Override FortiGuard server (Local FortiManager)
 
Override FortiGuard server (Local FortiManager)
Configure and enable alternate FortiManager FDS devices, rather than using the local FortiManager system. You can set up as many alternate FDS locations, and select what services are used.
Figure 295: Override FortiGuard server
Configure the following settings:
Additional number of private FortiGuard servers (excluding this one) (1) +
Select the plus (+) icon to add a private FortiGuard server.
When adding a private server, you must enter its IP address and time zone.
Enable Antivirus and IPS Update Service for Private Server
When one or more private FortiGuard servers are configured, update antivirus and IPS through this private server instead of using the default FDN.
This option is available only when a private server has been configured.
Enable Web Filter and Email Filter Update Service for Private Server
When one or more private FortiGuard servers are configured, update the web filter and email filter through this private server instead of using the default FDN.
This option is available only when a private server has been configured.
Allow FortiGates to access public FortiGuard servers when private servers unavailable
When one or more private FortiGuard servers are configured, managed FortiGate units will go to those private servers for FortiGuard updates. Enable this feature to allow those FortiGate units to then try to access the public FDN servers if the private servers are unreachable.
This option is available only when a private server has been configured.
 
The FortiManager system’s network interface settings can restrict which network interfaces provide FDN services. For more information, see “Configuring network interfaces”.