FortiManager can act as a local FortiGuard server to provide FortiGuard services, such as AV engines and signatures, IPS engines and signatures, web filtering lookups, and firmware upgrades to your FortiGates.
FortiManager provides the resources by communicating with the FortiGuard Distribution Network (FDN) on a regular basis to keep the local services up to date, and providing the information to managed devices through the FortiGuard module. The FortiGuard module communicates with devices by using the FortiGuard protocol.
The FortiGuard module is often used to keep FortiGates up to date when FortiGates are not permitted to access the Internet.
For more information, see FortiGuard.