Which discovery scan type is prone to miss a device, if the device is quiet...

 Discovery Scan Types: FortiSIEM uses various scan types to discover devices on a network.

 Layer 2 (L2) Scan: An L2 scan discovers devices based on ARP tables and MAC address information from adjacent devices.

Limitation: If a device is quiet (not actively communicating) and its entry is not present in the ARP table of adjacent devices, the L2 scan may miss it.

 Other Scan Types:

CMDB Scan: Based on the existing Configuration Management Database (CMDB) entries.

Range Scan: Scans a specified IP range for devices.

Smart Scan: Uses a combination of methods to discover devices.

 References: FortiSIEM 6.3 User Guide, Device Discovery section, which explains the different types of discovery scans and their characteristics.