Thanks. Not really what I´m looking for. I wan´t to use this solution:
DNS Logging (401757)
FortiOS logging now includes the Detailed DNS log message type. DNS events were previously recorded as event logs. In FortiOS 5.6 DNS log messages are a new category that also includes more DNS log messages to provide additional detail about DNS activity through the FortiGate. You can enable DNS logging from the CLI using the following command (shown in this example for memory logging):
config log memory filterset dns enableend
DNS log messages include details of each DNS query and response. DNS log messages are recorded for all DNS traffic though the FortiGate and originated by the FortiGate.
The detailed DNS logs can be used for low-impact security investigation. Most network activity involves DNS activity of some kinds. Analyzing DNS logs can provide a lot of details about the activity on your network without using flow or proxy-based resource intensive techniques.