Chapter 11 IPsec VPN for FortiOS 5.0 : Monitoring and troubleshooting : Logging VPN events
  
Logging VPN events
You can configure the FortiGate unit to log VPN events. For IPsec VPNs, phase 1 and phase 2 authentication and encryption events are logged. For information about how to interpret log messages, see the FortiGate Log Message Reference.
To log VPN events
1. Go to Log & Report > Log Config > Log Settings.
2. Verify that the VPN activity event option is selected.
3. Select Apply.
To view event logs
1. Go to Log & Report > Event Log > VPN.
2. Select the Log location.