A FortiClient fails to establish a VPN tunnel with a FortiGate unit. Which of the following
statements is a possible cause for the failure to establish the VPN tunnel?

A.
An IPSec DHCP server is not enabled on the external interface of the FortiGate unit.

B.
The phase 1 configuration on the FortiGate unit uses Aggressive mode while FortiClient
uses Main mode.

C.
There is a mismatch between the FortiGate unit and the FortiClient IP addresses in the
phase 2 settings.

D.
There is no IPSec firewall policy configured for the policy-based VPN.