Charles wants to use IPSec and needs to be able to determine the IPSec policy for traffic based on the port it is being sent to on the remote system. Which IPSec mode should he use?

Unlike IPSec's tunnel mode, IPSec transport mode allows different policies per port. The IP addresses in the outer header for transport mode packets are used to determine the policy applied to the packet. IPSec doesn't have a PSK mode, but WPA2 does. IKE is used to set up security associations in IPSec but doesn't allow this type of mode setting.