Your company has a main office and is adding a branch office. You are connecting the main office and branch office networks. You install ISA Server 2006 on a computer at each office, and you create a site-to-site VPN connection between the ISA Server computers. You create remote site networks on the ISA Server computers at both offices. You choose the L2TP over IPSec VPN protocol. You want to use a preshared key for the IPSec authentication. You open the Routing and Remote Access console and enter the preshared key in the Properties dialog box for the Routing and Remote Access server. The site-to-site L2TP over IPSec connection is successful.
You then restart the ISA Server computers and discover that the site-to-site connection fails. You need to ensure that the L2TP over IPSec site-to-site VPN connections continue to function properly after the ISA Server computers are restarted. What should you do?

A.
Re-enter the preshared keys on the ISA Server computers at both offices. Change the preshared keys so that they include mixed-case letters, numbers, and symbols.

B.
Remove all certificates for the ISA Server computers at both offices.

C.
On the ISA Server computers at both offices, remove the preshared key from the Routing and Remote Access console, and enter the key on the Authentication tab of the Virtual Private Networks (VPN) Properties dialog box.

D.
Install user certificates on the ISA Server computers in both offices and enable EAP user authentication for the demand-dial accounts.