Your network consists of one Active Directory domain. The domain contains servers that run Windows Server 2008.
The servers are configured as shown in the following table:
All client computers run Windows Vista Service Pack 1 (SP1).
Remote domain users at a customer site report that they can access Server2 from the Internet by using the URL https://portal.contoso.com. They also report that a firewall at the customer site prevents all other outbound connections.
You need to implement a solution to enable remote users to access files on Server3 from a VPN connection.
Which connection should you enable on Server1?
A. IPsec Tunnel mode
B. L2TP
C. PPTP
D. Secure Socket Tunneling Protocol (SSTP)