You work as the enterprise administrator at ABC.com. ABC.com has a domain named ABC.com. The ABC.com network servers run Microsoft Windows Server 2008 and the client computers run Microsoft Windows Vista. ABC.com has two computers configured as follows:

ABC-SR01 configured as an ISA server on the internal network.

ABC-SR02 configured to host the Virtual Private Network (VPN) service over the Point-to-Point Tunneling Protocol (PPTP).

During the course of the day the Marketing division members state the error message below is received when connecting to ABC-SR02.

“Error 721: The remote computer is not responding”

How would you configure the Windows Firewall for the Marketing division members to logon to ABC-SR02?

A.
By opening port 439 on the Windows firewall.

B.
By opening port 443 on the Windows firewall.

C.
By opening port 25 on the Windows firewall.

D.
By opening port 1723 on the Windows firewall.

Explanation:
To establish VPN connectivity through PPTP, you need to make sure that TCP Port 1723 is opened on the Firewall and IP Protocol 47 (GRE) is configured.

The Error 721 occurs when the VPN is configured to use PPTP, which uses GRE protocol for tunneled data, and the network firewall does not permit Generic Routing Encapsulation (GRE) protocol traffic. To resolve this problem, you need to configure the network firewall to permit GRE protocol 47 and make sure that the network firewall permits TCP traffic on port 1723.

Reference: RAS Error Code / Error 721:

http://www.chicagotech.net/raserrors.htm#Error%20721

Reference: You receive an “Error 721” error message when you try to establish a VPN connection through your Windows Server-based remote access server

http://support.microsoft.com/default.aspx?scid=KB;EN-US;888201