You work as an IT engineer in an international company which is named WINTEL. You are in charge of the network of the company. You install Windows Small Business Server (SBS) 2008 on a sever which is named server1 and you enable a virtual private network (VPN) on the server. You have an external firewall device used on your network. When the users plan to use the VPN to connect to the network, each of them gives a report that they get the error message as the following: “Error 800: Unable to establish the VPN connection.” Now you are assigned a task to make sure that all users can use the VPN to connect to the network. What action should perform?

A.
You should open port 1722 on the external firewall device.

B.
You should open port 1723 on the external firewall device.

C.
You should open port 1724 on the external firewall device.

D.
You should open port 1721 on the external firewall device.