The VPN server provides a routed connection to the network to which the VPN server is attached. On a site-to-site VPN connection, the packets sent from either router across the VPN connection typically do not originate at the routers. The calling router (the VPN client) authenticates itself to the answering router (the VPN server), and, for mutual authentication, the answering router authenticates itself to the calling router.
The student/worker. This person has responsibilities to attend to, and uses a VPN provided by their school or company to access resources on their network when they’re at home or traveling. In most cases, this person already has a free VPN service provided to them, so they’re not exactly shopping around. Also, if they’re worried about security, they can always fire up their VPN when using airport or cafe WI-Fi to ensure no one’s snooping on their connection. Photo by Ed Yourdon.
Password Authentication Protocol (PAP) is a clear-text authentication scheme. The NAS requests the user name and password, and PAP returns them in clear text (unencrypted). Obviously, this authentication scheme is not secure because a malicious user could capture the user's name and password and use it to get subsequent access to the NAS and all of the resources provided by the NAS. PAP provides no protection against replay attacks or remote client impersonation once the user's password is compromised.
Think about it this way: If your car pulls out of your driveway, someone can follow you and see where you are going, how long you are at your destination, and when you are coming back. They might even be able to peek inside your car and learn more about you. With a VPN service, you are essentially driving into a closed parking garage, switching to a different car, and driving out, so that no one who was originally following you knows where you went.