A computer, such as a Microsoft client, that supports the PPTP network protocol can connect to a PPTP server in two ways:
·by establishing a dial-up IP connection to an ISP’s network access server
·by an IP-enabled LAN connection
PPTP clients that use an ISP’s network access server must be configured with a modem, a PPTP driver, and a VPN device to make the separate connections to the ISP and the PPTP server. The first connection is a dial-up connection using the PPP protocol over the modem to an Internet service provider. The second connection is a VPN connection using PPTP, over the modem and the ISP connection, to tunnel across the Internet to a VPN device on the PPTP server. The second connection requires the first connection because the tunnel between the VPN devices is established by using the modem and PPP connection to the Internet.
In contrast to PPTP clients that use an ISP’s network access server, clients that use an IP-enabled LAN connection need only be configured with a PPTP driver and a VPN device. Because they are already connected to the LAN, they only need to make one connection: they must use a VPN device to create a connection to a PPTP server on a LAN.