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To use PPTP, you set up a PPP session between the client and server, typically over the Internet. Once the session is established, you create a second dial-up session that dials through the existing PPP session, using PPTP. The PPTP session tunnels through the existing PPP connection, creating a secure session. In this way, you can use the Internet to create a secure session between the client and the server. Also called a virtual private network (VPN), this type of connection is very inexpensive when compared with a direct connection.


PPTP is a good idea for network administrators who want to connect several LANs, but don’t want to pay for dedicated leased lines. But, as with any network technology, there can be disadvantages, including:


■    PPTP is not available on all types of servers.


■    PPTP is not a fully accepted standard.


■    PPTP is more difficult to set up than PPP.


■    Tunneling can reduce throughput.


You can implement PPTP in two ways. First, you can set up a server to act as the gateway to the Internet and the one that does all the tunneling. The workstations will run normally without any additional configuration. You would normally use this method to connect entire networks. Figure 7.3 shows two networks connected using PPTP. Notice how the TCP/IP packets are tunneled through an intermediate TCP/IP network (in this case, the Internet).


FIGURE 7.3 A PPTP implementation connecting two LANs over the Internet


IP Packets    IP Packets

Internet


The second way to use PPTP is to configure a single, remote workstation to connect to a corporate network over the Internet. The workstation is configured to connect to the Internet via an ISP, and the VPN client is configured with the address of the VPN remote access server, as shown in Figure 7.4. PPTP is often used to connect remote workstations to corporate LANs when a workstation must communicate with a corporate network over a dial-up PPP link through an ISP and the link must be secure.

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