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Understanding VPNs and PPTP 23
Understanding VPNs
and PPTP
Virtual private networks (VPN) are private, secure networks created in public
networks such as the Internet. A VPN is essentially a secure, private tunnel within
the Internet. Since VPN calls are placed through a local ISP, they eliminate long
distance charges that would occur from directly dialing to a remote private
network.
One of the protocols which enables a VPN to be created is PPTP. The PPTP protocol
allows for multiple workstations to establish a secure multi-protocol connection to
a remote, private network via a single, locally-dialed ISP account as shown in
Figure 10. Any networking protocols such as IP, IPX and NetBEUI can be supported
transparently through the tunnel. While the ISDN LAN Modem supports PPTP, it
does not play an active role in creating or terminating a tunnel.
Figure 10
Connection to an Remote Private Network via an ISP
The main steps for creating a VPN are as follows. Each step is explained in detail in
subsequent sections.
■ Set up the server side of the tunnel connection
■ Set up the client side of the tunnel connection
■ Initiate a tunnel between client and server using your client software
Setting Up the Server
Side of the Tunnel
In order to establish a tunnel, the client side must be able to dial into a PPTP tunnel
server on the remote private network such as 3Com’s NETBuilder, PathBuilder, and
Total Control Hub as well as Microsoft’s Windows NT server version 4.0 or later. If
you use Windows NT 4.0, then Service Pack 3 or greater and RAS must be
installed. Also, the protocols required for the private network must be installed on
the PPTP tunnel server. It is recommended that an experienced network
administrator set up the server side. Note that protocols required for the private
network must be installed on each PPTP tunnel client as well as the PPTP tunnel
server.
Setting Up the Client
Side of the Tunnel
In order to establish a tunnel, the client side must have PPTP tunnel client software
such as Windows Dial-Up Networking version 1.2 or higher which includes the
required software VPN adapter or Windows NT operating system with Service Pack
3, or Network TeleSystem’s TunnelBuilder™ VPN software for Windows 3.11 and
Macintosh operating systems. This software should reside on all workstations that
wish to create a tunnel to the tunnel server. Follow instructions provided for
installation and set up.
From the Edge to the Heart
of the Network.
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Internet Service
Provider
LAN Modem
Tunnel
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Corporate
network