3Com 3C892 manual Understanding VPNs, Pptp, Network

Understanding VPNs and PPTP 23

Understanding VPNs	Virtual private networks (VPN) are private, secure networks created in public
and PPTP	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.

Internet Service

Provider

LAN Modem	Tunnel
	terminator

Corporate

network

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 In order to establish a tunnel, the client side must be able to dial into a PPTP tunnel Side of the 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 In order to establish a tunnel, the client side must have PPTP tunnel client software Side of the Tunnel 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.