A client needs to set up a TUN/TAP (tunneling/tap) interface. Those who know more about networking will understand a TAP as a layer 2 virtual device, whereas TUN is a layer 3 device. As such, TAP is a bridging mechanism to connect two networks (with the same subnet), and TUN is a routing mechanism to connect two networks that are not of the same subnet.
For all practical purposes, a TUN/TAP interface is like a virtual ethernet interface (but obviously without the physical layer). This means a TUN/TAP interface also needs to be configured like a regular Ethernet NIC, with its own MAC address and etc.
Most operating systems, including Windows 2000 (and later versions), have TUN/TAP ability. This module will discuss how to set up a TAP/TUN interface in Windows.