Install tun
Unlike Linux, Windows does not come with tun. Luckily, the team of the OpenVPN project have developed tap-windows, which has become the de-facto "tun for Windows". It comes as a double-clickable Windows installer.
On computer B, download the version 9.21.2, and double-click to install.
Note
If you have 9.9.x installed, you need to uninstall it before installing 9.21.x, as there are known issues with doing an upgrade.
Install the utilities so you'll have some handy shortcuts to create and remove tun interfaces.
Create a single tun interface by running the menu selection above as Administrator. It appears in your network connections, as any other interface. (In Windows 7/Vista Control Panel, select "Network and Internet" > "Network and Sharing Center" > "Change adapter settings". Alternatively, in the Start Menu Search box, simply execute ncpa.cpl.)
