The purpose of this document is to lead the users to configure theirs OpenVPN clients to access to a VPN server. We will see how to install and configure the most used OpenVPN’s GUI for Microsoft Windows, Linux, Mac OS X and Windows Mobile for Pocket PC. At the end of the document we will learn to use the OpenVPN’s command line interface. This last possibility is useful, because the openvpn command, which you can execute by using the prompt (Unix Shell or Windows Prompt) accepts the same parameters and has the same behavior regardless from which Operating System you use. In addition, you could use the openvpn command in a script to automatically start the VPN connection.
More precisely, we will see how to access to a VPN server builded with ZeroShell and configured with the default parameters. To obtain an OpenVPN server with the default behavior, you only need, after you have activated Zeroshell on your network, to enable the OpenVPN service by clicking on the Enabled flag in the [VPN]->[OpenVPN] section of the Zeroshell’s web interface. By default, the OpenVPN server of Zeroshell listens on the port 1194/TCP with TLS/SSL encryption and LZO compression enabled. The user authentication well be checked by using username and password credentials, but we will try the X.509 authentication as well.
For further details about the configuration of an OpenVPN server builded with ZeroShell, you can read the “An OpenVPN server using Zeroshell” how-to.

The sections in which this how-to is divided are as follows below. Keep in mind that the first section, which is related to the configuration file of OpenVPN, it is common to the other ones, because the configuration file do not depend on the GUI or Operating System that you use.

The configuration file of OpenVPN

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Because the large number of parameters you can define either in the configuration file or in the command line, you could configure OpenVPN in many different manners. In any case, to obtain a connection with a Zeroshell VPN server, you only need to define a small number of them in your client’s configuration file. In order to further simplify the configuration of the OpenVPN client, you could download an example of configuration file by clicking on the link OpenVPN Client configuration.The file has comments that explain the meaning of the parameters, but only 2 of them you surely need to change to obtain a VPN connection with Zeroshell:

remote zeroshell.example.com 1194You have to replace zeroshell.example.com with the hostname or the IP address of the OpenVPN server. The Zeroshell’s default configuration requires that the OpenVPN service listens on the port 1194/TCP and therefore you must not modify the second parameter (1194).
ca CA.pemThe ca parameter specify a file (in PEM format), that contains the X.509 Certification Authority with which the server certificate has been signed. To get the CA’s X.509 certificate, you only need to click on the CA hyperlink in the Zeroshell’s login page. If you save the CA’s certificate with the name CA.pem in the same directory of the configuration file, the you do not need to change the parameter. Otherwise, you must specify the absolute path of the file.
Keep in mind that certificate of the Certification Authority is required also if you do not use the X.509 client authentication but the “Only Password” authentication (Default in Zeroshell).

Notice, that you will always have to manually edit the configuration file. This is because the Graphical User Interfaces that we are going to learn do not assist you in the creation and maintenance of the OpenVPN’s configuration. They only help you to connect and disconnect the VPN, and ask for the username and password if they are required.

OpenVPN GUI for Windows

To install OpenVPN GUI for Windows on a Microsoft Windows XP 32/64 bits, follow the steps below:

Download the installer from the URL https://openvpn.net/index.php/open-source/downloads.html. Choose he file that contains the GUI and the OpenVPN software already included;
Start with the installation. Select the default options and confirm the installation of the TAP-Win32 Adapter V8 device (it is a Virtual Ethernet interface used by OpenVPN).
When the Installer has finished to work, the TrayBar contains the VPN icon with two red terminals and the Earth Globe symbol. Such terminals are yellow when OpenVPN is trying to establish the connection and they are green when you are finally connected with the VPN;
In the Windows Start Menu, click on [Start]->[All Programs]->[OpenVPN]->[OpenVPN configuration file directory]. You will be able to explore the folder:
Instalar windows para mac. C:Program FilesOpenVPNconfig
in which you must copy the files zeroshell.ovpn that contains the OpenVPN configuration and CA.pem that is the X.509 Certification Authority certificate. You can look at the previous section for details on how to obtain these files;
Edit the file zeroshell.ovpn and replace zeroshell.example.com with the hostname or the IP address of the OpenVPN router;
At this point, you have finished to install and configure the OpenVPN client and its GUI. With a double-click on the OpenVPN icon in the Tray Bar, you can try to start the VPN connection. A dialog box will appear and request you to type the username and the password to be authenticated (look at the note *). If the authentication step is successfully completed, then the VPN connection will be established and the two yellow terminals will become green.

By right-clicking on the OpenVPN icon in the Traybar appears a contextual menu with several useful options: Connect, Disconnect, Show Status, View Log, Edit Config, Proxy Settings. Particularly useful to solve connection problems is the item View Log that allows to know the reason of the failures.

If instead the VPN is connected (the two terminals are green), but you are not able to reach the remote LAN or Internet using the Virtual Private Network, then you should use the ipconfig /all command from the Windows Prompt. Here there is an example of the lines of output about the virtual Ethernet interface:

To be sure that the IP traffic is actually routed across the VPN and hence encrypted, you must check that the IP Address and the Default Gateway assigned to the TAP Virtual Interface belong to the remote LAN you are connected. To better check this condition, you could also use the tracert /d <Remote IP Address> command: if the first hop that is printed belongs to a subnet of the remote LAN then your VPN works fine and the traffic that reaches the remote site is encrypted across Internet.

Tunnelblick for Mac OS X

A Graphical User Interface for OpenVPN on Mac OS X is a package called Tunnelblick. To install this GUI, follow the steps below:

Download the package from the site https://tunnelblick.net. It is a disk image file which contains the GUI, the OpenVPN software, and some documentation;
Double-click on the .dmg file;
A Finder window appears on the desktop. The window contains Tunnelblick.app. Double-click it;
A dialog box will ask you to confirm that you wish to install Tunnelblick.app to Applications. Click the Install button;
A dialog box will ask if you wish to launch Tunnelblick. Click the Launch button;
A dialog box will ask for an administrator username/password to secure Tunnelblick. Type administrator credentials and click the OK button;
A dialog box will appear welcoming you to Tunnelblick. Click the Create and open configuration folder button;
A Finder window will open with the configuration folder. The window will contain only an alias to Tunnelblick.app. Drag the files zeroshell.ovpn and CA.pem to the window. If you don’t know how to

Client Openvpn For Mac Os X