There are a few possible clients to choose from. One popular OpenVPN client for OS X is Tunnelblick. Tunnelblick is free and open source. Another client is Viscosity. It has a cost of $9USD with a 30 day trial. Finally, my client of choice is Shimo, which is not just an OpenVPN client (like the other two), but also works with a number of other VPN and VPN-like solutions: Cisco VPN, IPSec, PPTP/L2TP, SSH, and so forth. Shimo is more expensive than the others, but not by much: it is only €14.95 (about $21USD).
Shimo is also easy to use with OpenVPN. If you have followed along with the other OpenVPN tutorials in this series, you will have a copy of the client certificate, key, and the CA certificate on your system. If not, you will need to obtain them from the server, where they would have been generated, and securely copy (using SSH or a USB disk) them to your computer. Next, start Shimo and head to the Preferences. In the Profiles pane, add a new OpenVPN profile.Under the General tab, name your new connection — something like "OpenVPN Home" would suffice. In the Authentication pane, you will need to select your Certificate Authority file (ca.crt), Local Certificate (client.crt), and Private Key File (client.key). Make sure the Authentication Method is set to Certificate (Figure A). There is no need to set the username and password unless it is required by the server (for the purposes of this series, we elected to use just certificates without further authentication mechanisms).
In the Connection tab, enter in the name of the remote host (i.e., openvpn-server.domain.com). Ensure the Tunnel Device is TUN and the Protocol is UDP (Figure B); unless you have changed the connection port on the server, leave it at the default 1194. Set Compression to Automatic, and enable Automatic Reconnection. You can also elect to send keep-alive packets every few seconds to ensure the connection stays up (i.e., maybe send a keep-alive packet ever 120 seconds or so).
That's it! You can save the preferences for this profile; go to the Shimo menu icon, and select the new OpenVPN network from the list, and Shimo will establish the connection. If you have enabled the OpenVPN server to push DNS and DNS domain information to clients, when you connect, you will be able to access systems on the remote network by their computer names directly rather than IP addresses.
If you have an iPhone, you're in for an even bigger treat. With iPhone tethering, you can be on the road, anywhere, and securely access the home or work network simply by connecting your iPhone to the laptop (via USB or Bluetooth) and enabling tethering on the iPhone (via Settings | General | Network | Internet Tethering). Once the connection between the Mac and iPhone is established, simply fire up Shimo or whatever OpenVPN client you have chosen, and establish the VPN connection. This works so well that I have been able to obtain a kerberos-ticket and access a kerberos-authentication-only web site on the internal network while sitting in my car across town.
If you only need to use OpenVPN, Shimo may be overkill. It is a fantastic and robust OpenVPN client, but you may wish to give something like Tunnelblick a go first to see if it meets your needs. The latest version of Tunnelblick is 3.0, but it requires you to edit the OpenVPN client configuration directly.
This makes it a lightweight frontend to the OpenVPN command-line program, and the configuration for such can be found in the previous tip about configuring the Linux client. Primarily, you will need to change the "remote" directive to point to the OpenVPN server, and ensure that the ca, cert, and key directives are correct. These directives look for those files in the directory that the configuration file resides in, so you will want to copy those files to ~/Library/Application Support/Tunnelblick/Configurations/.
Once that is done and the configuration file has been saved, use the Tunnelblick menu icon to initiate a connection to the specified OpenVPN server and watch the OpenVPN log output as it connects.
There are a few options to establishing connections to OpenVPN on the Mac. Tunnelblick is good, if a little rough. It is, after all, a simple frontend to the openvpn command line program. Shimo is great if you need a little more power, flexibility, and hand-holding. It is also the best of the bunch if you need to connect to different types of VPNs.
Download the PDF, "How to set up OpenVPN server and create Linux and Mac OS X clients."
Vincent Danen works on the Red Hat Security Response Team and lives in Canada. He has been writing about and developing on Linux for over 10 years and is a veteran Mac user.