|Original author(s)||James Yonan|
|Developer(s)||OpenVPN project / OpenVPN Technologies, Inc.|
|Initial release||1.1.0 / April 10, 2002|
|Stable release||2.3.1 (March 29, 2013[±])|
|Preview release||2.x (Git HEAD) (Every Sunday 05:00 GMT -5 Main Mirror) [±]|
OpenVPN is an open source software application that implements virtual private network (VPN) techniques for creating secure point-to-point or site-to-site connections in routed or bridged configurations and remote access facilities. It uses a custom security protocol that utilizes SSL/TLS for key exchange. It is capable of traversing network address translators (NATs) and firewalls. It was written by James Yonan and is published under the GNU General Public License (GPL).
OpenVPN allows peers to authenticate each other using a pre-shared secret key, certificates, or username/password. When used in a multiclient-server configuration, it allows the server to release an authentication certificate for every client, using signature and Certificate authority. It uses the OpenSSL encryption library extensively, as well as the SSLv3/TLSv1 protocol, and contains many security and control features.
OpenVPN uses the OpenSSL library to provide encryption of both the data and control channels. It lets OpenSSL do all the encryption and authentication work, allowing OpenVPN to use all the ciphers available in the OpenSSL package. It can also use the HMAC packet authentication feature to add an additional layer of security to the connection (referred to as an "HMAC Firewall" by the creator). It can also use hardware acceleration to get better encryption performance. Support for PolarSSL is coming in version 2.3
OpenVPN has several ways to authenticate peers to each another. OpenVPN offers pre-shared keys, certificate-based, and username/password-based authentication. Preshared secret key is the easiest, with certificate based being the most robust and feature-rich. In version 2.0 username/password authentications can be enabled, both with or without certificates. However to make use of username/password authentications, OpenVPN depends on third-party modules. See the Extensibility paragraph for more info.
||This section needs additional citations for verification. (July 2009)|
OpenVPN can run over User Datagram Protocol (UDP) or Transmission Control Protocol (TCP) transports, multiplexing created SSL tunnels on a single TCP/UDP port (RFC 3948 for UDP). It has the ability to work through most proxy servers (including HTTP) and is good at working through Network address translation (NAT) and getting out through firewalls. The server configuration has the ability to "push" certain network configuration options to the clients. These include IP addresses, routing commands, and a few connection options. OpenVPN offers two types of interfaces for networking via the Universal TUN/TAP driver. It can create either a layer-3 based IP tunnel (TUN), or a layer-2 based Ethernet TAP that can carry any type of Ethernet traffic. OpenVPN can optionally use the LZO compression library to compress the data stream. Port 1194 is the official IANA assigned port number for OpenVPN. Newer versions of the program now default to that port. A feature in the 2.0 version allows for one process to manage several simultaneous tunnels, as opposed to the original "one tunnel per process" restriction on the 1.x series.
OpenVPN's use of common network protocols (TCP and UDP) makes it a desirable alternative to IPsec in situations where an ISP may block specific VPN protocols in order to force users to subscribe to a higher-priced, "business grade," service tier. [example needed]
OpenVPN offers several internal security features. It runs in userspace, instead of requiring IP stack (and therefore kernel) operation. OpenVPN has the ability to drop root privileges, use mlockall to prevent swapping sensitive data to disk, enter a chroot jail after initialization and apply a SELinux context after initialization.
OpenVPN can be extended with third-party plug-ins or scripts which can be called at defined entry points. The purpose of this is often to extend OpenVPN with more advanced logging, enhanced authentication with username and passwords, dynamic firewall updates, RADIUS integration and so on. The plug-ins are dynamically loadable modules, usually written in C, while the scripts interface can execute any scripts or binaries available to OpenVPN. In the OpenVPN source code there are some examples of such plug-ins, including a PAM authentication plug-in. There also exists several third party plug-ins to authenticate against LDAP or SQL databases such as SQLite and MySQL. There is an overview over many of these extensions in the related project wiki page for the OpenVPN community.
It is available on Solaris, Linux, OpenBSD, FreeBSD, NetBSD, QNX, Mac OS X, and Windows 2000/XP/Vista/7. While some mobile phone OSes (Palm OS, etc.) do not support OpenVPN, it is available for Maemo, Windows Mobile 6.5 and below, iOS 3GS+ devices, jailbroken iOS 3.1.2+ devices, Android 4.0+ devices, and Android devices that have had the Cyanogenmod aftermarket firmware flashed or have the correct kernel module installed. It is not a "web-based" VPN, meaning that it is not shown as a web page such as Citrix or TS Web access - the program is installed independently and configured by editing text files manually, rather than through a GUI-based wizard. OpenVPN is not compatible with IPsec or any other VPN package. The entire package consists of one binary for both client and server connections, an optional configuration file, and one or more key files depending on the authentication method used.
Notable client software 
While OpenVPN is a command-line utility, it provides a management interface specifically designed to allow for establishment and control of an OpenVPN daemon by external software. This has allowed for the development of a number of third-party clients that provide a GUI for connecting to an OpenVPN server.
|Client||Operating System||Cost||Developer||Latest release||Link||Notes|
|OpenVPN Connect||Microsoft Windows & Mac OS X||Free||OpenVPN Technologies, Inc.||184.108.40.2067 / April 11, 2011||Commercial version download||Designed for use with OpenVPN Access Server, a commercial version of OpenVPN.|
|OpenVPN Connect for Android||Android 4.0+||Free||OpenVPN Technologies, Inc.||1.1.11 / March 29, 2013||Google Play Download||Designed for use with OpenVPN Community, OpenVPN Access Server, and PrivateTunnel. Allows only tun connections.|
|Viscosity||Microsoft Windows & Mac OS X||Paid||SparkLabs||1.4.3 / January 22, 2013||sparklabs.com/viscosity||Requires .NET on Windows.|
|OpenVPN MI GUI||Microsoft Windows||Free||Boris Wesslowski||20130109 / January 9, 2013||openvpn-mi-gui.inside-security.de||Enhanced version of the bundled Windows GUI client.|
|SecurepointSSLVPN||Microsoft Windows||Free||Securepoint GmbH||v1 / November 9, 2012||sourceforge.net/projects/securepoint||Multiple connections, TAP-Wins32 Adapter control, no administrator permission is needed to set the route, OTP support, configuration management|
|OpenVPN Portable||Microsoft Windows||Free||Lukas Landis||1.8.2 / December 7, 2012||sourceforge.net/projects/ovpnp||Installs TAP-Win32 Adapter V9 at startup and uninstalls adapter after shutdown.|
|tunXten||Microsoft Windows||Paid||TungstenMine||220.127.116.11 / April 8, 2013||www.tunxten.com||Can be used for free, with restrictions.|
|Tunnelblick||Mac OS X||Free||Tunnelblick||3.2.8 / August 10, 2012||code.google.com/p/tunnelblick|
|Shimo||Mac OS X||Paid||ChungwaSoft||2.3.3 / January 17, 2011||shimoapp.com|
|OpenVPN Settings||Android 1.5+||Free||Friedrich Schäuffelhut||0.4.14 / November 26, 2012||code.google.com/p/android-openvpn-settings||Requires a rooted device.|
|OpenVPN for Android||Android 4.0.3+||Free||Arne Schwabe||0.5.36a / April 17, 2013||code.google.com/p/ics-openvpn||Allows only tun connections|
|GuizmOVPN||iOS||Paid||Guizmo||1.1.7 / August 4, 2012||GuizmOVPN.com||Only available for JailBroken iOS devices.|
|OpenVPN Connect||iOS||Free||OpenVPN Technologies||1.0.0 / January 16, 2013||iTunes App Store - OpenVPN Connect|
|Umbrella Mobility||iOS||Free||OpenDNS||1.0.7 / January 30, 2013||iTunes App Store - OpenVPN Connect|
Firmware implementations 
OpenVPN has been integrated into routing firmware packages such as Vyatta, pfSense, DD-WRT, OpenWrt and Tomato, allowing users to run OpenVPN in client or server mode from their network routers. A router running OpenVPN in client mode, for example, facilitates users within that network to access their VPN without having to install OpenVPN on each computer on that network.
|AsusWRT-Merlin||Free||Open Source private development||lostrealm.ca|
|IPFire||Free||Community driven development||ipfire.org|
|OpenWRT||Free||Community driven development||OpenWRT.org|
|PfSense||Free||BSD Perimeter LLC||pfsense.org|
There are many support options for OpenVPN. The primary method for community support is through the OpenVPN mailing lists. Other sources of support, not directly affiliated with OpenVPN include:
|OpenVPN Documentation||2.0 Manual 2.1 Manual 2.2 Manual 2.3 Manual|
|IRC||#openvpn on irc.freenode.net|
|Forum||Official OpenVPN forums|
|Community||Official OpenVPN wiki/bug tracker
OpenVPN e.V. community
Secure Computing Networks OpenVPN Wiki
See also 
- OpenSSH, which also implements a level-2/3 "tun"-based VPN
- stunnel encrypt any TCP connection (single port service) over SSL
- UDP hole punching, a technique for establishing UDP "connections" between firewalled/NATed network nodes
- Point-to-Point Tunneling Protocol (PPTP) Microsoft method for implementing VPN
- Secure Socket Tunneling Protocol (SSTP) Microsoft method for implementing PPP over SSL VPN
- BartVPN, a VPN client implementing OpenVPN
- SourceForge.net - OpenVPN: openvpn-announce
- "OpenVPN Security Overview". Retrieved 28 September 2011.
- LinuxSecurity.com - OpenVPN: An Introduction and Interview with Founder, James Yonan
- Network security hacks By Andrew Lockhart - Hack #104 - Create a Cross-platform VPN
- IPv6 Deployment Guide By 6net - Chapter 5 - Integration and Transition
- OpenVPN man page, section "TLS Mode Options"
- User Centric Media: First International Conference, UCMedia 2009, Venice, Italy, December 9–11, 2009, Revised Selected Papers By Patros Daras, Oscar Mayora Ibarra - Scalable IPTV Delivery to Home via VPN - Proposed Scheme
- "OpenVPN script entry points". Openvpn.net. Retrieved 2012-07-30.
- OpenVPN plug-in entry points for C based modules[dead link]
- "OpenVPN example plug-ins". Openvpn.git.sourceforge.net. Retrieved 2012-07-30.
- "OpenVPN Maemo package". Maemo.org. Retrieved 2012-07-30.
- "OpenVPN for PocketPC". Ovpnppc.ziggurat29.com. 2007-04-01. Retrieved 2012-07-30.
- "OpenVPN Connect". OpenVPN Technologies. 2013-01-16. Retrieved 2013-01-16.
- "GuizmOVPN - OpenVPN GUI for iPhone/iPad". guizmovpn.com. 2007-09-30. Retrieved 2012-09-30.
- cyanogen (7 July 2010). "CHANGELOG at eclair from CyanogenMod's android_vendor_cyanogen". Github. Retrieved 28 October 2010.Nexus One Cyanogenmod changelog
- "How to setup and configure OpenVPN on Android rooted device | VPN blog is actual information about VPN". Vpnblog.info. Retrieved 2012-07-30.
- "Management Interface". Openvpn.net. Retrieved 2012-07-30.
- "Access Server Overview". Openvpn.net. Retrieved 2012-07-30.
- "tunXten OpenVPN GUI Client | FAQ". Tunxten.com. Retrieved 2012-07-30.
- dd-wrt.com - OpenVPN
- Geek-Pages.com - OpenVPN server and client on DD-WRT
- "Easy OpenVPN server setup guide - OpenWrt Wiki". Wiki.openwrt.org. Retrieved 2012-07-30.
- "TomatoVPN". Tomatovpn.keithmoyer.com. Retrieved 2012-07-30.
- LinksysInfo.org – VPN build with Web GUI
- OpenVPN project homepage
- OpenVPN presentation and demonstration video Hampshire Linux User Group. Archive.org. details.