OpenVPN

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OpenVPN
Ovpntech logo-s REVISED.png
Original author(s) James Yonan
Developer(s) OpenVPN project / OpenVPN Technologies, Inc.
Initial release 0.90 / May 13, 2001; 13 years ago (2001-05-13)[1]
Stable release 2.3.5 (28 October 2014; 29 days ago (2014-10-28)) [±]
Preview release 2.x (Git HEAD) (Every Sunday 05:00 UTC Main Mirror) [±]
Written in C
Platform Cross-platform
Type VPN
License GNU GPL
Website openvpn.net

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[2] 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).[3]

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 has been ported and embedded to several systems. For example, DD-WRT has the OpenVPN server function. SoftEther VPN, a multi-protocol VPN server, has an implementation of OpenVPN protocol.

Architecture[edit]

Encryption[edit]

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.[4][5] Support for PolarSSL is available starting from version 2.3.[6]

Authentication[edit]

OpenVPN has several ways to authenticate peers with each other. 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.

Networking[edit]

OpenVPN can run over User Datagram Protocol (UDP) or Transmission Control Protocol (TCP) transports, multiplexing created SSL tunnels on a single TCP/UDP port[7] (RFC 3948 for UDP).[8] From 2.3.x series on, OpenVPN fully supports IPv6 as protocol of the virtual network inside a tunnel and the OpenVPN applications can also establish connections via IPv6.[9] 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]

Security[edit]

OpenVPN offers several internal security features. It has up to 256-bit Encryption through OpenSSL library although some service providers may offer lower rates effectively making the connection faster.[10] 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 runs a custom security protocol based on SSL and TLS.[2] OpenVPN offers support of smart cards via PKCS#11 based cryptographic tokens.

Extensibility[edit]

OpenVPN can be extended with third-party plug-ins or scripts which can be called at defined entry points.[11][12] 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[13] there are some examples of such plug-ins, including a PAM authentication plug-in. Several third party plug-ins also exist 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.

Platforms[edit]

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,[14] Windows Mobile 6.5 and below,[15] iOS 3GS+ devices,[16] jailbroken iOS 3.1.2+ devices,[17] Android 4.0+ devices, and Android devices that have had the Cyanogenmod aftermarket firmware flashed[18] or have the correct kernel module installed.[19] It is not a "web-based" VPN, meaning that it is not shown as a web page such as Citrix or Terminal Services 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.

Firmware implementations[edit]

OpenVPN has been integrated into router firmware packages such as Vyatta, pfSense, DD-WRT,[20] OpenWrt[21] and Tomato,[22][23] 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.

Firmware Package Cost Developer Link
DD-WRT Free NewMedia-NET GmbH dd-wrt.com
IPFire Free Community driven development ipfire.org
OpenWRT Free Community driven development OpenWRT.org
PfSense Free BSD Perimeter LLC pfsense.org
Tomato Free Keith Moyer tomatovpn.keithmoyer.com

OpenVPN has also been implemented in some default manufacturer router firmware, such as the D-Link DSR-250[24] and all recent MikroTik Routers.[25] It's important to mention that MikroTik's implementation does not support the UDP protocol (as well as LZO compression), but only the TCP protocol, which has a negative impact on transfer speeds (TCP has at best about 1/3 of the UDP performance). MikroTik claims that they won't continue to impove their OpenVPN implementation (i.e. add UDP support): "It was said before - we have stopped developing OpenVPN in favor of SSTP" [26]

Software implementations[edit]

OpenVPN has been integrated into SoftEther VPN, an open-source multi-protocol VPN server, to allow users connect to the VPN server from existing OpenVPN clients.

Community[edit]

A circa 2005 version of the OpenVPN community logo.

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:

Support Source Description
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[edit]

References[edit]

  1. ^ OpenVPN Change Log - OpenVPN Change Log
  2. ^ a b "OpenVPN Security Overview". Retrieved 28 September 2011. 
  3. ^ LinuxSecurity.com - OpenVPN: An Introduction and Interview with Founder, James Yonan
  4. ^ Network security hacks By Andrew Lockhart - Hack #104 - Create a Cross-platform VPN
  5. ^ IPv6 Deployment Guide By 6net - Chapter 5 - Integration and Transition
  6. ^ Overview of changes in OpenVPN v2.3 - ChangesInOpenvpn23 - OpenVPN Community
  7. ^ OpenVPN man page, section "TLS Mode Options"
  8. ^ 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
  9. ^ OpenVPN community wiki, IPv6 in OpenVPN - retrieved 2013-12-08
  10. ^ "VPN Newbie Guide: Picking between OpenVPN, PPTP and L2TP". vpnpick.com. Retrieved 2014-03-30. 
  11. ^ "OpenVPN script entry points". Openvpn.net. Retrieved 2012-07-30. 
  12. ^ OpenVPN plug-in entry points for C based modules[dead link]
  13. ^ "OpenVPN example plug-ins". Openvpn.git.sourceforge.net. Retrieved 2012-07-30. 
  14. ^ "OpenVPN Maemo package". Maemo.org. Retrieved 2012-07-30. 
  15. ^ "OpenVPN for PocketPC". Ovpnppc.ziggurat29.com. 2007-04-01. Retrieved 2012-07-30. 
  16. ^ "OpenVPN Connect". OpenVPN Technologies. 2013-01-16. Retrieved 2013-01-16. 
  17. ^ "GuizmOVPN - OpenVPN GUI for iPhone/iPad". guizmovpn.com. 2007-09-30. Retrieved 2012-09-30. 
  18. ^ cyanogen (7 July 2010). "CHANGELOG at eclair from CyanogenMod's android_vendor_cyanogen". GitHub. Retrieved 28 October 2010. Nexus One Cyanogenmod changelog
  19. ^ "How to setup and configure OpenVPN on Android rooted device | VPN blog is actual information about VPN". Vpnblog.info. Retrieved 2012-07-30. 
  20. ^ dd-wrt.com - OpenVPN
  21. ^ "Easy OpenVPN server setup guide - OpenWrt Wiki". Wiki.openwrt.org. Retrieved 2012-07-30. 
  22. ^ "TomatoVPN". Tomatovpn.keithmoyer.com. Retrieved 2012-07-30. 
  23. ^ LinksysInfo.org – VPN build with Web GUI
  24. ^ http://www.dlink.com/us/en/business-solutions/security/services-routers/-/media/Business_Products/DSR/DSR%20250/Manual/DSR%20250_Manual_104_EN_US.pdf
  25. ^ http://wiki.mikrotik.com/wiki/OpenVPN
  26. ^ http://forum.mikrotik.com/viewtopic.php?f=2&t=46133

External links[edit]