OpenVPN Copyright (C) 2002-2023 OpenVPN Inc OpenVPN has been written to try to avoid features that are not standardized well across different OSes, so porting OpenVPN itself will probably be straightforward if a tun or tap driver already exists. Where special OS features are used, they are usually bracketed with #ifdef HAVE_SOME_FUNCTION. PLATFORM STATUS: Tier 1 platforms - actively tested for every source commit, across multiple operating system versions * Windows 7 and newer * Windows Server 2012 and newer * Linux * FreeBSD * macOS Tier 2 platforms - it worked at some point, but is not actively tested on "latest OS, latest OS libraries" so might break if larger changes are done on the platform side * OpenBSD * NetBSD * DragonFly BSD * Solaris * AIX For underlying CPU architecture, everything 32 bit or 64 bit (Intel, AMD, ARM, PowerPC, SPARC*) should work fine. 16 bit Architectures are unlikely to work. PORTING GUIDELINE TO A NEW PLATFORM: * Make sure that OpenSSL will build on your platform. * Make sure that a tun or tap virtual device driver exists for your platform. See http://vtun.sourceforge.net/tun/ for examples of tun and tap drivers that have been written for Linux, Solaris, and FreeBSD. * Make sure you have autoconf 2.50+ and automake 1.6+. * Edit configure.ac, adding platform specific config code, and a TARGET_YOUROS define. * Add platform-specific includes to syshead.h. * Add an #ifdef TARGET_YOUROS to the do_ifconfig() function in tun.c to generate a correct "ifconfig" command for your platform. Note that OpenVPN determines the ifconfig path at ./configure time. * Possibly add an ifconfig_order() variant for your OS so openvpn knows whether to call ifconfig before or after tun/tap dev open. * Add an #ifdef TARGET_YOUROS block in tun.c and define the open_tun, close_tun, read_tun, and write_tun functions. If your tun/tap virtual device is sufficiently generic, you may be able to use the default case. * Add appropriate code to route.c to handle the route command on your platform. This is necessary for the --route option to work correctly. * After you successfully build OpenVPN, run the loopback tests as described in INSTALL. * For the next test, confirm that the UDP socket functionality is working independently of the tun device, by doing something like: ./openvpn --remote localhost --verb 9 --ping 1 --dev null * Now try with --remote [a real host] * Now try with a real tun/tap device, you will need to figure out the appropriate ifconfig command to use once openvpn has opened the tun/tap device. * Once you have simple tests working on the tun device, try more complex tests such as using TLS mode. * Stress test the link by doing ping -f across it. * Make sure that packet fragmenting is happening correctly by doing a ping -s 2000 or higher. * Ensure that OpenVPN on your platform will talk to OpenVPN on other platforms such as Linux. Some tun/tap driver implementations will prepend unnecessary stuff onto the datagram that must be disabled with an explicit ioctl call if cross-platform compatibility is to be preserved. You can see some examples of this in tun.c. * Try the ultimate stress test which is --gremlin --reneg-sec 10 in TLS mode then do a flood ping across the tunnel (ping -f remote-endpoint) in both directions and let it run overnight. --gremlin will induce massive corruption and packet loss, but you win if you wake up the next morning and both peers are still running and occasionally even succeeding in their attempted once-per-10-seconds TLS handshake. * When it's working, submit your patch to and rejoice :)