Under certain circumstances, it is not possible to directly connect to an OpenVPN server. This happens most often when firewalls are restricting UDP-based traffic. In such cases, OpenVPN can connect to an OpenVPN server via an intermediary host known as a proxy. OpenVPN supports two types of proxies, SOCKS and HTTP-based, both of which work only using TCP-based configurations. This recipe will outline how to access an OpenVPN server via a SOCKS proxy, whereas the next two recipes will show how to use an HTTP proxy, both with and without authentication.
SOCKS proxies can very easily be set up using almost any SSH client. On Linux and Mac OS X, it can be done using the ssh or slogin commands, whereas, on Windows, the free SSH client PuTTY can be used. In this recipe, we will use SSH on a Linux client to set up a public SOCKS proxy. A Windows OpenVPN client will connect using this proxy.
