== Overview ==

A Nagios plugin for checking whether or not an OpenVPN server is
alive.

We don't actually interact with the OpenVPN server; we merely send it
a a magic (heretofore unexplained) byte sequence and ensure that we
get some kind of response.

If the server uses a TLS auth key, the response will be empty but at
least it will come, preventing a timeout.

== Examples ==

Perform a basic check using the default port and protocol:

  $ check_openvpn-simple vpn1.example.com
  OK 22.471ms

Check a server that runs on TCP/443 (this is used to sneak past
firewalls that allow HTTPS but block other traffic):

  $ check_openvpn-simple --tcp --port 443 vpn2.example.com
  OK 14.801ms