I am having trouble getting OpenVPN 1.x to talk with OpenVPN 2.0

While OpenVPN 2.0 is compatible with OpenVPN 1.x, some of the default options have changed. For this reason, if you want to connect OpenVPN 1.x to 2.0, add the following to your 1.x config file to set it to the defaults which 2.0 is already using:

  port 1194
  tun-mtu 1500
  tun-mtu-extra 32
  mssfix 1450
  key-method 2

Also note that OpenVPN 1.x cannot connect as a client to an OpenVPN 2.0 server running in the new --mode server mode. This is because OpenVPN 1.x lacks the --pulldirective which is essential to the operation of OpenVPN 2.0's client/server mode.