openvpn-2.0.5 doesn't seem to like using the tap device on NetBSD.
First, it doesn't seem to know that it's a cloning device, so it tries
to open /dev/tap{1,2,3,...} and gets ENXIO (Device not configured).  If
I manually do "ifconfig tap1 create" before launching openvpn, then it
successfully opens the device, but it prints an error about not knowing
how to ifconfig the device on this OS.  If I hack openvpn's tun.c to
make it treat NetBSD more like OpenBSD, then it gets a lot further.  It
configures the interface, and adds the route that I want. tcpdump shows
incoming traffic (broadcasts from other hosts), and outgoing traffic
(mostly ARP requests sent by me).  But it appears that my traffic never
makes it to the far end, because I never receive a response to my ARP
requests.

Is anybody successfully using openvpn on netBSD with "dev tap" and 
"proto tcp"?

--apb (Alan Barrett)