sudo port install openvpn2
sudo port install tuntaposx

or you can download tuntaposx package manually from here

let’s check it after installation

bash-3.2# ls /dev/tap*
/dev/tap0 /dev/tap10 /dev/tap12 /dev/tap14 /dev/tap2 /dev/tap4 /dev/tap6 /dev/tap8
/dev/tap1 /dev/tap11 /dev/tap13 /dev/tap15 /dev/tap3 /dev/tap5 /dev/tap7 /dev/tap9
bash-3.2# ls /dev/tun*
/dev/tun0 /dev/tun10 /dev/tun12 /dev/tun14 /dev/tun2 /dev/tun4 /dev/tun6 /dev/tun8
/dev/tun1 /dev/tun11 /dev/tun13 /dev/tun15 /dev/tun3 /dev/tun5 /dev/tun7 /dev/tun9

TunTAP creates virtual interfaces using the supplied kernel extensions.Configure it to startup at boot.
launchctl load -w /Library/LaunchDaemons/org.macports.tuntaposx.plist
If you don’t have tuntaposx installed, it is possible to get the following error when you try and make vpn connection:
Cannot allocate TUN/TAP dev dynamically
Exiting due to fatal error


Now, run the vpn client
sudo openvpn2 router-udp-1197-client.ovpn