how to start up tap when use libbsd？

Tue Apr 18 05:07:25 UTC 2017

hi，     I try to port a vpn package to rtems, I used libbsd, and I find tap source has been included in libbsd,But I do not know how to create a tap when use
libbsd , I try to used ifconfig command to create tap  but failure,Can you give me some advice?

ifconfig tap0 create inet 192.168.20.1 255.255.255.0 up
ifconfig: SIOCIFCREATE2: Invalid argument

best regards
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.rtems.org/pipermail/devel/attachments/20170418/9098f120/attachment.html>