Tinc on Darwin relies on a tunnel driver for its data acquisition from the kernel. OS X version 10.6.8 and later have a built-in tun driver called "utun". Tinc also supports the driver from http://tuntaposx.sourceforge.net/, which supports both tun and tap style devices.
By default, tinc expects the tuntaposx driver to be installed.
To use the utun driver, set add
Device = utunX to tinc.conf,
where X is the desired number for the utun interface.
You can also omit the number, in which case the first free number will be chosen.