Musing of a chubby Ginger kid.

OpenSSH uses the tun interface for creating point-to-point virtual interfaces for routing the traffic over the SSH tunnel. Kernel configuration:

Device Drivers --->
Network Device Support --->
Universal TUN/TAP device driver support

These are probably already installed on you various distributions of Linux, FreeBSD, etc already but if not build that module.

To load the modules:

# modprobe tun

Refer to your specific distribution documentation for autoloading the modules.