While the User-Mode port cannot directly talk to any physical
hardware devices, this choice and the following transport options
provide one or more virtual network devices through which the UML
kernels can talk to each other, the host, and with the host's help,
machines on the outside world.

For more information, including explanations of the networking and
sample configurations, see
<http://user-mode-linux.sourceforge.net/old/networking.html>.

If you'd like to be able to enable networking in the User-Mode
linux environment, say Y; otherwise say N. Note that you must
enable at least one of the following transport options to actually
make use of UML networking.

source code:

/arch/um/drivers/