Please enable support for dummy interfaces

It would be quite beneficial if dhcp3 server supported Linux dummy ethernet devices by default. For example I would like to use dummy interface on a virtualization host to provide net install and/or LTSP services for virtual machines. This requires working PXE booting setup, which requires DHCP server in the subnet. A clean way to implement this is to add a dummy interface on the server and configure virtualized network interfaces on the virtual machines that are bridged to the dummy interface on the host and have the host services (DHCP, TFTP etc.) listen the bridged dummy interface.

Using of dummy interfaces is explicitly disabled in the DHCP server source. The behavior can only be toggled during build time. It's controlled by the macro SKIP_DUMMY_INTERFACES in includes/cf/linux.h. That definition should be commented out.

The actual code that skips dummy interfaces only checks if the name of the interface begins with the string 'dummy'. Thus one can work-around this problem by renaming the interfaces provided by the dummy ethernet driver by editing udev rules. However, this is not very nice thing to do. And neither is the decision by maintainers of ISC DHCP just blindly ignore all interfaces with some string of their choosing in the name of the interface. Since the administrator has already mechanism to limit DHCP server to use only those interfaces that are wanted, this kind of arbitrary limitation by the software should go away.

Existing Debian bug report of this problem and details of the work-around: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=430528