I decided I wanted to provide DHCP to two different VLAN's each with their own subnet, connected to the same network card in my default router. All packets arriving on that network jack are tagged for either one or the other VLAN.
Initially I had trouble with the DHCP server only seeing packets on the root eth0 device and ignoring all the packets on the vlan devices (eth0.1 for instance.) There's a couple of changes I had to make for this to work. These instructions assume an Ubuntu server
The steps are:
Configure the VLAN devices