1) put in a list of the mac addresses you want to allow in the follwing format:
#computer model 1
dhcp-mac=set:green,00:aa:bb:*:*:*
#computer model 2
dhcp-mac=set:green,00:cc:dd:*:*:*
#computer model 3
dhcp-mac=set:green,00:ee:ff:*:*:*
etc...
note: the *:*:* is a wildcard so that you can have a range of mac addresses
which is usefull for office enviroments where they only use a few
models of desktops or laptops at a time.
#this is to provide a null route for anything not on the white list
dhcp-option=3
#provide the correct gateway to that on the whitelist:
dhcp-option=tag:green,3,10.x.x.1
#if the gateway doesn't end in .1 make sure to change it (and the x.x of course)
#for addded security can put the non-whitelisted mac's on a different subnet, from the whitelisted (green tag) ones
dhcp-range=192.168.x.3,192.168.x.200,255.255.255.0,1h
dhcp-range=tag:green,10.x.x.3,10.x.x.200,255.255.255.0,1h