I have a router that has a primary address and a couple of secondaries on the ethernet interface. This is a simple question I know it but I am having trouble solving this issue. When a host looks for a DHCP address it uses the address that is on the ethernet interface which is the PC's gateway. If there are secondary addresses on an ethernet interface does the PC request a DHCP address using all of the addresses on the ethernet interface?
Assuming you are using an "ip helper-address .." this will only work for the primary interface. It will not work for secondary interfaces so any clients on the secondary networks will not be able to get IP addresses.
If your addressing was contiguous you could just enlarge the DHCP scope on your DHCP server.
What you really need to do is to create subinterfaces on your router interface for each subnet ie. 802.1q routing on a stick. With subinterfaces each one can use their own ip helper-address.