Preboot Execution Environment (PXE) is a broadcast UPD technology that natively works on networks where the server and client both exist on.

In order for PXE to work on additional networks, you must tell the clients where the PXE server is (through DHCP), or you must tell the network where the PXE server is (IP Helper).

You must add multiple entries to each DHCP scope in your environment, or add 1 IP Helper per network.

Using IP Helpers are recommended because of their ease of management and their ability to make instant changes if needed.  

If you are choosing DHCP options then the following are the settings you need to set on your DHCP server:
Predefined Option 43 - 010400000000FF 
Custom-made Option 60 - String - PXEClient 
Predefined Option 66 - IP or Hostname of the WDS Server (The IP of the smartImager server) 
Predefined Option 67 - \boot\x86\wdsnbp.com (or \boot\x64\wdsnbp.com for 64 bit)

Extra configuration may be needed if you are restricting ports in your environment:

The following are the ports that need to be open to the WDS server:
UDP - 67, 68, 69, 4011
TCP - 135, 137, 138, 139, 5040