DHCP and Pdhcp

Does anyone know what option has to be configured on the DHCP server to
provide to the clients where the PXEclient is running if the DHcp and the
Proxy DHCP are not running on the same server. I know it is option 60 if
they are on the same server but if not how does the DHCP server notify the
clients the server that does have the Pdhcp info?

TIA

BQ