Controllerless Networks

Hi,
One of my client has a requirment to use external DHCP server for guests, where he doesn't want to bring the guest VLAN on his network and keep the VLAN on controller. What is the possibility to achieve this.
The controller we have its 7205.
When creating the DHCP on the controller it works fine and also client gets the internet. The only limitation is that controller is providing limited ips, where we need to a have bigger pool for the guests.

Unfortunately, the subnet needs to be routable to the DHCP server for ip addresses to be assigned.  The DHCP server would not be able to know how to deliver addresses back to the controller, if that was not the case.  The DHCP server either needs to be routable or layer 2 connected to the guest network for it to work the way you want.

Thanks joseph for the respone.
Can't we use ip helper address on the guest vlan lets say from guest vlan dhcp is reachable. Will it work.

The ip interface that the helper address is on needs to be routable to the dhcp server.  The only way is if the dhcp server has a layer 2 interface that it shares with the guest network.