remote users connetced by SD-RED 20 do not get ip from windows DHCP


we have SG115 UTM  in our network and remote location connected to us by SD-RED 20  device.

we have internal windows DHCP server for assigning ip to users but remote location users can not get ip from our windows DHCP server and we have to use  SG115 DHCP service to assign  ip to remote users.

can anyone help me?