def unassign_physical(interface)
      interface.ip = nil if interface.subnet.ipam?
      interface.subnet_id = nil
      unless interface.save
        @errors.push(interface.errors.full_messages)
      end
    end
def unassign_physical(interface)
      interface.ip = nil if interface.subnet.ipam?
      interface.subnet_id = nil
      unless interface.save
        @errors.push(interface.errors.full_messages)
      end
    end
if subnet has IP suggesting enabled we also clear the IP that was suggested
 this IP will be used for another interface