A method and apparatus for routing received connection demands through a photonic switch having multiple parallel instances of a switching plane is provided. Routing respects the constraint that each cell of the switch accommodates a maximum of one lightpath. Connection demands are routed one at a time via switching plane instances where it is possible without violating the constraint. When a demand cannot be routed, a re-arrangement step is performed. A previously routed demand that conflicts with the blocked demand is identified and de-allocated. The blocked demand is then routed in place of this de-allocated demand, which is now considered blocked. The process repeats until no blocked demands remain. Attempts to route additional demands of lower priority can also be made by checking whether each lower priority demand can be routed given the configuration of the switch to route existing demands.