A multiprocessor computer system includes processing element nodes interconnected by physical communications links in a n-dimensional topology, which includes at least two global partitions. Routers route messages between processing element nodes and include ports for receiving and sending messages, and lookup tables having a local router table having directions for routing between processor element nodes within a global partition, and a global router table having directions for routing between processor element nodes located in different global partitions. The directions from the local table are selected for routing from the next router along a given route if the current processing element node is in a destination global partition or if the current processing element node is one plus or minus hop from reaching the destination global partition and the route is exiting on a port that routes to the destination global partition, else the directions from the global router table are selected for routing from the next router.