1. A data processing system comprising: one or more physical memories; one or more physical processors, configured to provide: an operating system, stored on at least one of the one or more physical memories, that stores a plurality of first network routing tables each comprising one or more entries, each entry indicating at least part of a route over a network to a respective destination; at a user level, a copy of at least one of the respective first network routing tables; and a network data transmission function transmitting data using routing information from the copy network routing table and without accessing the first network routing tables, wherein the copy network routing table is configured to be read by means of memory mapping.