1. A data processing system comprising: a soft switching entity supported at a privileged software domain, the soft switching entity having a second routing table and being coupled to a second control plane interface arranged to receive routing table instructions; and a network interface device comprising: one or more network connection ports for connection to a network; a first routing table supported at a memory of the network interface device; a controller operable to modify the first routing table; a first control plane interface of the controller arranged to receive routing table update instructions carried in one or more control packets received at the said ports; and a filter configured to monitor data received at the one or more ports and, on identifying the one or more control packets, trap said control packets and pass the control packets or data contained therein to the first and second control plane interfaces, wherein: the first control plane interface is configured to, on receiving a routing table update instruction, cause the controller to update the first routing table in accordance with the routing table update instruction; and on receiving a routing table update instruction at the second control plane interface, the second control plane interface is configured to cause the second routing table to be updated in accordance with the routing table update instruction.