A network interface device for use with a host computer that includes a host processor and a memory, and which is configured to concurrently run a master operating system and at least one virtual operating system. The device includes a bus interface that communicates over a bus with the host processor and the memory, and a network interface, which is coupled to send and receive data packets carrying data over a packet network. A protocol processor is coupled between the bus interface and the network interface so as to convey the data between the network interface and the memory while performing protocol processing on the data packets under instructions from the at least one virtual operating system, while bypassing the master operating system.