1. A packet forwarding device for processing a data packet, the packet forwarding device comprising: an input port, the input port being operable to receive a data packet; a processor, the processor being connected to the input port and being operable to: determine a virtual local area network destination for the received data packet, including identifying a set of rules that are associated with the virtual local area network destination; and apply the set of rules to the data packet; and an output port, the output port being connected to the processor and being operable to: output the data packet to its virtual local area network destination, using the result from the application of the rules if a virtual local area network destination has been determined for the received data packet; and drop the data packet if a virtual local area network destination has not been determined for the received data packet.