Abstract: A system and method for controlling traffic in a packet-based communication system is disclosed. A number indicative of the source of a request packet may be modified to receive a shifted source number which may be, according to embodiments of the invention, in an unused shifted range of source numbers. A destination number in a received packet may be extracted and if it is in the shifted range of port numbers that packet may be determined as a response packet, the shifted port number may be un-shifted back and its restored value may be used to direct that packet to the device which issued the request, substantially without having to extract any additional information from the packet.