One embodiment of the present invention includes a system that translates addresses in a data packet based upon a user identifier in the data packet. The system receives the data packet sent from a source node to a destination node by a user. This data packet includes a source address of the source node, a destination address of the destination node and the user identifier that identifies the user. The system uses the user identifier to look up communication privileges associated with the user. If the communication privileges allow the user to communicate with the destination node, the system replaces the source address in the data packet with a privileged address, and forwards the data packet to the destination node. In a variation on this embodiment, the privileged address is recognized by a system firewall so that it facilitates passage of the packet through firewall. In another variation, the privileged address specifies a return address of a given address translation unit and thereby facilitates load balancing across multiple address translation units. In a further variation, the system receives a reply packet from the destination node directed to the privileged address, and replaces the privileged address in the reply packet with the source address so that the reply packet is directed to the source node, before forwarding the reply packet to the source node. In another variation, receiving the reply packet includes acting as a proxy for the privileged address under the address resolution protocol. Another variation further includes authenticating, encrypting and optionally compressing the data packet.