1. A computer-implemented method of providing multi-level security systems, comprising: defining, for each of a plurality of security classifications to be used by a multi-level security (“MLS”) system when sending outbound packets to at least one communication partner system, a unique source address; and for each of the outbound packets sent from the MLS system, using the unique source address defined for the security classification of the outbound packet as a source address in the outbound packet, thereby conveying the security classification of each of the outbound packets through the source address used in the outbound packet.