Discusses a network-level access control technique that applies the non-discretionary access control model to individual data packets that are exchanged between hosts or subnets. The proposed technique examines the incoming data's integrity properties to prevent applications within a node or subnetwork from so-called subversive channels. It checks outgoing data's secrecy requirements before transmission. Security labels are used to identify data packets as members of different categories and security levels. Additional tags store context information to validate the trustworthiness of a packet's content. Labels and tags of a data packet reflect events that may be relevant to access control throughout its life. As opposed to stateful filtering, which is based on the history of a flow of packets, our approach works on the history of an individual packet. Any state information is part of the packet rather than being stored in all the nodes inspecting the packet; i.e. nodes do not need to create and maintain state information.