A multi-level security device is disclosed for providing security between a user and at least one computer network, wherein the user is selected from the group consisting of a host computer and at least a second network. A secure network interface Unit (SNIU) that operates at a user layer communications protocol, which communicates with other like SNIU devices by establishing an association at a session layer of a communication stack in order to create a global security perimeter for end-to-end communications. The SNIU includes a host/network interface for receiving messages sent between the user and the at least one network, which is operative to convert the received messages to and from a format utilized by the at least one network. A message parser for determining whether the association already exists with another SNIU device. A session manager coupled to the interface for identifying and verifying the user requesting access to the network. The session manager also for transmitting the messages received from the user when the message parser determines the association already exists. An association manager coupled to the interface for establishing an association with other like SNIU devices when the message parser determines the association does not exist.