This paper presents a new model that precisely describes the mechanisms that enforces the security policy and requirements for a multi-level secure Local Area Network. These mechanisms attempt to insure secure flow of information between entitien assigned to different security classes in different compiler systems connected to the network. The mechanisms also control the access to the network devices by the subject with different security clearances. Implementation of the security model has beer shown during a complete discussion of the method of implementing the security requirements. The paper also gives an assessment of the proposed model compared to some commercial systems.