This proposal addresses the prototype development of a secure local area network (LAN) that incorporates network security devices and a network security center. The secure LAN will provide a processing environment where transmission of data at multiple security levels may be accomplished with confidence in the preservation of the security and integrity of the data. The phase ii work will develop a prototype secure LAN that is not only fully functional, but that is based on the requirements for a class al system as defined by the department of defense trusted computer system evaluation criteria. The al criteria stipulate verified design, and thus a key aspect of the phase ii effort will be the verification of a formal top-level specification of the system against a mathematical model of network security.