This paper describes the networking approach being implemented in the MDHC simulation facility. The real time system consists of distributed multi processor VME chassis and other components driving four dome simulators and several auxiliary stations. All can be run together interactively, separately, or in various groups. The system is controlled by one or more System Control Stations (SCS) that themselves are distributed systems. Two distinct networks are used: an Ethernet for loading, starting, control, and data collection, and a Proteon Pronet 80 high speed token ring LAN for real time communications. One of the principles of the system architecture is to separate the control and command functions and make them invisible to the real time application. The same principle of separation suggests the segregation of the command, control, and data collection traffic from real time communications. The SCS maintains an "open window" into memory of the real time system over Ethernet and can read and write memory, transparently to the real time application. The ethernet service that makes this possible is one of the highlights of this paper. The other is the performance of the Pronet LAN as documented by analysis and experiment.