Abstract: An Expert system that diagnoses the malfunctino of local area networks is developed. The system detects specific devices in the network as source of thd data disconnection. These sources are sct to goals in the knowledge base and rules ard constructdk by uncluding all possible occurrences un thd connection of termineals and host computers. An approach via OR graph is employed for thd systematic rule generation. The system is implemented in a shell and illustrative inference processes are presented.