Determination of network topology

An apparatus and method for determining the topology of a computer network including data-relay devices (A, B, C) and node devices (d, ... k) based on a comparison of source addresses heard by the various data relay-devices. A source address table is compiled for each port of each data-relay device, and for each select pair of ports the addresses in the source tables are compared to determine whether there is an intersection of heard devices. In order to account for directed transmissions which are not heard at every port, further comparison is made of all of the other ports of the device, eliminating the ports for which the intersection is the empty set. From the determined connections, a topology of the network is graphed showing direct and transitive connections. In cases where there is both a direct and transitive connection, the redundant direct connection is eliminated.