Method for operating a network having a prescribable topology, wherein the topology contains a plurality of network devices which are connected to one another and interchange data via multiwire data lines connected to their data ports, wherein test messages are also sent to the data lines in order to check whether or not two data ports on two network devices have the connection between them via the interposed data line, characterized in that, in a prescribable time interval, the number of CRC errors which have occurred and the number of data items transmitted in this time interval are ascertained on a data line between two data ports, and at least these two values are used to calculate an error rate which is a measure of the operability of the multiwire data line.