A method is described for operating a communication network with a plurality of subscribers. Data exchange between the subscribers takes place in the form of telegrams, which comprise data sections. The subscribers interpret an end portion of the telegrams as a check value for the absence of errors in preceding data sections. The telegrams are processed in pass-through, so that the telegrams are forwarded to a respective next subscriber while being received. If an error is detected when receiving a telegram, the subscribers send the telegram to the next subscriber with a characterizing data section at the end, so that the telegram has an end portion representing an invalid check value. The telegram is characterized by the characterizing data section, which is part of the end portion, so that the telegram is not to be considered as an initial error but as a subsequent error.