A communication network element (10) comprising: an optical path (12) for an optical communication signal (14); a monitoring port (16) arranged to output an optical monitoring signal; an optical splitter (20) provided in the optical path, the optical splitter arranged to receive the optical communication signal and to split off a part of the optical communication signal to form the optical monitoring signal; and optical isolation apparatus (22) connected between the optical splitter and the monitoring port, the optical isolation apparatus arranged to transmit the optical monitoring signal propagating towards the monitoring port and arranged to apply an attenuation, IA, to an attacking optical signal (24) propagating from the monitoring port towards the optical splitter to thereby prevent a substantial part of the attacking optical signal being transmitted to the optical path.