Hardware Data Diodes provide network traffic for out-of-band monitoring, specifically designed not to send traffic back onto the network. These purpose-built network hardware devices enforce one-way data flow for SPAN links with physical hardware separation, guaranteeing protection of critical digital systems, such as industrial control systems (ICS), from inbound cyber threats. The portable Hardware Date Diode accepts two (2) SPAN inputs in ports A and B and sends out copies of each SPAN input individually out ports C and D with no aggregation.