FDR cables are usually passive copper DAC cables which support Mellanox' custom "Fourteen Data Rate". For suitable cables see page 8 of https://network.nvidia.com/files/pdf/firmware/ConnectIB-FW-10_0100_6440-release_notes.pdf For what FDR means see table of InfiniBand - Wikipedia Instead of 10 Gbps x 4 per link, Mellanox is running it at 14 Gbps x 4 (hence "fourteen"). 14*4=56 Gbps. Datacenter-wise its long been a dead end, that's why gear which supports it is as cheap as it is (SX6012 switch for a 100 bucks etc.). Awesome for home use and experimentation of course.