Genuine Amphenol 400G QSFP-DD (QSFP Double Density) loopback adapter modules provide the ideal 400-Gigabit Ethernet/HDR InfiniBand rated port testing solution for QSFP-DD enabled ports (28.0 Gbps x 8 channels -- 8X). This low-profile passive QSFP-DD 400G loopback cable features typical insertion loss (attenuation) characteristics of a mere 0dB; consuming no more than 0.0 Watts of power in the process. Compatible with both copper and optical QSFP28 enabled ports, our loopbacks perfectly replicate the performance range typical of a short-length QSFP-DD 400-Gigabit connection between the latest QSFP-DD equipped adapter cards, blade servers, routers, and switches. Protocol-independent design ensures compatibility with all present and emerging signal standards, including 400-Gigabit Ethernet (400GbE), 8x HDR InfiniBand, SONET and beyond.  Backwards compatible with all previous QSFP standards including QSFP+, QSFP28 and 200G QSFP-DD.