The Cisco QSFP-4SFP25G-CU3M is a high-speed, passive direct-attach copper (DAC) breakout cable. It is designed to connect a single 100 Gigabit Ethernet QSFP28 port on one end to four independent 25 Gigabit Ethernet SFP28 ports on the other, providing a cost-effective and power-efficient solution for high-density networking in data centers .