Cisco 40GBASE-CR4 QSFP+ Direct Attach Copper Cable, Passive Twinax, QSFP+ to QSFP+, 0.5m, 40Gbps, Black

The Cisco QSFP-H40G-CU0-5M= is a 0.5 m passive twinax direct attach copper cable with QSFP+ connectors on both ends, for 40 Gigabit Ethernet links between Cisco switches and routers sitting directly above or below each other in the same rack.

A DAC replaces two optical transceivers and a fibre patch cord with a single factory-terminated assembly: lower cost, negligible power draw and no fibre end-faces to clean. The trade-off is reach and flexibility — the length is fixed, and copper twinax is meant for links inside one rack or to the rack next to it.

• 1 × Cisco QSFP-H40G-CU0-5M= passive copper cable, 0.5 m, with QSFP+ connectors attached at both ends
• No separate QSFP+ transceivers are needed — the connectors are part of the cable

• 0.5 m is the shortest Cisco 40G copper cable: ideal for stacked switches or a spine-to-leaf jumper one or two rack units apart, with no slack to coil.
• Passive copper is offered by Cisco from 0.5 to 5 m; for 7 and 10 m Cisco uses active cables.
• Hot-swappable: plug it in or pull it out while both devices are running; the port recognises the cable and brings the link up without separate optics.
• Measure the real cable route (through cable managers, around the rack posts) before choosing the length — a DAC cannot be shortened, and a long cable coiled inside the rack blocks airflow.

• It is not a breakout cable — to split one 40G port into four 10G SFP+ ports you need the separate QSFP-4SFP10G-CU breakout cables.
• It will not fit SFP+ or SFP28 ports — both ends must be 40G QSFP+ (or QSFP28 ports that run in 40G mode).
• It cannot be extended or joined to another cable — if the distance grows, the answer is optics plus fibre, not a second DAC.
• It is not a breakout cable: it connects one port to one port of the same type.