QSFP-4SFP25G-CUxM-BCC | Cisco Compatible 100GB QSFP to 4 x 25GB SFP25G Direct Attach Breakout Cable | 1M to 5M

Q: Will this work in place of the Cisco QSFP-4SFP25G-CU1M?
A: Yes. This cable is a plug-and-play replacement for the Cisco QSFP-4SFP25G-CU1M series. It conforms to the same IEEE 802.3bj 100GBASE-CR4 and 802.3by 25GBASE-CR standards, uses identical QSFP28 and SFP28 form factors, and delivers the same 103.1 Gb/s aggregate data rate over passive copper. The cable will initialize automatically when inserted into any Cisco 100G QSFP28 port.

Q: Which Cisco platforms support this breakout cable?
A: This cable is compatible with any Cisco switch or router featuring 100G QSFP28 ports that support 100GBASE-CR4 passive copper breakout operation. This includes platforms in the Catalyst 9000 and Nexus 3000, 9200, 9300, 9500, and 9800 series that have been verified to support QSFP28 direct attach breakout cables per Cisco documentation.

Q: Do the 3M and 5M lengths require FEC to be enabled on the switch?
A: The 3M and 5M lengths comply with the CA-25G-L cable class defined in IEEE 802.3by clause 110.10, which requires RS-FEC (Reed-Solomon Forward Error Correction) to be enabled on both ends of each 25G lane. The 1M, 1.5M, and 2M lengths can operate with or without FEC depending on cable quality and insertion loss. Most Cisco platforms enable FEC by default on 100G and 25G interfaces.

Q: Can I connect the four SFP28 ends to different switches or servers?
A: Yes. Each of the four 25G SFP28 lanes is electrically and logically independent. You can connect them to four separate devices, provided each device is within the specified cable length from the QSFP28 end. The breakout point is typically 0.33M from the QSFP28 connector. This topology is common in leaf-spine architectures where one 100G uplink fans out to four 25G downstream connections.

Q: What is the signal integrity difference between passive copper and active optical breakout cables at these lengths?
A: Passive copper uses the raw electrical signal with no retiming or amplification, which limits reach to 5 meters due to insertion loss and crosstalk accumulation in twinax. Active optical cables convert to light and back, extending reach to 5 to 30 meters with lower power per meter, but add 2 to 5 microseconds of latency and require external power at each connector. For distances under 5 meters, passive copper offers lower cost, lower latency, and simpler thermal management.