HPE 845420-B21 QSFP28 to 4x25G SFP28 7M Active Optical Cable
Overview
The HPE 845420-B21 is a 7-meter active optical cable (AOC) that breaks a single 100G QSFP28 port out to four independent 25G SFP28 connections — the standard approach for top-of-rack switch uplinks feeding four 25GbE servers without consuming four discrete switch ports or four separate transceivers. Active optical construction handles signal conditioning internally, eliminating the need for external transceivers at either end and simplifying cable management in dense rack environments. At 7 meters, 845420-B21 spans typical in-rack and short cross-row distances that passive DAC cables cannot reliably cover.
Compatibility
The 845420-B21 is designed for HPE FlexFabric and Aruba switch platforms with QSFP28 uplink ports, and HPE ProLiant and Synergy server adapters with 25GbE SFP28 ports. Compatible switch families include HPE FlexFabric 5940 and 5945 series and HPE Aruba 8400/8320 series. The SFP28 breakout ends seat into 25GbE host adapters across HPE ProLiant Gen9 and Gen10 servers. Verify your specific switch and adapter firmware supports 100G-to-4x25G breakout mode before deployment — not all port configurations enable breakout by default. This cable is not cross-compatible with Cisco, Juniper, or other vendor platforms without explicit vendor qualification.
Installation Notes
Active optical cables are not hot-plug tolerant during link training on some platforms — seat both ends before powering the port where possible. The integrated optics in an AOC are sensitive to sharp bends; maintain bend radius above the minimum specified for the cable jacket (typically 30mm) to avoid insertion loss penalties. At 7 meters, route with slack to avoid tension on the QSFP28 and SFP28 connectors. Label all four SFP28 breakout legs at installation — downstream troubleshooting in a 25G breakout topology is significantly faster when physical lane-to-port mapping is documented.
