HPE 845408-B21 100G QSFP28 to QSFP28 Passive Copper DAC, 5 m — the 845408-B21 is a fixed-length passive copper Direct Attach Cable for 100 Gb/s point-to-point switch-to-switch and switch-to-NIC linking. MPN: 845408-B21. This product IS a passive copper twinax assembly with integrated QSFP28 connectors at both ends; it is NOT an Active Optical Cable, NOT a fiber transceiver, NOT a 1:4 breakout. OEM: HPE. Condition: refurbished.
Engineering Context
The 845408-B21 is a 5-meter passive twinax copper assembly. Each direction carries 4x25 Gb/s NRZ lanes for 100 Gb/s line rate per IEEE 802.3bj 100GBASE-CR4 signaling. As a passive cable it consumes essentially zero power — link-side electronics on the host adapter and switch handle equalization, pre-emphasis, and clock recovery. End-to-end latency is sub-100 ns since there is no electrical-to-optical conversion. Typical conductor gauge for a 5 m 100G DAC is 26–28 AWG, which constrains practical reach to short top-of-rack and intra-row runs.
Deployment & Use Cases
Used inside a single rack or between adjacent racks for 100GbE or InfiniBand EDR fabric connections. Common configurations: HPE FlexFabric and Aruba CX 8325/8400 100G uplinks, ConnectX-4/ConnectX-5 server NICs to HPE/Mellanox SN2700-series spine switches, NVMe-oF storage targets in the same rack, and EDR InfiniBand HPC nodes feeding a top-of-rack switch. Typical workloads: VMware vSAN HCI, Ceph and ZFS storage backbones, RoCE/RDMA traffic between compute nodes.
Technical Specifications
Brand: HPE
MPN: 845408-B21
Cable Type: Passive copper Direct Attach (DAC)
Connectors: QSFP28 to QSFP28
Length: 5 m
Data Rate: 100 Gb/s (4x25G NRZ)
Compliance: IEEE 802.3bj 100GBASE-CR4
Protocols: 100GbE / InfiniBand EDR (host-dependent)
Conductor: Twinax copper
Power Draw: Passive (≈0 W)
Latency: Sub-100 ns (no optical conversion)
Condition: Refurbished
Compatibility & Constraints
Compatible with HPE FlexFabric, HPE Aruba CX 8325/8400, HPE/Mellanox Spectrum SN2700 series, and Mellanox ConnectX-4/ConnectX-5 100G adapters that accept passive copper QSFP28 cables. NOT a 1:4 breakout — both ends are full QSFP28 100G, so use this only for switch-to-switch or switch-to-NIC 100G links. NOT compatible with QSFP+ (40 Gb) ports without explicit speed-down support; check switch firmware for 100G→40G compatibility. NOT an Active Optical Cable — practical reach is limited to about 5 m at this AWG, so for longer runs use AOC or transceivers + fiber. Vendor whitelisting may apply on some HPE switches; firmware updates can lift restrictions on third-party DACs.
Why Choose T.E.S IT-SOLUTIONS
T.E.S IT-SOLUTIONS tests all 100G QSFP28 DACs for link integrity, bit-error rate (BER) under sustained traffic, and connector retention prior to dispatch. Lab-verified stock, 1–3 business day handling, global shipping. Technical consultation available for HPE 100G top-of-rack cabling design. Visit tes-itsolutions.com.