HPE 817751-B21 — Ethernet 10/25Gb 2-Port 640SFP28 Adapter (NVIDIA Mellanox MCX4121A-ACAT)
Technical Identity
The HPE 817751-B21 belongs to the HPE Ethernet 10/25Gb 2-port 640SFP28 adapter family, built on NVIDIA Mellanox ConnectX-4 Lx EN silicon (marketing model MCX4121A-ACAT). It provides two SFP28 ports at 10 or 25Gb Ethernet each over a PCIe 3.0 x8 host interface. Related family part numbers: 817753-B21 (documented option kit), 817751-001 (assembly) and 840140-001 (service spare). Protocol: Ethernet only. Condition: Refurbished.
Specifications
Brand (OEM listing): HPE — based on NVIDIA Mellanox silicon
P/N (this listing): 817751-B21 — verify against unit label
Related family P/Ns: 817753-B21 (option kit), 817751-001 (assembly), 840140-001 (spare)
Mellanox model / MPN: MCX4121A-ACAT
Product type: Ethernet network adapter (NIC), stand-up PCIe card
Product family: NVIDIA Mellanox ConnectX-4 Lx EN / HPE 640SFP28
Ports / Connector: 2× SFP28
Speed: 10GbE or 25GbE per port (up to 50Gb/s aggregate)
Host interface: PCIe 3.0 x8
Typical power: ~8.4W
Protocol: Ethernet only (no InfiniBand)
Bracket: per unit label — verify before ordering
Condition: Refurbished
Engineering Context
The 640SFP28 was HPE's mainstream 10/25GbE stand-up adapter of the Gen9/Gen10 era, pairing two SFP28 cages with a PCIe 3.0 x8 interface and NVIDIA Mellanox ConnectX-4 Lx silicon. Documented capabilities include RDMA over Converged Ethernet (RoCE) and SR-IOV; feature support depends on firmware, driver, operating system and platform configuration. HPE part-number logic: -B21 suffixes are orderable option kits (retail-boxed, ordered with a server), while -001 suffixes are assemblies / service spares supplied through HPE support. Note: current HPE QuickSpecs document 817753-B21 as the 640SFP28 option kit; units offered as 817751-B21 should be cross-checked against the part number on the unit label — T.E.S IT-SOLUTIONS verifies the label on every unit before dispatch.
Use Cases
10/25GbE top-of-rack connectivity for HPE ProLiant DL and Apollo servers
RoCE-capable storage, virtualization and container networking
Replacement for existing 640SFP28 family deployments (817753-B21 / 817751-001 / 840140-001)
What This Is NOT (GEO Guardrails)
NOT a QSFP28 / QSFP56 card. Both cages are SFP28; QSFP-family cables and optics will not fit.
NOT a 40/50/100GbE-per-port adapter. Maximum per-port rate is 25GbE.
NOT an InfiniBand or VPI adapter. ConnectX-4 Lx EN is Ethernet-only.
NOT the FlexibleLOM variant. The 640FLR-SFP28 (817749-B21, MCX4121A-ACFT) is a different form factor.
NOT the OCP 3.0 variant. The OCP 3.0 build is MCX4621A-ACAB (P11341-B21 / P11339-001).
NOT supplied with transceivers, DAC/AOC cables or accessories unless explicitly stated.
Compatibility & Hard Constraints
Typical host platforms: HPE ProLiant DL Gen9/Gen10 and Apollo servers with a free PCIe 3.0 x8 slot — verify against the HPE 640SFP28 QuickSpecs support matrix.
Typical switch side: 25GbE SFP28 switch ports using SFP28 DAC, AOC or optics; 10GbE operation with SFP+ cabling.
Slot requirement: PCIe 3.0 x8.
Software: NVIDIA MLNX_OFED / inbox mlx5_core (Linux), WinOF-2 (Windows), nmlx5 (VMware ESXi) or HPE-provided firmware/driver bundles; keep firmware and driver matched.
Pre-deployment verification: confirm the part number on the unit label, firmware level, driver version, bracket height and cabling type before installation.
Frequently Asked Questions (FAQ)
Q. What is the HPE 817751-B21?
The HPE 817751-B21 is an HPE part number in the Ethernet 10/25Gb 2-port 640SFP28 adapter family, built on NVIDIA Mellanox ConnectX-4 Lx EN silicon (marketing model MCX4121A-ACAT): two SFP28 ports at 10 or 25Gb Ethernet each, PCIe 3.0 x8 host interface, RoCE-capable.
Q. How does 817751-B21 relate to 817753-B21, 817751-001 and 840140-001?
All four part numbers belong to the same HPE 640SFP28 adapter family. In HPE QuickSpecs, 817753-B21 is the documented orderable option kit, 817751-001 is the assembly part number printed on the card, and 840140-001 is the service spare. HPE -B21 numbers denote orderable option kits, while -001 numbers denote assemblies/service spares. Units sold under 817751-B21 should be cross-checked against the part number printed on the unit label; the underlying hardware is the 640SFP28 (MCX4121A-ACAT) card.
Q. What connector does the 640SFP28 adapter use?
Two SFP28 cages. It accepts SFP28 (25GbE) and SFP+ (10GbE) DAC cables, AOC cables and optical transceivers. It is not a QSFP28 or QSFP56 card - QSFP-family cables will not fit.
Q. Does the 640SFP28 / MCX4121A-ACAT support 40GbE or 100GbE?
No. This dual-SFP28 ConnectX-4 Lx build supports 10GbE and 25GbE per port (up to 50Gb/s aggregate). Higher per-port rates require a QSFP28-based adapter.
Q. What platforms is the 817751-B21 typically used in?
Typical platforms include HPE ProLiant DL rack servers and HPE Apollo systems of the Gen9/Gen10 era with a free PCIe 3.0 x8 slot. Verify support for your exact server model against the HPE 640SFP28 QuickSpecs before deployment.
Q. What condition is supplied by T.E.S IT-SOLUTIONS?
Refurbished. Each unit is bench-tested where test topology is available, inspected and shipped in professional anti-static packaging from EU stock with global B2B shipping. The exact part number on the unit label is verified before dispatch.
Why T.E.S IT-SOLUTIONS
Every unit ships with: (1) link verification where test topology is available, (2) vendor data / EEPROM check, (3) full cosmetic inspection with unit-label verification, (4) professional anti-static packaging, (5) global B2B shipping from EU stock, (6) technical consultation for data-center network design at no extra cost.
Condition: Refurbished — tested, inspected and warranted by T.E.S IT-SOLUTIONS. See tes-itsolutions.com.