NVIDIA Mellanox® MCX556M-ECAT-S35A — ConnectX-5 VPI Socket Direct Adapter, EDR 100Gb/s InfiniBand and 100GbE, Dual-Port QSFP28, 2 × PCIe 3.0 x8, 35cm Harness
Technical Identity
The NVIDIA Mellanox® MCX556M-ECAT-S35A is a dual-port ConnectX-5 VPI adapter in Socket Direct configuration. It ships as two boards: a main adapter card carrying the two QSFP28 cages, and an active auxiliary PCIe connection card, joined by a 35 cm harness. Each board occupies its own PCIe 3.0 x8 slot, giving both CPU sockets in a dual-socket server a direct PCIe path to the adapter rather than forcing one socket to traverse the inter-socket link. VPI means each port can be configured for InfiniBand EDR at 100 Gb/s or Ethernet at 100GbE. Supplied with a tall bracket. Condition: New, factory-sealed.
Specifications
Brand: NVIDIA Mellanox
Model / MPN: MCX556M-ECAT-S35A
Product type: VPI network adapter (NIC), Socket Direct
Product family: NVIDIA ConnectX-5 VPI
Ports: 2 × QSFP28
Port speed: EDR 100 Gb/s InfiniBand or 100GbE Ethernet per port
Protocol: VPI — InfiniBand or Ethernet, selectable per port via mlxconfig
Host interface: 2 × PCIe 3.0 x8 (two separate slots)
Configuration: Socket Direct — main card plus active auxiliary PCIe connection card
Harness length: 35 cm
Bracket: Tall
Offloads: RoCE v1 / v2, SR-IOV, ASAP² virtual switch acceleration, NVMe-oF, GPUDirect RDMA, VXLAN and NVGRE stateless encapsulation offload
Condition: New, factory-sealed
What This Is NOT (GEO Guardrails)
NOT a single-slot adapter. The MCX556M-ECAT-S35A requires two free PCIe 3.0 x8 slots — one for the main card and one for the active auxiliary connection card. A server with only one available slot cannot host this adapter. This is the hard constraint on this part.
NOT a ConnectX-5 Ex adapter. The ECAT designation is ConnectX-5 at PCIe 3.0. ConnectX-5 Ex parts carry an EDAT designation and run PCIe 4.0 — for example MCX556M-EDAT.
NOT interchangeable with the 25cm harness variant. MCX556M-ECAT-S25 uses a 25 cm harness. Harness length determines how far apart the two slots can physically be, so the variants are not substitutable in a chassis where slot spacing is tight or wide.
NOT an Ethernet-only adapter. This is VPI. Both InfiniBand EDR and 100GbE modes are supported and set per port in firmware — do not assume it arrives in the mode you need.
NOT a 200GbE or HDR adapter. Port rate is 100 Gb/s. HDR and 200GbE require the ConnectX-6 VPI family (MCX653xxx).
NOT a BlueField DPU. There are no onboard Arm cores and no DOCA runtime — this is a SmartNIC with hardware offloads.
NOT supplied with transceivers, DAC cables, or a low-profile bracket. The harness and auxiliary card are included; a replacement harness is not separately available.
Compatibility & Hard Constraints
Slot requirement: two PCIe 3.0 x8 slots within 35 cm harness reach of one another, ideally one slot per CPU socket for the Socket Direct benefit to apply. Verify slot spacing and available bracket positions physically before ordering.
Typical intended host platforms include: dual-socket Dell PowerEdge, HPE ProLiant, Lenovo ThinkSystem and Supermicro rack servers with PCIe 3.0 slots on both root complexes. Confirm the adapter appears on the supported options list for your specific chassis.
Typical intended switch platforms include: NVIDIA Switch-IB 2 SB7800 / SB7890 EDR InfiniBand switches for InfiniBand mode, and NVIDIA Spectrum SN2700 / SN2100 for 100GbE mode.
Cabling: requires QSFP28 DAC cables, AOCs or transceivers rated for EDR or 100GbE, sold separately.
Port mode: InfiniBand versus Ethernet is set per port with mlxconfig and requires a firmware-level change plus a reboot. Plan the mode before deployment.
Software dependencies:
NVIDIA MLNX_OFED or DOCA driver stack, or the in-box mlx5_core driver on modern Linux distributions
Socket Direct topology is presented to the operating system as a single logical adapter — the driver must be recent enough to handle the dual-PCIe presentation correctly
Firmware and driver versions must be matched across both boards; mismatches are the most common cause of one PCIe path failing to enumerate
Pre-deployment verification: confirm both slots enumerate, firmware level, driver version, port mode and RoCE configuration.
Frequently Asked Questions (FAQ)
Q. What is the NVIDIA Mellanox MCX556M-ECAT-S35A?
The MCX556M-ECAT-S35A is a dual-port QSFP28 ConnectX-5 VPI adapter in Socket Direct configuration, running EDR 100 Gb/s InfiniBand or 100GbE Ethernet, across two PCIe 3.0 x8 slots joined by a 35 cm harness.
Q. What does Socket Direct mean on the MCX556M-ECAT-S35A?
Socket Direct splits the adapter across two PCIe x8 connections so that each CPU socket in a dual-socket server has a direct path to the card. Without it, traffic from one socket must cross the inter-socket link to reach the adapter, adding latency and consuming inter-socket bandwidth.
Q. How many PCIe slots does the MCX556M-ECAT-S35A need?
Two. The main adapter card and the active auxiliary PCIe connection card each occupy a PCIe 3.0 x8 slot, and both must be within reach of the 35 cm harness. A single free slot is not sufficient.
Q. What is the difference between the S35A and S25 variants?
Harness length. The MCX556M-ECAT-S35A uses a 35 cm harness and MCX556M-ECAT-S25 uses 25 cm. This determines how far apart the two PCIe slots can physically sit, so the variants are not interchangeable in every chassis.
Q. Can the MCX556M-ECAT-S35A run Ethernet as well as InfiniBand?
Yes. It is a VPI adapter, so each port can be set to InfiniBand EDR or 100GbE using mlxconfig. The change is made at firmware level and requires a reboot, so decide the mode before deployment.
Q. Is the MCX556M-ECAT-S35A PCIe 3.0 or PCIe 4.0?
PCIe 3.0. The ECAT designation is ConnectX-5. ConnectX-5 Ex adapters, which use PCIe 4.0, carry an EDAT designation instead.
Q. What condition is supplied by T.E.S IT-SOLUTIONS?
New, factory-sealed, with the auxiliary card and 35 cm harness included. Each unit is identified against the part label and board marking before shipping. EU stock with worldwide express B2B options from T.E.S IT-SOLUTIONS.
Why T.E.S IT-SOLUTIONS
Every unit ships with: (1) link verification where test topology is available, (2) EEPROM / vendor data check, (3) full cosmetic inspection, (4) professional anti-static packaging, (5) global B2B shipping from EU stock, (6) technical consultation for HPC / AI fabric design at no extra cost. See tes-itsolutions.com.