NVIDIA Mellanox MCX4131A-BCAT ConnectX-4 Lx EN Single-Port QSFP28 40GbE Adapter: This is a single-port Ethernet network interface card based on the ConnectX-4 Lx EN ASIC. The QSFP28 port runs at 40GbE and the host interface is PCIe 3.0 x8. The card ships with a tall (full-height) PCIe bracket. NVIDIA P/N 900-9X429-0014-0T0. This is an Ethernet-only (EN) card — it is not VPI and does not support InfiniBand. This is a refurbished unit, not a new-sealed factory part.
Engineering Context
ConnectX-4 Lx is the lower-power, Ethernet-only sibling of ConnectX-4. It supports stateless TCP/UDP/IP offloads, hardware VXLAN/NVGRE/GENEVE encap-decap, RoCE v1/v2 for RDMA over Ethernet, ASAP² accelerated switching for OVS offload, and SR-IOV with up to 256 virtual functions. The QSFP28 cage is electrically backward-compatible with QSFP+ at 40GbE — both 4x10G NRZ (40GBASE-SR4/CR4/LR4) and 4x25G NRZ links can be terminated in this cage, but this BCAT SKU is rated to 40GbE maximum. PCIe 3.0 x8 at 8GT/s provides 64 Gb/s of host bandwidth, comfortably above 40 Gb/s line rate.
Deployment & Use Cases
40GbE uplinks for hypervisor hosts running VMware ESXi, KVM, or Hyper-V. RoCE-accelerated storage clients for iSER, SMB Direct, and NVMe-oF over Ethernet. OpenStack Neutron and Kubernetes nodes with overlay networking offload. SDN data-plane offload via OVS-DPDK and ASAP². Edge caching, CDN ingest, and high-throughput analytics nodes. Replacement for older ConnectX-3 EN 40GbE cards needing modern offload features.
Technical Specifications
OEM: NVIDIA Mellanox
Part Number: MCX4131A-BCAT
NVIDIA P/N: 900-9X429-0014-0T0
Controller: ConnectX-4 Lx EN
Ports: 1x QSFP28
Data Rate: 40GbE
Host Interface: PCIe 3.0 x8 (8GT/s)
Bracket: Tall (full-height)
Form Factor: Standard PCIe HHHL
Protocol: Ethernet (EN-only, not VPI)
Offloads: RoCE v1/v2, VXLAN, NVGRE, GENEVE, ASAP², SR-IOV (up to 256 VFs)
Condition: Refurbished — Tested by T.E.S IT-SOLUTIONS
Compatibility & Constraints
Requires a PCIe 3.0 x8 (or wider) slot. Compatible with NVIDIA Spectrum, SwitchX-2, and any standards-compliant 40GbE switch. The QSFP28 port supports 40GBASE-CR4 DACs, 40GBASE-SR4/LR4 transceivers, and QSFP+ AOCs at 40GbE. This SKU is rated to 40GbE — for 50GbE see MCX4131A-GCAT, for 25GbE see MCX4111A-ACAT. Does NOT support InfiniBand. Driver support: MLNX_OFED for Linux, WinOF-2 for Windows Server, native NMLX5 driver in VMware ESXi 6.5+. SR-IOV requires VT-d/IOMMU enabled in BIOS.
Why Choose T.E.S IT-SOLUTIONS
T.E.S IT-SOLUTIONS bench-tests every ConnectX-4 Lx adapter for link training at 40GbE, PCIe enumeration, and firmware integrity. T.E.S IT-SOLUTIONS ships globally with 1–3 business day handling and offers expert support on Ethernet fabric integration.