Mellanox MCX4121A-ACAT ConnectX®-4 Lx EN NIC usable in PCIE 5.0 x16 slot with x8 bifurcation/lanes?

I’m interested in installing a 25GbE MCX4121A-ACAT NIC in the remaining PCIE 5.0 x16 slot that only has x8 bifurcated lanes. Two questions:

  1. Is the MCX4121A-ACAT Connectx-4 capable of Zero-touch RoCE (no ECN, no PFC) like Connectx-6?
  2. Will the x8 lanes of PCIE 5.0 limit the 25GbE capacity? I assume it should run at full speed with 2-4x PCIE speed per lane despite half the lanes but has this been tested and shown to work?


Hello Jon!

Thanks for contacting us!
Regarding your questions.

  1. Zero-touch RoCE is not supported on the ConnectX-4. Support for that started with the ConnectX-6

  2. The MCX4121A-ACAT ConnectX-4 Lx EN NIC is designed to operate with PCIe 3.0 x8.
    The PCIe 5.0 x8 slot you’re planning to use should not limit the 25GbE capacity of the NIC. PCIe 5.0 offers a significant increase in bandwidth per lane over PCIe 3.0, so even with half the lanes (x8 instead of x16), the total bandwidth should be more than sufficient to support the full 25GbE capacity of the NIC.
    However, it’s important to note that while this should theoretically work, this has not been tested by NVIDIA.