I am testing a QSFP112 400G SR4 optical module with a ConnectX-7 (MCX755106AC-HEAT) dual-port QSFP NIC using an MPO-12 Type-B cable.
The module appears in “Ready” state and data path state is “DPActivated”.
The mlxlink --show_module output shows:
State = Disable
Supported Cable Speed (Ext.) = 0x00000000 ()
Compliance = Unspecified / Undefined
Power Class reported as 1.5 W
Voltage only 120 mV instead of ~3.3 V
RX Power = –40 dBm on all 4 lanes
Recommendation = “Cable speed not enabled”
TX power from the my device is normal (~3 dBm), but the NIC’s RX path appears completely off.
What conditions or module attributes does ConnectX-7 check before enabling a 400G SR4 module?
If a module appears physically present but the port is disabled with RX power extremely low,
what is the recommended troubleshooting approach at NIC side provided that TX power is ok?
Also, are there specific power class or compliance code requirements for modules to be accepted by ConnectX-7?
From the NIC side this behavior usually indicates that ConnectX-7 has detected the module as present but not compliant, so it intentionally keeps the port in low-power / disabled state and does not enable the RX path.
On ConnectX-7, a QSFP112 module is only powered up and RX enabled after several CMIS / EEPROM checks pass, including:
Valid media compliance (e.g. explicit 400GBASE-SR4 / 802.3db identification)
A non-zero supported cable speed bitmap including 400G
A reasonable power class for 400G SR4 (typically Class 6 or higher)
Correct host electrical interface (400GAUI-8)
In your output, the combination of Compliance = Unspecified, Supported Cable Speed = 0, and Power Class = 1.5 W strongly suggests that the module is not being recognized as a valid 400G SR4 device. In this case the firmware will keep Vcc near 0 V, resulting in RX power around –40 dBm even though the remote TX is present.
Recommended troubleshooting on the NIC side:
Verify the NIC firmware supports QSFP112 SR4 (upgrade to a recent CX-7 FW if needed).
Confirm third-party modules are allowed (ALLOW_UNSUPPORTED_CABLES), though this will not override invalid CMIS fields.
Compare behavior with an NVIDIA-qualified 400G SR4 module to isolate EEPROM / CMIS issues.
In short, this is not an optical link problem but a module identification / CMIS compliance issue. If the module does not advertise valid 400G SR4 compliance and power class, ConnectX-7 will not enable the RX path.
Thank you for your response.
Could you please recommend an optical module and cable that are compatible with this NIC for establishing an optical link?