How to check FEC status on ConnectX-4 100G NIC

How can I check the current status of FEC on ConnectX-4 100G NIC?

“ethtool” only shows Speed, Duplex, but no FEC status.

(BTW, I saw a few Q&A that FEC cannot be configured manually for ConnectX-4 100G NIC.)


FEC cannot be disabled on 100G NIC .

The ways to disable FEC on the card:

  1. Connect it to a switch that does not support FEC because our cards set to auto-negotiate by default, meaning if the other side also supports FEC, FEC is enabled. if not, FEC is disabled.

  2. Disable FEC from the switch side, if it’s Mellanox switch then you can run: “fae interface ib 1/1 fec-override no-fec” in console terminal mode.

  3. MFT 4.7 and higher have the mlxlink tool that can provide the status of FEC

Verify FEC is disabled - “mlxlink -d <device_id> --show_fec |grep -i fec”


mst start

mst status → to get the device id

“mlxlink -d /dev/mst/mt4117_pciconf0 --show_fec |grep -i fec”