Understanding ethtool rx-fcs for mlx5 Drivers

Version 6

    One of the features of ethtool is rx-fcs. Normally, a packet's FCS field is truncated by ASIC HW before  it is sent to the application socket buffer (SKB). Ethtool allows to set the rx-fcs parameter so that FCS does not get truncated, allowing to pass it to the application for analysis.

    This feature is supported in Kernel 4.12 or MLNX_OFED 4.1 for mlx5 driver.





    1. Get the current configuration of the rx-fcs parameter.

    # ethtool -k eth1 | grep rx-fcs

    rx-fcs: off


    2. Set rx-fcs to instruct the ASIC not to truncate the FCS field of the packet.

    # ethtool -K eth1 rx-fcs on



    3. Send a packet and see that the receiver side is getting the full FCS as part of the SKB. This can be done by any sniffing tool such as tcpdump.