HowTo Configure Switch Interface Using Cumulus Linux

Version 7

    In this post we will show how to change the port MTU and speed in Cumulus Linux OS. In addition, there are some useful commands.

    This post assumes that you already have Cumulus Linux installed on a Mellanox Spectrum switch.





    1. Two servers connected to a Cumulus Linux Switch.


    Make sure to have valid licence installed.



    1. Log into the switch using the following credentials:

    Username: cumulus

    Password: CumulusLinux!


    2. Switch to root user. Run sudo -i.

    Password: CumulusLinux!

    # sudo -i

    [sudo] password for cumulus:



    Please send these support file(s) to










    3. Open /etc/network/interfaces. Run:

    # vi /etc/network/interfaces


    4.  Change link MTU and speed as follows:


    auto swp5

    iface swp5

      link-speed 100000

      mtu 1500


    # swp6


    auto swp6

    iface swp6

      link-speed 40000

      mtu 9000


    Note: When changing the speed to 40GbE, you may need to force the speed on the server side as well. For more information please refer to HowTo Change the Ethernet Port Speed of Mellanox Adapters (Linux).

    Run the following on the server side on the link connected to port 6 (swp6), to change the link to 40Mb/s.

    # ethtool -s ens785f1 speed 40000 autoneg off

    If you want to split the port, please refer to HowTo Configure Breakout Cables 40G => 4x10G Using Cumulus Linux.


    5. Apply the configuration. Run:

    # ifreload -a

    6. Check the link status. Run:

    # netshow interface


           Name    Speed      MTU  Mode           Summary

    -----  ------  -------  -----  -------------  ------------------------

    UP     lo      N/A      65536  Loopback       IP:, ::1/128

    UP     eth0    1G        1500  Mgmt           IP:

    ADMDN  eth1    0M        1500  Mgmt

    UP     swp5    100G      1500  NotConfigured

    UP     swp6    40G       9000  NotConfigured


    You can see that both links, swp5 and swp6, are UP with the configured MTU and speed.


    For other useful commands, check  Cumulus Linux: Useful Commands.


    1. If you are using 100GbE adapters (e.g. ConnectX®-4), you may need to set the port speed on the server as well. Run:

    # ethtool -s ens785f1 speed 100000 autoneg off