I am unable to set a 10G or 40G port to 10/100M speed. I am unable to establish a link between a 10G or 40G port and a 10/100M Ethernet segment.
Cumulus Linux, all versions
Use an intervening 1G switch to connect to the slower Ethernet segment. The following configuration, for example, can be used to set a 10G port to 1G:
auto swp1 iface swp1 link-speed 1000 link-duplex full link-autoneg off
For more information on configuring port speeds, see the Cumulus Linux User Guide:
Speed reduction from 10G or 40G to 10/100M is unsupported at the hardware layer.