Troubleshooting Tip: Interface link in down state between FortiChassis and 3rd party vendor device over 100GB transceiver

One of the possible issues for connection not establishing is a FEC mismatch between FortiChassis and a 3rd party. In the example below establishment between 6301F and Cisco 9000 series switch is observed. The original setting on the Cisco switch is auto detect, which should detect that the FEC settings are turned off on the FortiChassis side.

Port 27 from the 6301F is configured as in the snippet below:

edit "port27"
    set vdom "root"
    set mediatype lr
    set speed 100Gfull

end

Under these conditions, the following command cannot enable FEC:

edit "port27"

    set forward-error-correction rs-fec

end

The error message is provided below:

command parse error before 'forward-error-correction'
Command fail. Return code -61

In order to enable this command, the following change should be introduced:

edit "port27"

    set mediatype sr <----- Unlocks the option to enable forward-error-correction.

    set forward-error-correction rs-fec <----- Now the command is unlocked.

end

This command will result in matching the FEC settings and bringing the link to the UP state.