Troubleshooting Tip: FortiSwitch is not load balancing the outgoing traffic via the LACP links

Consider a setup where FortiSwitch is connected to a 3rd party switch using ports 9 and 10 in LACP:

For example, trunk configuration:

FortiSwitch# show switch trunk

    edit "MCLAG-1"

        set mode lacp-active

        set members "port9" "port10"

end

The linerate below shows that received traffic is load-balanced on ports 9 and 10 at 279 and 251 Mbps, respectively. However, the transmit traffic from the FortiSwitch is sent mostly on port 9, at 203 Mbps, while port 10 is underutilised.

FortiSwitch# diagnose switch physical-ports linerate up

port9 | 203Mbps | 279 Mbps

port10 | 0.5Mbps | 251 Mbps

The trunk load balance hash algorithm occurs in Hardware. Try the configuration below on the FortiSwitch to modify the hashing algorithm:

config switch global
    set trunk-hash-mode L4-port hash
    set trunk-hash-unicast-src-port enable
    set trunk-hash-unkunicast-src-dst enable
end

config system settings
    set ip-ecmp-mode source-ip-based dst-ip-based port-based
end