Comment 13 for bug 1774666

I've added "mtu: 9000" to the bonds section, which now reads as follows;

    bonds:
        eth1:
            mtu: 9000
            interfaces:
            - enp5s0f0
            - enp5s0f1
            - enp6s0f0
            - enp6s0f1
            parameters:
                down-delay: 0
                lacp-rate: fast
                mii-monitor-interval: 100
                mode: 802.3ad
                transmit-hash-policy: encap3+4
                up-delay: 0

I re-ran netplan apply, but the bond had the same MTU as before. I also tried restarting systemd-networkd as I could see that the relevant .netdev files in /run/systemd/network/ had MTUBytes set to 9000. However, the interface remained at 1500 bytes.

After a system restart however, the bond interface is now running at a MTU of 9000. dmesg now only has messages for the member interfaces being increased from 1500 to 9000 MTU - the messages regarding the MTU being lowered from 9000 to 1500 when the bond was being configured are no longer present.