[CentOS] MTU report question

Mon Dec 14 13:46:30 UTC 2020
Patrick Bégou <Patrick.Begou at legi.grenoble-inp.fr>


I'm deploying a CentOS8 (not stream 😁) cluster and I have a question
about MTU on the interfaces. I have a connectX6 Mellanox interface where
I need IBoIP setup.
I've setup this interface via nmcli and set the MTU to 65520 with:

    nmcli connection modify ib0 mtu 65520
    nmcli connection up ib0

Running "nmcli connection show ib0" report:

    infiniband.mtu:                         65520

But "ip addr show ib0" report a mtu of 2044:

    6: ib0: <BROADCAST,MULTICAST,UP,LOWER_UP> *mtu 2044 *qdisc mq state
    UP group default qlen 256

Why ? Who is wrong (possibly me....)?