Documentation has conflicting information for supportability of MTU changes. This is correct in 4.14 but all versions above is incorrect:

https://docs.openshift.com/container-platform/4.15/networking/changing-cluster-network-mtu.html

We start by saying:

As a cluster administrator, you can change the MTU for the cluster network after cluster installation. This change is disruptive as cluster nodes must be rebooted to finalize the MTU change. You can change the MTU only for clusters using the OVN-Kubernetes or OpenShift SDN network plugins.

And then on the next point we mention:

Only the OVN-Kubernetes cluster network plugin supports changing the MTU value.

    4.15, 4.16 and 4.17

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