Changing the cluster network MTU | Networking | OpenShift Container Platform 4.10

Set the following values in the Cluster Network Operator configuration:

• spec.migration.mtu.machine.to

• spec.migration.mtu.network.from

• spec.migration.mtu.network.to

Cluster Network Operator (CNO): Confirms that each field is set to a valid value.

• The mtu.machine.to must be set to either the new hardware MTU or to the current hardware MTU if the MTU for the hardware is not changing. This value is transient and is used as part of the migration process. Separately, if you specify a hardware MTU that is different from your existing hardware MTU value, you must manually configure the MTU to persist by other means, such as with a machine config, DHCP setting, or a Linux kernel command line.

• The mtu.network.from field must equal the network.status.clusterNetworkMTU field, which is the current MTU of the cluster network.

• The mtu.network.to field must be set to the target cluster network MTU and must be lower than the hardware MTU to allow for the overlay overhead of the cluster network provider. For OVN-Kubernetes, the overhead is 100 bytes and for OpenShift SDN the overhead is 50 bytes.

If the values provided are valid, the CNO writes out a new temporary configuration with the MTU for the cluster network set to the value of the mtu.network.to field.

Machine Config Operator (MCO): Performs a rolling reboot of each node in the cluster.