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Copy file name to clipboardExpand all lines: modules/nw-cluster-mtu-change.adoc
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@@ -23,8 +23,7 @@ ifndef::outposts[= Changing the cluster network MTU]
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ifdef::outposts[= Changing the cluster network MTU to support AWS Outposts]
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ifdef::outposts[]
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During installation, the maximum transmission unit (MTU) for the cluster network is detected automatically based on the MTU of the primary network interface of nodes in the cluster.
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You might need to decrease the MTU value for the cluster network to support an AWS Outposts subnet.
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During installation, the maximum transmission unit (MTU) for the cluster network is detected automatically based on the MTU of the primary network interface of nodes in the cluster. You might need to decrease the MTU value for the cluster network to support an AWS Outposts subnet.
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endif::outposts[]
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ifndef::outposts[As a cluster administrator, you can increase or decrease the maximum transmission unit (MTU) for your cluster.]
. Prepare your configuration for the hardware MTU:
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** If your hardware MTU is specified with DHCP, update your DHCP configuration such as with the following dnsmasq configuration:
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.. If your hardware MTU is specified with DHCP, update your DHCP configuration such as with the following dnsmasq configuration:
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[source,text]
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----
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dhcp-option-force=26,<mtu>
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dhcp-option-force=26,<mtu> <1>
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----
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<1> Where `<mtu>` specifies the hardware MTU for the DHCP server to advertise.
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.. If your hardware MTU is specified with a kernel command line with PXE, update that configuration accordingly.
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.. If your hardware MTU is specified in a NetworkManager connection configuration, complete the following steps. This approach is the default for {product-title} if you do not explicitly specify your network configuration with DHCP, a kernel command line, or some other method. Your cluster nodes must all use the same underlying network configuration for the following procedure to work unmodified.
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--
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where:
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`<mtu>`:: Specifies the hardware MTU for the DHCP server to advertise.
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--
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** If your hardware MTU is specified with a kernel command line with PXE, update that configuration accordingly.
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** If your hardware MTU is specified in a NetworkManager connection configuration, complete the following steps. This approach is the default for {product-title} if you do not explicitly specify your network configuration with DHCP, a kernel command line, or some other method. Your cluster nodes must all use the same underlying network configuration for the following procedure to work unmodified.
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... Find the primary network interface by entering the following command:
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[source,terminal]
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----
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$ oc debug node/<node_name> -- chroot /host nmcli -g connection.interface-name c show ovs-if-phys0
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$ oc debug node/<node_name> -- chroot /host nmcli -g connection.interface-name c show ovs-if-phys0 <1>
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<1> where `<node_name>` specifies the name of a node in your cluster.
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--
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where:
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`<node_name>`:: Specifies the name of a node in your cluster.
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--
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... Create the following NetworkManager configuration in the `<interface>-mtu.conf` file:
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.Example NetworkManager connection configuration
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[source,ini]
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----
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[connection-<interface>-mtu]
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match-device=interface-name:<interface>
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ethernet.mtu=<mtu>
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match-device=interface-name:<interface> <1>
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ethernet.mtu=<mtu> <2>
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----
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<1> Where `<interface>` specifies the primary network interface name.
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<2> Where `<mtu>` specifies the new hardware MTU value.
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--
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where:
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`<mtu>`:: Specifies the new hardware MTU value.
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`<interface>`:: Specifies the primary network interface name.
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--
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... Create two `MachineConfig` objects, one for the control plane nodes and another for the worker nodes in your cluster:
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.... Create the following Butane config in the `control-plane-interface.bu` file:
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... Create the following Butane config in the `control-plane-interface.bu` file, which is the `MachineConfig` object for the control plane nodes:
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[source,yaml,subs="attributes+"]
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[source,yaml,subs="attributes+"]
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----
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variant: openshift
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version: {product-version}.0
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----
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<1> Specify the NetworkManager connection name for the primary network interface.
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<2> Specify the local filename for the updated NetworkManager configuration file from the previous step.
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.... Create the following Butane config in the `worker-interface.bu` file:
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[source,yaml, subs="attributes+"]
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... Create the following Butane config in the `worker-interface.bu` file, which is the `MachineConfig` object for the compute nodes:
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[source,yaml,subs="attributes+"]
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----
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variant: openshift
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version: {product-version}.0
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----
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<1> Specify the NetworkManager connection name for the primary network interface.
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<2> Specify the local filename for the updated NetworkManager configuration file from the previous step.
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.... Create `MachineConfig` objects from the Butane configs by running the following command:
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... Create `MachineConfig` objects from the Butane configs by running the following command:
Copy file name to clipboardExpand all lines: networking/changing-cluster-network-mtu.adoc
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[role="_abstract"]
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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.
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