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28 lines
2.1 KiB
Plaintext
28 lines
2.1 KiB
Plaintext
// Module included in the following assemblies:
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//
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// * /networking/networking_overview/cidr-range-definitions.adoc
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:_mod-docs-content-type: CONCEPT
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[id="host-prefix-description_{context}"]
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= Host prefix
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[role="_abstract"]
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To allocate a dedicated pool of IP addresses for pods on each node in {product-title}, specify the subnet prefix length in the hostPrefix parameter. Defining an appropriate prefix ensures that every machine has sufficient unique addresses to support its scheduled workloads without exhausting the cluster's network resources.
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ifdef::openshift-rosa,openshift-rosa-hcp,openshift-dedicated[]
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For example, if you set the `hostPrefix` parameter to `/23`, each machine is assigned a `/23` subnet from the pod CIDR address range. The default is `/23`, allowing 512 cluster nodes and 512 pods per node. Note that where 512 cluster nodes and 512 pods are beyond the maximum supported.
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endif::openshift-rosa,openshift-rosa-hcp,openshift-dedicated[]
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ifdef::openshift-enterprise,openshift-rosa,openshift-rosa-hcp,openshift-dedicated[]
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For example, if the host prefix is set to `/23`, each machine is assigned a `/23` subnet from the pod CIDR address range. The default is `/23`, allowing 510 cluster nodes and 510 pod IP addresses per node.
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Consider another example where you set the `clusterNetwork.cidr` parameter to `10.128.0.0/16`, you define the complete address space for the cluster. This assigns a pool of 65,536 IP addresses to your cluster. If you then set the `hostPrefix` parameter to `/23`, you define a subnet slice to each node in the cluster, where the `/23` slice becomes a subnet of the `/16` subnet network. This assigns 512 IP addresses to each node, where 2 IP addresses get reserved for networking and broadcasting purposes. The following example calculation uses these IP address figures to determine the maximum number of nodes that you can create for your cluster:
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[source,text]
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----
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65536 / 512 = 128
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----
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You can use the link:https://access.redhat.com/labs/ocpnc/[Red Hat OpenShift Network Calculator] to calculate the maximum number of nodes for your cluster.
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endif::openshift-enterprise,openshift-rosa,openshift-rosa-hcp,openshift-dedicated[]
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