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Chapter 20. CIDR range definitions
If your cluster uses OVN-Kubernetes, you must specify non-overlapping ranges for Classless Inter-Domain Routing (CIDR) subnet ranges.
The following subnet types are mandatory for a cluster that uses OVN-Kubernetes:
- Join: Uses a join switch to connect gateway routers to distributed routers. A join switch reduces the number of IP addresses for a distributed router. For a cluster that uses the OVN-Kubernetes plugin, an IP address from a dedicated subnet is assigned to any logical port that attaches to the join switch.
- Masquerade: Prevents collisions for identical source and destination IP addresses that are sent from a node as hairpin traffic to the same node after a load balancer makes a routing decision.
- Transit: A transit switch is a type of distributed switch that spans across all nodes in the cluster. A transit switch routes traffic between different zones. For a cluster that uses the OVN-Kubernetes plugin, an IP address from a dedicated subnet is assigned to any logical port that attaches to the transit switch.
Starting from OpenShift Container Platform 4.14.38, you can change the join and transit CIDR ranges for your cluster as a post-installation task.
OVN-Kubernetes, the default network provider in OpenShift Container Platform 4.14 and later versions, internally uses the following IP address subnet ranges:
-
:
V4JoinSubnet100.64.0.0/16 -
:
V6JoinSubnetfd98::/64 -
:
V4TransitSwitchSubnet100.88.0.0/16 -
:
V6TransitSwitchSubnetfd97::/64 -
:
defaultV4MasqueradeSubnet169.254.169.0/29 -
:
defaultV6MasqueradeSubnetfd69::/125
The earlier list includes join, transit, and masquerade IPv4 and IPv6 address subnets. If your cluster uses OVN-Kubernetes, do not include any of these IP address subnet ranges in any other CIDR definitions in your cluster or infrastructure.
20.1. Machine CIDR
In the Machine classless inter-domain routing (CIDR) field, you must specify the IP address range for machines or cluster nodes.
You cannot change Machine CIDR ranges after you created your cluster.
The default is
10.0.0.0/1620.2. Service CIDR
In the Service CIDR field, you must specify the IP address range for services. The range must be large enough to accommodate your workload. The address block must not overlap with any external service accessed from within the cluster. The default is
172.30.0.0/1620.3. Pod CIDR
In the pod CIDR field, you must specify the IP address range for pods.
The pod CIDR is the same as the
clusterNetwork10.128.0.0/1420.4. Host prefix
In the
hostPrefixFor example, if the host prefix is set to
/23/23/23Consider another example where you set the
clusterNetwork.cidr10.128.0.0/16hostPrefix/23/23/1665536 / 512 = 128You can use the Red Hat OpenShift Network Calculator to calculate the maximum number of nodes for your cluster.
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