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Understanding the Cluster Network Operator - Networking Operators | Networking | OpenShift Container Platform 4.17
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Cluster Network Operator in OpenShift Container Platform

You can use the Cluster Network Operator (CNO) to deploy and manage cluster network components on an OpenShift Container Platform cluster, including the Container Network Interface (CNI) network plugin selected for the cluster during installation.

Cluster Network Operator

The Cluster Network Operator implements the network API from the operator.openshift.io API group. The Operator deploys the OVN-Kubernetes network plugin, or the network provider plugin that you selected during cluster installation, by using a daemon set.

Procedure

The Cluster Network Operator is deployed during installation as a Kubernetes Deployment.

  1. Run the following command to view the Deployment status:

    $ oc get -n openshift-network-operator deployment/network-operator
    Example output
    NAME               READY   UP-TO-DATE   AVAILABLE   AGE
network-operator   1/1     1            1           56m

  2. Run the following command to view the state of the Cluster Network Operator:

    $ oc get clusteroperator/network
    Example output
    NAME      VERSION   AVAILABLE   PROGRESSING   DEGRADED   SINCE
network   4.16.1     True        False         False      50m

    The following fields provide information about the status of the operator: AVAILABLE, PROGRESSING, and DEGRADED. The AVAILABLE field is True when the Cluster Network Operator reports an available status condition.

Viewing the cluster network configuration

Every new OpenShift Container Platform installation has a network.config object named cluster.

Procedure

  • Use the oc describe command to view the cluster network configuration:

    $ oc describe network.config/cluster
    Example output
    Name:         cluster
Namespace:
Labels:       <none>
Annotations:  <none>
API Version:  config.openshift.io/v1
Kind:         Network
Metadata:
  Creation Timestamp:  2024-08-08T11:25:56Z
  Generation:          3
  Resource Version:    29821
  UID:                 808dd2be-5077-4ff7-b6bb-21b7110126c7
Spec: (1)
  Cluster Network:
    Cidr:         10.128.0.0/14
    Host Prefix:  23
  External IP:
    Policy:
  Network Diagnostics:
    Mode:
    Source Placement:
    Target Placement:
  Network Type:  OVNKubernetes
  Service Network:
    172.30.0.0/16
Status: (2)
  Cluster Network:
    Cidr:               10.128.0.0/14
    Host Prefix:        23
  Cluster Network MTU:  1360
  Conditions:
    Last Transition Time:  2024-08-08T11:51:50Z
    Message:
    Observed Generation:   0
    Reason:                AsExpected
    Status:                True
    Type:                  NetworkDiagnosticsAvailable
  Network Type:            OVNKubernetes
  Service Network:
    172.30.0.0/16
Events:  <none>
    1 The Spec field displays the configured state of the cluster network.
    2 The Status field displays the current state of the cluster network configuration.

Viewing Cluster Network Operator status

You can inspect the status and view the details of the Cluster Network Operator using the oc describe command.

Procedure

  • Run the following command to view the status of the Cluster Network Operator:

    $ oc describe clusteroperators/network

Enabling IP forwarding globally

From OpenShift Container Platform 4.14 onward, global IP address forwarding is disabled on OVN-Kubernetes based cluster deployments to prevent undesirable effects for cluster administrators with nodes acting as routers. However, in some cases where an administrator expects traffic to be forwarded a new configuration parameter ipForwarding is available to allow forwarding of all IP traffic.

To re-enable IP forwarding for all traffic on OVN-Kubernetes managed interfaces set the gatewayConfig.ipForwarding specification in the Cluster Network Operator to Global following this procedure:

Procedure

  1. Backup the existing network configuration by running the following command:

    $ oc get network.operator cluster -o yaml > network-config-backup.yaml

  2. Run the following command to modify the existing network configuration:

    $ oc edit network.operator cluster

    1. Add or update the following block under spec as illustrated in the following example:

      spec:
  clusterNetwork:
  - cidr: 10.128.0.0/14
    hostPrefix: 23
  serviceNetwork:
  - 172.30.0.0/16
  networkType: OVNKubernetes
  clusterNetworkMTU: 8900
  defaultNetwork:
    ovnKubernetesConfig:
      gatewayConfig:
        ipForwarding: Global

    2. Save and close the file.

  3. After applying the changes, the OpenShift Cluster Network Operator (CNO) applies the update across the cluster. You can monitor the progress by using the following command:

    $ oc get clusteroperators network

    The status should eventually report as Available, Progressing=False, and Degraded=False.

  4. Alternatively, you can enable IP forwarding globally by running the following command:

    $ oc patch network.operator cluster -p '{"spec":{"defaultNetwork":{"ovnKubernetesConfig":{"gatewayConfig":{"ipForwarding": "Global"}}}}}

    The other valid option for this parameter is Restricted in case you want to revert this change. Restricted is the default and with that setting global IP address forwarding is disabled.

Viewing Cluster Network Operator logs

You can view Cluster Network Operator logs by using the oc logs command.

Procedure

  • Run the following command to view the logs of the Cluster Network Operator:

    $ oc logs --namespace=openshift-network-operator deployment/network-operator

Cluster Network Operator configuration

The configuration for the cluster network is specified as part of the Cluster Network Operator (CNO) configuration and stored in a custom resource (CR) object that is named cluster. The CR specifies the fields for the Network API in the operator.openshift.io API group.

The CNO configuration inherits the following fields during cluster installation from the Network API in the Network.config.openshift.io API group:

clusterNetwork

IP address pools from which pod IP addresses are allocated.

serviceNetwork

IP address pool for services.

defaultNetwork.type

Cluster network plugin. OVNKubernetes is the only supported plugin during installation.

After cluster installation, you can only modify the clusterNetwork IP address range.

You can specify the cluster network plugin configuration for your cluster by setting the fields for the defaultNetwork object in the CNO object named cluster.

Cluster Network Operator configuration object

The fields for the Cluster Network Operator (CNO) are described in the following table:

Table 1. Cluster Network Operator configuration object
Field Type Description

metadata.name

string

The name of the CNO object. This name is always cluster.

spec.clusterNetwork

array

A list specifying the blocks of IP addresses from which pod IP addresses are allocated and the subnet prefix length assigned to each individual node in the cluster. For example:

spec:
  clusterNetwork:
  - cidr: 10.128.0.0/19
    hostPrefix: 23
  - cidr: 10.128.32.0/19
    hostPrefix: 23

spec.serviceNetwork

array

A block of IP addresses for services. The OVN-Kubernetes network plugin supports only a single IP address block for the service network. For example:

spec:
  serviceNetwork:
  - 172.30.0.0/14

This value is ready-only and inherited from the Network.config.openshift.io object named cluster during cluster installation.

spec.defaultNetwork

object

Configures the network plugin for the cluster network.

spec.kubeProxyConfig

object

The fields for this object specify the kube-proxy configuration. If you are using the OVN-Kubernetes cluster network plugin, the kube-proxy configuration has no effect.

defaultNetwork object configuration

The values for the defaultNetwork object are defined in the following table:

Table 2. defaultNetwork object
Field Type Description

type

string

OVNKubernetes. The Red Hat OpenShift Networking network plugin is selected during installation. This value cannot be changed after cluster installation.

OpenShift Container Platform uses the OVN-Kubernetes network plugin by default. OpenShift SDN is no longer available as an installation choice for new clusters.

ovnKubernetesConfig

object

This object is only valid for the OVN-Kubernetes network plugin.
Configuration for the OVN-Kubernetes network plugin

The following table describes the configuration fields for the OVN-Kubernetes network plugin:

Table 3. ovnKubernetesConfig object
Field Type Description

mtu

integer

The maximum transmission unit (MTU) for the Geneve (Generic Network Virtualization Encapsulation) overlay network. This value is normally configured automatically.

genevePort

integer

The UDP port for the Geneve overlay network.

ipsecConfig

object

An object describing the IPsec mode for the cluster.

ipv4

object

Specifies a configuration object for IPv4 settings.

ipv6

object

Specifies a configuration object for IPv6 settings.

policyAuditConfig

object

Specify a configuration object for customizing network policy audit logging. If unset, the defaults audit log settings are used.

gatewayConfig

object

Optional: Specify a configuration object for customizing how egress traffic is sent to the node gateway.

While migrating egress traffic, you can expect some disruption to workloads and service traffic until the Cluster Network Operator (CNO) successfully rolls out the changes.
Table 4. ovnKubernetesConfig.ipv4 object
Field Type Description

internalTransitSwitchSubnet

string

If your existing network infrastructure overlaps with the 100.88.0.0/16 IPv4 subnet, you can specify a different IP address range for internal use by OVN-Kubernetes. The subnet for the distributed transit switch that enables east-west traffic. This subnet cannot overlap with any other subnets used by OVN-Kubernetes or on the host itself. It must be large enough to accommodate one IP address per node in your cluster.

The default value is 100.88.0.0/16.

internalJoinSubnet

string

If your existing network infrastructure overlaps with the 100.64.0.0/16 IPv4 subnet, you can specify a different IP address range for internal use by OVN-Kubernetes. You must ensure that the IP address range does not overlap with any other subnet used by your OpenShift Container Platform installation. The IP address range must be larger than the maximum number of nodes that can be added to the cluster. For example, if the clusterNetwork.cidr value is 10.128.0.0/14 and the clusterNetwork.hostPrefix value is /23, then the maximum number of nodes is 2^(23-14)=512.

The default value is 100.64.0.0/16.
Table 5. ovnKubernetesConfig.ipv6 object
Field Type Description

internalTransitSwitchSubnet

string

If your existing network infrastructure overlaps with the fd97::/64 IPv6 subnet, you can specify a different IP address range for internal use by OVN-Kubernetes. The subnet for the distributed transit switch that enables east-west traffic. This subnet cannot overlap with any other subnets used by OVN-Kubernetes or on the host itself. It must be large enough to accommodate one IP address per node in your cluster.

The default value is fd97::/64.

internalJoinSubnet

string

If your existing network infrastructure overlaps with the fd98::/64 IPv6 subnet, you can specify a different IP address range for internal use by OVN-Kubernetes. You must ensure that the IP address range does not overlap with any other subnet used by your OpenShift Container Platform installation. The IP address range must be larger than the maximum number of nodes that can be added to the cluster.

The default value is fd98::/64.
Table 6. policyAuditConfig object
Field Type Description

rateLimit

integer

The maximum number of messages to generate every second per node. The default value is 20 messages per second.

maxFileSize

integer

The maximum size for the audit log in bytes. The default value is 50000000 or 50 MB.

maxLogFiles

integer

The maximum number of log files that are retained.

destination

string

One of the following additional audit log targets:

libc

The libc syslog() function of the journald process on the host.

udp:<host>:<port>

A syslog server. Replace <host>:<port> with the host and port of the syslog server.

unix:<file>

A Unix Domain Socket file specified by <file>.

null

Do not send the audit logs to any additional target.

syslogFacility

string

The syslog facility, such as kern, as defined by RFC5424. The default value is local0.
Table 7. gatewayConfig object
Field Type Description

routingViaHost

boolean

Set this field to true to send egress traffic from pods to the host networking stack. For highly-specialized installations and applications that rely on manually configured routes in the kernel routing table, you might want to route egress traffic to the host networking stack. By default, egress traffic is processed in OVN to exit the cluster and is not affected by specialized routes in the kernel routing table. The default value is false.

This field has an interaction with the Open vSwitch hardware offloading feature. If you set this field to true, you do not receive the performance benefits of the offloading because egress traffic is processed by the host networking stack.

ipForwarding

object

You can control IP forwarding for all traffic on OVN-Kubernetes managed interfaces by using the ipForwarding specification in the Network resource. Specify Restricted to only allow IP forwarding for Kubernetes related traffic. Specify Global to allow forwarding of all IP traffic. For new installations, the default is Restricted. For updates to OpenShift Container Platform 4.14 or later, the default is Global.

ipv4

object

Optional: Specify an object to configure the internal OVN-Kubernetes masquerade address for host to service traffic for IPv4 addresses.

ipv6

object

Optional: Specify an object to configure the internal OVN-Kubernetes masquerade address for host to service traffic for IPv6 addresses.
Table 8. gatewayConfig.ipv4 object
Field Type Description

internalMasqueradeSubnet

string

The masquerade IPv4 addresses that are used internally to enable host to service traffic. The host is configured with these IP addresses as well as the shared gateway bridge interface. The default value is 169.254.169.0/29.

For OpenShift Container Platform 4.17 and later versions, clusters use 169.254.0.0/17 as the default masquerade subnet. For upgraded clusters, there is no change to the default masquerade subnet.
Table 9. gatewayConfig.ipv6 object
Field Type Description

internalMasqueradeSubnet

string

The masquerade IPv6 addresses that are used internally to enable host to service traffic. The host is configured with these IP addresses as well as the shared gateway bridge interface. The default value is fd69::/125.

For OpenShift Container Platform 4.17 and later versions, clusters use fd69::/112 as the default masquerade subnet. For upgraded clusters, there is no change to the default masquerade subnet.
Table 10. ipsecConfig object
Field Type Description

mode

string

Specifies the behavior of the IPsec implementation. Must be one of the following values:

  • Disabled: IPsec is not enabled on cluster nodes.

  • External: IPsec is enabled for network traffic with external hosts.

  • Full: IPsec is enabled for pod traffic and network traffic with external hosts.

You can only change the configuration for your cluster network plugin during cluster installation, except for the gatewayConfig field that can be changed at runtime as a postinstallation activity.
Example OVN-Kubernetes configuration with IPSec enabled
defaultNetwork:
  type: OVNKubernetes
  ovnKubernetesConfig:
    mtu: 1400
    genevePort: 6081
      ipsecConfig:
        mode: Full

Cluster Network Operator example configuration

A complete CNO configuration is specified in the following example:

Example Cluster Network Operator object
apiVersion: operator.openshift.io/v1
kind: Network
metadata:
  name: cluster
spec:
  clusterNetwork:
  - cidr: 10.128.0.0/14
    hostPrefix: 23
  serviceNetwork:
  - 172.30.0.0/16
  networkType: OVNKubernetes
      clusterNetworkMTU: 8900

Additional resources