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Chapter 7. OVN-Kubernetes network plugin

7.1. About the OVN-Kubernetes network plugin

The OpenShift Dedicated cluster uses a virtualized network for pod and service networks.

Part of Red Hat OpenShift Networking, the OVN-Kubernetes network plugin is the default network provider for OpenShift Dedicated. OVN-Kubernetes is based on Open Virtual Network (OVN) and provides an overlay-based networking implementation. A cluster that uses the OVN-Kubernetes plugin also runs Open vSwitch (OVS) on each node. OVN configures OVS on each node to implement the declared network configuration.

Note

OVN-Kubernetes is the default networking solution for OpenShift Dedicated and single-node OpenShift deployments.

OVN-Kubernetes, which arose from the OVS project, uses many of the same constructs, such as open flow rules, to determine how packets travel through the network. For more information, see the Open Virtual Network website.

OVN-Kubernetes is a series of daemons for OVS that translate virtual network configurations into OpenFlow rules. OpenFlow is a protocol for communicating with network switches and routers, providing a means for remotely controlling the flow of network traffic on a network device so that network administrators can configure, manage, and monitor the flow of network traffic.

OVN-Kubernetes provides more of the advanced functionality not available with OpenFlow. OVN supports distributed virtual routing, distributed logical switches, access control, Dynamic Host Configuration Protocol (DHCP), and DNS. OVN implements distributed virtual routing within logic flows that equate to open flows. For example, if you have a pod that sends out a DHCP request to the DHCP server on the network, a logic flow rule in the request helps the OVN-Kubernetes handle the packet so that the server can respond with gateway, DNS server, IP address, and other information.

OVN-Kubernetes runs a daemon on each node. There are daemon sets for the databases and for the OVN controller that run on every node. The OVN controller programs the Open vSwitch daemon on the nodes to support the network provider features: egress IPs, firewalls, routers, hybrid networking, IPSEC encryption, IPv6, network policy, network policy logs, hardware offloading, and multicast.

7.1.1. OVN-Kubernetes purpose

The OVN-Kubernetes network plugin is an open-source, fully-featured Kubernetes CNI plugin that uses Open Virtual Network (OVN) to manage network traffic flows. OVN is a community developed, vendor-agnostic network virtualization solution. The OVN-Kubernetes network plugin uses the following technologies:

  • OVN to manage network traffic flows.
  • Kubernetes network policy support and logs, including ingress and egress rules.
  • The Generic Network Virtualization Encapsulation (Geneve) protocol, rather than Virtual Extensible LAN (VXLAN), to create an overlay network between nodes.

The OVN-Kubernetes network plugin supports the following capabilities:

  • Hybrid clusters that can run both Linux and Microsoft Windows workloads. This environment is known as hybrid networking.
  • Offloading of network data processing from the host central processing unit (CPU) to compatible network cards and data processing units (DPUs). This is known as hardware offloading.
  • IPv4-primary dual-stack networking on bare-metal, VMware vSphere, IBM Power®, IBM Z®, and RHOSP platforms.
  • IPv6 single-stack networking on a bare-metal platform.
  • IPv6-primary dual-stack networking for a cluster running on a bare-metal, a VMware vSphere, or an RHOSP platform.
  • Egress firewall devices and egress IP addresses.
  • Egress router devices that operate in redirect mode.
  • IPsec encryption of intracluster communications.

7.1.2. OVN-Kubernetes IPv6 and dual-stack limitations

The OVN-Kubernetes network plugin has the following limitations:

  • For clusters configured for dual-stack networking, both IPv4 and IPv6 traffic must use the same network interface as the default gateway. If this requirement is not met, pods on the host in the ovnkube-node daemon set enter the CrashLoopBackOff state. If you display a pod with a command such as oc get pod -n openshift-ovn-kubernetes -l app=ovnkube-node -o yaml, the status field contains more than one message about the default gateway, as shown in the following output: 

    I1006 16:09:50.985852   60651 helper_linux.go:73] Found default gateway interface br-ex 192.168.127.1
I1006 16:09:50.985923   60651 helper_linux.go:73] Found default gateway interface ens4 fe80::5054:ff:febe:bcd4
F1006 16:09:50.985939   60651 ovnkube.go:130] multiple gateway interfaces detected: br-ex ens4

    The only resolution is to reconfigure the host networking so that both IP families use the same network interface for the default gateway.

  • For clusters configured for dual-stack networking, both the IPv4 and IPv6 routing tables must contain the default gateway. If this requirement is not met, pods on the host in the ovnkube-node daemon set enter the CrashLoopBackOff state. If you display a pod with a command such as oc get pod -n openshift-ovn-kubernetes -l app=ovnkube-node -o yaml, the status field contains more than one message about the default gateway, as shown in the following output: 

    I0512 19:07:17.589083  108432 helper_linux.go:74] Found default gateway interface br-ex 192.168.123.1
F0512 19:07:17.589141  108432 ovnkube.go:133] failed to get default gateway interface

    The only resolution is to reconfigure the host networking so that both IP families contain the default gateway.

7.1.3. Session affinity

Session affinity is a feature that applies to Kubernetes Service objects. You can use session affinity if you want to ensure that each time you connect to a <service_VIP>:<Port>, the traffic is always load balanced to the same back end. For more information, including how to set session affinity based on a client’s IP address, see Session affinity.

Stickiness timeout for session affinity

The OVN-Kubernetes network plugin for OpenShift Dedicated calculates the stickiness timeout for a session from a client based on the last packet. For example, if you run a curl command 10 times, the sticky session timer starts from the tenth packet not the first. As a result, if the client is continuously contacting the service, then the session never times out. The timeout starts when the service has not received a packet for the amount of time set by the timeoutSeconds parameter.

7.2. Migrating from OpenShift SDN network plugin to OVN-Kubernetes network plugin

As an OpenShift Dedicated cluster administrator, you can initiate the migration from the OpenShift SDN network plugin to the OVN-Kubernetes network plugin and verify the migration status using the OCM CLI.

Some considerations before starting migration initiation are:

  • The cluster version must be 4.16.24 and above.
  • The migration process cannot be interrupted.
  • Migrating back to the SDN network plugin is not possible.
  • Cluster nodes will be rebooted during migration.
  • There will be no impact to workloads that are resilient to node disruptions.
  • Migration time can vary between several minutes and hours, depending on the cluster size and workload configurations.

7.2.1. Initiating migration using the OpenShift Cluster Manager API command-line interface (ocm) CLI

Warning

You can only initiate migration on clusters that are version 4.16.24 and above.

Prerequisites

Important

OpenShift Cluster Manager API command-line interface (ocm) is a Technology Preview feature only. For more information about the support scope of Red Hat Technology Preview features, see Technology Preview Features Support Scope.

Procedure

  1. Create a JSON file with the following content: 

    {
  "type": "sdnToOvn"
}

    • Optional: Within the JSON file, you can configure internal subnets using any or all of the options join, masquerade, and transit, along with a single CIDR per option, as shown in the following example: 

      {
  "type": "sdnToOvn",
  "sdn_to_ovn": {
    "transit_ipv4": "192.168.255.0/24",
    "join_ipv4": "192.168.255.0/24",
    "masquerade_ipv4": "192.168.255.0/24"
  }
}
      Note

      OVN-Kubernetes reserves the following IP address ranges:

      100.64.0.0/16. This IP address range is used for the internalJoinSubnet parameter of OVN-Kubernetes by default.

      100.88.0.0/16. This IP address range is used for the internalTransSwitchSubnet parameter of OVN-Kubernetes by default.

      If these IP addresses have been used by OpenShift SDN or any external networks that might communicate with this cluster, you must patch them to use a different IP address range before initiating the limited live migration. For more information, see Patching OVN-Kubernetes address ranges in the Additional resources section.

  2. To initiate the migration, run the following post request in a terminal window: 

    $ ocm post /api/clusters_mgmt/v1/clusters/{cluster_id}/migrations 1
  --body=myjsonfile.json 2
    1
    Replace {cluster_id} with the ID of the cluster you want to migrate to the OVN-Kubernetes network plugin.
    2
    Replace myjsonfile.json with the name of the JSON file you created in the previous step.

    Example output

    {
  "kind": "ClusterMigration",
  "href": "/api/clusters_mgmt/v1/clusters/2gnts65ra30sclb114p8qdc26g5c8o3e/migrations/2gois8j244rs0qrfu9ti2o790jssgh9i",
  "id": "7sois8j244rs0qrhu9ti2o790jssgh9i",
  "cluster_id": "2gnts65ra30sclb114p8qdc26g5c8o3e",
  "type": "sdnToOvn",
  "state": {
    "value": "scheduled",
    "description": ""
  },
  "sdn_to_ovn": {
    "transit_ipv4": "100.65.0.0/16",
    "join_ipv4": "100.66.0.0/16"
  },
  "creation_timestamp": "2025-02-05T14:56:34.878467542Z",
  "updated_timestamp": "2025-02-05T14:56:34.878467542Z"
}

Verification

  • To check the status of the migration, run the following command: 

    $ ocm get cluster $cluster_id/migration 1
    1
    Replace $cluster_id with the ID of the cluster that the migration was applied to.

Additional resources

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