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The OKD 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 OKD. 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.

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

OVN-Kubernetes purpose

The OVN-Kubnernetes 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-Kubnernetes network plugin:

  • Uses OVN (Open Virtual Network) to manage network traffic flows. OVN is a community developed, vendor-agnostic network virtualization solution.

  • Implements Kubernetes network policy support, including ingress and egress rules.

  • Uses the Geneve (Generic Network Virtualization Encapsulation) protocol rather than VXLAN to create an overlay network between nodes.

The OVN-Kubernetes network plugin provides the following advantages over OpenShift SDN.

  • Full support for IPv6 single-stack and IPv4/IPv6 dual-stack networking on supported platforms

  • Support for hybrid clusters with both Linux and Microsoft Windows workloads

  • Optional IPsec encryption of intra-cluster communications

  • Offload of network data processing from host CPU to compatible network cards and data processing units (DPUs)

Supported network plugin feature matrix

Red Hat OpenShift Networking offers two options for the network plugin, OpenShift SDN and OVN-Kubernetes, for the network plugin. The following table summarizes the current feature support for both network plugins:

Table 1. Default CNI network plugin feature comparison
Feature OVN-Kubernetes OpenShift SDN

Egress IPs

Supported

Supported

Egress firewall [1]

Supported

Supported

Egress router

Supported [2]

Supported

Hybrid networking

Supported

Not supported

IPsec encryption for intra-cluster communication

Supported

Not supported

IPv6

Supported [3]

Not supported

Kubernetes network policy

Supported

Partially supported [4]

Kubernetes network policy logs

Supported

Not supported

Hardware offloading

Supported

Not supported

Multicast

Supported

Supported

  1. Egress firewall is also known as egress network policy in OpenShift SDN. This is not the same as network policy egress.

  2. Egress router for OVN-Kubernetes supports only redirect mode.

  3. IPv6 is supported only on bare metal, IBM Power, and IBM Z clusters.

  4. Network policy for OpenShift SDN does not support egress rules and some ipBlock rules.

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.