About the OVN-Kubernetes network plugin - OVN-Kubernetes network plugin | Networking

OVN-Kubernetes purpose
Supported network plugin feature matrix
OVN-Kubernetes IPv6 and dual-stack limitations
Session affinity

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, 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, allowing network administrators to 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, DHCP and DNS. OVN implements distributed virtual routing within logic flows which equate to open flows. So for example if you have a pod that sends out a DHCP request on the network, it sends out that broadcast looking for DHCP address there will be a logic flow rule that matches that packet, and it responds giving it a gateway, a DNS server an IP address and so on.

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.

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 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] ^[4]	Not supported
Kubernetes network policy	Supported	Supported
Kubernetes network policy logs	Supported	Not supported
Hardware offloading	Supported	Not supported
Multicast	Supported	Supported

Egress firewall is also known as egress network policy in OpenShift SDN. This is not the same as network policy egress.
Egress router for OVN-Kubernetes supports only redirect mode.
IPv6 is supported only on bare metal, IBM Power, and IBM Z clusters.
IPv6 single stack does not support Kubernetes NMState and is not supported on IBM Power and IBM Z clusters.

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.

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 OKD 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.

Additional resources