Chapter 1. Understanding multiple networks

By default, OVN-Kubernetes serves as the Container Network Interface (CNI) of an OpenShift Container Platform cluster. This network interface is what administrators use to create default networks.

Both user-defined networks and Network Attachment Definitions can serve as the following network types:

The following diagram shows a cluster that has an existing default network infrastructure that uses a physical network interface, eth0, to connect to two namespaces. Pods or virtual machines (VMs) in one namespace run in isolation from pods or VMs in the other namespace. You can create only one primary network. However, you can create multiple secondary networks for each namespace.

Figure 1.1. Diagram showing namespaces with multiple secondary UDNs

During cluster installation, OpenShift Container Platform administrators can configure alternative default secondary pod networks by leveraging the Multus CNI plugin. With Multus, you can use multiple CNI plugins such as ipvlan, macvlan, or Network Attachment Definitions together to serve as secondary networks for pods.

You can define an secondary network based on the available CNI plugins and attach one or more of these networks to your pods. You can define more than one secondary network for your cluster depending on your needs. This gives you flexibility when you configure pods that deliver network functionality, such as switching or routing. For more information, see the links in the Additional resources: