NetworkAttachmentDefinition CR - Multiple networks | Networking

Approaches to managing a primary network
Creating a primary network attachment with the Cluster Network Operator
Configuration for a primary network attachment
Creating a primary network attachment by applying a YAML manifest

Use the NetworkAttachmentDefinition (NAD) resource to create primary networks when you need to use CNI plugins other than OVN-Kubernetes, such as IPVLAN or MACVLAN, or when you require direct control over the Container Network Interface (CNI) configuration for advanced networking scenarios.

Approaches to managing a primary network

You can manage the life cycle of a primary network created by a NAD CR through the Cluster Network Operator (CNO) or a YAML manifest. Using the CNO provides automated management of the network resource, while applying a YAML manifest allows for direct control over the network configuration.

Modifying the Cluster Network Operator (CNO) configuration: With this method, the CNO automatically creates and manages the NetworkAttachmentDefinition object. In addition to managing the object lifecycle, the CNO ensures that a DHCP is available for a primary network that uses a DHCP assigned IP address.
Applying a YAML manifest: With this method, you can manage the primary network directly by creating an NetworkAttachmentDefinition object. This approach allows for the invocation of multiple CNI plugins in order to attach primary network interfaces in a pod.

Each approach is mutually exclusive and you can only use one approach for managing a primary network at a time. For either approach, the primary network is managed by a Container Network Interface (CNI) plugin that you configure.

When deploying OKD nodes with multiple network interfaces on OpenStack with OVN SDN, DNS configuration of the secondary interface might take precedence over the DNS configuration of the primary interface. In this case, remove the DNS nameservers for the subnet ID that is attached to the secondary interface by running the following command:

$ openstack subnet set --dns-nameserver 0.0.0.0 <subnet_id>

Creating a primary network attachment with the Cluster Network Operator

When you specify a primary network to create by using the Cluster Network Operator (CNO), the (CNO) creates the NetworkAttachmentDefinition custom resource definition (CRD) automatically and manages it.

Do not edit the NetworkAttachmentDefinition CRDs that the Cluster Network Operator manages. Doing so might disrupt network traffic on your primary network.

Prerequisites

Install the OpenShift cli (oc).
Log in as a user with cluster-admin privileges.

Procedure

Optional: Create the namespace for the primary networks:
```
$ oc create namespace <namespace_name>
```
To edit the CNO configuration, enter the following command:
```
$ oc edit networks.operator.openshift.io cluster
```

Modify the CR that you are creating by adding the configuration for the primary network that you are creating, as in the following example CR.

apiVersion: operator.openshift.io/v1
kind: Network
metadata:
  name: cluster
spec:
  # ...
  additionalNetworks:
  - name: tertiary-net
    namespace: namespace2
    type: Raw
    rawCNIConfig: |-
      {
        "cniVersion": "0.3.1",
        "name": "tertiary-net",
        "type": "ipvlan",
        "master": "eth1",
        "mode": "l2",
        "ipam": {
          "type": "static",
          "addresses": [
            {
              "address": "192.168.1.23/24"
            }
          ]
        }
      }

Save your changes and quit the text editor to commit your changes.

Verification

Confirm that the CNO created the NetworkAttachmentDefinition CRD by running the following command. A delay might exist before the CNO creates the CRD. The expected output shows the name of the NAD CRD and the creation age in minutes.
```
$ oc get network-attachment-definitions -n <namespace>
```
where:

<namespace>

Specifies the namespace for the network attachment that you added to the CNO configuration.

Configuration for a primary network attachment

You configure a primary network by using the NetworkAttachmentDefinition API in the k8s.cni.cncf.io API group.

The configuration for the API is described in the following table:

Table 1. `NetworkAttachmentDefinition` API fields
Field	Type	Description
`metadata.name`	`string`	The name for the primary network.
`metadata.namespace`	`string`	The namespace that the object is associated with.
`spec.config`	`string`	The CNI plugin configuration in JSON format.

Creating a primary network attachment by applying a YAML manifest

Create a primary network attachment by directly applying a NetworkAttachmentDefinition YAML manifest. This gives you full control over the network configuration without relying on the Cluster Network Operator to manage the resource automatically.