Enabling multicast for a project - OVN-Kubernetes default CNI network provider | Networking

About multicast
Enabling multicast between pods

About multicast

With IP multicast, data is broadcast to many IP addresses simultaneously.

At this time, multicast is best used for low-bandwidth coordination or service discovery and not a high-bandwidth solution.

Multicast traffic between OpenShift Container Platform pods is disabled by default. If you are using the OVN-Kubernetes default Container Network Interface (CNI) network provider, you can enable multicast on a per-project basis.

Enabling multicast between pods

You can enable multicast between pods for your project.

Prerequisites

Install the OpenShift CLI (oc).
You must log in to the cluster with a user that has the cluster-admin role.

Procedure

Run the following command to enable multicast for a project. Replace <namespace> with the namespace for the project you want to enable multicast for.
```
$ oc annotate namespace <namespace> \
    k8s.ovn.org/multicast-enabled=true
```

Verification

To verify that multicast is enabled for a project, complete the following procedure:

Change your current project to the project that you enabled multicast for. Replace <project> with the project name.
```
$ oc project <project>
```

Create a pod to act as a multicast receiver:

$ cat <<EOF| oc create -f -
apiVersion: v1
kind: Pod
metadata:
  name: mlistener
  labels:
    app: multicast-verify
spec:
  containers:
    - name: mlistener
      image: registry.access.redhat.com/ubi8
      command: ["/bin/sh", "-c"]
      args:
        ["dnf -y install socat hostname && sleep inf"]
      ports:
        - containerPort: 30102
          name: mlistener
          protocol: UDP
EOF

Create a pod to act as a multicast sender:

$ cat <<EOF| oc create -f -
apiVersion: v1
kind: Pod
metadata:
  name: msender
  labels:
    app: multicast-verify
spec:
  containers:
    - name: msender
      image: registry.access.redhat.com/ubi8
      command: ["/bin/sh", "-c"]
      args:
        ["dnf -y install socat && sleep inf"]
EOF

In a new terminal window or tab, start the multicast listener.

Get the IP address for the Pod:

$ POD_IP=$(oc get pods mlistener -o jsonpath='{.status.podIP}')

Start the multicast listener by entering the following command:

$ oc exec mlistener -i -t -- \
    socat UDP4-RECVFROM:30102,ip-add-membership=224.1.0.1:$POD_IP,fork EXEC:hostname

Start the multicast transmitter.

Get the pod network IP address range:

$ CIDR=$(oc get Network.config.openshift.io cluster \
    -o jsonpath='{.status.clusterNetwork[0].cidr}')

To send a multicast message, enter the following command:

$ oc exec msender -i -t -- \
    /bin/bash -c "echo | socat STDIO UDP4-DATAGRAM:224.1.0.1:30102,range=$CIDR,ip-multicast-ttl=64"

If multicast is working, the previous command returns the following output:

mlistener