Chapter 9. OpenShift SDN network plugin
9.1. Enabling multicast for a project
9.1.1. 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.
-
By default, network policies affect all connections in a namespace. However, multicast is unaffected by network policies. If multicast is enabled in the same namespace as your network policies, it is always allowed, even if there is a
deny-allnetwork policy. Cluster administrators should consider the implications to the exemption of multicast from network policies before enabling it.
Multicast traffic between OpenShift Dedicated pods is disabled by default. If you are using the OVN-Kubernetes network plugin, you can enable multicast on a per-project basis.
9.1.2. 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-adminor thededicated-adminrole.
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=trueTipYou can alternatively apply the following YAML to add the annotation:
apiVersion: v1 kind: Namespace metadata: name: <namespace> annotations: 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/ubi9 command: ["/bin/sh", "-c"] args: ["dnf -y install socat hostname && sleep inf"] ports: - containerPort: 30102 name: mlistener protocol: UDP EOFCreate 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/ubi9 command: ["/bin/sh", "-c"] args: ["dnf -y install socat && sleep inf"] EOFIn 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
