Chapter 8. OpenShift SDN network plugin 8.1. Enabling multicast for a project 8.1.1. About multicast With IP multicast, data is broadcast to many IP addresses simultaneously. Important 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-all network policy. Cluster administrators should consider the implications to the exemption of multicast from network policies before enabling it. Multicast traffic between Red Hat OpenShift Service on AWS pods is disabled by default. If you are using the OVN-Kubernetes network plugin, you can enable multicast on a per-project basis. 8.1.2. 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-admin or the dedicated-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. USD oc annotate namespace <namespace> \ k8s.ovn.org/multicast-enabled=true Tip You 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. USD oc project <project> Create a pod to act as a multicast receiver: USD 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 EOF Create a pod to act as a multicast sender: USD 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"] EOF In a new terminal window or tab, start the multicast listener. Get the IP address for the Pod: USD POD_IP=USD(oc get pods mlistener -o jsonpath='{.status.podIP}') Start the multicast listener by entering the following command: USD oc exec mlistener -i -t -- \ socat UDP4-RECVFROM:30102,ip-add-membership=224.1.0.1:USDPOD_IP,fork EXEC:hostname Start the multicast transmitter. Get the pod network IP address range: USD CIDR=USD(oc get Network.config.openshift.io cluster \ -o jsonpath='{.status.clusterNetwork[0].cidr}') To send a multicast message, enter the following command: USD oc exec msender -i -t -- \ /bin/bash -c "echo | socat STDIO UDP4-DATAGRAM:224.1.0.1:30102,range=USDCIDR,ip-multicast-ttl=64" If multicast is working, the command returns the following output: mlistener

Commands:
oc annotate namespace <namespace> k8s.ovn.org/multicast-enabled=true
apiVersion: v1 kind: Namespace metadata: name: <namespace> annotations: k8s.ovn.org/multicast-enabled: "true"
oc project <project>
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 EOF
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"] EOF
POD_IP=USD(oc get pods mlistener -o jsonpath='{.status.podIP}')
oc exec mlistener -i -t -- socat UDP4-RECVFROM:30102,ip-add-membership=224.1.0.1:USDPOD_IP,fork EXEC:hostname
CIDR=USD(oc get Network.config.openshift.io cluster -o jsonpath='{.status.clusterNetwork[0].cidr}')
oc exec msender -i -t -- /bin/bash -c "echo | socat STDIO UDP4-DATAGRAM:224.1.0.1:30102,range=USDCIDR,ip-multicast-ttl=64"
mlistener